company,questionId,questionName,difficulty level,Tags,Content
LinkedIn,364,Nested List Weight Sum II,Med,"Stack, Depth-First Search, Breadth-First Search",
LinkedIn,432,All O`one Data Structure,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure to store the strings' count with the ability to return the strings with minimum and maximum counts. Implement the AllOne class: AllOne() Initializes the object of the data structure. inc(String key) Increments the count of the string key by 1. If key does not exist in the data structure; insert it with count 1. dec(String key) Decrements the count of the string key by 1. If the count of key is 0 after the decrement; remove it from the data structure. It is guaranteed that key exists in the data structure before the decrement. getMaxKey() Returns one of the keys with the maximal count. If no element exists; return an empty string """". getMinKey() Returns one of the keys with the minimum count. If no element exists; return an empty string """". Note that each function must run in O(1) average time complexity. Example 1: Input [""AllOne""; ""inc""; ""inc""; ""getMaxKey""; ""getMinKey""; ""inc""; ""getMaxKey""; ""getMinKey""] [[]; [""hello""]; [""hello""]; []; []; [""leet""]; []; []] Output [null; null; null; ""hello""; ""hello""; null; ""hello""; ""leet""] Explanation AllOne allOne = new AllOne(); allOne.inc(""hello""); allOne.inc(""hello""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""hello"" allOne.inc(""leet""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""leet"" Constraints: 1 <= key.length <= 10 key consists of lowercase English letters. It is guaranteed that for each call to dec; key is existing in the data structure. At most 5 * 104 calls will be made to inc; dec; getMaxKey; and getMinKey."
LinkedIn,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
LinkedIn,716,Max Stack,Hard,"Linked List, Stack, Design, Doubly-Linked List, Ordered Set",
LinkedIn,254,Factor Combinations,Med,Backtracking,
LinkedIn,277,Find the Celebrity,Med,"Two Pointers, Graph, Interactive",
LinkedIn,360,Sort Transformed Array,Med,"Array, Math, Two Pointers, Sorting",
LinkedIn,1650,Lowest Common Ancestor of a Binary Tree III,Med,"Hash Table, Bit Manipulation, Tree, Depth-First Search",
LinkedIn,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
LinkedIn,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
LinkedIn,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
LinkedIn,156,Binary Tree Upside Down,Med,"Tree, Depth-First Search, Binary Tree",
LinkedIn,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
LinkedIn,205,Isomorphic Strings,Easy,"Hash Table, String","Given two strings s and t; determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character; but a character may map to itself. Example 1: Input: s = ""egg""; t = ""add"" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = ""foo""; t = ""bar"" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = ""paper""; t = ""title"" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character."
LinkedIn,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
LinkedIn,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
LinkedIn,235,Lowest Common Ancestor of a Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given a binary search tree (BST); find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [2;1]; p = 2; q = 1 Output: 2 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.
LinkedIn,339,Nested List Weight Sum,Med,"Depth-First Search, Breadth-First Search",
LinkedIn,341,Flatten Nested List Iterator,Med,"Stack, Tree, Depth-First Search, Design, Queue, Iterator",You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it. Implement the NestedIterator class: NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList. int next() Returns the next integer in the nested list. boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise. Your code will be tested with the following pseudocode: initialize iterator with nestedList res = [] while iterator.hasNext() append iterator.next() to the end of res return res If res matches the expected flattened list; then your code will be judged as correct. Example 1: Input: nestedList = [[1;1];2;[1;1]] Output: [1;1;2;1;1] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;1;2;1;1]. Example 2: Input: nestedList = [1;[4;[6]]] Output: [1;4;6] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;4;6]. Constraints: 1 <= nestedList.length <= 500 The values of the integers in the nested list is in the range [-106; 106].
LinkedIn,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
LinkedIn,611,Valid Triangle Number,Med,"Array, Two Pointers, Binary Search, Greedy, Sorting",Given an integer array nums; return the number of triplets chosen from the array that can make triangles if we take them as side lengths of a triangle. Example 1: Input: nums = [2;2;3;4] Output: 3 Explanation: Valid combinations are: 2;3;4 (using the first 2) 2;3;4 (using the second 2) 2;2;3 Example 2: Input: nums = [4;2;3;4] Output: 4 Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 1000
LinkedIn,489,Robot Room Cleaner,Hard,"Array, Math, Dynamic Programming, Combinatorics","Bob is standing at cell (0; 0); and he wants to reach destination: (row; column). He can only travel right and down. You are going to help Bob by providing instructions for him to reach destination. The instructions are represented as a string; where each character is either: 'H'; meaning move horizontally (go right); or 'V'; meaning move vertically (go down). Multiple instructions will lead Bob to destination. For example; if destination is (2; 3); both ""HHHVV"" and ""HVHVH"" are valid instructions. However; Bob is very picky. Bob has a lucky number k; and he wants the kth lexicographically smallest instructions that will lead him to destination. k is 1-indexed. Given an integer array destination and an integer k; return the kth lexicographically smallest instructions that will take Bob to destination. Example 1: Input: destination = [2;3]; k = 1 Output: ""HHHVV"" Explanation: All the instructions that reach (2; 3) in lexicographic order are as follows: [""HHHVV""; ""HHVHV""; ""HHVVH""; ""HVHHV""; ""HVHVH""; ""HVVHH""; ""VHHHV""; ""VHHVH""; ""VHVHH""; ""VVHHH""]. Example 2: Input: destination = [2;3]; k = 2 Output: ""HHVHV"" Example 3: Input: destination = [2;3]; k = 3 Output: ""HHVVH"" Constraints: destination.length == 2 1 <= row; column <= 15 1 <= k <= nCr(row + column; row); where nCr(a; b) denotes a choose b​​​​​."
LinkedIn,886,Possible Bipartition,Med,"String, Stack","Given a balanced parentheses string s; return the score of the string. The score of a balanced parentheses string is based on the following rule: ""()"" has score 1. AB has score A + B; where A and B are balanced parentheses strings. (A) has score 2 * A; where A is a balanced parentheses string. Example 1: Input: s = ""()"" Output: 1 Example 2: Input: s = ""(())"" Output: 2 Example 3: Input: s = ""()()"" Output: 2 Constraints: 2 <= s.length <= 50 s consists of only '(' and ')'. s is a balanced parentheses string."
LinkedIn,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Backend,432,All O`one Data Structure,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure to store the strings' count with the ability to return the strings with minimum and maximum counts. Implement the AllOne class: AllOne() Initializes the object of the data structure. inc(String key) Increments the count of the string key by 1. If key does not exist in the data structure; insert it with count 1. dec(String key) Decrements the count of the string key by 1. If the count of key is 0 after the decrement; remove it from the data structure. It is guaranteed that key exists in the data structure before the decrement. getMaxKey() Returns one of the keys with the maximal count. If no element exists; return an empty string """". getMinKey() Returns one of the keys with the minimum count. If no element exists; return an empty string """". Note that each function must run in O(1) average time complexity. Example 1: Input [""AllOne""; ""inc""; ""inc""; ""getMaxKey""; ""getMinKey""; ""inc""; ""getMaxKey""; ""getMinKey""] [[]; [""hello""]; [""hello""]; []; []; [""leet""]; []; []] Output [null; null; null; ""hello""; ""hello""; null; ""hello""; ""leet""] Explanation AllOne allOne = new AllOne(); allOne.inc(""hello""); allOne.inc(""hello""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""hello"" allOne.inc(""leet""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""leet"" Constraints: 1 <= key.length <= 10 key consists of lowercase English letters. It is guaranteed that for each call to dec; key is existing in the data structure. At most 5 * 104 calls will be made to inc; dec; getMaxKey; and getMinKey."
Backend,364,Nested List Weight Sum II,Med,"Stack, Depth-First Search, Breadth-First Search",
Backend,187,Repeated DNA Sequences,Med,"Hash Table, String, Bit Manipulation, Sliding Window, Rolling Hash, Hash Function","The DNA sequence is composed of a series of nucleotides abbreviated as 'A'; 'C'; 'G'; and 'T'. For example; ""ACGAATTCCG"" is a DNA sequence. When studying DNA; it is useful to identify repeated sequences within the DNA. Given a string s that represents a DNA sequence; return all the 10-letter-long sequences (substrings) that occur more than once in a DNA molecule. You may return the answer in any order. Example 1: Input: s = ""AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"" Output: [""AAAAACCCCC"";""CCCCCAAAAA""] Example 2: Input: s = ""AAAAAAAAAAAAA"" Output: [""AAAAAAAAAA""] Constraints: 1 <= s.length <= 105 s[i] is either 'A'; 'C'; 'G'; or 'T'."
Backend,366,Find Leaves of Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",
Backend,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Backend,47,Permutations II,Med,"Array, Backtracking",Given a collection of numbers; nums; that might contain duplicates; return all possible unique permutations in any order. Example 1: Input: nums = [1;1;2] Output: [[1;1;2]; [1;2;1]; [2;1;1]] Example 2: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Constraints: 1 <= nums.length <= 8 -10 <= nums[i] <= 10
Backend,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Backend,671,Second Minimum Node In a Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given a non-empty special binary tree consisting of nodes with the non-negative value; where each node in this tree has exactly two or zero sub-node. If the node has two sub-nodes; then this node's value is the smaller value among its two sub-nodes. More formally; the property root.val = min(root.left.val; root.right.val) always holds. Given such a binary tree; you need to output the second minimum value in the set made of all the nodes' value in the whole tree. If no such second minimum value exists; output -1 instead. Example 1: Input: root = [2;2;5;null;null;5;7] Output: 5 Explanation: The smallest value is 2; the second smallest value is 5. Example 2: Input: root = [2;2;2] Output: -1 Explanation: The smallest value is 2; but there isn't any second smallest value. Constraints: The number of nodes in the tree is in the range [1; 25]. 1 <= Node.val <= 231 - 1 root.val == min(root.left.val; root.right.val) for each internal node of the tree.
Backend,1644,Lowest Common Ancestor of a Binary Tree II,Med,"String, Greedy","Given a string s of lowercase letters; you need to find the maximum number of non-empty substrings of s that meet the following conditions: The substrings do not overlap; that is for any two substrings s[i..j] and s[x..y]; either j < x or i > y is true. A substring that contains a certain character c must also contain all occurrences of c. Find the maximum number of substrings that meet the above conditions. If there are multiple solutions with the same number of substrings; return the one with minimum total length. It can be shown that there exists a unique solution of minimum total length. Notice that you can return the substrings in any order. Example 1: Input: s = ""adefaddaccc"" Output: [""e"";""f"";""ccc""] Explanation: The following are all the possible substrings that meet the conditions: [ ""adefaddaccc"" ""adefadda""; ""ef""; ""e""; ""f""; ""ccc""; ] If we choose the first string; we cannot choose anything else and we'd get only 1. If we choose ""adefadda""; we are left with ""ccc"" which is the only one that doesn't overlap; thus obtaining 2 substrings. Notice also; that it's not optimal to choose ""ef"" since it can be split into two. Therefore; the optimal way is to choose [""e"";""f"";""ccc""] which gives us 3 substrings. No other solution of the same number of substrings exist. Example 2: Input: s = ""abbaccd"" Output: [""d"";""bb"";""cc""] Explanation: Notice that while the set of substrings [""d"";""abba"";""cc""] also has length 3; it's considered incorrect since it has larger total length. Constraints: 1 <= s.length <= 105 s contains only lowercase English letters."
Backend,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Backend,277,Find the Celebrity,Med,"Two Pointers, Graph, Interactive",
Backend,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Backend,235,Lowest Common Ancestor of a Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given a binary search tree (BST); find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [2;1]; p = 2; q = 1 Output: 2 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.
Backend,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Backend,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
Meta,1249,Minimum Remove to Make Valid Parentheses,Med,"Array, Hash Table, Binary Search, Design","Implement a SnapshotArray that supports the following interface: SnapshotArray(int length) initializes an array-like data structure with the given length. Initially; each element equals 0. void set(index; val) sets the element at the given index to be equal to val. int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1. int get(index; snap_id) returns the value at the given index; at the time we took the snapshot with the given snap_id Example 1: Input: [""SnapshotArray"";""set"";""snap"";""set"";""get""] [[3];[0;5];[];[0;6];[0;0]] Output: [null;null;0;null;5] Explanation: SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3 snapshotArr.set(0;5); // Set array[0] = 5 snapshotArr.snap(); // Take a snapshot; return snap_id = 0 snapshotArr.set(0;6); snapshotArr.get(0;0); // Get the value of array[0] with snap_id = 0; return 5 Constraints: 1 <= length <= 5 * 104 0 <= index < length 0 <= val <= 109 0 <= snap_id < (the total number of times we call snap()) At most 5 * 104 calls will be made to set; snap; and get."
Meta,408,Valid Word Abbreviation,Easy,"Two Pointers, String",
Meta,680,Valid Palindrome II,Easy,"Two Pointers, String, Greedy","Given a string s; return true if the s can be palindrome after deleting at most one character from it. Example 1: Input: s = ""aba"" Output: true Example 2: Input: s = ""abca"" Output: true Explanation: You could delete the character 'c'. Example 3: Input: s = ""abc"" Output: false Constraints: 1 <= s.length <= 105 s consists of lowercase English letters."
Meta,227,Basic Calculator II,Med,"Math, String, Stack","Given a string s which represents an expression; evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""3+2*2"" Output: 7 Example 2: Input: s = "" 3/2 "" Output: 1 Example 3: Input: s = "" 3+5 / 2 "" Output: 5 Constraints: 1 <= s.length <= 3 * 105 s consists of integers and operators ('+'; '-'; '*'; '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0; 231 - 1]. The answer is guaranteed to fit in a 32-bit integer."
Meta,314,Binary Tree Vertical Order Traversal,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Sorting, Binary Tree",
Meta,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Meta,1650,Lowest Common Ancestor of a Binary Tree III,Med,"Hash Table, Bit Manipulation, Tree, Depth-First Search",
Meta,339,Nested List Weight Sum,Med,"Depth-First Search, Breadth-First Search",
Meta,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
Meta,236,Lowest Common Ancestor of a Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",Given a binary tree; find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3. Example 2: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [1;2]; p = 1; q = 2 Output: 1 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the tree.
Meta,1091,Shortest Path in Binary Matrix,Med,"Tree, Depth-First Search, Binary Tree",
Meta,71,Simplify Path,Med,"String, Stack","You are given an absolute path for a Unix-style file system; which always begins with a slash '/'. Your task is to transform this absolute path into its simplified canonical path. The rules of a Unix-style file system are as follows: A single period '.' represents the current directory. A double period '..' represents the previous/parent directory. Multiple consecutive slashes such as '//' and '///' are treated as a single slash '/'. Any sequence of periods that does not match the rules above should be treated as a valid directory or file name. For example; '...' and '....' are valid directory or file names. The simplified canonical path should follow these rules: The path must start with a single slash '/'. Directories within the path must be separated by exactly one slash '/'. The path must not end with a slash '/'; unless it is the root directory. The path must not have any single or double periods ('.' and '..') used to denote current or parent directories. Return the simplified canonical path. Example 1: Input: path = ""/home/"" Output: ""/home"" Explanation: The trailing slash should be removed. Example 2: Input: path = ""/home//foo/"" Output: ""/home/foo"" Explanation: Multiple consecutive slashes are replaced by a single one. Example 3: Input: path = ""/home/user/Documents/../Pictures"" Output: ""/home/user/Pictures"" Explanation: A double period "".."" refers to the directory up a level (the parent directory). Example 4: Input: path = ""/../"" Output: ""/"" Explanation: Going one level up from the root directory is not possible. Example 5: Input: path = ""/.../a/../b/c/../d/./"" Output: ""/.../b/d"" Explanation: ""..."" is a valid name for a directory in this problem. Constraints: 1 <= path.length <= 3000 path consists of English letters; digits; period '.'; slash '/' or '_'. path is a valid absolute Unix path."
Meta,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
Meta,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Meta,1570,Dot Product of Two Sparse Vectors,Med,"Array, Stack, Monotonic Stack",You are given an integer array prices where prices[i] is the price of the ith item in a shop. There is a special discount for items in the shop. If you buy the ith item; then you will receive a discount equivalent to prices[j] where j is the minimum index such that j > i and prices[j] <= prices[i]. Otherwise; you will not receive any discount at all. Return an integer array answer where answer[i] is the final price you will pay for the ith item of the shop; considering the special discount. Example 1: Input: prices = [8;4;6;2;3] Output: [4;2;4;2;3] Explanation: For item 0 with price[0]=8 you will receive a discount equivalent to prices[1]=4; therefore; the final price you will pay is 8 - 4 = 4. For item 1 with price[1]=4 you will receive a discount equivalent to prices[3]=2; therefore; the final price you will pay is 4 - 2 = 2. For item 2 with price[2]=6 you will receive a discount equivalent to prices[3]=2; therefore; the final price you will pay is 6 - 2 = 4. For items 3 and 4 you will not receive any discount at all. Example 2: Input: prices = [1;2;3;4;5] Output: [1;2;3;4;5] Explanation: In this case; for all items; you will not receive any discount at all. Example 3: Input: prices = [10;1;1;6] Output: [9;0;1;6] Constraints: 1 <= prices.length <= 500 1 <= prices[i] <= 1000
Meta,938,Range Sum of BST,Easy,"Array, Math, String, Binary Search, Dynamic Programming","Given an array of digits which is sorted in non-decreasing order. You can write numbers using each digits[i] as many times as we want. For example; if digits = ['1';'3';'5']; we may write numbers such as '13'; '551'; and '1351315'. Return the number of positive integers that can be generated that are less than or equal to a given integer n. Example 1: Input: digits = [""1"";""3"";""5"";""7""]; n = 100 Output: 20 Explanation: The 20 numbers that can be written are: 1; 3; 5; 7; 11; 13; 15; 17; 31; 33; 35; 37; 51; 53; 55; 57; 71; 73; 75; 77. Example 2: Input: digits = [""1"";""4"";""9""]; n = 1000000000 Output: 29523 Explanation: We can write 3 one digit numbers; 9 two digit numbers; 27 three digit numbers; 81 four digit numbers; 243 five digit numbers; 729 six digit numbers; 2187 seven digit numbers; 6561 eight digit numbers; and 19683 nine digit numbers. In total; this is 29523 integers that can be written using the digits array. Example 3: Input: digits = [""7""]; n = 8 Output: 1 Constraints: 1 <= digits.length <= 9 digits[i].length == 1 digits[i] is a digit from '1' to '9'. All the values in digits are unique. digits is sorted in non-decreasing order. 1 <= n <= 109"
Meta,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Meta,199,Binary Tree Right Side View,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; imagine yourself standing on the right side of it; return the values of the nodes you can see ordered from top to bottom. Example 1: Input: root = [1;2;3;null;5;null;4] Output: [1;3;4] Example 2: Input: root = [1;null;3] Output: [1;3] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Meta,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Meta,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Meta,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Meta,543,Diameter of Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them. Example 1: Input: root = [1;2;3;4;5] Output: 3 Explanation: 3 is the length of the path [4;2;1;3] or [5;2;1;3]. Example 2: Input: root = [1;2] Output: 1 Constraints: The number of nodes in the tree is in the range [1; 104]. -100 <= Node.val <= 100
Meta,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Meta,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Meta,125,Valid Palindrome,Easy,"Two Pointers, String","A phrase is a palindrome if; after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters; it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s; return true if it is a palindrome; or false otherwise. Example 1: Input: s = ""A man; a plan; a canal: Panama"" Output: true Explanation: ""amanaplanacanalpanama"" is a palindrome. Example 2: Input: s = ""race a car"" Output: false Explanation: ""raceacar"" is not a palindrome. Example 3: Input: s = "" "" Output: true Explanation: s is an empty string """" after removing non-alphanumeric characters. Since an empty string reads the same forward and backward; it is a palindrome. Constraints: 1 <= s.length <= 2 * 105 s consists only of printable ASCII characters."
Meta,973,K Closest Points to Origin,Med,"String, Stack, Greedy, Queue","You are given two strings stamp and target. Initially; there is a string s of length target.length with all s[i] == '?'. In one turn; you can place stamp over s and replace every letter in the s with the corresponding letter from stamp. For example; if stamp = ""abc"" and target = ""abcba""; then s is ""?????"" initially. In one turn you can: place stamp at index 0 of s to obtain ""abc??""; place stamp at index 1 of s to obtain ""?abc?""; or place stamp at index 2 of s to obtain ""??abc"". Note that stamp must be fully contained in the boundaries of s in order to stamp (i.e.; you cannot place stamp at index 3 of s). We want to convert s to target using at most 10 * target.length turns. Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns; return an empty array. Example 1: Input: stamp = ""abc""; target = ""ababc"" Output: [0;2] Explanation: Initially s = ""?????"". - Place stamp at index 0 to get ""abc??"". - Place stamp at index 2 to get ""ababc"". [1;0;2] would also be accepted as an answer; as well as some other answers. Example 2: Input: stamp = ""abca""; target = ""aabcaca"" Output: [3;0;1] Explanation: Initially s = ""???????"". - Place stamp at index 3 to get ""???abca"". - Place stamp at index 0 to get ""abcabca"". - Place stamp at index 1 to get ""aabcaca"". Constraints: 1 <= stamp.length <= target.length <= 1000 stamp and target consist of lowercase English letters."
Meta,1762,Buildings With an Ocean View,Med,"Array, Greedy, Heap (Priority Queue)",You are given an integer array heights representing the heights of buildings; some bricks; and some ladders. You start your journey from building 0 and move to the next building by possibly using bricks or ladders. While moving from building i to building i+1 (0-indexed); If the current building's height is greater than or equal to the next building's height; you do not need a ladder or bricks. If the current building's height is less than the next building's height; you can either use one ladder or (h[i+1] - h[i]) bricks. Return the furthest building index (0-indexed) you can reach if you use the given ladders and bricks optimally. Example 1: Input: heights = [4;2;7;6;9;14;12]; bricks = 5; ladders = 1 Output: 4 Explanation: Starting at building 0; you can follow these steps: - Go to building 1 without using ladders nor bricks since 4 >= 2. - Go to building 2 using 5 bricks. You must use either bricks or ladders because 2 < 7. - Go to building 3 without using ladders nor bricks since 7 >= 6. - Go to building 4 using your only ladder. You must use either bricks or ladders because 6 < 9. It is impossible to go beyond building 4 because you do not have any more bricks or ladders. Example 2: Input: heights = [4;12;2;7;3;18;20;3;19]; bricks = 10; ladders = 2 Output: 7 Example 3: Input: heights = [14;3;19;3]; bricks = 17; ladders = 0 Output: 3 Constraints: 1 <= heights.length <= 105 1 <= heights[i] <= 106 0 <= bricks <= 109 0 <= ladders <= heights.length
Meta,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Meta,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Meta,791,Custom Sort String,Med,"Tree, Binary Search Tree, Recursion, Binary Tree",
Meta,921,Minimum Add to Make Parentheses Valid,Med,"Array, Matrix, Simulation",You start at the cell (rStart; cStart) of an rows x cols grid facing east. The northwest corner is at the first row and column in the grid; and the southeast corner is at the last row and column. You will walk in a clockwise spiral shape to visit every position in this grid. Whenever you move outside the grid's boundary; we continue our walk outside the grid (but may return to the grid boundary later.). Eventually; we reach all rows * cols spaces of the grid. Return an array of coordinates representing the positions of the grid in the order you visited them. Example 1: Input: rows = 1; cols = 4; rStart = 0; cStart = 0 Output: [[0;0];[0;1];[0;2];[0;3]] Example 2: Input: rows = 5; cols = 6; rStart = 1; cStart = 4 Output: [[1;4];[1;5];[2;5];[2;4];[2;3];[1;3];[0;3];[0;4];[0;5];[3;5];[3;4];[3;3];[3;2];[2;2];[1;2];[0;2];[4;5];[4;4];[4;3];[4;2];[4;1];[3;1];[2;1];[1;1];[0;1];[4;0];[3;0];[2;0];[1;0];[0;0]] Constraints: 1 <= rows; cols <= 100 0 <= rStart < rows 0 <= cStart < cols
Meta,986,Interval List Intersections,Med,"Array, String, Enumeration","Given an array arr of 4 digits; find the latest 24-hour time that can be made using each digit exactly once. 24-hour times are formatted as ""HH:MM""; where HH is between 00 and 23; and MM is between 00 and 59. The earliest 24-hour time is 00:00; and the latest is 23:59. Return the latest 24-hour time in ""HH:MM"" format. If no valid time can be made; return an empty string. Example 1: Input: arr = [1;2;3;4] Output: ""23:41"" Explanation: The valid 24-hour times are ""12:34""; ""12:43""; ""13:24""; ""13:42""; ""14:23""; ""14:32""; ""21:34""; ""21:43""; ""23:14""; and ""23:41"". Of these times; ""23:41"" is the latest. Example 2: Input: arr = [5;5;5;5] Output: """" Explanation: There are no valid 24-hour times as ""55:55"" is not valid. Constraints: arr.length == 4 0 <= arr[i] <= 9"
Meta,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Meta,426,Convert Binary Search Tree to Sorted Doubly Linked List,Med,,
Meta,670,Maximum Swap,Med,"Math, Greedy",You are given an integer num. You can swap two digits at most once to get the maximum valued number. Return the maximum valued number you can get. Example 1: Input: num = 2736 Output: 7236 Explanation: Swap the number 2 and the number 7. Example 2: Input: num = 9973 Output: 9973 Explanation: No swap. Constraints: 0 <= num <= 108
Meta,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Meta,129,Sum Root to Leaf Numbers,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree containing digits from 0 to 9 only. Each root-to-leaf path in the tree represents a number. For example; the root-to-leaf path 1 -> 2 -> 3 represents the number 123. Return the total sum of all root-to-leaf numbers. Test cases are generated so that the answer will fit in a 32-bit integer. A leaf node is a node with no children. Example 1: Input: root = [1;2;3] Output: 25 Explanation: The root-to-leaf path 1->2 represents the number 12. The root-to-leaf path 1->3 represents the number 13. Therefore; sum = 12 + 13 = 25. Example 2: Input: root = [4;9;0;5;1] Output: 1026 Explanation: The root-to-leaf path 4->9->5 represents the number 495. The root-to-leaf path 4->9->1 represents the number 491. The root-to-leaf path 4->0 represents the number 40. Therefore; sum = 495 + 491 + 40 = 1026. Constraints: The number of nodes in the tree is in the range [1; 1000]. 0 <= Node.val <= 9 The depth of the tree will not exceed 10.
Meta,346,Moving Average from Data Stream,Easy,"Array, Design, Queue, Data Stream",
Meta,987,Vertical Order Traversal of a Binary Tree,Hard,"Array, Queue, Sorting, Simulation",You are given an integer array deck. There is a deck of cards where every card has a unique integer. The integer on the ith card is deck[i]. You can order the deck in any order you want. Initially; all the cards start face down (unrevealed) in one deck. You will do the following steps repeatedly until all cards are revealed: Take the top card of the deck; reveal it; and take it out of the deck. If there are still cards in the deck then put the next top card of the deck at the bottom of the deck. If there are still unrevealed cards; go back to step 1. Otherwise; stop. Return an ordering of the deck that would reveal the cards in increasing order. Note that the first entry in the answer is considered to be the top of the deck. Example 1: Input: deck = [17;13;11;2;3;5;7] Output: [2;13;3;11;5;17;7] Explanation: We get the deck in the order [17;13;11;2;3;5;7] (this order does not matter); and reorder it. After reordering; the deck starts as [2;13;3;11;5;17;7]; where 2 is the top of the deck. We reveal 2; and move 13 to the bottom. The deck is now [3;11;5;17;7;13]. We reveal 3; and move 11 to the bottom. The deck is now [5;17;7;13;11]. We reveal 5; and move 17 to the bottom. The deck is now [7;13;11;17]. We reveal 7; and move 13 to the bottom. The deck is now [11;17;13]. We reveal 11; and move 17 to the bottom. The deck is now [13;17]. We reveal 13; and move 17 to the bottom. The deck is now [17]. We reveal 17. Since all the cards revealed are in increasing order; the answer is correct. Example 2: Input: deck = [1;1000] Output: [1;1000] Constraints: 1 <= deck.length <= 1000 1 <= deck[i] <= 106 All the values of deck are unique.
Meta,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Meta,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Meta,1539,Kth Missing Positive Number,Easy,"Array, Sorting, Heap (Priority Queue)",Given a 2D integer array nums; return all elements of nums in diagonal order as shown in the below images. Example 1: Input: nums = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;4;2;7;5;3;8;6;9] Example 2: Input: nums = [[1;2;3;4;5];[6;7];[8];[9;10;11];[12;13;14;15;16]] Output: [1;6;2;8;7;3;9;4;12;10;5;13;11;14;15;16] Constraints: 1 <= nums.length <= 105 1 <= nums[i].length <= 105 1 <= sum(nums[i].length) <= 105 1 <= nums[i][j] <= 105
Meta,133,Clone Graph,Med,"Hash Table, Depth-First Search, Breadth-First Search, Graph",Given a reference of a node in a connected undirected graph. Return a deep copy (clone) of the graph. Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors. class Node { public int val; public List<Node> neighbors; } Test case format: For simplicity; each node's value is the same as the node's index (1-indexed). For example; the first node with val == 1; the second node with val == 2; and so on. The graph is represented in the test case using an adjacency list. An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph. The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph. Example 1: Input: adjList = [[2;4];[1;3];[2;4];[1;3]] Output: [[2;4];[1;3];[2;4];[1;3]] Explanation: There are 4 nodes in the graph. 1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). 3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). Example 2: Input: adjList = [[]] Output: [[]] Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors. Example 3: Input: adjList = [] Output: [] Explanation: This an empty graph; it does not have any nodes. Constraints: The number of nodes in the graph is in the range [0; 100]. 1 <= Node.val <= 100 Node.val is unique for each node. There are no repeated edges and no self-loops in the graph. The Graph is connected and all nodes can be visited starting from the given node.
Meta,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Meta,636,Exclusive Time of Functions,Med,"Array, Stack","On a single-threaded CPU; we execute a program containing n functions. Each function has a unique ID between 0 and n-1. Function calls are stored in a call stack: when a function call starts; its ID is pushed onto the stack; and when a function call ends; its ID is popped off the stack. The function whose ID is at the top of the stack is the current function being executed. Each time a function starts or ends; we write a log with the ID; whether it started or ended; and the timestamp. You are given a list logs; where logs[i] represents the ith log message formatted as a string ""{function_id}:{""start"" | ""end""}:{timestamp}"". For example; ""0:start:3"" means a function call with function ID 0 started at the beginning of timestamp 3; and ""1:end:2"" means a function call with function ID 1 ended at the end of timestamp 2. Note that a function can be called multiple times; possibly recursively. A function's exclusive time is the sum of execution times for all function calls in the program. For example; if a function is called twice; one call executing for 2 time units and another call executing for 1 time unit; the exclusive time is 2 + 1 = 3. Return the exclusive time of each function in an array; where the value at the ith index represents the exclusive time for the function with ID i. Example 1: Input: n = 2; logs = [""0:start:0"";""1:start:2"";""1:end:5"";""0:end:6""] Output: [3;4] Explanation: Function 0 starts at the beginning of time 0; then it executes 2 for units of time and reaches the end of time 1. Function 1 starts at the beginning of time 2; executes for 4 units of time; and ends at the end of time 5. Function 0 resumes execution at the beginning of time 6 and executes for 1 unit of time. So function 0 spends 2 + 1 = 3 units of total time executing; and function 1 spends 4 units of total time executing. Example 2: Input: n = 1; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""0:start:6"";""0:end:6"";""0:end:7""] Output: [8] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls itself again. Function 0 (2nd recursive call) starts at the beginning of time 6 and executes for 1 unit of time. Function 0 (initial call) resumes execution at the beginning of time 7 and executes for 1 unit of time. So function 0 spends 2 + 4 + 1 + 1 = 8 units of total time executing. Example 3: Input: n = 2; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""1:start:6"";""1:end:6"";""0:end:7""] Output: [7;1] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls function 1. Function 1 starts at the beginning of time 6; executes 1 unit of time; and ends at the end of time 6. Function 0 resumes execution at the beginning of time 6 and executes for 2 units of time. So function 0 spends 2 + 4 + 1 = 7 units of total time executing; and function 1 spends 1 unit of total time executing. Constraints: 1 <= n <= 100 1 <= logs.length <= 500 0 <= function_id < n 0 <= timestamp <= 109 No two start events will happen at the same timestamp. No two end events will happen at the same timestamp. Each function has an ""end"" log for each ""start"" log."
Meta,163,Missing Ranges,Easy,Array,
Meta,498,Diagonal Traverse,Med,"Array, Matrix, Simulation",Given an m x n matrix mat; return an array of all the elements of the array in a diagonal order. Example 1: Input: mat = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;4;7;5;3;6;8;9] Example 2: Input: mat = [[1;2];[3;4]] Output: [1;2;3;4] Constraints: m == mat.length n == mat[i].length 1 <= m; n <= 104 1 <= m * n <= 104 -105 <= mat[i][j] <= 105
Meta,766,Toeplitz Matrix,Easy,"Linked List, Depth-First Search, Doubly-Linked List",You are given a doubly linked list; which contains nodes that have a next pointer; a previous pointer; and an additional child pointer. This child pointer may or may not point to a separate doubly linked list; also containing these special nodes. These child lists may have one or more children of their own; and so on; to produce a multilevel data structure as shown in the example below. Given the head of the first level of the list; flatten the list so that all the nodes appear in a single-level; doubly linked list. Let curr be a node with a child list. The nodes in the child list should appear after curr and before curr.next in the flattened list. Return the head of the flattened list. The nodes in the list must have all of their child pointers set to null. Example 1: Input: head = [1;2;3;4;5;6;null;null;null;7;8;9;10;null;null;11;12] Output: [1;2;3;7;8;11;12;9;10;4;5;6] Explanation: The multilevel linked list in the input is shown. After flattening the multilevel linked list it becomes: Example 2: Input: head = [1;2;null;3] Output: [1;3;2] Explanation: The multilevel linked list in the input is shown. After flattening the multilevel linked list it becomes: Example 3: Input: head = [] Output: [] Explanation: There could be empty list in the input. Constraints: The number of Nodes will not exceed 1000. 1 <= Node.val <= 105 How the multilevel linked list is represented in test cases: We use the multilevel linked list from Example 1 above: 1---2---3---4---5---6--NULL | 7---8---9---10--NULL | 11--12--NULL The serialization of each level is as follows: [1;2;3;4;5;6;null] [7;8;9;10;null] [11;12;null] To serialize all levels together; we will add nulls in each level to signify no node connects to the upper node of the previous level. The serialization becomes: [1; 2; 3; 4; 5; 6; null] | [null; null; 7; 8; 9; 10; null] | [ null; 11; 12; null] Merging the serialization of each level and removing trailing nulls we obtain: [1;2;3;4;5;6;null;null;null;7;8;9;10;null;null;11;12]
Meta,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
Meta,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Meta,708,Insert into a Sorted Circular Linked List,Med,,
Meta,65,Valid Number,Hard,String,"Given a string s; return whether s is a valid number. For example; all the following are valid numbers: ""2""; ""0089""; ""-0.1""; ""+3.14""; ""4.""; ""-.9""; ""2e10""; ""-90E3""; ""3e+7""; ""+6e-1""; ""53.5e93""; ""-123.456e789""; while the following are not valid numbers: ""abc""; ""1a""; ""1e""; ""e3""; ""99e2.5""; ""--6""; ""-+3""; ""95a54e53"". Formally; a valid number is defined using one of the following definitions: An integer number followed by an optional exponent. A decimal number followed by an optional exponent. An integer number is defined with an optional sign '-' or '+' followed by digits. A decimal number is defined with an optional sign '-' or '+' followed by one of the following definitions: Digits followed by a dot '.'. Digits followed by a dot '.' followed by digits. A dot '.' followed by digits. An exponent is defined with an exponent notation 'e' or 'E' followed by an integer number. The digits are defined as one or more digits. Example 1: Input: s = ""0"" Output: true Example 2: Input: s = ""e"" Output: false Example 3: Input: s = ""."" Output: false Constraints: 1 <= s.length <= 20 s consists of only English letters (both uppercase and lowercase); digits (0-9); plus '+'; minus '-'; or dot '.'."
Meta,249,Group Shifted Strings,Med,"Array, Hash Table, String",
Meta,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Meta,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Meta,173,Binary Search Tree Iterator,Med,"Stack, Tree, Design, Binary Search Tree, Binary Tree, Iterator","Implement the BSTIterator class that represents an iterator over the in-order traversal of a binary search tree (BST): BSTIterator(TreeNode root) Initializes an object of the BSTIterator class. The root of the BST is given as part of the constructor. The pointer should be initialized to a non-existent number smaller than any element in the BST. boolean hasNext() Returns true if there exists a number in the traversal to the right of the pointer; otherwise returns false. int next() Moves the pointer to the right; then returns the number at the pointer. Notice that by initializing the pointer to a non-existent smallest number; the first call to next() will return the smallest element in the BST. You may assume that next() calls will always be valid. That is; there will be at least a next number in the in-order traversal when next() is called. Example 1: Input [""BSTIterator""; ""next""; ""next""; ""hasNext""; ""next""; ""hasNext""; ""next""; ""hasNext""; ""next""; ""hasNext""] [[[7; 3; 15; null; null; 9; 20]]; []; []; []; []; []; []; []; []; []] Output [null; 3; 7; true; 9; true; 15; true; 20; false] Explanation BSTIterator bSTIterator = new BSTIterator([7; 3; 15; null; null; 9; 20]); bSTIterator.next(); // return 3 bSTIterator.next(); // return 7 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 9 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 15 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 20 bSTIterator.hasNext(); // return False Constraints: The number of nodes in the tree is in the range [1; 105]. 0 <= Node.val <= 106 At most 105 calls will be made to hasNext; and next. Follow up: Could you implement next() and hasNext() to run in average O(1) time and use O(h) memory; where h is the height of the tree?"
Meta,398,Random Pick Index,Med,"Hash Table, Math, Reservoir Sampling, Randomized","Given an integer array nums with possible duplicates; randomly output the index of a given target number. You can assume that the given target number must exist in the array. Implement the Solution class: Solution(int[] nums) Initializes the object with the array nums. int pick(int target) Picks a random index i from nums where nums[i] == target. If there are multiple valid i's; then each index should have an equal probability of returning. Example 1: Input [""Solution""; ""pick""; ""pick""; ""pick""] [[[1; 2; 3; 3; 3]]; [3]; [1]; [3]] Output [null; 4; 0; 2] Explanation Solution solution = new Solution([1; 2; 3; 3; 3]); solution.pick(3); // It should return either index 2; 3; or 4 randomly. Each index should have equal probability of returning. solution.pick(1); // It should return 0. Since in the array only nums[0] is equal to 1. solution.pick(3); // It should return either index 2; 3; or 4 randomly. Each index should have equal probability of returning. Constraints: 1 <= nums.length <= 2 * 104 -231 <= nums[i] <= 231 - 1 target is an integer from nums. At most 104 calls will be made to pick."
Meta,1047,Remove All Adjacent Duplicates In String,Easy,"Array, Greedy, Sorting",Given an integer array nums and an integer k; modify the array in the following way: choose an index i and replace nums[i] with -nums[i]. You should apply this process exactly k times. You may choose the same index i multiple times. Return the largest possible sum of the array after modifying it in this way. Example 1: Input: nums = [4;2;3]; k = 1 Output: 5 Explanation: Choose index 1 and nums becomes [4;-2;3]. Example 2: Input: nums = [3;-1;0;2]; k = 3 Output: 6 Explanation: Choose indices (1; 2; 2) and nums becomes [3;1;0;2]. Example 3: Input: nums = [2;-3;-1;5;-4]; k = 2 Output: 13 Explanation: Choose indices (1; 4) and nums becomes [2;3;-1;5;4]. Constraints: 1 <= nums.length <= 104 -100 <= nums[i] <= 100 1 <= k <= 104
Meta,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Meta,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Meta,415,Add Strings,Easy,"Math, String, Simulation","Given two non-negative integers; num1 and num2 represented as string; return the sum of num1 and num2 as a string. You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly. Example 1: Input: num1 = ""11""; num2 = ""123"" Output: ""134"" Example 2: Input: num1 = ""456""; num2 = ""77"" Output: ""533"" Example 3: Input: num1 = ""0""; num2 = ""0"" Output: ""0"" Constraints: 1 <= num1.length; num2.length <= 104 num1 and num2 consist of only digits. num1 and num2 don't have any leading zeros except for the zero itself."
Meta,523,Continuous Subarray Sum,Med,"Array, Hash Table, Math, Prefix Sum",Given an integer array nums and an integer k; return true if nums has a good subarray or false otherwise. A good subarray is a subarray where: its length is at least two; and the sum of the elements of the subarray is a multiple of k. Note that: A subarray is a contiguous part of the array. An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k. Example 1: Input: nums = [23;2;4;6;7]; k = 6 Output: true Explanation: [2; 4] is a continuous subarray of size 2 whose elements sum up to 6. Example 2: Input: nums = [23;2;6;4;7]; k = 6 Output: true Explanation: [23; 2; 6; 4; 7] is an continuous subarray of size 5 whose elements sum up to 42. 42 is a multiple of 6 because 42 = 7 * 6 and 7 is an integer. Example 3: Input: nums = [23;2;6;4;7]; k = 13 Output: false Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109 0 <= sum(nums[i]) <= 231 - 1 1 <= k <= 231 - 1
Meta,1768,Merge Strings Alternately,Easy,"Array, Math, Stack, Tree, Design, Binary Tree",
Meta,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Meta,282,Expression Add Operators,Hard,"Math, String, Backtracking","Given a string num that contains only digits and an integer target; return all possibilities to insert the binary operators '+'; '-'; and/or '*' between the digits of num so that the resultant expression evaluates to the target value. Note that operands in the returned expressions should not contain leading zeros. Example 1: Input: num = ""123""; target = 6 Output: [""1*2*3"";""1+2+3""] Explanation: Both ""1*2*3"" and ""1+2+3"" evaluate to 6. Example 2: Input: num = ""232""; target = 8 Output: [""2*3+2"";""2+3*2""] Explanation: Both ""2*3+2"" and ""2+3*2"" evaluate to 8. Example 3: Input: num = ""3456237490""; target = 9191 Output: [] Explanation: There are no expressions that can be created from ""3456237490"" to evaluate to 9191. Constraints: 1 <= num.length <= 10 num consists of only digits. -231 <= target <= 231 - 1"
Meta,827,Making A Large Island,Hard,"Array, Two Pointers, String","Sometimes people repeat letters to represent extra feeling. For example: ""hello"" -> ""heeellooo"" ""hi"" -> ""hiiii"" In these strings like ""heeellooo""; we have groups of adjacent letters that are all the same: ""h""; ""eee""; ""ll""; ""ooo"". You are given a string s and an array of query strings words. A query word is stretchy if it can be made to be equal to s by any number of applications of the following extension operation: choose a group consisting of characters c; and add some number of characters c to the group so that the size of the group is three or more. For example; starting with ""hello""; we could do an extension on the group ""o"" to get ""hellooo""; but we cannot get ""helloo"" since the group ""oo"" has a size less than three. Also; we could do another extension like ""ll"" -> ""lllll"" to get ""helllllooo"". If s = ""helllllooo""; then the query word ""hello"" would be stretchy because of these two extension operations: query = ""hello"" -> ""hellooo"" -> ""helllllooo"" = s. Return the number of query strings that are stretchy. Example 1: Input: s = ""heeellooo""; words = [""hello""; ""hi""; ""helo""] Output: 1 Explanation: We can extend ""e"" and ""o"" in the word ""hello"" to get ""heeellooo"". We can't extend ""helo"" to get ""heeellooo"" because the group ""ll"" is not size 3 or more. Example 2: Input: s = ""zzzzzyyyyy""; words = [""zzyy"";""zy"";""zyy""] Output: 3 Constraints: 1 <= s.length; words.length <= 100 1 <= words[i].length <= 100 s and words[i] consist of lowercase letters."
Meta,863,All Nodes Distance K in Binary Tree,Med,"Dynamic Programming, Tree, Depth-First Search, Graph",There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Return an array answer of length n where answer[i] is the sum of the distances between the ith node in the tree and all other nodes. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;3];[2;4];[2;5]] Output: [8;12;6;10;10;10] Explanation: The tree is shown above. We can see that dist(0;1) + dist(0;2) + dist(0;3) + dist(0;4) + dist(0;5) equals 1 + 1 + 2 + 2 + 2 = 8. Hence; answer[0] = 8; and so on. Example 2: Input: n = 1; edges = [] Output: [0] Example 3: Input: n = 2; edges = [[1;0]] Output: [1;1] Constraints: 1 <= n <= 3 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n ai != bi The given input represents a valid tree.
Meta,8,String to Integer (atoi),Med,String,"Implement the myAtoi(string s) function; which converts a string to a 32-bit signed integer. The algorithm for myAtoi(string s) is as follows: Whitespace: Ignore any leading whitespace ("" ""). Signedness: Determine the sign by checking if the next character is '-' or '+'; assuming positivity if neither present. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read; then the result is 0. Rounding: If the integer is out of the 32-bit signed integer range [-231; 231 - 1]; then round the integer to remain in the range. Specifically; integers less than -231 should be rounded to -231; and integers greater than 231 - 1 should be rounded to 231 - 1. Return the integer as the final result. Example 1: Input: s = ""42"" Output: 42 Explanation: The underlined characters are what is read in and the caret is the current reader position. Step 1: ""42"" (no characters read because there is no leading whitespace) ^ Step 2: ""42"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""42"" (""42"" is read in) ^ Example 2: Input: s = "" -042"" Output: -42 Explanation: Step 1: "" -042"" (leading whitespace is read and ignored) ^ Step 2: "" -042"" ('-' is read; so the result should be negative) ^ Step 3: "" -042"" (""042"" is read in; leading zeros ignored in the result) ^ Example 3: Input: s = ""1337c0d3"" Output: 1337 Explanation: Step 1: ""1337c0d3"" (no characters read because there is no leading whitespace) ^ Step 2: ""1337c0d3"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""1337c0d3"" (""1337"" is read in; reading stops because the next character is a non-digit) ^ Example 4: Input: s = ""0-1"" Output: 0 Explanation: Step 1: ""0-1"" (no characters read because there is no leading whitespace) ^ Step 2: ""0-1"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""0-1"" (""0"" is read in; reading stops because the next character is a non-digit) ^ Example 5: Input: s = ""words and 987"" Output: 0 Explanation: Reading stops at the first non-digit character 'w'. Constraints: 0 <= s.length <= 200 s consists of English letters (lower-case and upper-case); digits (0-9); ' '; '+'; '-'; and '.'."
Meta,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Meta,2667,Create Hello World Function,Easy,"Array, Hash Table, Math, Stack, Sliding Window",
Meta,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Meta,270,Closest Binary Search Tree Value,Easy,"Binary Search, Tree, Depth-First Search, Binary Search Tree, Binary Tree",
Meta,691,Stickers to Spell Word,Hard,"Array, String, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask","We are given n different types of stickers. Each sticker has a lowercase English word on it. You would like to spell out the given string target by cutting individual letters from your collection of stickers and rearranging them. You can use each sticker more than once if you want; and you have infinite quantities of each sticker. Return the minimum number of stickers that you need to spell out target. If the task is impossible; return -1. Note: In all test cases; all words were chosen randomly from the 1000 most common US English words; and target was chosen as a concatenation of two random words. Example 1: Input: stickers = [""with"";""example"";""science""]; target = ""thehat"" Output: 3 Explanation: We can use 2 ""with"" stickers; and 1 ""example"" sticker. After cutting and rearrange the letters of those stickers; we can form the target ""thehat"". Also; this is the minimum number of stickers necessary to form the target string. Example 2: Input: stickers = [""notice"";""possible""]; target = ""basicbasic"" Output: -1 Explanation: We cannot form the target ""basicbasic"" from cutting letters from the given stickers. Constraints: n == stickers.length 1 <= n <= 50 1 <= stickers[i].length <= 10 1 <= target.length <= 15 stickers[i] and target consist of lowercase English letters."
Meta,721,Accounts Merge,Med,"Array, Hash Table, String, Depth-First Search, Breadth-First Search, Union Find, Sorting","Given a list of accounts where each element accounts[i] is a list of strings; where the first element accounts[i][0] is a name; and the rest of the elements are emails representing emails of the account. Now; we would like to merge these accounts. Two accounts definitely belong to the same person if there is some common email to both accounts. Note that even if two accounts have the same name; they may belong to different people as people could have the same name. A person can have any number of accounts initially; but all of their accounts definitely have the same name. After merging the accounts; return the accounts in the following format: the first element of each account is the name; and the rest of the elements are emails in sorted order. The accounts themselves can be returned in any order. Example 1: Input: accounts = [[""John"";""johnsmith@mail.com"";""john_newyork@mail.com""];[""John"";""johnsmith@mail.com"";""john00@mail.com""];[""Mary"";""mary@mail.com""];[""John"";""johnnybravo@mail.com""]] Output: [[""John"";""john00@mail.com"";""john_newyork@mail.com"";""johnsmith@mail.com""];[""Mary"";""mary@mail.com""];[""John"";""johnnybravo@mail.com""]] Explanation: The first and second John's are the same person as they have the common email ""johnsmith@mail.com"". The third John and Mary are different people as none of their email addresses are used by other accounts. We could return these lists in any order; for example the answer [['Mary'; 'mary@mail.com']; ['John'; 'johnnybravo@mail.com']; ['John'; 'john00@mail.com'; 'john_newyork@mail.com'; 'johnsmith@mail.com']] would still be accepted. Example 2: Input: accounts = [[""Gabe"";""Gabe0@m.co"";""Gabe3@m.co"";""Gabe1@m.co""];[""Kevin"";""Kevin3@m.co"";""Kevin5@m.co"";""Kevin0@m.co""];[""Ethan"";""Ethan5@m.co"";""Ethan4@m.co"";""Ethan0@m.co""];[""Hanzo"";""Hanzo3@m.co"";""Hanzo1@m.co"";""Hanzo0@m.co""];[""Fern"";""Fern5@m.co"";""Fern1@m.co"";""Fern0@m.co""]] Output: [[""Ethan"";""Ethan0@m.co"";""Ethan4@m.co"";""Ethan5@m.co""];[""Gabe"";""Gabe0@m.co"";""Gabe1@m.co"";""Gabe3@m.co""];[""Hanzo"";""Hanzo0@m.co"";""Hanzo1@m.co"";""Hanzo3@m.co""];[""Kevin"";""Kevin0@m.co"";""Kevin3@m.co"";""Kevin5@m.co""];[""Fern"";""Fern0@m.co"";""Fern1@m.co"";""Fern5@m.co""]] Constraints: 1 <= accounts.length <= 1000 2 <= accounts[i].length <= 10 1 <= accounts[i][j].length <= 30 accounts[i][0] consists of English letters. accounts[i][j] (for j > 0) is a valid email."
Meta,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Meta,219,Contains Duplicate II,Easy,"Array, Hash Table, Sliding Window",Given an integer array nums and an integer k; return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k. Example 1: Input: nums = [1;2;3;1]; k = 3 Output: true Example 2: Input: nums = [1;0;1;1]; k = 1 Output: true Example 3: Input: nums = [1;2;3;1;2;3]; k = 2 Output: false Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109 0 <= k <= 105
Meta,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Meta,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
Meta,16,3Sum Closest,Med,"Array, Two Pointers, Sorting",Given an integer array nums of length n and an integer target; find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution. Example 1: Input: nums = [-1;2;1;-4]; target = 1 Output: 2 Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2). Example 2: Input: nums = [0;0;0]; target = 1 Output: 0 Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0). Constraints: 3 <= nums.length <= 500 -1000 <= nums[i] <= 1000 -104 <= target <= 104
Meta,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
Meta,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
Meta,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Meta,197,Rising Temperature,Easy,Database,Table: Weather +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | recordDate | date | | temperature | int | +---------------+---------+ id is the column with unique values for this table. There are no different rows with the same recordDate. This table contains information about the temperature on a certain day. Write a solution to find all dates' id with higher temperatures compared to its previous dates (yesterday). Return the result table in any order. The result format is in the following example. Example 1: Input: Weather table: +----+------------+-------------+ | id | recordDate | temperature | +----+------------+-------------+ | 1 | 2015-01-01 | 10 | | 2 | 2015-01-02 | 25 | | 3 | 2015-01-03 | 20 | | 4 | 2015-01-04 | 30 | +----+------------+-------------+ Output: +----+ | id | +----+ | 2 | | 4 | +----+ Explanation: In 2015-01-02; the temperature was higher than the previous day (10 -> 25). In 2015-01-04; the temperature was higher than the previous day (20 -> 30).
Meta,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Meta,269,Alien Dictionary,Hard,"Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort",
Meta,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
Meta,536,Construct Binary Tree from String,Med,"String, Stack, Tree, Depth-First Search, Binary Tree",
Meta,539,Minimum Time Difference,Med,"Array, Math, String, Sorting","Given a list of 24-hour clock time points in ""HH:MM"" format; return the minimum minutes difference between any two time-points in the list. Example 1: Input: timePoints = [""23:59"";""00:00""] Output: 1 Example 2: Input: timePoints = [""00:00"";""23:59"";""00:00""] Output: 0 Constraints: 2 <= timePoints.length <= 2 * 104 timePoints[i] is in the format ""HH:MM""."
Meta,658,Find K Closest Elements,Med,"Array, Two Pointers, Binary Search, Sliding Window, Sorting, Heap (Priority Queue)",Given a sorted integer array arr; two integers k and x; return the k closest integers to x in the array. The result should also be sorted in ascending order. An integer a is closer to x than an integer b if: |a - x| < |b - x|; or |a - x| == |b - x| and a < b Example 1: Input: arr = [1;2;3;4;5]; k = 4; x = 3 Output: [1;2;3;4] Example 2: Input: arr = [1;1;2;3;4;5]; k = 4; x = -1 Output: [1;1;2;3] Constraints: 1 <= k <= arr.length 1 <= arr.length <= 104 arr is sorted in ascending order. -104 <= arr[i]; x <= 104
Meta,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Meta,824,Goat Latin,Easy,"Array, String","You are given a string s of lowercase English letters and an array widths denoting how many pixels wide each lowercase English letter is. Specifically; widths[0] is the width of 'a'; widths[1] is the width of 'b'; and so on. You are trying to write s across several lines; where each line is no longer than 100 pixels. Starting at the beginning of s; write as many letters on the first line such that the total width does not exceed 100 pixels. Then; from where you stopped in s; continue writing as many letters as you can on the second line. Continue this process until you have written all of s. Return an array result of length 2 where: result[0] is the total number of lines. result[1] is the width of the last line in pixels. Example 1: Input: widths = [10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10]; s = ""abcdefghijklmnopqrstuvwxyz"" Output: [3;60] Explanation: You can write s as follows: abcdefghij // 100 pixels wide klmnopqrst // 100 pixels wide uvwxyz // 60 pixels wide There are a total of 3 lines; and the last line is 60 pixels wide. Example 2: Input: widths = [4;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10;10]; s = ""bbbcccdddaaa"" Output: [2;4] Explanation: You can write s as follows: bbbcccdddaa // 98 pixels wide a // 4 pixels wide There are a total of 2 lines; and the last line is 4 pixels wide. Constraints: widths.length == 26 2 <= widths[i] <= 10 1 <= s.length <= 1000 s contains only lowercase English letters."
Meta,875,Koko Eating Bananas,Med,"Array, Two Pointers, Dynamic Programming, Enumeration",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr; return the length of the longest subarray; which is a mountain. Return 0 if there is no mountain subarray. Example 1: Input: arr = [2;1;4;7;3;2;5] Output: 5 Explanation: The largest mountain is [1;4;7;3;2] which has length 5. Example 2: Input: arr = [2;2;2] Output: 0 Explanation: There is no mountain. Constraints: 1 <= arr.length <= 104 0 <= arr[i] <= 104 Follow up: Can you solve it using only one pass? Can you solve it in O(1) space?
Meta,1216,Valid Palindrome III,Hard,Concurrency,"You have a function printNumber that can be called with an integer parameter and prints it to the console. For example; calling printNumber(7) prints 7 to the console. You are given an instance of the class ZeroEvenOdd that has three functions: zero; even; and odd. The same instance of ZeroEvenOdd will be passed to three different threads: Thread A: calls zero() that should only output 0's. Thread B: calls even() that should only output even numbers. Thread C: calls odd() that should only output odd numbers. Modify the given class to output the series ""010203040506..."" where the length of the series must be 2n. Implement the ZeroEvenOdd class: ZeroEvenOdd(int n) Initializes the object with the number n that represents the numbers that should be printed. void zero(printNumber) Calls printNumber to output one zero. void even(printNumber) Calls printNumber to output one even number. void odd(printNumber) Calls printNumber to output one odd number. Example 1: Input: n = 2 Output: ""0102"" Explanation: There are three threads being fired asynchronously. One of them calls zero(); the other calls even(); and the last one calls odd(). ""0102"" is the correct output. Example 2: Input: n = 5 Output: ""0102030405"" Constraints: 1 <= n <= 1000"
Meta,1424,Diagonal Traverse II,Med,"Array, Breadth-First Search, Graph",You have n boxes labeled from 0 to n - 1. You are given four arrays: status; candies; keys; and containedBoxes where: status[i] is 1 if the ith box is open and 0 if the ith box is closed; candies[i] is the number of candies in the ith box; keys[i] is a list of the labels of the boxes you can open after opening the ith box. containedBoxes[i] is a list of the boxes you found inside the ith box. You are given an integer array initialBoxes that contains the labels of the boxes you initially have. You can take all the candies in any open box and you can use the keys in it to open new boxes and you also can use the boxes you find in it. Return the maximum number of candies you can get following the rules above. Example 1: Input: status = [1;0;1;0]; candies = [7;5;4;100]; keys = [[];[];[1];[]]; containedBoxes = [[1;2];[3];[];[]]; initialBoxes = [0] Output: 16 Explanation: You will be initially given box 0. You will find 7 candies in it and boxes 1 and 2. Box 1 is closed and you do not have a key for it so you will open box 2. You will find 4 candies and a key to box 1 in box 2. In box 1; you will find 5 candies and box 3 but you will not find a key to box 3 so box 3 will remain closed. Total number of candies collected = 7 + 4 + 5 = 16 candy. Example 2: Input: status = [1;0;0;0;0;0]; candies = [1;1;1;1;1;1]; keys = [[1;2;3;4;5];[];[];[];[];[]]; containedBoxes = [[1;2;3;4;5];[];[];[];[];[]]; initialBoxes = [0] Output: 6 Explanation: You have initially box 0. Opening it you can find boxes 1;2;3;4 and 5 and their keys. The total number of candies will be 6. Constraints: n == status.length == candies.length == keys.length == containedBoxes.length 1 <= n <= 1000 status[i] is either 0 or 1. 1 <= candies[i] <= 1000 0 <= keys[i].length <= n 0 <= keys[i][j] < n All values of keys[i] are unique. 0 <= containedBoxes[i].length <= n 0 <= containedBoxes[i][j] < n All values of containedBoxes[i] are unique. Each box is contained in one box at most. 0 <= initialBoxes.length <= n 0 <= initialBoxes[i] < n
Meta,1757,Recyclable and Low Fat Products,Easy,"Array, Dynamic Programming, Breadth-First Search",A certain bug's home is on the x-axis at position x. Help them get there from position 0. The bug jumps according to the following rules: It can jump exactly a positions forward (to the right). It can jump exactly b positions backward (to the left). It cannot jump backward twice in a row. It cannot jump to any forbidden positions. The bug may jump forward beyond its home; but it cannot jump to positions numbered with negative integers. Given an array of integers forbidden; where forbidden[i] means that the bug cannot jump to the position forbidden[i]; and integers a; b; and x; return the minimum number of jumps needed for the bug to reach its home. If there is no possible sequence of jumps that lands the bug on position x; return -1. Example 1: Input: forbidden = [14;4;18;1;15]; a = 3; b = 15; x = 9 Output: 3 Explanation: 3 jumps forward (0 -> 3 -> 6 -> 9) will get the bug home. Example 2: Input: forbidden = [8;3;16;6;12;20]; a = 15; b = 13; x = 11 Output: -1 Example 3: Input: forbidden = [1;6;2;14;5;17;4]; a = 16; b = 9; x = 7 Output: 2 Explanation: One jump forward (0 -> 16) then one jump backward (16 -> 7) will get the bug home. Constraints: 1 <= forbidden.length <= 1000 1 <= a; b; forbidden[i] <= 2000 0 <= x <= 2000 All the elements in forbidden are distinct. Position x is not forbidden.
Meta,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Meta,26,Remove Duplicates from Sorted Array,Easy,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums. Consider the number of unique elements of nums to be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;2] Output: 2; nums = [1;2;_] Explanation: Your function should return k = 2; with the first two elements of nums being 1 and 2 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;2;2;3;3;4] Output: 5; nums = [0;1;2;3;4;_;_;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums being 0; 1; 2; 3; and 4 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -100 <= nums[i] <= 100 nums is sorted in non-decreasing order.
Meta,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Meta,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Meta,378,Kth Smallest Element in a Sorted Matrix,Med,"Array, Binary Search, Sorting, Heap (Priority Queue), Matrix",Given an n x n matrix where each of the rows and columns is sorted in ascending order; return the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order; not the kth distinct element. You must find a solution with a memory complexity better than O(n2). Example 1: Input: matrix = [[1;5;9];[10;11;13];[12;13;15]]; k = 8 Output: 13 Explanation: The elements in the matrix are [1;5;9;10;11;12;13;13;15]; and the 8th smallest number is 13 Example 2: Input: matrix = [[-5]]; k = 1 Output: -5 Constraints: n == matrix.length == matrix[i].length 1 <= n <= 300 -109 <= matrix[i][j] <= 109 All the rows and columns of matrix are guaranteed to be sorted in non-decreasing order. 1 <= k <= n2 Follow up: Could you solve the problem with a constant memory (i.e.; O(1) memory complexity)? Could you solve the problem in O(n) time complexity? The solution may be too advanced for an interview but you may find reading this paper fun.
Meta,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Meta,480,Sliding Window Median,Hard,"Array, Hash Table, Sliding Window, Heap (Priority Queue)",The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value. So the median is the mean of the two middle values. For examples; if arr = [2;3;4]; the median is 3. For examples; if arr = [1;2;3;4]; the median is (2 + 3) / 2 = 2.5. You are given an integer array nums and an integer k. There is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the median array for each window in the original array. Answers within 10-5 of the actual value will be accepted. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [1.00000;-1.00000;-1.00000;3.00000;5.00000;6.00000] Explanation: Window position Median --------------- ----- [1 3 -1] -3 5 3 6 7 1 1 [3 -1 -3] 5 3 6 7 -1 1 3 [-1 -3 5] 3 6 7 -1 1 3 -1 [-3 5 3] 6 7 3 1 3 -1 -3 [5 3 6] 7 5 1 3 -1 -3 5 [3 6 7] 6 Example 2: Input: nums = [1;2;3;4;2;3;1;4;2]; k = 3 Output: [2.00000;3.00000;3.00000;3.00000;2.00000;3.00000;2.00000] Constraints: 1 <= k <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Meta,647,Palindromic Substrings,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the number of palindromic substrings in it. A string is a palindrome when it reads the same backward as forward. A substring is a contiguous sequence of characters within the string. Example 1: Input: s = ""abc"" Output: 3 Explanation: Three palindromic strings: ""a""; ""b""; ""c"". Example 2: Input: s = ""aaa"" Output: 6 Explanation: Six palindromic strings: ""a""; ""a""; ""a""; ""aa""; ""aa""; ""aaa"". Constraints: 1 <= s.length <= 1000 s consists of lowercase English letters."
Meta,1644,Lowest Common Ancestor of a Binary Tree II,Med,"String, Greedy","Given a string s of lowercase letters; you need to find the maximum number of non-empty substrings of s that meet the following conditions: The substrings do not overlap; that is for any two substrings s[i..j] and s[x..y]; either j < x or i > y is true. A substring that contains a certain character c must also contain all occurrences of c. Find the maximum number of substrings that meet the above conditions. If there are multiple solutions with the same number of substrings; return the one with minimum total length. It can be shown that there exists a unique solution of minimum total length. Notice that you can return the substrings in any order. Example 1: Input: s = ""adefaddaccc"" Output: [""e"";""f"";""ccc""] Explanation: The following are all the possible substrings that meet the conditions: [ ""adefaddaccc"" ""adefadda""; ""ef""; ""e""; ""f""; ""ccc""; ] If we choose the first string; we cannot choose anything else and we'd get only 1. If we choose ""adefadda""; we are left with ""ccc"" which is the only one that doesn't overlap; thus obtaining 2 substrings. Notice also; that it's not optimal to choose ""ef"" since it can be split into two. Therefore; the optimal way is to choose [""e"";""f"";""ccc""] which gives us 3 substrings. No other solution of the same number of substrings exist. Example 2: Input: s = ""abbaccd"" Output: [""d"";""bb"";""cc""] Explanation: Notice that while the set of substrings [""d"";""abba"";""cc""] also has length 3; it's considered incorrect since it has larger total length. Constraints: 1 <= s.length <= 105 s contains only lowercase English letters."
Meta,1868,Product of Two Run-Length Encoded Arrays,Med,,
Meta,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Meta,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Meta,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Meta,38,Count and Say,Med,String,"The count-and-say sequence is a sequence of digit strings defined by the recursive formula: countAndSay(1) = ""1"" countAndSay(n) is the run-length encoding of countAndSay(n - 1). Run-length encoding (RLE) is a string compression method that works by replacing consecutive identical characters (repeated 2 or more times) with the concatenation of the character and the number marking the count of the characters (length of the run). For example; to compress the string ""3322251"" we replace ""33"" with ""23""; replace ""222"" with ""32""; replace ""5"" with ""15"" and replace ""1"" with ""11"". Thus the compressed string becomes ""23321511"". Given a positive integer n; return the nth element of the count-and-say sequence. Example 1: Input: n = 4 Output: ""1211"" Explanation: countAndSay(1) = ""1"" countAndSay(2) = RLE of ""1"" = ""11"" countAndSay(3) = RLE of ""11"" = ""21"" countAndSay(4) = RLE of ""21"" = ""1211"" Example 2: Input: n = 1 Output: ""1"" Explanation: This is the base case. Constraints: 1 <= n <= 30 Follow up: Could you solve it iteratively?"
Meta,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Meta,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Meta,66,Plus One,Easy,"Array, Math",You are given a large integer represented as an integer array digits; where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0's. Increment the large integer by one and return the resulting array of digits. Example 1: Input: digits = [1;2;3] Output: [1;2;4] Explanation: The array represents the integer 123. Incrementing by one gives 123 + 1 = 124. Thus; the result should be [1;2;4]. Example 2: Input: digits = [4;3;2;1] Output: [4;3;2;2] Explanation: The array represents the integer 4321. Incrementing by one gives 4321 + 1 = 4322. Thus; the result should be [4;3;2;2]. Example 3: Input: digits = [9] Output: [1;0] Explanation: The array represents the integer 9. Incrementing by one gives 9 + 1 = 10. Thus; the result should be [1;0]. Constraints: 1 <= digits.length <= 100 0 <= digits[i] <= 9 digits does not contain any leading 0's.
Meta,78,Subsets,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums of unique elements; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;3] Output: [[];[1];[2];[1;2];[3];[1;3];[2;3];[1;2;3]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10 All the numbers of nums are unique.
Meta,113,Path Sum II,Med,"Backtracking, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path should be returned as a list of the node values; not node references. A root-to-leaf path is a path starting from the root and ending at any leaf node. A leaf is a node with no children. Example 1: Input: root = [5;4;8;11;null;13;4;7;2;null;null;5;1]; targetSum = 22 Output: [[5;4;11;2];[5;8;4;5]] Explanation: There are two paths whose sum equals targetSum: 5 + 4 + 11 + 2 = 22 5 + 8 + 4 + 5 = 22 Example 2: Input: root = [1;2;3]; targetSum = 5 Output: [] Example 3: Input: root = [1;2]; targetSum = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 5000]. -1000 <= Node.val <= 1000 -1000 <= targetSum <= 1000
Meta,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Meta,128,Longest Consecutive Sequence,Med,"Array, Hash Table, Union Find",Given an unsorted array of integers nums; return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time. Example 1: Input: nums = [100;4;200;1;3;2] Output: 4 Explanation: The longest consecutive elements sequence is [1; 2; 3; 4]. Therefore its length is 4. Example 2: Input: nums = [0;3;7;2;5;8;4;6;0;1] Output: 9 Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109
Meta,140,Word Break II,Hard,"Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization","Given a string s and a dictionary of strings wordDict; add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""catsanddog""; wordDict = [""cat"";""cats"";""and"";""sand"";""dog""] Output: [""cats and dog"";""cat sand dog""] Example 2: Input: s = ""pineapplepenapple""; wordDict = [""apple"";""pen"";""applepen"";""pine"";""pineapple""] Output: [""pine apple pen apple"";""pineapple pen apple"";""pine applepen apple""] Explanation: Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: [] Constraints: 1 <= s.length <= 20 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 10 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique. Input is generated in a way that the length of the answer doesn't exceed 105."
Meta,143,Reorder List,Med,"Linked List, Two Pointers, Stack, Recursion",You are given the head of a singly linked-list. The list can be represented as: L0 → L1 → … → Ln - 1 → Ln Reorder the list to be on the following form: L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → … You may not modify the values in the list's nodes. Only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4] Output: [1;4;2;3] Example 2: Input: head = [1;2;3;4;5] Output: [1;5;2;4;3] Constraints: The number of nodes in the list is in the range [1; 5 * 104]. 1 <= Node.val <= 1000
Meta,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
Meta,179,Largest Number,Med,"Array, String, Greedy, Sorting","Given a list of non-negative integers nums; arrange them such that they form the largest number and return it. Since the result may be very large; so you need to return a string instead of an integer. Example 1: Input: nums = [10;2] Output: ""210"" Example 2: Input: nums = [3;30;34;5;9] Output: ""9534330"" Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 109"
Meta,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Meta,246,Strobogrammatic Number,Easy,"Hash Table, Two Pointers, String",
Meta,348,Design Tic-Tac-Toe,Med,"Array, Hash Table, Design, Matrix, Simulation",
Meta,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
Meta,494,Target Sum,Med,"Array, Dynamic Programming, Backtracking","You are given an integer array nums and an integer target. You want to build an expression out of nums by adding one of the symbols '+' and '-' before each integer in nums and then concatenate all the integers. For example; if nums = [2; 1]; you can add a '+' before 2 and a '-' before 1 and concatenate them to build the expression ""+2-1"". Return the number of different expressions that you can build; which evaluates to target. Example 1: Input: nums = [1;1;1;1;1]; target = 3 Output: 5 Explanation: There are 5 ways to assign symbols to make the sum of nums be target 3. -1 + 1 + 1 + 1 + 1 = 3 +1 - 1 + 1 + 1 + 1 = 3 +1 + 1 - 1 + 1 + 1 = 3 +1 + 1 + 1 - 1 + 1 = 3 +1 + 1 + 1 + 1 - 1 = 3 Example 2: Input: nums = [1]; target = 1 Output: 1 Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 1000 0 <= sum(nums[i]) <= 1000 -1000 <= target <= 1000"
Meta,825,Friends Of Appropriate Ages,Med,"Array, Greedy, Matrix",There is a city composed of n x n blocks; where each block contains a single building shaped like a vertical square prism. You are given a 0-indexed n x n integer matrix grid where grid[r][c] represents the height of the building located in the block at row r and column c. A city's skyline is the outer contour formed by all the building when viewing the side of the city from a distance. The skyline from each cardinal direction north; east; south; and west may be different. We are allowed to increase the height of any number of buildings by any amount (the amount can be different per building). The height of a 0-height building can also be increased. However; increasing the height of a building should not affect the city's skyline from any cardinal direction. Return the maximum total sum that the height of the buildings can be increased by without changing the city's skyline from any cardinal direction. Example 1: Input: grid = [[3;0;8;4];[2;4;5;7];[9;2;6;3];[0;3;1;0]] Output: 35 Explanation: The building heights are shown in the center of the above image. The skylines when viewed from each cardinal direction are drawn in red. The grid after increasing the height of buildings without affecting skylines is: gridNew = [ [8; 4; 8; 7]; [7; 4; 7; 7]; [9; 4; 8; 7]; [3; 3; 3; 3] ] Example 2: Input: grid = [[0;0;0];[0;0;0];[0;0;0]] Output: 0 Explanation: Increasing the height of any building will result in the skyline changing. Constraints: n == grid.length n == grid[r].length 2 <= n <= 50 0 <= grid[r][c] <= 100
Meta,953,Verifying an Alien Dictionary,Easy,"Two Pointers, String","Given a string s; reverse the string according to the following rules: All the characters that are not English letters remain in the same position. All the English letters (lowercase or uppercase) should be reversed. Return s after reversing it. Example 1: Input: s = ""ab-cd"" Output: ""dc-ba"" Example 2: Input: s = ""a-bC-dEf-ghIj"" Output: ""j-Ih-gfE-dCba"" Example 3: Input: s = ""Test1ng-Leet=code-Q!"" Output: ""Qedo1ct-eeLg=ntse-T!"" Constraints: 1 <= s.length <= 100 s consists of characters with ASCII values in the range [33; 122]. s does not contain '\""' or '\\'."
Meta,977,Squares of a Sorted Array,Easy,"String, Dynamic Programming","Given a string s; return the number of distinct non-empty subsequences of s. Since the answer may be very large; return it modulo 109 + 7. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not. Example 1: Input: s = ""abc"" Output: 7 Explanation: The 7 distinct subsequences are ""a""; ""b""; ""c""; ""ab""; ""ac""; ""bc""; and ""abc"". Example 2: Input: s = ""aba"" Output: 6 Explanation: The 6 distinct subsequences are ""a""; ""b""; ""ab""; ""aa""; ""ba""; and ""aba"". Example 3: Input: s = ""aaa"" Output: 3 Explanation: The 3 distinct subsequences are ""a""; ""aa"" and ""aaa"". Constraints: 1 <= s.length <= 2000 s consists of lowercase English letters."
Meta,2914,Minimum Number of Changes to Make Binary String Beautiful,Med,"Array, Binary Search, Breadth-First Search, Union Find, Matrix",You are given a 0-indexed 2D matrix grid of size n x n; where (r; c) represents: A cell containing a thief if grid[r][c] = 1 An empty cell if grid[r][c] = 0 You are initially positioned at cell (0; 0). In one move; you can move to any adjacent cell in the grid; including cells containing thieves. The safeness factor of a path on the grid is defined as the minimum manhattan distance from any cell in the path to any thief in the grid. Return the maximum safeness factor of all paths leading to cell (n - 1; n - 1). An adjacent cell of cell (r; c); is one of the cells (r; c + 1); (r; c - 1); (r + 1; c) and (r - 1; c) if it exists. The Manhattan distance between two cells (a; b) and (x; y) is equal to |a - x| + |b - y|; where |val| denotes the absolute value of val. Example 1: Input: grid = [[1;0;0];[0;0;0];[0;0;1]] Output: 0 Explanation: All paths from (0; 0) to (n - 1; n - 1) go through the thieves in cells (0; 0) and (n - 1; n - 1). Example 2: Input: grid = [[0;0;1];[0;0;0];[0;0;0]] Output: 2 Explanation: The path depicted in the picture above has a safeness factor of 2 since: - The closest cell of the path to the thief at cell (0; 2) is cell (0; 0). The distance between them is | 0 - 0 | + | 0 - 2 | = 2. It can be shown that there are no other paths with a higher safeness factor. Example 3: Input: grid = [[0;0;0;1];[0;0;0;0];[0;0;0;0];[1;0;0;0]] Output: 2 Explanation: The path depicted in the picture above has a safeness factor of 2 since: - The closest cell of the path to the thief at cell (0; 3) is cell (1; 2). The distance between them is | 0 - 1 | + | 3 - 2 | = 2. - The closest cell of the path to the thief at cell (3; 0) is cell (3; 2). The distance between them is | 3 - 3 | + | 0 - 2 | = 2. It can be shown that there are no other paths with a higher safeness factor. Constraints: 1 <= grid.length == n <= 400 grid[i].length == n grid[i][j] is either 0 or 1. There is at least one thief in the grid.
Meta,7,Reverse Integer,Med,Math,Given a signed 32-bit integer x; return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231; 231 - 1]; then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: Input: x = 123 Output: 321 Example 2: Input: x = -123 Output: -321 Example 3: Input: x = 120 Output: 21 Constraints: -231 <= x <= 231 - 1
Meta,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Meta,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Meta,57,Insert Interval,Med,Array,You are given an array of non-overlapping intervals intervals where intervals[i] = [starti; endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start; end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary). Return intervals after the insertion. Note that you don't need to modify intervals in-place. You can make a new array and return it. Example 1: Input: intervals = [[1;3];[6;9]]; newInterval = [2;5] Output: [[1;5];[6;9]] Example 2: Input: intervals = [[1;2];[3;5];[6;7];[8;10];[12;16]]; newInterval = [4;8] Output: [[1;2];[3;10];[12;16]] Explanation: Because the new interval [4;8] overlaps with [3;5];[6;7];[8;10]. Constraints: 0 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 105 intervals is sorted by starti in ascending order. newInterval.length == 2 0 <= start <= end <= 105
Meta,116,Populating Next Right Pointers in Each Node,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given a perfect binary tree where all leaves are on the same level; and every parent has two children. The binary tree has the following definition: struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;6;7] Output: [1;#;2;3;#;4;5;6;7;#] Explanation: Given the above perfect binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 212 - 1]. -1000 <= Node.val <= 1000 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Meta,231,Power of Two,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of two. Otherwise; return false. An integer n is a power of two; if there exists an integer x such that n == 2x. Example 1: Input: n = 1 Output: true Explanation: 20 = 1 Example 2: Input: n = 16 Output: true Explanation: 24 = 16 Example 3: Input: n = 3 Output: false Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Meta,278,First Bad Version,Easy,"Binary Search, Interactive",You are a product manager and currently leading a team to develop a new product. Unfortunately; the latest version of your product fails the quality check. Since each version is developed based on the previous version; all the versions after a bad version are also bad. Suppose you have n versions [1; 2; ...; n] and you want to find out the first bad one; which causes all the following ones to be bad. You are given an API bool isBadVersion(version) which returns whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API. Example 1: Input: n = 5; bad = 4 Output: 4 Explanation: call isBadVersion(3) -> false call isBadVersion(5) -> true call isBadVersion(4) -> true Then 4 is the first bad version. Example 2: Input: n = 1; bad = 1 Output: 1 Constraints: 1 <= bad <= n <= 231 - 1
Meta,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Meta,301,Remove Invalid Parentheses,Hard,"String, Backtracking, Breadth-First Search","Given a string s that contains parentheses and letters; remove the minimum number of invalid parentheses to make the input string valid. Return a list of unique strings that are valid with the minimum number of removals. You may return the answer in any order. Example 1: Input: s = ""()())()"" Output: [""(())()"";""()()()""] Example 2: Input: s = ""(a)())()"" Output: [""(a())()"";""(a)()()""] Example 3: Input: s = "")("" Output: [""""] Constraints: 1 <= s.length <= 25 s consists of lowercase English letters and parentheses '(' and ')'. There will be at most 20 parentheses in s."
Meta,392,Is Subsequence,Easy,"Two Pointers, String, Dynamic Programming","Given two strings s and t; return true if s is a subsequence of t; or false otherwise. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not). Example 1: Input: s = ""abc""; t = ""ahbgdc"" Output: true Example 2: Input: s = ""axc""; t = ""ahbgdc"" Output: false Constraints: 0 <= s.length <= 100 0 <= t.length <= 104 s and t consist only of lowercase English letters. Follow up: Suppose there are lots of incoming s; say s1; s2; ...; sk where k >= 109; and you want to check one by one to see if t has its subsequence. In this scenario; how would you change your code?"
Meta,796,Rotate String,Easy,Math,Given four integers sx; sy; tx; and ty; return true if it is possible to convert the point (sx; sy) to the point (tx; ty) through some operations; or false otherwise. The allowed operation on some point (x; y) is to convert it to either (x; x + y) or (x + y; y). Example 1: Input: sx = 1; sy = 1; tx = 3; ty = 5 Output: true Explanation: One series of moves that transforms the starting point to the target is: (1; 1) -> (1; 2) (1; 2) -> (3; 2) (3; 2) -> (3; 5) Example 2: Input: sx = 1; sy = 1; tx = 2; ty = 2 Output: false Example 3: Input: sx = 1; sy = 1; tx = 1; ty = 1 Output: true Constraints: 1 <= sx; sy; tx; ty <= 109
Meta,958,Check Completeness of a Binary Tree,Med,"Array, Two Pointers, Sorting",Given an array of integers nums; half of the integers in nums are odd; and the other half are even. Sort the array so that whenever nums[i] is odd; i is odd; and whenever nums[i] is even; i is even. Return any answer array that satisfies this condition. Example 1: Input: nums = [4;2;5;7] Output: [4;5;2;7] Explanation: [4;7;2;5]; [2;5;4;7]; [2;7;4;5] would also have been accepted. Example 2: Input: nums = [2;3] Output: [2;3] Constraints: 2 <= nums.length <= 2 * 104 nums.length is even. Half of the integers in nums are even. 0 <= nums[i] <= 1000 Follow Up: Could you solve it in-place?
Meta,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
Meta,1609,Even Odd Tree,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",
Meta,3043,Find the Length of the Longest Common Prefix,Med,"Array, Breadth-First Search, Matrix",
Meta,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Meta,27,Remove Element,Easy,"Array, Two Pointers",Given an integer array nums and an integer val; remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val. Consider the number of elements in nums which are not equal to val be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the elements which are not equal to val. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int val = ...; // Value to remove int[] expectedNums = [...]; // The expected answer with correct length. // It is sorted with no values equaling val. int k = removeElement(nums; val); // Calls your implementation assert k == expectedNums.length; sort(nums; 0; k); // Sort the first k elements of nums for (int i = 0; i < actualLength; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [3;2;2;3]; val = 3 Output: 2; nums = [2;2;_;_] Explanation: Your function should return k = 2; with the first two elements of nums being 2. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;1;2;2;3;0;4;2]; val = 2 Output: 5; nums = [0;1;4;0;3;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums containing 0; 0; 1; 3; and 4. Note that the five elements can be returned in any order. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 0 <= nums.length <= 100 0 <= nums[i] <= 50 0 <= val <= 100
Meta,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Meta,43,Multiply Strings,Med,"Math, String, Simulation","Given two non-negative integers num1 and num2 represented as strings; return the product of num1 and num2; also represented as a string. Note: You must not use any built-in BigInteger library or convert the inputs to integer directly. Example 1: Input: num1 = ""2""; num2 = ""3"" Output: ""6"" Example 2: Input: num1 = ""123""; num2 = ""456"" Output: ""56088"" Constraints: 1 <= num1.length; num2.length <= 200 num1 and num2 consist of digits only. Both num1 and num2 do not contain any leading zero; except the number 0 itself."
Meta,44,Wildcard Matching,Hard,"String, Dynamic Programming, Greedy, Recursion","Given an input string (s) and a pattern (p); implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""*"" Output: true Explanation: '*' matches any sequence. Example 3: Input: s = ""cb""; p = ""?a"" Output: false Explanation: '?' matches 'c'; but the second letter is 'a'; which does not match 'b'. Constraints: 0 <= s.length; p.length <= 2000 s contains only lowercase English letters. p contains only lowercase English letters; '?' or '*'."
Meta,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Meta,63,Unique Paths II,Med,"Array, Dynamic Programming, Matrix",You are given an m x n integer array grid. There is a robot initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. An obstacle and space are marked as 1 or 0 respectively in grid. A path that the robot takes cannot include any square that is an obstacle. Return the number of possible unique paths that the robot can take to reach the bottom-right corner. The testcases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: obstacleGrid = [[0;0;0];[0;1;0];[0;0;0]] Output: 2 Explanation: There is one obstacle in the middle of the 3x3 grid above. There are two ways to reach the bottom-right corner: 1. Right -> Right -> Down -> Down 2. Down -> Down -> Right -> Right Example 2: Input: obstacleGrid = [[0;1];[0;0]] Output: 1 Constraints: m == obstacleGrid.length n == obstacleGrid[i].length 1 <= m; n <= 100 obstacleGrid[i][j] is 0 or 1.
Meta,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Meta,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Meta,84,Largest Rectangle in Histogram,Hard,"Array, Stack, Monotonic Stack",Given an array of integers heights representing the histogram's bar height where the width of each bar is 1; return the area of the largest rectangle in the histogram. Example 1: Input: heights = [2;1;5;6;2;3] Output: 10 Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area; which has an area = 10 units. Example 2: Input: heights = [2;4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104
Meta,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Meta,103,Binary Tree Zigzag Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the zigzag level order traversal of its nodes' values. (i.e.; from left to right; then right to left for the next level and alternate between). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[20;9];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100
Meta,104,Maximum Depth of Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return its maximum depth. A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 3 Example 2: Input: root = [1;null;2] Output: 2 Constraints: The number of nodes in the tree is in the range [0; 104]. -100 <= Node.val <= 100
Meta,109,Convert Sorted List to Binary Search Tree,Med,"Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree",Given the head of a singly linked list where elements are sorted in ascending order; convert it to a height-balanced binary search tree. Example 1: Input: head = [-10;-3;0;5;9] Output: [0;-3;9;-10;null;5] Explanation: One possible answer is [0;-3;9;-10;null;5]; which represents the shown height balanced BST. Example 2: Input: head = [] Output: [] Constraints: The number of nodes in head is in the range [0; 2 * 104]. -105 <= Node.val <= 105
Meta,114,Flatten Binary Tree to Linked List,Med,"Linked List, Stack, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; flatten the tree into a ""linked list"": The ""linked list"" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. The ""linked list"" should be in the same order as a pre-order traversal of the binary tree. Example 1: Input: root = [1;2;5;3;4;null;6] Output: [1;null;2;null;3;null;4;null;5;null;6] Example 2: Input: root = [] Output: [] Example 3: Input: root = [0] Output: [0] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100 Follow up: Can you flatten the tree in-place (with O(1) extra space)?"
Meta,118,Pascal's Triangle,Easy,"Array, Dynamic Programming",Given an integer numRows; return the first numRows of Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: numRows = 5 Output: [[1];[1;1];[1;2;1];[1;3;3;1];[1;4;6;4;1]] Example 2: Input: numRows = 1 Output: [[1]] Constraints: 1 <= numRows <= 30
Meta,142,Linked List Cycle II,Med,"Hash Table, Linked List, Two Pointers",Given the head of a linked list; return the node where the cycle begins. If there is no cycle; return null. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to (0-indexed). It is -1 if there is no cycle. Note that pos is not passed as a parameter. Do not modify the linked list. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: tail connects to node index 1 Explanation: There is a cycle in the linked list; where tail connects to the second node. Example 2: Input: head = [1;2]; pos = 0 Output: tail connects to node index 0 Explanation: There is a cycle in the linked list; where tail connects to the first node. Example 3: Input: head = [1]; pos = -1 Output: no cycle Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Meta,145,Binary Tree Postorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the postorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [3;2;1] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [4;6;7;5;2;9;8;3;1] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of the nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Meta,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Meta,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Meta,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
Meta,273,Integer to English Words,Hard,"Math, String, Recursion","Convert a non-negative integer num to its English words representation. Example 1: Input: num = 123 Output: ""One Hundred Twenty Three"" Example 2: Input: num = 12345 Output: ""Twelve Thousand Three Hundred Forty Five"" Example 3: Input: num = 1234567 Output: ""One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"" Constraints: 0 <= num <= 231 - 1"
Meta,317,Shortest Distance from All Buildings,Hard,"Array, Breadth-First Search, Matrix",
Meta,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Meta,333,Largest BST Subtree,Med,"Dynamic Programming, Tree, Depth-First Search, Binary Search Tree, Binary Tree",
Meta,419,Battleships in a Board,Med,"Array, Depth-First Search, Matrix","Given an m x n matrix board where each cell is a battleship 'X' or empty '.'; return the number of the battleships on board. Battleships can only be placed horizontally or vertically on board. In other words; they can only be made of the shape 1 x k (1 row; k columns) or k x 1 (k rows; 1 column); where k can be of any size. At least one horizontal or vertical cell separates between two battleships (i.e.; there are no adjacent battleships). Example 1: Input: board = [[""X"";""."";""."";""X""];[""."";""."";""."";""X""];[""."";""."";""."";""X""]] Output: 2 Example 2: Input: board = [["".""]] Output: 0 Constraints: m == board.length n == board[i].length 1 <= m; n <= 200 board[i][j] is either '.' or 'X'. Follow up: Could you do it in one-pass; using only O(1) extra memory and without modifying the values board?"
Meta,432,All O`one Data Structure,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure to store the strings' count with the ability to return the strings with minimum and maximum counts. Implement the AllOne class: AllOne() Initializes the object of the data structure. inc(String key) Increments the count of the string key by 1. If key does not exist in the data structure; insert it with count 1. dec(String key) Decrements the count of the string key by 1. If the count of key is 0 after the decrement; remove it from the data structure. It is guaranteed that key exists in the data structure before the decrement. getMaxKey() Returns one of the keys with the maximal count. If no element exists; return an empty string """". getMinKey() Returns one of the keys with the minimum count. If no element exists; return an empty string """". Note that each function must run in O(1) average time complexity. Example 1: Input [""AllOne""; ""inc""; ""inc""; ""getMaxKey""; ""getMinKey""; ""inc""; ""getMaxKey""; ""getMinKey""] [[]; [""hello""]; [""hello""]; []; []; [""leet""]; []; []] Output [null; null; null; ""hello""; ""hello""; null; ""hello""; ""leet""] Explanation AllOne allOne = new AllOne(); allOne.inc(""hello""); allOne.inc(""hello""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""hello"" allOne.inc(""leet""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""leet"" Constraints: 1 <= key.length <= 10 key consists of lowercase English letters. It is guaranteed that for each call to dec; key is existing in the data structure. At most 5 * 104 calls will be made to inc; dec; getMaxKey; and getMinKey."
Meta,529,Minesweeper,Med,"Array, Depth-First Search, Breadth-First Search, Matrix","Let's play the minesweeper game (Wikipedia; online game)! You are given an m x n char matrix board representing the game board where: 'M' represents an unrevealed mine; 'E' represents an unrevealed empty square; 'B' represents a revealed blank square that has no adjacent mines (i.e.; above; below; left; right; and all 4 diagonals); digit ('1' to '8') represents how many mines are adjacent to this revealed square; and 'X' represents a revealed mine. You are also given an integer array click where click = [clickr; clickc] represents the next click position among all the unrevealed squares ('M' or 'E'). Return the board after revealing this position according to the following rules: If a mine 'M' is revealed; then the game is over. You should change it to 'X'. If an empty square 'E' with no adjacent mines is revealed; then change it to a revealed blank 'B' and all of its adjacent unrevealed squares should be revealed recursively. If an empty square 'E' with at least one adjacent mine is revealed; then change it to a digit ('1' to '8') representing the number of adjacent mines. Return the board when no more squares will be revealed. Example 1: Input: board = [[""E"";""E"";""E"";""E"";""E""];[""E"";""E"";""M"";""E"";""E""];[""E"";""E"";""E"";""E"";""E""];[""E"";""E"";""E"";""E"";""E""]]; click = [3;0] Output: [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""M"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]] Example 2: Input: board = [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""M"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]]; click = [1;2] Output: [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""X"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]] Constraints: m == board.length n == board[i].length 1 <= m; n <= 50 board[i][j] is either 'M'; 'E'; 'B'; or a digit from '1' to '8'. click.length == 2 0 <= clickr < m 0 <= clickc < n board[clickr][clickc] is either 'M' or 'E'."
Meta,545,Boundary of Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",
Meta,616,Add Bold Tag in String,Med,"Array, Hash Table, String, Trie, String Matching",
Meta,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
Meta,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
Meta,930,Binary Subarrays With Sum,Med,"Dynamic Programming, Tree, Recursion, Memoization, Binary Tree",Given an integer n; return a list of all possible full binary trees with n nodes. Each node of each tree in the answer must have Node.val == 0. Each element of the answer is the root node of one possible tree. You may return the final list of trees in any order. A full binary tree is a binary tree where each node has exactly 0 or 2 children. Example 1: Input: n = 7 Output: [[0;0;0;null;null;0;0;null;null;0;0];[0;0;0;null;null;0;0;0;0];[0;0;0;0;0;0;0];[0;0;0;0;0;null;null;null;null;0;0];[0;0;0;0;0;null;null;0;0]] Example 2: Input: n = 3 Output: [[0;0;0]] Constraints: 1 <= n <= 20
Meta,934,Shortest Bridge,Med,"Array, Dynamic Programming, Bit Manipulation",Given an integer array arr; return the number of distinct bitwise ORs of all the non-empty subarrays of arr. The bitwise OR of a subarray is the bitwise OR of each integer in the subarray. The bitwise OR of a subarray of one integer is that integer. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: arr = [0] Output: 1 Explanation: There is only one possible result: 0. Example 2: Input: arr = [1;1;2] Output: 3 Explanation: The possible subarrays are [1]; [1]; [2]; [1; 1]; [1; 2]; [1; 1; 2]. These yield the results 1; 1; 2; 1; 3; 3. There are 3 unique values; so the answer is 3. Example 3: Input: arr = [1;2;4] Output: 6 Explanation: The possible results are 1; 2; 3; 4; 6; and 7. Constraints: 1 <= arr.length <= 5 * 104 0 <= arr[i] <= 109
Meta,1371,Find the Longest Substring Containing Vowels in Even Counts,Med,"String, Stack","Given a string s of '(' ; ')' and lowercase English characters. Your task is to remove the minimum number of parentheses ( '(' or ')'; in any positions ) so that the resulting parentheses string is valid and return any valid string. Formally; a parentheses string is valid if and only if: It is the empty string; contains only lowercase characters; or It can be written as AB (A concatenated with B); where A and B are valid strings; or It can be written as (A); where A is a valid string. Example 1: Input: s = ""lee(t(c)o)de)"" Output: ""lee(t(c)o)de"" Explanation: ""lee(t(co)de)"" ; ""lee(t(c)ode)"" would also be accepted. Example 2: Input: s = ""a)b(c)d"" Output: ""ab(c)d"" Example 3: Input: s = ""))(("" Output: """" Explanation: An empty string is also valid. Constraints: 1 <= s.length <= 105 s[i] is either '(' ; ')'; or lowercase English letter."
Meta,12,Integer to Roman,Med,"Hash Table, Math, String","Seven different symbols represent Roman numerals with the following values: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules: If the value does not start with 4 or 9; select the symbol of the maximal value that can be subtracted from the input; append that symbol to the result; subtract its value; and convert the remainder to a Roman numeral. If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol; for example; 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV); 9 (IX); 40 (XL); 90 (XC); 400 (CD) and 900 (CM). Only powers of 10 (I; X; C; M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V); 50 (L); or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form. Given an integer; convert it to a Roman numeral. Example 1: Input: num = 3749 Output: ""MMMDCCXLIX"" Explanation: 3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M) 700 = DCC as 500 (D) + 100 (C) + 100 (C) 40 = XL as 10 (X) less of 50 (L) 9 = IX as 1 (I) less of 10 (X) Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places Example 2: Input: num = 58 Output: ""LVIII"" Explanation: 50 = L 8 = VIII Example 3: Input: num = 1994 Output: ""MCMXCIV"" Explanation: 1000 = M 900 = CM 90 = XC 4 = IV Constraints: 1 <= num <= 3999"
Meta,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Meta,29,Divide Two Integers,Med,"Math, Bit Manipulation",Given two integers dividend and divisor; divide two integers without using multiplication; division; and mod operator. The integer division should truncate toward zero; which means losing its fractional part. For example; 8.345 would be truncated to 8; and -2.7335 would be truncated to -2. Return the quotient after dividing dividend by divisor. Note: Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−231; 231 − 1]. For this problem; if the quotient is strictly greater than 231 - 1; then return 231 - 1; and if the quotient is strictly less than -231; then return -231. Example 1: Input: dividend = 10; divisor = 3 Output: 3 Explanation: 10/3 = 3.33333.. which is truncated to 3. Example 2: Input: dividend = 7; divisor = -3 Output: -2 Explanation: 7/-3 = -2.33333.. which is truncated to -2. Constraints: -231 <= dividend; divisor <= 231 - 1 divisor != 0
Meta,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Meta,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
Meta,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Meta,62,Unique Paths,Med,"Math, Dynamic Programming, Combinatorics",There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n; return the number of possible unique paths that the robot can take to reach the bottom-right corner. The test cases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: m = 3; n = 7 Output: 28 Example 2: Input: m = 3; n = 2 Output: 3 Explanation: From the top-left corner; there are a total of 3 ways to reach the bottom-right corner: 1. Right -> Down -> Down 2. Down -> Down -> Right 3. Down -> Right -> Down Constraints: 1 <= m; n <= 100
Meta,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
Meta,80,Remove Duplicates from Sorted Array II,Med,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same. Since it is impossible to change the length of the array in some languages; you must instead have the result be placed in the first part of the array nums. More formally; if there are k elements after removing the duplicates; then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements. Return k after placing the final result in the first k slots of nums. Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;1;2;2;3] Output: 5; nums = [1;1;2;2;3;_] Explanation: Your function should return k = 5; with the first five elements of nums being 1; 1; 2; 2 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;1;2;3;3] Output: 7; nums = [0;0;1;1;2;3;3;_;_] Explanation: Your function should return k = 7; with the first seven elements of nums being 0; 0; 1; 1; 2; 3 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -104 <= nums[i] <= 104 nums is sorted in non-decreasing order.
Meta,81,Search in Rotated Sorted Array II,Med,"Array, Binary Search",There is an integer array nums sorted in non-decreasing order (not necessarily with distinct values). Before being passed to your function; nums is rotated at an unknown pivot index k (0 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;4;4;5;6;6;7] might be rotated at pivot index 5 and become [4;5;6;6;7;0;1;2;4;4]. Given the array nums after the rotation and an integer target; return true if target is in nums; or false if it is not in nums. You must decrease the overall operation steps as much as possible. Example 1: Input: nums = [2;5;6;0;0;1;2]; target = 0 Output: true Example 2: Input: nums = [2;5;6;0;0;1;2]; target = 3 Output: false Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 nums is guaranteed to be rotated at some pivot. -104 <= target <= 104 Follow up: This problem is similar to Search in Rotated Sorted Array; but nums may contain duplicates. Would this affect the runtime complexity? How and why?
Meta,94,Binary Tree Inorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the inorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [1;3;2] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [4;2;6;5;7;1;3;9;8] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Meta,96,Unique Binary Search Trees,Med,"Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree",Given an integer n; return the number of structurally unique BST's (binary search trees) which has exactly n nodes of unique values from 1 to n. Example 1: Input: n = 3 Output: 5 Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 19
Meta,102,Binary Tree Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the level order traversal of its nodes' values. (i.e.; from left to right; level by level). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[9;20];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -1000 <= Node.val <= 1000
Meta,105,Construct Binary Tree from Preorder and Inorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree; construct and return the binary tree. Example 1: Input: preorder = [3;9;20;15;7]; inorder = [9;3;15;20;7] Output: [3;9;20;null;null;15;7] Example 2: Input: preorder = [-1]; inorder = [-1] Output: [-1] Constraints: 1 <= preorder.length <= 3000 inorder.length == preorder.length -3000 <= preorder[i]; inorder[i] <= 3000 preorder and inorder consist of unique values. Each value of inorder also appears in preorder. preorder is guaranteed to be the preorder traversal of the tree. inorder is guaranteed to be the inorder traversal of the tree.
Meta,126,Word Ladder II,Hard,"Hash Table, String, Backtracking, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return all the shortest transformation sequences from beginWord to endWord; or an empty list if no such sequence exists. Each sequence should be returned as a list of the words [beginWord; s1; s2; ...; sk]. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: [[""hit"";""hot"";""dot"";""dog"";""cog""];[""hit"";""hot"";""lot"";""log"";""cog""]] Explanation: There are 2 shortest transformation sequences: ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> ""cog"" ""hit"" -> ""hot"" -> ""lot"" -> ""log"" -> ""cog"" Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: [] Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 5 endWord.length == beginWord.length 1 <= wordList.length <= 500 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique. The sum of all shortest transformation sequences does not exceed 105."
Meta,131,Palindrome Partitioning,Med,"String, Dynamic Programming, Backtracking","Given a string s; partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s. Example 1: Input: s = ""aab"" Output: [[""a"";""a"";""b""];[""aa"";""b""]] Example 2: Input: s = ""a"" Output: [[""a""]] Constraints: 1 <= s.length <= 16 s contains only lowercase English letters."
Meta,135,Candy,Hard,"Array, Greedy",There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings. You are giving candies to these children subjected to the following requirements: Each child must have at least one candy. Children with a higher rating get more candies than their neighbors. Return the minimum number of candies you need to have to distribute the candies to the children. Example 1: Input: ratings = [1;0;2] Output: 5 Explanation: You can allocate to the first; second and third child with 2; 1; 2 candies respectively. Example 2: Input: ratings = [1;2;2] Output: 4 Explanation: You can allocate to the first; second and third child with 1; 2; 1 candies respectively. The third child gets 1 candy because it satisfies the above two conditions. Constraints: n == ratings.length 1 <= n <= 2 * 104 0 <= ratings[i] <= 2 * 104
Meta,136,Single Number,Easy,"Array, Bit Manipulation",Given a non-empty array of integers nums; every element appears twice except for one. Find that single one. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;1] Output: 1 Example 2: Input: nums = [4;1;2;1;2] Output: 4 Example 3: Input: nums = [1] Output: 1 Constraints: 1 <= nums.length <= 3 * 104 -3 * 104 <= nums[i] <= 3 * 104 Each element in the array appears twice except for one element which appears only once.
Meta,168,Excel Sheet Column Title,Easy,"Math, String","Given an integer columnNumber; return its corresponding column title as it appears in an Excel sheet. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: Input: columnNumber = 1 Output: ""A"" Example 2: Input: columnNumber = 28 Output: ""AB"" Example 3: Input: columnNumber = 701 Output: ""ZY"" Constraints: 1 <= columnNumber <= 231 - 1"
Meta,181,Employees Earning More Than Their Managers,Easy,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | salary | int | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID of an employee; their name; salary; and the ID of their manager. Write a solution to find the employees who earn more than their managers. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +----+-------+--------+-----------+ | id | name | salary | managerId | +----+-------+--------+-----------+ | 1 | Joe | 70000 | 3 | | 2 | Henry | 80000 | 4 | | 3 | Sam | 60000 | Null | | 4 | Max | 90000 | Null | +----+-------+--------+-----------+ Output: +----------+ | Employee | +----------+ | Joe | +----------+ Explanation: Joe is the only employee who earns more than his manager.
Meta,205,Isomorphic Strings,Easy,"Hash Table, String","Given two strings s and t; determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character; but a character may map to itself. Example 1: Input: s = ""egg""; t = ""add"" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = ""foo""; t = ""bar"" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = ""paper""; t = ""title"" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character."
Meta,229,Majority Element II,Med,"Array, Hash Table, Sorting, Counting",Given an integer array of size n; find all elements that appear more than ⌊ n/3 ⌋ times. Example 1: Input: nums = [3;2;3] Output: [3] Example 2: Input: nums = [1] Output: [1] Example 3: Input: nums = [1;2] Output: [1;2] Constraints: 1 <= nums.length <= 5 * 104 -109 <= nums[i] <= 109 Follow up: Could you solve the problem in linear time and in O(1) space?
Meta,230,Kth Smallest Element in a BST,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree; and an integer k; return the kth smallest value (1-indexed) of all the values of the nodes in the tree. Example 1: Input: root = [3;1;4;null;2]; k = 1 Output: 1 Example 2: Input: root = [5;3;6;2;4;null;null;1]; k = 3 Output: 3 Constraints: The number of nodes in the tree is n. 1 <= k <= n <= 104 0 <= Node.val <= 104 Follow up: If the BST is modified often (i.e.; we can do insert and delete operations) and you need to find the kth smallest frequently; how would you optimize?
Meta,266,Palindrome Permutation,Easy,"Hash Table, String, Bit Manipulation",
Meta,296,Best Meeting Point,Hard,"Array, Math, Sorting, Matrix",
Meta,325,Maximum Size Subarray Sum Equals k,Med,"Array, Hash Table, Prefix Sum",
Meta,350,Intersection of Two Arrays II,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must appear as many times as it shows in both arrays and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2;2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [4;9] Explanation: [9;4] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000 Follow up: What if the given array is already sorted? How would you optimize your algorithm? What if nums1's size is small compared to nums2's size? Which algorithm is better? What if elements of nums2 are stored on disk; and the memory is limited such that you cannot load all elements into the memory at once?
Meta,371,Sum of Two Integers,Med,"Math, Bit Manipulation",Given two integers a and b; return the sum of the two integers without using the operators + and -. Example 1: Input: a = 1; b = 2 Output: 3 Example 2: Input: a = 2; b = 3 Output: 5 Constraints: -1000 <= a; b <= 1000
Meta,381,Insert Delete GetRandom O(1) - Duplicates allowed,Hard,"Array, Hash Table, Math, Design, Randomized","RandomizedCollection is a data structure that contains a collection of numbers; possibly duplicates (i.e.; a multiset). It should support inserting and removing specific elements and also reporting a random element. Implement the RandomizedCollection class: RandomizedCollection() Initializes the empty RandomizedCollection object. bool insert(int val) Inserts an item val into the multiset; even if the item is already present. Returns true if the item is not present; false otherwise. bool remove(int val) Removes an item val from the multiset if present. Returns true if the item is present; false otherwise. Note that if val has multiple occurrences in the multiset; we only remove one of them. int getRandom() Returns a random element from the current multiset of elements. The probability of each element being returned is linearly related to the number of the same values the multiset contains. You must implement the functions of the class such that each function works on average O(1) time complexity. Note: The test cases are generated such that getRandom will only be called if there is at least one item in the RandomizedCollection. Example 1: Input [""RandomizedCollection""; ""insert""; ""insert""; ""insert""; ""getRandom""; ""remove""; ""getRandom""] [[]; [1]; [1]; [2]; []; [1]; []] Output [null; true; false; true; 2; true; 1] Explanation RandomizedCollection randomizedCollection = new RandomizedCollection(); randomizedCollection.insert(1); // return true since the collection does not contain 1. // Inserts 1 into the collection. randomizedCollection.insert(1); // return false since the collection contains 1. // Inserts another 1 into the collection. Collection now contains [1;1]. randomizedCollection.insert(2); // return true since the collection does not contain 2. // Inserts 2 into the collection. Collection now contains [1;1;2]. randomizedCollection.getRandom(); // getRandom should: // - return 1 with probability 2/3; or // - return 2 with probability 1/3. randomizedCollection.remove(1); // return true since the collection contains 1. // Removes 1 from the collection. Collection now contains [1;2]. randomizedCollection.getRandom(); // getRandom should return 1 or 2; both equally likely. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls in total will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Meta,383,Ransom Note,Easy,"Hash Table, String, Counting","Given two strings ransomNote and magazine; return true if ransomNote can be constructed by using the letters from magazine and false otherwise. Each letter in magazine can only be used once in ransomNote. Example 1: Input: ransomNote = ""a""; magazine = ""b"" Output: false Example 2: Input: ransomNote = ""aa""; magazine = ""ab"" Output: false Example 3: Input: ransomNote = ""aa""; magazine = ""aab"" Output: true Constraints: 1 <= ransomNote.length; magazine.length <= 105 ransomNote and magazine consist of lowercase English letters."
Meta,386,Lexicographical Numbers,Med,"Depth-First Search, Trie",Given an integer n; return all the numbers in the range [1; n] sorted in lexicographical order. You must write an algorithm that runs in O(n) time and uses O(1) extra space. Example 1: Input: n = 13 Output: [1;10;11;12;13;2;3;4;5;6;7;8;9] Example 2: Input: n = 2 Output: [1;2] Constraints: 1 <= n <= 5 * 104
Meta,450,Delete Node in a BST,Med,"Tree, Binary Search Tree, Binary Tree",Given a root node reference of a BST and a key; delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST. Basically; the deletion can be divided into two stages: Search for a node to remove. If the node is found; delete the node. Example 1: Input: root = [5;3;6;2;4;null;7]; key = 3 Output: [5;4;6;2;null;null;7] Explanation: Given key to delete is 3. So we find the node with value 3 and delete it. One valid answer is [5;4;6;2;null;null;7]; shown in the above BST. Please notice that another valid answer is [5;2;6;null;4;null;7] and it's also accepted. Example 2: Input: root = [5;3;6;2;4;null;7]; key = 0 Output: [5;3;6;2;4;null;7] Explanation: The tree does not contain a node with value = 0. Example 3: Input: root = []; key = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -105 <= Node.val <= 105 Each node has a unique value. root is a valid binary search tree. -105 <= key <= 105 Follow up: Could you solve it with time complexity O(height of tree)?
Meta,490,The Maze,Med,"Array, Depth-First Search, Breadth-First Search, Matrix",
Meta,605,Can Place Flowers,Easy,"Array, Greedy",You have a long flowerbed in which some of the plots are planted; and some are not. However; flowers cannot be planted in adjacent plots. Given an integer array flowerbed containing 0's and 1's; where 0 means empty and 1 means not empty; and an integer n; return true if n new flowers can be planted in the flowerbed without violating the no-adjacent-flowers rule and false otherwise. Example 1: Input: flowerbed = [1;0;0;0;1]; n = 1 Output: true Example 2: Input: flowerbed = [1;0;0;0;1]; n = 2 Output: false Constraints: 1 <= flowerbed.length <= 2 * 104 flowerbed[i] is 0 or 1. There are no two adjacent flowers in flowerbed. 0 <= n <= flowerbed.length
Meta,643,Maximum Average Subarray I,Easy,"Array, Sliding Window",You are given an integer array nums consisting of n elements; and an integer k. Find a contiguous subarray whose length is equal to k that has the maximum average value and return this value. Any answer with a calculation error less than 10-5 will be accepted. Example 1: Input: nums = [1;12;-5;-6;50;3]; k = 4 Output: 12.75000 Explanation: Maximum average is (12 - 5 - 6 + 50) / 4 = 51 / 4 = 12.75 Example 2: Input: nums = [5]; k = 1 Output: 5.00000 Constraints: n == nums.length 1 <= k <= n <= 105 -104 <= nums[i] <= 104
Meta,695,Max Area of Island,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island. Return the maximum area of an island in grid. If there is no island; return 0. Example 1: Input: grid = [[0;0;1;0;0;0;0;1;0;0;0;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;1;1;0;1;0;0;0;0;0;0;0;0];[0;1;0;0;1;1;0;0;1;0;1;0;0];[0;1;0;0;1;1;0;0;1;1;1;0;0];[0;0;0;0;0;0;0;0;0;0;1;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;0;0;0;0;0;0;1;1;0;0;0;0]] Output: 6 Explanation: The answer is not 11; because the island must be connected 4-directionally. Example 2: Input: grid = [[0;0;0;0;0;0;0;0]] Output: 0 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 50 grid[i][j] is either 0 or 1.
Meta,704,Binary Search,Easy,,
Meta,852,Peak Index in a Mountain Array,Med,"Array, Two Pointers, Binary Search, Sorting",There are n persons on a social media website. You are given an integer array ages where ages[i] is the age of the ith person. A Person x will not send a friend request to a person y (x != y) if any of the following conditions is true: age[y] <= 0.5 * age[x] + 7 age[y] > age[x] age[y] > 100 && age[x] < 100 Otherwise; x will send a friend request to y. Note that if x sends a request to y; y will not necessarily send a request to x. Also; a person will not send a friend request to themself. Return the total number of friend requests made. Example 1: Input: ages = [16;16] Output: 2 Explanation: 2 people friend request each other. Example 2: Input: ages = [16;17;18] Output: 2 Explanation: Friend requests are made 17 -> 16; 18 -> 17. Example 3: Input: ages = [20;30;100;110;120] Output: 3 Explanation: Friend requests are made 110 -> 100; 120 -> 110; 120 -> 100. Constraints: n == ages.length 1 <= n <= 2 * 104 1 <= ages[i] <= 120
Meta,862,Shortest Subarray with Sum at Least K,Hard,"Array, Hash Table, String, Sorting","You are given a 0-indexed string s that you must perform k replacement operations on. The replacement operations are given as three 0-indexed parallel arrays; indices; sources; and targets; all of length k. To complete the ith replacement operation: Check if the substring sources[i] occurs at index indices[i] in the original string s. If it does not occur; do nothing. Otherwise if it does occur; replace that substring with targets[i]. For example; if s = ""abcd""; indices[i] = 0; sources[i] = ""ab""; and targets[i] = ""eee""; then the result of this replacement will be ""eeecd"". All replacement operations must occur simultaneously; meaning the replacement operations should not affect the indexing of each other. The testcases will be generated such that the replacements will not overlap. For example; a testcase with s = ""abc""; indices = [0; 1]; and sources = [""ab"";""bc""] will not be generated because the ""ab"" and ""bc"" replacements overlap. Return the resulting string after performing all replacement operations on s. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""abcd""; indices = [0; 2]; sources = [""a""; ""cd""]; targets = [""eee""; ""ffff""] Output: ""eeebffff"" Explanation: ""a"" occurs at index 0 in s; so we replace it with ""eee"". ""cd"" occurs at index 2 in s; so we replace it with ""ffff"". Example 2: Input: s = ""abcd""; indices = [0; 2]; sources = [""ab"";""ec""]; targets = [""eee"";""ffff""] Output: ""eeecd"" Explanation: ""ab"" occurs at index 0 in s; so we replace it with ""eee"". ""ec"" does not occur at index 2 in s; so we do nothing. Constraints: 1 <= s.length <= 1000 k == indices.length == sources.length == targets.length 1 <= k <= 100 0 <= indexes[i] < s.length 1 <= sources[i].length; targets[i].length <= 50 s consists of only lowercase English letters. sources[i] and targets[i] consist of only lowercase English letters."
Meta,983,Minimum Cost For Tickets,Med,"Array, Stack, Simulation",Given two integer arrays pushed and popped each with distinct values; return true if this could have been the result of a sequence of push and pop operations on an initially empty stack; or false otherwise. Example 1: Input: pushed = [1;2;3;4;5]; popped = [4;5;3;2;1] Output: true Explanation: We might do the following sequence: push(1); push(2); push(3); push(4); pop() -> 4; push(5); pop() -> 5; pop() -> 3; pop() -> 2; pop() -> 1 Example 2: Input: pushed = [1;2;3;4;5]; popped = [4;3;5;1;2] Output: false Explanation: 1 cannot be popped before 2. Constraints: 1 <= pushed.length <= 1000 0 <= pushed[i] <= 1000 All the elements of pushed are unique. popped.length == pushed.length popped is a permutation of pushed.
Meta,1197,Minimum Knight Moves,Med,"String, Stack, Recursion","A boolean expression is an expression that evaluates to either true or false. It can be in one of the following shapes: 't' that evaluates to true. 'f' that evaluates to false. '!(subExpr)' that evaluates to the logical NOT of the inner expression subExpr. '&(subExpr1; subExpr2; ...; subExprn)' that evaluates to the logical AND of the inner expressions subExpr1; subExpr2; ...; subExprn where n >= 1. '|(subExpr1; subExpr2; ...; subExprn)' that evaluates to the logical OR of the inner expressions subExpr1; subExpr2; ...; subExprn where n >= 1. Given a string expression that represents a boolean expression; return the evaluation of that expression. It is guaranteed that the given expression is valid and follows the given rules. Example 1: Input: expression = ""&(|(f))"" Output: false Explanation: First; evaluate |(f) --> f. The expression is now ""&(f)"". Then; evaluate &(f) --> f. The expression is now ""f"". Finally; return false. Example 2: Input: expression = ""|(f;f;f;t)"" Output: true Explanation: The evaluation of (false OR false OR false OR true) is true. Example 3: Input: expression = ""!(&(f;t))"" Output: true Explanation: First; evaluate &(f;t) --> (false AND true) --> false --> f. The expression is now ""!(f)"". Then; evaluate !(f) --> NOT false --> true. We return true. Constraints: 1 <= expression.length <= 2 * 104 expression[i] is one following characters: '('; ')'; '&'; '|'; '!'; 't'; 'f'; and ';'."
Meta,1106,Parsing A Boolean Expression,Hard,"Array, Hash Table, Depth-First Search, Breadth-First Search",There is a 1 million by 1 million grid on an XY-plane; and the coordinates of each grid square are (x; y). We start at the source = [sx; sy] square and want to reach the target = [tx; ty] square. There is also an array of blocked squares; where each blocked[i] = [xi; yi] represents a blocked square with coordinates (xi; yi). Each move; we can walk one square north; east; south; or west if the square is not in the array of blocked squares. We are also not allowed to walk outside of the grid. Return true if and only if it is possible to reach the target square from the source square through a sequence of valid moves. Example 1: Input: blocked = [[0;1];[1;0]]; source = [0;0]; target = [0;2] Output: false Explanation: The target square is inaccessible starting from the source square because we cannot move. We cannot move north or east because those squares are blocked. We cannot move south or west because we cannot go outside of the grid. Example 2: Input: blocked = []; source = [0;0]; target = [999999;999999] Output: true Explanation: Because there are no blocked cells; it is possible to reach the target square. Constraints: 0 <= blocked.length <= 200 blocked[i].length == 2 0 <= xi; yi < 106 source.length == target.length == 2 0 <= sx; sy; tx; ty < 106 source != target It is guaranteed that source and target are not blocked.
Meta,1110,Delete Nodes And Return Forest,Med,,
Meta,1331,Rank Transform of an Array,Easy,"Array, Backtracking, Matrix",In a gold mine grid of size m x n; each cell in this mine has an integer representing the amount of gold in that cell; 0 if it is empty. Return the maximum amount of gold you can collect under the conditions: Every time you are located in a cell you will collect all the gold in that cell. From your position; you can walk one step to the left; right; up; or down. You can't visit the same cell more than once. Never visit a cell with 0 gold. You can start and stop collecting gold from any position in the grid that has some gold. Example 1: Input: grid = [[0;6;0];[5;8;7];[0;9;0]] Output: 24 Explanation: [[0;6;0]; [5;8;7]; [0;9;0]] Path to get the maximum gold; 9 -> 8 -> 7. Example 2: Input: grid = [[1;0;7];[2;0;6];[3;4;5];[0;3;0];[9;0;20]] Output: 28 Explanation: [[1;0;7]; [2;0;6]; [3;4;5]; [0;3;0]; [9;0;20]] Path to get the maximum gold; 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 15 0 <= grid[i][j] <= 100 There are at most 25 cells containing gold.
Meta,1209,Remove All Adjacent Duplicates in String II,Med,Concurrency,
Meta,1233,Remove Sub-Folders from the Filesystem,Med,"Array, Divide and Conquer, Interactive",
Meta,1275,Find Winner on a Tic Tac Toe Game,Easy,"Tree, Depth-First Search, Breadth-First Search, Union Find, Graph, Binary Tree",You have n binary tree nodes numbered from 0 to n - 1 where node i has two children leftChild[i] and rightChild[i]; return true if and only if all the given nodes form exactly one valid binary tree. If node i has no left child then leftChild[i] will equal -1; similarly for the right child. Note that the nodes have no values and that we only use the node numbers in this problem. Example 1: Input: n = 4; leftChild = [1;-1;3;-1]; rightChild = [2;-1;-1;-1] Output: true Example 2: Input: n = 4; leftChild = [1;-1;3;-1]; rightChild = [2;3;-1;-1] Output: false Example 3: Input: n = 2; leftChild = [1;0]; rightChild = [-1;-1] Output: false Constraints: n == leftChild.length == rightChild.length 1 <= n <= 104 -1 <= leftChild[i]; rightChild[i] <= n - 1
Meta,1344,Angle Between Hands of a Clock,Med,"Array, Hash Table",Given an array nums of positive integers; return the longest possible length of an array prefix of nums; such that it is possible to remove exactly one element from this prefix so that every number that has appeared in it will have the same number of occurrences. If after removing one element there are no remaining elements; it's still considered that every appeared number has the same number of ocurrences (0). Example 1: Input: nums = [2;2;1;1;5;3;3;5] Output: 7 Explanation: For the subarray [2;2;1;1;5;3;3] of length 7; if we remove nums[4] = 5; we will get [2;2;1;1;3;3]; so that each number will appear exactly twice. Example 2: Input: nums = [1;1;1;2;2;2;3;3;3;4;4;4;5] Output: 13 Constraints: 2 <= nums.length <= 105 1 <= nums[i] <= 105
Meta,1367,Linked List in Binary Tree,Med,"Array, Dynamic Programming, Sorting",Given n cuboids where the dimensions of the ith cuboid is cuboids[i] = [widthi; lengthi; heighti] (0-indexed). Choose a subset of cuboids and place them on each other. You can place cuboid i on cuboid j if widthi <= widthj and lengthi <= lengthj and heighti <= heightj. You can rearrange any cuboid's dimensions by rotating it to put it on another cuboid. Return the maximum height of the stacked cuboids. Example 1: Input: cuboids = [[50;45;20];[95;37;53];[45;23;12]] Output: 190 Explanation: Cuboid 1 is placed on the bottom with the 53x37 side facing down with height 95. Cuboid 0 is placed next with the 45x20 side facing down with height 50. Cuboid 2 is placed next with the 23x12 side facing down with height 45. The total height is 95 + 50 + 45 = 190. Example 2: Input: cuboids = [[38;25;45];[76;35;3]] Output: 76 Explanation: You can't place any of the cuboids on the other. We choose cuboid 1 and rotate it so that the 35x3 side is facing down and its height is 76. Example 3: Input: cuboids = [[7;11;17];[7;17;11];[11;7;17];[11;17;7];[17;7;11];[17;11;7]] Output: 102 Explanation: After rearranging the cuboids; you can see that all cuboids have the same dimension. You can place the 11x7 side down on all cuboids so their heights are 17. The maximum height of stacked cuboids is 6 * 17 = 102. Constraints: n == cuboids.length 1 <= n <= 100 1 <= widthi; lengthi; heighti <= 100
Meta,1497,Check If Array Pairs Are Divisible by k,Med,"Array, Stack, Design","Design a stack that supports increment operations on its elements. Implement the CustomStack class: CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack. void push(int x) Adds x to the top of the stack if the stack has not reached the maxSize. int pop() Pops and returns the top of the stack or -1 if the stack is empty. void inc(int k; int val) Increments the bottom k elements of the stack by val. If there are less than k elements in the stack; increment all the elements in the stack. Example 1: Input [""CustomStack"";""push"";""push"";""pop"";""push"";""push"";""push"";""increment"";""increment"";""pop"";""pop"";""pop"";""pop""] [[3];[1];[2];[];[2];[3];[4];[5;100];[2;100];[];[];[];[]] Output [null;null;null;2;null;null;null;null;null;103;202;201;-1] Explanation CustomStack stk = new CustomStack(3); // Stack is Empty [] stk.push(1); // stack becomes [1] stk.push(2); // stack becomes [1; 2] stk.pop(); // return 2 --> Return top of the stack 2; stack becomes [1] stk.push(2); // stack becomes [1; 2] stk.push(3); // stack becomes [1; 2; 3] stk.push(4); // stack still [1; 2; 3]; Do not add another elements as size is 4 stk.increment(5; 100); // stack becomes [101; 102; 103] stk.increment(2; 100); // stack becomes [201; 202; 103] stk.pop(); // return 103 --> Return top of the stack 103; stack becomes [201; 202] stk.pop(); // return 202 --> Return top of the stack 202; stack becomes [201] stk.pop(); // return 201 --> Return top of the stack 201; stack becomes [] stk.pop(); // return -1 --> Stack is empty return -1. Constraints: 1 <= maxSize; x; k <= 1000 0 <= val <= 100 At most 1000 calls will be made to each method of increment; push and pop each separately."
Meta,1498,Number of Subsequences That Satisfy the Given Sum Condition,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given two binary trees original and cloned and given a reference to a node target in the original tree. The cloned tree is a copy of the original tree. Return a reference to the same node in the cloned tree. Note that you are not allowed to change any of the two trees or the target node and the answer must be a reference to a node in the cloned tree. Example 1: Input: tree = [7;4;3;null;null;6;19]; target = 3 Output: 3 Explanation: In all examples the original and cloned trees are shown. The target node is a green node from the original tree. The answer is the yellow node from the cloned tree. Example 2: Input: tree = [7]; target = 7 Output: 7 Example 3: Input: tree = [8;null;6;null;5;null;4;null;3;null;2;null;1]; target = 4 Output: 4 Constraints: The number of nodes in the tree is in the range [1; 104]. The values of the nodes of the tree are unique. target node is a node from the original tree and is not null. Follow up: Could you solve the problem if repeated values on the tree are allowed?
Meta,1590,Make Sum Divisible by P,Med,,
Meta,1652,Defuse the Bomb,Easy,"String, Greedy","You are given a 0-indexed binary string target of length n. You have another binary string s of length n that is initially set to all zeros. You want to make s equal to target. In one operation; you can pick an index i where 0 <= i < n and flip all bits in the inclusive range [i; n - 1]. Flip means changing '0' to '1' and '1' to '0'. Return the minimum number of operations needed to make s equal to target. Example 1: Input: target = ""10111"" Output: 3 Explanation: Initially; s = ""00000"". Choose index i = 2: ""00000"" -> ""00111"" Choose index i = 0: ""00111"" -> ""11000"" Choose index i = 1: ""11000"" -> ""10111"" We need at least 3 flip operations to form target. Example 2: Input: target = ""101"" Output: 3 Explanation: Initially; s = ""000"". Choose index i = 0: ""000"" -> ""111"" Choose index i = 1: ""111"" -> ""100"" Choose index i = 2: ""100"" -> ""101"" We need at least 3 flip operations to form target. Example 3: Input: target = ""00000"" Output: 0 Explanation: We do not need any operations since the initial s already equals target. Constraints: n == target.length 1 <= n <= 105 target[i] is either '0' or '1'."
Meta,1778,Shortest Path in a Hidden Grid,Med,"Dynamic Programming, Bit Manipulation, Memoization, Bitmask",You are given four integers; m; n; introvertsCount; and extrovertsCount. You have an m x n grid; and there are two types of people: introverts and extroverts. There are introvertsCount introverts and extrovertsCount extroverts. You should decide how many people you want to live in the grid and assign each of them one grid cell. Note that you do not have to have all the people living in the grid. The happiness of each person is calculated as follows: Introverts start with 120 happiness and lose 30 happiness for each neighbor (introvert or extrovert). Extroverts start with 40 happiness and gain 20 happiness for each neighbor (introvert or extrovert). Neighbors live in the directly adjacent cells north; east; south; and west of a person's cell. The grid happiness is the sum of each person's happiness. Return the maximum possible grid happiness. Example 1: Input: m = 2; n = 3; introvertsCount = 1; extrovertsCount = 2 Output: 240 Explanation: Assume the grid is 1-indexed with coordinates (row; column). We can put the introvert in cell (1;1) and put the extroverts in cells (1;3) and (2;3). - Introvert at (1;1) happiness: 120 (starting happiness) - (0 * 30) (0 neighbors) = 120 - Extrovert at (1;3) happiness: 40 (starting happiness) + (1 * 20) (1 neighbor) = 60 - Extrovert at (2;3) happiness: 40 (starting happiness) + (1 * 20) (1 neighbor) = 60 The grid happiness is 120 + 60 + 60 = 240. The above figure shows the grid in this example with each person's happiness. The introvert stays in the light green cell while the extroverts live on the light purple cells. Example 2: Input: m = 3; n = 1; introvertsCount = 2; extrovertsCount = 1 Output: 260 Explanation: Place the two introverts in (1;1) and (3;1) and the extrovert at (2;1). - Introvert at (1;1) happiness: 120 (starting happiness) - (1 * 30) (1 neighbor) = 90 - Extrovert at (2;1) happiness: 40 (starting happiness) + (2 * 20) (2 neighbors) = 80 - Introvert at (3;1) happiness: 120 (starting happiness) - (1 * 30) (1 neighbor) = 90 The grid happiness is 90 + 80 + 90 = 260. Example 3: Input: m = 2; n = 2; introvertsCount = 4; extrovertsCount = 0 Output: 240 Constraints: 1 <= m; n <= 5 0 <= introvertsCount; extrovertsCount <= min(m * n; 6)
Meta,2090,K Radius Subarray Averages,Med,"Dynamic Programming, Graph, Topological Sort, Shortest Path",You are in a city that consists of n intersections numbered from 0 to n - 1 with bi-directional roads between some intersections. The inputs are generated such that you can reach any intersection from any other intersection and that there is at most one road between any two intersections. You are given an integer n and a 2D integer array roads where roads[i] = [ui; vi; timei] means that there is a road between intersections ui and vi that takes timei minutes to travel. You want to know in how many ways you can travel from intersection 0 to intersection n - 1 in the shortest amount of time. Return the number of ways you can arrive at your destination in the shortest amount of time. Since the answer may be large; return it modulo 109 + 7. Example 1: Input: n = 7; roads = [[0;6;7];[0;1;2];[1;2;3];[1;3;3];[6;3;3];[3;5;1];[6;5;1];[2;5;1];[0;4;5];[4;6;2]] Output: 4 Explanation: The shortest amount of time it takes to go from intersection 0 to intersection 6 is 7 minutes. The four ways to get there in 7 minutes are: - 0 ➝ 6 - 0 ➝ 4 ➝ 6 - 0 ➝ 1 ➝ 2 ➝ 5 ➝ 6 - 0 ➝ 1 ➝ 3 ➝ 5 ➝ 6 Example 2: Input: n = 2; roads = [[1;0;10]] Output: 1 Explanation: There is only one way to go from intersection 0 to intersection 1; and it takes 10 minutes. Constraints: 1 <= n <= 200 n - 1 <= roads.length <= n * (n - 1) / 2 roads[i].length == 3 0 <= ui; vi <= n - 1 1 <= timei <= 109 ui != vi There is at most one road connecting any two intersections. You can reach any intersection from any other intersection.
Meta,2235,Add Two Integers,Easy,String,"You are given a string title consisting of one or more words separated by a single space; where each word consists of English letters. Capitalize the string by changing the capitalization of each word such that: If the length of the word is 1 or 2 letters; change all letters to lowercase. Otherwise; change the first letter to uppercase and the remaining letters to lowercase. Return the capitalized title. Example 1: Input: title = ""capiTalIze tHe titLe"" Output: ""Capitalize The Title"" Explanation: Since all the words have a length of at least 3; the first letter of each word is uppercase; and the remaining letters are lowercase. Example 2: Input: title = ""First leTTeR of EACH Word"" Output: ""First Letter of Each Word"" Explanation: The word ""of"" has length 2; so it is all lowercase. The remaining words have a length of at least 3; so the first letter of each remaining word is uppercase; and the remaining letters are lowercase. Example 3: Input: title = ""i lOve leetcode"" Output: ""i Love Leetcode"" Explanation: The word ""i"" has length 1; so it is lowercase. The remaining words have a length of at least 3; so the first letter of each remaining word is uppercase; and the remaining letters are lowercase. Constraints: 1 <= title.length <= 100 title consists of words separated by a single space without any leading or trailing spaces. Each word consists of uppercase and lowercase English letters and is non-empty."
Meta,2236,Root Equals Sum of Children,Easy,"Linked List, Two Pointers, Stack",In a linked list of size n; where n is even; the ith node (0-indexed) of the linked list is known as the twin of the (n-1-i)th node; if 0 <= i <= (n / 2) - 1. For example; if n = 4; then node 0 is the twin of node 3; and node 1 is the twin of node 2. These are the only nodes with twins for n = 4. The twin sum is defined as the sum of a node and its twin. Given the head of a linked list with even length; return the maximum twin sum of the linked list. Example 1: Input: head = [5;4;2;1] Output: 6 Explanation: Nodes 0 and 1 are the twins of nodes 3 and 2; respectively. All have twin sum = 6. There are no other nodes with twins in the linked list. Thus; the maximum twin sum of the linked list is 6. Example 2: Input: head = [4;2;2;3] Output: 7 Explanation: The nodes with twins present in this linked list are: - Node 0 is the twin of node 3 having a twin sum of 4 + 3 = 7. - Node 1 is the twin of node 2 having a twin sum of 2 + 2 = 4. Thus; the maximum twin sum of the linked list is max(7; 4) = 7. Example 3: Input: head = [1;100000] Output: 100001 Explanation: There is only one node with a twin in the linked list having twin sum of 1 + 100000 = 100001. Constraints: The number of nodes in the list is an even integer in the range [2; 105]. 1 <= Node.val <= 105
Meta,2406,Divide Intervals Into Minimum Number of Groups,Med,"Hash Table, String","You are given the strings key and message; which represent a cipher key and a secret message; respectively. The steps to decode message are as follows: Use the first appearance of all 26 lowercase English letters in key as the order of the substitution table. Align the substitution table with the regular English alphabet. Each letter in message is then substituted using the table. Spaces ' ' are transformed to themselves. For example; given key = ""happy boy"" (actual key would have at least one instance of each letter in the alphabet); we have the partial substitution table of ('h' -> 'a'; 'a' -> 'b'; 'p' -> 'c'; 'y' -> 'd'; 'b' -> 'e'; 'o' -> 'f'). Return the decoded message. Example 1: Input: key = ""the quick brown fox jumps over the lazy dog""; message = ""vkbs bs t suepuv"" Output: ""this is a secret"" Explanation: The diagram above shows the substitution table. It is obtained by taking the first appearance of each letter in ""the quick brown fox jumps over the lazy dog"". Example 2: Input: key = ""eljuxhpwnyrdgtqkviszcfmabo""; message = ""zwx hnfx lqantp mnoeius ycgk vcnjrdb"" Output: ""the five boxing wizards jump quickly"" Explanation: The diagram above shows the substitution table. It is obtained by taking the first appearance of each letter in ""eljuxhpwnyrdgtqkviszcfmabo"". Constraints: 26 <= key.length <= 2000 key consists of lowercase English letters and ' '. key contains every letter in the English alphabet ('a' to 'z') at least once. 1 <= message.length <= 2000 message consists of lowercase English letters and ' '."
Meta,3011,Find if Array Can Be Sorted,Med,,
Meta,3097,Shortest Subarray With OR at Least K II,Med,Database,
Meta,3133,Minimum Array End,Med,,
Meta,6,Zigzag Conversion,Med,String,"The string ""PAYPALISHIRING"" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: ""PAHNAPLSIIGYIR"" Write the code that will take a string and make this conversion given a number of rows: string convert(string s; int numRows); Example 1: Input: s = ""PAYPALISHIRING""; numRows = 3 Output: ""PAHNAPLSIIGYIR"" Example 2: Input: s = ""PAYPALISHIRING""; numRows = 4 Output: ""PINALSIGYAHRPI"" Explanation: P I N A L S I G Y A H R P I Example 3: Input: s = ""A""; numRows = 1 Output: ""A"" Constraints: 1 <= s.length <= 1000 s consists of English letters (lower-case and upper-case); ';' and '.'. 1 <= numRows <= 1000"
Meta,18,4Sum,Med,"Array, Two Pointers, Sorting",Given an array nums of n integers; return an array of all the unique quadruplets [nums[a]; nums[b]; nums[c]; nums[d]] such that: 0 <= a; b; c; d < n a; b; c; and d are distinct. nums[a] + nums[b] + nums[c] + nums[d] == target You may return the answer in any order. Example 1: Input: nums = [1;0;-1;0;-2;2]; target = 0 Output: [[-2;-1;1;2];[-2;0;0;2];[-1;0;0;1]] Example 2: Input: nums = [2;2;2;2;2]; target = 8 Output: [[2;2;2;2]] Constraints: 1 <= nums.length <= 200 -109 <= nums[i] <= 109 -109 <= target <= 109
Meta,24,Swap Nodes in Pairs,Med,"Linked List, Recursion",Given a linked list; swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e.; only nodes themselves may be changed.) Example 1: Input: head = [1;2;3;4] Output: [2;1;4;3] Explanation: Example 2: Input: head = [] Output: [] Example 3: Input: head = [1] Output: [1] Example 4: Input: head = [1;2;3] Output: [2;1;3] Constraints: The number of nodes in the list is in the range [0; 100]. 0 <= Node.val <= 100
Meta,32,Longest Valid Parentheses,Hard,"String, Dynamic Programming, Stack","Given a string containing just the characters '(' and ')'; return the length of the longest valid (well-formed) parentheses substring. Example 1: Input: s = ""(()"" Output: 2 Explanation: The longest valid parentheses substring is ""()"". Example 2: Input: s = "")()())"" Output: 4 Explanation: The longest valid parentheses substring is ""()()"". Example 3: Input: s = """" Output: 0 Constraints: 0 <= s.length <= 3 * 104 s[i] is '('; or ')'."
Meta,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
Meta,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Meta,67,Add Binary,Easy,"Math, String, Bit Manipulation, Simulation","Given two binary strings a and b; return their sum as a binary string. Example 1: Input: a = ""11""; b = ""1"" Output: ""100"" Example 2: Input: a = ""1010""; b = ""1011"" Output: ""10101"" Constraints: 1 <= a.length; b.length <= 104 a and b consist only of '0' or '1' characters. Each string does not contain leading zeros except for the zero itself."
Meta,69,Sqrt(x),Easy,"Math, Binary Search",Given a non-negative integer x; return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. For example; do not use pow(x; 0.5) in c++ or x ** 0.5 in python. Example 1: Input: x = 4 Output: 2 Explanation: The square root of 4 is 2; so we return 2. Example 2: Input: x = 8 Output: 2 Explanation: The square root of 8 is 2.82842...; and since we round it down to the nearest integer; 2 is returned. Constraints: 0 <= x <= 231 - 1
Meta,73,Set Matrix Zeroes,Med,"Array, Hash Table, Matrix",Given an m x n integer matrix matrix; if an element is 0; set its entire row and column to 0's. You must do it in place. Example 1: Input: matrix = [[1;1;1];[1;0;1];[1;1;1]] Output: [[1;0;1];[0;0;0];[1;0;1]] Example 2: Input: matrix = [[0;1;2;0];[3;4;5;2];[1;3;1;5]] Output: [[0;0;0;0];[0;4;5;0];[0;3;1;0]] Constraints: m == matrix.length n == matrix[0].length 1 <= m; n <= 200 -231 <= matrix[i][j] <= 231 - 1 Follow up: A straightforward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space; but still not the best solution. Could you devise a constant space solution?
Meta,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Meta,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Meta,82,Remove Duplicates from Sorted List II,Med,"Linked List, Two Pointers",Given the head of a sorted linked list; delete all nodes that have duplicate numbers; leaving only distinct numbers from the original list. Return the linked list sorted as well. Example 1: Input: head = [1;2;3;3;4;4;5] Output: [1;2;5] Example 2: Input: head = [1;1;1;2;3] Output: [2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Meta,93,Restore IP Addresses,Med,"String, Backtracking","A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. For example; ""0.1.2.201"" and ""192.168.1.1"" are valid IP addresses; but ""0.011.255.245""; ""192.168.1.312"" and ""192.168@1.1"" are invalid IP addresses. Given a string s containing only digits; return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order. Example 1: Input: s = ""25525511135"" Output: [""255.255.11.135"";""255.255.111.35""] Example 2: Input: s = ""0000"" Output: [""0.0.0.0""] Example 3: Input: s = ""101023"" Output: [""1.0.10.23"";""1.0.102.3"";""10.1.0.23"";""10.10.2.3"";""101.0.2.3""] Constraints: 1 <= s.length <= 20 s consists of digits only."
Meta,112,Path Sum,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum. A leaf is a node with no children. Example 1: Input: root = [5;4;8;11;null;13;4;7;2;null;null;null;1]; targetSum = 22 Output: true Explanation: The root-to-leaf path with the target sum is shown. Example 2: Input: root = [1;2;3]; targetSum = 5 Output: false Explanation: There are two root-to-leaf paths in the tree: (1 --> 2): The sum is 3. (1 --> 3): The sum is 4. There is no root-to-leaf path with sum = 5. Example 3: Input: root = []; targetSum = 0 Output: false Explanation: Since the tree is empty; there are no root-to-leaf paths. Constraints: The number of nodes in the tree is in the range [0; 5000]. -1000 <= Node.val <= 1000 -1000 <= targetSum <= 1000
Meta,117,Populating Next Right Pointers in Each Node II,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given a binary tree struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;null;7] Output: [1;#;2;3;#;4;5;7;#] Explanation: Given the above binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 6000]. -100 <= Node.val <= 100 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Meta,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Meta,134,Gas Station,Med,"Array, Greedy",There are n gas stations along a circular route; where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations. Given two integer arrays gas and cost; return the starting gas station's index if you can travel around the circuit once in the clockwise direction; otherwise return -1. If there exists a solution; it is guaranteed to be unique. Example 1: Input: gas = [1;2;3;4;5]; cost = [3;4;5;1;2] Output: 3 Explanation: Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 4. Your tank = 4 - 1 + 5 = 8 Travel to station 0. Your tank = 8 - 2 + 1 = 7 Travel to station 1. Your tank = 7 - 3 + 2 = 6 Travel to station 2. Your tank = 6 - 4 + 3 = 5 Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. Therefore; return 3 as the starting index. Example 2: Input: gas = [2;3;4]; cost = [3;4;3] Output: -1 Explanation: You can't start at station 0 or 1; as there is not enough gas to travel to the next station. Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 0. Your tank = 4 - 3 + 2 = 3 Travel to station 1. Your tank = 3 - 3 + 3 = 3 You cannot travel back to station 2; as it requires 4 unit of gas but you only have 3. Therefore; you can't travel around the circuit once no matter where you start. Constraints: n == gas.length == cost.length 1 <= n <= 105 0 <= gas[i]; cost[i] <= 104
Meta,137,Single Number II,Med,"Array, Bit Manipulation",Given an integer array nums where every element appears three times except for one; which appears exactly once. Find the single element and return it. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;3;2] Output: 3 Example 2: Input: nums = [0;1;0;1;0;1;99] Output: 99 Constraints: 1 <= nums.length <= 3 * 104 -231 <= nums[i] <= 231 - 1 Each element in nums appears exactly three times except for one element which appears once.
Meta,149,Max Points on a Line,Hard,"Array, Hash Table, Math, Geometry",Given an array of points where points[i] = [xi; yi] represents a point on the X-Y plane; return the maximum number of points that lie on the same straight line. Example 1: Input: points = [[1;1];[2;2];[3;3]] Output: 3 Example 2: Input: points = [[1;1];[3;2];[5;3];[4;1];[2;3];[1;4]] Output: 4 Constraints: 1 <= points.length <= 300 points[i].length == 2 -104 <= xi; yi <= 104 All the points are unique.
Meta,150,Evaluate Reverse Polish Notation,Med,"Array, Math, Stack","You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression. Return an integer that represents the value of the expression. Note that: The valid operators are '+'; '-'; '*'; and '/'. Each operand may be an integer or another expression. The division between two integers always truncates toward zero. There will not be any division by zero. The input represents a valid arithmetic expression in a reverse polish notation. The answer and all the intermediate calculations can be represented in a 32-bit integer. Example 1: Input: tokens = [""2"";""1"";""+"";""3"";""*""] Output: 9 Explanation: ((2 + 1) * 3) = 9 Example 2: Input: tokens = [""4"";""13"";""5"";""/"";""+""] Output: 6 Explanation: (4 + (13 / 5)) = 6 Example 3: Input: tokens = [""10"";""6"";""9"";""3"";""+"";""-11"";""*"";""/"";""*"";""17"";""+"";""5"";""+""] Output: 22 Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 = ((10 * (6 / (12 * -11))) + 17) + 5 = ((10 * (6 / -132)) + 17) + 5 = ((10 * 0) + 17) + 5 = (0 + 17) + 5 = 17 + 5 = 22 Constraints: 1 <= tokens.length <= 104 tokens[i] is either an operator: ""+""; ""-""; ""*""; or ""/""; or an integer in the range [-200; 200]."
Meta,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Meta,188,Best Time to Buy and Sell Stock IV,Hard,"Array, Dynamic Programming",You are given an integer array prices where prices[i] is the price of a given stock on the ith day; and an integer k. Find the maximum profit you can achieve. You may complete at most k transactions: i.e. you may buy at most k times and sell at most k times. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: k = 2; prices = [2;4;1] Output: 2 Explanation: Buy on day 1 (price = 2) and sell on day 2 (price = 4); profit = 4-2 = 2. Example 2: Input: k = 2; prices = [3;2;6;5;0;3] Output: 7 Explanation: Buy on day 2 (price = 2) and sell on day 3 (price = 6); profit = 6-2 = 4. Then buy on day 5 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Constraints: 1 <= k <= 100 1 <= prices.length <= 1000 0 <= prices[i] <= 1000
Meta,195,Tenth Line,Easy,Shell,Given a text file file.txt; print just the 10th line of the file. Example: Assume that file.txt has the following content: Line 1 Line 2 Line 3 Line 4 Line 5 Line 6 Line 7 Line 8 Line 9 Line 10 Your script should output the tenth line; which is: Line 10 Note: 1. If the file contains less than 10 lines; what should you output? 2. There's at least three different solutions. Try to explore all possibilities.
Meta,202,Happy Number,Easy,"Hash Table, Math, Two Pointers",Write an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer; replace the number by the sum of the squares of its digits. Repeat the process until the number equals 1 (where it will stay); or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy. Return true if n is a happy number; and false if not. Example 1: Input: n = 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1 Example 2: Input: n = 2 Output: false Constraints: 1 <= n <= 231 - 1
Meta,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Meta,212,Word Search II,Hard,"Array, String, Backtracking, Trie, Matrix","Given an m x n board of characters and a list of strings words; return all words on the board. Each word must be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example 1: Input: board = [[""o"";""a"";""a"";""n""];[""e"";""t"";""a"";""e""];[""i"";""h"";""k"";""r""];[""i"";""f"";""l"";""v""]]; words = [""oath"";""pea"";""eat"";""rain""] Output: [""eat"";""oath""] Example 2: Input: board = [[""a"";""b""];[""c"";""d""]]; words = [""abcb""] Output: [] Constraints: m == board.length n == board[i].length 1 <= m; n <= 12 board[i][j] is a lowercase English letter. 1 <= words.length <= 3 * 104 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. All the strings of words are unique."
Meta,228,Summary Ranges,Easy,Array,"You are given a sorted unique integer array nums. A range [a;b] is the set of all integers from a to b (inclusive). Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is; each element of nums is covered by exactly one of the ranges; and there is no integer x such that x is in one of the ranges but not in nums. Each range [a;b] in the list should be output as: ""a->b"" if a != b ""a"" if a == b Example 1: Input: nums = [0;1;2;4;5;7] Output: [""0->2"";""4->5"";""7""] Explanation: The ranges are: [0;2] --> ""0->2"" [4;5] --> ""4->5"" [7;7] --> ""7"" Example 2: Input: nums = [0;2;3;4;6;8;9] Output: [""0"";""2->4"";""6"";""8->9""] Explanation: The ranges are: [0;0] --> ""0"" [2;4] --> ""2->4"" [6;6] --> ""6"" [8;9] --> ""8->9"" Constraints: 0 <= nums.length <= 20 -231 <= nums[i] <= 231 - 1 All the values of nums are unique. nums is sorted in ascending order."
Meta,234,Palindrome Linked List,Easy,"Linked List, Two Pointers, Stack, Recursion",Given the head of a singly linked list; return true if it is a palindrome or false otherwise. Example 1: Input: head = [1;2;2;1] Output: true Example 2: Input: head = [1;2] Output: false Constraints: The number of nodes in the list is in the range [1; 105]. 0 <= Node.val <= 9 Follow up: Could you do it in O(n) time and O(1) space?
Meta,235,Lowest Common Ancestor of a Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given a binary search tree (BST); find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [2;1]; p = 2; q = 1 Output: 2 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.
Meta,240,Search a 2D Matrix II,Med,"Array, Binary Search, Divide and Conquer, Matrix",Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. Example 1: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 5 Output: true Example 2: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 20 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= n; m <= 300 -109 <= matrix[i][j] <= 109 All the integers in each row are sorted in ascending order. All the integers in each column are sorted in ascending order. -109 <= target <= 109
Meta,242,Valid Anagram,Easy,"Hash Table, String, Sorting","Given two strings s and t; return true if t is an anagram of s; and false otherwise. Example 1: Input: s = ""anagram""; t = ""nagaram"" Output: true Example 2: Input: s = ""rat""; t = ""car"" Output: false Constraints: 1 <= s.length; t.length <= 5 * 104 s and t consist of lowercase English letters. Follow up: What if the inputs contain Unicode characters? How would you adapt your solution to such a case?"
Meta,252,Meeting Rooms,Easy,"Array, Sorting",
Meta,286,Walls and Gates,Med,"Array, Breadth-First Search, Matrix",
Meta,287,Find the Duplicate Number,Med,"Array, Two Pointers, Binary Search, Bit Manipulation",Given an array of integers nums containing n + 1 integers where each integer is in the range [1; n] inclusive. There is only one repeated number in nums; return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Example 1: Input: nums = [1;3;4;2;2] Output: 2 Example 2: Input: nums = [3;1;3;4;2] Output: 3 Example 3: Input: nums = [3;3;3;3;3] Output: 3 Constraints: 1 <= n <= 105 nums.length == n + 1 1 <= nums[i] <= n All the integers in nums appear only once except for precisely one integer which appears two or more times. Follow up: How can we prove that at least one duplicate number must exist in nums? Can you solve the problem in linear runtime complexity?
Meta,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
Meta,303,Range Sum Query - Immutable,Easy,"Array, Design, Prefix Sum","Given an integer array nums; handle multiple queries of the following type: Calculate the sum of the elements of nums between indices left and right inclusive where left <= right. Implement the NumArray class: NumArray(int[] nums) Initializes the object with the integer array nums. int sumRange(int left; int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]). Example 1: Input [""NumArray""; ""sumRange""; ""sumRange""; ""sumRange""] [[[-2; 0; 3; -5; 2; -1]]; [0; 2]; [2; 5]; [0; 5]] Output [null; 1; -1; -3] Explanation NumArray numArray = new NumArray([-2; 0; 3; -5; 2; -1]); numArray.sumRange(0; 2); // return (-2) + 0 + 3 = 1 numArray.sumRange(2; 5); // return 3 + (-5) + 2 + (-1) = -1 numArray.sumRange(0; 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3 Constraints: 1 <= nums.length <= 104 -105 <= nums[i] <= 105 0 <= left <= right < nums.length At most 104 calls will be made to sumRange."
Meta,316,Remove Duplicate Letters,Med,"String, Stack, Greedy, Monotonic Stack","Given a string s; remove duplicate letters so that every letter appears once and only once. You must make sure your result is the smallest in lexicographical order among all possible results. Example 1: Input: s = ""bcabc"" Output: ""abc"" Example 2: Input: s = ""cbacdcbc"" Output: ""acdb"" Constraints: 1 <= s.length <= 104 s consists of lowercase English letters. Note: This question is the same as 1081: https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/"
Meta,328,Odd Even Linked List,Med,Linked List,Given the head of a singly linked list; group all the nodes with odd indices together followed by the nodes with even indices; and return the reordered list. The first node is considered odd; and the second node is even; and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input. You must solve the problem in O(1) extra space complexity and O(n) time complexity. Example 1: Input: head = [1;2;3;4;5] Output: [1;3;5;2;4] Example 2: Input: head = [2;1;3;5;6;4;7] Output: [2;3;6;7;1;5;4] Constraints: The number of nodes in the linked list is in the range [0; 104]. -106 <= Node.val <= 106
Meta,334,Increasing Triplet Subsequence,Med,"Array, Greedy",Given an integer array nums; return true if there exists a triple of indices (i; j; k) such that i < j < k and nums[i] < nums[j] < nums[k]. If no such indices exists; return false. Example 1: Input: nums = [1;2;3;4;5] Output: true Explanation: Any triplet where i < j < k is valid. Example 2: Input: nums = [5;4;3;2;1] Output: false Explanation: No triplet exists. Example 3: Input: nums = [2;1;5;0;4;6] Output: true Explanation: The triplet (3; 4; 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6. Constraints: 1 <= nums.length <= 5 * 105 -231 <= nums[i] <= 231 - 1 Follow up: Could you implement a solution that runs in O(n) time complexity and O(1) space complexity?
Meta,338,Counting Bits,Easy,"Dynamic Programming, Bit Manipulation",Given an integer n; return an array ans of length n + 1 such that for each i (0 <= i <= n); ans[i] is the number of 1's in the binary representation of i. Example 1: Input: n = 2 Output: [0;1;1] Explanation: 0 --> 0 1 --> 1 2 --> 10 Example 2: Input: n = 5 Output: [0;1;1;2;1;2] Explanation: 0 --> 0 1 --> 1 2 --> 10 3 --> 11 4 --> 100 5 --> 101 Constraints: 0 <= n <= 105 Follow up: It is very easy to come up with a solution with a runtime of O(n log n). Can you do it in linear time O(n) and possibly in a single pass? Can you do it without using any built-in function (i.e.; like __builtin_popcount in C++)?
Meta,340,Longest Substring with At Most K Distinct Characters,Med,"Hash Table, String, Sliding Window",
Meta,344,Reverse String,Easy,"Two Pointers, String","Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory. Example 1: Input: s = [""h"";""e"";""l"";""l"";""o""] Output: [""o"";""l"";""l"";""e"";""h""] Example 2: Input: s = [""H"";""a"";""n"";""n"";""a"";""h""] Output: [""h"";""a"";""n"";""n"";""a"";""H""] Constraints: 1 <= s.length <= 105 s[i] is a printable ascii character."
Meta,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
Meta,410,Split Array Largest Sum,Hard,"Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum",Given an integer array nums and an integer k; split nums into k non-empty subarrays such that the largest sum of any subarray is minimized. Return the minimized largest sum of the split. A subarray is a contiguous part of the array. Example 1: Input: nums = [7;2;5;10;8]; k = 2 Output: 18 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [7;2;5] and [10;8]; where the largest sum among the two subarrays is only 18. Example 2: Input: nums = [1;2;3;4;5]; k = 2 Output: 9 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [1;2;3] and [4;5]; where the largest sum among the two subarrays is only 9. Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 106 1 <= k <= min(50; nums.length)
Meta,416,Partition Equal Subset Sum,Med,"Array, Dynamic Programming",Given an integer array nums; return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise. Example 1: Input: nums = [1;5;11;5] Output: true Explanation: The array can be partitioned as [1; 5; 5] and [11]. Example 2: Input: nums = [1;2;3;5] Output: false Explanation: The array cannot be partitioned into equal sum subsets. Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 100
Meta,435,Non-overlapping Intervals,Med,"Array, Dynamic Programming, Greedy, Sorting",Given an array of intervals intervals where intervals[i] = [starti; endi]; return the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping. Note that intervals which only touch at a point are non-overlapping. For example; [1; 2] and [2; 3] are non-overlapping. Example 1: Input: intervals = [[1;2];[2;3];[3;4];[1;3]] Output: 1 Explanation: [1;3] can be removed and the rest of the intervals are non-overlapping. Example 2: Input: intervals = [[1;2];[1;2];[1;2]] Output: 2 Explanation: You need to remove two [1;2] to make the rest of the intervals non-overlapping. Example 3: Input: intervals = [[1;2];[2;3]] Output: 0 Explanation: You don't need to remove any of the intervals since they're already non-overlapping. Constraints: 1 <= intervals.length <= 105 intervals[i].length == 2 -5 * 104 <= starti < endi <= 5 * 104
Meta,437,Path Sum III,Med,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return the number of paths where the sum of the values along the path equals targetSum. The path does not need to start or end at the root or a leaf; but it must go downwards (i.e.; traveling only from parent nodes to child nodes). Example 1: Input: root = [10;5;-3;3;2;null;11;3;-2;null;1]; targetSum = 8 Output: 3 Explanation: The paths that sum to 8 are shown. Example 2: Input: root = [5;4;8;11;null;13;4;7;2;null;null;5;1]; targetSum = 22 Output: 3 Constraints: The number of nodes in the tree is in the range [0; 1000]. -109 <= Node.val <= 109 -1000 <= targetSum <= 1000
Meta,451,Sort Characters By Frequency,Med,"Hash Table, String, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given a string s; sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers; return any of them. Example 1: Input: s = ""tree"" Output: ""eert"" Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore ""eetr"" is also a valid answer. Example 2: Input: s = ""cccaaa"" Output: ""aaaccc"" Explanation: Both 'c' and 'a' appear three times; so both ""cccaaa"" and ""aaaccc"" are valid answers. Note that ""cacaca"" is incorrect; as the same characters must be together. Example 3: Input: s = ""Aabb"" Output: ""bbAa"" Explanation: ""bbaA"" is also a valid answer; but ""Aabb"" is incorrect. Note that 'A' and 'a' are treated as two different characters. Constraints: 1 <= s.length <= 5 * 105 s consists of uppercase and lowercase English letters and digits."
Meta,453,Minimum Moves to Equal Array Elements,Med,"Array, Math",Given an integer array nums of size n; return the minimum number of moves required to make all array elements equal. In one move; you can increment n - 1 elements of the array by 1. Example 1: Input: nums = [1;2;3] Output: 3 Explanation: Only three moves are needed (remember each move increments two elements): [1;2;3] => [2;3;3] => [3;4;3] => [4;4;4] Example 2: Input: nums = [1;1;1] Output: 0 Constraints: n == nums.length 1 <= nums.length <= 105 -109 <= nums[i] <= 109 The answer is guaranteed to fit in a 32-bit integer.
Meta,455,Assign Cookies,Easy,"Array, Two Pointers, Greedy, Sorting",Assume you are an awesome parent and want to give your children some cookies. But; you should give each child at most one cookie. Each child i has a greed factor g[i]; which is the minimum size of a cookie that the child will be content with; and each cookie j has a size s[j]. If s[j] >= g[i]; we can assign the cookie j to the child i; and the child i will be content. Your goal is to maximize the number of your content children and output the maximum number. Example 1: Input: g = [1;2;3]; s = [1;1] Output: 1 Explanation: You have 3 children and 2 cookies. The greed factors of 3 children are 1; 2; 3. And even though you have 2 cookies; since their size is both 1; you could only make the child whose greed factor is 1 content. You need to output 1. Example 2: Input: g = [1;2]; s = [1;2;3] Output: 2 Explanation: You have 2 children and 3 cookies. The greed factors of 2 children are 1; 2. You have 3 cookies and their sizes are big enough to gratify all of the children; You need to output 2. Constraints: 1 <= g.length <= 3 * 104 0 <= s.length <= 3 * 104 1 <= g[i]; s[j] <= 231 - 1 Note: This question is the same as 2410: Maximum Matching of Players With Trainers.
Meta,468,Validate IP Address,Med,String,"Given a string queryIP; return ""IPv4"" if IP is a valid IPv4 address; ""IPv6"" if IP is a valid IPv6 address or ""Neither"" if IP is not a correct IP of any type. A valid IPv4 address is an IP in the form ""x1.x2.x3.x4"" where 0 <= xi <= 255 and xi cannot contain leading zeros. For example; ""192.168.1.1"" and ""192.168.1.0"" are valid IPv4 addresses while ""192.168.01.1""; ""192.168.1.00""; and ""192.168@1.1"" are invalid IPv4 addresses. A valid IPv6 address is an IP in the form ""x1:x2:x3:x4:x5:x6:x7:x8"" where: 1 <= xi.length <= 4 xi is a hexadecimal string which may contain digits; lowercase English letter ('a' to 'f') and upper-case English letters ('A' to 'F'). Leading zeros are allowed in xi. For example; ""2001:0db8:85a3:0000:0000:8a2e:0370:7334"" and ""2001:db8:85a3:0:0:8A2E:0370:7334"" are valid IPv6 addresses; while ""2001:0db8:85a3::8A2E:037j:7334"" and ""02001:0db8:85a3:0000:0000:8a2e:0370:7334"" are invalid IPv6 addresses. Example 1: Input: queryIP = ""172.16.254.1"" Output: ""IPv4"" Explanation: This is a valid IPv4 address; return ""IPv4"". Example 2: Input: queryIP = ""2001:0db8:85a3:0:0:8A2E:0370:7334"" Output: ""IPv6"" Explanation: This is a valid IPv6 address; return ""IPv6"". Example 3: Input: queryIP = ""256.256.256.256"" Output: ""Neither"" Explanation: This is neither a IPv4 address nor a IPv6 address. Constraints: queryIP consists only of English letters; digits and the characters '.' and ':'."
Meta,493,Reverse Pairs,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums; return the number of reverse pairs in the array. A reverse pair is a pair (i; j) where: 0 <= i < j < nums.length and nums[i] > 2 * nums[j]. Example 1: Input: nums = [1;3;2;3;1] Output: 2 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 3; nums[4] = 1; 3 > 2 * 1 Example 2: Input: nums = [2;4;3;5;1] Output: 3 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 4; nums[4] = 1; 4 > 2 * 1 (2; 4) --> nums[2] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 5; nums[4] = 1; 5 > 2 * 1 Constraints: 1 <= nums.length <= 5 * 104 -231 <= nums[i] <= 231 - 1
Meta,510,Inorder Successor in BST II,Med,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",
Meta,525,Contiguous Array,Med,"Array, Hash Table, Prefix Sum",Given a binary array nums; return the maximum length of a contiguous subarray with an equal number of 0 and 1. Example 1: Input: nums = [0;1] Output: 2 Explanation: [0; 1] is the longest contiguous subarray with an equal number of 0 and 1. Example 2: Input: nums = [0;1;0] Output: 2 Explanation: [0; 1] (or [1; 0]) is a longest contiguous subarray with equal number of 0 and 1. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Meta,1721,Swapping Nodes in a Linked List,Med,"Array, Simulation",You are the operator of a Centennial Wheel that has four gondolas; and each gondola has room for up to four people. You have the ability to rotate the gondolas counterclockwise; which costs you runningCost dollars. You are given an array customers of length n where customers[i] is the number of new customers arriving just before the ith rotation (0-indexed). This means you must rotate the wheel i times before the customers[i] customers arrive. You cannot make customers wait if there is room in the gondola. Each customer pays boardingCost dollars when they board on the gondola closest to the ground and will exit once that gondola reaches the ground again. You can stop the wheel at any time; including before serving all customers. If you decide to stop serving customers; all subsequent rotations are free in order to get all the customers down safely. Note that if there are currently more than four customers waiting at the wheel; only four will board the gondola; and the rest will wait for the next rotation. Return the minimum number of rotations you need to perform to maximize your profit. If there is no scenario where the profit is positive; return -1. Example 1: Input: customers = [8;3]; boardingCost = 5; runningCost = 6 Output: 3 Explanation: The numbers written on the gondolas are the number of people currently there. 1. 8 customers arrive; 4 board and 4 wait for the next gondola; the wheel rotates. Current profit is 4 * $5 - 1 * $6 = $14. 2. 3 customers arrive; the 4 waiting board the wheel and the other 3 wait; the wheel rotates. Current profit is 8 * $5 - 2 * $6 = $28. 3. The final 3 customers board the gondola; the wheel rotates. Current profit is 11 * $5 - 3 * $6 = $37. The highest profit was $37 after rotating the wheel 3 times. Example 2: Input: customers = [10;9;6]; boardingCost = 6; runningCost = 4 Output: 7 Explanation: 1. 10 customers arrive; 4 board and 6 wait for the next gondola; the wheel rotates. Current profit is 4 * $6 - 1 * $4 = $20. 2. 9 customers arrive; 4 board and 11 wait (2 originally waiting; 9 newly waiting); the wheel rotates. Current profit is 8 * $6 - 2 * $4 = $40. 3. The final 6 customers arrive; 4 board and 13 wait; the wheel rotates. Current profit is 12 * $6 - 3 * $4 = $60. 4. 4 board and 9 wait; the wheel rotates. Current profit is 16 * $6 - 4 * $4 = $80. 5. 4 board and 5 wait; the wheel rotates. Current profit is 20 * $6 - 5 * $4 = $100. 6. 4 board and 1 waits; the wheel rotates. Current profit is 24 * $6 - 6 * $4 = $120. 7. 1 boards; the wheel rotates. Current profit is 25 * $6 - 7 * $4 = $122. The highest profit was $122 after rotating the wheel 7 times. Example 3: Input: customers = [3;4;0;5;1]; boardingCost = 1; runningCost = 92 Output: -1 Explanation: 1. 3 customers arrive; 3 board and 0 wait; the wheel rotates. Current profit is 3 * $1 - 1 * $92 = -$89. 2. 4 customers arrive; 4 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 2 * $92 = -$177. 3. 0 customers arrive; 0 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 3 * $92 = -$269. 4. 5 customers arrive; 4 board and 1 waits; the wheel rotates. Current profit is 11 * $1 - 4 * $92 = -$357. 5. 1 customer arrives; 2 board and 0 wait; the wheel rotates. Current profit is 13 * $1 - 5 * $92 = -$447. The profit was never positive; so return -1. Constraints: n == customers.length 1 <= n <= 105 0 <= customers[i] <= 50 1 <= boardingCost; runningCost <= 100
Meta,530,Minimum Absolute Difference in BST,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree",Given the root of a Binary Search Tree (BST); return the minimum absolute difference between the values of any two different nodes in the tree. Example 1: Input: root = [4;2;6;1;3] Output: 1 Example 2: Input: root = [1;0;48;null;null;12;49] Output: 1 Constraints: The number of nodes in the tree is in the range [2; 104]. 0 <= Node.val <= 105 Note: This question is the same as 783: https://leetcode.com/problems/minimum-distance-between-bst-nodes/
Meta,556,Next Greater Element III,Med,"Math, Two Pointers, String",Given a positive integer n; find the smallest integer which has exactly the same digits existing in the integer n and is greater in value than n. If no such positive integer exists; return -1. Note that the returned integer should fit in 32-bit integer; if there is a valid answer but it does not fit in 32-bit integer; return -1. Example 1: Input: n = 12 Output: 21 Example 2: Input: n = 21 Output: -1 Constraints: 1 <= n <= 231 - 1
Meta,584,Find Customer Referee,Easy,Database,Table: Customer +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | referee_id | int | +-------------+---------+ In SQL; id is the primary key column for this table. Each row of this table indicates the id of a customer; their name; and the id of the customer who referred them. Find the names of the customer that are not referred by the customer with id = 2. Return the result table in any order. The result format is in the following example. Example 1: Input: Customer table: +----+------+------------+ | id | name | referee_id | +----+------+------------+ | 1 | Will | null | | 2 | Jane | null | | 3 | Alex | 2 | | 4 | Bill | null | | 5 | Zack | 1 | | 6 | Mark | 2 | +----+------+------------+ Output: +------+ | name | +------+ | Will | | Jane | | Bill | | Zack | +------+
Meta,610,Triangle Judgement,Easy,Database,Table: Triangle +-------------+------+ | Column Name | Type | +-------------+------+ | x | int | | y | int | | z | int | +-------------+------+ In SQL; (x; y; z) is the primary key column for this table. Each row of this table contains the lengths of three line segments. Report for every three line segments whether they can form a triangle. Return the result table in any order. The result format is in the following example. Example 1: Input: Triangle table: +----+----+----+ | x | y | z | +----+----+----+ | 13 | 15 | 30 | | 10 | 20 | 15 | +----+----+----+ Output: +----+----+----+----------+ | x | y | z | triangle | +----+----+----+----------+ | 13 | 15 | 30 | No | | 10 | 20 | 15 | Yes | +----+----+----+----------+
Meta,629,K Inverse Pairs Array,Hard,Dynamic Programming,For an integer array nums; an inverse pair is a pair of integers [i; j] where 0 <= i < j < nums.length and nums[i] > nums[j]. Given two integers n and k; return the number of different arrays consisting of numbers from 1 to n such that there are exactly k inverse pairs. Since the answer can be huge; return it modulo 109 + 7. Example 1: Input: n = 3; k = 0 Output: 1 Explanation: Only the array [1;2;3] which consists of numbers from 1 to 3 has exactly 0 inverse pairs. Example 2: Input: n = 3; k = 1 Output: 2 Explanation: The array [1;3;2] and [2;1;3] have exactly 1 inverse pair. Constraints: 1 <= n <= 1000 0 <= k <= 1000
Meta,632,Smallest Range Covering Elements from K Lists,Hard,"Array, Hash Table, Greedy, Sliding Window, Sorting, Heap (Priority Queue)",You have k lists of sorted integers in non-decreasing order. Find the smallest range that includes at least one number from each of the k lists. We define the range [a; b] is smaller than range [c; d] if b - a < d - c or a < c if b - a == d - c. Example 1: Input: nums = [[4;10;15;24;26];[0;9;12;20];[5;18;22;30]] Output: [20;24] Explanation: List 1: [4; 10; 15; 24;26]; 24 is in range [20;24]. List 2: [0; 9; 12; 20]; 20 is in range [20;24]. List 3: [5; 18; 22; 30]; 22 is in range [20;24]. Example 2: Input: nums = [[1;2;3];[1;2;3];[1;2;3]] Output: [1;1] Constraints: nums.length == k 1 <= k <= 3500 1 <= nums[i].length <= 50 -105 <= nums[i][j] <= 105 nums[i] is sorted in non-decreasing order.
Meta,725,Split Linked List in Parts,Med,Linked List,Given the head of a singly linked list and an integer k; split the linked list into k consecutive linked list parts. The length of each part should be as equal as possible: no two parts should have a size differing by more than one. This may lead to some parts being null. The parts should be in the order of occurrence in the input list; and parts occurring earlier should always have a size greater than or equal to parts occurring later. Return an array of the k parts. Example 1: Input: head = [1;2;3]; k = 5 Output: [[1];[2];[3];[];[]] Explanation: The first element output[0] has output[0].val = 1; output[0].next = null. The last element output[4] is null; but its string representation as a ListNode is []. Example 2: Input: head = [1;2;3;4;5;6;7;8;9;10]; k = 3 Output: [[1;2;3;4];[5;6;7];[8;9;10]] Explanation: The input has been split into consecutive parts with size difference at most 1; and earlier parts are a larger size than the later parts. Constraints: The number of nodes in the list is in the range [0; 1000]. 0 <= Node.val <= 1000 1 <= k <= 50
Meta,700,Search in a Binary Search Tree,Easy,,
Meta,703,Kth Largest Element in a Stream,Easy,,
Meta,787,Cheapest Flights Within K Stops,Med,"Array, Breadth-First Search, Matrix",On an 2 x 3 board; there are five tiles labeled from 1 to 5; and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of the board is solved if and only if the board is [[1;2;3];[4;5;0]]. Given the puzzle board board; return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved; return -1. Example 1: Input: board = [[1;2;3];[4;0;5]] Output: 1 Explanation: Swap the 0 and the 5 in one move. Example 2: Input: board = [[1;2;3];[5;4;0]] Output: -1 Explanation: No number of moves will make the board solved. Example 3: Input: board = [[4;1;2];[5;0;3]] Output: 5 Explanation: 5 is the smallest number of moves that solves the board. An example path: After move 0: [[4;1;2];[5;0;3]] After move 1: [[4;1;2];[0;5;3]] After move 2: [[0;1;2];[4;5;3]] After move 3: [[1;0;2];[4;5;3]] After move 4: [[1;2;0];[4;5;3]] After move 5: [[1;2;3];[4;5;0]] Constraints: board.length == 2 board[i].length == 3 0 <= board[i][j] <= 5 Each value board[i][j] is unique.
Meta,814,Binary Tree Pruning,Med,"Array, Prefix Sum",You are given an array nums. You can rotate it by a non-negative integer k so that the array becomes [nums[k]; nums[k + 1]; ... nums[nums.length - 1]; nums[0]; nums[1]; ...; nums[k-1]]. Afterward; any entries that are less than or equal to their index are worth one point. For example; if we have nums = [2;4;1;3;0]; and we rotate by k = 2; it becomes [1;3;0;2;4]. This is worth 3 points because 1 > 0 [no points]; 3 > 1 [no points]; 0 <= 2 [one point]; 2 <= 3 [one point]; 4 <= 4 [one point]. Return the rotation index k that corresponds to the highest score we can achieve if we rotated nums by it. If there are multiple answers; return the smallest such index k. Example 1: Input: nums = [2;3;1;4;0] Output: 3 Explanation: Scores for each k are listed below: k = 0; nums = [2;3;1;4;0]; score 2 k = 1; nums = [3;1;4;0;2]; score 3 k = 2; nums = [1;4;0;2;3]; score 3 k = 3; nums = [4;0;2;3;1]; score 4 k = 4; nums = [0;2;3;1;4]; score 3 So we should choose k = 3; which has the highest score. Example 2: Input: nums = [1;3;0;2;4] Output: 0 Explanation: nums will always have 3 points no matter how it shifts. So we will choose the smallest k; which is 0. Constraints: 1 <= nums.length <= 105 0 <= nums[i] < nums.length
Meta,622,Design Circular Queue,Med,,
Meta,489,Robot Room Cleaner,Hard,"Array, Math, Dynamic Programming, Combinatorics","Bob is standing at cell (0; 0); and he wants to reach destination: (row; column). He can only travel right and down. You are going to help Bob by providing instructions for him to reach destination. The instructions are represented as a string; where each character is either: 'H'; meaning move horizontally (go right); or 'V'; meaning move vertically (go down). Multiple instructions will lead Bob to destination. For example; if destination is (2; 3); both ""HHHVV"" and ""HVHVH"" are valid instructions. However; Bob is very picky. Bob has a lucky number k; and he wants the kth lexicographically smallest instructions that will lead him to destination. k is 1-indexed. Given an integer array destination and an integer k; return the kth lexicographically smallest instructions that will take Bob to destination. Example 1: Input: destination = [2;3]; k = 1 Output: ""HHHVV"" Explanation: All the instructions that reach (2; 3) in lexicographic order are as follows: [""HHHVV""; ""HHVHV""; ""HHVVH""; ""HVHHV""; ""HVHVH""; ""HVVHH""; ""VHHHV""; ""VHHVH""; ""VHVHH""; ""VVHHH""]. Example 2: Input: destination = [2;3]; k = 2 Output: ""HHVHV"" Example 3: Input: destination = [2;3]; k = 3 Output: ""HHVVH"" Constraints: destination.length == 2 1 <= row; column <= 15 1 <= k <= nCr(row + column; row); where nCr(a; b) denotes a choose b​​​​​."
Meta,876,Middle of the Linked List,Easy,"Array, Hash Table, Greedy, Sorting",Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize; and consists of groupSize consecutive cards. Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize; return true if she can rearrange the cards; or false otherwise. Example 1: Input: hand = [1;2;3;6;2;3;4;7;8]; groupSize = 3 Output: true Explanation: Alice's hand can be rearranged as [1;2;3];[2;3;4];[6;7;8] Example 2: Input: hand = [1;2;3;4;5]; groupSize = 4 Output: false Explanation: Alice's hand can not be rearranged into groups of 4. Constraints: 1 <= hand.length <= 104 0 <= hand[i] <= 109 1 <= groupSize <= hand.length Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/
Meta,912,Sort an Array,Med,"Array, Math, Binary Search, Prefix Sum, Randomized","You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index. You need to implement the function pickIndex(); which randomly picks an index in the range [0; w.length - 1] (inclusive) and returns it. The probability of picking an index i is w[i] / sum(w). For example; if w = [1; 3]; the probability of picking index 0 is 1 / (1 + 3) = 0.25 (i.e.; 25%); and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e.; 75%). Example 1: Input [""Solution"";""pickIndex""] [[[1]];[]] Output [null;0] Explanation Solution solution = new Solution([1]); solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w. Example 2: Input [""Solution"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex""] [[[1;3]];[];[];[];[];[]] Output [null;1;1;1;1;0] Explanation Solution solution = new Solution([1; 3]); solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4. solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4. Since this is a randomization problem; multiple answers are allowed. All of the following outputs can be considered correct: [null;1;1;1;1;0] [null;1;1;1;1;1] [null;1;1;1;0;0] [null;1;1;1;0;1] [null;1;0;1;0;0] ...... and so on. Constraints: 1 <= w.length <= 104 1 <= w[i] <= 105 pickIndex will be called at most 104 times."
Meta,509,Fibonacci Number,Easy,"Tree, Binary Search Tree, Binary Tree",
Meta,1071,Greatest Common Divisor of Strings,Easy,"Array, Bit Manipulation",You are given a binary array nums (0-indexed). We define xi as the number whose binary representation is the subarray nums[0..i] (from most-significant-bit to least-significant-bit). For example; if nums = [1;0;1]; then x0 = 1; x1 = 2; and x2 = 5. Return an array of booleans answer where answer[i] is true if xi is divisible by 5. Example 1: Input: nums = [0;1;1] Output: [true;false;false] Explanation: The input numbers in binary are 0; 01; 011; which are 0; 1; and 3 in base-10. Only the first number is divisible by 5; so answer[0] is true. Example 2: Input: nums = [1;1;1] Output: [false;false;false] Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Meta,1382,Balance a Binary Search Tree,Med,"Array, Simulation",You are given a 0-indexed 2D integer array brackets where brackets[i] = [upperi; percenti] means that the ith tax bracket has an upper bound of upperi and is taxed at a rate of percenti. The brackets are sorted by upper bound (i.e. upperi-1 < upperi for 0 < i < brackets.length). Tax is calculated as follows: The first upper0 dollars earned are taxed at a rate of percent0. The next upper1 - upper0 dollars earned are taxed at a rate of percent1. The next upper2 - upper1 dollars earned are taxed at a rate of percent2. And so on. You are given an integer income representing the amount of money you earned. Return the amount of money that you have to pay in taxes. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: brackets = [[3;50];[7;10];[12;25]]; income = 10 Output: 2.65000 Explanation: Based on your income; you have 3 dollars in the 1st tax bracket; 4 dollars in the 2nd tax bracket; and 3 dollars in the 3rd tax bracket. The tax rate for the three tax brackets is 50%; 10%; and 25%; respectively. In total; you pay $3 * 50% + $4 * 10% + $3 * 25% = $2.65 in taxes. Example 2: Input: brackets = [[1;0];[4;25];[5;50]]; income = 2 Output: 0.25000 Explanation: Based on your income; you have 1 dollar in the 1st tax bracket and 1 dollar in the 2nd tax bracket. The tax rate for the two tax brackets is 0% and 25%; respectively. In total; you pay $1 * 0% + $1 * 25% = $0.25 in taxes. Example 3: Input: brackets = [[2;50]]; income = 0 Output: 0.00000 Explanation: You have no income to tax; so you have to pay a total of $0 in taxes. Constraints: 1 <= brackets.length <= 100 1 <= upperi <= 1000 0 <= percenti <= 100 0 <= income <= 1000 upperi is sorted in ascending order. All the values of upperi are unique. The upper bound of the last tax bracket is greater than or equal to income.
Meta,1514,Path with Maximum Probability,Med,"Array, Prefix Sum",Given an array of integers nums; you start with an initial positive value startValue. In each iteration; you calculate the step by step sum of startValue plus elements in nums (from left to right). Return the minimum positive value of startValue such that the step by step sum is never less than 1. Example 1: Input: nums = [-3;2;-3;4;2] Output: 5 Explanation: If you choose startValue = 4; in the third iteration your step by step sum is less than 1. step by step sum startValue = 4 | startValue = 5 | nums (4 -3 ) = 1 | (5 -3 ) = 2 | -3 (1 +2 ) = 3 | (2 +2 ) = 4 | 2 (3 -3 ) = 0 | (4 -3 ) = 1 | -3 (0 +4 ) = 4 | (1 +4 ) = 5 | 4 (4 +2 ) = 6 | (5 +2 ) = 7 | 2 Example 2: Input: nums = [1;2] Output: 1 Explanation: Minimum start value should be positive. Example 3: Input: nums = [1;-2;-3] Output: 5 Constraints: 1 <= nums.length <= 100 -100 <= nums[i] <= 100
Meta,1428,Leftmost Column with at Least a One,Med,"Array, Depth-First Search, Breadth-First Search",Given an array of non-negative integers arr; you are initially positioned at start index of the array. When you are at index i; you can jump to i + arr[i] or i - arr[i]; check if you can reach any index with value 0. Notice that you can not jump outside of the array at any time. Example 1: Input: arr = [4;2;3;0;3;1;2]; start = 5 Output: true Explanation: All possible ways to reach at index 3 with value 0 are: index 5 -> index 4 -> index 1 -> index 3 index 5 -> index 6 -> index 4 -> index 1 -> index 3 Example 2: Input: arr = [4;2;3;0;3;1;2]; start = 0 Output: true Explanation: One possible way to reach at index 3 with value 0 is: index 0 -> index 4 -> index 1 -> index 3 Example 3: Input: arr = [3;0;2;1;2]; start = 2 Output: false Explanation: There is no way to reach at index 1 with value 0. Constraints: 1 <= arr.length <= 5 * 104 0 <= arr[i] < arr.length 0 <= start < arr.length
Meta,2303,Calculate Amount Paid in Taxes,Easy,"Hash Table, String, Rolling Hash, Counting, Hash Function",
Meta,1251,Average Selling Price,Easy,"Two Pointers, String, Dynamic Programming, Greedy, Rolling Hash, Hash Function","You are given a string text. You should split it to k substrings (subtext1; subtext2; ...; subtextk) such that: subtexti is a non-empty string. The concatenation of all the substrings is equal to text (i.e.; subtext1 + subtext2 + ... + subtextk == text). subtexti == subtextk - i + 1 for all valid values of i (i.e.; 1 <= i <= k). Return the largest possible value of k. Example 1: Input: text = ""ghiabcdefhelloadamhelloabcdefghi"" Output: 7 Explanation: We can split the string on ""(ghi)(abcdef)(hello)(adam)(hello)(abcdef)(ghi)"". Example 2: Input: text = ""merchant"" Output: 1 Explanation: We can split the string on ""(merchant)"". Example 3: Input: text = ""antaprezatepzapreanta"" Output: 11 Explanation: We can split the string on ""(a)(nt)(a)(pre)(za)(tep)(za)(pre)(a)(nt)(a)"". Constraints: 1 <= text.length <= 1000 text consists only of lowercase English characters."
Meta,1280,Students and Examinations,Easy,"Array, Sliding Window",
Meta,1378,Replace Employee ID With The Unique Identifier,Easy,"Array, Math, Simulation",There is an m x n matrix that is initialized to all 0's. There is also a 2D array indices where each indices[i] = [ri; ci] represents a 0-indexed location to perform some increment operations on the matrix. For each location indices[i]; do both of the following: Increment all the cells on row ri. Increment all the cells on column ci. Given m; n; and indices; return the number of odd-valued cells in the matrix after applying the increment to all locations in indices. Example 1: Input: m = 2; n = 3; indices = [[0;1];[1;1]] Output: 6 Explanation: Initial matrix = [[0;0;0];[0;0;0]]. After applying first increment it becomes [[1;2;1];[0;1;0]]. The final matrix is [[1;3;1];[1;3;1]]; which contains 6 odd numbers. Example 2: Input: m = 2; n = 2; indices = [[1;1];[0;0]] Output: 0 Explanation: Final matrix = [[2;2];[2;2]]. There are no odd numbers in the final matrix. Constraints: 1 <= m; n <= 50 1 <= indices.length <= 100 0 <= ri < m 0 <= ci < n Follow up: Could you solve this in O(n + m + indices.length) time with only O(n + m) extra space?
Meta,1438,Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit,Med,Database,
Meta,1493,Longest Subarray of 1's After Deleting One Element,Med,"Tree, Depth-First Search, Breadth-First Search, Graph",Given an undirected tree consisting of n vertices numbered from 1 to n. A frog starts jumping from vertex 1. In one second; the frog jumps from its current vertex to another unvisited vertex if they are directly connected. The frog can not jump back to a visited vertex. In case the frog can jump to several vertices; it jumps randomly to one of them with the same probability. Otherwise; when the frog can not jump to any unvisited vertex; it jumps forever on the same vertex. The edges of the undirected tree are given in the array edges; where edges[i] = [ai; bi] means that exists an edge connecting the vertices ai and bi. Return the probability that after t seconds the frog is on the vertex target. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: n = 7; edges = [[1;2];[1;3];[1;7];[2;4];[2;6];[3;5]]; t = 2; target = 4 Output: 0.16666666666666666 Explanation: The figure above shows the given graph. The frog starts at vertex 1; jumping with 1/3 probability to the vertex 2 after second 1 and then jumping with 1/2 probability to vertex 4 after second 2. Thus the probability for the frog is on the vertex 4 after 2 seconds is 1/3 * 1/2 = 1/6 = 0.16666666666666666. Example 2: Input: n = 7; edges = [[1;2];[1;3];[1;7];[2;4];[2;6];[3;5]]; t = 1; target = 7 Output: 0.3333333333333333 Explanation: The figure above shows the given graph. The frog starts at vertex 1; jumping with 1/3 = 0.3333333333333333 probability to the vertex 7 after second 1. Constraints: 1 <= n <= 100 edges.length == n - 1 edges[i].length == 2 1 <= ai; bi <= n 1 <= t <= 50 1 <= target <= n
Meta,1512,Number of Good Pairs,Easy,"Hash Table, String, Design","An underground railway system is keeping track of customer travel times between different stations. They are using this data to calculate the average time it takes to travel from one station to another. Implement the UndergroundSystem class: void checkIn(int id; string stationName; int t) A customer with a card ID equal to id; checks in at the station stationName at time t. A customer can only be checked into one place at a time. void checkOut(int id; string stationName; int t) A customer with a card ID equal to id; checks out from the station stationName at time t. double getAverageTime(string startStation; string endStation) Returns the average time it takes to travel from startStation to endStation. The average time is computed from all the previous traveling times from startStation to endStation that happened directly; meaning a check in at startStation followed by a check out from endStation. The time it takes to travel from startStation to endStation may be different from the time it takes to travel from endStation to startStation. There will be at least one customer that has traveled from startStation to endStation before getAverageTime is called. You may assume all calls to the checkIn and checkOut methods are consistent. If a customer checks in at time t1 then checks out at time t2; then t1 < t2. All events happen in chronological order. Example 1: Input [""UndergroundSystem"";""checkIn"";""checkIn"";""checkIn"";""checkOut"";""checkOut"";""checkOut"";""getAverageTime"";""getAverageTime"";""checkIn"";""getAverageTime"";""checkOut"";""getAverageTime""] [[];[45;""Leyton"";3];[32;""Paradise"";8];[27;""Leyton"";10];[45;""Waterloo"";15];[27;""Waterloo"";20];[32;""Cambridge"";22];[""Paradise"";""Cambridge""];[""Leyton"";""Waterloo""];[10;""Leyton"";24];[""Leyton"";""Waterloo""];[10;""Waterloo"";38];[""Leyton"";""Waterloo""]] Output [null;null;null;null;null;null;null;14.00000;11.00000;null;11.00000;null;12.00000] Explanation UndergroundSystem undergroundSystem = new UndergroundSystem(); undergroundSystem.checkIn(45; ""Leyton""; 3); undergroundSystem.checkIn(32; ""Paradise""; 8); undergroundSystem.checkIn(27; ""Leyton""; 10); undergroundSystem.checkOut(45; ""Waterloo""; 15); // Customer 45 ""Leyton"" -> ""Waterloo"" in 15-3 = 12 undergroundSystem.checkOut(27; ""Waterloo""; 20); // Customer 27 ""Leyton"" -> ""Waterloo"" in 20-10 = 10 undergroundSystem.checkOut(32; ""Cambridge""; 22); // Customer 32 ""Paradise"" -> ""Cambridge"" in 22-8 = 14 undergroundSystem.getAverageTime(""Paradise""; ""Cambridge""); // return 14.00000. One trip ""Paradise"" -> ""Cambridge""; (14) / 1 = 14 undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 11.00000. Two trips ""Leyton"" -> ""Waterloo""; (10 + 12) / 2 = 11 undergroundSystem.checkIn(10; ""Leyton""; 24); undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 11.00000 undergroundSystem.checkOut(10; ""Waterloo""; 38); // Customer 10 ""Leyton"" -> ""Waterloo"" in 38-24 = 14 undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 12.00000. Three trips ""Leyton"" -> ""Waterloo""; (10 + 12 + 14) / 3 = 12 Example 2: Input [""UndergroundSystem"";""checkIn"";""checkOut"";""getAverageTime"";""checkIn"";""checkOut"";""getAverageTime"";""checkIn"";""checkOut"";""getAverageTime""] [[];[10;""Leyton"";3];[10;""Paradise"";8];[""Leyton"";""Paradise""];[5;""Leyton"";10];[5;""Paradise"";16];[""Leyton"";""Paradise""];[2;""Leyton"";21];[2;""Paradise"";30];[""Leyton"";""Paradise""]] Output [null;null;null;5.00000;null;null;5.50000;null;null;6.66667] Explanation UndergroundSystem undergroundSystem = new UndergroundSystem(); undergroundSystem.checkIn(10; ""Leyton""; 3); undergroundSystem.checkOut(10; ""Paradise""; 8); // Customer 10 ""Leyton"" -> ""Paradise"" in 8-3 = 5 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 5.00000; (5) / 1 = 5 undergroundSystem.checkIn(5; ""Leyton""; 10); undergroundSystem.checkOut(5; ""Paradise""; 16); // Customer 5 ""Leyton"" -> ""Paradise"" in 16-10 = 6 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 5.50000; (5 + 6) / 2 = 5.5 undergroundSystem.checkIn(2; ""Leyton""; 21); undergroundSystem.checkOut(2; ""Paradise""; 30); // Customer 2 ""Leyton"" -> ""Paradise"" in 30-21 = 9 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 6.66667; (5 + 6 + 9) / 3 = 6.66667 Constraints: 1 <= id; t <= 106 1 <= stationName.length; startStation.length; endStation.length <= 10 All strings consist of uppercase and lowercase English letters and digits. There will be at most 2 * 104 calls in total to checkIn; checkOut; and getAverageTime. Answers within 10-5 of the actual value will be accepted."
Meta,1545,Find Kth Bit in Nth Binary String,Med,"Array, Dynamic Programming","Given an array of integers cost and an integer target; return the maximum integer you can paint under the following rules: The cost of painting a digit (i + 1) is given by cost[i] (0-indexed). The total cost used must be equal to target. The integer does not have 0 digits. Since the answer may be very large; return it as a string. If there is no way to paint any integer given the condition; return ""0"". Example 1: Input: cost = [4;3;2;5;6;7;2;5;5]; target = 9 Output: ""7772"" Explanation: The cost to paint the digit '7' is 2; and the digit '2' is 3. Then cost(""7772"") = 2*3+ 3*1 = 9. You could also paint ""977""; but ""7772"" is the largest number. Digit cost 1 -> 4 2 -> 3 3 -> 2 4 -> 5 5 -> 6 6 -> 7 7 -> 2 8 -> 5 9 -> 5 Example 2: Input: cost = [7;6;5;5;5;6;8;7;8]; target = 12 Output: ""85"" Explanation: The cost to paint the digit '8' is 7; and the digit '5' is 5. Then cost(""85"") = 7 + 5 = 12. Example 3: Input: cost = [2;4;6;2;4;6;4;4;4]; target = 5 Output: ""0"" Explanation: It is impossible to paint any integer with total cost equal to target. Constraints: cost.length == 9 1 <= cost[i]; target <= 5000"
Meta,1574,Shortest Subarray to be Removed to Make Array Sorted,Med,"Array, Sorting, Heap (Priority Queue)",Given the array of integers nums; you will choose two different indices i and j of that array. Return the maximum value of (nums[i]-1)*(nums[j]-1). Example 1: Input: nums = [3;4;5;2] Output: 12 Explanation: If you choose the indices i=1 and j=2 (indexed from 0); you will get the maximum value; that is; (nums[1]-1)*(nums[2]-1) = (4-1)*(5-1) = 3*4 = 12. Example 2: Input: nums = [1;5;4;5] Output: 16 Explanation: Choosing the indices i=1 and j=3 (indexed from 0); you will get the maximum value of (5-1)*(5-1) = 16. Example 3: Input: nums = [3;7] Output: 12 Constraints: 2 <= nums.length <= 500 1 <= nums[i] <= 10^3
Meta,1579,Remove Max Number of Edges to Keep Graph Fully Traversable,Hard,Database,
Meta,1593,Split a String Into the Max Number of Unique Substrings,Med,,
Meta,1639,Number of Ways to Form a Target String Given a Dictionary,Hard,Database,
Meta,1671,Minimum Number of Removals to Make Mountain Array,Hard,Database,
Meta,1667,Fix Names in a Table,Easy,"String, Recursion, Simulation","Given two positive integers n and k; the binary string Sn is formed as follows: S1 = ""0"" Si = Si - 1 + ""1"" + reverse(invert(Si - 1)) for i > 1 Where + denotes the concatenation operation; reverse(x) returns the reversed string x; and invert(x) inverts all the bits in x (0 changes to 1 and 1 changes to 0). For example; the first four strings in the above sequence are: S1 = ""0"" S2 = ""011"" S3 = ""0111001"" S4 = ""011100110110001"" Return the kth bit in Sn. It is guaranteed that k is valid for the given n. Example 1: Input: n = 3; k = 1 Output: ""0"" Explanation: S3 is ""0111001"". The 1st bit is ""0"". Example 2: Input: n = 4; k = 11 Output: ""1"" Explanation: S4 is ""011100110110001"". The 11th bit is ""1"". Constraints: 1 <= n <= 20 1 <= k <= 2n - 1"
Meta,1845,Seat Reservation Manager,Med,"Array, Greedy, Sorting, Matrix",You are given a binary matrix matrix of size m x n; and you are allowed to rearrange the columns of the matrix in any order. Return the area of the largest submatrix within matrix where every element of the submatrix is 1 after reordering the columns optimally. Example 1: Input: matrix = [[0;0;1];[1;1;1];[1;0;1]] Output: 4 Explanation: You can rearrange the columns as shown above. The largest submatrix of 1s; in bold; has an area of 4. Example 2: Input: matrix = [[1;0;1;0;1]] Output: 3 Explanation: You can rearrange the columns as shown above. The largest submatrix of 1s; in bold; has an area of 3. Example 3: Input: matrix = [[1;1;0];[1;0;1]] Output: 2 Explanation: Notice that you must rearrange entire columns; and there is no way to make a submatrix of 1s larger than an area of 2. Constraints: m == matrix.length n == matrix[i].length 1 <= m * n <= 105 matrix[i][j] is either 0 or 1.
Meta,1891,Cutting Ribbons,Med,"Array, Two Pointers, Binary Search, Graph, Sorting",You are given an undirected graph defined by an integer n; the number of nodes; and a 2D integer array edges; the edges in the graph; where edges[i] = [ui; vi] indicates that there is an undirected edge between ui and vi. You are also given an integer array queries. Let incident(a; b) be defined as the number of edges that are connected to either node a or b. The answer to the jth query is the number of pairs of nodes (a; b) that satisfy both of the following conditions: a < b incident(a; b) > queries[j] Return an array answers such that answers.length == queries.length and answers[j] is the answer of the jth query. Note that there can be multiple edges between the same two nodes. Example 1: Input: n = 4; edges = [[1;2];[2;4];[1;3];[2;3];[2;1]]; queries = [2;3] Output: [6;5] Explanation: The calculations for incident(a; b) are shown in the table above. The answers for each of the queries are as follows: - answers[0] = 6. All the pairs have an incident(a; b) value greater than 2. - answers[1] = 5. All the pairs except (3; 4) have an incident(a; b) value greater than 3. Example 2: Input: n = 5; edges = [[1;5];[1;5];[3;4];[2;5];[1;3];[5;1];[2;3];[2;5]]; queries = [1;2;3;4;5] Output: [10;10;9;8;6] Constraints: 2 <= n <= 2 * 104 1 <= edges.length <= 105 1 <= ui; vi <= n ui != vi 1 <= queries.length <= 20 0 <= queries[j] < edges.length
Meta,2022,Convert 1D Array Into 2D Array,Easy,"Array, Dynamic Programming",The alternating sum of a 0-indexed array is defined as the sum of the elements at even indices minus the sum of the elements at odd indices. For example; the alternating sum of [4;2;5;3] is (4 + 5) - (2 + 3) = 4. Given an array nums; return the maximum alternating sum of any subsequence of nums (after reindexing the elements of the subsequence). A subsequence of an array is a new array generated from the original array by deleting some elements (possibly none) without changing the remaining elements' relative order. For example; [2;7;4] is a subsequence of [4;2;3;7;2;1;4] (the underlined elements); while [2;4;2] is not. Example 1: Input: nums = [4;2;5;3] Output: 7 Explanation: It is optimal to choose the subsequence [4;2;5] with alternating sum (4 + 5) - 2 = 7. Example 2: Input: nums = [5;6;7;8] Output: 8 Explanation: It is optimal to choose the subsequence [8] with alternating sum 8. Example 3: Input: nums = [6;2;1;2;4;5] Output: 10 Explanation: It is optimal to choose the subsequence [6;1;5] with alternating sum (6 + 5) - 1 = 10. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105
Meta,2034,Stock Price Fluctuation,Med,"Array, Hash Table",The minimum absolute difference of an array a is defined as the minimum value of |a[i] - a[j]|; where 0 <= i < j < a.length and a[i] != a[j]. If all elements of a are the same; the minimum absolute difference is -1. For example; the minimum absolute difference of the array [5;2;3;7;2] is |2 - 3| = 1. Note that it is not 0 because a[i] and a[j] must be different. You are given an integer array nums and the array queries where queries[i] = [li; ri]. For each query i; compute the minimum absolute difference of the subarray nums[li...ri] containing the elements of nums between the 0-based indices li and ri (inclusive). Return an array ans where ans[i] is the answer to the ith query. A subarray is a contiguous sequence of elements in an array. The value of |x| is defined as: x if x >= 0. -x if x < 0. Example 1: Input: nums = [1;3;4;8]; queries = [[0;1];[1;2];[2;3];[0;3]] Output: [2;1;4;1] Explanation: The queries are processed as follows: - queries[0] = [0;1]: The subarray is [1;3] and the minimum absolute difference is |1-3| = 2. - queries[1] = [1;2]: The subarray is [3;4] and the minimum absolute difference is |3-4| = 1. - queries[2] = [2;3]: The subarray is [4;8] and the minimum absolute difference is |4-8| = 4. - queries[3] = [0;3]: The subarray is [1;3;4;8] and the minimum absolute difference is |3-4| = 1. Example 2: Input: nums = [4;5;2;2;7;10]; queries = [[2;3];[0;2];[0;5];[3;5]] Output: [-1;1;1;3] Explanation: The queries are processed as follows: - queries[0] = [2;3]: The subarray is [2;2] and the minimum absolute difference is -1 because all the elements are the same. - queries[1] = [0;2]: The subarray is [4;5;2] and the minimum absolute difference is |4-5| = 1. - queries[2] = [0;5]: The subarray is [4;5;2;2;7;10] and the minimum absolute difference is |4-5| = 1. - queries[3] = [3;5]: The subarray is [2;7;10] and the minimum absolute difference is |7-10| = 3. Constraints: 2 <= nums.length <= 105 1 <= nums[i] <= 100 1 <= queries.length <= 2 * 104 0 <= li < ri < nums.length
Meta,2035,Partition Array Into Two Arrays to Minimize Sum Difference,Hard,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given two m x n binary matrices grid1 and grid2 containing only 0's (representing water) and 1's (representing land). An island is a group of 1's connected 4-directionally (horizontal or vertical). Any cells outside of the grid are considered water cells. An island in grid2 is considered a sub-island if there is an island in grid1 that contains all the cells that make up this island in grid2. Return the number of islands in grid2 that are considered sub-islands. Example 1: Input: grid1 = [[1;1;1;0;0];[0;1;1;1;1];[0;0;0;0;0];[1;0;0;0;0];[1;1;0;1;1]]; grid2 = [[1;1;1;0;0];[0;0;1;1;1];[0;1;0;0;0];[1;0;1;1;0];[0;1;0;1;0]] Output: 3 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are three sub-islands. Example 2: Input: grid1 = [[1;0;1;0;1];[1;1;1;1;1];[0;0;0;0;0];[1;1;1;1;1];[1;0;1;0;1]]; grid2 = [[0;0;0;0;0];[1;1;1;1;1];[0;1;0;1;0];[0;1;0;1;0];[1;0;0;0;1]] Output: 2 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are two sub-islands. Constraints: m == grid1.length == grid2.length n == grid1[i].length == grid2[i].length 1 <= m; n <= 500 grid1[i][j] and grid2[i][j] are either 0 or 1.
Meta,2419,Longest Subarray With Maximum Bitwise AND,Med,"Array, Stack, Union Find, Monotonic Stack",You are given an integer array nums and an integer threshold. Find any subarray of nums of length k such that every element in the subarray is greater than threshold / k. Return the size of any such subarray. If there is no such subarray; return -1. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;3;4;3;1]; threshold = 6 Output: 3 Explanation: The subarray [3;4;3] has a size of 3; and every element is greater than 6 / 3 = 2. Note that this is the only valid subarray. Example 2: Input: nums = [6;5;6;5;8]; threshold = 7 Output: 1 Explanation: The subarray [8] has a size of 1; and 8 > 7 / 1 = 7. So 1 is returned. Note that the subarray [6;5] has a size of 2; and every element is greater than 7 / 2 = 3.5. Similarly; the subarrays [6;5;6]; [6;5;6;5]; [6;5;6;5;8] also satisfy the given conditions. Therefore; 2; 3; 4; or 5 may also be returned. Constraints: 1 <= nums.length <= 105 1 <= nums[i]; threshold <= 109
Meta,2427,Number of Common Factors,Easy,"Hash Table, String, Bit Manipulation, Counting","Given a string s consisting of lowercase English letters; return the first letter to appear twice. Note: A letter a appears twice before another letter b if the second occurrence of a is before the second occurrence of b. s will contain at least one letter that appears twice. Example 1: Input: s = ""abccbaacz"" Output: ""c"" Explanation: The letter 'a' appears on the indexes 0; 5 and 6. The letter 'b' appears on the indexes 1 and 4. The letter 'c' appears on the indexes 2; 3 and 7. The letter 'z' appears on the index 8. The letter 'c' is the first letter to appear twice; because out of all the letters the index of its second occurrence is the smallest. Example 2: Input: s = ""abcdd"" Output: ""d"" Explanation: The only letter that appears twice is 'd' so we return 'd'. Constraints: 2 <= s.length <= 100 s consists of lowercase English letters. s has at least one repeated letter."
Meta,2501,Longest Square Streak in an Array,Med,Database,
Meta,2707,Extra Characters in a String,Med,"Array, Hash Table, Two Pointers",You are given two 2D integer arrays nums1 and nums2. nums1[i] = [idi; vali] indicate that the number with the id idi has a value equal to vali. nums2[i] = [idi; vali] indicate that the number with the id idi has a value equal to vali. Each array contains unique ids and is sorted in ascending order by id. Merge the two arrays into one array that is sorted in ascending order by id; respecting the following conditions: Only ids that appear in at least one of the two arrays should be included in the resulting array. Each id should be included only once and its value should be the sum of the values of this id in the two arrays. If the id does not exist in one of the two arrays then its value in that array is considered to be 0. Return the resulting array. The returned array must be sorted in ascending order by id. Example 1: Input: nums1 = [[1;2];[2;3];[4;5]]; nums2 = [[1;4];[3;2];[4;1]] Output: [[1;6];[2;3];[3;2];[4;6]] Explanation: The resulting array contains the following: - id = 1; the value of this id is 2 + 4 = 6. - id = 2; the value of this id is 3. - id = 3; the value of this id is 2. - id = 4; the value of this id is 5 + 1 = 6. Example 2: Input: nums1 = [[2;4];[3;6];[5;5]]; nums2 = [[1;3];[4;3]] Output: [[1;3];[2;4];[3;6];[4;3];[5;5]] Explanation: There are no common ids; so we just include each id with its value in the resulting list. Constraints: 1 <= nums1.length; nums2.length <= 200 nums1[i].length == nums2[j].length == 2 1 <= idi; vali <= 1000 Both arrays contain unique ids. Both arrays are in strictly ascending order by id.
Meta,2723,Add Two Promises,Easy,String,"You are given a binary string s consisting only of zeroes and ones. A substring of s is considered balanced if all zeroes are before ones and the number of zeroes is equal to the number of ones inside the substring. Notice that the empty substring is considered a balanced substring. Return the length of the longest balanced substring of s. A substring is a contiguous sequence of characters within a string. Example 1: Input: s = ""01000111"" Output: 6 Explanation: The longest balanced substring is ""000111""; which has length 6. Example 2: Input: s = ""00111"" Output: 4 Explanation: The longest balanced substring is ""0011""; which has length 4. Example 3: Input: s = ""111"" Output: 0 Explanation: There is no balanced substring except the empty substring; so the answer is 0. Constraints: 1 <= s.length <= 50 '0' <= s[i] <= '1'"
Meta,2807,Insert Greatest Common Divisors in Linked List,Med,,"Given an array of asynchronous functions functions; return a new promise promise. Each function in the array accepts no arguments and returns a promise. All the promises should be executed in parallel. promise resolves: When all the promises returned from functions were resolved successfully in parallel. The resolved value of promise should be an array of all the resolved values of promises in the same order as they were in the functions. The promise should resolve when all the asynchronous functions in the array have completed execution in parallel. promise rejects: When any of the promises returned from functions were rejected. promise should also reject with the reason of the first rejection. Please solve it without using the built-in Promise.all function. Example 1: Input: functions = [ () => new Promise(resolve => setTimeout(() => resolve(5); 200)) ] Output: {""t"": 200; ""resolved"": [5]} Explanation: promiseAll(functions).then(console.log); // [5] The single function was resolved at 200ms with a value of 5. Example 2: Input: functions = [ () => new Promise(resolve => setTimeout(() => resolve(1); 200)); () => new Promise((resolve; reject) => setTimeout(() => reject(""Error""); 100)) ] Output: {""t"": 100; ""rejected"": ""Error""} Explanation: Since one of the promises rejected; the returned promise also rejected with the same error at the same time. Example 3: Input: functions = [ () => new Promise(resolve => setTimeout(() => resolve(4); 50)); () => new Promise(resolve => setTimeout(() => resolve(10); 150)); () => new Promise(resolve => setTimeout(() => resolve(16); 100)) ] Output: {""t"": 150; ""resolved"": [4; 10; 16]} Explanation: All the promises resolved with a value. The returned promise resolved when the last promise resolved. Constraints: functions is an array of functions that returns promises 1 <= functions.length <= 10"
Meta,2877,Create a DataFrame from List,Easy,"String, Greedy, Enumeration","Given three strings a; b; and c; your task is to find a string that has the minimum length and contains all three strings as substrings. If there are multiple such strings; return the lexicographically smallest one. Return a string denoting the answer to the problem. Notes A string a is lexicographically smaller than a string b (of the same length) if in the first position where a and b differ; string a has a letter that appears earlier in the alphabet than the corresponding letter in b. A substring is a contiguous sequence of characters within a string. Example 1: Input: a = ""abc""; b = ""bca""; c = ""aaa"" Output: ""aaabca"" Explanation: We show that ""aaabca"" contains all the given strings: a = ans[2...4]; b = ans[3..5]; c = ans[0..2]. It can be shown that the length of the resulting string would be at least 6 and ""aaabca"" is the lexicographically smallest one. Example 2: Input: a = ""ab""; b = ""ba""; c = ""aba"" Output: ""aba"" Explanation: We show that the string ""aba"" contains all the given strings: a = ans[0..1]; b = ans[1..2]; c = ans[0..2]. Since the length of c is 3; the length of the resulting string would be at least 3. It can be shown that ""aba"" is the lexicographically smallest one. Constraints: 1 <= a.length; b.length; c.length <= 100 a; b; c consist only of lowercase English letters."
Google,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Google,2995,Viewers Turned Streamers,Hard,"Union Find, Interactive, Counting",
Google,1526,Minimum Number of Increments on Subarrays to Form a Target Array,Hard,"Hash Table, String","HTML entity parser is the parser that takes HTML code as input and replace all the entities of the special characters by the characters itself. The special characters and their entities for HTML are: Quotation Mark: the entity is "" and symbol character is "". Single Quote Mark: the entity is ' and symbol character is '. Ampersand: the entity is & and symbol character is &. Greater Than Sign: the entity is > and symbol character is >. Less Than Sign: the entity is < and symbol character is <. Slash: the entity is ⁄ and symbol character is /. Given the input text string to the HTML parser; you have to implement the entity parser. Return the text after replacing the entities by the special characters. Example 1: Input: text = ""& is an HTML entity but &ambassador; is not."" Output: ""& is an HTML entity but &ambassador; is not."" Explanation: The parser will replace the & entity by & Example 2: Input: text = ""and I quote: ""..."""" Output: ""and I quote: \""...\"""" Constraints: 1 <= text.length <= 105 The string may contain any possible characters out of all the 256 ASCII characters."
Google,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Google,2667,Create Hello World Function,Easy,"Array, Hash Table, Math, Stack, Sliding Window",
Google,1768,Merge Strings Alternately,Easy,"Array, Math, Stack, Tree, Design, Binary Tree",
Google,1757,Recyclable and Low Fat Products,Easy,"Array, Dynamic Programming, Breadth-First Search",A certain bug's home is on the x-axis at position x. Help them get there from position 0. The bug jumps according to the following rules: It can jump exactly a positions forward (to the right). It can jump exactly b positions backward (to the left). It cannot jump backward twice in a row. It cannot jump to any forbidden positions. The bug may jump forward beyond its home; but it cannot jump to positions numbered with negative integers. Given an array of integers forbidden; where forbidden[i] means that the bug cannot jump to the position forbidden[i]; and integers a; b; and x; return the minimum number of jumps needed for the bug to reach its home. If there is no possible sequence of jumps that lands the bug on position x; return -1. Example 1: Input: forbidden = [14;4;18;1;15]; a = 3; b = 15; x = 9 Output: 3 Explanation: 3 jumps forward (0 -> 3 -> 6 -> 9) will get the bug home. Example 2: Input: forbidden = [8;3;16;6;12;20]; a = 15; b = 13; x = 11 Output: -1 Example 3: Input: forbidden = [1;6;2;14;5;17;4]; a = 16; b = 9; x = 7 Output: 2 Explanation: One jump forward (0 -> 16) then one jump backward (16 -> 7) will get the bug home. Constraints: 1 <= forbidden.length <= 1000 1 <= a; b; forbidden[i] <= 2000 0 <= x <= 2000 All the elements in forbidden are distinct. Position x is not forbidden.
Google,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Google,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Google,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Google,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Google,13,Roman to Integer,Easy,"Hash Table, Math, String","Roman numerals are represented by seven different symbols: I; V; X; L; C; D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example; 2 is written as II in Roman numeral; just two ones added together. 12 is written as XII; which is simply X + II. The number 27 is written as XXVII; which is XX + V + II. Roman numerals are usually written largest to smallest from left to right. However; the numeral for four is not IIII. Instead; the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine; which is written as IX. There are six instances where subtraction is used: I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral; convert it to an integer. Example 1: Input: s = ""III"" Output: 3 Explanation: III = 3. Example 2: Input: s = ""LVIII"" Output: 58 Explanation: L = 50; V= 5; III = 3. Example 3: Input: s = ""MCMXCIV"" Output: 1994 Explanation: M = 1000; CM = 900; XC = 90 and IV = 4. Constraints: 1 <= s.length <= 15 s contains only the characters ('I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M'). It is guaranteed that s is a valid roman numeral in the range [1; 3999]."
Google,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Google,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Google,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Google,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
Google,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Google,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Google,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Google,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Google,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Google,2235,Add Two Integers,Easy,String,"You are given a string title consisting of one or more words separated by a single space; where each word consists of English letters. Capitalize the string by changing the capitalization of each word such that: If the length of the word is 1 or 2 letters; change all letters to lowercase. Otherwise; change the first letter to uppercase and the remaining letters to lowercase. Return the capitalized title. Example 1: Input: title = ""capiTalIze tHe titLe"" Output: ""Capitalize The Title"" Explanation: Since all the words have a length of at least 3; the first letter of each word is uppercase; and the remaining letters are lowercase. Example 2: Input: title = ""First leTTeR of EACH Word"" Output: ""First Letter of Each Word"" Explanation: The word ""of"" has length 2; so it is all lowercase. The remaining words have a length of at least 3; so the first letter of each remaining word is uppercase; and the remaining letters are lowercase. Example 3: Input: title = ""i lOve leetcode"" Output: ""i Love Leetcode"" Explanation: The word ""i"" has length 1; so it is lowercase. The remaining words have a length of at least 3; so the first letter of each remaining word is uppercase; and the remaining letters are lowercase. Constraints: 1 <= title.length <= 100 title consists of words separated by a single space without any leading or trailing spaces. Each word consists of uppercase and lowercase English letters and is non-empty."
Google,3355,Zero Array Transformation I,Med,"Array, Prefix Sum",You are given a binary array possible of length n. Alice and Bob are playing a game that consists of n levels. Some of the levels in the game are impossible to clear while others can always be cleared. In particular; if possible[i] == 0; then the ith level is impossible to clear for both the players. A player gains 1 point on clearing a level and loses 1 point if the player fails to clear it. At the start of the game; Alice will play some levels in the given order starting from the 0th level; after which Bob will play for the rest of the levels. Alice wants to know the minimum number of levels she should play to gain more points than Bob; if both players play optimally to maximize their points. Return the minimum number of levels Alice should play to gain more points. If this is not possible; return -1. Note that each player must play at least 1 level. Example 1: Input: possible = [1;0;1;0] Output: 1 Explanation: Let's look at all the levels that Alice can play up to: If Alice plays only level 0 and Bob plays the rest of the levels; Alice has 1 point; while Bob has -1 + 1 - 1 = -1 point. If Alice plays till level 1 and Bob plays the rest of the levels; Alice has 1 - 1 = 0 points; while Bob has 1 - 1 = 0 points. If Alice plays till level 2 and Bob plays the rest of the levels; Alice has 1 - 1 + 1 = 1 point; while Bob has -1 point. Alice must play a minimum of 1 level to gain more points. Example 2: Input: possible = [1;1;1;1;1] Output: 3 Explanation: Let's look at all the levels that Alice can play up to: If Alice plays only level 0 and Bob plays the rest of the levels; Alice has 1 point; while Bob has 4 points. If Alice plays till level 1 and Bob plays the rest of the levels; Alice has 2 points; while Bob has 3 points. If Alice plays till level 2 and Bob plays the rest of the levels; Alice has 3 points; while Bob has 2 points. If Alice plays till level 3 and Bob plays the rest of the levels; Alice has 4 points; while Bob has 1 point. Alice must play a minimum of 3 levels to gain more points. Example 3: Input: possible = [0;0] Output: -1 Explanation: The only possible way is for both players to play 1 level each. Alice plays level 0 and loses 1 point. Bob plays level 1 and loses 1 point. As both players have equal points; Alice can't gain more points than Bob. Constraints: 2 <= n == possible.length <= 105 possible[i] is either 0 or 1.
Google,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Google,128,Longest Consecutive Sequence,Med,"Array, Hash Table, Union Find",Given an unsorted array of integers nums; return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time. Example 1: Input: nums = [100;4;200;1;3;2] Output: 4 Explanation: The longest consecutive elements sequence is [1; 2; 3; 4]. Therefore its length is 4. Example 2: Input: nums = [0;3;7;2;5;8;4;6;0;1] Output: 9 Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109
Google,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Google,2663,Lexicographically Smallest Beautiful String,Hard,"Math, Greedy",You are given an integer money denoting the amount of money (in dollars) that you have and another integer children denoting the number of children that you must distribute the money to. You have to distribute the money according to the following rules: All money must be distributed. Everyone must receive at least 1 dollar. Nobody receives 4 dollars. Return the maximum number of children who may receive exactly 8 dollars if you distribute the money according to the aforementioned rules. If there is no way to distribute the money; return -1. Example 1: Input: money = 20; children = 3 Output: 1 Explanation: The maximum number of children with 8 dollars will be 1. One of the ways to distribute the money is: - 8 dollars to the first child. - 9 dollars to the second child. - 3 dollars to the third child. It can be proven that no distribution exists such that number of children getting 8 dollars is greater than 1. Example 2: Input: money = 16; children = 2 Output: 2 Explanation: Each child can be given 8 dollars. Constraints: 1 <= money <= 200 2 <= children <= 30
Google,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Google,359,Logger Rate Limiter,Easy,"Hash Table, Design, Data Stream",
Google,179,Largest Number,Med,"Array, String, Greedy, Sorting","Given a list of non-negative integers nums; arrange them such that they form the largest number and return it. Since the result may be very large; so you need to return a string instead of an integer. Example 1: Input: nums = [10;2] Output: ""210"" Example 2: Input: nums = [3;30;34;5;9] Output: ""9534330"" Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 109"
Google,7,Reverse Integer,Med,Math,Given a signed 32-bit integer x; return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231; 231 - 1]; then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: Input: x = 123 Output: 321 Example 2: Input: x = -123 Output: -321 Example 3: Input: x = 120 Output: 21 Constraints: -231 <= x <= 231 - 1
Google,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Google,28,Find the Index of the First Occurrence in a String,Easy,"Two Pointers, String, String Matching","Given two strings needle and haystack; return the index of the first occurrence of needle in haystack; or -1 if needle is not part of haystack. Example 1: Input: haystack = ""sadbutsad""; needle = ""sad"" Output: 0 Explanation: ""sad"" occurs at index 0 and 6. The first occurrence is at index 0; so we return 0. Example 2: Input: haystack = ""leetcode""; needle = ""leeto"" Output: -1 Explanation: ""leeto"" did not occur in ""leetcode""; so we return -1. Constraints: 1 <= haystack.length; needle.length <= 104 haystack and needle consist of only lowercase English characters."
Google,939,Minimum Area Rectangle,Med,"String, Dynamic Programming, Prefix Sum","You are given a string s of length n where s[i] is either: 'D' means decreasing; or 'I' means increasing. A permutation perm of n + 1 integers of all the integers in the range [0; n] is called a valid permutation if for all valid i: If s[i] == 'D'; then perm[i] > perm[i + 1]; and If s[i] == 'I'; then perm[i] < perm[i + 1]. Return the number of valid permutations perm. Since the answer may be large; return it modulo 109 + 7. Example 1: Input: s = ""DID"" Output: 5 Explanation: The 5 valid permutations of (0; 1; 2; 3) are: (1; 0; 3; 2) (2; 0; 3; 1) (2; 1; 3; 0) (3; 0; 2; 1) (3; 1; 2; 0) Example 2: Input: s = ""D"" Output: 1 Constraints: n == s.length 1 <= n <= 200 s[i] is either 'I' or 'D'."
Google,27,Remove Element,Easy,"Array, Two Pointers",Given an integer array nums and an integer val; remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val. Consider the number of elements in nums which are not equal to val be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the elements which are not equal to val. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int val = ...; // Value to remove int[] expectedNums = [...]; // The expected answer with correct length. // It is sorted with no values equaling val. int k = removeElement(nums; val); // Calls your implementation assert k == expectedNums.length; sort(nums; 0; k); // Sort the first k elements of nums for (int i = 0; i < actualLength; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [3;2;2;3]; val = 3 Output: 2; nums = [2;2;_;_] Explanation: Your function should return k = 2; with the first two elements of nums being 2. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;1;2;2;3;0;4;2]; val = 2 Output: 5; nums = [0;1;4;0;3;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums containing 0; 0; 1; 3; and 4. Note that the five elements can be returned in any order. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 0 <= nums.length <= 100 0 <= nums[i] <= 50 0 <= val <= 100
Google,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Google,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
Google,3318,Find X-Sum of All K-Long Subarrays I,Easy,"Array, Dynamic Programming, Memoization",Given an array of integers called nums; you can perform any of the following operation while nums contains at least 2 elements: Choose the first two elements of nums and delete them. Choose the last two elements of nums and delete them. Choose the first and the last elements of nums and delete them. The score of the operation is the sum of the deleted elements. Your task is to find the maximum number of operations that can be performed; such that all operations have the same score. Return the maximum number of operations possible that satisfy the condition mentioned above. Example 1: Input: nums = [3;2;1;2;3;4] Output: 3 Explanation: We perform the following operations: - Delete the first two elements; with score 3 + 2 = 5; nums = [1;2;3;4]. - Delete the first and the last elements; with score 1 + 4 = 5; nums = [2;3]. - Delete the first and the last elements; with score 2 + 3 = 5; nums = []. We are unable to perform any more operations as nums is empty. Example 2: Input: nums = [3;2;6;1;4] Output: 2 Explanation: We perform the following operations: - Delete the first two elements; with score 3 + 2 = 5; nums = [6;1;4]. - Delete the last two elements; with score 1 + 4 = 5; nums = [6]. It can be proven that we can perform at most 2 operations. Constraints: 2 <= nums.length <= 2000 1 <= nums[i] <= 1000
Google,3356,Zero Array Transformation II,Med,"Array, Hash Table, String, Trie","You are given an array arr of size n consisting of non-empty strings. Find a string array answer of size n such that: answer[i] is the shortest substring of arr[i] that does not occur as a substring in any other string in arr. If multiple such substrings exist; answer[i] should be the lexicographically smallest. And if no such substring exists; answer[i] should be an empty string. Return the array answer. Example 1: Input: arr = [""cab"";""ad"";""bad"";""c""] Output: [""ab"";"""";""ba"";""""] Explanation: We have the following: - For the string ""cab""; the shortest substring that does not occur in any other string is either ""ca"" or ""ab""; we choose the lexicographically smaller substring; which is ""ab"". - For the string ""ad""; there is no substring that does not occur in any other string. - For the string ""bad""; the shortest substring that does not occur in any other string is ""ba"". - For the string ""c""; there is no substring that does not occur in any other string. Example 2: Input: arr = [""abc"";""bcd"";""abcd""] Output: ["""";"""";""abcd""] Explanation: We have the following: - For the string ""abc""; there is no substring that does not occur in any other string. - For the string ""bcd""; there is no substring that does not occur in any other string. - For the string ""abcd""; the shortest substring that does not occur in any other string is ""abcd"". Constraints: n == arr.length 2 <= n <= 100 1 <= arr[i].length <= 20 arr[i] consists only of lowercase English letters."
Google,26,Remove Duplicates from Sorted Array,Easy,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums. Consider the number of unique elements of nums to be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;2] Output: 2; nums = [1;2;_] Explanation: Your function should return k = 2; with the first two elements of nums being 1 and 2 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;2;2;3;3;4] Output: 5; nums = [0;1;2;3;4;_;_;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums being 0; 1; 2; 3; and 4 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -100 <= nums[i] <= 100 nums is sorted in non-decreasing order.
Google,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Google,1381,Design a Stack With Increment Operation,Med,"Array, String, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask","Given a list of words; list of single letters (might be repeating) and score of every character. Return the maximum score of any valid set of words formed by using the given letters (words[i] cannot be used two or more times). It is not necessary to use all characters in letters and each letter can only be used once. Score of letters 'a'; 'b'; 'c'; ... ;'z' is given by score[0]; score[1]; ... ; score[25] respectively. Example 1: Input: words = [""dog"";""cat"";""dad"";""good""]; letters = [""a"";""a"";""c"";""d"";""d"";""d"";""g"";""o"";""o""]; score = [1;0;9;5;0;0;3;0;0;0;0;0;0;0;2;0;0;0;0;0;0;0;0;0;0;0] Output: 23 Explanation: Score a=1; c=9; d=5; g=3; o=2 Given letters; we can form the words ""dad"" (5+1+5) and ""good"" (3+2+2+5) with a score of 23. Words ""dad"" and ""dog"" only get a score of 21. Example 2: Input: words = [""xxxz"";""ax"";""bx"";""cx""]; letters = [""z"";""a"";""b"";""c"";""x"";""x"";""x""]; score = [4;4;4;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;5;0;10] Output: 27 Explanation: Score a=4; b=4; c=4; x=5; z=10 Given letters; we can form the words ""ax"" (4+5); ""bx"" (4+5) and ""cx"" (4+5) with a score of 27. Word ""xxxz"" only get a score of 25. Example 3: Input: words = [""leetcode""]; letters = [""l"";""e"";""t"";""c"";""o"";""d""]; score = [0;0;1;1;1;0;0;0;0;0;0;1;0;0;1;0;0;0;0;1;0;0;0;0;0;0] Output: 0 Explanation: Letter ""e"" can only be used once. Constraints: 1 <= words.length <= 14 1 <= words[i].length <= 15 1 <= letters.length <= 100 letters[i].length == 1 score.length == 26 0 <= score[i] <= 10 words[i]; letters[i] contains only lower case English letters."
Google,3349,Adjacent Increasing Subarrays Detection I,Easy,"Hash Table, String, Sliding Window","Given a string s; return the maximum length of a substring such that it contains at most two occurrences of each character. Example 1: Input: s = ""bcbbbcba"" Output: 4 Explanation: The following substring has a length of 4 and contains at most two occurrences of each character: ""bcbbbcba"". Example 2: Input: s = ""aaaa"" Output: 2 Explanation: The following substring has a length of 2 and contains at most two occurrences of each character: ""aaaa"". Constraints: 2 <= s.length <= 100 s consists only of lowercase English letters."
Google,3346,Maximum Frequency of an Element After Performing Operations I,Med,"String, Greedy","You are given a string s and an integer k. Define a function distance(s1; s2) between two strings s1 and s2 of the same length n as: The sum of the minimum distance between s1[i] and s2[i] when the characters from 'a' to 'z' are placed in a cyclic order; for all i in the range [0; n - 1]. For example; distance(""ab""; ""cd"") == 4; and distance(""a""; ""z"") == 1. You can change any letter of s to any other lowercase English letter; any number of times. Return a string denoting the lexicographically smallest string t you can get after some changes; such that distance(s; t) <= k. Example 1: Input: s = ""zbbz""; k = 3 Output: ""aaaz"" Explanation: Change s to ""aaaz"". The distance between ""zbbz"" and ""aaaz"" is equal to k = 3. Example 2: Input: s = ""xaxcd""; k = 4 Output: ""aawcd"" Explanation: The distance between ""xaxcd"" and ""aawcd"" is equal to k = 4. Example 3: Input: s = ""lol""; k = 0 Output: ""lol"" Explanation: It's impossible to change any character as k = 0. Constraints: 1 <= s.length <= 100 0 <= k <= 2000 s consists only of lowercase English letters."
Google,3347,Maximum Frequency of an Element After Performing Operations II,Hard,"Array, Simulation",You are given a 1-indexed array of distinct integers nums of length n. You need to distribute all the elements of nums between two arrays arr1 and arr2 using n operations. In the first operation; append nums[1] to arr1. In the second operation; append nums[2] to arr2. Afterwards; in the ith operation: If the last element of arr1 is greater than the last element of arr2; append nums[i] to arr1. Otherwise; append nums[i] to arr2. The array result is formed by concatenating the arrays arr1 and arr2. For example; if arr1 == [1;2;3] and arr2 == [4;5;6]; then result = [1;2;3;4;5;6]. Return the array result. Example 1: Input: nums = [2;1;3] Output: [2;3;1] Explanation: After the first 2 operations; arr1 = [2] and arr2 = [1]. In the 3rd operation; as the last element of arr1 is greater than the last element of arr2 (2 > 1); append nums[3] to arr1. After 3 operations; arr1 = [2;3] and arr2 = [1]. Hence; the array result formed by concatenation is [2;3;1]. Example 2: Input: nums = [5;4;3;8] Output: [5;3;4;8] Explanation: After the first 2 operations; arr1 = [5] and arr2 = [4]. In the 3rd operation; as the last element of arr1 is greater than the last element of arr2 (5 > 4); append nums[3] to arr1; hence arr1 becomes [5;3]. In the 4th operation; as the last element of arr2 is greater than the last element of arr1 (4 > 3); append nums[4] to arr2; hence arr2 becomes [4;8]. After 4 operations; arr1 = [5;3] and arr2 = [4;8]. Hence; the array result formed by concatenation is [5;3;4;8]. Constraints: 3 <= n <= 50 1 <= nums[i] <= 100 All elements in nums are distinct.
Google,84,Largest Rectangle in Histogram,Hard,"Array, Stack, Monotonic Stack",Given an array of integers heights representing the histogram's bar height where the width of each bar is 1; return the area of the largest rectangle in the histogram. Example 1: Input: heights = [2;1;5;6;2;3] Output: 10 Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area; which has an area = 10 units. Example 2: Input: heights = [2;4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104
Google,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Google,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
Google,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Google,3026,Maximum Good Subarray Sum,Med,"Math, Greedy",You are given positive integers n and target. An array nums is beautiful if it meets the following conditions: nums.length == n. nums consists of pairwise distinct positive integers. There doesn't exist two distinct indices; i and j; in the range [0; n - 1]; such that nums[i] + nums[j] == target. Return the minimum possible sum that a beautiful array could have modulo 109 + 7. Example 1: Input: n = 2; target = 3 Output: 4 Explanation: We can see that nums = [1;3] is beautiful. - The array nums has length n = 2. - The array nums consists of pairwise distinct positive integers. - There doesn't exist two distinct indices; i and j; with nums[i] + nums[j] == 3. It can be proven that 4 is the minimum possible sum that a beautiful array could have. Example 2: Input: n = 3; target = 3 Output: 8 Explanation: We can see that nums = [1;3;4] is beautiful. - The array nums has length n = 3. - The array nums consists of pairwise distinct positive integers. - There doesn't exist two distinct indices; i and j; with nums[i] + nums[j] == 3. It can be proven that 8 is the minimum possible sum that a beautiful array could have. Example 3: Input: n = 1; target = 1 Output: 1 Explanation: We can see; that nums = [1] is beautiful. Constraints: 1 <= n <= 109 1 <= target <= 109
Google,3020,Find the Maximum Number of Elements in Subset,Med,,
Google,3350,Adjacent Increasing Subarrays Detection II,Med,"Array, Binary Indexed Tree, Segment Tree, Simulation",You are given a 1-indexed array of integers nums of length n. We define a function greaterCount such that greaterCount(arr; val) returns the number of elements in arr that are strictly greater than val. You need to distribute all the elements of nums between two arrays arr1 and arr2 using n operations. In the first operation; append nums[1] to arr1. In the second operation; append nums[2] to arr2. Afterwards; in the ith operation: If greaterCount(arr1; nums[i]) > greaterCount(arr2; nums[i]); append nums[i] to arr1. If greaterCount(arr1; nums[i]) < greaterCount(arr2; nums[i]); append nums[i] to arr2. If greaterCount(arr1; nums[i]) == greaterCount(arr2; nums[i]); append nums[i] to the array with a lesser number of elements. If there is still a tie; append nums[i] to arr1. The array result is formed by concatenating the arrays arr1 and arr2. For example; if arr1 == [1;2;3] and arr2 == [4;5;6]; then result = [1;2;3;4;5;6]. Return the integer array result. Example 1: Input: nums = [2;1;3;3] Output: [2;3;1;3] Explanation: After the first 2 operations; arr1 = [2] and arr2 = [1]. In the 3rd operation; the number of elements greater than 3 is zero in both arrays. Also; the lengths are equal; hence; append nums[3] to arr1. In the 4th operation; the number of elements greater than 3 is zero in both arrays. As the length of arr2 is lesser; hence; append nums[4] to arr2. After 4 operations; arr1 = [2;3] and arr2 = [1;3]. Hence; the array result formed by concatenation is [2;3;1;3]. Example 2: Input: nums = [5;14;3;1;2] Output: [5;3;1;2;14] Explanation: After the first 2 operations; arr1 = [5] and arr2 = [14]. In the 3rd operation; the number of elements greater than 3 is one in both arrays. Also; the lengths are equal; hence; append nums[3] to arr1. In the 4th operation; the number of elements greater than 1 is greater in arr1 than arr2 (2 > 1). Hence; append nums[4] to arr1. In the 5th operation; the number of elements greater than 2 is greater in arr1 than arr2 (2 > 1). Hence; append nums[5] to arr1. After 5 operations; arr1 = [5;3;1;2] and arr2 = [14]. Hence; the array result formed by concatenation is [5;3;1;2;14]. Example 3: Input: nums = [3;3;3;3] Output: [3;3;3;3] Explanation: At the end of 4 operations; arr1 = [3;3] and arr2 = [3;3]. Hence; the array result formed by concatenation is [3;3;3;3]. Constraints: 3 <= n <= 105 1 <= nums[i] <= 109
Google,3351,Sum of Good Subsequences,Hard,"Array, Greedy, Sorting",You are given an array happiness of length n; and a positive integer k. There are n children standing in a queue; where the ith child has happiness value happiness[i]. You want to select k children from these n children in k turns. In each turn; when you select a child; the happiness value of all the children that have not been selected till now decreases by 1. Note that the happiness value cannot become negative and gets decremented only if it is positive. Return the maximum sum of the happiness values of the selected children you can achieve by selecting k children. Example 1: Input: happiness = [1;2;3]; k = 2 Output: 4 Explanation: We can pick 2 children in the following way: - Pick the child with the happiness value == 3. The happiness value of the remaining children becomes [0;1]. - Pick the child with the happiness value == 1. The happiness value of the remaining child becomes [0]. Note that the happiness value cannot become less than 0. The sum of the happiness values of the selected children is 3 + 1 = 4. Example 2: Input: happiness = [1;1;1;1]; k = 2 Output: 1 Explanation: We can pick 2 children in the following way: - Pick any child with the happiness value == 1. The happiness value of the remaining children becomes [0;0;0]. - Pick the child with the happiness value == 0. The happiness value of the remaining child becomes [0;0]. The sum of the happiness values of the selected children is 1 + 0 = 1. Example 3: Input: happiness = [2;3;4;5]; k = 1 Output: 5 Explanation: We can pick 1 child in the following way: - Pick the child with the happiness value == 5. The happiness value of the remaining children becomes [1;2;3]. The sum of the happiness values of the selected children is 5. Constraints: 1 <= n == happiness.length <= 2 * 105 1 <= happiness[i] <= 108 1 <= k <= n
Google,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Google,67,Add Binary,Easy,"Math, String, Bit Manipulation, Simulation","Given two binary strings a and b; return their sum as a binary string. Example 1: Input: a = ""11""; b = ""1"" Output: ""100"" Example 2: Input: a = ""1010""; b = ""1011"" Output: ""10101"" Constraints: 1 <= a.length; b.length <= 104 a and b consist only of '0' or '1' characters. Each string does not contain leading zeros except for the zero itself."
Google,136,Single Number,Easy,"Array, Bit Manipulation",Given a non-empty array of integers nums; every element appears twice except for one. Find that single one. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;1] Output: 1 Example 2: Input: nums = [4;1;2;1;2] Output: 4 Example 3: Input: nums = [1] Output: 1 Constraints: 1 <= nums.length <= 3 * 104 -3 * 104 <= nums[i] <= 3 * 104 Each element in the array appears twice except for one element which appears only once.
Google,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Google,242,Valid Anagram,Easy,"Hash Table, String, Sorting","Given two strings s and t; return true if t is an anagram of s; and false otherwise. Example 1: Input: s = ""anagram""; t = ""nagaram"" Output: true Example 2: Input: s = ""rat""; t = ""car"" Output: false Constraints: 1 <= s.length; t.length <= 5 * 104 s and t consist of lowercase English letters. Follow up: What if the inputs contain Unicode characters? How would you adapt your solution to such a case?"
Google,567,Permutation in String,Med,"Hash Table, Two Pointers, String, Sliding Window","Given two strings s1 and s2; return true if s2 contains a permutation of s1; or false otherwise. In other words; return true if one of s1's permutations is the substring of s2. Example 1: Input: s1 = ""ab""; s2 = ""eidbaooo"" Output: true Explanation: s2 contains one permutation of s1 (""ba""). Example 2: Input: s1 = ""ab""; s2 = ""eidboaoo"" Output: false Constraints: 1 <= s1.length; s2.length <= 104 s1 and s2 consist of lowercase English letters."
Google,584,Find Customer Referee,Easy,Database,Table: Customer +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | referee_id | int | +-------------+---------+ In SQL; id is the primary key column for this table. Each row of this table indicates the id of a customer; their name; and the id of the customer who referred them. Find the names of the customer that are not referred by the customer with id = 2. Return the result table in any order. The result format is in the following example. Example 1: Input: Customer table: +----+------+------------+ | id | name | referee_id | +----+------+------------+ | 1 | Will | null | | 2 | Jane | null | | 3 | Alex | 2 | | 4 | Bill | null | | 5 | Zack | 1 | | 6 | Mark | 2 | +----+------+------------+ Output: +------+ | name | +------+ | Will | | Jane | | Bill | | Zack | +------+
Google,1101,The Earliest Moment When Everyone Become Friends,Med,"Graph, Topological Sort",
Google,2458,Height of Binary Tree After Subtree Removal Queries,Hard,"Array, Greedy, Sorting",
Google,2981,Find Longest Special Substring That Occurs Thrice I,Med,,
Google,2985,Calculate Compressed Mean,Easy,,
Google,2987,Find Expensive Cities,Easy,,
Google,2989,Class Performance,Med,,
Google,2990,Loan Types,Easy,,
Google,2991,Top Three Wineries,Hard,,
Google,3008,Find Beautiful Indices in the Given Array II,Hard,,
Google,3028,Ant on the Boundary,Easy,,
Google,3024,Type of Triangle,Easy,"Math, String, Dynamic Programming, String Matching","You are given two strings s and t of equal length n. You can perform the following operation on the string s: Remove a suffix of s of length l where 0 < l < n and append it at the start of s. For example; let s = 'abcd' then in one operation you can remove the suffix 'cd' and append it in front of s making s = 'cdab'. You are also given an integer k. Return the number of ways in which s can be transformed into t in exactly k operations. Since the answer can be large; return it modulo 109 + 7. Example 1: Input: s = ""abcd""; t = ""cdab""; k = 2 Output: 2 Explanation: First way: In first operation; choose suffix from index = 3; so resulting s = ""dabc"". In second operation; choose suffix from index = 3; so resulting s = ""cdab"". Second way: In first operation; choose suffix from index = 1; so resulting s = ""bcda"". In second operation; choose suffix from index = 1; so resulting s = ""cdab"". Example 2: Input: s = ""ababab""; t = ""ababab""; k = 1 Output: 2 Explanation: First way: Choose suffix from index = 2; so resulting s = ""ababab"". Second way: Choose suffix from index = 4; so resulting s = ""ababab"". Constraints: 2 <= s.length <= 5 * 105 1 <= k <= 1015 s.length == t.length s and t consist of only lowercase English alphabets."
Google,73,Set Matrix Zeroes,Med,"Array, Hash Table, Matrix",Given an m x n integer matrix matrix; if an element is 0; set its entire row and column to 0's. You must do it in place. Example 1: Input: matrix = [[1;1;1];[1;0;1];[1;1;1]] Output: [[1;0;1];[0;0;0];[1;0;1]] Example 2: Input: matrix = [[0;1;2;0];[3;4;5;2];[1;3;1;5]] Output: [[0;0;0;0];[0;4;5;0];[0;3;1;0]] Constraints: m == matrix.length n == matrix[0].length 1 <= m; n <= 200 -231 <= matrix[i][j] <= 231 - 1 Follow up: A straightforward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space; but still not the best solution. Could you devise a constant space solution?
Google,118,Pascal's Triangle,Easy,"Array, Dynamic Programming",Given an integer numRows; return the first numRows of Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: numRows = 5 Output: [[1];[1;1];[1;2;1];[1;3;3;1];[1;4;6;4;1]] Example 2: Input: numRows = 1 Output: [[1]] Constraints: 1 <= numRows <= 30
Google,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Google,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
Google,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Google,231,Power of Two,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of two. Otherwise; return false. An integer n is a power of two; if there exists an integer x such that n == 2x. Example 1: Input: n = 1 Output: true Explanation: 20 = 1 Example 2: Input: n = 16 Output: true Explanation: 24 = 16 Example 3: Input: n = 3 Output: false Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Google,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Google,349,Intersection of Two Arrays,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must be unique and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [9;4] Explanation: [4;9] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000
Google,595,Big Countries,Easy,Database,Table: World +-------------+---------+ | Column Name | Type | +-------------+---------+ | name | varchar | | continent | varchar | | area | int | | population | int | | gdp | bigint | +-------------+---------+ name is the primary key (column with unique values) for this table. Each row of this table gives information about the name of a country; the continent to which it belongs; its area; the population; and its GDP value. A country is big if: it has an area of at least three million (i.e.; 3000000 km2); or it has a population of at least twenty-five million (i.e.; 25000000). Write a solution to find the name; population; and area of the big countries. Return the result table in any order. The result format is in the following example. Example 1: Input: World table: +-------------+-----------+---------+------------+--------------+ | name | continent | area | population | gdp | +-------------+-----------+---------+------------+--------------+ | Afghanistan | Asia | 652230 | 25500100 | 20343000000 | | Albania | Europe | 28748 | 2831741 | 12960000000 | | Algeria | Africa | 2381741 | 37100000 | 188681000000 | | Andorra | Europe | 468 | 78115 | 3712000000 | | Angola | Africa | 1246700 | 20609294 | 100990000000 | +-------------+-----------+---------+------------+--------------+ Output: +-------------+------------+---------+ | name | population | area | +-------------+------------+---------+ | Afghanistan | 25500100 | 652230 | | Algeria | 37100000 | 2381741 | +-------------+------------+---------+
Google,670,Maximum Swap,Med,"Math, Greedy",You are given an integer num. You can swap two digits at most once to get the maximum valued number. Return the maximum valued number you can get. Example 1: Input: num = 2736 Output: 7236 Explanation: Swap the number 2 and the number 7. Example 2: Input: num = 9973 Output: 9973 Explanation: No swap. Constraints: 0 <= num <= 108
Google,715,Range Module,Hard,"Design, Segment Tree, Ordered Set","A Range Module is a module that tracks ranges of numbers. Design a data structure to track the ranges represented as half-open intervals and query about them. A half-open interval [left; right) denotes all the real numbers x where left <= x < right. Implement the RangeModule class: RangeModule() Initializes the object of the data structure. void addRange(int left; int right) Adds the half-open interval [left; right); tracking every real number in that interval. Adding an interval that partially overlaps with currently tracked numbers should add any numbers in the interval [left; right) that are not already tracked. boolean queryRange(int left; int right) Returns true if every real number in the interval [left; right) is currently being tracked; and false otherwise. void removeRange(int left; int right) Stops tracking every real number currently being tracked in the half-open interval [left; right). Example 1: Input [""RangeModule""; ""addRange""; ""removeRange""; ""queryRange""; ""queryRange""; ""queryRange""] [[]; [10; 20]; [14; 16]; [10; 14]; [13; 15]; [16; 17]] Output [null; null; null; true; false; true] Explanation RangeModule rangeModule = new RangeModule(); rangeModule.addRange(10; 20); rangeModule.removeRange(14; 16); rangeModule.queryRange(10; 14); // return True;(Every number in [10; 14) is being tracked) rangeModule.queryRange(13; 15); // return False;(Numbers like 14; 14.03; 14.17 in [13; 15) are not being tracked) rangeModule.queryRange(16; 17); // return True; (The number 16 in [16; 17) is still being tracked; despite the remove operation) Constraints: 1 <= left < right <= 109 At most 104 calls will be made to addRange; queryRange; and removeRange."
Google,962,Maximum Width Ramp,Med,"String, Dynamic Programming","A binary string is monotone increasing if it consists of some number of 0's (possibly none); followed by some number of 1's (also possibly none). You are given a binary string s. You can flip s[i] changing it from 0 to 1 or from 1 to 0. Return the minimum number of flips to make s monotone increasing. Example 1: Input: s = ""00110"" Output: 1 Explanation: We flip the last digit to get 00111. Example 2: Input: s = ""010110"" Output: 2 Explanation: We flip to get 011111; or alternatively 000111. Example 3: Input: s = ""00011000"" Output: 2 Explanation: We flip to get 00000000. Constraints: 1 <= s.length <= 105 s[i] is either '0' or '1'."
Google,1825,Finding MK Average,Hard,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",You are given an integer array jobs; where jobs[i] is the amount of time it takes to complete the ith job. There are k workers that you can assign jobs to. Each job should be assigned to exactly one worker. The working time of a worker is the sum of the time it takes to complete all jobs assigned to them. Your goal is to devise an optimal assignment such that the maximum working time of any worker is minimized. Return the minimum possible maximum working time of any assignment. Example 1: Input: jobs = [3;2;3]; k = 3 Output: 3 Explanation: By assigning each person one job; the maximum time is 3. Example 2: Input: jobs = [1;2;4;7;8]; k = 2 Output: 11 Explanation: Assign the jobs the following way: Worker 1: 1; 2; 8 (working time = 1 + 2 + 8 = 11) Worker 2: 4; 7 (working time = 4 + 7 = 11) The maximum working time is 11. Constraints: 1 <= k <= jobs.length <= 12 1 <= jobs[i] <= 107
Google,2877,Create a DataFrame from List,Easy,"String, Greedy, Enumeration","Given three strings a; b; and c; your task is to find a string that has the minimum length and contains all three strings as substrings. If there are multiple such strings; return the lexicographically smallest one. Return a string denoting the answer to the problem. Notes A string a is lexicographically smaller than a string b (of the same length) if in the first position where a and b differ; string a has a letter that appears earlier in the alphabet than the corresponding letter in b. A substring is a contiguous sequence of characters within a string. Example 1: Input: a = ""abc""; b = ""bca""; c = ""aaa"" Output: ""aaabca"" Explanation: We show that ""aaabca"" contains all the given strings: a = ans[2...4]; b = ans[3..5]; c = ans[0..2]. It can be shown that the length of the resulting string would be at least 6 and ""aaabca"" is the lexicographically smallest one. Example 2: Input: a = ""ab""; b = ""ba""; c = ""aba"" Output: ""aba"" Explanation: We show that the string ""aba"" contains all the given strings: a = ans[0..1]; b = ans[1..2]; c = ans[0..2]. Since the length of c is 3; the length of the resulting string would be at least 3. It can be shown that ""aba"" is the lexicographically smallest one. Constraints: 1 <= a.length; b.length; c.length <= 100 a; b; c consist only of lowercase English letters."
Google,6,Zigzag Conversion,Med,String,"The string ""PAYPALISHIRING"" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: ""PAHNAPLSIIGYIR"" Write the code that will take a string and make this conversion given a number of rows: string convert(string s; int numRows); Example 1: Input: s = ""PAYPALISHIRING""; numRows = 3 Output: ""PAHNAPLSIIGYIR"" Example 2: Input: s = ""PAYPALISHIRING""; numRows = 4 Output: ""PINALSIGYAHRPI"" Explanation: P I N A L S I G Y A H R P I Example 3: Input: s = ""A""; numRows = 1 Output: ""A"" Constraints: 1 <= s.length <= 1000 s consists of English letters (lower-case and upper-case); ';' and '.'. 1 <= numRows <= 1000"
Google,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Google,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Google,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Google,35,Search Insert Position,Easy,"Array, Binary Search",Given a sorted array of distinct integers and a target value; return the index if the target is found. If not; return the index where it would be if it were inserted in order. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [1;3;5;6]; target = 5 Output: 2 Example 2: Input: nums = [1;3;5;6]; target = 2 Output: 1 Example 3: Input: nums = [1;3;5;6]; target = 7 Output: 4 Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 nums contains distinct values sorted in ascending order. -104 <= target <= 104
Google,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Google,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
Google,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Google,205,Isomorphic Strings,Easy,"Hash Table, String","Given two strings s and t; determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character; but a character may map to itself. Example 1: Input: s = ""egg""; t = ""add"" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = ""foo""; t = ""bar"" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = ""paper""; t = ""title"" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character."
Google,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Google,354,Russian Doll Envelopes,Hard,"Array, Binary Search, Dynamic Programming, Sorting",You are given a 2D array of integers envelopes where envelopes[i] = [wi; hi] represents the width and the height of an envelope. One envelope can fit into another if and only if both the width and height of one envelope are greater than the other envelope's width and height. Return the maximum number of envelopes you can Russian doll (i.e.; put one inside the other). Note: You cannot rotate an envelope. Example 1: Input: envelopes = [[5;4];[6;4];[6;7];[2;3]] Output: 3 Explanation: The maximum number of envelopes you can Russian doll is 3 ([2;3] => [5;4] => [6;7]). Example 2: Input: envelopes = [[1;1];[1;1];[1;1]] Output: 1 Constraints: 1 <= envelopes.length <= 105 envelopes[i].length == 2 1 <= wi; hi <= 105
Google,410,Split Array Largest Sum,Hard,"Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum",Given an integer array nums and an integer k; split nums into k non-empty subarrays such that the largest sum of any subarray is minimized. Return the minimized largest sum of the split. A subarray is a contiguous part of the array. Example 1: Input: nums = [7;2;5;10;8]; k = 2 Output: 18 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [7;2;5] and [10;8]; where the largest sum among the two subarrays is only 18. Example 2: Input: nums = [1;2;3;4;5]; k = 2 Output: 9 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [1;2;3] and [4;5]; where the largest sum among the two subarrays is only 9. Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 106 1 <= k <= min(50; nums.length)
Google,796,Rotate String,Easy,Math,Given four integers sx; sy; tx; and ty; return true if it is possible to convert the point (sx; sy) to the point (tx; ty) through some operations; or false otherwise. The allowed operation on some point (x; y) is to convert it to either (x; x + y) or (x + y; y). Example 1: Input: sx = 1; sy = 1; tx = 3; ty = 5 Output: true Explanation: One series of moves that transforms the starting point to the target is: (1; 1) -> (1; 2) (1; 2) -> (3; 2) (3; 2) -> (3; 5) Example 2: Input: sx = 1; sy = 1; tx = 2; ty = 2 Output: false Example 3: Input: sx = 1; sy = 1; tx = 1; ty = 1 Output: true Constraints: 1 <= sx; sy; tx; ty <= 109
Google,843,Guess the Word,Hard,"Array, Hash Table, Dynamic Programming, Sorting",Given an array of unique integers; arr; where each integer arr[i] is strictly greater than 1. We make a binary tree using these integers; and each number may be used for any number of times. Each non-leaf node's value should be equal to the product of the values of its children. Return the number of binary trees we can make. The answer may be too large so return the answer modulo 109 + 7. Example 1: Input: arr = [2;4] Output: 3 Explanation: We can make these trees: [2]; [4]; [4; 2; 2] Example 2: Input: arr = [2;4;5;10] Output: 7 Explanation: We can make these trees: [2]; [4]; [5]; [10]; [4; 2; 2]; [10; 2; 5]; [10; 5; 2]. Constraints: 1 <= arr.length <= 1000 2 <= arr[i] <= 109 All the values of arr are unique.
Google,852,Peak Index in a Mountain Array,Med,"Array, Two Pointers, Binary Search, Sorting",There are n persons on a social media website. You are given an integer array ages where ages[i] is the age of the ith person. A Person x will not send a friend request to a person y (x != y) if any of the following conditions is true: age[y] <= 0.5 * age[x] + 7 age[y] > age[x] age[y] > 100 && age[x] < 100 Otherwise; x will send a friend request to y. Note that if x sends a request to y; y will not necessarily send a request to x. Also; a person will not send a friend request to themself. Return the total number of friend requests made. Example 1: Input: ages = [16;16] Output: 2 Explanation: 2 people friend request each other. Example 2: Input: ages = [16;17;18] Output: 2 Explanation: Friend requests are made 17 -> 16; 18 -> 17. Example 3: Input: ages = [20;30;100;110;120] Output: 3 Explanation: Friend requests are made 110 -> 100; 120 -> 110; 120 -> 100. Constraints: n == ages.length 1 <= n <= 2 * 104 1 <= ages[i] <= 120
Google,1110,Delete Nodes And Return Forest,Med,,
Google,18,4Sum,Med,"Array, Two Pointers, Sorting",Given an array nums of n integers; return an array of all the unique quadruplets [nums[a]; nums[b]; nums[c]; nums[d]] such that: 0 <= a; b; c; d < n a; b; c; and d are distinct. nums[a] + nums[b] + nums[c] + nums[d] == target You may return the answer in any order. Example 1: Input: nums = [1;0;-1;0;-2;2]; target = 0 Output: [[-2;-1;1;2];[-2;0;0;2];[-1;0;0;1]] Example 2: Input: nums = [2;2;2;2;2]; target = 8 Output: [[2;2;2;2]] Constraints: 1 <= nums.length <= 200 -109 <= nums[i] <= 109 -109 <= target <= 109
Google,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Google,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Google,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Google,61,Rotate List,Med,"Linked List, Two Pointers",Given the head of a linked list; rotate the list to the right by k places. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [4;5;1;2;3] Example 2: Input: head = [0;1;2]; k = 4 Output: [2;0;1] Constraints: The number of nodes in the list is in the range [0; 500]. -100 <= Node.val <= 100 0 <= k <= 2 * 109
Google,189,Rotate Array,Med,"Array, Math, Two Pointers",Given an integer array nums; rotate the array to the right by k steps; where k is non-negative. Example 1: Input: nums = [1;2;3;4;5;6;7]; k = 3 Output: [5;6;7;1;2;3;4] Explanation: rotate 1 steps to the right: [7;1;2;3;4;5;6] rotate 2 steps to the right: [6;7;1;2;3;4;5] rotate 3 steps to the right: [5;6;7;1;2;3;4] Example 2: Input: nums = [-1;-100;3;99]; k = 2 Output: [3;99;-1;-100] Explanation: rotate 1 steps to the right: [99;-1;-100;3] rotate 2 steps to the right: [3;99;-1;-100] Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 0 <= k <= 105 Follow up: Try to come up with as many solutions as you can. There are at least three different ways to solve this problem. Could you do it in-place with O(1) extra space?
Google,249,Group Shifted Strings,Med,"Array, Hash Table, String",
Google,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Google,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Google,424,Longest Repeating Character Replacement,Med,"Hash Table, String, Sliding Window","You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times. Return the length of the longest substring containing the same letter you can get after performing the above operations. Example 1: Input: s = ""ABAB""; k = 2 Output: 4 Explanation: Replace the two 'A's with two 'B's or vice versa. Example 2: Input: s = ""AABABBA""; k = 1 Output: 4 Explanation: Replace the one 'A' in the middle with 'B' and form ""AABBBBA"". The substring ""BBBB"" has the longest repeating letters; which is 4. There may exists other ways to achieve this answer too. Constraints: 1 <= s.length <= 105 s consists of only uppercase English letters. 0 <= k <= s.length"
Google,432,All O`one Data Structure,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure to store the strings' count with the ability to return the strings with minimum and maximum counts. Implement the AllOne class: AllOne() Initializes the object of the data structure. inc(String key) Increments the count of the string key by 1. If key does not exist in the data structure; insert it with count 1. dec(String key) Decrements the count of the string key by 1. If the count of key is 0 after the decrement; remove it from the data structure. It is guaranteed that key exists in the data structure before the decrement. getMaxKey() Returns one of the keys with the maximal count. If no element exists; return an empty string """". getMinKey() Returns one of the keys with the minimum count. If no element exists; return an empty string """". Note that each function must run in O(1) average time complexity. Example 1: Input [""AllOne""; ""inc""; ""inc""; ""getMaxKey""; ""getMinKey""; ""inc""; ""getMaxKey""; ""getMinKey""] [[]; [""hello""]; [""hello""]; []; []; [""leet""]; []; []] Output [null; null; null; ""hello""; ""hello""; null; ""hello""; ""leet""] Explanation AllOne allOne = new AllOne(); allOne.inc(""hello""); allOne.inc(""hello""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""hello"" allOne.inc(""leet""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""leet"" Constraints: 1 <= key.length <= 10 key consists of lowercase English letters. It is guaranteed that for each call to dec; key is existing in the data structure. At most 5 * 104 calls will be made to inc; dec; getMaxKey; and getMinKey."
Google,496,Next Greater Element I,Easy,"Array, Hash Table, Stack, Monotonic Stack",The next greater element of some element x in an array is the first greater element that is to the right of x in the same array. You are given two distinct 0-indexed integer arrays nums1 and nums2; where nums1 is a subset of nums2. For each 0 <= i < nums1.length; find the index j such that nums1[i] == nums2[j] and determine the next greater element of nums2[j] in nums2. If there is no next greater element; then the answer for this query is -1. Return an array ans of length nums1.length such that ans[i] is the next greater element as described above. Example 1: Input: nums1 = [4;1;2]; nums2 = [1;3;4;2] Output: [-1;3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 4 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. - 1 is underlined in nums2 = [1;3;4;2]. The next greater element is 3. - 2 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. Example 2: Input: nums1 = [2;4]; nums2 = [1;2;3;4] Output: [3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 2 is underlined in nums2 = [1;2;3;4]. The next greater element is 3. - 4 is underlined in nums2 = [1;2;3;4]. There is no next greater element; so the answer is -1. Constraints: 1 <= nums1.length <= nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 104 All integers in nums1 and nums2 are unique. All the integers of nums1 also appear in nums2. Follow up: Could you find an O(nums1.length + nums2.length) solution?
Google,525,Contiguous Array,Med,"Array, Hash Table, Prefix Sum",Given a binary array nums; return the maximum length of a contiguous subarray with an equal number of 0 and 1. Example 1: Input: nums = [0;1] Output: 2 Explanation: [0; 1] is the longest contiguous subarray with an equal number of 0 and 1. Example 2: Input: nums = [0;1;0] Output: 2 Explanation: [0; 1] (or [1; 0]) is a longest contiguous subarray with equal number of 0 and 1. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Google,539,Minimum Time Difference,Med,"Array, Math, String, Sorting","Given a list of 24-hour clock time points in ""HH:MM"" format; return the minimum minutes difference between any two time-points in the list. Example 1: Input: timePoints = [""23:59"";""00:00""] Output: 1 Example 2: Input: timePoints = [""00:00"";""23:59"";""00:00""] Output: 0 Constraints: 2 <= timePoints.length <= 2 * 104 timePoints[i] is in the format ""HH:MM""."
Google,632,Smallest Range Covering Elements from K Lists,Hard,"Array, Hash Table, Greedy, Sliding Window, Sorting, Heap (Priority Queue)",You have k lists of sorted integers in non-decreasing order. Find the smallest range that includes at least one number from each of the k lists. We define the range [a; b] is smaller than range [c; d] if b - a < d - c or a < c if b - a == d - c. Example 1: Input: nums = [[4;10;15;24;26];[0;9;12;20];[5;18;22;30]] Output: [20;24] Explanation: List 1: [4; 10; 15; 24;26]; 24 is in range [20;24]. List 2: [0; 9; 12; 20]; 20 is in range [20;24]. List 3: [5; 18; 22; 30]; 22 is in range [20;24]. Example 2: Input: nums = [[1;2;3];[1;2;3];[1;2;3]] Output: [1;1] Constraints: nums.length == k 1 <= k <= 3500 1 <= nums[i].length <= 50 -105 <= nums[i][j] <= 105 nums[i] is sorted in non-decreasing order.
Google,695,Max Area of Island,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island. Return the maximum area of an island in grid. If there is no island; return 0. Example 1: Input: grid = [[0;0;1;0;0;0;0;1;0;0;0;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;1;1;0;1;0;0;0;0;0;0;0;0];[0;1;0;0;1;1;0;0;1;0;1;0;0];[0;1;0;0;1;1;0;0;1;1;1;0;0];[0;0;0;0;0;0;0;0;0;0;1;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;0;0;0;0;0;0;1;1;0;0;0;0]] Output: 6 Explanation: The answer is not 11; because the island must be connected 4-directionally. Example 2: Input: grid = [[0;0;0;0;0;0;0;0]] Output: 0 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 50 grid[i][j] is either 0 or 1.
Google,704,Binary Search,Easy,,
Google,818,Race Car,Hard,"Math, String, Enumeration",
Google,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
Google,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
Google,1497,Check If Array Pairs Are Divisible by k,Med,"Array, Stack, Design","Design a stack that supports increment operations on its elements. Implement the CustomStack class: CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack. void push(int x) Adds x to the top of the stack if the stack has not reached the maxSize. int pop() Pops and returns the top of the stack or -1 if the stack is empty. void inc(int k; int val) Increments the bottom k elements of the stack by val. If there are less than k elements in the stack; increment all the elements in the stack. Example 1: Input [""CustomStack"";""push"";""push"";""pop"";""push"";""push"";""push"";""increment"";""increment"";""pop"";""pop"";""pop"";""pop""] [[3];[1];[2];[];[2];[3];[4];[5;100];[2;100];[];[];[];[]] Output [null;null;null;2;null;null;null;null;null;103;202;201;-1] Explanation CustomStack stk = new CustomStack(3); // Stack is Empty [] stk.push(1); // stack becomes [1] stk.push(2); // stack becomes [1; 2] stk.pop(); // return 2 --> Return top of the stack 2; stack becomes [1] stk.push(2); // stack becomes [1; 2] stk.push(3); // stack becomes [1; 2; 3] stk.push(4); // stack still [1; 2; 3]; Do not add another elements as size is 4 stk.increment(5; 100); // stack becomes [101; 102; 103] stk.increment(2; 100); // stack becomes [201; 202; 103] stk.pop(); // return 103 --> Return top of the stack 103; stack becomes [201; 202] stk.pop(); // return 202 --> Return top of the stack 202; stack becomes [201] stk.pop(); // return 201 --> Return top of the stack 201; stack becomes [] stk.pop(); // return -1 --> Stack is empty return -1. Constraints: 1 <= maxSize; x; k <= 1000 0 <= val <= 100 At most 1000 calls will be made to each method of increment; push and pop each separately."
Google,3287,Find the Maximum Sequence Value of Array,Hard,Database,
Google,16,3Sum Closest,Med,"Array, Two Pointers, Sorting",Given an integer array nums of length n and an integer target; find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution. Example 1: Input: nums = [-1;2;1;-4]; target = 1 Output: 2 Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2). Example 2: Input: nums = [0;0;0]; target = 1 Output: 0 Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0). Constraints: 3 <= nums.length <= 500 -1000 <= nums[i] <= 1000 -104 <= target <= 104
Google,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Google,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Google,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
Google,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Google,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Google,57,Insert Interval,Med,Array,You are given an array of non-overlapping intervals intervals where intervals[i] = [starti; endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start; end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary). Return intervals after the insertion. Note that you don't need to modify intervals in-place. You can make a new array and return it. Example 1: Input: intervals = [[1;3];[6;9]]; newInterval = [2;5] Output: [[1;5];[6;9]] Example 2: Input: intervals = [[1;2];[3;5];[6;7];[8;10];[12;16]]; newInterval = [4;8] Output: [[1;2];[3;10];[12;16]] Explanation: Because the new interval [4;8] overlaps with [3;5];[6;7];[8;10]. Constraints: 0 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 105 intervals is sorted by starti in ascending order. newInterval.length == 2 0 <= start <= end <= 105
Google,66,Plus One,Easy,"Array, Math",You are given a large integer represented as an integer array digits; where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0's. Increment the large integer by one and return the resulting array of digits. Example 1: Input: digits = [1;2;3] Output: [1;2;4] Explanation: The array represents the integer 123. Incrementing by one gives 123 + 1 = 124. Thus; the result should be [1;2;4]. Example 2: Input: digits = [4;3;2;1] Output: [4;3;2;2] Explanation: The array represents the integer 4321. Incrementing by one gives 4321 + 1 = 4322. Thus; the result should be [4;3;2;2]. Example 3: Input: digits = [9] Output: [1;0] Explanation: The array represents the integer 9. Incrementing by one gives 9 + 1 = 10. Thus; the result should be [1;0]. Constraints: 1 <= digits.length <= 100 0 <= digits[i] <= 9 digits does not contain any leading 0's.
Google,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
Google,100,Same Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the roots of two binary trees p and q; write a function to check if they are the same or not. Two binary trees are considered the same if they are structurally identical; and the nodes have the same value. Example 1: Input: p = [1;2;3]; q = [1;2;3] Output: true Example 2: Input: p = [1;2]; q = [1;null;2] Output: false Example 3: Input: p = [1;2;1]; q = [1;1;2] Output: false Constraints: The number of nodes in both trees is in the range [0; 100]. -104 <= Node.val <= 104
Google,101,Symmetric Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; check whether it is a mirror of itself (i.e.; symmetric around its center). Example 1: Input: root = [1;2;2;3;4;4;3] Output: true Example 2: Input: root = [1;2;2;null;3;null;3] Output: false Constraints: The number of nodes in the tree is in the range [1; 1000]. -100 <= Node.val <= 100 Follow up: Could you solve it both recursively and iteratively?
Google,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Google,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Google,125,Valid Palindrome,Easy,"Two Pointers, String","A phrase is a palindrome if; after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters; it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s; return true if it is a palindrome; or false otherwise. Example 1: Input: s = ""A man; a plan; a canal: Panama"" Output: true Explanation: ""amanaplanacanalpanama"" is a palindrome. Example 2: Input: s = ""race a car"" Output: false Explanation: ""raceacar"" is not a palindrome. Example 3: Input: s = "" "" Output: true Explanation: s is an empty string """" after removing non-alphanumeric characters. Since an empty string reads the same forward and backward; it is a palindrome. Constraints: 1 <= s.length <= 2 * 105 s consists only of printable ASCII characters."
Google,141,Linked List Cycle,Easy,"Hash Table, Linked List, Two Pointers",Given head; the head of a linked list; determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise; return false. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 1st node (0-indexed). Example 2: Input: head = [1;2]; pos = 0 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 0th node. Example 3: Input: head = [1]; pos = -1 Output: false Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Google,150,Evaluate Reverse Polish Notation,Med,"Array, Math, Stack","You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression. Return an integer that represents the value of the expression. Note that: The valid operators are '+'; '-'; '*'; and '/'. Each operand may be an integer or another expression. The division between two integers always truncates toward zero. There will not be any division by zero. The input represents a valid arithmetic expression in a reverse polish notation. The answer and all the intermediate calculations can be represented in a 32-bit integer. Example 1: Input: tokens = [""2"";""1"";""+"";""3"";""*""] Output: 9 Explanation: ((2 + 1) * 3) = 9 Example 2: Input: tokens = [""4"";""13"";""5"";""/"";""+""] Output: 6 Explanation: (4 + (13 / 5)) = 6 Example 3: Input: tokens = [""10"";""6"";""9"";""3"";""+"";""-11"";""*"";""/"";""*"";""17"";""+"";""5"";""+""] Output: 22 Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 = ((10 * (6 / (12 * -11))) + 17) + 5 = ((10 * (6 / -132)) + 17) + 5 = ((10 * 0) + 17) + 5 = (0 + 17) + 5 = 17 + 5 = 22 Constraints: 1 <= tokens.length <= 104 tokens[i] is either an operator: ""+""; ""-""; ""*""; or ""/""; or an integer in the range [-200; 200]."
Google,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Google,217,Contains Duplicate,Easy,"Array, Hash Table, Sorting",Given an integer array nums; return true if any value appears at least twice in the array; and return false if every element is distinct. Example 1: Input: nums = [1;2;3;1] Output: true Explanation: The element 1 occurs at the indices 0 and 3. Example 2: Input: nums = [1;2;3;4] Output: false Explanation: All elements are distinct. Example 3: Input: nums = [1;1;1;3;3;4;3;2;4;2] Output: true Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109
Google,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Google,225,Implement Stack using Queues,Easy,"Stack, Design, Queue","Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push; top; pop; and empty). Implement the MyStack class: void push(int x) Pushes element x to the top of the stack. int pop() Removes the element on the top of the stack and returns it. int top() Returns the element on the top of the stack. boolean empty() Returns true if the stack is empty; false otherwise. Notes: You must use only standard operations of a queue; which means that only push to back; peek/pop from front; size and is empty operations are valid. Depending on your language; the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations. Example 1: Input [""MyStack""; ""push""; ""push""; ""top""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 2; 2; false] Explanation MyStack myStack = new MyStack(); myStack.push(1); myStack.push(2); myStack.top(); // return 2 myStack.pop(); // return 2 myStack.empty(); // return False Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; top; and empty. All the calls to pop and top are valid. Follow-up: Can you implement the stack using only one queue?"
Google,278,First Bad Version,Easy,"Binary Search, Interactive",You are a product manager and currently leading a team to develop a new product. Unfortunately; the latest version of your product fails the quality check. Since each version is developed based on the previous version; all the versions after a bad version are also bad. Suppose you have n versions [1; 2; ...; n] and you want to find out the first bad one; which causes all the following ones to be bad. You are given an API bool isBadVersion(version) which returns whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API. Example 1: Input: n = 5; bad = 4 Output: 4 Explanation: call isBadVersion(3) -> false call isBadVersion(5) -> true call isBadVersion(4) -> true Then 4 is the first bad version. Example 2: Input: n = 1; bad = 1 Output: 1 Constraints: 1 <= bad <= n <= 231 - 1
Google,386,Lexicographical Numbers,Med,"Depth-First Search, Trie",Given an integer n; return all the numbers in the range [1; n] sorted in lexicographical order. You must write an algorithm that runs in O(n) time and uses O(1) extra space. Example 1: Input: n = 13 Output: [1;10;11;12;13;2;3;4;5;6;7;8;9] Example 2: Input: n = 2 Output: [1;2] Constraints: 1 <= n <= 5 * 104
Google,416,Partition Equal Subset Sum,Med,"Array, Dynamic Programming",Given an integer array nums; return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise. Example 1: Input: nums = [1;5;11;5] Output: true Explanation: The array can be partitioned as [1; 5; 5] and [11]. Example 2: Input: nums = [1;2;3;5] Output: false Explanation: The array cannot be partitioned into equal sum subsets. Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 100
Google,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Google,862,Shortest Subarray with Sum at Least K,Hard,"Array, Hash Table, String, Sorting","You are given a 0-indexed string s that you must perform k replacement operations on. The replacement operations are given as three 0-indexed parallel arrays; indices; sources; and targets; all of length k. To complete the ith replacement operation: Check if the substring sources[i] occurs at index indices[i] in the original string s. If it does not occur; do nothing. Otherwise if it does occur; replace that substring with targets[i]. For example; if s = ""abcd""; indices[i] = 0; sources[i] = ""ab""; and targets[i] = ""eee""; then the result of this replacement will be ""eeecd"". All replacement operations must occur simultaneously; meaning the replacement operations should not affect the indexing of each other. The testcases will be generated such that the replacements will not overlap. For example; a testcase with s = ""abc""; indices = [0; 1]; and sources = [""ab"";""bc""] will not be generated because the ""ab"" and ""bc"" replacements overlap. Return the resulting string after performing all replacement operations on s. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""abcd""; indices = [0; 2]; sources = [""a""; ""cd""]; targets = [""eee""; ""ffff""] Output: ""eeebffff"" Explanation: ""a"" occurs at index 0 in s; so we replace it with ""eee"". ""cd"" occurs at index 2 in s; so we replace it with ""ffff"". Example 2: Input: s = ""abcd""; indices = [0; 2]; sources = [""ab"";""ec""]; targets = [""eee"";""ffff""] Output: ""eeecd"" Explanation: ""ab"" occurs at index 0 in s; so we replace it with ""eee"". ""ec"" does not occur at index 2 in s; so we do nothing. Constraints: 1 <= s.length <= 1000 k == indices.length == sources.length == targets.length 1 <= k <= 100 0 <= indexes[i] < s.length 1 <= sources[i].length; targets[i].length <= 50 s consists of only lowercase English letters. sources[i] and targets[i] consist of only lowercase English letters."
Google,975,Odd Even Jump,Hard,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root node of a binary search tree and two integers low and high; return the sum of values of all nodes with a value in the inclusive range [low; high]. Example 1: Input: root = [10;5;15;3;7;null;18]; low = 7; high = 15 Output: 32 Explanation: Nodes 7; 10; and 15 are in the range [7; 15]. 7 + 10 + 15 = 32. Example 2: Input: root = [10;5;15;3;7;13;18;1;null;6]; low = 6; high = 10 Output: 23 Explanation: Nodes 6; 7; and 10 are in the range [6; 10]. 6 + 7 + 10 = 23. Constraints: The number of nodes in the tree is in the range [1; 2 * 104]. 1 <= Node.val <= 105 1 <= low <= high <= 105 All Node.val are unique.
Google,1071,Greatest Common Divisor of Strings,Easy,"Array, Bit Manipulation",You are given a binary array nums (0-indexed). We define xi as the number whose binary representation is the subarray nums[0..i] (from most-significant-bit to least-significant-bit). For example; if nums = [1;0;1]; then x0 = 1; x1 = 2; and x2 = 5. Return an array of booleans answer where answer[i] is true if xi is divisible by 5. Example 1: Input: nums = [0;1;1] Output: [true;false;false] Explanation: The input numbers in binary are 0; 01; 011; which are 0; 1; and 3 in base-10. Only the first number is divisible by 5; so answer[0] is true. Example 2: Input: nums = [1;1;1] Output: [false;false;false] Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Google,1331,Rank Transform of an Array,Easy,"Array, Backtracking, Matrix",In a gold mine grid of size m x n; each cell in this mine has an integer representing the amount of gold in that cell; 0 if it is empty. Return the maximum amount of gold you can collect under the conditions: Every time you are located in a cell you will collect all the gold in that cell. From your position; you can walk one step to the left; right; up; or down. You can't visit the same cell more than once. Never visit a cell with 0 gold. You can start and stop collecting gold from any position in the grid that has some gold. Example 1: Input: grid = [[0;6;0];[5;8;7];[0;9;0]] Output: 24 Explanation: [[0;6;0]; [5;8;7]; [0;9;0]] Path to get the maximum gold; 9 -> 8 -> 7. Example 2: Input: grid = [[1;0;7];[2;0;6];[3;4;5];[0;3;0];[9;0;20]] Output: 28 Explanation: [[1;0;7]; [2;0;6]; [3;4;5]; [0;3;0]; [9;0;20]] Path to get the maximum gold; 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 15 0 <= grid[i][j] <= 100 There are at most 25 cells containing gold.
Google,1405,Longest Happy String,Med,Database,
Google,1207,Unique Number of Occurrences,Easy,"Array, Hash Table, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; each node in the tree has a distinct value. After deleting all nodes with a value in to_delete; we are left with a forest (a disjoint union of trees). Return the roots of the trees in the remaining forest. You may return the result in any order. Example 1: Input: root = [1;2;3;4;5;6;7]; to_delete = [3;5] Output: [[1;2;null;4];[6];[7]] Example 2: Input: root = [1;2;4;null;3]; to_delete = [3] Output: [[1;2;4]] Constraints: The number of nodes in the given tree is at most 1000. Each node has a distinct value between 1 and 1000. to_delete.length <= 1000 to_delete contains distinct values between 1 and 1000.
Google,1963,Minimum Number of Swaps to Make the String Balanced,Med,"Array, Math, Bit Manipulation",The XOR sum of a list is the bitwise XOR of all its elements. If the list only contains one element; then its XOR sum will be equal to this element. For example; the XOR sum of [1;2;3;4] is equal to 1 XOR 2 XOR 3 XOR 4 = 4; and the XOR sum of [3] is equal to 3. You are given two 0-indexed arrays arr1 and arr2 that consist only of non-negative integers. Consider the list containing the result of arr1[i] AND arr2[j] (bitwise AND) for every (i; j) pair where 0 <= i < arr1.length and 0 <= j < arr2.length. Return the XOR sum of the aforementioned list. Example 1: Input: arr1 = [1;2;3]; arr2 = [6;5] Output: 0 Explanation: The list = [1 AND 6; 1 AND 5; 2 AND 6; 2 AND 5; 3 AND 6; 3 AND 5] = [0;1;2;0;2;1]. The XOR sum = 0 XOR 1 XOR 2 XOR 0 XOR 2 XOR 1 = 0. Example 2: Input: arr1 = [12]; arr2 = [4] Output: 4 Explanation: The list = [12 AND 4] = [4]. The XOR sum = 4. Constraints: 1 <= arr1.length; arr2.length <= 105 0 <= arr1[i]; arr2[j] <= 109
Google,2534,Time Taken to Cross the Door,Hard,Database,
Google,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Google,29,Divide Two Integers,Med,"Math, Bit Manipulation",Given two integers dividend and divisor; divide two integers without using multiplication; division; and mod operator. The integer division should truncate toward zero; which means losing its fractional part. For example; 8.345 would be truncated to 8; and -2.7335 would be truncated to -2. Return the quotient after dividing dividend by divisor. Note: Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−231; 231 − 1]. For this problem; if the quotient is strictly greater than 231 - 1; then return 231 - 1; and if the quotient is strictly less than -231; then return -231. Example 1: Input: dividend = 10; divisor = 3 Output: 3 Explanation: 10/3 = 3.33333.. which is truncated to 3. Example 2: Input: dividend = 7; divisor = -3 Output: -2 Explanation: 7/-3 = -2.33333.. which is truncated to -2. Constraints: -231 <= dividend; divisor <= 231 - 1 divisor != 0
Google,32,Longest Valid Parentheses,Hard,"String, Dynamic Programming, Stack","Given a string containing just the characters '(' and ')'; return the length of the longest valid (well-formed) parentheses substring. Example 1: Input: s = ""(()"" Output: 2 Explanation: The longest valid parentheses substring is ""()"". Example 2: Input: s = "")()())"" Output: 4 Explanation: The longest valid parentheses substring is ""()()"". Example 3: Input: s = """" Output: 0 Constraints: 0 <= s.length <= 3 * 104 s[i] is '('; or ')'."
Google,62,Unique Paths,Med,"Math, Dynamic Programming, Combinatorics",There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n; return the number of possible unique paths that the robot can take to reach the bottom-right corner. The test cases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: m = 3; n = 7 Output: 28 Example 2: Input: m = 3; n = 2 Output: 3 Explanation: From the top-left corner; there are a total of 3 ways to reach the bottom-right corner: 1. Right -> Down -> Down 2. Down -> Down -> Right 3. Down -> Right -> Down Constraints: 1 <= m; n <= 100
Google,69,Sqrt(x),Easy,"Math, Binary Search",Given a non-negative integer x; return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. For example; do not use pow(x; 0.5) in c++ or x ** 0.5 in python. Example 1: Input: x = 4 Output: 2 Explanation: The square root of 4 is 2; so we return 2. Example 2: Input: x = 8 Output: 2 Explanation: The square root of 8 is 2.82842...; and since we round it down to the nearest integer; 2 is returned. Constraints: 0 <= x <= 231 - 1
Google,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Google,83,Remove Duplicates from Sorted List,Easy,Linked List,Given the head of a sorted linked list; delete all duplicates such that each element appears only once. Return the linked list sorted as well. Example 1: Input: head = [1;1;2] Output: [1;2] Example 2: Input: head = [1;1;2;3;3] Output: [1;2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Google,85,Maximal Rectangle,Hard,"Array, Dynamic Programming, Stack, Matrix, Monotonic Stack","Given a rows x cols binary matrix filled with 0's and 1's; find the largest rectangle containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 6 Explanation: The maximal rectangle is shown in the above picture. Example 2: Input: matrix = [[""0""]] Output: 0 Example 3: Input: matrix = [[""1""]] Output: 1 Constraints: rows == matrix.length cols == matrix[i].length 1 <= row; cols <= 200 matrix[i][j] is '0' or '1'."
Google,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
Google,134,Gas Station,Med,"Array, Greedy",There are n gas stations along a circular route; where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations. Given two integer arrays gas and cost; return the starting gas station's index if you can travel around the circuit once in the clockwise direction; otherwise return -1. If there exists a solution; it is guaranteed to be unique. Example 1: Input: gas = [1;2;3;4;5]; cost = [3;4;5;1;2] Output: 3 Explanation: Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 4. Your tank = 4 - 1 + 5 = 8 Travel to station 0. Your tank = 8 - 2 + 1 = 7 Travel to station 1. Your tank = 7 - 3 + 2 = 6 Travel to station 2. Your tank = 6 - 4 + 3 = 5 Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. Therefore; return 3 as the starting index. Example 2: Input: gas = [2;3;4]; cost = [3;4;3] Output: -1 Explanation: You can't start at station 0 or 1; as there is not enough gas to travel to the next station. Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 0. Your tank = 4 - 3 + 2 = 3 Travel to station 1. Your tank = 3 - 3 + 3 = 3 You cannot travel back to station 2; as it requires 4 unit of gas but you only have 3. Therefore; you can't travel around the circuit once no matter where you start. Constraints: n == gas.length == cost.length 1 <= n <= 105 0 <= gas[i]; cost[i] <= 104
Google,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Google,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Google,202,Happy Number,Easy,"Hash Table, Math, Two Pointers",Write an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer; replace the number by the sum of the squares of its digits. Repeat the process until the number equals 1 (where it will stay); or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy. Return true if n is a happy number; and false if not. Example 1: Input: n = 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1 Example 2: Input: n = 2 Output: false Constraints: 1 <= n <= 231 - 1
Google,204,Count Primes,Med,"Array, Math, Enumeration, Number Theory",Given an integer n; return the number of prime numbers that are strictly less than n. Example 1: Input: n = 10 Output: 4 Explanation: There are 4 prime numbers less than 10; they are 2; 3; 5; 7. Example 2: Input: n = 0 Output: 0 Example 3: Input: n = 1 Output: 0 Constraints: 0 <= n <= 5 * 106
Google,214,Shortest Palindrome,Hard,"String, Rolling Hash, String Matching, Hash Function","You are given a string s. You can convert s to a palindrome by adding characters in front of it. Return the shortest palindrome you can find by performing this transformation. Example 1: Input: s = ""aacecaaa"" Output: ""aaacecaaa"" Example 2: Input: s = ""abcd"" Output: ""dcbabcd"" Constraints: 0 <= s.length <= 5 * 104 s consists of lowercase English letters only."
Google,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Google,226,Invert Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; invert the tree; and return its root. Example 1: Input: root = [4;2;7;1;3;6;9] Output: [4;7;2;9;6;3;1] Example 2: Input: root = [2;1;3] Output: [2;3;1] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Google,228,Summary Ranges,Easy,Array,"You are given a sorted unique integer array nums. A range [a;b] is the set of all integers from a to b (inclusive). Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is; each element of nums is covered by exactly one of the ranges; and there is no integer x such that x is in one of the ranges but not in nums. Each range [a;b] in the list should be output as: ""a->b"" if a != b ""a"" if a == b Example 1: Input: nums = [0;1;2;4;5;7] Output: [""0->2"";""4->5"";""7""] Explanation: The ranges are: [0;2] --> ""0->2"" [4;5] --> ""4->5"" [7;7] --> ""7"" Example 2: Input: nums = [0;2;3;4;6;8;9] Output: [""0"";""2->4"";""6"";""8->9""] Explanation: The ranges are: [0;0] --> ""0"" [2;4] --> ""2->4"" [6;6] --> ""6"" [8;9] --> ""8->9"" Constraints: 0 <= nums.length <= 20 -231 <= nums[i] <= 231 - 1 All the values of nums are unique. nums is sorted in ascending order."
Google,234,Palindrome Linked List,Easy,"Linked List, Two Pointers, Stack, Recursion",Given the head of a singly linked list; return true if it is a palindrome or false otherwise. Example 1: Input: head = [1;2;2;1] Output: true Example 2: Input: head = [1;2] Output: false Constraints: The number of nodes in the list is in the range [1; 105]. 0 <= Node.val <= 9 Follow up: Could you do it in O(n) time and O(1) space?
Google,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
Google,258,Add Digits,Easy,"Math, Simulation, Number Theory",Given an integer num; repeatedly add all its digits until the result has only one digit; and return it. Example 1: Input: num = 38 Output: 2 Explanation: The process is 38 --> 3 + 8 --> 11 11 --> 1 + 1 --> 2 Since 2 has only one digit; return it. Example 2: Input: num = 0 Output: 0 Constraints: 0 <= num <= 231 - 1 Follow up: Could you do it without any loop/recursion in O(1) runtime?
Google,346,Moving Average from Data Stream,Easy,"Array, Design, Queue, Data Stream",
Google,392,Is Subsequence,Easy,"Two Pointers, String, Dynamic Programming","Given two strings s and t; return true if s is a subsequence of t; or false otherwise. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not). Example 1: Input: s = ""abc""; t = ""ahbgdc"" Output: true Example 2: Input: s = ""axc""; t = ""ahbgdc"" Output: false Constraints: 0 <= s.length <= 100 0 <= t.length <= 104 s and t consist only of lowercase English letters. Follow up: Suppose there are lots of incoming s; say s1; s2; ...; sk where k >= 109; and you want to check one by one to see if t has its subsequence. In this scenario; how would you change your code?"
Google,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Google,540,Single Element in a Sorted Array,Med,"Array, Binary Search",You are given a sorted array consisting of only integers where every element appears exactly twice; except for one element which appears exactly once. Return the single element that appears only once. Your solution must run in O(log n) time and O(1) space. Example 1: Input: nums = [1;1;2;3;3;4;4;8;8] Output: 2 Example 2: Input: nums = [3;3;7;7;10;11;11] Output: 10 Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 105
Google,547,Number of Provinces,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",There are n cities. Some of them are connected; while some are not. If city a is connected directly with city b; and city b is connected directly with city c; then city a is connected indirectly with city c. A province is a group of directly or indirectly connected cities and no other cities outside of the group. You are given an n x n matrix isConnected where isConnected[i][j] = 1 if the ith city and the jth city are directly connected; and isConnected[i][j] = 0 otherwise. Return the total number of provinces. Example 1: Input: isConnected = [[1;1;0];[1;1;0];[0;0;1]] Output: 2 Example 2: Input: isConnected = [[1;0;0];[0;1;0];[0;0;1]] Output: 3 Constraints: 1 <= n <= 200 n == isConnected.length n == isConnected[i].length isConnected[i][j] is 1 or 0. isConnected[i][i] == 1 isConnected[i][j] == isConnected[j][i]
Google,570,Managers with at Least 5 Direct Reports,Med,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | department | varchar | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the name of an employee; their department; and the id of their manager. If managerId is null; then the employee does not have a manager. No employee will be the manager of themself. Write a solution to find managers with at least five direct reports. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +-----+-------+------------+-----------+ | id | name | department | managerId | +-----+-------+------------+-----------+ | 101 | John | A | null | | 102 | Dan | A | 101 | | 103 | James | A | 101 | | 104 | Amy | A | 101 | | 105 | Anne | A | 101 | | 106 | Ron | B | 101 | +-----+-------+------------+-----------+ Output: +------+ | name | +------+ | John | +------+
Google,652,Find Duplicate Subtrees,Med,"Hash Table, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return all duplicate subtrees. For each kind of duplicate subtrees; you only need to return the root node of any one of them. Two trees are duplicate if they have the same structure with the same node values. Example 1: Input: root = [1;2;3;4;null;2;4;null;null;4] Output: [[2;4];[4]] Example 2: Input: root = [2;1;1] Output: [[1]] Example 3: Input: root = [2;2;2;3;null;3;null] Output: [[2;3];[3]] Constraints: The number of the nodes in the tree will be in the range [1; 5000] -200 <= Node.val <= 200
Google,721,Accounts Merge,Med,"Array, Hash Table, String, Depth-First Search, Breadth-First Search, Union Find, Sorting","Given a list of accounts where each element accounts[i] is a list of strings; where the first element accounts[i][0] is a name; and the rest of the elements are emails representing emails of the account. Now; we would like to merge these accounts. Two accounts definitely belong to the same person if there is some common email to both accounts. Note that even if two accounts have the same name; they may belong to different people as people could have the same name. A person can have any number of accounts initially; but all of their accounts definitely have the same name. After merging the accounts; return the accounts in the following format: the first element of each account is the name; and the rest of the elements are emails in sorted order. The accounts themselves can be returned in any order. Example 1: Input: accounts = [[""John"";""johnsmith@mail.com"";""john_newyork@mail.com""];[""John"";""johnsmith@mail.com"";""john00@mail.com""];[""Mary"";""mary@mail.com""];[""John"";""johnnybravo@mail.com""]] Output: [[""John"";""john00@mail.com"";""john_newyork@mail.com"";""johnsmith@mail.com""];[""Mary"";""mary@mail.com""];[""John"";""johnnybravo@mail.com""]] Explanation: The first and second John's are the same person as they have the common email ""johnsmith@mail.com"". The third John and Mary are different people as none of their email addresses are used by other accounts. We could return these lists in any order; for example the answer [['Mary'; 'mary@mail.com']; ['John'; 'johnnybravo@mail.com']; ['John'; 'john00@mail.com'; 'john_newyork@mail.com'; 'johnsmith@mail.com']] would still be accepted. Example 2: Input: accounts = [[""Gabe"";""Gabe0@m.co"";""Gabe3@m.co"";""Gabe1@m.co""];[""Kevin"";""Kevin3@m.co"";""Kevin5@m.co"";""Kevin0@m.co""];[""Ethan"";""Ethan5@m.co"";""Ethan4@m.co"";""Ethan0@m.co""];[""Hanzo"";""Hanzo3@m.co"";""Hanzo1@m.co"";""Hanzo0@m.co""];[""Fern"";""Fern5@m.co"";""Fern1@m.co"";""Fern0@m.co""]] Output: [[""Ethan"";""Ethan0@m.co"";""Ethan4@m.co"";""Ethan5@m.co""];[""Gabe"";""Gabe0@m.co"";""Gabe1@m.co"";""Gabe3@m.co""];[""Hanzo"";""Hanzo0@m.co"";""Hanzo1@m.co"";""Hanzo3@m.co""];[""Kevin"";""Kevin0@m.co"";""Kevin3@m.co"";""Kevin5@m.co""];[""Fern"";""Fern0@m.co"";""Fern1@m.co"";""Fern5@m.co""]] Constraints: 1 <= accounts.length <= 1000 2 <= accounts[i].length <= 10 1 <= accounts[i][j].length <= 30 accounts[i][0] consists of English letters. accounts[i][j] (for j > 0) is a valid email."
Google,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Google,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
Google,703,Kth Largest Element in a Stream,Easy,,
Google,641,Design Circular Deque,Med,,
Google,875,Koko Eating Bananas,Med,"Array, Two Pointers, Dynamic Programming, Enumeration",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr; return the length of the longest subarray; which is a mountain. Return 0 if there is no mountain subarray. Example 1: Input: arr = [2;1;4;7;3;2;5] Output: 5 Explanation: The largest mountain is [1;4;7;3;2] which has length 5. Example 2: Input: arr = [2;2;2] Output: 0 Explanation: There is no mountain. Constraints: 1 <= arr.length <= 104 0 <= arr[i] <= 104 Follow up: Can you solve it using only one pass? Can you solve it in O(1) space?
Google,987,Vertical Order Traversal of a Binary Tree,Hard,"Array, Queue, Sorting, Simulation",You are given an integer array deck. There is a deck of cards where every card has a unique integer. The integer on the ith card is deck[i]. You can order the deck in any order you want. Initially; all the cards start face down (unrevealed) in one deck. You will do the following steps repeatedly until all cards are revealed: Take the top card of the deck; reveal it; and take it out of the deck. If there are still cards in the deck then put the next top card of the deck at the bottom of the deck. If there are still unrevealed cards; go back to step 1. Otherwise; stop. Return an ordering of the deck that would reveal the cards in increasing order. Note that the first entry in the answer is considered to be the top of the deck. Example 1: Input: deck = [17;13;11;2;3;5;7] Output: [2;13;3;11;5;17;7] Explanation: We get the deck in the order [17;13;11;2;3;5;7] (this order does not matter); and reorder it. After reordering; the deck starts as [2;13;3;11;5;17;7]; where 2 is the top of the deck. We reveal 2; and move 13 to the bottom. The deck is now [3;11;5;17;7;13]. We reveal 3; and move 11 to the bottom. The deck is now [5;17;7;13;11]. We reveal 5; and move 17 to the bottom. The deck is now [7;13;11;17]. We reveal 7; and move 13 to the bottom. The deck is now [11;17;13]. We reveal 11; and move 17 to the bottom. The deck is now [13;17]. We reveal 13; and move 17 to the bottom. The deck is now [17]. We reveal 17. Since all the cards revealed are in increasing order; the answer is correct. Example 2: Input: deck = [1;1000] Output: [1;1000] Constraints: 1 <= deck.length <= 1000 1 <= deck[i] <= 106 All the values of deck are unique.
Google,1249,Minimum Remove to Make Valid Parentheses,Med,"Array, Hash Table, Binary Search, Design","Implement a SnapshotArray that supports the following interface: SnapshotArray(int length) initializes an array-like data structure with the given length. Initially; each element equals 0. void set(index; val) sets the element at the given index to be equal to val. int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1. int get(index; snap_id) returns the value at the given index; at the time we took the snapshot with the given snap_id Example 1: Input: [""SnapshotArray"";""set"";""snap"";""set"";""get""] [[3];[0;5];[];[0;6];[0;0]] Output: [null;null;0;null;5] Explanation: SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3 snapshotArr.set(0;5); // Set array[0] = 5 snapshotArr.snap(); // Take a snapshot; return snap_id = 0 snapshotArr.set(0;6); snapshotArr.get(0;0); // Get the value of array[0] with snap_id = 0; return 5 Constraints: 1 <= length <= 5 * 104 0 <= index < length 0 <= val <= 109 0 <= snap_id < (the total number of times we call snap()) At most 5 * 104 calls will be made to set; snap; and get."
Google,1277,Count Square Submatrices with All Ones,Med,"Array, Dynamic Programming, Greedy","Given an array of digits digits; return the largest multiple of three that can be formed by concatenating some of the given digits in any order. If there is no answer return an empty string. Since the answer may not fit in an integer data type; return the answer as a string. Note that the returning answer must not contain unnecessary leading zeros. Example 1: Input: digits = [8;1;9] Output: ""981"" Example 2: Input: digits = [8;6;7;1;0] Output: ""8760"" Example 3: Input: digits = [1] Output: """" Constraints: 1 <= digits.length <= 104 0 <= digits[i] <= 9"
Google,1492,The kth Factor of n,Med,"Tree, Depth-First Search, Breadth-First Search",A company has n employees with a unique ID for each employee from 0 to n - 1. The head of the company is the one with headID. Each employee has one direct manager given in the manager array where manager[i] is the direct manager of the i-th employee; manager[headID] = -1. Also; it is guaranteed that the subordination relationships have a tree structure. The head of the company wants to inform all the company employees of an urgent piece of news. He will inform his direct subordinates; and they will inform their subordinates; and so on until all employees know about the urgent news. The i-th employee needs informTime[i] minutes to inform all of his direct subordinates (i.e.; After informTime[i] minutes; all his direct subordinates can start spreading the news). Return the number of minutes needed to inform all the employees about the urgent news. Example 1: Input: n = 1; headID = 0; manager = [-1]; informTime = [0] Output: 0 Explanation: The head of the company is the only employee in the company. Example 2: Input: n = 6; headID = 2; manager = [2;2;-1;2;2;2]; informTime = [0;0;1;0;0;0] Output: 1 Explanation: The head of the company with id = 2 is the direct manager of all the employees in the company and needs 1 minute to inform them all. The tree structure of the employees in the company is shown. Constraints: 1 <= n <= 105 0 <= headID < n manager.length == n 0 <= manager[i] < n manager[headID] == -1 informTime.length == n 0 <= informTime[i] <= 1000 informTime[i] == 0 if employee i has no subordinates. It is guaranteed that all the employees can be informed.
Google,1942,The Number of the Smallest Unoccupied Chair,Med,Database,Table: Employee +---------------+---------+ | Column Name | Type | +---------------+---------+ | employee_id | int | | department_id | int | | primary_flag | varchar | +---------------+---------+ (employee_id; department_id) is the primary key (combination of columns with unique values) for this table. employee_id is the id of the employee. department_id is the id of the department to which the employee belongs. primary_flag is an ENUM (category) of type ('Y'; 'N'). If the flag is 'Y'; the department is the primary department for the employee. If the flag is 'N'; the department is not the primary. Employees can belong to multiple departments. When the employee joins other departments; they need to decide which department is their primary department. Note that when an employee belongs to only one department; their primary column is 'N'. Write a solution to report all the employees with their primary department. For employees who belong to one department; report their only department. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +-------------+---------------+--------------+ | employee_id | department_id | primary_flag | +-------------+---------------+--------------+ | 1 | 1 | N | | 2 | 1 | Y | | 2 | 2 | N | | 3 | 3 | N | | 4 | 2 | N | | 4 | 3 | Y | | 4 | 4 | N | +-------------+---------------+--------------+ Output: +-------------+---------------+ | employee_id | department_id | +-------------+---------------+ | 1 | 1 | | 2 | 1 | | 3 | 3 | | 4 | 3 | +-------------+---------------+ Explanation: - The Primary department for employee 1 is 1. - The Primary department for employee 2 is 1. - The Primary department for employee 3 is 3. - The Primary department for employee 4 is 3.
Google,2018,Check if Word Can Be Placed In Crossword,Med,"Array, Binary Search, Sorting, Prefix Sum",You have n packages that you are trying to place in boxes; one package in each box. There are m suppliers that each produce boxes of different sizes (with infinite supply). A package can be placed in a box if the size of the package is less than or equal to the size of the box. The package sizes are given as an integer array packages; where packages[i] is the size of the ith package. The suppliers are given as a 2D integer array boxes; where boxes[j] is an array of box sizes that the jth supplier produces. You want to choose a single supplier and use boxes from them such that the total wasted space is minimized. For each package in a box; we define the space wasted to be size of the box - size of the package. The total wasted space is the sum of the space wasted in all the boxes. For example; if you have to fit packages with sizes [2;3;5] and the supplier offers boxes of sizes [4;8]; you can fit the packages of size-2 and size-3 into two boxes of size-4 and the package with size-5 into a box of size-8. This would result in a waste of (4-2) + (4-3) + (8-5) = 6. Return the minimum total wasted space by choosing the box supplier optimally; or -1 if it is impossible to fit all the packages inside boxes. Since the answer may be large; return it modulo 109 + 7. Example 1: Input: packages = [2;3;5]; boxes = [[4;8];[2;8]] Output: 6 Explanation: It is optimal to choose the first supplier; using two size-4 boxes and one size-8 box. The total waste is (4-2) + (4-3) + (8-5) = 6. Example 2: Input: packages = [2;3;5]; boxes = [[1;4];[2;3];[3;4]] Output: -1 Explanation: There is no box that the package of size 5 can fit in. Example 3: Input: packages = [3;5;8;10;11;12]; boxes = [[12];[11;9];[10;5;14]] Output: 9 Explanation: It is optimal to choose the third supplier; using two size-5 boxes; two size-10 boxes; and two size-14 boxes. The total waste is (5-3) + (5-5) + (10-8) + (10-10) + (14-11) + (14-12) = 9. Constraints: n == packages.length m == boxes.length 1 <= n <= 105 1 <= m <= 105 1 <= packages[i] <= 105 1 <= boxes[j].length <= 105 1 <= boxes[j][k] <= 105 sum(boxes[j].length) <= 105 The elements in boxes[j] are distinct.
Google,2620,Counter,Easy,"Hash Table, Design, Queue, Counting, Data Stream","For a stream of integers; implement a data structure that checks if the last k integers parsed in the stream are equal to value. Implement the DataStream class: DataStream(int value; int k) Initializes the object with an empty integer stream and the two integers value and k. boolean consec(int num) Adds num to the stream of integers. Returns true if the last k integers are equal to value; and false otherwise. If there are less than k integers; the condition does not hold true; so returns false. Example 1: Input [""DataStream""; ""consec""; ""consec""; ""consec""; ""consec""] [[4; 3]; [4]; [4]; [4]; [3]] Output [null; false; false; true; false] Explanation DataStream dataStream = new DataStream(4; 3); //value = 4; k = 3 dataStream.consec(4); // Only 1 integer is parsed; so returns False. dataStream.consec(4); // Only 2 integers are parsed. // Since 2 is less than k; returns False. dataStream.consec(4); // The 3 integers parsed are all equal to value; so returns True. dataStream.consec(3); // The last k integers parsed in the stream are [4;4;3]. // Since 3 is not equal to value; it returns False. Constraints: 1 <= value; num <= 109 1 <= k <= 105 At most 105 calls will be made to consec."
Google,2703,Return Length of Arguments Passed,Easy,"Array, Segment Tree",You are given two 0-indexed arrays nums1 and nums2 and a 2D array queries of queries. There are three types of queries: For a query of type 1; queries[i] = [1; l; r]. Flip the values from 0 to 1 and from 1 to 0 in nums1 from index l to index r. Both l and r are 0-indexed. For a query of type 2; queries[i] = [2; p; 0]. For every index 0 <= i < n; set nums2[i] = nums2[i] + nums1[i] * p. For a query of type 3; queries[i] = [3; 0; 0]. Find the sum of the elements in nums2. Return an array containing all the answers to the third type queries. Example 1: Input: nums1 = [1;0;1]; nums2 = [0;0;0]; queries = [[1;1;1];[2;1;0];[3;0;0]] Output: [3] Explanation: After the first query nums1 becomes [1;1;1]. After the second query; nums2 becomes [1;1;1]; so the answer to the third query is 3. Thus; [3] is returned. Example 2: Input: nums1 = [1]; nums2 = [5]; queries = [[2;0;0];[3;0;0]] Output: [5] Explanation: After the first query; nums2 remains [5]; so the answer to the second query is 5. Thus; [5] is returned. Constraints: 1 <= nums1.length;nums2.length <= 105 nums1.length = nums2.length 1 <= queries.length <= 105 queries[i].length = 3 0 <= l <= r <= nums1.length - 1 0 <= p <= 106 0 <= nums1[i] <= 1 0 <= nums2[i] <= 109
Google,2812,Find the Safest Path in a Grid,Med,Math,Given two integers; num and t. A number is achievable if it can become equal to num after applying the following operation: Increase or decrease the number by 1; and simultaneously increase or decrease num by 1. Return the maximum achievable number after applying the operation at most t times. Example 1: Input: num = 4; t = 1 Output: 6 Explanation: Apply the following operation once to make the maximum achievable number equal to num: Decrease the maximum achievable number by 1; and increase num by 1. Example 2: Input: num = 3; t = 2 Output: 7 Explanation: Apply the following operation twice to make the maximum achievable number equal to num: Decrease the maximum achievable number by 1; and increase num by 1. Constraints: 1 <= num; t <= 50
Google,2914,Minimum Number of Changes to Make Binary String Beautiful,Med,"Array, Binary Search, Breadth-First Search, Union Find, Matrix",You are given a 0-indexed 2D matrix grid of size n x n; where (r; c) represents: A cell containing a thief if grid[r][c] = 1 An empty cell if grid[r][c] = 0 You are initially positioned at cell (0; 0). In one move; you can move to any adjacent cell in the grid; including cells containing thieves. The safeness factor of a path on the grid is defined as the minimum manhattan distance from any cell in the path to any thief in the grid. Return the maximum safeness factor of all paths leading to cell (n - 1; n - 1). An adjacent cell of cell (r; c); is one of the cells (r; c + 1); (r; c - 1); (r + 1; c) and (r - 1; c) if it exists. The Manhattan distance between two cells (a; b) and (x; y) is equal to |a - x| + |b - y|; where |val| denotes the absolute value of val. Example 1: Input: grid = [[1;0;0];[0;0;0];[0;0;1]] Output: 0 Explanation: All paths from (0; 0) to (n - 1; n - 1) go through the thieves in cells (0; 0) and (n - 1; n - 1). Example 2: Input: grid = [[0;0;1];[0;0;0];[0;0;0]] Output: 2 Explanation: The path depicted in the picture above has a safeness factor of 2 since: - The closest cell of the path to the thief at cell (0; 2) is cell (0; 0). The distance between them is | 0 - 0 | + | 0 - 2 | = 2. It can be shown that there are no other paths with a higher safeness factor. Example 3: Input: grid = [[0;0;0;1];[0;0;0;0];[0;0;0;0];[1;0;0;0]] Output: 2 Explanation: The path depicted in the picture above has a safeness factor of 2 since: - The closest cell of the path to the thief at cell (0; 3) is cell (1; 2). The distance between them is | 0 - 1 | + | 3 - 2 | = 2. - The closest cell of the path to the thief at cell (3; 0) is cell (3; 2). The distance between them is | 3 - 3 | + | 0 - 2 | = 2. It can be shown that there are no other paths with a higher safeness factor. Constraints: 1 <= grid.length == n <= 400 grid[i].length == n grid[i][j] is either 0 or 1. There is at least one thief in the grid.
Google,12,Integer to Roman,Med,"Hash Table, Math, String","Seven different symbols represent Roman numerals with the following values: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules: If the value does not start with 4 or 9; select the symbol of the maximal value that can be subtracted from the input; append that symbol to the result; subtract its value; and convert the remainder to a Roman numeral. If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol; for example; 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV); 9 (IX); 40 (XL); 90 (XC); 400 (CD) and 900 (CM). Only powers of 10 (I; X; C; M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V); 50 (L); or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form. Given an integer; convert it to a Roman numeral. Example 1: Input: num = 3749 Output: ""MMMDCCXLIX"" Explanation: 3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M) 700 = DCC as 500 (D) + 100 (C) + 100 (C) 40 = XL as 10 (X) less of 50 (L) 9 = IX as 1 (I) less of 10 (X) Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places Example 2: Input: num = 58 Output: ""LVIII"" Explanation: 50 = L 8 = VIII Example 3: Input: num = 1994 Output: ""MCMXCIV"" Explanation: 1000 = M 900 = CM 90 = XC 4 = IV Constraints: 1 <= num <= 3999"
Google,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
Google,24,Swap Nodes in Pairs,Med,"Linked List, Recursion",Given a linked list; swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e.; only nodes themselves may be changed.) Example 1: Input: head = [1;2;3;4] Output: [2;1;4;3] Explanation: Example 2: Input: head = [] Output: [] Example 3: Input: head = [1] Output: [1] Example 4: Input: head = [1;2;3] Output: [2;1;3] Constraints: The number of nodes in the list is in the range [0; 100]. 0 <= Node.val <= 100
Google,43,Multiply Strings,Med,"Math, String, Simulation","Given two non-negative integers num1 and num2 represented as strings; return the product of num1 and num2; also represented as a string. Note: You must not use any built-in BigInteger library or convert the inputs to integer directly. Example 1: Input: num1 = ""2""; num2 = ""3"" Output: ""6"" Example 2: Input: num1 = ""123""; num2 = ""456"" Output: ""56088"" Constraints: 1 <= num1.length; num2.length <= 200 num1 and num2 consist of digits only. Both num1 and num2 do not contain any leading zero; except the number 0 itself."
Google,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Google,80,Remove Duplicates from Sorted Array II,Med,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same. Since it is impossible to change the length of the array in some languages; you must instead have the result be placed in the first part of the array nums. More formally; if there are k elements after removing the duplicates; then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements. Return k after placing the final result in the first k slots of nums. Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;1;2;2;3] Output: 5; nums = [1;1;2;2;3;_] Explanation: Your function should return k = 5; with the first five elements of nums being 1; 1; 2; 2 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;1;2;3;3] Output: 7; nums = [0;0;1;1;2;3;3;_;_] Explanation: Your function should return k = 7; with the first seven elements of nums being 0; 0; 1; 1; 2; 3 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -104 <= nums[i] <= 104 nums is sorted in non-decreasing order.
Google,92,Reverse Linked List II,Med,Linked List,Given the head of a singly linked list and two integers left and right where left <= right; reverse the nodes of the list from position left to position right; and return the reversed list. Example 1: Input: head = [1;2;3;4;5]; left = 2; right = 4 Output: [1;4;3;2;5] Example 2: Input: head = [5]; left = 1; right = 1 Output: [5] Constraints: The number of nodes in the list is n. 1 <= n <= 500 -500 <= Node.val <= 500 1 <= left <= right <= n Follow up: Could you do it in one pass?
Google,93,Restore IP Addresses,Med,"String, Backtracking","A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. For example; ""0.1.2.201"" and ""192.168.1.1"" are valid IP addresses; but ""0.011.255.245""; ""192.168.1.312"" and ""192.168@1.1"" are invalid IP addresses. Given a string s containing only digits; return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order. Example 1: Input: s = ""25525511135"" Output: [""255.255.11.135"";""255.255.111.35""] Example 2: Input: s = ""0000"" Output: [""0.0.0.0""] Example 3: Input: s = ""101023"" Output: [""1.0.10.23"";""1.0.102.3"";""10.1.0.23"";""10.10.2.3"";""101.0.2.3""] Constraints: 1 <= s.length <= 20 s consists of digits only."
Google,94,Binary Tree Inorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the inorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [1;3;2] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [4;2;6;5;7;1;3;9;8] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Google,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Google,102,Binary Tree Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the level order traversal of its nodes' values. (i.e.; from left to right; level by level). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[9;20];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -1000 <= Node.val <= 1000
Google,130,Surrounded Regions,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","You are given an m x n matrix board containing letters 'X' and 'O'; capture regions that are surrounded: Connect: A cell is connected to adjacent cells horizontally or vertically. Region: To form a region connect every 'O' cell. Surround: The region is surrounded with 'X' cells if you can connect the region with 'X' cells and none of the region cells are on the edge of the board. A surrounded region is captured by replacing all 'O's with 'X's in the input matrix board. Example 1: Input: board = [[""X"";""X"";""X"";""X""];[""X"";""O"";""O"";""X""];[""X"";""X"";""O"";""X""];[""X"";""O"";""X"";""X""]] Output: [[""X"";""X"";""X"";""X""];[""X"";""X"";""X"";""X""];[""X"";""X"";""X"";""X""];[""X"";""O"";""X"";""X""]] Explanation: In the above diagram; the bottom region is not captured because it is on the edge of the board and cannot be surrounded. Example 2: Input: board = [[""X""]] Output: [[""X""]] Constraints: m == board.length n == board[i].length 1 <= m; n <= 200 board[i][j] is 'X' or 'O'."
Google,230,Kth Smallest Element in a BST,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree; and an integer k; return the kth smallest value (1-indexed) of all the values of the nodes in the tree. Example 1: Input: root = [3;1;4;null;2]; k = 1 Output: 1 Example 2: Input: root = [5;3;6;2;4;null;null;1]; k = 3 Output: 3 Constraints: The number of nodes in the tree is n. 1 <= k <= n <= 104 0 <= Node.val <= 104 Follow up: If the BST is modified often (i.e.; we can do insert and delete operations) and you need to find the kth smallest frequently; how would you optimize?
Google,236,Lowest Common Ancestor of a Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",Given a binary tree; find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3. Example 2: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [1;2]; p = 1; q = 2 Output: 1 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the tree.
Google,263,Ugly Number,Easy,Math,An ugly number is a positive integer which does not have a prime factor other than 2; 3; and 5. Given an integer n; return true if n is an ugly number. Example 1: Input: n = 6 Output: true Explanation: 6 = 2 × 3 Example 2: Input: n = 1 Output: true Explanation: 1 has no prime factors. Example 3: Input: n = 14 Output: false Explanation: 14 is not ugly since it includes the prime factor 7. Constraints: -231 <= n <= 231 - 1
Google,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Google,328,Odd Even Linked List,Med,Linked List,Given the head of a singly linked list; group all the nodes with odd indices together followed by the nodes with even indices; and return the reordered list. The first node is considered odd; and the second node is even; and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input. You must solve the problem in O(1) extra space complexity and O(n) time complexity. Example 1: Input: head = [1;2;3;4;5] Output: [1;3;5;2;4] Example 2: Input: head = [2;1;3;5;6;4;7] Output: [2;3;6;7;1;5;4] Constraints: The number of nodes in the linked list is in the range [0; 104]. -106 <= Node.val <= 106
Google,332,Reconstruct Itinerary,Hard,"Depth-First Search, Graph, Eulerian Circuit","You are given a list of airline tickets where tickets[i] = [fromi; toi] represent the departure and the arrival airports of one flight. Reconstruct the itinerary in order and return it. All of the tickets belong to a man who departs from ""JFK""; thus; the itinerary must begin with ""JFK"". If there are multiple valid itineraries; you should return the itinerary that has the smallest lexical order when read as a single string. For example; the itinerary [""JFK""; ""LGA""] has a smaller lexical order than [""JFK""; ""LGB""]. You may assume all tickets form at least one valid itinerary. You must use all the tickets once and only once. Example 1: Input: tickets = [[""MUC"";""LHR""];[""JFK"";""MUC""];[""SFO"";""SJC""];[""LHR"";""SFO""]] Output: [""JFK"";""MUC"";""LHR"";""SFO"";""SJC""] Example 2: Input: tickets = [[""JFK"";""SFO""];[""JFK"";""ATL""];[""SFO"";""ATL""];[""ATL"";""JFK""];[""ATL"";""SFO""]] Output: [""JFK"";""ATL"";""JFK"";""SFO"";""ATL"";""SFO""] Explanation: Another possible reconstruction is [""JFK"";""SFO"";""ATL"";""JFK"";""ATL"";""SFO""] but it is larger in lexical order. Constraints: 1 <= tickets.length <= 300 tickets[i].length == 2 fromi.length == 3 toi.length == 3 fromi and toi consist of uppercase English letters. fromi != toi"
Google,383,Ransom Note,Easy,"Hash Table, String, Counting","Given two strings ransomNote and magazine; return true if ransomNote can be constructed by using the letters from magazine and false otherwise. Each letter in magazine can only be used once in ransomNote. Example 1: Input: ransomNote = ""a""; magazine = ""b"" Output: false Example 2: Input: ransomNote = ""aa""; magazine = ""ab"" Output: false Example 3: Input: ransomNote = ""aa""; magazine = ""aab"" Output: true Constraints: 1 <= ransomNote.length; magazine.length <= 105 ransomNote and magazine consist of lowercase English letters."
Google,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
Google,389,Find the Difference,Easy,"Hash Table, String, Bit Manipulation, Sorting","You are given two strings s and t. String t is generated by random shuffling string s and then add one more letter at a random position. Return the letter that was added to t. Example 1: Input: s = ""abcd""; t = ""abcde"" Output: ""e"" Explanation: 'e' is the letter that was added. Example 2: Input: s = """"; t = ""y"" Output: ""y"" Constraints: 0 <= s.length <= 1000 t.length == s.length + 1 s and t consist of lowercase English letters."
Google,412,Fizz Buzz,Easy,"Math, String, Simulation","Given an integer n; return a string array answer (1-indexed) where: answer[i] == ""FizzBuzz"" if i is divisible by 3 and 5. answer[i] == ""Fizz"" if i is divisible by 3. answer[i] == ""Buzz"" if i is divisible by 5. answer[i] == i (as a string) if none of the above conditions are true. Example 1: Input: n = 3 Output: [""1"";""2"";""Fizz""] Example 2: Input: n = 5 Output: [""1"";""2"";""Fizz"";""4"";""Buzz""] Example 3: Input: n = 15 Output: [""1"";""2"";""Fizz"";""4"";""Buzz"";""Fizz"";""7"";""8"";""Fizz"";""Buzz"";""11"";""Fizz"";""13"";""14"";""FizzBuzz""] Constraints: 1 <= n <= 104"
Google,417,Pacific Atlantic Water Flow,Med,"Array, Depth-First Search, Breadth-First Search, Matrix",There is an m x n rectangular island that borders both the Pacific Ocean and Atlantic Ocean. The Pacific Ocean touches the island's left and top edges; and the Atlantic Ocean touches the island's right and bottom edges. The island is partitioned into a grid of square cells. You are given an m x n integer matrix heights where heights[r][c] represents the height above sea level of the cell at coordinate (r; c). The island receives a lot of rain; and the rain water can flow to neighboring cells directly north; south; east; and west if the neighboring cell's height is less than or equal to the current cell's height. Water can flow from any cell adjacent to an ocean into the ocean. Return a 2D list of grid coordinates result where result[i] = [ri; ci] denotes that rain water can flow from cell (ri; ci) to both the Pacific and Atlantic oceans. Example 1: Input: heights = [[1;2;2;3;5];[3;2;3;4;4];[2;4;5;3;1];[6;7;1;4;5];[5;1;1;2;4]] Output: [[0;4];[1;3];[1;4];[2;2];[3;0];[3;1];[4;0]] Explanation: The following cells can flow to the Pacific and Atlantic oceans; as shown below: [0;4]: [0;4] -> Pacific Ocean [0;4] -> Atlantic Ocean [1;3]: [1;3] -> [0;3] -> Pacific Ocean [1;3] -> [1;4] -> Atlantic Ocean [1;4]: [1;4] -> [1;3] -> [0;3] -> Pacific Ocean [1;4] -> Atlantic Ocean [2;2]: [2;2] -> [1;2] -> [0;2] -> Pacific Ocean [2;2] -> [2;3] -> [2;4] -> Atlantic Ocean [3;0]: [3;0] -> Pacific Ocean [3;0] -> [4;0] -> Atlantic Ocean [3;1]: [3;1] -> [3;0] -> Pacific Ocean [3;1] -> [4;1] -> Atlantic Ocean [4;0]: [4;0] -> Pacific Ocean [4;0] -> Atlantic Ocean Note that there are other possible paths for these cells to flow to the Pacific and Atlantic oceans. Example 2: Input: heights = [[1]] Output: [[0;0]] Explanation: The water can flow from the only cell to the Pacific and Atlantic oceans. Constraints: m == heights.length n == heights[r].length 1 <= m; n <= 200 0 <= heights[r][c] <= 105
Google,440,K-th Smallest in Lexicographical Order,Hard,Trie,Given two integers n and k; return the kth lexicographically smallest integer in the range [1; n]. Example 1: Input: n = 13; k = 2 Output: 10 Explanation: The lexicographical order is [1; 10; 11; 12; 13; 2; 3; 4; 5; 6; 7; 8; 9]; so the second smallest number is 10. Example 2: Input: n = 1; k = 1 Output: 1 Constraints: 1 <= k <= n <= 109
Google,442,Find All Duplicates in an Array,Med,"Array, Hash Table",Given an integer array nums of length n where all the integers of nums are in the range [1; n] and each integer appears at most twice; return an array of all the integers that appears twice. You must write an algorithm that runs in O(n) time and uses only constant auxiliary space; excluding the space needed to store the output Example 1: Input: nums = [4;3;2;7;8;2;3;1] Output: [2;3] Example 2: Input: nums = [1;1;2] Output: [1] Example 3: Input: nums = [1] Output: [] Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i] <= n Each element in nums appears once or twice.
Google,459,Repeated Substring Pattern,Easy,"String, String Matching","Given a string s; check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. Example 1: Input: s = ""abab"" Output: true Explanation: It is the substring ""ab"" twice. Example 2: Input: s = ""aba"" Output: false Example 3: Input: s = ""abcabcabcabc"" Output: true Explanation: It is the substring ""abc"" four times or the substring ""abcabc"" twice. Constraints: 1 <= s.length <= 104 s consists of lowercase English letters."
Google,543,Diameter of Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them. Example 1: Input: root = [1;2;3;4;5] Output: 3 Explanation: 3 is the length of the path [4;2;1;3] or [5;2;1;3]. Example 2: Input: root = [1;2] Output: 1 Constraints: The number of nodes in the tree is in the range [1; 104]. -100 <= Node.val <= 100
Google,592,Fraction Addition and Subtraction,Med,"Math, String, Simulation","Given a string expression representing an expression of fraction addition and subtraction; return the calculation result in string format. The final result should be an irreducible fraction. If your final result is an integer; change it to the format of a fraction that has a denominator 1. So in this case; 2 should be converted to 2/1. Example 1: Input: expression = ""-1/2+1/2"" Output: ""0/1"" Example 2: Input: expression = ""-1/2+1/2+1/3"" Output: ""1/3"" Example 3: Input: expression = ""1/3-1/2"" Output: ""-1/6"" Constraints: The input string only contains '0' to '9'; '/'; '+' and '-'. So does the output. Each fraction (input and output) has the format ±numerator/denominator. If the first input fraction or the output is positive; then '+' will be omitted. The input only contains valid irreducible fractions; where the numerator and denominator of each fraction will always be in the range [1; 10]. If the denominator is 1; it means this fraction is actually an integer in a fraction format defined above. The number of given fractions will be in the range [1; 10]. The numerator and denominator of the final result are guaranteed to be valid and in the range of 32-bit int."
Google,725,Split Linked List in Parts,Med,Linked List,Given the head of a singly linked list and an integer k; split the linked list into k consecutive linked list parts. The length of each part should be as equal as possible: no two parts should have a size differing by more than one. This may lead to some parts being null. The parts should be in the order of occurrence in the input list; and parts occurring earlier should always have a size greater than or equal to parts occurring later. Return an array of the k parts. Example 1: Input: head = [1;2;3]; k = 5 Output: [[1];[2];[3];[];[]] Explanation: The first element output[0] has output[0].val = 1; output[0].next = null. The last element output[4] is null; but its string representation as a ListNode is []. Example 2: Input: head = [1;2;3;4;5;6;7;8;9;10]; k = 3 Output: [[1;2;3;4];[5;6;7];[8;9;10]] Explanation: The input has been split into consecutive parts with size difference at most 1; and earlier parts are a larger size than the later parts. Constraints: The number of nodes in the list is in the range [0; 1000]. 0 <= Node.val <= 1000 1 <= k <= 50
Google,743,Network Delay Time,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",
Google,746,Min Cost Climbing Stairs,Easy,"Array, Hash Table, String, Design, Trie","Design a special dictionary that searches the words in it by a prefix and a suffix. Implement the WordFilter class: WordFilter(string[] words) Initializes the object with the words in the dictionary. f(string pref; string suff) Returns the index of the word in the dictionary; which has the prefix pref and the suffix suff. If there is more than one valid index; return the largest of them. If there is no such word in the dictionary; return -1. Example 1: Input [""WordFilter""; ""f""] [[[""apple""]]; [""a""; ""e""]] Output [null; 0] Explanation WordFilter wordFilter = new WordFilter([""apple""]); wordFilter.f(""a""; ""e""); // return 0; because the word at index 0 has prefix = ""a"" and suffix = ""e"". Constraints: 1 <= words.length <= 104 1 <= words[i].length <= 7 1 <= pref.length; suff.length <= 7 words[i]; pref and suff consist of lowercase English letters only. At most 104 calls will be made to the function f."
Google,921,Minimum Add to Make Parentheses Valid,Med,"Array, Matrix, Simulation",You start at the cell (rStart; cStart) of an rows x cols grid facing east. The northwest corner is at the first row and column in the grid; and the southeast corner is at the last row and column. You will walk in a clockwise spiral shape to visit every position in this grid. Whenever you move outside the grid's boundary; we continue our walk outside the grid (but may return to the grid boundary later.). Eventually; we reach all rows * cols spaces of the grid. Return an array of coordinates representing the positions of the grid in the order you visited them. Example 1: Input: rows = 1; cols = 4; rStart = 0; cStart = 0 Output: [[0;0];[0;1];[0;2];[0;3]] Example 2: Input: rows = 5; cols = 6; rStart = 1; cStart = 4 Output: [[1;4];[1;5];[2;5];[2;4];[2;3];[1;3];[0;3];[0;4];[0;5];[3;5];[3;4];[3;3];[3;2];[2;2];[1;2];[0;2];[4;5];[4;4];[4;3];[4;2];[4;1];[3;1];[2;1];[1;1];[0;1];[4;0];[3;0];[2;0];[1;0];[0;0]] Constraints: 1 <= rows; cols <= 100 0 <= rStart < rows 0 <= cStart < cols
Google,509,Fibonacci Number,Easy,"Tree, Binary Search Tree, Binary Tree",
Google,973,K Closest Points to Origin,Med,"String, Stack, Greedy, Queue","You are given two strings stamp and target. Initially; there is a string s of length target.length with all s[i] == '?'. In one turn; you can place stamp over s and replace every letter in the s with the corresponding letter from stamp. For example; if stamp = ""abc"" and target = ""abcba""; then s is ""?????"" initially. In one turn you can: place stamp at index 0 of s to obtain ""abc??""; place stamp at index 1 of s to obtain ""?abc?""; or place stamp at index 2 of s to obtain ""??abc"". Note that stamp must be fully contained in the boundaries of s in order to stamp (i.e.; you cannot place stamp at index 3 of s). We want to convert s to target using at most 10 * target.length turns. Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns; return an empty array. Example 1: Input: stamp = ""abc""; target = ""ababc"" Output: [0;2] Explanation: Initially s = ""?????"". - Place stamp at index 0 to get ""abc??"". - Place stamp at index 2 to get ""ababc"". [1;0;2] would also be accepted as an answer; as well as some other answers. Example 2: Input: stamp = ""abca""; target = ""aabcaca"" Output: [3;0;1] Explanation: Initially s = ""???????"". - Place stamp at index 3 to get ""???abca"". - Place stamp at index 0 to get ""abcabca"". - Place stamp at index 1 to get ""aabcaca"". Constraints: 1 <= stamp.length <= target.length <= 1000 stamp and target consist of lowercase English letters."
Google,986,Interval List Intersections,Med,"Array, String, Enumeration","Given an array arr of 4 digits; find the latest 24-hour time that can be made using each digit exactly once. 24-hour times are formatted as ""HH:MM""; where HH is between 00 and 23; and MM is between 00 and 59. The earliest 24-hour time is 00:00; and the latest is 23:59. Return the latest 24-hour time in ""HH:MM"" format. If no valid time can be made; return an empty string. Example 1: Input: arr = [1;2;3;4] Output: ""23:41"" Explanation: The valid 24-hour times are ""12:34""; ""12:43""; ""13:24""; ""13:42""; ""14:23""; ""14:32""; ""21:34""; ""21:43""; ""23:14""; and ""23:41"". Of these times; ""23:41"" is the latest. Example 2: Input: arr = [5;5;5;5] Output: """" Explanation: There are no valid 24-hour times as ""55:55"" is not valid. Constraints: arr.length == 4 0 <= arr[i] <= 9"
Google,992,Subarrays with K Different Integers,Hard,"Array, String, Greedy","You are given an array of n strings strs; all of the same length. We may choose any deletion indices; and we delete all the characters in those indices for each string. For example; if we have strs = [""abcdef"";""uvwxyz""] and deletion indices {0; 2; 3}; then the final array after deletions is [""bef""; ""vyz""]. Suppose we chose a set of deletion indices answer such that after deletions; the final array has its elements in lexicographic order (i.e.; strs[0] <= strs[1] <= strs[2] <= ... <= strs[n - 1]). Return the minimum possible value of answer.length. Example 1: Input: strs = [""ca"";""bb"";""ac""] Output: 1 Explanation: After deleting the first column; strs = [""a""; ""b""; ""c""]. Now strs is in lexicographic order (ie. strs[0] <= strs[1] <= strs[2]). We require at least 1 deletion since initially strs was not in lexicographic order; so the answer is 1. Example 2: Input: strs = [""xc"";""yb"";""za""] Output: 0 Explanation: strs is already in lexicographic order; so we do not need to delete anything. Note that the rows of strs are not necessarily in lexicographic order: i.e.; it is NOT necessarily true that (strs[0][0] <= strs[0][1] <= ...) Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: We have to delete every column. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Google,1007,Minimum Domino Rotations For Equal Row,Med,"Backtracking, Breadth-First Search",Given two integers n and k; return an array of all the integers of length n where the difference between every two consecutive digits is k. You may return the answer in any order. Note that the integers should not have leading zeros. Integers as 02 and 043 are not allowed. Example 1: Input: n = 3; k = 7 Output: [181;292;707;818;929] Explanation: Note that 070 is not a valid number; because it has leading zeroes. Example 2: Input: n = 2; k = 1 Output: [10;12;21;23;32;34;43;45;54;56;65;67;76;78;87;89;98] Constraints: 2 <= n <= 9 0 <= k <= 9
Google,1143,Longest Common Subsequence,Med,"Array, Hash Table, Binary Search, Matrix, Counting",
Google,1148,Article Views I,Easy,"Array, Math",Given two numbers arr1 and arr2 in base -2; return the result of adding them together. Each number is given in array format: as an array of 0s and 1s; from most significant bit to least significant bit. For example; arr = [1;1;0;1] represents the number (-2)^3 + (-2)^2 + (-2)^0 = -3. A number arr in array; format is also guaranteed to have no leading zeros: either arr == [0] or arr[0] == 1. Return the result of adding arr1 and arr2 in the same format: as an array of 0s and 1s with no leading zeros. Example 1: Input: arr1 = [1;1;1;1;1]; arr2 = [1;0;1] Output: [1;0;0;0;0] Explanation: arr1 represents 11; arr2 represents 5; the output represents 16. Example 2: Input: arr1 = [0]; arr2 = [0] Output: [0] Example 3: Input: arr1 = [0]; arr2 = [1] Output: [1] Constraints: 1 <= arr1.length; arr2.length <= 1000 arr1[i] and arr2[i] are 0 or 1 arr1 and arr2 have no leading zeros
Google,1310,XOR Queries of a Subarray,Med,"Array, Simulation",You want to water n plants in your garden with a watering can. The plants are arranged in a row and are labeled from 0 to n - 1 from left to right where the ith plant is located at x = i. There is a river at x = -1 that you can refill your watering can at. Each plant needs a specific amount of water. You will water the plants in the following way: Water the plants in order from left to right. After watering the current plant; if you do not have enough water to completely water the next plant; return to the river to fully refill the watering can. You cannot refill the watering can early. You are initially at the river (i.e.; x = -1). It takes one step to move one unit on the x-axis. Given a 0-indexed integer array plants of n integers; where plants[i] is the amount of water the ith plant needs; and an integer capacity representing the watering can capacity; return the number of steps needed to water all the plants. Example 1: Input: plants = [2;2;3;3]; capacity = 5 Output: 14 Explanation: Start at the river with a full watering can: - Walk to plant 0 (1 step) and water it. Watering can has 3 units of water. - Walk to plant 1 (1 step) and water it. Watering can has 1 unit of water. - Since you cannot completely water plant 2; walk back to the river to refill (2 steps). - Walk to plant 2 (3 steps) and water it. Watering can has 2 units of water. - Since you cannot completely water plant 3; walk back to the river to refill (3 steps). - Walk to plant 3 (4 steps) and water it. Steps needed = 1 + 1 + 2 + 3 + 3 + 4 = 14. Example 2: Input: plants = [1;1;1;4;2;3]; capacity = 4 Output: 30 Explanation: Start at the river with a full watering can: - Water plants 0; 1; and 2 (3 steps). Return to river (3 steps). - Water plant 3 (4 steps). Return to river (4 steps). - Water plant 4 (5 steps). Return to river (5 steps). - Water plant 5 (6 steps). Steps needed = 3 + 3 + 4 + 4 + 5 + 5 + 6 = 30. Example 3: Input: plants = [7;7;7;7;7;7;7]; capacity = 8 Output: 49 Explanation: You have to refill before watering each plant. Steps needed = 1 + 1 + 2 + 2 + 3 + 3 + 4 + 4 + 5 + 5 + 6 + 6 + 7 = 49. Constraints: n == plants.length 1 <= n <= 1000 1 <= plants[i] <= 106 max(plants[i]) <= capacity <= 109
Google,1581,Customer Who Visited but Did Not Make Any Transactions,Easy,"Array, Two Pointers, Sorting",Given an array of integers arr and an integer k. A value arr[i] is said to be stronger than a value arr[j] if |arr[i] - m| > |arr[j] - m| where m is the median of the array. If |arr[i] - m| == |arr[j] - m|; then arr[i] is said to be stronger than arr[j] if arr[i] > arr[j]. Return a list of the strongest k values in the array. return the answer in any arbitrary order. Median is the middle value in an ordered integer list. More formally; if the length of the list is n; the median is the element in position ((n - 1) / 2) in the sorted list (0-indexed). For arr = [6; -3; 7; 2; 11]; n = 5 and the median is obtained by sorting the array arr = [-3; 2; 6; 7; 11] and the median is arr[m] where m = ((5 - 1) / 2) = 2. The median is 6. For arr = [-7; 22; 17; 3]; n = 4 and the median is obtained by sorting the array arr = [-7; 3; 17; 22] and the median is arr[m] where m = ((4 - 1) / 2) = 1. The median is 3. Example 1: Input: arr = [1;2;3;4;5]; k = 2 Output: [5;1] Explanation: Median is 3; the elements of the array sorted by the strongest are [5;1;4;2;3]. The strongest 2 elements are [5; 1]. [1; 5] is also accepted answer. Please note that although |5 - 3| == |1 - 3| but 5 is stronger than 1 because 5 > 1. Example 2: Input: arr = [1;1;3;5;5]; k = 2 Output: [5;5] Explanation: Median is 3; the elements of the array sorted by the strongest are [5;5;1;1;3]. The strongest 2 elements are [5; 5]. Example 3: Input: arr = [6;7;11;7;6;8]; k = 5 Output: [11;8;6;6;7] Explanation: Median is 7; the elements of the array sorted by the strongest are [11;8;6;6;7;7]. Any permutation of [11;8;6;6;7] is accepted. Constraints: 1 <= arr.length <= 105 -105 <= arr[i] <= 105 1 <= k <= arr.length
Google,1684,Count the Number of Consistent Strings,Easy,"Array, Hash Table, Binary Search, Simulation","Given an array arr that represents a permutation of numbers from 1 to n. You have a binary string of size n that initially has all its bits set to zero. At each step i (assuming both the binary string and arr are 1-indexed) from 1 to n; the bit at position arr[i] is set to 1. You are also given an integer m. Find the latest step at which there exists a group of ones of length m. A group of ones is a contiguous substring of 1's such that it cannot be extended in either direction. Return the latest step at which there exists a group of ones of length exactly m. If no such group exists; return -1. Example 1: Input: arr = [3;5;1;2;4]; m = 1 Output: 4 Explanation: Step 1: ""00100""; groups: [""1""] Step 2: ""00101""; groups: [""1""; ""1""] Step 3: ""10101""; groups: [""1""; ""1""; ""1""] Step 4: ""11101""; groups: [""111""; ""1""] Step 5: ""11111""; groups: [""11111""] The latest step at which there exists a group of size 1 is step 4. Example 2: Input: arr = [3;1;5;4;2]; m = 2 Output: -1 Explanation: Step 1: ""00100""; groups: [""1""] Step 2: ""10100""; groups: [""1""; ""1""] Step 3: ""10101""; groups: [""1""; ""1""; ""1""] Step 4: ""10111""; groups: [""1""; ""111""] Step 5: ""11111""; groups: [""11111""] No group of size 2 exists during any step. Constraints: n == arr.length 1 <= m <= n <= 105 1 <= arr[i] <= n All integers in arr are distinct."
Google,1752,Check if Array Is Sorted and Rotated,Easy,"Array, Hash Table, Sorting",A sequence of numbers is called arithmetic if it consists of at least two elements; and the difference between every two consecutive elements is the same. More formally; a sequence s is arithmetic if and only if s[i+1] - s[i] == s[1] - s[0] for all valid i. For example; these are arithmetic sequences: 1; 3; 5; 7; 9 7; 7; 7; 7 3; -1; -5; -9 The following sequence is not arithmetic: 1; 1; 2; 5; 7 You are given an array of n integers; nums; and two arrays of m integers each; l and r; representing the m range queries; where the ith query is the range [l[i]; r[i]]. All the arrays are 0-indexed. Return a list of boolean elements answer; where answer[i] is true if the subarray nums[l[i]]; nums[l[i]+1]; ... ; nums[r[i]] can be rearranged to form an arithmetic sequence; and false otherwise. Example 1: Input: nums = [4;6;5;9;3;7]; l = [0;0;2]; r = [2;3;5] Output: [true;false;true] Explanation: In the 0th query; the subarray is [4;6;5]. This can be rearranged as [6;5;4]; which is an arithmetic sequence. In the 1st query; the subarray is [4;6;5;9]. This cannot be rearranged as an arithmetic sequence. In the 2nd query; the subarray is [5;9;3;7]. This can be rearranged as [3;5;7;9]; which is an arithmetic sequence. Example 2: Input: nums = [-12;-9;-3;-12;-6;15;20;-25;-20;-15;-10]; l = [0;1;6;4;8;7]; r = [4;4;9;7;9;10] Output: [false;true;false;false;true;true] Constraints: n == nums.length m == l.length m == r.length 2 <= n <= 500 1 <= m <= 500 0 <= l[i] < r[i] < n -105 <= nums[i] <= 105
Google,1903,Largest Odd Number in String,Easy,"Array, Hash Table, Stack, Design, Binary Indexed Tree, Ordered Set",
Google,2035,Partition Array Into Two Arrays to Minimize Sum Difference,Hard,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given two m x n binary matrices grid1 and grid2 containing only 0's (representing water) and 1's (representing land). An island is a group of 1's connected 4-directionally (horizontal or vertical). Any cells outside of the grid are considered water cells. An island in grid2 is considered a sub-island if there is an island in grid1 that contains all the cells that make up this island in grid2. Return the number of islands in grid2 that are considered sub-islands. Example 1: Input: grid1 = [[1;1;1;0;0];[0;1;1;1;1];[0;0;0;0;0];[1;0;0;0;0];[1;1;0;1;1]]; grid2 = [[1;1;1;0;0];[0;0;1;1;1];[0;1;0;0;0];[1;0;1;1;0];[0;1;0;1;0]] Output: 3 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are three sub-islands. Example 2: Input: grid1 = [[1;0;1;0;1];[1;1;1;1;1];[0;0;0;0;0];[1;1;1;1;1];[1;0;1;0;1]]; grid2 = [[0;0;0;0;0];[1;1;1;1;1];[0;1;0;1;0];[0;1;0;1;0];[1;0;0;0;1]] Output: 2 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are two sub-islands. Constraints: m == grid1.length == grid2.length n == grid1[i].length == grid2[i].length 1 <= m; n <= 500 grid1[i][j] and grid2[i][j] are either 0 or 1.
Google,2070,Most Beautiful Item for Each Query,Med,String,
Google,2064,Minimized Maximum of Products Distributed to Any Store,Med,Database,
Google,2641,Cousins in Binary Tree II,Med,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Matrix",You are given a 0-indexed m x n binary matrix grid. You can move from a cell (row; col) to any of the cells (row + 1; col) or (row; col + 1) that has the value 1. The matrix is disconnected if there is no path from (0; 0) to (m - 1; n - 1). You can flip the value of at most one (possibly none) cell. You cannot flip the cells (0; 0) and (m - 1; n - 1). Return true if it is possible to make the matrix disconnect or false otherwise. Note that flipping a cell changes its value from 0 to 1 or from 1 to 0. Example 1: Input: grid = [[1;1;1];[1;0;0];[1;1;1]] Output: true Explanation: We can change the cell shown in the diagram above. There is no path from (0; 0) to (2; 2) in the resulting grid. Example 2: Input: grid = [[1;1;1];[1;0;1];[1;1;1]] Output: false Explanation: It is not possible to change at most one cell such that there is not path from (0; 0) to (2; 2). Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 1000 1 <= m * n <= 105 grid[i][j] is either 0 or 1. grid[0][0] == grid[m - 1][n - 1] == 1
Google,2563,Count the Number of Fair Pairs,Med,"String, Binary Search","You are given a string; message; and a positive integer; limit. You must split message into one or more parts based on limit. Each resulting part should have the suffix ""<a/b>""; where ""b"" is to be replaced with the total number of parts and ""a"" is to be replaced with the index of the part; starting from 1 and going up to b. Additionally; the length of each resulting part (including its suffix) should be equal to limit; except for the last part whose length can be at most limit. The resulting parts should be formed such that when their suffixes are removed and they are all concatenated in order; they should be equal to message. Also; the result should contain as few parts as possible. Return the parts message would be split into as an array of strings. If it is impossible to split message as required; return an empty array. Example 1: Input: message = ""this is really a very awesome message""; limit = 9 Output: [""thi<1/14>"";""s i<2/14>"";""s r<3/14>"";""eal<4/14>"";""ly <5/14>"";""a v<6/14>"";""ery<7/14>"";"" aw<8/14>"";""eso<9/14>"";""me<10/14>"";"" m<11/14>"";""es<12/14>"";""sa<13/14>"";""ge<14/14>""] Explanation: The first 9 parts take 3 characters each from the beginning of message. The next 5 parts take 2 characters each to finish splitting message. In this example; each part; including the last; has length 9. It can be shown it is not possible to split message into less than 14 parts. Example 2: Input: message = ""short message""; limit = 15 Output: [""short mess<1/2>"";""age<2/2>""] Explanation: Under the given constraints; the string can be split into two parts: - The first part comprises of the first 10 characters; and has a length 15. - The next part comprises of the last 3 characters; and has a length 8. Constraints: 1 <= message.length <= 104 message consists only of lowercase English letters and ' '. 1 <= limit <= 104"
Google,2635,Apply Transform Over Each Element in Array,Easy,"Math, Number Theory",There exists an infinitely large grid. You are currently at point (1; 1); and you need to reach the point (targetX; targetY) using a finite number of steps. In one step; you can move from point (x; y) to any one of the following points: (x; y - x) (x - y; y) (2 * x; y) (x; 2 * y) Given two integers targetX and targetY representing the X-coordinate and Y-coordinate of your final position; return true if you can reach the point from (1; 1) using some number of steps; and false otherwise. Example 1: Input: targetX = 6; targetY = 9 Output: false Explanation: It is impossible to reach (6;9) from (1;1) using any sequence of moves; so false is returned. Example 2: Input: targetX = 4; targetY = 7 Output: true Explanation: You can follow the path (1;1) -> (1;2) -> (1;4) -> (1;8) -> (1;7) -> (2;7) -> (4;7). Constraints: 1 <= targetX; targetY <= 109
Google,2938,Separate Black and White Balls,Med,,
Google,3043,Find the Length of the Longest Common Prefix,Med,"Array, Breadth-First Search, Matrix",
Google,3163,String Compression III,Med,"Array, Hash Table",You are given a 0-indexed integer array nums. The distinct count of a subarray of nums is defined as: Let nums[i..j] be a subarray of nums consisting of all the indices from i to j such that 0 <= i <= j < nums.length. Then the number of distinct values in nums[i..j] is called the distinct count of nums[i..j]. Return the sum of the squares of distinct counts of all subarrays of nums. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;2;1] Output: 15 Explanation: Six possible subarrays are: [1]: 1 distinct value [2]: 1 distinct value [1]: 1 distinct value [1;2]: 2 distinct values [2;1]: 2 distinct values [1;2;1]: 2 distinct values The sum of the squares of the distinct counts in all subarrays is equal to 12 + 12 + 12 + 22 + 22 + 22 = 15. Example 2: Input: nums = [1;1] Output: 3 Explanation: Three possible subarrays are: [1]: 1 distinct value [1]: 1 distinct value [1;1]: 1 distinct value The sum of the squares of the distinct counts in all subarrays is equal to 12 + 12 + 12 = 3. Constraints: 1 <= nums.length <= 100 1 <= nums[i] <= 100
Google,3254,Find the Power of K-Size Subarrays I,Med,"Array, Hash Table",
Google,8,String to Integer (atoi),Med,String,"Implement the myAtoi(string s) function; which converts a string to a 32-bit signed integer. The algorithm for myAtoi(string s) is as follows: Whitespace: Ignore any leading whitespace ("" ""). Signedness: Determine the sign by checking if the next character is '-' or '+'; assuming positivity if neither present. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read; then the result is 0. Rounding: If the integer is out of the 32-bit signed integer range [-231; 231 - 1]; then round the integer to remain in the range. Specifically; integers less than -231 should be rounded to -231; and integers greater than 231 - 1 should be rounded to 231 - 1. Return the integer as the final result. Example 1: Input: s = ""42"" Output: 42 Explanation: The underlined characters are what is read in and the caret is the current reader position. Step 1: ""42"" (no characters read because there is no leading whitespace) ^ Step 2: ""42"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""42"" (""42"" is read in) ^ Example 2: Input: s = "" -042"" Output: -42 Explanation: Step 1: "" -042"" (leading whitespace is read and ignored) ^ Step 2: "" -042"" ('-' is read; so the result should be negative) ^ Step 3: "" -042"" (""042"" is read in; leading zeros ignored in the result) ^ Example 3: Input: s = ""1337c0d3"" Output: 1337 Explanation: Step 1: ""1337c0d3"" (no characters read because there is no leading whitespace) ^ Step 2: ""1337c0d3"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""1337c0d3"" (""1337"" is read in; reading stops because the next character is a non-digit) ^ Example 4: Input: s = ""0-1"" Output: 0 Explanation: Step 1: ""0-1"" (no characters read because there is no leading whitespace) ^ Step 2: ""0-1"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""0-1"" (""0"" is read in; reading stops because the next character is a non-digit) ^ Example 5: Input: s = ""words and 987"" Output: 0 Explanation: Reading stops at the first non-digit character 'w'. Constraints: 0 <= s.length <= 200 s consists of English letters (lower-case and upper-case); digits (0-9); ' '; '+'; '-'; and '.'."
Google,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Google,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
Google,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Google,51,N-Queens,Hard,"Array, Backtracking","The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n; return all distinct solutions to the n-queens puzzle. You may return the answer in any order. Each solution contains a distinct board configuration of the n-queens' placement; where 'Q' and '.' both indicate a queen and an empty space; respectively. Example 1: Input: n = 4 Output: [["".Q.."";""...Q"";""Q..."";""..Q.""];[""..Q."";""Q..."";""...Q"";"".Q..""]] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above Example 2: Input: n = 1 Output: [[""Q""]] Constraints: 1 <= n <= 9"
Google,64,Minimum Path Sum,Med,"Array, Dynamic Programming, Matrix",Given a m x n grid filled with non-negative numbers; find a path from top left to bottom right; which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1;3;1];[1;5;1];[4;2;1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. Example 2: Input: grid = [[1;2;3];[4;5;6]] Output: 12 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 200 0 <= grid[i][j] <= 200
Google,68,Text Justification,Hard,"Array, String, Simulation","Given an array of strings words and a width maxWidth; format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is; pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words; the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text; it should be left-justified; and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = [""This""; ""is""; ""an""; ""example""; ""of""; ""text""; ""justification.""]; maxWidth = 16 Output: [ ""This is an""; ""example of text""; ""justification. "" ] Example 2: Input: words = [""What"";""must"";""be"";""acknowledgment"";""shall"";""be""]; maxWidth = 16 Output: [ ""What must be""; ""acknowledgment ""; ""shall be "" ] Explanation: Note that the last line is ""shall be "" instead of ""shall be""; because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = [""Science"";""is"";""what"";""we"";""understand"";""well"";""enough"";""to"";""explain"";""to"";""a"";""computer."";""Art"";""is"";""everything"";""else"";""we"";""do""]; maxWidth = 20 Output: [ ""Science is what we""; ""understand well""; ""enough to explain to""; ""a computer. Art is""; ""everything else we""; ""do "" ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth"
Google,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Google,77,Combinations,Med,Backtracking,Given two integers n and k; return all possible combinations of k numbers chosen from the range [1; n]. You may return the answer in any order. Example 1: Input: n = 4; k = 2 Output: [[1;2];[1;3];[1;4];[2;3];[2;4];[3;4]] Explanation: There are 4 choose 2 = 6 total combinations. Note that combinations are unordered; i.e.; [1;2] and [2;1] are considered to be the same combination. Example 2: Input: n = 1; k = 1 Output: [[1]] Explanation: There is 1 choose 1 = 1 total combination. Constraints: 1 <= n <= 20 1 <= k <= n
Google,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Google,82,Remove Duplicates from Sorted List II,Med,"Linked List, Two Pointers",Given the head of a sorted linked list; delete all nodes that have duplicate numbers; leaving only distinct numbers from the original list. Return the linked list sorted as well. Example 1: Input: head = [1;2;3;3;4;4;5] Output: [1;2;5] Example 2: Input: head = [1;1;1;2;3] Output: [2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Google,96,Unique Binary Search Trees,Med,"Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree",Given an integer n; return the number of structurally unique BST's (binary search trees) which has exactly n nodes of unique values from 1 to n. Example 1: Input: n = 3 Output: 5 Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 19
Google,103,Binary Tree Zigzag Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the zigzag level order traversal of its nodes' values. (i.e.; from left to right; then right to left for the next level and alternate between). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[20;9];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100
Google,104,Maximum Depth of Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return its maximum depth. A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 3 Example 2: Input: root = [1;null;2] Output: 2 Constraints: The number of nodes in the tree is in the range [0; 104]. -100 <= Node.val <= 100
Google,119,Pascal's Triangle II,Easy,"Array, Dynamic Programming",Given an integer rowIndex; return the rowIndexth (0-indexed) row of the Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: rowIndex = 3 Output: [1;3;3;1] Example 2: Input: rowIndex = 0 Output: [1] Example 3: Input: rowIndex = 1 Output: [1;1] Constraints: 0 <= rowIndex <= 33 Follow up: Could you optimize your algorithm to use only O(rowIndex) extra space?
Google,145,Binary Tree Postorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the postorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [3;2;1] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [4;6;7;5;2;9;8;3;1] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of the nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Google,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Google,160,Intersection of Two Linked Lists,Easy,"Hash Table, Linked List, Two Pointers",Given the heads of two singly linked-lists headA and headB; return the node at which the two lists intersect. If the two linked lists have no intersection at all; return null. For example; the following two linked lists begin to intersect at node c1: The test cases are generated such that there are no cycles anywhere in the entire linked structure. Note that the linked lists must retain their original structure after the function returns. Custom Judge: The inputs to the judge are given as follows (your program is not given these inputs): intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node. listA - The first linked list. listB - The second linked list. skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node. skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node. The judge will then create the linked structure based on these inputs and pass the two heads; headA and headB to your program. If you correctly return the intersected node; then your solution will be accepted. Example 1: Input: intersectVal = 8; listA = [4;1;8;4;5]; listB = [5;6;1;8;4;5]; skipA = 2; skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [4;1;8;4;5]. From the head of B; it reads as [5;6;1;8;4;5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words; they point to two different locations in memory; while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory. Example 2: Input: intersectVal = 2; listA = [1;9;1;2;4]; listB = [3;2;4]; skipA = 3; skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [1;9;1;2;4]. From the head of B; it reads as [3;2;4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B. Example 3: Input: intersectVal = 0; listA = [2;6;4]; listB = [1;5]; skipA = 3; skipB = 2 Output: No intersection Explanation: From the head of A; it reads as [2;6;4]. From the head of B; it reads as [1;5]. Since the two lists do not intersect; intersectVal must be 0; while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect; so return null. Constraints: The number of nodes of listA is in the m. The number of nodes of listB is in the n. 1 <= m; n <= 3 * 104 1 <= Node.val <= 105 0 <= skipA <= m 0 <= skipB <= n intersectVal is 0 if listA and listB do not intersect. intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect. Follow up: Could you write a solution that runs in O(m + n) time and use only O(1) memory?
Google,166,Fraction to Recurring Decimal,Med,"Hash Table, Math, String","Given two integers representing the numerator and denominator of a fraction; return the fraction in string format. If the fractional part is repeating; enclose the repeating part in parentheses. If multiple answers are possible; return any of them. It is guaranteed that the length of the answer string is less than 104 for all the given inputs. Example 1: Input: numerator = 1; denominator = 2 Output: ""0.5"" Example 2: Input: numerator = 2; denominator = 1 Output: ""2"" Example 3: Input: numerator = 4; denominator = 333 Output: ""0.(012)"" Constraints: -231 <= numerator; denominator <= 231 - 1 denominator != 0"
Google,168,Excel Sheet Column Title,Easy,"Math, String","Given an integer columnNumber; return its corresponding column title as it appears in an Excel sheet. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: Input: columnNumber = 1 Output: ""A"" Example 2: Input: columnNumber = 28 Output: ""AB"" Example 3: Input: columnNumber = 701 Output: ""ZY"" Constraints: 1 <= columnNumber <= 231 - 1"
Google,175,Combine Two Tables,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | personId | int | | lastName | varchar | | firstName | varchar | +-------------+---------+ personId is the primary key (column with unique values) for this table. This table contains information about the ID of some persons and their first and last names. Table: Address +-------------+---------+ | Column Name | Type | +-------------+---------+ | addressId | int | | personId | int | | city | varchar | | state | varchar | +-------------+---------+ addressId is the primary key (column with unique values) for this table. Each row of this table contains information about the city and state of one person with ID = PersonId. Write a solution to report the first name; last name; city; and state of each person in the Person table. If the address of a personId is not present in the Address table; report null instead. Return the result table in any order. The result format is in the following example. Example 1: Input: Person table: +----------+----------+-----------+ | personId | lastName | firstName | +----------+----------+-----------+ | 1 | Wang | Allen | | 2 | Alice | Bob | +----------+----------+-----------+ Address table: +-----------+----------+---------------+------------+ | addressId | personId | city | state | +-----------+----------+---------------+------------+ | 1 | 2 | New York City | New York | | 2 | 3 | Leetcode | California | +-----------+----------+---------------+------------+ Output: +-----------+----------+---------------+----------+ | firstName | lastName | city | state | +-----------+----------+---------------+----------+ | Allen | Wang | Null | Null | | Bob | Alice | New York City | New York | +-----------+----------+---------------+----------+ Explanation: There is no address in the address table for the personId = 1 so we return null in their city and state. addressId = 1 contains information about the address of personId = 2.
Google,176,Second Highest Salary,Med,Database,Table: Employee +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | salary | int | +-------------+------+ id is the primary key (column with unique values) for this table. Each row of this table contains information about the salary of an employee. Write a solution to find the second highest distinct salary from the Employee table. If there is no second highest salary; return null (return None in Pandas). The result format is in the following example. Example 1: Input: Employee table: +----+--------+ | id | salary | +----+--------+ | 1 | 100 | | 2 | 200 | | 3 | 300 | +----+--------+ Output: +---------------------+ | SecondHighestSalary | +---------------------+ | 200 | +---------------------+ Example 2: Input: Employee table: +----+--------+ | id | salary | +----+--------+ | 1 | 100 | +----+--------+ Output: +---------------------+ | SecondHighestSalary | +---------------------+ | null | +---------------------+
Google,191,Number of 1 Bits,Easy,"Divide and Conquer, Bit Manipulation",Given a positive integer n; write a function that returns the number of set bits in its binary representation (also known as the Hamming weight). Example 1: Input: n = 11 Output: 3 Explanation: The input binary string 1011 has a total of three set bits. Example 2: Input: n = 128 Output: 1 Explanation: The input binary string 10000000 has a total of one set bit. Example 3: Input: n = 2147483645 Output: 30 Explanation: The input binary string 1111111111111111111111111111101 has a total of thirty set bits. Constraints: 1 <= n <= 231 - 1 Follow up: If this function is called many times; how would you optimize it?
Google,211,Design Add and Search Words Data Structure,Med,"String, Depth-First Search, Design, Trie","Design a data structure that supports adding new words and finding if a string matches any previously added string. Implement the WordDictionary class: WordDictionary() Initializes the object. void addWord(word) Adds word to the data structure; it can be matched later. bool search(word) Returns true if there is any string in the data structure that matches word or false otherwise. word may contain dots '.' where dots can be matched with any letter. Example: Input [""WordDictionary"";""addWord"";""addWord"";""addWord"";""search"";""search"";""search"";""search""] [[];[""bad""];[""dad""];[""mad""];[""pad""];[""bad""];["".ad""];[""b..""]] Output [null;null;null;null;false;true;true;true] Explanation WordDictionary wordDictionary = new WordDictionary(); wordDictionary.addWord(""bad""); wordDictionary.addWord(""dad""); wordDictionary.addWord(""mad""); wordDictionary.search(""pad""); // return False wordDictionary.search(""bad""); // return True wordDictionary.search("".ad""); // return True wordDictionary.search(""b..""); // return True Constraints: 1 <= word.length <= 25 word in addWord consists of lowercase English letters. word in search consist of '.' or lowercase English letters. There will be at most 2 dots in word for search queries. At most 104 calls will be made to addWord and search."
Google,213,House Robber II,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile; adjacent houses have a security system connected; and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [2;3;2] Output: 3 Explanation: You cannot rob house 1 (money = 2) and then rob house 3 (money = 2); because they are adjacent houses. Example 2: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 3: Input: nums = [1;2;3] Output: 3 Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 1000
Google,219,Contains Duplicate II,Easy,"Array, Hash Table, Sliding Window",Given an integer array nums and an integer k; return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k. Example 1: Input: nums = [1;2;3;1]; k = 3 Output: true Example 2: Input: nums = [1;0;1;1]; k = 1 Output: true Example 3: Input: nums = [1;2;3;1;2;3]; k = 2 Output: false Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109 0 <= k <= 105
Google,229,Majority Element II,Med,"Array, Hash Table, Sorting, Counting",Given an integer array of size n; find all elements that appear more than ⌊ n/3 ⌋ times. Example 1: Input: nums = [3;2;3] Output: [3] Example 2: Input: nums = [1] Output: [1] Example 3: Input: nums = [1;2] Output: [1;2] Constraints: 1 <= nums.length <= 5 * 104 -109 <= nums[i] <= 109 Follow up: Could you solve the problem in linear time and in O(1) space?
Google,235,Lowest Common Ancestor of a Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given a binary search tree (BST); find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [2;1]; p = 2; q = 1 Output: 2 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.
Google,237,Delete Node in a Linked List,Med,Linked List,There is a singly-linked list head and we want to delete a node node in it. You are given the node to be deleted node. You will not be given access to the first node of head. All the values of the linked list are unique; and it is guaranteed that the given node node is not the last node in the linked list. Delete the given node. Note that by deleting the node; we do not mean removing it from memory. We mean: The value of the given node should not exist in the linked list. The number of nodes in the linked list should decrease by one. All the values before node should be in the same order. All the values after node should be in the same order. Custom testing: For the input; you should provide the entire linked list head and the node to be given node. node should not be the last node of the list and should be an actual node in the list. We will build the linked list and pass the node to your function. The output will be the entire list after calling your function. Example 1: Input: head = [4;5;1;9]; node = 5 Output: [4;1;9] Explanation: You are given the second node with value 5; the linked list should become 4 -> 1 -> 9 after calling your function. Example 2: Input: head = [4;5;1;9]; node = 1 Output: [4;5;9] Explanation: You are given the third node with value 1; the linked list should become 4 -> 5 -> 9 after calling your function. Constraints: The number of the nodes in the given list is in the range [2; 1000]. -1000 <= Node.val <= 1000 The value of each node in the list is unique. The node to be deleted is in the list and is not a tail node.
Google,241,Different Ways to Add Parentheses,Med,"Math, String, Dynamic Programming, Recursion, Memoization","Given a string expression of numbers and operators; return all possible results from computing all the different possible ways to group numbers and operators. You may return the answer in any order. The test cases are generated such that the output values fit in a 32-bit integer and the number of different results does not exceed 104. Example 1: Input: expression = ""2-1-1"" Output: [0;2] Explanation: ((2-1)-1) = 0 (2-(1-1)) = 2 Example 2: Input: expression = ""2*3-4*5"" Output: [-34;-14;-10;-10;10] Explanation: (2*(3-(4*5))) = -34 ((2*3)-(4*5)) = -14 ((2*(3-4))*5) = -10 (2*((3-4)*5)) = -10 (((2*3)-4)*5) = 10 Constraints: 1 <= expression.length <= 20 expression consists of digits and the operator '+'; '-'; and '*'. All the integer values in the input expression are in the range [0; 99]. The integer values in the input expression do not have a leading '-' or '+' denoting the sign."
Google,268,Missing Number,Easy,"Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting",Given an array nums containing n distinct numbers in the range [0; n]; return the only number in the range that is missing from the array. Example 1: Input: nums = [3;0;1] Output: 2 Explanation: n = 3 since there are 3 numbers; so all numbers are in the range [0;3]. 2 is the missing number in the range since it does not appear in nums. Example 2: Input: nums = [0;1] Output: 2 Explanation: n = 2 since there are 2 numbers; so all numbers are in the range [0;2]. 2 is the missing number in the range since it does not appear in nums. Example 3: Input: nums = [9;6;4;2;3;5;7;0;1] Output: 8 Explanation: n = 9 since there are 9 numbers; so all numbers are in the range [0;9]. 8 is the missing number in the range since it does not appear in nums. Constraints: n == nums.length 1 <= n <= 104 0 <= nums[i] <= n All the numbers of nums are unique. Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?
Google,269,Alien Dictionary,Hard,"Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort",
Google,301,Remove Invalid Parentheses,Hard,"String, Backtracking, Breadth-First Search","Given a string s that contains parentheses and letters; remove the minimum number of invalid parentheses to make the input string valid. Return a list of unique strings that are valid with the minimum number of removals. You may return the answer in any order. Example 1: Input: s = ""()())()"" Output: [""(())()"";""()()()""] Example 2: Input: s = ""(a)())()"" Output: [""(a())()"";""(a)()()""] Example 3: Input: s = "")("" Output: [""""] Constraints: 1 <= s.length <= 25 s consists of lowercase English letters and parentheses '(' and ')'. There will be at most 20 parentheses in s."
Google,303,Range Sum Query - Immutable,Easy,"Array, Design, Prefix Sum","Given an integer array nums; handle multiple queries of the following type: Calculate the sum of the elements of nums between indices left and right inclusive where left <= right. Implement the NumArray class: NumArray(int[] nums) Initializes the object with the integer array nums. int sumRange(int left; int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]). Example 1: Input [""NumArray""; ""sumRange""; ""sumRange""; ""sumRange""] [[[-2; 0; 3; -5; 2; -1]]; [0; 2]; [2; 5]; [0; 5]] Output [null; 1; -1; -3] Explanation NumArray numArray = new NumArray([-2; 0; 3; -5; 2; -1]); numArray.sumRange(0; 2); // return (-2) + 0 + 3 = 1 numArray.sumRange(2; 5); // return 3 + (-5) + 2 + (-1) = -1 numArray.sumRange(0; 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3 Constraints: 1 <= nums.length <= 104 -105 <= nums[i] <= 105 0 <= left <= right < nums.length At most 104 calls will be made to sumRange."
Google,312,Burst Balloons,Hard,"Array, Dynamic Programming",You are given n balloons; indexed from 0 to n - 1. Each balloon is painted with a number on it represented by an array nums. You are asked to burst all the balloons. If you burst the ith balloon; you will get nums[i - 1] * nums[i] * nums[i + 1] coins. If i - 1 or i + 1 goes out of bounds of the array; then treat it as if there is a balloon with a 1 painted on it. Return the maximum coins you can collect by bursting the balloons wisely. Example 1: Input: nums = [3;1;5;8] Output: 167 Explanation: nums = [3;1;5;8] --> [3;5;8] --> [3;8] --> [8] --> [] coins = 3*1*5 + 3*5*8 + 1*3*8 + 1*8*1 = 167 Example 2: Input: nums = [1;5] Output: 10 Constraints: n == nums.length 1 <= n <= 300 0 <= nums[i] <= 100
Google,314,Binary Tree Vertical Order Traversal,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Sorting, Binary Tree",
Google,318,Maximum Product of Word Lengths,Med,"Array, String, Bit Manipulation","Given a string array words; return the maximum value of length(word[i]) * length(word[j]) where the two words do not share common letters. If no such two words exist; return 0. Example 1: Input: words = [""abcw"";""baz"";""foo"";""bar"";""xtfn"";""abcdef""] Output: 16 Explanation: The two words can be ""abcw""; ""xtfn"". Example 2: Input: words = [""a"";""ab"";""abc"";""d"";""cd"";""bcd"";""abcd""] Output: 4 Explanation: The two words can be ""ab""; ""cd"". Example 3: Input: words = [""a"";""aa"";""aaa"";""aaaa""] Output: 0 Explanation: No such pair of words. Constraints: 2 <= words.length <= 1000 1 <= words[i].length <= 1000 words[i] consists only of lowercase English letters."
Google,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Google,341,Flatten Nested List Iterator,Med,"Stack, Tree, Depth-First Search, Design, Queue, Iterator",You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it. Implement the NestedIterator class: NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList. int next() Returns the next integer in the nested list. boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise. Your code will be tested with the following pseudocode: initialize iterator with nestedList res = [] while iterator.hasNext() append iterator.next() to the end of res return res If res matches the expected flattened list; then your code will be judged as correct. Example 1: Input: nestedList = [[1;1];2;[1;1]] Output: [1;1;2;1;1] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;1;2;1;1]. Example 2: Input: nestedList = [1;[4;[6]]] Output: [1;4;6] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;4;6]. Constraints: 1 <= nestedList.length <= 500 The values of the integers in the nested list is in the range [-106; 106].
Google,350,Intersection of Two Arrays II,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must appear as many times as it shows in both arrays and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2;2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [4;9] Explanation: [9;4] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000 Follow up: What if the given array is already sorted? How would you optimize your algorithm? What if nums1's size is small compared to nums2's size? Which algorithm is better? What if elements of nums2 are stored on disk; and the memory is limited such that you cannot load all elements into the memory at once?
Google,351,Android Unlock Patterns,Med,"Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",
Google,362,Design Hit Counter,Med,"Array, Binary Search, Design, Queue, Data Stream",
Google,366,Find Leaves of Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",
Google,377,Combination Sum IV,Med,"Array, Dynamic Programming",Given an array of distinct integers nums and a target integer target; return the number of possible combinations that add up to target. The test cases are generated so that the answer can fit in a 32-bit integer. Example 1: Input: nums = [1;2;3]; target = 4 Output: 7 Explanation: The possible combination ways are: (1; 1; 1; 1) (1; 1; 2) (1; 2; 1) (1; 3) (2; 1; 1) (2; 2) (3; 1) Note that different sequences are counted as different combinations. Example 2: Input: nums = [9]; target = 3 Output: 0 Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 1000 All the elements of nums are unique. 1 <= target <= 1000 Follow up: What if negative numbers are allowed in the given array? How does it change the problem? What limitation we need to add to the question to allow negative numbers?
Google,382,Linked List Random Node,Med,"Linked List, Math, Reservoir Sampling, Randomized","Given a singly linked list; return a random node's value from the linked list. Each node must have the same probability of being chosen. Implement the Solution class: Solution(ListNode head) Initializes the object with the head of the singly-linked list head. int getRandom() Chooses a node randomly from the list and returns its value. All the nodes of the list should be equally likely to be chosen. Example 1: Input [""Solution""; ""getRandom""; ""getRandom""; ""getRandom""; ""getRandom""; ""getRandom""] [[[1; 2; 3]]; []; []; []; []; []] Output [null; 1; 3; 2; 2; 3] Explanation Solution solution = new Solution([1; 2; 3]); solution.getRandom(); // return 1 solution.getRandom(); // return 3 solution.getRandom(); // return 2 solution.getRandom(); // return 2 solution.getRandom(); // return 3 // getRandom() should return either 1; 2; or 3 randomly. Each element should have equal probability of returning. Constraints: The number of nodes in the linked list will be in the range [1; 104]. -104 <= Node.val <= 104 At most 104 calls will be made to getRandom. Follow up: What if the linked list is extremely large and its length is unknown to you? Could you solve this efficiently without using extra space?"
Google,409,Longest Palindrome,Easy,"Hash Table, String, Greedy","Given a string s which consists of lowercase or uppercase letters; return the length of the longest palindrome that can be built with those letters. Letters are case sensitive; for example; ""Aa"" is not considered a palindrome. Example 1: Input: s = ""abccccdd"" Output: 7 Explanation: One longest palindrome that can be built is ""dccaccd""; whose length is 7. Example 2: Input: s = ""a"" Output: 1 Explanation: The longest palindrome that can be built is ""a""; whose length is 1. Constraints: 1 <= s.length <= 2000 s consists of lowercase and/or uppercase English letters only."
Google,451,Sort Characters By Frequency,Med,"Hash Table, String, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given a string s; sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers; return any of them. Example 1: Input: s = ""tree"" Output: ""eert"" Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore ""eetr"" is also a valid answer. Example 2: Input: s = ""cccaaa"" Output: ""aaaccc"" Explanation: Both 'c' and 'a' appear three times; so both ""cccaaa"" and ""aaaccc"" are valid answers. Note that ""cacaca"" is incorrect; as the same characters must be together. Example 3: Input: s = ""Aabb"" Output: ""bbAa"" Explanation: ""bbaA"" is also a valid answer; but ""Aabb"" is incorrect. Note that 'A' and 'a' are treated as two different characters. Constraints: 1 <= s.length <= 5 * 105 s consists of uppercase and lowercase English letters and digits."
Google,453,Minimum Moves to Equal Array Elements,Med,"Array, Math",Given an integer array nums of size n; return the minimum number of moves required to make all array elements equal. In one move; you can increment n - 1 elements of the array by 1. Example 1: Input: nums = [1;2;3] Output: 3 Explanation: Only three moves are needed (remember each move increments two elements): [1;2;3] => [2;3;3] => [3;4;3] => [4;4;4] Example 2: Input: nums = [1;1;1] Output: 0 Constraints: n == nums.length 1 <= nums.length <= 105 -109 <= nums[i] <= 109 The answer is guaranteed to fit in a 32-bit integer.
Google,493,Reverse Pairs,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums; return the number of reverse pairs in the array. A reverse pair is a pair (i; j) where: 0 <= i < j < nums.length and nums[i] > 2 * nums[j]. Example 1: Input: nums = [1;3;2;3;1] Output: 2 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 3; nums[4] = 1; 3 > 2 * 1 Example 2: Input: nums = [2;4;3;5;1] Output: 3 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 4; nums[4] = 1; 4 > 2 * 1 (2; 4) --> nums[2] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 5; nums[4] = 1; 5 > 2 * 1 Constraints: 1 <= nums.length <= 5 * 104 -231 <= nums[i] <= 231 - 1
Google,506,Relative Ranks,Easy,"Array, Sorting, Heap (Priority Queue)","You are given an integer array score of size n; where score[i] is the score of the ith athlete in a competition. All the scores are guaranteed to be unique. The athletes are placed based on their scores; where the 1st place athlete has the highest score; the 2nd place athlete has the 2nd highest score; and so on. The placement of each athlete determines their rank: The 1st place athlete's rank is ""Gold Medal"". The 2nd place athlete's rank is ""Silver Medal"". The 3rd place athlete's rank is ""Bronze Medal"". For the 4th place to the nth place athlete; their rank is their placement number (i.e.; the xth place athlete's rank is ""x""). Return an array answer of size n where answer[i] is the rank of the ith athlete. Example 1: Input: score = [5;4;3;2;1] Output: [""Gold Medal"";""Silver Medal"";""Bronze Medal"";""4"";""5""] Explanation: The placements are [1st; 2nd; 3rd; 4th; 5th]. Example 2: Input: score = [10;3;8;9;4] Output: [""Gold Medal"";""5"";""Bronze Medal"";""Silver Medal"";""4""] Explanation: The placements are [1st; 5th; 3rd; 2nd; 4th]. Constraints: n == score.length 1 <= n <= 104 0 <= score[i] <= 106 All the values in score are unique."
Google,523,Continuous Subarray Sum,Med,"Array, Hash Table, Math, Prefix Sum",Given an integer array nums and an integer k; return true if nums has a good subarray or false otherwise. A good subarray is a subarray where: its length is at least two; and the sum of the elements of the subarray is a multiple of k. Note that: A subarray is a contiguous part of the array. An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k. Example 1: Input: nums = [23;2;4;6;7]; k = 6 Output: true Explanation: [2; 4] is a continuous subarray of size 2 whose elements sum up to 6. Example 2: Input: nums = [23;2;6;4;7]; k = 6 Output: true Explanation: [23; 2; 6; 4; 7] is an continuous subarray of size 5 whose elements sum up to 42. 42 is a multiple of 6 because 42 = 7 * 6 and 7 is an integer. Example 3: Input: nums = [23;2;6;4;7]; k = 13 Output: false Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109 0 <= sum(nums[i]) <= 231 - 1 1 <= k <= 231 - 1
Google,577,Employee Bonus,Easy,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | empId | int | | name | varchar | | supervisor | int | | salary | int | +-------------+---------+ empId is the column with unique values for this table. Each row of this table indicates the name and the ID of an employee in addition to their salary and the id of their manager. Table: Bonus +-------------+------+ | Column Name | Type | +-------------+------+ | empId | int | | bonus | int | +-------------+------+ empId is the column of unique values for this table. empId is a foreign key (reference column) to empId from the Employee table. Each row of this table contains the id of an employee and their respective bonus. Write a solution to report the name and bonus amount of each employee with a bonus less than 1000. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +-------+--------+------------+--------+ | empId | name | supervisor | salary | +-------+--------+------------+--------+ | 3 | Brad | null | 4000 | | 1 | John | 3 | 1000 | | 2 | Dan | 3 | 2000 | | 4 | Thomas | 3 | 4000 | +-------+--------+------------+--------+ Bonus table: +-------+-------+ | empId | bonus | +-------+-------+ | 2 | 500 | | 4 | 2000 | +-------+-------+ Output: +------+-------+ | name | bonus | +------+-------+ | Brad | null | | John | null | | Dan | 500 | +------+-------+
Google,605,Can Place Flowers,Easy,"Array, Greedy",You have a long flowerbed in which some of the plots are planted; and some are not. However; flowers cannot be planted in adjacent plots. Given an integer array flowerbed containing 0's and 1's; where 0 means empty and 1 means not empty; and an integer n; return true if n new flowers can be planted in the flowerbed without violating the no-adjacent-flowers rule and false otherwise. Example 1: Input: flowerbed = [1;0;0;0;1]; n = 1 Output: true Example 2: Input: flowerbed = [1;0;0;0;1]; n = 2 Output: false Constraints: 1 <= flowerbed.length <= 2 * 104 flowerbed[i] is 0 or 1. There are no two adjacent flowers in flowerbed. 0 <= n <= flowerbed.length
Google,642,Design Search Autocomplete System,Hard,"String, Depth-First Search, Design, Trie, Sorting, Heap (Priority Queue), Data Stream",
Google,643,Maximum Average Subarray I,Easy,"Array, Sliding Window",You are given an integer array nums consisting of n elements; and an integer k. Find a contiguous subarray whose length is equal to k that has the maximum average value and return this value. Any answer with a calculation error less than 10-5 will be accepted. Example 1: Input: nums = [1;12;-5;-6;50;3]; k = 4 Output: 12.75000 Explanation: Maximum average is (12 - 5 - 6 + 50) / 4 = 51 / 4 = 12.75 Example 2: Input: nums = [5]; k = 1 Output: 5.00000 Constraints: n == nums.length 1 <= k <= n <= 105 -104 <= nums[i] <= 104
Google,680,Valid Palindrome II,Easy,"Two Pointers, String, Greedy","Given a string s; return true if the s can be palindrome after deleting at most one character from it. Example 1: Input: s = ""aba"" Output: true Example 2: Input: s = ""abca"" Output: true Explanation: You could delete the character 'c'. Example 3: Input: s = ""abc"" Output: false Constraints: 1 <= s.length <= 105 s consists of lowercase English letters."
Google,681,Next Closest Time,Med,"Hash Table, String, Backtracking, Enumeration",
Google,713,Subarray Product Less Than K,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of integers nums and an integer k; return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k. Example 1: Input: nums = [10;5;2;6]; k = 100 Output: 8 Explanation: The 8 subarrays that have product less than 100 are: [10]; [5]; [2]; [6]; [10; 5]; [5; 2]; [2; 6]; [5; 2; 6] Note that [10; 5; 2] is not included as the product of 100 is not strictly less than k. Example 2: Input: nums = [1;2;3]; k = 0 Output: 0 Constraints: 1 <= nums.length <= 3 * 104 1 <= nums[i] <= 1000 0 <= k <= 106
Google,590,N-ary Tree Postorder Traversal,Easy,,
Google,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
Google,772,Basic Calculator III,Hard,"Array, Divide and Conquer, Tree, Matrix",Given a n * n matrix grid of 0's and 1's only. We want to represent grid with a Quad-Tree. Return the root of the Quad-Tree representing grid. A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides; each node has two attributes: val: True if the node represents a grid of 1's or False if the node represents a grid of 0's. Notice that you can assign the val to True or False when isLeaf is False; and both are accepted in the answer. isLeaf: True if the node is a leaf node on the tree or False if the node has four children. class Node { public boolean val; public boolean isLeaf; public Node topLeft; public Node topRight; public Node bottomLeft; public Node bottomRight; } We can construct a Quad-Tree from a two-dimensional area using the following steps: If the current grid has the same value (i.e all 1's or all 0's) set isLeaf True and set val to the value of the grid and set the four children to Null and stop. If the current grid has different values; set isLeaf to False and set val to any value and divide the current grid into four sub-grids as shown in the photo. Recurse for each of the children with the proper sub-grid. If you want to know more about the Quad-Tree; you can refer to the wiki. Quad-Tree format: You don't need to read this section for solving the problem. This is only if you want to understand the output format here. The output represents the serialized format of a Quad-Tree using level order traversal; where null signifies a path terminator where no node exists below. It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list [isLeaf; val]. If the value of isLeaf or val is True we represent it as 1 in the list [isLeaf; val] and if the value of isLeaf or val is False we represent it as 0. Example 1: Input: grid = [[0;1];[1;0]] Output: [[0;1];[1;0];[1;1];[1;1];[1;0]] Explanation: The explanation of this example is shown below: Notice that 0 represents False and 1 represents True in the photo representing the Quad-Tree. Example 2: Input: grid = [[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;1;1;1;1];[1;1;1;1;1;1;1;1];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0]] Output: [[0;1];[1;1];[0;1];[1;1];[1;0];null;null;null;null;[1;0];[1;0];[1;1];[1;1]] Explanation: All values in the grid are not the same. We divide the grid into four sub-grids. The topLeft; bottomLeft and bottomRight each has the same value. The topRight have different values so we divide it into 4 sub-grids where each has the same value. Explanation is shown in the photo below: Constraints: n == grid.length == grid[i].length n == 2x where 0 <= x <= 6
Google,833,Find And Replace in String,Med,"Array, Hash Table, Breadth-First Search",You are given an array routes representing bus routes where routes[i] is a bus route that the ith bus repeats forever. For example; if routes[0] = [1; 5; 7]; this means that the 0th bus travels in the sequence 1 -> 5 -> 7 -> 1 -> 5 -> 7 -> 1 -> ... forever. You will start at the bus stop source (You are not on any bus initially); and you want to go to the bus stop target. You can travel between bus stops by buses only. Return the least number of buses you must take to travel from source to target. Return -1 if it is not possible. Example 1: Input: routes = [[1;2;7];[3;6;7]]; source = 1; target = 6 Output: 2 Explanation: The best strategy is take the first bus to the bus stop 7; then take the second bus to the bus stop 6. Example 2: Input: routes = [[7;12];[4;5;15];[6];[15;19];[9;12;13]]; source = 15; target = 12 Output: -1 Constraints: 1 <= routes.length <= 500. 1 <= routes[i].length <= 105 All the values of routes[i] are unique. sum(routes[i].length) <= 105 0 <= routes[i][j] < 106 0 <= source; target < 106
Google,844,Backspace String Compare,Easy,,
Google,846,Hand of Straights,Med,,
Google,863,All Nodes Distance K in Binary Tree,Med,"Dynamic Programming, Tree, Depth-First Search, Graph",There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Return an array answer of length n where answer[i] is the sum of the distances between the ith node in the tree and all other nodes. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;3];[2;4];[2;5]] Output: [8;12;6;10;10;10] Explanation: The tree is shown above. We can see that dist(0;1) + dist(0;2) + dist(0;3) + dist(0;4) + dist(0;5) equals 1 + 1 + 2 + 2 + 2 = 8. Hence; answer[0] = 8; and so on. Example 2: Input: n = 1; edges = [] Output: [0] Example 3: Input: n = 2; edges = [[1;0]] Output: [1;1] Constraints: 1 <= n <= 3 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n ai != bi The given input represents a valid tree.
Google,867,Transpose Matrix,Easy,"Math, Dynamic Programming, Sliding Window, Probability and Statistics","Alice plays the following game; loosely based on the card game ""21"". Alice starts with 0 points and draws numbers while she has less than k points. During each draw; she gains an integer number of points randomly from the range [1; maxPts]; where maxPts is an integer. Each draw is independent and the outcomes have equal probabilities. Alice stops drawing numbers when she gets k or more points. Return the probability that Alice has n or fewer points. Answers within 10-5 of the actual answer are considered accepted. Example 1: Input: n = 10; k = 1; maxPts = 10 Output: 1.00000 Explanation: Alice gets a single card; then stops. Example 2: Input: n = 6; k = 1; maxPts = 10 Output: 0.60000 Explanation: Alice gets a single card; then stops. In 6 out of 10 possibilities; she is at or below 6 points. Example 3: Input: n = 21; k = 17; maxPts = 10 Output: 0.73278 Constraints: 0 <= k <= n <= 104 1 <= maxPts <= 104"
Google,876,Middle of the Linked List,Easy,"Array, Hash Table, Greedy, Sorting",Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize; and consists of groupSize consecutive cards. Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize; return true if she can rearrange the cards; or false otherwise. Example 1: Input: hand = [1;2;3;6;2;3;4;7;8]; groupSize = 3 Output: true Explanation: Alice's hand can be rearranged as [1;2;3];[2;3;4];[6;7;8] Example 2: Input: hand = [1;2;3;4;5]; groupSize = 4 Output: false Explanation: Alice's hand can not be rearranged into groups of 4. Constraints: 1 <= hand.length <= 104 0 <= hand[i] <= 109 1 <= groupSize <= hand.length Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/
Google,904,Fruit Into Baskets,Med,"Tree, Depth-First Search, Binary Tree",Consider all the leaves of a binary tree; from left to right order; the values of those leaves form a leaf value sequence. For example; in the given tree above; the leaf value sequence is (6; 7; 4; 9; 8). Two binary trees are considered leaf-similar if their leaf value sequence is the same. Return true if and only if the two given trees with head nodes root1 and root2 are leaf-similar. Example 1: Input: root1 = [3;5;1;6;2;9;8;null;null;7;4]; root2 = [3;5;1;6;7;4;2;null;null;null;null;null;null;9;8] Output: true Example 2: Input: root1 = [1;2;3]; root2 = [1;3;2] Output: false Constraints: The number of nodes in each tree will be in the range [1; 200]. Both of the given trees will have values in the range [0; 200].
Google,905,Sort Array By Parity,Easy,"Array, Hash Table, Dynamic Programming",A sequence x1; x2; ...; xn is Fibonacci-like if: n >= 3 xi + xi+1 == xi+2 for all i + 2 <= n Given a strictly increasing array arr of positive integers forming a sequence; return the length of the longest Fibonacci-like subsequence of arr. If one does not exist; return 0. A subsequence is derived from another sequence arr by deleting any number of elements (including none) from arr; without changing the order of the remaining elements. For example; [3; 5; 8] is a subsequence of [3; 4; 5; 6; 7; 8]. Example 1: Input: arr = [1;2;3;4;5;6;7;8] Output: 5 Explanation: The longest subsequence that is fibonacci-like: [1;2;3;5;8]. Example 2: Input: arr = [1;3;7;11;12;14;18] Output: 3 Explanation: The longest subsequence that is fibonacci-like: [1;11;12]; [3;11;14] or [7;11;18]. Constraints: 3 <= arr.length <= 1000 1 <= arr[i] < arr[i + 1] <= 109
Google,938,Range Sum of BST,Easy,"Array, Math, String, Binary Search, Dynamic Programming","Given an array of digits which is sorted in non-decreasing order. You can write numbers using each digits[i] as many times as we want. For example; if digits = ['1';'3';'5']; we may write numbers such as '13'; '551'; and '1351315'. Return the number of positive integers that can be generated that are less than or equal to a given integer n. Example 1: Input: digits = [""1"";""3"";""5"";""7""]; n = 100 Output: 20 Explanation: The 20 numbers that can be written are: 1; 3; 5; 7; 11; 13; 15; 17; 31; 33; 35; 37; 51; 53; 55; 57; 71; 73; 75; 77. Example 2: Input: digits = [""1"";""4"";""9""]; n = 1000000000 Output: 29523 Explanation: We can write 3 one digit numbers; 9 two digit numbers; 27 three digit numbers; 81 four digit numbers; 243 five digit numbers; 729 six digit numbers; 2187 seven digit numbers; 6561 eight digit numbers; and 19683 nine digit numbers. In total; this is 29523 integers that can be written using the digits array. Example 3: Input: digits = [""7""]; n = 8 Output: 1 Constraints: 1 <= digits.length <= 9 digits[i].length == 1 digits[i] is a digit from '1' to '9'. All the values in digits are unique. digits is sorted in non-decreasing order. 1 <= n <= 109"
Google,947,Most Stones Removed with Same Row or Column,Med,"Array, Hash Table, Binary Search, Design","You are given two integer arrays persons and times. In an election; the ith vote was cast for persons[i] at time times[i]. For each query at a time t; find the person that was leading the election at time t. Votes cast at time t will count towards our query. In the case of a tie; the most recent vote (among tied candidates) wins. Implement the TopVotedCandidate class: TopVotedCandidate(int[] persons; int[] times) Initializes the object with the persons and times arrays. int q(int t) Returns the number of the person that was leading the election at time t according to the mentioned rules. Example 1: Input [""TopVotedCandidate""; ""q""; ""q""; ""q""; ""q""; ""q""; ""q""] [[[0; 1; 1; 0; 0; 1; 0]; [0; 5; 10; 15; 20; 25; 30]]; [3]; [12]; [25]; [15]; [24]; [8]] Output [null; 0; 1; 1; 0; 0; 1] Explanation TopVotedCandidate topVotedCandidate = new TopVotedCandidate([0; 1; 1; 0; 0; 1; 0]; [0; 5; 10; 15; 20; 25; 30]); topVotedCandidate.q(3); // return 0; At time 3; the votes are [0]; and 0 is leading. topVotedCandidate.q(12); // return 1; At time 12; the votes are [0;1;1]; and 1 is leading. topVotedCandidate.q(25); // return 1; At time 25; the votes are [0;1;1;0;0;1]; and 1 is leading (as ties go to the most recent vote.) topVotedCandidate.q(15); // return 0 topVotedCandidate.q(24); // return 0 topVotedCandidate.q(8); // return 1 Constraints: 1 <= persons.length <= 5000 times.length == persons.length 0 <= persons[i] < persons.length 0 <= times[i] <= 109 times is sorted in a strictly increasing order. times[0] <= t <= 109 At most 104 calls will be made to q."
Google,977,Squares of a Sorted Array,Easy,"String, Dynamic Programming","Given a string s; return the number of distinct non-empty subsequences of s. Since the answer may be very large; return it modulo 109 + 7. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not. Example 1: Input: s = ""abc"" Output: 7 Explanation: The 7 distinct subsequences are ""a""; ""b""; ""c""; ""ab""; ""ac""; ""bc""; and ""abc"". Example 2: Input: s = ""aba"" Output: 6 Explanation: The 6 distinct subsequences are ""a""; ""b""; ""ab""; ""aa""; ""ba""; and ""aba"". Example 3: Input: s = ""aaa"" Output: 3 Explanation: The 3 distinct subsequences are ""a""; ""aa"" and ""aaa"". Constraints: 1 <= s.length <= 2000 s consists of lowercase English letters."
Google,983,Minimum Cost For Tickets,Med,"Array, Stack, Simulation",Given two integer arrays pushed and popped each with distinct values; return true if this could have been the result of a sequence of push and pop operations on an initially empty stack; or false otherwise. Example 1: Input: pushed = [1;2;3;4;5]; popped = [4;5;3;2;1] Output: true Explanation: We might do the following sequence: push(1); push(2); push(3); push(4); pop() -> 4; push(5); pop() -> 5; pop() -> 3; pop() -> 2; pop() -> 1 Example 2: Input: pushed = [1;2;3;4;5]; popped = [4;3;5;1;2] Output: false Explanation: 1 cannot be popped before 2. Constraints: 1 <= pushed.length <= 1000 0 <= pushed[i] <= 1000 All the elements of pushed are unique. popped.length == pushed.length popped is a permutation of pushed.
Google,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Google,1057,Campus Bikes,Med,"Math, Dynamic Programming",Given an integer n; return the number of positive integers in the range [1; n] that have at least one repeated digit. Example 1: Input: n = 20 Output: 1 Explanation: The only positive number (<= 20) with at least 1 repeated digit is 11. Example 2: Input: n = 100 Output: 10 Explanation: The positive numbers (<= 100) with atleast 1 repeated digit are 11; 22; 33; 44; 55; 66; 77; 88; 99; and 100. Example 3: Input: n = 1000 Output: 262 Constraints: 1 <= n <= 109
Google,1046,Last Stone Weight,Easy,"Array, Binary Search, Sliding Window, Prefix Sum",Given a binary array nums and an integer k; return the maximum number of consecutive 1's in the array if you can flip at most k 0's. Example 1: Input: nums = [1;1;1;0;0;0;1;1;1;1;0]; k = 2 Output: 6 Explanation: [1;1;1;0;0;1;1;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Example 2: Input: nums = [0;0;1;1;0;0;1;1;1;0;1;1;0;0;0;1;1;1;1]; k = 3 Output: 10 Explanation: [0;0;1;1;1;1;1;1;1;1;1;1;0;0;0;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1. 0 <= k <= nums.length
Google,1047,Remove All Adjacent Duplicates In String,Easy,"Array, Greedy, Sorting",Given an integer array nums and an integer k; modify the array in the following way: choose an index i and replace nums[i] with -nums[i]. You should apply this process exactly k times. You may choose the same index i multiple times. Return the largest possible sum of the array after modifying it in this way. Example 1: Input: nums = [4;2;3]; k = 1 Output: 5 Explanation: Choose index 1 and nums becomes [4;-2;3]. Example 2: Input: nums = [3;-1;0;2]; k = 3 Output: 6 Explanation: Choose indices (1; 2; 2) and nums becomes [3;1;0;2]. Example 3: Input: nums = [2;-3;-1;5;-4]; k = 2 Output: 13 Explanation: Choose indices (1; 4) and nums becomes [2;3;-1;5;4]. Constraints: 1 <= nums.length <= 104 -100 <= nums[i] <= 100 1 <= k <= 104
Google,1106,Parsing A Boolean Expression,Hard,"Array, Hash Table, Depth-First Search, Breadth-First Search",There is a 1 million by 1 million grid on an XY-plane; and the coordinates of each grid square are (x; y). We start at the source = [sx; sy] square and want to reach the target = [tx; ty] square. There is also an array of blocked squares; where each blocked[i] = [xi; yi] represents a blocked square with coordinates (xi; yi). Each move; we can walk one square north; east; south; or west if the square is not in the array of blocked squares. We are also not allowed to walk outside of the grid. Return true if and only if it is possible to reach the target square from the source square through a sequence of valid moves. Example 1: Input: blocked = [[0;1];[1;0]]; source = [0;0]; target = [0;2] Output: false Explanation: The target square is inaccessible starting from the source square because we cannot move. We cannot move north or east because those squares are blocked. We cannot move south or west because we cannot go outside of the grid. Example 2: Input: blocked = []; source = [0;0]; target = [999999;999999] Output: true Explanation: Because there are no blocked cells; it is possible to reach the target square. Constraints: 0 <= blocked.length <= 200 blocked[i].length == 2 0 <= xi; yi < 106 source.length == target.length == 2 0 <= sx; sy; tx; ty < 106 source != target It is guaranteed that source and target are not blocked.
Google,1146,Snapshot Array,Med,"Math, String","For two strings s and t; we say ""t divides s"" if and only if s = t + t + t + ... + t + t (i.e.; t is concatenated with itself one or more times). Given two strings str1 and str2; return the largest string x such that x divides both str1 and str2. Example 1: Input: str1 = ""ABCABC""; str2 = ""ABC"" Output: ""ABC"" Example 2: Input: str1 = ""ABABAB""; str2 = ""ABAB"" Output: ""AB"" Example 3: Input: str1 = ""LEET""; str2 = ""CODE"" Output: """" Constraints: 1 <= str1.length; str2.length <= 1000 str1 and str2 consist of English uppercase letters."
Google,1192,Critical Connections in a Network,Hard,"Array, Binary Search",
Google,1233,Remove Sub-Folders from the Filesystem,Med,"Array, Divide and Conquer, Interactive",
Google,2263,Make Array Non-decreasing or Non-increasing,Hard,"Array, Binary Search, Greedy, Sorting",You have n computers. You are given the integer n and a 0-indexed integer array batteries where the ith battery can run a computer for batteries[i] minutes. You are interested in running all n computers simultaneously using the given batteries. Initially; you can insert at most one battery into each computer. After that and at any integer time moment; you can remove a battery from a computer and insert another battery any number of times. The inserted battery can be a totally new battery or a battery from another computer. You may assume that the removing and inserting processes take no time. Note that the batteries cannot be recharged. Return the maximum number of minutes you can run all the n computers simultaneously. Example 1: Input: n = 2; batteries = [3;3;3] Output: 4 Explanation: Initially; insert battery 0 into the first computer and battery 1 into the second computer. After two minutes; remove battery 1 from the second computer and insert battery 2 instead. Note that battery 1 can still run for one minute. At the end of the third minute; battery 0 is drained; and you need to remove it from the first computer and insert battery 1 instead. By the end of the fourth minute; battery 1 is also drained; and the first computer is no longer running. We can run the two computers simultaneously for at most 4 minutes; so we return 4. Example 2: Input: n = 2; batteries = [1;1;1;1] Output: 2 Explanation: Initially; insert battery 0 into the first computer and battery 2 into the second computer. After one minute; battery 0 and battery 2 are drained so you need to remove them and insert battery 1 into the first computer and battery 3 into the second computer. After another minute; battery 1 and battery 3 are also drained so the first and second computers are no longer running. We can run the two computers simultaneously for at most 2 minutes; so we return 2. Constraints: 1 <= n <= batteries.length <= 105 1 <= batteries[i] <= 109
Google,1348,Tweet Counts Per Frequency,Med,"Array, Dynamic Programming",You are given two 0-indexed integer arrays nums1 and nums2; both of length n. You can choose two integers left and right where 0 <= left <= right < n and swap the subarray nums1[left...right] with the subarray nums2[left...right]. For example; if nums1 = [1;2;3;4;5] and nums2 = [11;12;13;14;15] and you choose left = 1 and right = 2; nums1 becomes [1;12;13;4;5] and nums2 becomes [11;2;3;14;15]. You may choose to apply the mentioned operation once or not do anything. The score of the arrays is the maximum of sum(nums1) and sum(nums2); where sum(arr) is the sum of all the elements in the array arr. Return the maximum possible score. A subarray is a contiguous sequence of elements within an array. arr[left...right] denotes the subarray that contains the elements of nums between indices left and right (inclusive). Example 1: Input: nums1 = [60;60;60]; nums2 = [10;90;10] Output: 210 Explanation: Choosing left = 1 and right = 1; we have nums1 = [60;90;60] and nums2 = [10;60;10]. The score is max(sum(nums1); sum(nums2)) = max(210; 80) = 210. Example 2: Input: nums1 = [20;40;20;70;30]; nums2 = [50;20;50;40;20] Output: 220 Explanation: Choosing left = 3; right = 4; we have nums1 = [20;40;20;40;20] and nums2 = [50;20;50;70;30]. The score is max(sum(nums1); sum(nums2)) = max(140; 220) = 220. Example 3: Input: nums1 = [7;11;13]; nums2 = [1;1;1] Output: 31 Explanation: We choose not to swap any subarray. The score is max(sum(nums1); sum(nums2)) = max(31; 3) = 31. Constraints: n == nums1.length == nums2.length 1 <= n <= 105 1 <= nums1[i]; nums2[i] <= 104
Google,1367,Linked List in Binary Tree,Med,"Array, Dynamic Programming, Sorting",Given n cuboids where the dimensions of the ith cuboid is cuboids[i] = [widthi; lengthi; heighti] (0-indexed). Choose a subset of cuboids and place them on each other. You can place cuboid i on cuboid j if widthi <= widthj and lengthi <= lengthj and heighti <= heightj. You can rearrange any cuboid's dimensions by rotating it to put it on another cuboid. Return the maximum height of the stacked cuboids. Example 1: Input: cuboids = [[50;45;20];[95;37;53];[45;23;12]] Output: 190 Explanation: Cuboid 1 is placed on the bottom with the 53x37 side facing down with height 95. Cuboid 0 is placed next with the 45x20 side facing down with height 50. Cuboid 2 is placed next with the 23x12 side facing down with height 45. The total height is 95 + 50 + 45 = 190. Example 2: Input: cuboids = [[38;25;45];[76;35;3]] Output: 76 Explanation: You can't place any of the cuboids on the other. We choose cuboid 1 and rotate it so that the 35x3 side is facing down and its height is 76. Example 3: Input: cuboids = [[7;11;17];[7;17;11];[11;7;17];[11;17;7];[17;7;11];[17;11;7]] Output: 102 Explanation: After rearranging the cuboids; you can see that all cuboids have the same dimension. You can place the 11x7 side down on all cuboids so their heights are 17. The maximum height of stacked cuboids is 6 * 17 = 102. Constraints: n == cuboids.length 1 <= n <= 100 1 <= widthi; lengthi; heighti <= 100
Google,1438,Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit,Med,Database,
Google,1480,Running Sum of 1d Array,Easy,Database,"Table: Movies +---------------+---------+ | Column Name | Type | +---------------+---------+ | movie_id | int | | title | varchar | +---------------+---------+ movie_id is the primary key (column with unique values) for this table. title is the name of the movie. Table: Users +---------------+---------+ | Column Name | Type | +---------------+---------+ | user_id | int | | name | varchar | +---------------+---------+ user_id is the primary key (column with unique values) for this table. The column 'name' has unique values. Table: MovieRating +---------------+---------+ | Column Name | Type | +---------------+---------+ | movie_id | int | | user_id | int | | rating | int | | created_at | date | +---------------+---------+ (movie_id; user_id) is the primary key (column with unique values) for this table. This table contains the rating of a movie by a user in their review. created_at is the user's review date. Write a solution to: Find the name of the user who has rated the greatest number of movies. In case of a tie; return the lexicographically smaller user name. Find the movie name with the highest average rating in February 2020. In case of a tie; return the lexicographically smaller movie name. The result format is in the following example. Example 1: Input: Movies table: +-------------+--------------+ | movie_id | title | +-------------+--------------+ | 1 | Avengers | | 2 | Frozen 2 | | 3 | Joker | +-------------+--------------+ Users table: +-------------+--------------+ | user_id | name | +-------------+--------------+ | 1 | Daniel | | 2 | Monica | | 3 | Maria | | 4 | James | +-------------+--------------+ MovieRating table: +-------------+--------------+--------------+-------------+ | movie_id | user_id | rating | created_at | +-------------+--------------+--------------+-------------+ | 1 | 1 | 3 | 2020-01-12 | | 1 | 2 | 4 | 2020-02-11 | | 1 | 3 | 2 | 2020-02-12 | | 1 | 4 | 1 | 2020-01-01 | | 2 | 1 | 5 | 2020-02-17 | | 2 | 2 | 2 | 2020-02-01 | | 2 | 3 | 2 | 2020-03-01 | | 3 | 1 | 3 | 2020-02-22 | | 3 | 2 | 4 | 2020-02-25 | +-------------+--------------+--------------+-------------+ Output: +--------------+ | results | +--------------+ | Daniel | | Frozen 2 | +--------------+ Explanation: Daniel and Monica have rated 3 movies (""Avengers""; ""Frozen 2"" and ""Joker"") but Daniel is smaller lexicographically. Frozen 2 and Joker have a rating average of 3.5 in February but Frozen 2 is smaller lexicographically."
Google,1512,Number of Good Pairs,Easy,"Hash Table, String, Design","An underground railway system is keeping track of customer travel times between different stations. They are using this data to calculate the average time it takes to travel from one station to another. Implement the UndergroundSystem class: void checkIn(int id; string stationName; int t) A customer with a card ID equal to id; checks in at the station stationName at time t. A customer can only be checked into one place at a time. void checkOut(int id; string stationName; int t) A customer with a card ID equal to id; checks out from the station stationName at time t. double getAverageTime(string startStation; string endStation) Returns the average time it takes to travel from startStation to endStation. The average time is computed from all the previous traveling times from startStation to endStation that happened directly; meaning a check in at startStation followed by a check out from endStation. The time it takes to travel from startStation to endStation may be different from the time it takes to travel from endStation to startStation. There will be at least one customer that has traveled from startStation to endStation before getAverageTime is called. You may assume all calls to the checkIn and checkOut methods are consistent. If a customer checks in at time t1 then checks out at time t2; then t1 < t2. All events happen in chronological order. Example 1: Input [""UndergroundSystem"";""checkIn"";""checkIn"";""checkIn"";""checkOut"";""checkOut"";""checkOut"";""getAverageTime"";""getAverageTime"";""checkIn"";""getAverageTime"";""checkOut"";""getAverageTime""] [[];[45;""Leyton"";3];[32;""Paradise"";8];[27;""Leyton"";10];[45;""Waterloo"";15];[27;""Waterloo"";20];[32;""Cambridge"";22];[""Paradise"";""Cambridge""];[""Leyton"";""Waterloo""];[10;""Leyton"";24];[""Leyton"";""Waterloo""];[10;""Waterloo"";38];[""Leyton"";""Waterloo""]] Output [null;null;null;null;null;null;null;14.00000;11.00000;null;11.00000;null;12.00000] Explanation UndergroundSystem undergroundSystem = new UndergroundSystem(); undergroundSystem.checkIn(45; ""Leyton""; 3); undergroundSystem.checkIn(32; ""Paradise""; 8); undergroundSystem.checkIn(27; ""Leyton""; 10); undergroundSystem.checkOut(45; ""Waterloo""; 15); // Customer 45 ""Leyton"" -> ""Waterloo"" in 15-3 = 12 undergroundSystem.checkOut(27; ""Waterloo""; 20); // Customer 27 ""Leyton"" -> ""Waterloo"" in 20-10 = 10 undergroundSystem.checkOut(32; ""Cambridge""; 22); // Customer 32 ""Paradise"" -> ""Cambridge"" in 22-8 = 14 undergroundSystem.getAverageTime(""Paradise""; ""Cambridge""); // return 14.00000. One trip ""Paradise"" -> ""Cambridge""; (14) / 1 = 14 undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 11.00000. Two trips ""Leyton"" -> ""Waterloo""; (10 + 12) / 2 = 11 undergroundSystem.checkIn(10; ""Leyton""; 24); undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 11.00000 undergroundSystem.checkOut(10; ""Waterloo""; 38); // Customer 10 ""Leyton"" -> ""Waterloo"" in 38-24 = 14 undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 12.00000. Three trips ""Leyton"" -> ""Waterloo""; (10 + 12 + 14) / 3 = 12 Example 2: Input [""UndergroundSystem"";""checkIn"";""checkOut"";""getAverageTime"";""checkIn"";""checkOut"";""getAverageTime"";""checkIn"";""checkOut"";""getAverageTime""] [[];[10;""Leyton"";3];[10;""Paradise"";8];[""Leyton"";""Paradise""];[5;""Leyton"";10];[5;""Paradise"";16];[""Leyton"";""Paradise""];[2;""Leyton"";21];[2;""Paradise"";30];[""Leyton"";""Paradise""]] Output [null;null;null;5.00000;null;null;5.50000;null;null;6.66667] Explanation UndergroundSystem undergroundSystem = new UndergroundSystem(); undergroundSystem.checkIn(10; ""Leyton""; 3); undergroundSystem.checkOut(10; ""Paradise""; 8); // Customer 10 ""Leyton"" -> ""Paradise"" in 8-3 = 5 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 5.00000; (5) / 1 = 5 undergroundSystem.checkIn(5; ""Leyton""; 10); undergroundSystem.checkOut(5; ""Paradise""; 16); // Customer 5 ""Leyton"" -> ""Paradise"" in 16-10 = 6 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 5.50000; (5 + 6) / 2 = 5.5 undergroundSystem.checkIn(2; ""Leyton""; 21); undergroundSystem.checkOut(2; ""Paradise""; 30); // Customer 2 ""Leyton"" -> ""Paradise"" in 30-21 = 9 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 6.66667; (5 + 6 + 9) / 3 = 6.66667 Constraints: 1 <= id; t <= 106 1 <= stationName.length; startStation.length; endStation.length <= 10 All strings consist of uppercase and lowercase English letters and digits. There will be at most 2 * 104 calls in total to checkIn; checkOut; and getAverageTime. Answers within 10-5 of the actual value will be accepted."
Google,1593,Split a String Into the Max Number of Unique Substrings,Med,,
Google,1672,Richest Customer Wealth,Easy,"Array, Binary Search, Interactive",
Google,1661,Average Time of Process per Machine,Easy,Graph,Given a directed acyclic graph; with n vertices numbered from 0 to n-1; and an array edges where edges[i] = [fromi; toi] represents a directed edge from node fromi to node toi. Find the smallest set of vertices from which all nodes in the graph are reachable. It's guaranteed that a unique solution exists. Notice that you can return the vertices in any order. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;5];[3;4];[4;2]] Output: [0;3] Explanation: It's not possible to reach all the nodes from a single vertex. From 0 we can reach [0;1;2;5]. From 3 we can reach [3;4;2;5]. So we output [0;3]. Example 2: Input: n = 5; edges = [[0;1];[2;1];[3;1];[1;4];[2;4]] Output: [0;2;3] Explanation: Notice that vertices 0; 3 and 2 are not reachable from any other node; so we must include them. Also any of these vertices can reach nodes 1 and 4. Constraints: 2 <= n <= 10^5 1 <= edges.length <= min(10^5; n * (n - 1) / 2) edges[i].length == 2 0 <= fromi; toi < n All pairs (fromi; toi) are distinct.
Google,1696,Jump Game VI,Med,"Array, Graph, Topological Sort, Matrix",There is a strange printer with the following two special requirements: On each turn; the printer will print a solid rectangular pattern of a single color on the grid. This will cover up the existing colors in the rectangle. Once the printer has used a color for the above operation; the same color cannot be used again. You are given a m x n matrix targetGrid; where targetGrid[row][col] is the color in the position (row; col) of the grid. Return true if it is possible to print the matrix targetGrid; otherwise; return false. Example 1: Input: targetGrid = [[1;1;1;1];[1;2;2;1];[1;2;2;1];[1;1;1;1]] Output: true Example 2: Input: targetGrid = [[1;1;1;1];[1;1;3;3];[1;1;3;4];[5;5;1;4]] Output: true Example 3: Input: targetGrid = [[1;2;1];[2;1;2];[1;2;1]] Output: false Explanation: It is impossible to form targetGrid because it is not allowed to print the same color in different turns. Constraints: m == targetGrid.length n == targetGrid[i].length 1 <= m; n <= 60 1 <= targetGrid[row][col] <= 60
Google,1743,Restore the Array From Adjacent Pairs,Med,"Hash Table, String, Dynamic Programming, Enumeration","Given two strings s and t; find the number of ways you can choose a non-empty substring of s and replace a single character by a different character such that the resulting substring is a substring of t. In other words; find the number of substrings in s that differ from some substring in t by exactly one character. For example; the underlined substrings in ""computer"" and ""computation"" only differ by the 'e'/'a'; so this is a valid way. Return the number of substrings that satisfy the condition above. A substring is a contiguous sequence of characters within a string. Example 1: Input: s = ""aba""; t = ""baba"" Output: 6 Explanation: The following are the pairs of substrings from s and t that differ by exactly 1 character: (""aba""; ""baba"") (""aba""; ""baba"") (""aba""; ""baba"") (""aba""; ""baba"") (""aba""; ""baba"") (""aba""; ""baba"") The underlined portions are the substrings that are chosen from s and t. ​​Example 2: Input: s = ""ab""; t = ""bb"" Output: 3 Explanation: The following are the pairs of substrings from s and t that differ by 1 character: (""ab""; ""bb"") (""ab""; ""bb"") (""ab""; ""bb"") ​​​​The underlined portions are the substrings that are chosen from s and t. Constraints: 1 <= s.length; t.length <= 100 s and t consist of lowercase English letters only."
Google,1834,Single-Threaded CPU,Med,"Array, Hash Table, Greedy",On a social network consisting of m users and some friendships between users; two users can communicate with each other if they know a common language. You are given an integer n; an array languages; and an array friendships where: There are n languages numbered 1 through n; languages[i] is the set of languages the i​​​​​​th​​​​ user knows; and friendships[i] = [u​​​​​​i​​​; v​​​​​​i] denotes a friendship between the users u​​​​​​​​​​​i​​​​​ and vi. You can choose one language and teach it to some users so that all friends can communicate with each other. Return the minimum number of users you need to teach. Note that friendships are not transitive; meaning if x is a friend of y and y is a friend of z; this doesn't guarantee that x is a friend of z. Example 1: Input: n = 2; languages = [[1];[2];[1;2]]; friendships = [[1;2];[1;3];[2;3]] Output: 1 Explanation: You can either teach user 1 the second language or user 2 the first language. Example 2: Input: n = 3; languages = [[2];[1;3];[1;2];[3]]; friendships = [[1;4];[1;2];[3;4];[2;3]] Output: 2 Explanation: Teach the third language to users 1 and 3; yielding two users to teach. Constraints: 2 <= n <= 500 languages.length == m 1 <= m <= 500 1 <= languages[i].length <= n 1 <= languages[i][j] <= n 1 <= u​​​​​​i < v​​​​​​i <= languages.length 1 <= friendships.length <= 500 All tuples (u​​​​​i; v​​​​​​i) are unique languages[i] contains only unique values
Google,1851,Minimum Interval to Include Each Query,Hard,"Array, Binary Search, Dynamic Programming, Sorting",You are given an array of events where events[i] = [startDayi; endDayi; valuei]. The ith event starts at startDayi and ends at endDayi; and if you attend this event; you will receive a value of valuei. You are also given an integer k which represents the maximum number of events you can attend. You can only attend one event at a time. If you choose to attend an event; you must attend the entire event. Note that the end day is inclusive: that is; you cannot attend two events where one of them starts and the other ends on the same day. Return the maximum sum of values that you can receive by attending events. Example 1: Input: events = [[1;2;4];[3;4;3];[2;3;1]]; k = 2 Output: 7 Explanation: Choose the green events; 0 and 1 (0-indexed) for a total value of 4 + 3 = 7. Example 2: Input: events = [[1;2;4];[3;4;3];[2;3;10]]; k = 2 Output: 10 Explanation: Choose event 2 for a total value of 10. Notice that you cannot attend any other event as they overlap; and that you do not have to attend k events. Example 3: Input: events = [[1;1;1];[2;2;2];[3;3;3];[4;4;4]]; k = 3 Output: 9 Explanation: Although the events do not overlap; you can only attend 3 events. Pick the highest valued three. Constraints: 1 <= k <= events.length 1 <= k * events.length <= 106 1 <= startDayi <= endDayi <= 109 1 <= valuei <= 106
Google,1978,Employees Whose Manager Left the Company,Easy,"Two Pointers, String, Greedy","You are given a string num; representing a large integer; and an integer k. We call some integer wonderful if it is a permutation of the digits in num and is greater in value than num. There can be many wonderful integers. However; we only care about the smallest-valued ones. For example; when num = ""5489355142"": The 1st smallest wonderful integer is ""5489355214"". The 2nd smallest wonderful integer is ""5489355241"". The 3rd smallest wonderful integer is ""5489355412"". The 4th smallest wonderful integer is ""5489355421"". Return the minimum number of adjacent digit swaps that needs to be applied to num to reach the kth smallest wonderful integer. The tests are generated in such a way that kth smallest wonderful integer exists. Example 1: Input: num = ""5489355142""; k = 4 Output: 2 Explanation: The 4th smallest wonderful number is ""5489355421"". To get this number: - Swap index 7 with index 8: ""5489355142"" -> ""5489355412"" - Swap index 8 with index 9: ""5489355412"" -> ""5489355421"" Example 2: Input: num = ""11112""; k = 4 Output: 4 Explanation: The 4th smallest wonderful number is ""21111"". To get this number: - Swap index 3 with index 4: ""11112"" -> ""11121"" - Swap index 2 with index 3: ""11121"" -> ""11211"" - Swap index 1 with index 2: ""11211"" -> ""12111"" - Swap index 0 with index 1: ""12111"" -> ""21111"" Example 3: Input: num = ""00123""; k = 1 Output: 1 Explanation: The 1st smallest wonderful number is ""00132"". To get this number: - Swap index 3 with index 4: ""00123"" -> ""00132"" Constraints: 2 <= num.length <= 1000 1 <= k <= 1000 num only consists of digits."
Google,2022,Convert 1D Array Into 2D Array,Easy,"Array, Dynamic Programming",The alternating sum of a 0-indexed array is defined as the sum of the elements at even indices minus the sum of the elements at odd indices. For example; the alternating sum of [4;2;5;3] is (4 + 5) - (2 + 3) = 4. Given an array nums; return the maximum alternating sum of any subsequence of nums (after reindexing the elements of the subsequence). A subsequence of an array is a new array generated from the original array by deleting some elements (possibly none) without changing the remaining elements' relative order. For example; [2;7;4] is a subsequence of [4;2;3;7;2;1;4] (the underlined elements); while [2;4;2] is not. Example 1: Input: nums = [4;2;5;3] Output: 7 Explanation: It is optimal to choose the subsequence [4;2;5] with alternating sum (4 + 5) - 2 = 7. Example 2: Input: nums = [5;6;7;8] Output: 8 Explanation: It is optimal to choose the subsequence [8] with alternating sum 8. Example 3: Input: nums = [6;2;1;2;4;5] Output: 10 Explanation: It is optimal to choose the subsequence [6;1;5] with alternating sum (6 + 5) - 1 = 10. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105
Google,2044,Count Number of Maximum Bitwise-OR Subsets,Med,"Hash Table, String, Bit Manipulation, Prefix Sum","A wonderful string is a string where at most one letter appears an odd number of times. For example; ""ccjjc"" and ""abab"" are wonderful; but ""ab"" is not. Given a string word that consists of the first ten lowercase English letters ('a' through 'j'); return the number of wonderful non-empty substrings in word. If the same substring appears multiple times in word; then count each occurrence separately. A substring is a contiguous sequence of characters in a string. Example 1: Input: word = ""aba"" Output: 4 Explanation: The four wonderful substrings are underlined below: - ""aba"" -> ""a"" - ""aba"" -> ""b"" - ""aba"" -> ""a"" - ""aba"" -> ""aba"" Example 2: Input: word = ""aabb"" Output: 9 Explanation: The nine wonderful substrings are underlined below: - ""aabb"" -> ""a"" - ""aabb"" -> ""aa"" - ""aabb"" -> ""aab"" - ""aabb"" -> ""aabb"" - ""aabb"" -> ""a"" - ""aabb"" -> ""abb"" - ""aabb"" -> ""b"" - ""aabb"" -> ""bb"" - ""aabb"" -> ""b"" Example 3: Input: word = ""he"" Output: 2 Explanation: The two wonderful substrings are underlined below: - ""he"" -> ""h"" - ""he"" -> ""e"" Constraints: 1 <= word.length <= 105 word consists of lowercase English letters from 'a' to 'j'."
Google,2115,Find All Possible Recipes from Given Supplies,Med,"String, Dynamic Programming","You are given a binary string binary. A subsequence of binary is considered good if it is not empty and has no leading zeros (with the exception of ""0""). Find the number of unique good subsequences of binary. For example; if binary = ""001""; then all the good subsequences are [""0""; ""0""; ""1""]; so the unique good subsequences are ""0"" and ""1"". Note that subsequences ""00""; ""01""; and ""001"" are not good because they have leading zeros. Return the number of unique good subsequences of binary. Since the answer may be very large; return it modulo 109 + 7. A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements. Example 1: Input: binary = ""001"" Output: 2 Explanation: The good subsequences of binary are [""0""; ""0""; ""1""]. The unique good subsequences are ""0"" and ""1"". Example 2: Input: binary = ""11"" Output: 2 Explanation: The good subsequences of binary are [""1""; ""1""; ""11""]. The unique good subsequences are ""1"" and ""11"". Example 3: Input: binary = ""101"" Output: 5 Explanation: The good subsequences of binary are [""1""; ""0""; ""1""; ""10""; ""11""; ""101""]. The unique good subsequences are ""0""; ""1""; ""10""; ""11""; and ""101"". Constraints: 1 <= binary.length <= 105 binary consists of only '0's and '1's."
Google,2220,Minimum Bit Flips to Convert Number,Easy,"Array, Hash Table, String, Graph, Topological Sort","You have information about n different recipes. You are given a string array recipes and a 2D string array ingredients. The ith recipe has the name recipes[i]; and you can create it if you have all the needed ingredients from ingredients[i]. Ingredients to a recipe may need to be created from other recipes; i.e.; ingredients[i] may contain a string that is in recipes. You are also given a string array supplies containing all the ingredients that you initially have; and you have an infinite supply of all of them. Return a list of all the recipes that you can create. You may return the answer in any order. Note that two recipes may contain each other in their ingredients. Example 1: Input: recipes = [""bread""]; ingredients = [[""yeast"";""flour""]]; supplies = [""yeast"";""flour"";""corn""] Output: [""bread""] Explanation: We can create ""bread"" since we have the ingredients ""yeast"" and ""flour"". Example 2: Input: recipes = [""bread"";""sandwich""]; ingredients = [[""yeast"";""flour""];[""bread"";""meat""]]; supplies = [""yeast"";""flour"";""meat""] Output: [""bread"";""sandwich""] Explanation: We can create ""bread"" since we have the ingredients ""yeast"" and ""flour"". We can create ""sandwich"" since we have the ingredient ""meat"" and can create the ingredient ""bread"". Example 3: Input: recipes = [""bread"";""sandwich"";""burger""]; ingredients = [[""yeast"";""flour""];[""bread"";""meat""];[""sandwich"";""meat"";""bread""]]; supplies = [""yeast"";""flour"";""meat""] Output: [""bread"";""sandwich"";""burger""] Explanation: We can create ""bread"" since we have the ingredients ""yeast"" and ""flour"". We can create ""sandwich"" since we have the ingredient ""meat"" and can create the ingredient ""bread"". We can create ""burger"" since we have the ingredient ""meat"" and can create the ingredients ""bread"" and ""sandwich"". Constraints: n == recipes.length == ingredients.length 1 <= n <= 100 1 <= ingredients[i].length; supplies.length <= 100 1 <= recipes[i].length; ingredients[i][j].length; supplies[k].length <= 10 recipes[i]; ingredients[i][j]; and supplies[k] consist only of lowercase English letters. All the values of recipes and supplies combined are unique. Each ingredients[i] does not contain any duplicate values."
Google,2275,Largest Combination With Bitwise AND Greater Than Zero,Med,"String, Sliding Window, Rolling Hash, Hash Function","The hash of a 0-indexed string s of length k; given integers p and m; is computed using the following function: hash(s; p; m) = (val(s[0]) * p0 + val(s[1]) * p1 + ... + val(s[k-1]) * pk-1) mod m. Where val(s[i]) represents the index of s[i] in the alphabet from val('a') = 1 to val('z') = 26. You are given a string s and the integers power; modulo; k; and hashValue. Return sub; the first substring of s of length k such that hash(sub; power; modulo) == hashValue. The test cases will be generated such that an answer always exists. A substring is a contiguous non-empty sequence of characters within a string. Example 1: Input: s = ""leetcode""; power = 7; modulo = 20; k = 2; hashValue = 0 Output: ""ee"" Explanation: The hash of ""ee"" can be computed to be hash(""ee""; 7; 20) = (5 * 1 + 5 * 7) mod 20 = 40 mod 20 = 0. ""ee"" is the first substring of length 2 with hashValue 0. Hence; we return ""ee"". Example 2: Input: s = ""fbxzaad""; power = 31; modulo = 100; k = 3; hashValue = 32 Output: ""fbx"" Explanation: The hash of ""fbx"" can be computed to be hash(""fbx""; 31; 100) = (6 * 1 + 2 * 31 + 24 * 312) mod 100 = 23132 mod 100 = 32. The hash of ""bxz"" can be computed to be hash(""bxz""; 31; 100) = (2 * 1 + 24 * 31 + 26 * 312) mod 100 = 25732 mod 100 = 32. ""fbx"" is the first substring of length 3 with hashValue 32. Hence; we return ""fbx"". Note that ""bxz"" also has a hash of 32 but it appears later than ""fbx"". Constraints: 1 <= k <= s.length <= 2 * 104 1 <= power; modulo <= 109 0 <= hashValue < modulo s consists of lowercase English letters only. The test cases are generated such that an answer always exists."
Google,2284,Sender With Largest Word Count,Med,"Math, Sorting",You are given an integer num. Rearrange the digits of num such that its value is minimized and it does not contain any leading zeros. Return the rearranged number with minimal value. Note that the sign of the number does not change after rearranging the digits. Example 1: Input: num = 310 Output: 103 Explanation: The possible arrangements for the digits of 310 are 013; 031; 103; 130; 301; 310. The arrangement with the smallest value that does not contain any leading zeros is 103. Example 2: Input: num = -7605 Output: -7650 Explanation: Some possible arrangements for the digits of -7605 are -7650; -6705; -5076; -0567. The arrangement with the smallest value that does not contain any leading zeros is -7650. Constraints: -1015 <= num <= 1015
Google,2326,Spiral Matrix IV,Med,"String, Binary Search, Rolling Hash, Suffix Array, String Matching, Hash Function","You are building a string s of length n one character at a time; prepending each new character to the front of the string. The strings are labeled from 1 to n; where the string with length i is labeled si. For example; for s = ""abaca""; s1 == ""a""; s2 == ""ca""; s3 == ""aca""; etc. The score of si is the length of the longest common prefix between si and sn (Note that s == sn). Given the final string s; return the sum of the score of every si. Example 1: Input: s = ""babab"" Output: 9 Explanation: For s1 == ""b""; the longest common prefix is ""b"" which has a score of 1. For s2 == ""ab""; there is no common prefix so the score is 0. For s3 == ""bab""; the longest common prefix is ""bab"" which has a score of 3. For s4 == ""abab""; there is no common prefix so the score is 0. For s5 == ""babab""; the longest common prefix is ""babab"" which has a score of 5. The sum of the scores is 1 + 0 + 3 + 0 + 5 = 9; so we return 9. Example 2: Input: s = ""azbazbzaz"" Output: 14 Explanation: For s2 == ""az""; the longest common prefix is ""az"" which has a score of 2. For s6 == ""azbzaz""; the longest common prefix is ""azb"" which has a score of 3. For s9 == ""azbazbzaz""; the longest common prefix is ""azbazbzaz"" which has a score of 9. For all other si; the score is 0. The sum of the scores is 2 + 3 + 9 = 14; so we return 14. Constraints: 1 <= s.length <= 105 s consists of lowercase English letters."
Google,2336,Smallest Number in Infinite Set,Med,Database,
Google,2402,Meeting Rooms III,Hard,"Array, Math, Bit Manipulation",You are given a 0-indexed integer array nums. In one operation; select any non-negative integer x and an index i; then update nums[i] to be equal to nums[i] AND (nums[i] XOR x). Note that AND is the bitwise AND operation and XOR is the bitwise XOR operation. Return the maximum possible bitwise XOR of all elements of nums after applying the operation any number of times. Example 1: Input: nums = [3;2;4;6] Output: 7 Explanation: Apply the operation with x = 4 and i = 3; num[3] = 6 AND (6 XOR 4) = 6 AND 2 = 2. Now; nums = [3; 2; 4; 2] and the bitwise XOR of all the elements = 3 XOR 2 XOR 4 XOR 2 = 7. It can be shown that 7 is the maximum possible bitwise XOR. Note that other operations may be used to achieve a bitwise XOR of 7. Example 2: Input: nums = [1;2;3;9;2] Output: 11 Explanation: Apply the operation zero times. The bitwise XOR of all the elements = 1 XOR 2 XOR 3 XOR 9 XOR 2 = 11. It can be shown that 11 is the maximum possible bitwise XOR. Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 108
Google,2406,Divide Intervals Into Minimum Number of Groups,Med,"Hash Table, String","You are given the strings key and message; which represent a cipher key and a secret message; respectively. The steps to decode message are as follows: Use the first appearance of all 26 lowercase English letters in key as the order of the substitution table. Align the substitution table with the regular English alphabet. Each letter in message is then substituted using the table. Spaces ' ' are transformed to themselves. For example; given key = ""happy boy"" (actual key would have at least one instance of each letter in the alphabet); we have the partial substitution table of ('h' -> 'a'; 'a' -> 'b'; 'p' -> 'c'; 'y' -> 'd'; 'b' -> 'e'; 'o' -> 'f'). Return the decoded message. Example 1: Input: key = ""the quick brown fox jumps over the lazy dog""; message = ""vkbs bs t suepuv"" Output: ""this is a secret"" Explanation: The diagram above shows the substitution table. It is obtained by taking the first appearance of each letter in ""the quick brown fox jumps over the lazy dog"". Example 2: Input: key = ""eljuxhpwnyrdgtqkviszcfmabo""; message = ""zwx hnfx lqantp mnoeius ycgk vcnjrdb"" Output: ""the five boxing wizards jump quickly"" Explanation: The diagram above shows the substitution table. It is obtained by taking the first appearance of each letter in ""eljuxhpwnyrdgtqkviszcfmabo"". Constraints: 26 <= key.length <= 2000 key consists of lowercase English letters and ' '. key contains every letter in the English alphabet ('a' to 'z') at least once. 1 <= message.length <= 2000 message consists of lowercase English letters and ' '."
Google,2419,Longest Subarray With Maximum Bitwise AND,Med,"Array, Stack, Union Find, Monotonic Stack",You are given an integer array nums and an integer threshold. Find any subarray of nums of length k such that every element in the subarray is greater than threshold / k. Return the size of any such subarray. If there is no such subarray; return -1. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;3;4;3;1]; threshold = 6 Output: 3 Explanation: The subarray [3;4;3] has a size of 3; and every element is greater than 6 / 3 = 2. Note that this is the only valid subarray. Example 2: Input: nums = [6;5;6;5;8]; threshold = 7 Output: 1 Explanation: The subarray [8] has a size of 1; and 8 > 7 / 1 = 7. So 1 is returned. Note that the subarray [6;5] has a size of 2; and every element is greater than 7 / 2 = 3.5. Similarly; the subarrays [6;5;6]; [6;5;6;5]; [6;5;6;5;8] also satisfy the given conditions. Therefore; 2; 3; 4; or 5 may also be returned. Constraints: 1 <= nums.length <= 105 1 <= nums[i]; threshold <= 109
Google,2707,Extra Characters in a String,Med,"Array, Hash Table, Two Pointers",You are given two 2D integer arrays nums1 and nums2. nums1[i] = [idi; vali] indicate that the number with the id idi has a value equal to vali. nums2[i] = [idi; vali] indicate that the number with the id idi has a value equal to vali. Each array contains unique ids and is sorted in ascending order by id. Merge the two arrays into one array that is sorted in ascending order by id; respecting the following conditions: Only ids that appear in at least one of the two arrays should be included in the resulting array. Each id should be included only once and its value should be the sum of the values of this id in the two arrays. If the id does not exist in one of the two arrays then its value in that array is considered to be 0. Return the resulting array. The returned array must be sorted in ascending order by id. Example 1: Input: nums1 = [[1;2];[2;3];[4;5]]; nums2 = [[1;4];[3;2];[4;1]] Output: [[1;6];[2;3];[3;2];[4;6]] Explanation: The resulting array contains the following: - id = 1; the value of this id is 2 + 4 = 6. - id = 2; the value of this id is 3. - id = 3; the value of this id is 2. - id = 4; the value of this id is 5 + 1 = 6. Example 2: Input: nums1 = [[2;4];[3;6];[5;5]]; nums2 = [[1;3];[4;3]] Output: [[1;3];[2;4];[3;6];[4;3];[5;5]] Explanation: There are no common ids; so we just include each id with its value in the resulting list. Constraints: 1 <= nums1.length; nums2.length <= 200 nums1[i].length == nums2[j].length == 2 1 <= idi; vali <= 1000 Both arrays contain unique ids. Both arrays are in strictly ascending order by id.
Google,2704,To Be Or Not To Be,Easy,"Math, Greedy",You are given an integer num. You know that Bob will sneakily remap one of the 10 possible digits (0 to 9) to another digit. Return the difference between the maximum and minimum values Bob can make by remapping exactly one digit in num. Notes: When Bob remaps a digit d1 to another digit d2; Bob replaces all occurrences of d1 in num with d2. Bob can remap a digit to itself; in which case num does not change. Bob can remap different digits for obtaining minimum and maximum values respectively. The resulting number after remapping can contain leading zeroes. Example 1: Input: num = 11891 Output: 99009 Explanation: To achieve the maximum value; Bob can remap the digit 1 to the digit 9 to yield 99899. To achieve the minimum value; Bob can remap the digit 1 to the digit 0; yielding 890. The difference between these two numbers is 99009. Example 2: Input: num = 90 Output: 99 Explanation: The maximum value that can be returned by the function is 99 (if 0 is replaced by 9) and the minimum value that can be returned by the function is 0 (if 9 is replaced by 0). Thus; we return 99. Constraints: 1 <= num <= 108
Google,3110,Score of a String,Easy,,
Google,3097,Shortest Subarray With OR at Least K II,Med,Database,
Google,3319,K-th Largest Perfect Subtree Size in Binary Tree,Med,,
Google,3286,Find a Safe Walk Through a Grid,Med,Database,
Google,30,Substring with Concatenation of All Words,Hard,"Hash Table, String, Sliding Window","You are given a string s and an array of strings words. All the strings of words are of the same length. A concatenated string is a string that exactly contains all the strings of any permutation of words concatenated. For example; if words = [""ab"";""cd"";""ef""]; then ""abcdef""; ""abefcd""; ""cdabef""; ""cdefab""; ""efabcd""; and ""efcdab"" are all concatenated strings. ""acdbef"" is not a concatenated string because it is not the concatenation of any permutation of words. Return an array of the starting indices of all the concatenated substrings in s. You can return the answer in any order. Example 1: Input: s = ""barfoothefoobarman""; words = [""foo"";""bar""] Output: [0;9] Explanation: The substring starting at 0 is ""barfoo"". It is the concatenation of [""bar"";""foo""] which is a permutation of words. The substring starting at 9 is ""foobar"". It is the concatenation of [""foo"";""bar""] which is a permutation of words. Example 2: Input: s = ""wordgoodgoodgoodbestword""; words = [""word"";""good"";""best"";""word""] Output: [] Explanation: There is no concatenated substring. Example 3: Input: s = ""barfoofoobarthefoobarman""; words = [""bar"";""foo"";""the""] Output: [6;9;12] Explanation: The substring starting at 6 is ""foobarthe"". It is the concatenation of [""foo"";""bar"";""the""]. The substring starting at 9 is ""barthefoo"". It is the concatenation of [""bar"";""the"";""foo""]. The substring starting at 12 is ""thefoobar"". It is the concatenation of [""the"";""foo"";""bar""]. Constraints: 1 <= s.length <= 104 1 <= words.length <= 5000 1 <= words[i].length <= 30 s and words[i] consist of lowercase English letters."
Google,44,Wildcard Matching,Hard,"String, Dynamic Programming, Greedy, Recursion","Given an input string (s) and a pattern (p); implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""*"" Output: true Explanation: '*' matches any sequence. Example 3: Input: s = ""cb""; p = ""?a"" Output: false Explanation: '?' matches 'c'; but the second letter is 'a'; which does not match 'b'. Constraints: 0 <= s.length; p.length <= 2000 s contains only lowercase English letters. p contains only lowercase English letters; '?' or '*'."
Google,47,Permutations II,Med,"Array, Backtracking",Given a collection of numbers; nums; that might contain duplicates; return all possible unique permutations in any order. Example 1: Input: nums = [1;1;2] Output: [[1;1;2]; [1;2;1]; [2;1;1]] Example 2: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Constraints: 1 <= nums.length <= 8 -10 <= nums[i] <= 10
Google,58,Length of Last Word,Easy,String,"Given a string s consisting of words and spaces; return the length of the last word in the string. A word is a maximal substring consisting of non-space characters only. Example 1: Input: s = ""Hello World"" Output: 5 Explanation: The last word is ""World"" with length 5. Example 2: Input: s = "" fly me to the moon "" Output: 4 Explanation: The last word is ""moon"" with length 4. Example 3: Input: s = ""luffy is still joyboy"" Output: 6 Explanation: The last word is ""joyboy"" with length 6. Constraints: 1 <= s.length <= 104 s consists of only English letters and spaces ' '. There will be at least one word in s."
Google,63,Unique Paths II,Med,"Array, Dynamic Programming, Matrix",You are given an m x n integer array grid. There is a robot initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. An obstacle and space are marked as 1 or 0 respectively in grid. A path that the robot takes cannot include any square that is an obstacle. Return the number of possible unique paths that the robot can take to reach the bottom-right corner. The testcases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: obstacleGrid = [[0;0;0];[0;1;0];[0;0;0]] Output: 2 Explanation: There is one obstacle in the middle of the 3x3 grid above. There are two ways to reach the bottom-right corner: 1. Right -> Right -> Down -> Down 2. Down -> Down -> Right -> Right Example 2: Input: obstacleGrid = [[0;1];[0;0]] Output: 1 Constraints: m == obstacleGrid.length n == obstacleGrid[i].length 1 <= m; n <= 100 obstacleGrid[i][j] is 0 or 1.
Google,81,Search in Rotated Sorted Array II,Med,"Array, Binary Search",There is an integer array nums sorted in non-decreasing order (not necessarily with distinct values). Before being passed to your function; nums is rotated at an unknown pivot index k (0 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;4;4;5;6;6;7] might be rotated at pivot index 5 and become [4;5;6;6;7;0;1;2;4;4]. Given the array nums after the rotation and an integer target; return true if target is in nums; or false if it is not in nums. You must decrease the overall operation steps as much as possible. Example 1: Input: nums = [2;5;6;0;0;1;2]; target = 0 Output: true Example 2: Input: nums = [2;5;6;0;0;1;2]; target = 3 Output: false Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 nums is guaranteed to be rotated at some pivot. -104 <= target <= 104 Follow up: This problem is similar to Search in Rotated Sorted Array; but nums may contain duplicates. Would this affect the runtime complexity? How and why?
Google,86,Partition List,Med,"Linked List, Two Pointers",Given the head of a linked list and a value x; partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of the two partitions. Example 1: Input: head = [1;4;3;2;5;2]; x = 3 Output: [1;2;2;4;3;5] Example 2: Input: head = [2;1]; x = 2 Output: [1;2] Constraints: The number of nodes in the list is in the range [0; 200]. -100 <= Node.val <= 100 -200 <= x <= 200
Google,90,Subsets II,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums that may contain duplicates; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;2] Output: [[];[1];[1;2];[1;2;2];[2];[2;2]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10
Google,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Google,106,Construct Binary Tree from Inorder and Postorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays inorder and postorder where inorder is the inorder traversal of a binary tree and postorder is the postorder traversal of the same tree; construct and return the binary tree. Example 1: Input: inorder = [9;3;15;20;7]; postorder = [9;15;7;20;3] Output: [3;9;20;null;null;15;7] Example 2: Input: inorder = [-1]; postorder = [-1] Output: [-1] Constraints: 1 <= inorder.length <= 3000 postorder.length == inorder.length -3000 <= inorder[i]; postorder[i] <= 3000 inorder and postorder consist of unique values. Each value of postorder also appears in inorder. inorder is guaranteed to be the inorder traversal of the tree. postorder is guaranteed to be the postorder traversal of the tree.
Google,110,Balanced Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given a binary tree; determine if it is height-balanced. Example 1: Input: root = [3;9;20;null;null;15;7] Output: true Example 2: Input: root = [1;2;2;3;3;null;null;4;4] Output: false Example 3: Input: root = [] Output: true Constraints: The number of nodes in the tree is in the range [0; 5000]. -104 <= Node.val <= 104
Google,113,Path Sum II,Med,"Backtracking, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path should be returned as a list of the node values; not node references. A root-to-leaf path is a path starting from the root and ending at any leaf node. A leaf is a node with no children. Example 1: Input: root = [5;4;8;11;null;13;4;7;2;null;null;5;1]; targetSum = 22 Output: [[5;4;11;2];[5;8;4;5]] Explanation: There are two paths whose sum equals targetSum: 5 + 4 + 11 + 2 = 22 5 + 8 + 4 + 5 = 22 Example 2: Input: root = [1;2;3]; targetSum = 5 Output: [] Example 3: Input: root = [1;2]; targetSum = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 5000]. -1000 <= Node.val <= 1000 -1000 <= targetSum <= 1000
Google,114,Flatten Binary Tree to Linked List,Med,"Linked List, Stack, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; flatten the tree into a ""linked list"": The ""linked list"" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. The ""linked list"" should be in the same order as a pre-order traversal of the binary tree. Example 1: Input: root = [1;2;5;3;4;null;6] Output: [1;null;2;null;3;null;4;null;5;null;6] Example 2: Input: root = [] Output: [] Example 3: Input: root = [0] Output: [0] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100 Follow up: Can you flatten the tree in-place (with O(1) extra space)?"
Google,123,Best Time to Buy and Sell Stock III,Hard,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete at most two transactions. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: prices = [3;3;5;0;0;3;1;4] Output: 6 Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Then buy on day 7 (price = 1) and sell on day 8 (price = 4); profit = 4-1 = 3. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Note that you cannot buy on day 1; buy on day 2 and sell them later; as you are engaging multiple transactions at the same time. You must sell before buying again. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transaction is done; i.e. max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 105
Google,126,Word Ladder II,Hard,"Hash Table, String, Backtracking, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return all the shortest transformation sequences from beginWord to endWord; or an empty list if no such sequence exists. Each sequence should be returned as a list of the words [beginWord; s1; s2; ...; sk]. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: [[""hit"";""hot"";""dot"";""dog"";""cog""];[""hit"";""hot"";""lot"";""log"";""cog""]] Explanation: There are 2 shortest transformation sequences: ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> ""cog"" ""hit"" -> ""hot"" -> ""lot"" -> ""log"" -> ""cog"" Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: [] Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 5 endWord.length == beginWord.length 1 <= wordList.length <= 500 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique. The sum of all shortest transformation sequences does not exceed 105."
Google,131,Palindrome Partitioning,Med,"String, Dynamic Programming, Backtracking","Given a string s; partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s. Example 1: Input: s = ""aab"" Output: [[""a"";""a"";""b""];[""aa"";""b""]] Example 2: Input: s = ""a"" Output: [[""a""]] Constraints: 1 <= s.length <= 16 s contains only lowercase English letters."
Google,133,Clone Graph,Med,"Hash Table, Depth-First Search, Breadth-First Search, Graph",Given a reference of a node in a connected undirected graph. Return a deep copy (clone) of the graph. Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors. class Node { public int val; public List<Node> neighbors; } Test case format: For simplicity; each node's value is the same as the node's index (1-indexed). For example; the first node with val == 1; the second node with val == 2; and so on. The graph is represented in the test case using an adjacency list. An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph. The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph. Example 1: Input: adjList = [[2;4];[1;3];[2;4];[1;3]] Output: [[2;4];[1;3];[2;4];[1;3]] Explanation: There are 4 nodes in the graph. 1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). 3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). Example 2: Input: adjList = [[]] Output: [[]] Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors. Example 3: Input: adjList = [] Output: [] Explanation: This an empty graph; it does not have any nodes. Constraints: The number of nodes in the graph is in the range [0; 100]. 1 <= Node.val <= 100 Node.val is unique for each node. There are no repeated edges and no self-loops in the graph. The Graph is connected and all nodes can be visited starting from the given node.
Google,135,Candy,Hard,"Array, Greedy",There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings. You are giving candies to these children subjected to the following requirements: Each child must have at least one candy. Children with a higher rating get more candies than their neighbors. Return the minimum number of candies you need to have to distribute the candies to the children. Example 1: Input: ratings = [1;0;2] Output: 5 Explanation: You can allocate to the first; second and third child with 2; 1; 2 candies respectively. Example 2: Input: ratings = [1;2;2] Output: 4 Explanation: You can allocate to the first; second and third child with 1; 2; 1 candies respectively. The third child gets 1 candy because it satisfies the above two conditions. Constraints: n == ratings.length 1 <= n <= 2 * 104 0 <= ratings[i] <= 2 * 104
Google,148,Sort List,Med,"Linked List, Two Pointers, Divide and Conquer, Sorting, Merge Sort",Given the head of a linked list; return the list after sorting it in ascending order. Example 1: Input: head = [4;2;1;3] Output: [1;2;3;4] Example 2: Input: head = [-1;5;3;4;0] Output: [-1;0;3;4;5] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is in the range [0; 5 * 104]. -105 <= Node.val <= 105 Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?
Google,149,Max Points on a Line,Hard,"Array, Hash Table, Math, Geometry",Given an array of points where points[i] = [xi; yi] represents a point on the X-Y plane; return the maximum number of points that lie on the same straight line. Example 1: Input: points = [[1;1];[2;2];[3;3]] Output: 3 Example 2: Input: points = [[1;1];[3;2];[5;3];[4;1];[2;3];[1;4]] Output: 4 Constraints: 1 <= points.length <= 300 points[i].length == 2 -104 <= xi; yi <= 104 All the points are unique.
Google,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
Google,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Google,167,Two Sum II - Input Array Is Sorted,Med,"Array, Two Pointers, Binary Search",Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order; find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 1 <= index1 < index2 <= numbers.length. Return the indices of the two numbers; index1 and index2; added by one as an integer array [index1; index2] of length 2. The tests are generated such that there is exactly one solution. You may not use the same element twice. Your solution must use only constant extra space. Example 1: Input: numbers = [2;7;11;15]; target = 9 Output: [1;2] Explanation: The sum of 2 and 7 is 9. Therefore; index1 = 1; index2 = 2. We return [1; 2]. Example 2: Input: numbers = [2;3;4]; target = 6 Output: [1;3] Explanation: The sum of 2 and 4 is 6. Therefore index1 = 1; index2 = 3. We return [1; 3]. Example 3: Input: numbers = [-1;0]; target = -1 Output: [1;2] Explanation: The sum of -1 and 0 is -1. Therefore index1 = 1; index2 = 2. We return [1; 2]. Constraints: 2 <= numbers.length <= 3 * 104 -1000 <= numbers[i] <= 1000 numbers is sorted in non-decreasing order. -1000 <= target <= 1000 The tests are generated such that there is exactly one solution.
Google,197,Rising Temperature,Easy,Database,Table: Weather +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | recordDate | date | | temperature | int | +---------------+---------+ id is the column with unique values for this table. There are no different rows with the same recordDate. This table contains information about the temperature on a certain day. Write a solution to find all dates' id with higher temperatures compared to its previous dates (yesterday). Return the result table in any order. The result format is in the following example. Example 1: Input: Weather table: +----+------------+-------------+ | id | recordDate | temperature | +----+------------+-------------+ | 1 | 2015-01-01 | 10 | | 2 | 2015-01-02 | 25 | | 3 | 2015-01-03 | 20 | | 4 | 2015-01-04 | 30 | +----+------------+-------------+ Output: +----+ | id | +----+ | 2 | | 4 | +----+ Explanation: In 2015-01-02; the temperature was higher than the previous day (10 -> 25). In 2015-01-04; the temperature was higher than the previous day (20 -> 30).
Google,209,Minimum Size Subarray Sum,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of positive integers nums and a positive integer target; return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray; return 0 instead. Example 1: Input: target = 7; nums = [2;3;1;2;4;3] Output: 2 Explanation: The subarray [4;3] has the minimal length under the problem constraint. Example 2: Input: target = 4; nums = [1;4;4] Output: 1 Example 3: Input: target = 11; nums = [1;1;1;1;1;1;1;1] Output: 0 Constraints: 1 <= target <= 109 1 <= nums.length <= 105 1 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution of which the time complexity is O(n log(n)).
Google,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Google,218,The Skyline Problem,Hard,"Array, Divide and Conquer, Binary Indexed Tree, Segment Tree, Line Sweep, Heap (Priority Queue), Ordered Set","A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Given the locations and heights of all the buildings; return the skyline formed by these buildings collectively. The geometric information of each building is given in the array buildings where buildings[i] = [lefti; righti; heighti]: lefti is the x coordinate of the left edge of the ith building. righti is the x coordinate of the right edge of the ith building. heighti is the height of the ith building. You may assume all buildings are perfect rectangles grounded on an absolutely flat surface at height 0. The skyline should be represented as a list of ""key points"" sorted by their x-coordinate in the form [[x1;y1];[x2;y2];...]. Each key point is the left endpoint of some horizontal segment in the skyline except the last point in the list; which always has a y-coordinate 0 and is used to mark the skyline's termination where the rightmost building ends. Any ground between the leftmost and rightmost buildings should be part of the skyline's contour. Note: There must be no consecutive horizontal lines of equal height in the output skyline. For instance; [...;[2 3];[4 5];[7 5];[11 5];[12 7];...] is not acceptable; the three lines of height 5 should be merged into one in the final output as such: [...;[2 3];[4 5];[12 7];...] Example 1: Input: buildings = [[2;9;10];[3;7;15];[5;12;12];[15;20;10];[19;24;8]] Output: [[2;10];[3;15];[7;12];[12;0];[15;10];[20;8];[24;0]] Explanation: Figure A shows the buildings of the input. Figure B shows the skyline formed by those buildings. The red points in figure B represent the key points in the output list. Example 2: Input: buildings = [[0;2;3];[2;5;3]] Output: [[0;3];[5;0]] Constraints: 1 <= buildings.length <= 104 0 <= lefti < righti <= 231 - 1 1 <= heighti <= 231 - 1 buildings is sorted by lefti in non-decreasing order."
Google,222,Count Complete Tree Nodes,Easy,"Binary Search, Bit Manipulation, Tree, Binary Tree",Given the root of a complete binary tree; return the number of the nodes in the tree. According to Wikipedia; every level; except possibly the last; is completely filled in a complete binary tree; and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h. Design an algorithm that runs in less than O(n) time complexity. Example 1: Input: root = [1;2;3;4;5;6] Output: 6 Example 2: Input: root = [] Output: 0 Example 3: Input: root = [1] Output: 1 Constraints: The number of nodes in the tree is in the range [0; 5 * 104]. 0 <= Node.val <= 5 * 104 The tree is guaranteed to be complete.
Google,232,Implement Queue using Stacks,Easy,"Stack, Design, Queue","Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push; peek; pop; and empty). Implement the MyQueue class: void push(int x) Pushes element x to the back of the queue. int pop() Removes the element from the front of the queue and returns it. int peek() Returns the element at the front of the queue. boolean empty() Returns true if the queue is empty; false otherwise. Notes: You must use only standard operations of a stack; which means only push to top; peek/pop from top; size; and is empty operations are valid. Depending on your language; the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack's standard operations. Example 1: Input [""MyQueue""; ""push""; ""push""; ""peek""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 1; 1; false] Explanation MyQueue myQueue = new MyQueue(); myQueue.push(1); // queue is: [1] myQueue.push(2); // queue is: [1; 2] (leftmost is front of the queue) myQueue.peek(); // return 1 myQueue.pop(); // return 1; queue is [2] myQueue.empty(); // return false Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; peek; and empty. All the calls to pop and peek are valid. Follow-up: Can you implement the queue such that each operation is amortized O(1) time complexity? In other words; performing n operations will take overall O(n) time even if one of those operations may take longer."
Google,233,Number of Digit One,Hard,"Math, Dynamic Programming, Recursion",Given an integer n; count the total number of digit 1 appearing in all non-negative integers less than or equal to n. Example 1: Input: n = 13 Output: 6 Example 2: Input: n = 0 Output: 0 Constraints: 0 <= n <= 109
Google,257,Binary Tree Paths,Easy,"String, Backtracking, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; return all root-to-leaf paths in any order. A leaf is a node with no children. Example 1: Input: root = [1;2;3;null;5] Output: [""1->2->5"";""1->3""] Example 2: Input: root = [1] Output: [""1""] Constraints: The number of nodes in the tree is in the range [1; 100]. -100 <= Node.val <= 100"
Google,261,Graph Valid Tree,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
Google,271,Encode and Decode Strings,Med,"Array, String, Design",
Google,273,Integer to English Words,Hard,"Math, String, Recursion","Convert a non-negative integer num to its English words representation. Example 1: Input: num = 123 Output: ""One Hundred Twenty Three"" Example 2: Input: num = 12345 Output: ""Twelve Thousand Three Hundred Forty Five"" Example 3: Input: num = 1234567 Output: ""One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"" Constraints: 0 <= num <= 231 - 1"
Google,280,Wiggle Sort,Med,"Array, Greedy, Sorting",
Google,282,Expression Add Operators,Hard,"Math, String, Backtracking","Given a string num that contains only digits and an integer target; return all possibilities to insert the binary operators '+'; '-'; and/or '*' between the digits of num so that the resultant expression evaluates to the target value. Note that operands in the returned expressions should not contain leading zeros. Example 1: Input: num = ""123""; target = 6 Output: [""1*2*3"";""1+2+3""] Explanation: Both ""1*2*3"" and ""1+2+3"" evaluate to 6. Example 2: Input: num = ""232""; target = 8 Output: [""2*3+2"";""2+3*2""] Explanation: Both ""2*3+2"" and ""2+3*2"" evaluate to 8. Example 3: Input: num = ""3456237490""; target = 9191 Output: [] Explanation: There are no expressions that can be created from ""3456237490"" to evaluate to 9191. Constraints: 1 <= num.length <= 10 num consists of only digits. -231 <= target <= 231 - 1"
Google,292,Nim Game,Easy,"Math, Brainteaser, Game Theory",You are playing the following Nim Game with your friend: Initially; there is a heap of stones on the table. You and your friend will alternate taking turns; and you go first. On each turn; the person whose turn it is will remove 1 to 3 stones from the heap. The one who removes the last stone is the winner. Given n; the number of stones in the heap; return true if you can win the game assuming both you and your friend play optimally; otherwise return false. Example 1: Input: n = 4 Output: false Explanation: These are the possible outcomes: 1. You remove 1 stone. Your friend removes 3 stones; including the last stone. Your friend wins. 2. You remove 2 stones. Your friend removes 2 stones; including the last stone. Your friend wins. 3. You remove 3 stones. Your friend removes the last stone. Your friend wins. In all outcomes; your friend wins. Example 2: Input: n = 1 Output: true Example 3: Input: n = 2 Output: true Constraints: 1 <= n <= 231 - 1
Google,308,Range Sum Query 2D - Mutable,Hard,"Array, Design, Binary Indexed Tree, Segment Tree, Matrix",
Google,309,Best Time to Buy and Sell Stock with Cooldown,Med,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete as many transactions as you like (i.e.; buy one and sell one share of the stock multiple times) with the following restrictions: After you sell your stock; you cannot buy stock on the next day (i.e.; cooldown one day). Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: prices = [1;2;3;0;2] Output: 3 Explanation: transactions = [buy; sell; cooldown; buy; sell] Example 2: Input: prices = [1] Output: 0 Constraints: 1 <= prices.length <= 5000 0 <= prices[i] <= 1000
Google,310,Minimum Height Trees,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",A tree is an undirected graph in which any two vertices are connected by exactly one path. In other words; any connected graph without simple cycles is a tree. Given a tree of n nodes labelled from 0 to n - 1; and an array of n - 1 edges where edges[i] = [ai; bi] indicates that there is an undirected edge between the two nodes ai and bi in the tree; you can choose any node of the tree as the root. When you select a node x as the root; the result tree has height h. Among all possible rooted trees; those with minimum height (i.e. min(h)) are called minimum height trees (MHTs). Return a list of all MHTs' root labels. You can return the answer in any order. The height of a rooted tree is the number of edges on the longest downward path between the root and a leaf. Example 1: Input: n = 4; edges = [[1;0];[1;2];[1;3]] Output: [1] Explanation: As shown; the height of the tree is 1 when the root is the node with label 1 which is the only MHT. Example 2: Input: n = 6; edges = [[3;0];[3;1];[3;2];[3;4];[5;4]] Output: [3;4] Constraints: 1 <= n <= 2 * 104 edges.length == n - 1 0 <= ai; bi < n ai != bi All the pairs (ai; bi) are distinct. The given input is guaranteed to be a tree and there will be no repeated edges.
Google,315,Count of Smaller Numbers After Self,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums; return an integer array counts where counts[i] is the number of smaller elements to the right of nums[i]. Example 1: Input: nums = [5;2;6;1] Output: [2;1;1;0] Explanation: To the right of 5 there are 2 smaller elements (2 and 1). To the right of 2 there is only 1 smaller element (1). To the right of 6 there is 1 smaller element (1). To the right of 1 there is 0 smaller element. Example 2: Input: nums = [-1] Output: [0] Example 3: Input: nums = [-1;-1] Output: [0;0] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104
Google,321,Create Maximum Number,Hard,"Array, Two Pointers, Stack, Greedy, Monotonic Stack",You are given two integer arrays nums1 and nums2 of lengths m and n respectively. nums1 and nums2 represent the digits of two numbers. You are also given an integer k. Create the maximum number of length k <= m + n from digits of the two numbers. The relative order of the digits from the same array must be preserved. Return an array of the k digits representing the answer. Example 1: Input: nums1 = [3;4;6;5]; nums2 = [9;1;2;5;8;3]; k = 5 Output: [9;8;6;5;3] Example 2: Input: nums1 = [6;7]; nums2 = [6;0;4]; k = 5 Output: [6;7;6;0;4] Example 3: Input: nums1 = [3;9]; nums2 = [8;9]; k = 3 Output: [9;8;9] Constraints: m == nums1.length n == nums2.length 1 <= m; n <= 500 0 <= nums1[i]; nums2[i] <= 9 1 <= k <= m + n
Google,334,Increasing Triplet Subsequence,Med,"Array, Greedy",Given an integer array nums; return true if there exists a triple of indices (i; j; k) such that i < j < k and nums[i] < nums[j] < nums[k]. If no such indices exists; return false. Example 1: Input: nums = [1;2;3;4;5] Output: true Explanation: Any triplet where i < j < k is valid. Example 2: Input: nums = [5;4;3;2;1] Output: false Explanation: No triplet exists. Example 3: Input: nums = [2;1;5;0;4;6] Output: true Explanation: The triplet (3; 4; 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6. Constraints: 1 <= nums.length <= 5 * 105 -231 <= nums[i] <= 231 - 1 Follow up: Could you implement a solution that runs in O(n) time complexity and O(1) space complexity?
Google,337,House Robber III,Med,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",The thief has found himself a new place for his thievery again. There is only one entrance to this area; called root. Besides the root; each house has one and only one parent house. After a tour; the smart thief realized that all houses in this place form a binary tree. It will automatically contact the police if two directly-linked houses were broken into on the same night. Given the root of the binary tree; return the maximum amount of money the thief can rob without alerting the police. Example 1: Input: root = [3;2;3;null;3;null;1] Output: 7 Explanation: Maximum amount of money the thief can rob = 3 + 3 + 1 = 7. Example 2: Input: root = [3;4;5;1;3;null;1] Output: 9 Explanation: Maximum amount of money the thief can rob = 4 + 5 = 9. Constraints: The number of nodes in the tree is in the range [1; 104]. 0 <= Node.val <= 104
Google,342,Power of Four,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of four. Otherwise; return false. An integer n is a power of four; if there exists an integer x such that n == 4x. Example 1: Input: n = 16 Output: true Example 2: Input: n = 5 Output: false Example 3: Input: n = 1 Output: true Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Google,344,Reverse String,Easy,"Two Pointers, String","Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory. Example 1: Input: s = [""h"";""e"";""l"";""l"";""o""] Output: [""o"";""l"";""l"";""e"";""h""] Example 2: Input: s = [""H"";""a"";""n"";""n"";""a"";""h""] Output: [""h"";""a"";""n"";""n"";""a"";""H""] Constraints: 1 <= s.length <= 105 s[i] is a printable ascii character."
Google,345,Reverse Vowels of a String,Easy,"Two Pointers, String","Given a string s; reverse only all the vowels in the string and return it. The vowels are 'a'; 'e'; 'i'; 'o'; and 'u'; and they can appear in both lower and upper cases; more than once. Example 1: Input: s = ""IceCreAm"" Output: ""AceCreIm"" Explanation: The vowels in s are ['I'; 'e'; 'e'; 'A']. On reversing the vowels; s becomes ""AceCreIm"". Example 2: Input: s = ""leetcode"" Output: ""leotcede"" Constraints: 1 <= s.length <= 3 * 105 s consist of printable ASCII characters."
Google,367,Valid Perfect Square,Easy,"Math, Binary Search",Given a positive integer num; return true if num is a perfect square or false otherwise. A perfect square is an integer that is the square of an integer. In other words; it is the product of some integer with itself. You must not use any built-in library function; such as sqrt. Example 1: Input: num = 16 Output: true Explanation: We return true because 4 * 4 = 16 and 4 is an integer. Example 2: Input: num = 14 Output: false Explanation: We return false because 3.742 * 3.742 = 14 and 3.742 is not an integer. Constraints: 1 <= num <= 231 - 1
Google,390,Elimination Game,Med,"Math, Recursion",You have a list arr of all integers in the range [1; n] sorted in a strictly increasing order. Apply the following algorithm on arr: Starting from left to right; remove the first number and every other number afterward until you reach the end of the list. Repeat the previous step again; but this time from right to left; remove the rightmost number and every other number from the remaining numbers. Keep repeating the steps again; alternating left to right and right to left; until a single number remains. Given the integer n; return the last number that remains in arr. Example 1: Input: n = 9 Output: 6 Explanation: arr = [1; 2; 3; 4; 5; 6; 7; 8; 9] arr = [2; 4; 6; 8] arr = [2; 6] arr = [6] Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 109
Google,399,Evaluate Division,Med,"Array, String, Depth-First Search, Breadth-First Search, Union Find, Graph, Shortest Path","You are given an array of variable pairs equations and an array of real numbers values; where equations[i] = [Ai; Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable. You are also given some queries; where queries[j] = [Cj; Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries. If a single answer cannot be determined; return -1.0. Note: The input is always valid. You may assume that evaluating the queries will not result in division by zero and that there is no contradiction. Note: The variables that do not occur in the list of equations are undefined; so the answer cannot be determined for them. Example 1: Input: equations = [[""a"";""b""];[""b"";""c""]]; values = [2.0;3.0]; queries = [[""a"";""c""];[""b"";""a""];[""a"";""e""];[""a"";""a""];[""x"";""x""]] Output: [6.00000;0.50000;-1.00000;1.00000;-1.00000] Explanation: Given: a / b = 2.0; b / c = 3.0 queries are: a / c = ?; b / a = ?; a / e = ?; a / a = ?; x / x = ? return: [6.0; 0.5; -1.0; 1.0; -1.0 ] note: x is undefined => -1.0 Example 2: Input: equations = [[""a"";""b""];[""b"";""c""];[""bc"";""cd""]]; values = [1.5;2.5;5.0]; queries = [[""a"";""c""];[""c"";""b""];[""bc"";""cd""];[""cd"";""bc""]] Output: [3.75000;0.40000;5.00000;0.20000] Example 3: Input: equations = [[""a"";""b""]]; values = [0.5]; queries = [[""a"";""b""];[""b"";""a""];[""a"";""c""];[""x"";""y""]] Output: [0.50000;2.00000;-1.00000;-1.00000] Constraints: 1 <= equations.length <= 20 equations[i].length == 2 1 <= Ai.length; Bi.length <= 5 values.length == equations.length 0.0 < values[i] <= 20.0 1 <= queries.length <= 20 queries[i].length == 2 1 <= Cj.length; Dj.length <= 5 Ai; Bi; Cj; Dj consist of lower case English letters and digits."
Google,402,Remove K Digits,Med,"String, Stack, Greedy, Monotonic Stack","Given string num representing a non-negative integer num; and an integer k; return the smallest possible integer after removing k digits from num. Example 1: Input: num = ""1432219""; k = 3 Output: ""1219"" Explanation: Remove the three digits 4; 3; and 2 to form the new number 1219 which is the smallest. Example 2: Input: num = ""10200""; k = 1 Output: ""200"" Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes. Example 3: Input: num = ""10""; k = 2 Output: ""0"" Explanation: Remove all the digits from the number and it is left with nothing which is 0. Constraints: 1 <= k <= num.length <= 105 num consists of only digits. num does not have any leading zeros except for the zero itself."
Google,414,Third Maximum Number,Easy,"Array, Sorting",Given an integer array nums; return the third distinct maximum number in this array. If the third maximum does not exist; return the maximum number. Example 1: Input: nums = [3;2;1] Output: 1 Explanation: The first distinct maximum is 3. The second distinct maximum is 2. The third distinct maximum is 1. Example 2: Input: nums = [1;2] Output: 2 Explanation: The first distinct maximum is 2. The second distinct maximum is 1. The third distinct maximum does not exist; so the maximum (2) is returned instead. Example 3: Input: nums = [2;2;3;1] Output: 1 Explanation: The first distinct maximum is 3. The second distinct maximum is 2 (both 2's are counted together since they have the same value). The third distinct maximum is 1. Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Can you find an O(n) solution?
Google,433,Minimum Genetic Mutation,Med,"Hash Table, String, Breadth-First Search","A gene string can be represented by an 8-character long string; with choices from 'A'; 'C'; 'G'; and 'T'. Suppose we need to investigate a mutation from a gene string startGene to a gene string endGene where one mutation is defined as one single character changed in the gene string. For example; ""AACCGGTT"" --> ""AACCGGTA"" is one mutation. There is also a gene bank bank that records all the valid gene mutations. A gene must be in bank to make it a valid gene string. Given the two gene strings startGene and endGene and the gene bank bank; return the minimum number of mutations needed to mutate from startGene to endGene. If there is no such a mutation; return -1. Note that the starting point is assumed to be valid; so it might not be included in the bank. Example 1: Input: startGene = ""AACCGGTT""; endGene = ""AACCGGTA""; bank = [""AACCGGTA""] Output: 1 Example 2: Input: startGene = ""AACCGGTT""; endGene = ""AAACGGTA""; bank = [""AACCGGTA"";""AACCGCTA"";""AAACGGTA""] Output: 2 Constraints: 0 <= bank.length <= 10 startGene.length == endGene.length == bank[i].length == 8 startGene; endGene; and bank[i] consist of only the characters ['A'; 'C'; 'G'; 'T']."
Google,435,Non-overlapping Intervals,Med,"Array, Dynamic Programming, Greedy, Sorting",Given an array of intervals intervals where intervals[i] = [starti; endi]; return the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping. Note that intervals which only touch at a point are non-overlapping. For example; [1; 2] and [2; 3] are non-overlapping. Example 1: Input: intervals = [[1;2];[2;3];[3;4];[1;3]] Output: 1 Explanation: [1;3] can be removed and the rest of the intervals are non-overlapping. Example 2: Input: intervals = [[1;2];[1;2];[1;2]] Output: 2 Explanation: You need to remove two [1;2] to make the rest of the intervals non-overlapping. Example 3: Input: intervals = [[1;2];[2;3]] Output: 0 Explanation: You don't need to remove any of the intervals since they're already non-overlapping. Constraints: 1 <= intervals.length <= 105 intervals[i].length == 2 -5 * 104 <= starti < endi <= 5 * 104
Google,438,Find All Anagrams in a String,Med,"Hash Table, String, Sliding Window","Given two strings s and p; return an array of all the start indices of p's anagrams in s. You may return the answer in any order. Example 1: Input: s = ""cbaebabacd""; p = ""abc"" Output: [0;6] Explanation: The substring with start index = 0 is ""cba""; which is an anagram of ""abc"". The substring with start index = 6 is ""bac""; which is an anagram of ""abc"". Example 2: Input: s = ""abab""; p = ""ab"" Output: [0;1;2] Explanation: The substring with start index = 0 is ""ab""; which is an anagram of ""ab"". The substring with start index = 1 is ""ba""; which is an anagram of ""ab"". The substring with start index = 2 is ""ab""; which is an anagram of ""ab"". Constraints: 1 <= s.length; p.length <= 3 * 104 s and p consist of lowercase English letters."
Google,446,Arithmetic Slices II - Subsequence,Hard,"Array, Dynamic Programming",Given an integer array nums; return the number of all the arithmetic subsequences of nums. A sequence of numbers is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same. For example; [1; 3; 5; 7; 9]; [7; 7; 7; 7]; and [3; -1; -5; -9] are arithmetic sequences. For example; [1; 1; 2; 5; 7] is not an arithmetic sequence. A subsequence of an array is a sequence that can be formed by removing some elements (possibly none) of the array. For example; [2;5;10] is a subsequence of [1;2;1;2;4;1;5;10]. The test cases are generated so that the answer fits in 32-bit integer. Example 1: Input: nums = [2;4;6;8;10] Output: 7 Explanation: All arithmetic subsequence slices are: [2;4;6] [4;6;8] [6;8;10] [2;4;6;8] [4;6;8;10] [2;4;6;8;10] [2;6;10] Example 2: Input: nums = [7;7;7;7;7] Output: 16 Explanation: Any subsequence of this array is arithmetic. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1
Google,448,Find All Numbers Disappeared in an Array,Easy,"Array, Hash Table",Given an array nums of n integers where nums[i] is in the range [1; n]; return an array of all the integers in the range [1; n] that do not appear in nums. Example 1: Input: nums = [4;3;2;7;8;2;3;1] Output: [5;6] Example 2: Input: nums = [1;1] Output: [2] Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i] <= n Follow up: Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.
Google,476,Number Complement,Easy,Bit Manipulation,"The complement of an integer is the integer you get when you flip all the 0's to 1's and all the 1's to 0's in its binary representation. For example; The integer 5 is ""101"" in binary and its complement is ""010"" which is the integer 2. Given an integer num; return its complement. Example 1: Input: num = 5 Output: 2 Explanation: The binary representation of 5 is 101 (no leading zero bits); and its complement is 010. So you need to output 2. Example 2: Input: num = 1 Output: 0 Explanation: The binary representation of 1 is 1 (no leading zero bits); and its complement is 0. So you need to output 0. Constraints: 1 <= num < 231 Note: This question is the same as 1009: https://leetcode.com/problems/complement-of-base-10-integer/"
Google,486,Predict the Winner,Med,"Array, Math, Dynamic Programming, Recursion, Game Theory",You are given an integer array nums. Two players are playing a game with this array: player 1 and player 2. Player 1 and player 2 take turns; with player 1 starting first. Both players start the game with a score of 0. At each turn; the player takes one of the numbers from either end of the array (i.e.; nums[0] or nums[nums.length - 1]) which reduces the size of the array by 1. The player adds the chosen number to their score. The game ends when there are no more elements in the array. Return true if Player 1 can win the game. If the scores of both players are equal; then player 1 is still the winner; and you should also return true. You may assume that both players are playing optimally. Example 1: Input: nums = [1;5;2] Output: false Explanation: Initially; player 1 can choose between 1 and 2. If he chooses 2 (or 1); then player 2 can choose from 1 (or 2) and 5. If player 2 chooses 5; then player 1 will be left with 1 (or 2). So; final score of player 1 is 1 + 2 = 3; and player 2 is 5. Hence; player 1 will never be the winner and you need to return false. Example 2: Input: nums = [1;5;233;7] Output: true Explanation: Player 1 first chooses 1. Then player 2 has to choose between 5 and 7. No matter which number player 2 choose; player 1 can choose 233. Finally; player 1 has more score (234) than player 2 (12); so you need to return True representing player1 can win. Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 107
Google,518,Coin Change II,Med,"Array, Dynamic Programming",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the number of combinations that make up that amount. If that amount of money cannot be made up by any combination of the coins; return 0. You may assume that you have an infinite number of each kind of coin. The answer is guaranteed to fit into a signed 32-bit integer. Example 1: Input: amount = 5; coins = [1;2;5] Output: 4 Explanation: there are four ways to make up the amount: 5=5 5=2+2+1 5=2+1+1+1 5=1+1+1+1+1 Example 2: Input: amount = 3; coins = [2] Output: 0 Explanation: the amount of 3 cannot be made up just with coins of 2. Example 3: Input: amount = 10; coins = [10] Output: 1 Constraints: 1 <= coins.length <= 300 1 <= coins[i] <= 5000 All the values of coins are unique. 0 <= amount <= 5000
Google,546,Remove Boxes,Hard,"Array, Dynamic Programming, Memoization",You are given several boxes with different colors represented by different positive numbers. You may experience several rounds to remove boxes until there is no box left. Each time you can choose some continuous boxes with the same color (i.e.; composed of k boxes; k >= 1); remove them and get k * k points. Return the maximum points you can get. Example 1: Input: boxes = [1;3;2;2;2;3;4;3;1] Output: 23 Explanation: [1; 3; 2; 2; 2; 3; 4; 3; 1] ----> [1; 3; 3; 4; 3; 1] (3*3=9 points) ----> [1; 3; 3; 3; 1] (1*1=1 points) ----> [1; 1] (3*3=9 points) ----> [] (2*2=4 points) Example 2: Input: boxes = [1;1;1] Output: 9 Example 3: Input: boxes = [1] Output: 1 Constraints: 1 <= boxes.length <= 100 1 <= boxes[i] <= 100
Google,552,Student Attendance Record II,Hard,Dynamic Programming,"An attendance record for a student can be represented as a string where each character signifies whether the student was absent; late; or present on that day. The record only contains the following three characters: 'A': Absent. 'L': Late. 'P': Present. Any student is eligible for an attendance award if they meet both of the following criteria: The student was absent ('A') for strictly fewer than 2 days total. The student was never late ('L') for 3 or more consecutive days. Given an integer n; return the number of possible attendance records of length n that make a student eligible for an attendance award. The answer may be very large; so return it modulo 109 + 7. Example 1: Input: n = 2 Output: 8 Explanation: There are 8 records with length 2 that are eligible for an award: ""PP""; ""AP""; ""PA""; ""LP""; ""PL""; ""AL""; ""LA""; ""LL"" Only ""AA"" is not eligible because there are 2 absences (there need to be fewer than 2). Example 2: Input: n = 1 Output: 3 Example 3: Input: n = 10101 Output: 183236316 Constraints: 1 <= n <= 105"
Google,564,Find the Closest Palindrome,Hard,"Math, String","Given a string n representing an integer; return the closest integer (not including itself); which is a palindrome. If there is a tie; return the smaller one. The closest is defined as the absolute difference minimized between two integers. Example 1: Input: n = ""123"" Output: ""121"" Example 2: Input: n = ""1"" Output: ""0"" Explanation: 0 and 2 are the closest palindromes but we return the smallest which is 0. Constraints: 1 <= n.length <= 18 n consists of only digits. n does not have leading zeros. n is representing an integer in the range [1; 1018 - 1]."
Google,572,Subtree of Another Tree,Easy,"Tree, Depth-First Search, String Matching, Binary Tree, Hash Function",Given the roots of two binary trees root and subRoot; return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise. A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself. Example 1: Input: root = [3;4;5;1;2]; subRoot = [4;1;2] Output: true Example 2: Input: root = [3;4;5;1;2;null;null;null;null;0]; subRoot = [4;1;2] Output: false Constraints: The number of nodes in the root tree is in the range [1; 2000]. The number of nodes in the subRoot tree is in the range [1; 1000]. -104 <= root.val <= 104 -104 <= subRoot.val <= 104
Google,581,Shortest Unsorted Continuous Subarray,Med,"Array, Two Pointers, Stack, Greedy, Sorting, Monotonic Stack",Given an integer array nums; you need to find one continuous subarray such that if you only sort this subarray in non-decreasing order; then the whole array will be sorted in non-decreasing order. Return the shortest such subarray and output its length. Example 1: Input: nums = [2;6;4;8;10;9;15] Output: 5 Explanation: You need to sort [6; 4; 8; 10; 9] in ascending order to make the whole array sorted in ascending order. Example 2: Input: nums = [1;2;3;4] Output: 0 Example 3: Input: nums = [1] Output: 0 Constraints: 1 <= nums.length <= 104 -105 <= nums[i] <= 105 Follow up: Can you solve it in O(n) time complexity?
Google,586,Customer Placing the Largest Number of Orders,Easy,Database,Table: Orders +-----------------+----------+ | Column Name | Type | +-----------------+----------+ | order_number | int | | customer_number | int | +-----------------+----------+ order_number is the primary key (column with unique values) for this table. This table contains information about the order ID and the customer ID. Write a solution to find the customer_number for the customer who has placed the largest number of orders. The test cases are generated so that exactly one customer will have placed more orders than any other customer. The result format is in the following example. Example 1: Input: Orders table: +--------------+-----------------+ | order_number | customer_number | +--------------+-----------------+ | 1 | 1 | | 2 | 2 | | 3 | 3 | | 4 | 3 | +--------------+-----------------+ Output: +-----------------+ | customer_number | +-----------------+ | 3 | +-----------------+ Explanation: The customer with number 3 has two orders; which is greater than either customer 1 or 2 because each of them only has one order. So the result is customer_number 3. Follow up: What if more than one customer has the largest number of orders; can you find all the customer_number in this case?
Google,617,Merge Two Binary Trees,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given two binary trees root1 and root2. Imagine that when you put one of them to cover the other; some nodes of the two trees are overlapped while the others are not. You need to merge the two trees into a new binary tree. The merge rule is that if two nodes overlap; then sum node values up as the new value of the merged node. Otherwise; the NOT null node will be used as the node of the new tree. Return the merged tree. Note: The merging process must start from the root nodes of both trees. Example 1: Input: root1 = [1;3;2;5]; root2 = [2;1;3;null;4;null;7] Output: [3;4;5;5;4;null;7] Example 2: Input: root1 = [1]; root2 = [1;2] Output: [2;2] Constraints: The number of nodes in both trees is in the range [0; 2000]. -104 <= Node.val <= 104
Google,620,Not Boring Movies,Easy,Database,"Table: Cinema +----------------+----------+ | Column Name | Type | +----------------+----------+ | id | int | | movie | varchar | | description | varchar | | rating | float | +----------------+----------+ id is the primary key (column with unique values) for this table. Each row contains information about the name of a movie; its genre; and its rating. rating is a 2 decimal places float in the range [0; 10] Write a solution to report the movies with an odd-numbered ID and a description that is not ""boring"". Return the result table ordered by rating in descending order. The result format is in the following example. Example 1: Input: Cinema table: +----+------------+-------------+--------+ | id | movie | description | rating | +----+------------+-------------+--------+ | 1 | War | great 3D | 8.9 | | 2 | Science | fiction | 8.5 | | 3 | irish | boring | 6.2 | | 4 | Ice song | Fantacy | 8.6 | | 5 | House card | Interesting | 9.1 | +----+------------+-------------+--------+ Output: +----+------------+-------------+--------+ | id | movie | description | rating | +----+------------+-------------+--------+ | 5 | House card | Interesting | 9.1 | | 1 | War | great 3D | 8.9 | +----+------------+-------------+--------+ Explanation: We have three movies with odd-numbered IDs: 1; 3; and 5. The movie with ID = 3 is boring so we do not include it in the answer."
Google,636,Exclusive Time of Functions,Med,"Array, Stack","On a single-threaded CPU; we execute a program containing n functions. Each function has a unique ID between 0 and n-1. Function calls are stored in a call stack: when a function call starts; its ID is pushed onto the stack; and when a function call ends; its ID is popped off the stack. The function whose ID is at the top of the stack is the current function being executed. Each time a function starts or ends; we write a log with the ID; whether it started or ended; and the timestamp. You are given a list logs; where logs[i] represents the ith log message formatted as a string ""{function_id}:{""start"" | ""end""}:{timestamp}"". For example; ""0:start:3"" means a function call with function ID 0 started at the beginning of timestamp 3; and ""1:end:2"" means a function call with function ID 1 ended at the end of timestamp 2. Note that a function can be called multiple times; possibly recursively. A function's exclusive time is the sum of execution times for all function calls in the program. For example; if a function is called twice; one call executing for 2 time units and another call executing for 1 time unit; the exclusive time is 2 + 1 = 3. Return the exclusive time of each function in an array; where the value at the ith index represents the exclusive time for the function with ID i. Example 1: Input: n = 2; logs = [""0:start:0"";""1:start:2"";""1:end:5"";""0:end:6""] Output: [3;4] Explanation: Function 0 starts at the beginning of time 0; then it executes 2 for units of time and reaches the end of time 1. Function 1 starts at the beginning of time 2; executes for 4 units of time; and ends at the end of time 5. Function 0 resumes execution at the beginning of time 6 and executes for 1 unit of time. So function 0 spends 2 + 1 = 3 units of total time executing; and function 1 spends 4 units of total time executing. Example 2: Input: n = 1; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""0:start:6"";""0:end:6"";""0:end:7""] Output: [8] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls itself again. Function 0 (2nd recursive call) starts at the beginning of time 6 and executes for 1 unit of time. Function 0 (initial call) resumes execution at the beginning of time 7 and executes for 1 unit of time. So function 0 spends 2 + 4 + 1 + 1 = 8 units of total time executing. Example 3: Input: n = 2; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""1:start:6"";""1:end:6"";""0:end:7""] Output: [7;1] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls function 1. Function 1 starts at the beginning of time 6; executes 1 unit of time; and ends at the end of time 6. Function 0 resumes execution at the beginning of time 6 and executes for 2 units of time. So function 0 spends 2 + 4 + 1 = 7 units of total time executing; and function 1 spends 1 unit of total time executing. Constraints: 1 <= n <= 100 1 <= logs.length <= 500 0 <= function_id < n 0 <= timestamp <= 109 No two start events will happen at the same timestamp. No two end events will happen at the same timestamp. Each function has an ""end"" log for each ""start"" log."
Google,682,Baseball Game,Easy,"Array, Stack, Simulation","You are keeping the scores for a baseball game with strange rules. At the beginning of the game; you start with an empty record. You are given a list of strings operations; where operations[i] is the ith operation you must apply to the record and is one of the following: An integer x. Record a new score of x. '+'. Record a new score that is the sum of the previous two scores. 'D'. Record a new score that is the double of the previous score. 'C'. Invalidate the previous score; removing it from the record. Return the sum of all the scores on the record after applying all the operations. The test cases are generated such that the answer and all intermediate calculations fit in a 32-bit integer and that all operations are valid. Example 1: Input: ops = [""5"";""2"";""C"";""D"";""+""] Output: 30 Explanation: ""5"" - Add 5 to the record; record is now [5]. ""2"" - Add 2 to the record; record is now [5; 2]. ""C"" - Invalidate and remove the previous score; record is now [5]. ""D"" - Add 2 * 5 = 10 to the record; record is now [5; 10]. ""+"" - Add 5 + 10 = 15 to the record; record is now [5; 10; 15]. The total sum is 5 + 10 + 15 = 30. Example 2: Input: ops = [""5"";""-2"";""4"";""C"";""D"";""9"";""+"";""+""] Output: 27 Explanation: ""5"" - Add 5 to the record; record is now [5]. ""-2"" - Add -2 to the record; record is now [5; -2]. ""4"" - Add 4 to the record; record is now [5; -2; 4]. ""C"" - Invalidate and remove the previous score; record is now [5; -2]. ""D"" - Add 2 * -2 = -4 to the record; record is now [5; -2; -4]. ""9"" - Add 9 to the record; record is now [5; -2; -4; 9]. ""+"" - Add -4 + 9 = 5 to the record; record is now [5; -2; -4; 9; 5]. ""+"" - Add 9 + 5 = 14 to the record; record is now [5; -2; -4; 9; 5; 14]. The total sum is 5 + -2 + -4 + 9 + 5 + 14 = 27. Example 3: Input: ops = [""1"";""C""] Output: 0 Explanation: ""1"" - Add 1 to the record; record is now [1]. ""C"" - Invalidate and remove the previous score; record is now []. Since the record is empty; the total sum is 0. Constraints: 1 <= operations.length <= 1000 operations[i] is ""C""; ""D""; ""+""; or a string representing an integer in the range [-3 * 104; 3 * 104]. For operation ""+""; there will always be at least two previous scores on the record. For operations ""C"" and ""D""; there will always be at least one previous score on the record."
Google,684,Redundant Connection,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",In this problem; a tree is an undirected graph that is connected and has no cycles. You are given a graph that started as a tree with n nodes labeled from 1 to n; with one additional edge added. The added edge has two different vertices chosen from 1 to n; and was not an edge that already existed. The graph is represented as an array edges of length n where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the graph. Return an edge that can be removed so that the resulting graph is a tree of n nodes. If there are multiple answers; return the answer that occurs last in the input. Example 1: Input: edges = [[1;2];[1;3];[2;3]] Output: [2;3] Example 2: Input: edges = [[1;2];[2;3];[3;4];[1;4];[1;5]] Output: [1;4] Constraints: n == edges.length 3 <= n <= 1000 edges[i].length == 2 1 <= ai < bi <= edges.length ai != bi There are no repeated edges. The given graph is connected.
Google,686,Repeated String Match,Med,"String, String Matching","Given two strings a and b; return the minimum number of times you should repeat string a so that string b is a substring of it. If it is impossible for b​​​​​​ to be a substring of a after repeating it; return -1. Notice: string ""abc"" repeated 0 times is """"; repeated 1 time is ""abc"" and repeated 2 times is ""abcabc"". Example 1: Input: a = ""abcd""; b = ""cdabcdab"" Output: 3 Explanation: We return 3 because by repeating a three times ""abcdabcdabcd""; b is a substring of it. Example 2: Input: a = ""a""; b = ""aa"" Output: 2 Constraints: 1 <= a.length; b.length <= 104 a and b consist of lowercase English letters."
Google,718,Maximum Length of Repeated Subarray,Med,"Array, Binary Search, Dynamic Programming, Sliding Window, Rolling Hash, Hash Function",Given two integer arrays nums1 and nums2; return the maximum length of a subarray that appears in both arrays. Example 1: Input: nums1 = [1;2;3;2;1]; nums2 = [3;2;1;4;7] Output: 3 Explanation: The repeated subarray with maximum length is [3;2;1]. Example 2: Input: nums1 = [0;0;0;0;0]; nums2 = [0;0;0;0;0] Output: 5 Explanation: The repeated subarray with maximum length is [0;0;0;0;0]. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 100
Google,724,Find Pivot Index,Easy,"Array, Prefix Sum",Given an array of integers nums; calculate the pivot index of this array. The pivot index is the index where the sum of all the numbers strictly to the left of the index is equal to the sum of all the numbers strictly to the index's right. If the index is on the left edge of the array; then the left sum is 0 because there are no elements to the left. This also applies to the right edge of the array. Return the leftmost pivot index. If no such index exists; return -1. Example 1: Input: nums = [1;7;3;6;5;6] Output: 3 Explanation: The pivot index is 3. Left sum = nums[0] + nums[1] + nums[2] = 1 + 7 + 3 = 11 Right sum = nums[4] + nums[5] = 5 + 6 = 11 Example 2: Input: nums = [1;2;3] Output: -1 Explanation: There is no index that satisfies the conditions in the problem statement. Example 3: Input: nums = [2;1;-1] Output: 0 Explanation: The pivot index is 0. Left sum = 0 (no elements to the left of index 0) Right sum = nums[1] + nums[2] = 1 + -1 = 0 Constraints: 1 <= nums.length <= 104 -1000 <= nums[i] <= 1000 Note: This question is the same as 1991: https://leetcode.com/problems/find-the-middle-index-in-array/
Google,729,My Calendar I,Med,"Array, Binary Search, Design, Segment Tree, Ordered Set","You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a double booking. A double booking happens when two events have some non-empty intersection (i.e.; some moment is common to both events.). The event can be represented as a pair of integers startTime and endTime that represents a booking on the half-open interval [startTime; endTime); the range of real numbers x such that startTime <= x < endTime. Implement the MyCalendar class: MyCalendar() Initializes the calendar object. boolean book(int startTime; int endTime) Returns true if the event can be added to the calendar successfully without causing a double booking. Otherwise; return false and do not add the event to the calendar. Example 1: Input [""MyCalendar""; ""book""; ""book""; ""book""] [[]; [10; 20]; [15; 25]; [20; 30]] Output [null; true; false; true] Explanation MyCalendar myCalendar = new MyCalendar(); myCalendar.book(10; 20); // return True myCalendar.book(15; 25); // return False; It can not be booked because time 15 is already booked by another event. myCalendar.book(20; 30); // return True; The event can be booked; as the first event takes every time less than 20; but not including 20. Constraints: 0 <= start < end <= 109 At most 1000 calls will be made to book."
Google,731,My Calendar II,Med,"Array, Binary Search, Design, Segment Tree, Prefix Sum, Ordered Set","You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a triple booking. A triple booking happens when three events have some non-empty intersection (i.e.; some moment is common to all the three events.). The event can be represented as a pair of integers startTime and endTime that represents a booking on the half-open interval [startTime; endTime); the range of real numbers x such that startTime <= x < endTime. Implement the MyCalendarTwo class: MyCalendarTwo() Initializes the calendar object. boolean book(int startTime; int endTime) Returns true if the event can be added to the calendar successfully without causing a triple booking. Otherwise; return false and do not add the event to the calendar. Example 1: Input [""MyCalendarTwo""; ""book""; ""book""; ""book""; ""book""; ""book""; ""book""] [[]; [10; 20]; [50; 60]; [10; 40]; [5; 15]; [5; 10]; [25; 55]] Output [null; true; true; true; false; true; true] Explanation MyCalendarTwo myCalendarTwo = new MyCalendarTwo(); myCalendarTwo.book(10; 20); // return True; The event can be booked. myCalendarTwo.book(50; 60); // return True; The event can be booked. myCalendarTwo.book(10; 40); // return True; The event can be double booked. myCalendarTwo.book(5; 15); // return False; The event cannot be booked; because it would result in a triple booking. myCalendarTwo.book(5; 10); // return True; The event can be booked; as it does not use time 10 which is already double booked. myCalendarTwo.book(25; 55); // return True; The event can be booked; as the time in [25; 40) will be double booked with the third event; the time [40; 50) will be single booked; and the time [50; 55) will be double booked with the second event. Constraints: 0 <= start < end <= 109 At most 1000 calls will be made to book."
Google,741,Cherry Pickup,Hard,"Array, Dynamic Programming, Matrix",You are given an n x n grid representing a field of cherries; each cell is one of three possible integers. 0 means the cell is empty; so you can pass through; 1 means the cell contains a cherry that you can pick up and pass through; or -1 means the cell contains a thorn that blocks your way. Return the maximum number of cherries you can collect by following the rules below: Starting at the position (0; 0) and reaching (n - 1; n - 1) by moving right or down through valid path cells (cells with value 0 or 1). After reaching (n - 1; n - 1); returning to (0; 0) by moving left or up through valid path cells. When passing through a path cell containing a cherry; you pick it up; and the cell becomes an empty cell 0. If there is no valid path between (0; 0) and (n - 1; n - 1); then no cherries can be collected. Example 1: Input: grid = [[0;1;-1];[1;0;-1];[1;1;1]] Output: 5 Explanation: The player started at (0; 0) and went down; down; right right to reach (2; 2). 4 cherries were picked up during this single trip; and the matrix becomes [[0;1;-1];[0;0;-1];[0;0;0]]. Then; the player went left; up; up; left to return home; picking up one more cherry. The total number of cherries picked up is 5; and this is the maximum possible. Example 2: Input: grid = [[1;1;-1];[1;-1;1];[-1;1;1]] Output: 0 Constraints: n == grid.length n == grid[i].length 1 <= n <= 50 grid[i][j] is -1; 0; or 1. grid[0][0] != -1 grid[n - 1][n - 1] != -1
Google,709,To Lower Case,Easy,,
Google,771,Jewels and Stones,Easy,"Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",
Google,779,K-th Symbol in Grammar,Med,"Array, Stack, Greedy, Sorting, Monotonic Stack",You are given an integer array arr. We split arr into some number of chunks (i.e.; partitions); and individually sort each chunk. After concatenating them; the result should equal the sorted array. Return the largest number of chunks we can make to sort the array. Example 1: Input: arr = [5;4;3;2;1] Output: 1 Explanation: Splitting into two or more chunks will not return the required result. For example; splitting into [5; 4]; [3; 2; 1] will result in [4; 5; 1; 2; 3]; which isn't sorted. Example 2: Input: arr = [2;1;3;4;4] Output: 4 Explanation: We can split into two chunks; such as [2; 1]; [3; 4; 4]. However; splitting into [2; 1]; [3]; [4]; [4] is the highest number of chunks possible. Constraints: 1 <= arr.length <= 2000 0 <= arr[i] <= 108
Google,785,Is Graph Bipartite?,Med,"Math, String, Stack, Recursion",
Google,706,Design HashMap,Easy,,
Google,810,Chalkboard XOR Game,Hard,"Array, Matrix","Given a Tic-Tac-Toe board as a string array board; return true if and only if it is possible to reach this board position during the course of a valid tic-tac-toe game. The board is a 3 x 3 array that consists of characters ' '; 'X'; and 'O'. The ' ' character represents an empty square. Here are the rules of Tic-Tac-Toe: Players take turns placing characters into empty squares ' '. The first player always places 'X' characters; while the second player always places 'O' characters. 'X' and 'O' characters are always placed into empty squares; never filled ones. The game ends when there are three of the same (non-empty) character filling any row; column; or diagonal. The game also ends if all squares are non-empty. No more moves can be played if the game is over. Example 1: Input: board = [""O "";"" "";"" ""] Output: false Explanation: The first player always plays ""X"". Example 2: Input: board = [""XOX"";"" X "";"" ""] Output: false Explanation: Players take turns making moves. Example 3: Input: board = [""XOX"";""O O"";""XOX""] Output: true Constraints: board.length == 3 board[i].length == 3 board[i][j] is either 'X'; 'O'; or ' '."
Google,827,Making A Large Island,Hard,"Array, Two Pointers, String","Sometimes people repeat letters to represent extra feeling. For example: ""hello"" -> ""heeellooo"" ""hi"" -> ""hiiii"" In these strings like ""heeellooo""; we have groups of adjacent letters that are all the same: ""h""; ""eee""; ""ll""; ""ooo"". You are given a string s and an array of query strings words. A query word is stretchy if it can be made to be equal to s by any number of applications of the following extension operation: choose a group consisting of characters c; and add some number of characters c to the group so that the size of the group is three or more. For example; starting with ""hello""; we could do an extension on the group ""o"" to get ""hellooo""; but we cannot get ""helloo"" since the group ""oo"" has a size less than three. Also; we could do another extension like ""ll"" -> ""lllll"" to get ""helllllooo"". If s = ""helllllooo""; then the query word ""hello"" would be stretchy because of these two extension operations: query = ""hello"" -> ""hellooo"" -> ""helllllooo"" = s. Return the number of query strings that are stretchy. Example 1: Input: s = ""heeellooo""; words = [""hello""; ""hi""; ""helo""] Output: 1 Explanation: We can extend ""e"" and ""o"" in the word ""hello"" to get ""heeellooo"". We can't extend ""helo"" to get ""heeellooo"" because the group ""ll"" is not size 3 or more. Example 2: Input: s = ""zzzzzyyyyy""; words = [""zzyy"";""zy"";""zyy""] Output: 3 Constraints: 1 <= s.length; words.length <= 100 1 <= words[i].length <= 100 s and words[i] consist of lowercase letters."
Google,489,Robot Room Cleaner,Hard,"Array, Math, Dynamic Programming, Combinatorics","Bob is standing at cell (0; 0); and he wants to reach destination: (row; column). He can only travel right and down. You are going to help Bob by providing instructions for him to reach destination. The instructions are represented as a string; where each character is either: 'H'; meaning move horizontally (go right); or 'V'; meaning move vertically (go down). Multiple instructions will lead Bob to destination. For example; if destination is (2; 3); both ""HHHVV"" and ""HVHVH"" are valid instructions. However; Bob is very picky. Bob has a lucky number k; and he wants the kth lexicographically smallest instructions that will lead him to destination. k is 1-indexed. Given an integer array destination and an integer k; return the kth lexicographically smallest instructions that will take Bob to destination. Example 1: Input: destination = [2;3]; k = 1 Output: ""HHHVV"" Explanation: All the instructions that reach (2; 3) in lexicographic order are as follows: [""HHHVV""; ""HHVHV""; ""HHVVH""; ""HVHHV""; ""HVHVH""; ""HVVHH""; ""VHHHV""; ""VHHVH""; ""VHVHH""; ""VVHHH""]. Example 2: Input: destination = [2;3]; k = 2 Output: ""HHVHV"" Example 3: Input: destination = [2;3]; k = 3 Output: ""HHVVH"" Constraints: destination.length == 2 1 <= row; column <= 15 1 <= k <= nCr(row + column; row); where nCr(a; b) denotes a choose b​​​​​."
Google,877,Stone Game,Med,"Dynamic Programming, Bit Manipulation, Breadth-First Search, Graph, Bitmask",You have an undirected; connected graph of n nodes labeled from 0 to n - 1. You are given an array graph where graph[i] is a list of all the nodes connected with node i by an edge. Return the length of the shortest path that visits every node. You may start and stop at any node; you may revisit nodes multiple times; and you may reuse edges. Example 1: Input: graph = [[1;2;3];[0];[0];[0]] Output: 4 Explanation: One possible path is [1;0;2;0;3] Example 2: Input: graph = [[1];[0;2;4];[1;3;4];[2];[1;2]] Output: 4 Explanation: One possible path is [0;1;4;2;3] Constraints: n == graph.length 1 <= n <= 12 0 <= graph[i].length < n graph[i] does not contain i. If graph[a] contains b; then graph[b] contains a. The input graph is always connected.
Google,881,Boats to Save People,Med,"Array, Depth-First Search, Graph, Topological Sort",There is a group of n people labeled from 0 to n - 1 where each person has a different amount of money and a different level of quietness. You are given an array richer where richer[i] = [ai; bi] indicates that ai has more money than bi and an integer array quiet where quiet[i] is the quietness of the ith person. All the given data in richer are logically correct (i.e.; the data will not lead you to a situation where x is richer than y and y is richer than x at the same time). Return an integer array answer where answer[x] = y if y is the least quiet person (that is; the person y with the smallest value of quiet[y]) among all people who definitely have equal to or more money than the person x. Example 1: Input: richer = [[1;0];[2;1];[3;1];[3;7];[4;3];[5;3];[6;3]]; quiet = [3;2;5;4;6;1;7;0] Output: [5;5;2;5;4;5;6;7] Explanation: answer[0] = 5. Person 5 has more money than 3; which has more money than 1; which has more money than 0. The only person who is quieter (has lower quiet[x]) is person 7; but it is not clear if they have more money than person 0. answer[7] = 7. Among all people that definitely have equal to or more money than person 7 (which could be persons 3; 4; 5; 6; or 7); the person who is the quietest (has lower quiet[x]) is person 7. The other answers can be filled out with similar reasoning. Example 2: Input: richer = []; quiet = [0] Output: [0] Constraints: n == quiet.length 1 <= n <= 500 0 <= quiet[i] < n All the values of quiet are unique. 0 <= richer.length <= n * (n - 1) / 2 0 <= ai; bi < n ai != bi All the pairs of richer are unique. The observations in richer are all logically consistent.
Google,884,Uncommon Words from Two Sentences,Easy,"String, Breadth-First Search","Strings s1 and s2 are k-similar (for some non-negative integer k) if we can swap the positions of two letters in s1 exactly k times so that the resulting string equals s2. Given two anagrams s1 and s2; return the smallest k for which s1 and s2 are k-similar. Example 1: Input: s1 = ""ab""; s2 = ""ba"" Output: 1 Explanation: The two string are 1-similar because we can use one swap to change s1 to s2: ""ab"" --> ""ba"". Example 2: Input: s1 = ""abc""; s2 = ""bca"" Output: 2 Explanation: The two strings are 2-similar because we can use two swaps to change s1 to s2: ""abc"" --> ""bac"" --> ""bca"". Constraints: 1 <= s1.length <= 20 s2.length == s1.length s1 and s2 contain only lowercase letters from the set {'a'; 'b'; 'c'; 'd'; 'e'; 'f'}. s2 is an anagram of s1."
Google,888,Fair Candy Swap,Easy,"Math, Geometry, Number Theory",There is a special square room with mirrors on each of the four walls. Except for the southwest corner; there are receptors on each of the remaining corners; numbered 0; 1; and 2. The square room has walls of length p and a laser ray from the southwest corner first meets the east wall at a distance q from the 0th receptor. Given the two integers p and q; return the number of the receptor that the ray meets first. The test cases are guaranteed so that the ray will meet a receptor eventually. Example 1: Input: p = 2; q = 1 Output: 2 Explanation: The ray meets receptor 2 the first time it gets reflected back to the left wall. Example 2: Input: p = 3; q = 1 Output: 1 Constraints: 1 <= q <= p <= 1000
Google,901,Online Stock Span,Med,"Array, Two Pointers, Greedy, Sorting",You are given two integer arrays nums1 and nums2 both of the same length. The advantage of nums1 with respect to nums2 is the number of indices i for which nums1[i] > nums2[i]. Return any permutation of nums1 that maximizes its advantage with respect to nums2. Example 1: Input: nums1 = [2;7;11;15]; nums2 = [1;10;4;11] Output: [2;11;7;15] Example 2: Input: nums1 = [12;24;8;32]; nums2 = [13;25;32;11] Output: [24;32;8;12] Constraints: 1 <= nums1.length <= 105 nums2.length == nums1.length 0 <= nums1[i]; nums2[i] <= 109
Google,907,Sum of Subarray Minimums,Med,"Array, Binary Search",Koko loves to eat bananas. There are n piles of bananas; the ith pile has piles[i] bananas. The guards have gone and will come back in h hours. Koko can decide her bananas-per-hour eating speed of k. Each hour; she chooses some pile of bananas and eats k bananas from that pile. If the pile has less than k bananas; she eats all of them instead and will not eat any more bananas during this hour. Koko likes to eat slowly but still wants to finish eating all the bananas before the guards return. Return the minimum integer k such that she can eat all the bananas within h hours. Example 1: Input: piles = [3;6;7;11]; h = 8 Output: 4 Example 2: Input: piles = [30;11;23;4;20]; h = 5 Output: 30 Example 3: Input: piles = [30;11;23;4;20]; h = 6 Output: 23 Constraints: 1 <= piles.length <= 104 piles.length <= h <= 109 1 <= piles[i] <= 109
Google,929,Unique Email Addresses,Easy,"Array, Hash Table, String, Sorting","You are given an array of strings of the same length words. In one move; you can swap any two even indexed characters or any two odd indexed characters of a string words[i]. Two strings words[i] and words[j] are special-equivalent if after any number of moves; words[i] == words[j]. For example; words[i] = ""zzxy"" and words[j] = ""xyzz"" are special-equivalent because we may make the moves ""zzxy"" -> ""xzzy"" -> ""xyzz"". A group of special-equivalent strings from words is a non-empty subset of words such that: Every pair of strings in the group are special equivalent; and The group is the largest size possible (i.e.; there is not a string words[i] not in the group such that words[i] is special-equivalent to every string in the group). Return the number of groups of special-equivalent strings from words. Example 1: Input: words = [""abcd"";""cdab"";""cbad"";""xyzz"";""zzxy"";""zzyx""] Output: 3 Explanation: One group is [""abcd""; ""cdab""; ""cbad""]; since they are all pairwise special equivalent; and none of the other strings is all pairwise special equivalent to these. The other two groups are [""xyzz""; ""zzxy""] and [""zzyx""]. Note that in particular; ""zzxy"" is not special equivalent to ""zzyx"". Example 2: Input: words = [""abc"";""acb"";""bac"";""bca"";""cab"";""cba""] Output: 3 Constraints: 1 <= words.length <= 1000 1 <= words[i].length <= 20 words[i] consist of lowercase English letters. All the strings are of the same length."
Google,930,Binary Subarrays With Sum,Med,"Dynamic Programming, Tree, Recursion, Memoization, Binary Tree",Given an integer n; return a list of all possible full binary trees with n nodes. Each node of each tree in the answer must have Node.val == 0. Each element of the answer is the root node of one possible tree. You may return the final list of trees in any order. A full binary tree is a binary tree where each node has exactly 0 or 2 children. Example 1: Input: n = 7 Output: [[0;0;0;null;null;0;0;null;null;0;0];[0;0;0;null;null;0;0;0;0];[0;0;0;0;0;0;0];[0;0;0;0;0;null;null;null;null;0;0];[0;0;0;0;0;null;null;0;0]] Example 2: Input: n = 3 Output: [[0;0;0]] Constraints: 1 <= n <= 20
Google,934,Shortest Bridge,Med,"Array, Dynamic Programming, Bit Manipulation",Given an integer array arr; return the number of distinct bitwise ORs of all the non-empty subarrays of arr. The bitwise OR of a subarray is the bitwise OR of each integer in the subarray. The bitwise OR of a subarray of one integer is that integer. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: arr = [0] Output: 1 Explanation: There is only one possible result: 0. Example 2: Input: arr = [1;1;2] Output: 3 Explanation: The possible subarrays are [1]; [1]; [2]; [1; 1]; [1; 2]; [1; 1; 2]. These yield the results 1; 1; 2; 1; 3; 3. There are 3 unique values; so the answer is 3. Example 3: Input: arr = [1;2;4] Output: 6 Explanation: The possible results are 1; 2; 3; 4; 6; and 7. Constraints: 1 <= arr.length <= 5 * 104 0 <= arr[i] <= 109
Google,974,Subarray Sums Divisible by K,Med,"Array, String, Sorting","You are given an array of logs. Each log is a space-delimited string of words; where the first word is the identifier. There are two types of logs: Letter-logs: All words (except the identifier) consist of lowercase English letters. Digit-logs: All words (except the identifier) consist of digits. Reorder these logs so that: The letter-logs come before all digit-logs. The letter-logs are sorted lexicographically by their contents. If their contents are the same; then sort them lexicographically by their identifiers. The digit-logs maintain their relative ordering. Return the final order of the logs. Example 1: Input: logs = [""dig1 8 1 5 1"";""let1 art can"";""dig2 3 6"";""let2 own kit dig"";""let3 art zero""] Output: [""let1 art can"";""let3 art zero"";""let2 own kit dig"";""dig1 8 1 5 1"";""dig2 3 6""] Explanation: The letter-log contents are all different; so their ordering is ""art can""; ""art zero""; ""own kit dig"". The digit-logs have a relative order of ""dig1 8 1 5 1""; ""dig2 3 6"". Example 2: Input: logs = [""a1 9 2 3 1"";""g1 act car"";""zo4 4 7"";""ab1 off key dog"";""a8 act zoo""] Output: [""g1 act car"";""a8 act zoo"";""ab1 off key dog"";""a1 9 2 3 1"";""zo4 4 7""] Constraints: 1 <= logs.length <= 100 3 <= logs[i].length <= 100 All the tokens of logs[i] are separated by a single space. logs[i] is guaranteed to have an identifier and at least one word after the identifier."
Google,981,Time Based Key-Value Store,Med,"Array, String","You are given an array of n strings strs; all of the same length. The strings can be arranged such that there is one on each line; making a grid. For example; strs = [""abc""; ""bce""; ""cae""] can be arranged as follows: abc bce cae You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed); columns 0 ('a'; 'b'; 'c') and 2 ('c'; 'e'; 'e') are sorted; while column 1 ('b'; 'c'; 'a') is not; so you would delete column 1. Return the number of columns that you will delete. Example 1: Input: strs = [""cba"";""daf"";""ghi""] Output: 1 Explanation: The grid looks as follows: cba daf ghi Columns 0 and 2 are sorted; but column 1 is not; so you only need to delete 1 column. Example 2: Input: strs = [""a"";""b""] Output: 0 Explanation: The grid looks as follows: a b Column 0 is the only column and is sorted; so you will not delete any columns. Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: The grid looks as follows: zyx wvu tsr All 3 columns are not sorted; so you will delete all 3. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 1000 strs[i] consists of lowercase English letters."
Google,997,Find the Town Judge,Easy,,
Google,1043,Partition Array for Maximum Sum,Med,"Array, Hash Table",There is a 2D grid of size n x n where each cell of this grid has a lamp that is initially turned off. You are given a 2D array of lamp positions lamps; where lamps[i] = [rowi; coli] indicates that the lamp at grid[rowi][coli] is turned on. Even if the same lamp is listed more than once; it is turned on. When a lamp is turned on; it illuminates its cell and all other cells in the same row; column; or diagonal. You are also given another 2D array queries; where queries[j] = [rowj; colj]. For the jth query; determine whether grid[rowj][colj] is illuminated or not. After answering the jth query; turn off the lamp at grid[rowj][colj] and its 8 adjacent lamps if they exist. A lamp is adjacent if its cell shares either a side or corner with grid[rowj][colj]. Return an array of integers ans; where ans[j] should be 1 if the cell in the jth query was illuminated; or 0 if the lamp was not. Example 1: Input: n = 5; lamps = [[0;0];[4;4]]; queries = [[1;1];[1;0]] Output: [1;0] Explanation: We have the initial grid with all lamps turned off. In the above picture we see the grid after turning on the lamp at grid[0][0] then turning on the lamp at grid[4][4]. The 0th query asks if the lamp at grid[1][1] is illuminated or not (the blue square). It is illuminated; so set ans[0] = 1. Then; we turn off all lamps in the red square. The 1st query asks if the lamp at grid[1][0] is illuminated or not (the blue square). It is not illuminated; so set ans[1] = 0. Then; we turn off all lamps in the red rectangle. Example 2: Input: n = 5; lamps = [[0;0];[4;4]]; queries = [[1;1];[1;1]] Output: [1;1] Example 3: Input: n = 5; lamps = [[0;0];[0;4]]; queries = [[0;4];[0;1];[1;4]] Output: [1;1;0] Constraints: 1 <= n <= 109 0 <= lamps.length <= 20000 0 <= queries.length <= 20000 lamps[i].length == 2 0 <= rowi; coli < n queries[j].length == 2 0 <= rowj; colj < n
Google,1074,Number of Submatrices That Sum to Target,Hard,"Array, Hash Table, Sorting, Heap (Priority Queue)",
Google,1068,Product Sales Analysis I,Easy,"Math, Dynamic Programming",
Google,1229,Meeting Scheduler,Med,"Breadth-First Search, Graph",You are given an integer n; the number of nodes in a directed graph where the nodes are labeled from 0 to n - 1. Each edge is red or blue in this graph; and there could be self-edges and parallel edges. You are given two arrays redEdges and blueEdges where: redEdges[i] = [ai; bi] indicates that there is a directed red edge from node ai to node bi in the graph; and blueEdges[j] = [uj; vj] indicates that there is a directed blue edge from node uj to node vj in the graph. Return an array answer of length n; where each answer[x] is the length of the shortest path from node 0 to node x such that the edge colors alternate along the path; or -1 if such a path does not exist. Example 1: Input: n = 3; redEdges = [[0;1];[1;2]]; blueEdges = [] Output: [0;1;-1] Example 2: Input: n = 3; redEdges = [[0;1]]; blueEdges = [[2;1]] Output: [0;1;-1] Constraints: 1 <= n <= 100 0 <= redEdges.length; blueEdges.length <= 400 redEdges[i].length == blueEdges[j].length == 2 0 <= ai; bi; uj; vj < n
Google,1089,Duplicate Zeros,Easy,String,
Google,1091,Shortest Path in Binary Matrix,Med,"Tree, Depth-First Search, Binary Tree",
Google,550,Game Play Analysis IV,Med,"Array, Breadth-First Search, Matrix",
Google,1164,Product Price at a Given Date,Med,"Array, Math",
Google,1185,Day of the Week,Easy,"Array, Binary Search, Interactive",(This problem is an interactive problem.) You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some i with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given a mountain array mountainArr; return the minimum index such that mountainArr.get(index) == target. If such an index does not exist; return -1. You cannot access the mountain array directly. You may only access the array using a MountainArray interface: MountainArray.get(k) returns the element of the array at index k (0-indexed). MountainArray.length() returns the length of the array. Submissions making more than 100 calls to MountainArray.get will be judged Wrong Answer. Also; any solutions that attempt to circumvent the judge will result in disqualification. Example 1: Input: mountainArr = [1;2;3;4;5;3;1]; target = 3 Output: 2 Explanation: 3 exists in the array; at index=2 and index=5. Return the minimum index; which is 2. Example 2: Input: mountainArr = [0;1;2;4;2;1]; target = 3 Output: -1 Explanation: 3 does not exist in the array; so we return -1. Constraints: 3 <= mountainArr.length() <= 104 0 <= target <= 109 0 <= mountainArr.get(index) <= 109
Google,1174,Immediate Food Delivery II,Med,Database,Table: Product +--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | | unit_price | int | +--------------+---------+ product_id is the primary key (column with unique values) of this table. Each row of this table indicates the name and the price of each product. Table: Sales +-------------+---------+ | Column Name | Type | +-------------+---------+ | seller_id | int | | product_id | int | | buyer_id | int | | sale_date | date | | quantity | int | | price | int | +-------------+---------+ This table can have duplicate rows. product_id is a foreign key (reference column) to the Product table. Each row of this table contains some information about one sale. Write a solution to report the products that were only sold in the first quarter of 2019. That is; between 2019-01-01 and 2019-03-31 inclusive. Return the result table in any order. The result format is in the following example. Example 1: Input: Product table: +------------+--------------+------------+ | product_id | product_name | unit_price | +------------+--------------+------------+ | 1 | S8 | 1000 | | 2 | G4 | 800 | | 3 | iPhone | 1400 | +------------+--------------+------------+ Sales table: +-----------+------------+----------+------------+----------+-------+ | seller_id | product_id | buyer_id | sale_date | quantity | price | +-----------+------------+----------+------------+----------+-------+ | 1 | 1 | 1 | 2019-01-21 | 2 | 2000 | | 1 | 2 | 2 | 2019-02-17 | 1 | 800 | | 2 | 2 | 3 | 2019-06-02 | 1 | 800 | | 3 | 3 | 4 | 2019-05-13 | 2 | 2800 | +-----------+------------+----------+------------+----------+-------+ Output: +-------------+--------------+ | product_id | product_name | +-------------+--------------+ | 1 | S8 | +-------------+--------------+ Explanation: The product with id 1 was only sold in the spring of 2019. The product with id 2 was sold in the spring of 2019 but was also sold after the spring of 2019. The product with id 3 was sold after spring 2019. We return only product 1 as it is the product that was only sold in the spring of 2019.
Google,1193,Monthly Transactions I,Med,Database,
Google,1514,Path with Maximum Probability,Med,"Array, Prefix Sum",Given an array of integers nums; you start with an initial positive value startValue. In each iteration; you calculate the step by step sum of startValue plus elements in nums (from left to right). Return the minimum positive value of startValue such that the step by step sum is never less than 1. Example 1: Input: nums = [-3;2;-3;4;2] Output: 5 Explanation: If you choose startValue = 4; in the third iteration your step by step sum is less than 1. step by step sum startValue = 4 | startValue = 5 | nums (4 -3 ) = 1 | (5 -3 ) = 2 | -3 (1 +2 ) = 3 | (2 +2 ) = 4 | 2 (3 -3 ) = 0 | (4 -3 ) = 1 | -3 (0 +4 ) = 4 | (1 +4 ) = 5 | 4 (4 +2 ) = 6 | (5 +2 ) = 7 | 2 Example 2: Input: nums = [1;2] Output: 1 Explanation: Minimum start value should be positive. Example 3: Input: nums = [1;-2;-3] Output: 5 Constraints: 1 <= nums.length <= 100 -100 <= nums[i] <= 100
Google,1691,Maximum Height by Stacking Cuboids,Hard,"Array, Depth-First Search, Breadth-First Search, Matrix, Strongly Connected Component",You are given an m x n binary grid grid where 1 represents land and 0 represents water. An island is a maximal 4-directionally (horizontal or vertical) connected group of 1's. The grid is said to be connected if we have exactly one island; otherwise is said disconnected. In one day; we are allowed to change any single land cell (1) into a water cell (0). Return the minimum number of days to disconnect the grid. Example 1: Input: grid = [[0;1;1;0];[0;1;1;0];[0;0;0;0]] Output: 2 Explanation: We need at least 2 days to get a disconnected grid. Change land grid[1][1] and grid[0][2] to water and get 2 disconnected island. Example 2: Input: grid = [[1;1]] Output: 2 Explanation: Grid of full water is also disconnected ([[1;1]] -> [[0;0]]); 0 islands. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 30 grid[i][j] is either 0 or 1.
Google,1251,Average Selling Price,Easy,"Two Pointers, String, Dynamic Programming, Greedy, Rolling Hash, Hash Function","You are given a string text. You should split it to k substrings (subtext1; subtext2; ...; subtextk) such that: subtexti is a non-empty string. The concatenation of all the substrings is equal to text (i.e.; subtext1 + subtext2 + ... + subtextk == text). subtexti == subtextk - i + 1 for all valid values of i (i.e.; 1 <= i <= k). Return the largest possible value of k. Example 1: Input: text = ""ghiabcdefhelloadamhelloabcdefghi"" Output: 7 Explanation: We can split the string on ""(ghi)(abcdef)(hello)(adam)(hello)(abcdef)(ghi)"". Example 2: Input: text = ""merchant"" Output: 1 Explanation: We can split the string on ""(merchant)"". Example 3: Input: text = ""antaprezatepzapreanta"" Output: 11 Explanation: We can split the string on ""(a)(nt)(a)(pre)(za)(tep)(za)(pre)(a)(nt)(a)"". Constraints: 1 <= text.length <= 1000 text consists only of lowercase English characters."
Google,2215,Find the Difference of Two Arrays,Easy,"Array, Hash Table, Sorting, Enumeration",You are given an integer array digits; where each element is a digit. The array may contain duplicates. You need to find all the unique integers that follow the given requirements: The integer consists of the concatenation of three elements from digits in any arbitrary order. The integer does not have leading zeros. The integer is even. For example; if the given digits were [1; 2; 3]; integers 132 and 312 follow the requirements. Return a sorted array of the unique integers. Example 1: Input: digits = [2;1;3;0] Output: [102;120;130;132;210;230;302;310;312;320] Explanation: All the possible integers that follow the requirements are in the output array. Notice that there are no odd integers or integers with leading zeros. Example 2: Input: digits = [2;2;8;8;2] Output: [222;228;282;288;822;828;882] Explanation: The same digit can be used as many times as it appears in digits. In this example; the digit 8 is used twice each time in 288; 828; and 882. Example 3: Input: digits = [3;7;5] Output: [] Explanation: No even integers can be formed using the given digits. Constraints: 3 <= digits.length <= 100 0 <= digits[i] <= 9
Google,1334,Find the City With the Smallest Number of Neighbors at a Threshold Distance,Med,"Math, Dynamic Programming, Greedy, Enumeration",Given two integers num and k; consider a set of positive integers with the following properties: The units digit of each integer is k. The sum of the integers is num. Return the minimum possible size of such a set; or -1 if no such set exists. Note: The set can contain multiple instances of the same integer; and the sum of an empty set is considered 0. The units digit of a number is the rightmost digit of the number. Example 1: Input: num = 58; k = 9 Output: 2 Explanation: One valid set is [9;49]; as the sum is 58 and each integer has a units digit of 9. Another valid set is [19;39]. It can be shown that 2 is the minimum possible size of a valid set. Example 2: Input: num = 37; k = 2 Output: -1 Explanation: It is not possible to obtain a sum of 37 using only integers that have a units digit of 2. Example 3: Input: num = 0; k = 7 Output: 0 Explanation: The sum of an empty set is considered 0. Constraints: 0 <= num <= 3000 0 <= k <= 9
Google,1347,Minimum Number of Steps to Make Two Strings Anagram,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
Google,1371,Find the Longest Substring Containing Vowels in Even Counts,Med,"String, Stack","Given a string s of '(' ; ')' and lowercase English characters. Your task is to remove the minimum number of parentheses ( '(' or ')'; in any positions ) so that the resulting parentheses string is valid and return any valid string. Formally; a parentheses string is valid if and only if: It is the empty string; contains only lowercase characters; or It can be written as AB (A concatenated with B); where A and B are valid strings; or It can be written as (A); where A is a valid string. Example 1: Input: s = ""lee(t(c)o)de)"" Output: ""lee(t(c)o)de"" Explanation: ""lee(t(co)de)"" ; ""lee(t(c)ode)"" would also be accepted. Example 2: Input: s = ""a)b(c)d"" Output: ""ab(c)d"" Example 3: Input: s = ""))(("" Output: """" Explanation: An empty string is also valid. Constraints: 1 <= s.length <= 105 s[i] is either '(' ; ')'; or lowercase English letter."
Google,1423,Maximum Points You Can Obtain from Cards,Med,"Hash Table, String, Sliding Window","Given a string s; return the maximum number of occurrences of any substring under the following rules: The number of unique characters in the substring must be less than or equal to maxLetters. The substring size must be between minSize and maxSize inclusive. Example 1: Input: s = ""aababcaab""; maxLetters = 2; minSize = 3; maxSize = 4 Output: 2 Explanation: Substring ""aab"" has 2 occurrences in the original string. It satisfies the conditions; 2 unique letters and size 3 (between minSize and maxSize). Example 2: Input: s = ""aaaa""; maxLetters = 1; minSize = 3; maxSize = 3 Output: 2 Explanation: Substring ""aaa"" occur 2 times in the string. It can overlap. Constraints: 1 <= s.length <= 105 1 <= maxLetters <= 26 1 <= minSize <= maxSize <= min(26; s.length) s consists of only lowercase English letters."
Google,1470,Shuffle the Array,Easy,"Hash Table, Binary Search, Design, Sorting, Ordered Set","A social media company is trying to monitor activity on their site by analyzing the number of tweets that occur in select periods of time. These periods can be partitioned into smaller time chunks based on a certain frequency (every minute; hour; or day). For example; the period [10; 10000] (in seconds) would be partitioned into the following time chunks with these frequencies: Every minute (60-second chunks): [10;69]; [70;129]; [130;189]; ...; [9970;10000] Every hour (3600-second chunks): [10;3609]; [3610;7209]; [7210;10000] Every day (86400-second chunks): [10;10000] Notice that the last chunk may be shorter than the specified frequency's chunk size and will always end with the end time of the period (10000 in the above example). Design and implement an API to help the company with their analysis. Implement the TweetCounts class: TweetCounts() Initializes the TweetCounts object. void recordTweet(String tweetName; int time) Stores the tweetName at the recorded time (in seconds). List<Integer> getTweetCountsPerFrequency(String freq; String tweetName; int startTime; int endTime) Returns a list of integers representing the number of tweets with tweetName in each time chunk for the given period of time [startTime; endTime] (in seconds) and frequency freq. freq is one of ""minute""; ""hour""; or ""day"" representing a frequency of every minute; hour; or day respectively. Example: Input [""TweetCounts"";""recordTweet"";""recordTweet"";""recordTweet"";""getTweetCountsPerFrequency"";""getTweetCountsPerFrequency"";""recordTweet"";""getTweetCountsPerFrequency""] [[];[""tweet3"";0];[""tweet3"";60];[""tweet3"";10];[""minute"";""tweet3"";0;59];[""minute"";""tweet3"";0;60];[""tweet3"";120];[""hour"";""tweet3"";0;210]] Output [null;null;null;null;[2];[2;1];null;[4]] Explanation TweetCounts tweetCounts = new TweetCounts(); tweetCounts.recordTweet(""tweet3""; 0); // New tweet ""tweet3"" at time 0 tweetCounts.recordTweet(""tweet3""; 60); // New tweet ""tweet3"" at time 60 tweetCounts.recordTweet(""tweet3""; 10); // New tweet ""tweet3"" at time 10 tweetCounts.getTweetCountsPerFrequency(""minute""; ""tweet3""; 0; 59); // return [2]; chunk [0;59] had 2 tweets tweetCounts.getTweetCountsPerFrequency(""minute""; ""tweet3""; 0; 60); // return [2;1]; chunk [0;59] had 2 tweets; chunk [60;60] had 1 tweet tweetCounts.recordTweet(""tweet3""; 120); // New tweet ""tweet3"" at time 120 tweetCounts.getTweetCountsPerFrequency(""hour""; ""tweet3""; 0; 210); // return [4]; chunk [0;210] had 4 tweets Constraints: 0 <= time; startTime; endTime <= 109 0 <= endTime - startTime <= 104 There will be at most 104 calls in total to recordTweet and getTweetCountsPerFrequency."
Google,1493,Longest Subarray of 1's After Deleting One Element,Med,"Tree, Depth-First Search, Breadth-First Search, Graph",Given an undirected tree consisting of n vertices numbered from 1 to n. A frog starts jumping from vertex 1. In one second; the frog jumps from its current vertex to another unvisited vertex if they are directly connected. The frog can not jump back to a visited vertex. In case the frog can jump to several vertices; it jumps randomly to one of them with the same probability. Otherwise; when the frog can not jump to any unvisited vertex; it jumps forever on the same vertex. The edges of the undirected tree are given in the array edges; where edges[i] = [ai; bi] means that exists an edge connecting the vertices ai and bi. Return the probability that after t seconds the frog is on the vertex target. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: n = 7; edges = [[1;2];[1;3];[1;7];[2;4];[2;6];[3;5]]; t = 2; target = 4 Output: 0.16666666666666666 Explanation: The figure above shows the given graph. The frog starts at vertex 1; jumping with 1/3 probability to the vertex 2 after second 1 and then jumping with 1/2 probability to vertex 4 after second 2. Thus the probability for the frog is on the vertex 4 after 2 seconds is 1/3 * 1/2 = 1/6 = 0.16666666666666666. Example 2: Input: n = 7; edges = [[1;2];[1;3];[1;7];[2;4];[2;6];[3;5]]; t = 1; target = 7 Output: 0.3333333333333333 Explanation: The figure above shows the given graph. The frog starts at vertex 1; jumping with 1/3 = 0.3333333333333333 probability to the vertex 7 after second 1. Constraints: 1 <= n <= 100 edges.length == n - 1 edges[i].length == 2 1 <= ai; bi <= n 1 <= t <= 50 1 <= target <= n
Google,1509,Minimum Difference Between Largest and Smallest Value in Three Moves,Med,Database,Table: Employees +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | name | varchar | +---------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table contains the id and the name of an employee in a company. Table: EmployeeUNI +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | unique_id | int | +---------------+---------+ (id; unique_id) is the primary key (combination of columns with unique values) for this table. Each row of this table contains the id and the corresponding unique id of an employee in the company. Write a solution to show the unique ID of each user; If a user does not have a unique ID replace just show null. Return the result table in any order. The result format is in the following example. Example 1: Input: Employees table: +----+----------+ | id | name | +----+----------+ | 1 | Alice | | 7 | Bob | | 11 | Meir | | 90 | Winston | | 3 | Jonathan | +----+----------+ EmployeeUNI table: +----+-----------+ | id | unique_id | +----+-----------+ | 3 | 1 | | 11 | 2 | | 90 | 3 | +----+-----------+ Output: +-----------+----------+ | unique_id | name | +-----------+----------+ | null | Alice | | null | Bob | | 2 | Meir | | 3 | Winston | | 1 | Jonathan | +-----------+----------+ Explanation: Alice and Bob do not have a unique ID; We will show null instead. The unique ID of Meir is 2. The unique ID of Winston is 3. The unique ID of Jonathan is 1.
Google,1525,Number of Good Ways to Split a String,Med,"Array, Binary Indexed Tree, Simulation",Given the array queries of positive integers between 1 and m; you have to process all queries[i] (from i=0 to i=queries.length-1) according to the following rules: In the beginning; you have the permutation P=[1;2;3;...;m]. For the current i; find the position of queries[i] in the permutation P (indexing from 0) and then move this at the beginning of the permutation P. Notice that the position of queries[i] in P is the result for queries[i]. Return an array containing the result for the given queries. Example 1: Input: queries = [3;1;2;1]; m = 5 Output: [2;1;2;1] Explanation: The queries are processed as follow: For i=0: queries[i]=3; P=[1;2;3;4;5]; position of 3 in P is 2; then we move 3 to the beginning of P resulting in P=[3;1;2;4;5]. For i=1: queries[i]=1; P=[3;1;2;4;5]; position of 1 in P is 1; then we move 1 to the beginning of P resulting in P=[1;3;2;4;5]. For i=2: queries[i]=2; P=[1;3;2;4;5]; position of 2 in P is 2; then we move 2 to the beginning of P resulting in P=[2;1;3;4;5]. For i=3: queries[i]=1; P=[2;1;3;4;5]; position of 1 in P is 1; then we move 1 to the beginning of P resulting in P=[1;2;3;4;5]. Therefore; the array containing the result is [2;1;2;1]. Example 2: Input: queries = [4;1;2;2]; m = 4 Output: [3;1;2;0] Example 3: Input: queries = [7;5;5;8;3]; m = 8 Output: [6;5;0;7;5] Constraints: 1 <= m <= 10^3 1 <= queries.length <= m 1 <= queries[i] <= m
Google,1518,Water Bottles,Easy,Database,
Google,1539,Kth Missing Positive Number,Easy,"Array, Sorting, Heap (Priority Queue)",Given a 2D integer array nums; return all elements of nums in diagonal order as shown in the below images. Example 1: Input: nums = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;4;2;7;5;3;8;6;9] Example 2: Input: nums = [[1;2;3;4;5];[6;7];[8];[9;10;11];[12;13;14;15;16]] Output: [1;6;2;8;7;3;9;4;12;10;5;13;11;14;15;16] Constraints: 1 <= nums.length <= 105 1 <= nums[i].length <= 105 1 <= sum(nums[i].length) <= 105 1 <= nums[i][j] <= 105
Google,1590,Make Sum Divisible by P,Med,,
Google,1652,Defuse the Bomb,Easy,"String, Greedy","You are given a 0-indexed binary string target of length n. You have another binary string s of length n that is initially set to all zeros. You want to make s equal to target. In one operation; you can pick an index i where 0 <= i < n and flip all bits in the inclusive range [i; n - 1]. Flip means changing '0' to '1' and '1' to '0'. Return the minimum number of operations needed to make s equal to target. Example 1: Input: target = ""10111"" Output: 3 Explanation: Initially; s = ""00000"". Choose index i = 2: ""00000"" -> ""00111"" Choose index i = 0: ""00111"" -> ""11000"" Choose index i = 1: ""11000"" -> ""10111"" We need at least 3 flip operations to form target. Example 2: Input: target = ""101"" Output: 3 Explanation: Initially; s = ""000"". Choose index i = 0: ""000"" -> ""111"" Choose index i = 1: ""111"" -> ""100"" Choose index i = 2: ""100"" -> ""101"" We need at least 3 flip operations to form target. Example 3: Input: target = ""00000"" Output: 0 Explanation: We do not need any operations since the initial s already equals target. Constraints: n == target.length 1 <= n <= 105 target[i] is either '0' or '1'."
Google,1658,Minimum Operations to Reduce X to Zero,Med,"Array, Greedy, Matrix",Given an n x n binary grid; in one step you can choose two adjacent rows of the grid and swap them. A grid is said to be valid if all the cells above the main diagonal are zeros. Return the minimum number of steps needed to make the grid valid; or -1 if the grid cannot be valid. The main diagonal of a grid is the diagonal that starts at cell (1; 1) and ends at cell (n; n). Example 1: Input: grid = [[0;0;1];[1;1;0];[1;0;0]] Output: 3 Example 2: Input: grid = [[0;1;1;0];[0;1;1;0];[0;1;1;0];[0;1;1;0]] Output: -1 Explanation: All rows are similar; swaps have no effect on the grid. Example 3: Input: grid = [[1;0;0];[1;1;0];[1;1;1]] Output: 0 Constraints: n == grid.length == grid[i].length 1 <= n <= 200 grid[i][j] is either 0 or 1
Google,1662,Check If Two String Arrays are Equivalent,Easy,"Array, Greedy, Bit Manipulation",You are given an integer array nums. You have an integer array arr of the same length with all values set to 0 initially. You also have the following modify function: You want to use the modify function to convert arr to nums using the minimum number of calls. Return the minimum number of function calls to make nums from arr. The test cases are generated so that the answer fits in a 32-bit signed integer. Example 1: Input: nums = [1;5] Output: 5 Explanation: Increment by 1 (second element): [0; 0] to get [0; 1] (1 operation). Double all the elements: [0; 1] -> [0; 2] -> [0; 4] (2 operations). Increment by 1 (both elements) [0; 4] -> [1; 4] -> [1; 5] (2 operations). Total of operations: 1 + 2 + 2 = 5. Example 2: Input: nums = [2;2] Output: 3 Explanation: Increment by 1 (both elements) [0; 0] -> [0; 1] -> [1; 1] (2 operations). Double all the elements: [1; 1] -> [2; 2] (1 operation). Total of operations: 2 + 1 = 3. Example 3: Input: nums = [4;2;5] Output: 6 Explanation: (initial)[0;0;0] -> [1;0;0] -> [1;0;1] -> [2;0;2] -> [2;1;2] -> [4;2;4] -> [4;2;5](nums). Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109
Google,1650,Lowest Common Ancestor of a Binary Tree III,Med,"Hash Table, Bit Manipulation, Tree, Depth-First Search",
Google,1700,Number of Students Unable to Eat Lunch,Easy,"Array, String, Dynamic Programming, Greedy","Alice has n balloons arranged on a rope. You are given a 0-indexed string colors where colors[i] is the color of the ith balloon. Alice wants the rope to be colorful. She does not want two consecutive balloons to be of the same color; so she asks Bob for help. Bob can remove some balloons from the rope to make it colorful. You are given a 0-indexed integer array neededTime where neededTime[i] is the time (in seconds) that Bob needs to remove the ith balloon from the rope. Return the minimum time Bob needs to make the rope colorful. Example 1: Input: colors = ""abaac""; neededTime = [1;2;3;4;5] Output: 3 Explanation: In the above image; 'a' is blue; 'b' is red; and 'c' is green. Bob can remove the blue balloon at index 2. This takes 3 seconds. There are no longer two consecutive balloons of the same color. Total time = 3. Example 2: Input: colors = ""abc""; neededTime = [1;2;3] Output: 0 Explanation: The rope is already colorful. Bob does not need to remove any balloons from the rope. Example 3: Input: colors = ""aabaa""; neededTime = [1;2;3;4;1] Output: 2 Explanation: Bob will remove the balloons at indices 0 and 4. Each balloons takes 1 second to remove. There are no longer two consecutive balloons of the same color. Total time = 1 + 1 = 2. Constraints: n == colors.length == neededTime.length 1 <= n <= 105 1 <= neededTime[i] <= 104 colors contains only lowercase English letters."
Google,1732,Find the Highest Altitude,Easy,"Dynamic Programming, Bit Manipulation, Memoization","Given an integer n; you must transform it into 0 using the following operations any number of times: Change the rightmost (0th) bit in the binary representation of n. Change the ith bit in the binary representation of n if the (i-1)th bit is set to 1 and the (i-2)th through 0th bits are set to 0. Return the minimum number of operations to transform n into 0. Example 1: Input: n = 3 Output: 2 Explanation: The binary representation of 3 is ""11"". ""11"" -> ""01"" with the 2nd operation since the 0th bit is 1. ""01"" -> ""00"" with the 1st operation. Example 2: Input: n = 6 Output: 4 Explanation: The binary representation of 6 is ""110"". ""110"" -> ""010"" with the 2nd operation since the 1st bit is 1 and 0th through 0th bits are 0. ""010"" -> ""011"" with the 1st operation. ""011"" -> ""001"" with the 2nd operation since the 0th bit is 1. ""001"" -> ""000"" with the 1st operation. Constraints: 0 <= n <= 109"
Google,1813,Sentence Similarity III,Med,"Array, Hash Table, Sliding Window",You are given an array of positive integers nums and want to erase a subarray containing unique elements. The score you get by erasing the subarray is equal to the sum of its elements. Return the maximum score you can get by erasing exactly one subarray. An array b is called to be a subarray of a if it forms a contiguous subsequence of a; that is; if it is equal to a[l];a[l+1];...;a[r] for some (l;r). Example 1: Input: nums = [4;2;4;5;6] Output: 17 Explanation: The optimal subarray here is [2;4;5;6]. Example 2: Input: nums = [5;2;1;2;5;2;1;2;5] Output: 8 Explanation: The optimal subarray here is [5;2;1] or [1;2;5]. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 104
Google,1845,Seat Reservation Manager,Med,"Array, Greedy, Sorting, Matrix",You are given a binary matrix matrix of size m x n; and you are allowed to rearrange the columns of the matrix in any order. Return the area of the largest submatrix within matrix where every element of the submatrix is 1 after reordering the columns optimally. Example 1: Input: matrix = [[0;0;1];[1;1;1];[1;0;1]] Output: 4 Explanation: You can rearrange the columns as shown above. The largest submatrix of 1s; in bold; has an area of 4. Example 2: Input: matrix = [[1;0;1;0;1]] Output: 3 Explanation: You can rearrange the columns as shown above. The largest submatrix of 1s; in bold; has an area of 3. Example 3: Input: matrix = [[1;1;0];[1;0;1]] Output: 2 Explanation: Notice that you must rearrange entire columns; and there is no way to make a submatrix of 1s larger than an area of 2. Constraints: m == matrix.length n == matrix[i].length 1 <= m * n <= 105 matrix[i][j] is either 0 or 1.
Google,1838,Frequency of the Most Frequent Element,Med,"String, Trie, Rolling Hash, Suffix Array, Hash Function",
Google,1820,Maximum Number of Accepted Invitations,Med,"Tree, Graph",You are given an array pairs; where pairs[i] = [xi; yi]; and: There are no duplicates. xi < yi Let ways be the number of rooted trees that satisfy the following conditions: The tree consists of nodes whose values appeared in pairs. A pair [xi; yi] exists in pairs if and only if xi is an ancestor of yi or yi is an ancestor of xi. Note: the tree does not have to be a binary tree. Two ways are considered to be different if there is at least one node that has different parents in both ways. Return: 0 if ways == 0 1 if ways == 1 2 if ways > 1 A rooted tree is a tree that has a single root node; and all edges are oriented to be outgoing from the root. An ancestor of a node is any node on the path from the root to that node (excluding the node itself). The root has no ancestors. Example 1: Input: pairs = [[1;2];[2;3]] Output: 1 Explanation: There is exactly one valid rooted tree; which is shown in the above figure. Example 2: Input: pairs = [[1;2];[2;3];[1;3]] Output: 2 Explanation: There are multiple valid rooted trees. Three of them are shown in the above figures. Example 3: Input: pairs = [[1;2];[2;3];[2;4];[1;5]] Output: 0 Explanation: There are no valid rooted trees. Constraints: 1 <= pairs.length <= 105 1 <= xi < yi <= 500 The elements in pairs are unique.
Google,1859,Sorting the Sentence,Easy,"Hash Table, String, Counting, Prefix Sum","You are given two strings a and b that consist of lowercase letters. In one operation; you can change any character in a or b to any lowercase letter. Your goal is to satisfy one of the following three conditions: Every letter in a is strictly less than every letter in b in the alphabet. Every letter in b is strictly less than every letter in a in the alphabet. Both a and b consist of only one distinct letter. Return the minimum number of operations needed to achieve your goal. Example 1: Input: a = ""aba""; b = ""caa"" Output: 2 Explanation: Consider the best way to make each condition true: 1) Change b to ""ccc"" in 2 operations; then every letter in a is less than every letter in b. 2) Change a to ""bbb"" and b to ""aaa"" in 3 operations; then every letter in b is less than every letter in a. 3) Change a to ""aaa"" and b to ""aaa"" in 2 operations; then a and b consist of one distinct letter. The best way was done in 2 operations (either condition 1 or condition 3). Example 2: Input: a = ""dabadd""; b = ""cda"" Output: 3 Explanation: The best way is to make condition 1 true by changing b to ""eee"". Constraints: 1 <= a.length; b.length <= 105 a and b consist only of lowercase letters."
Google,1894,Find the Student that Will Replace the Chalk,Med,"Two Pointers, String","You are given two strings word1 and word2. Merge the strings by adding letters in alternating order; starting with word1. If a string is longer than the other; append the additional letters onto the end of the merged string. Return the merged string. Example 1: Input: word1 = ""abc""; word2 = ""pqr"" Output: ""apbqcr"" Explanation: The merged string will be merged as so: word1: a b c word2: p q r merged: a p b q c r Example 2: Input: word1 = ""ab""; word2 = ""pqrs"" Output: ""apbqrs"" Explanation: Notice that as word2 is longer; ""rs"" is appended to the end. word1: a b word2: p q r s merged: a p b q r s Example 3: Input: word1 = ""abcd""; word2 = ""pq"" Output: ""apbqcd"" Explanation: Notice that as word1 is longer; ""cd"" is appended to the end. word1: a b c d word2: p q merged: a p b q c d Constraints: 1 <= word1.length; word2.length <= 100 word1 and word2 consist of lowercase English letters."
Google,1905,Count Sub Islands,Med,"Hash Table, Linked List, Design, Doubly-Linked List","There is an authentication system that works with authentication tokens. For each session; the user will receive a new authentication token that will expire timeToLive seconds after the currentTime. If the token is renewed; the expiry time will be extended to expire timeToLive seconds after the (potentially different) currentTime. Implement the AuthenticationManager class: AuthenticationManager(int timeToLive) constructs the AuthenticationManager and sets the timeToLive. generate(string tokenId; int currentTime) generates a new token with the given tokenId at the given currentTime in seconds. renew(string tokenId; int currentTime) renews the unexpired token with the given tokenId at the given currentTime in seconds. If there are no unexpired tokens with the given tokenId; the request is ignored; and nothing happens. countUnexpiredTokens(int currentTime) returns the number of unexpired tokens at the given currentTime. Note that if a token expires at time t; and another action happens on time t (renew or countUnexpiredTokens); the expiration takes place before the other actions. Example 1: Input [""AuthenticationManager""; ""renew""; ""generate""; ""countUnexpiredTokens""; ""generate""; ""renew""; ""renew""; ""countUnexpiredTokens""] [[5]; [""aaa""; 1]; [""aaa""; 2]; [6]; [""bbb""; 7]; [""aaa""; 8]; [""bbb""; 10]; [15]] Output [null; null; null; 1; null; null; null; 0] Explanation AuthenticationManager authenticationManager = new AuthenticationManager(5); // Constructs the AuthenticationManager with timeToLive = 5 seconds. authenticationManager.renew(""aaa""; 1); // No token exists with tokenId ""aaa"" at time 1; so nothing happens. authenticationManager.generate(""aaa""; 2); // Generates a new token with tokenId ""aaa"" at time 2. authenticationManager.countUnexpiredTokens(6); // The token with tokenId ""aaa"" is the only unexpired one at time 6; so return 1. authenticationManager.generate(""bbb""; 7); // Generates a new token with tokenId ""bbb"" at time 7. authenticationManager.renew(""aaa""; 8); // The token with tokenId ""aaa"" expired at time 7; and 8 >= 7; so at time 8 the renew request is ignored; and nothing happens. authenticationManager.renew(""bbb""; 10); // The token with tokenId ""bbb"" is unexpired at time 10; so the renew request is fulfilled and now the token will expire at time 15. authenticationManager.countUnexpiredTokens(15); // The token with tokenId ""bbb"" expires at time 15; and the token with tokenId ""aaa"" expired at time 7; so currently no token is unexpired; so return 0. Constraints: 1 <= timeToLive <= 108 1 <= currentTime <= 108 1 <= tokenId.length <= 5 tokenId consists only of lowercase letters. All calls to generate will contain unique values of tokenId. The values of currentTime across all the function calls will be strictly increasing. At most 2000 calls will be made to all functions combined."
Google,1920,Build Array from Permutation,Easy,"Math, String","You are given coordinates; a string that represents the coordinates of a square of the chessboard. Below is a chessboard for your reference. Return true if the square is white; and false if the square is black. The coordinate will always represent a valid chessboard square. The coordinate will always have the letter first; and the number second. Example 1: Input: coordinates = ""a1"" Output: false Explanation: From the chessboard above; the square with coordinates ""a1"" is black; so return false. Example 2: Input: coordinates = ""h3"" Output: true Explanation: From the chessboard above; the square with coordinates ""h3"" is white; so return true. Example 3: Input: coordinates = ""c7"" Output: false Constraints: coordinates.length == 2 'a' <= coordinates[0] <= 'h' '1' <= coordinates[1] <= '8'"
Google,1929,Concatenation of Array,Easy,"Binary Search, Greedy",You are given three positive integers: n; index; and maxSum. You want to construct an array nums (0-indexed) that satisfies the following conditions: nums.length == n nums[i] is a positive integer where 0 <= i < n. abs(nums[i] - nums[i+1]) <= 1 where 0 <= i < n-1. The sum of all the elements of nums does not exceed maxSum. nums[index] is maximized. Return nums[index] of the constructed array. Note that abs(x) equals x if x >= 0; and -x otherwise. Example 1: Input: n = 4; index = 2; maxSum = 6 Output: 2 Explanation: nums = [1;2;2;1] is one array that satisfies all the conditions. There are no arrays that satisfy all the conditions and have nums[2] == 3; so 2 is the maximum nums[2]. Example 2: Input: n = 6; index = 1; maxSum = 10 Output: 3 Constraints: 1 <= n <= maxSum <= 109 0 <= index < n
Google,1945,Sum of Digits of String After Convert,Easy,"Array, Hash Table",You are given the logs for users' actions on LeetCode; and an integer k. The logs are represented by a 2D integer array logs where each logs[i] = [IDi; timei] indicates that the user with IDi performed an action at the minute timei. Multiple users can perform actions simultaneously; and a single user can perform multiple actions in the same minute. The user active minutes (UAM) for a given user is defined as the number of unique minutes in which the user performed an action on LeetCode. A minute can only be counted once; even if multiple actions occur during it. You are to calculate a 1-indexed array answer of size k such that; for each j (1 <= j <= k); answer[j] is the number of users whose UAM equals j. Return the array answer as described above. Example 1: Input: logs = [[0;5];[1;2];[0;2];[0;5];[1;3]]; k = 5 Output: [0;2;0;0;0] Explanation: The user with ID=0 performed actions at minutes 5; 2; and 5 again. Hence; they have a UAM of 2 (minute 5 is only counted once). The user with ID=1 performed actions at minutes 2 and 3. Hence; they have a UAM of 2. Since both users have a UAM of 2; answer[2] is 2; and the remaining answer[j] values are 0. Example 2: Input: logs = [[1;1];[2;2];[2;3]]; k = 4 Output: [1;1;0;0] Explanation: The user with ID=1 performed a single action at minute 1. Hence; they have a UAM of 1. The user with ID=2 performed actions at minutes 2 and 3. Hence; they have a UAM of 2. There is one user with a UAM of 1 and one with a UAM of 2. Hence; answer[1] = 1; answer[2] = 1; and the remaining values are 0. Constraints: 1 <= logs.length <= 104 0 <= IDi <= 109 1 <= timei <= 105 k is in the range [The maximum UAM for a user; 105].
Google,1934,Confirmation Rate,Med,"Array, Hash Table, String","You are given a string s that contains some bracket pairs; with each pair containing a non-empty key. For example; in the string ""(name)is(age)yearsold""; there are two bracket pairs that contain the keys ""name"" and ""age"". You know the values of a wide range of keys. This is represented by a 2D string array knowledge where each knowledge[i] = [keyi; valuei] indicates that key keyi has a value of valuei. You are tasked to evaluate all of the bracket pairs. When you evaluate a bracket pair that contains some key keyi; you will: Replace keyi and the bracket pair with the key's corresponding valuei. If you do not know the value of the key; you will replace keyi and the bracket pair with a question mark ""?"" (without the quotation marks). Each key will appear at most once in your knowledge. There will not be any nested brackets in s. Return the resulting string after evaluating all of the bracket pairs. Example 1: Input: s = ""(name)is(age)yearsold""; knowledge = [[""name"";""bob""];[""age"";""two""]] Output: ""bobistwoyearsold"" Explanation: The key ""name"" has a value of ""bob""; so replace ""(name)"" with ""bob"". The key ""age"" has a value of ""two""; so replace ""(age)"" with ""two"". Example 2: Input: s = ""hi(name)""; knowledge = [[""a"";""b""]] Output: ""hi?"" Explanation: As you do not know the value of the key ""name""; replace ""(name)"" with ""?"". Example 3: Input: s = ""(a)(a)(a)aaa""; knowledge = [[""a"";""yes""]] Output: ""yesyesyesaaa"" Explanation: The same key can appear multiple times. The key ""a"" has a value of ""yes""; so replace all occurrences of ""(a)"" with ""yes"". Notice that the ""a""s not in a bracket pair are not evaluated. Constraints: 1 <= s.length <= 105 0 <= knowledge.length <= 105 knowledge[i].length == 2 1 <= keyi.length; valuei.length <= 10 s consists of lowercase English letters and round brackets '(' and ')'. Every open bracket '(' in s will have a corresponding close bracket ')'. The key in each bracket pair of s will be non-empty. There will not be any nested bracket pairs in s. keyi and valuei consist of lowercase English letters. Each keyi in knowledge is unique."
Google,1976,Number of Ways to Arrive at Destination,Med,"String, Backtracking","You are given a string s that consists of only digits. Check if we can split s into two or more non-empty substrings such that the numerical values of the substrings are in descending order and the difference between numerical values of every two adjacent substrings is equal to 1. For example; the string s = ""0090089"" can be split into [""0090""; ""089""] with numerical values [90;89]. The values are in descending order and adjacent values differ by 1; so this way is valid. Another example; the string s = ""001"" can be split into [""0""; ""01""]; [""00""; ""1""]; or [""0""; ""0""; ""1""]. However all the ways are invalid because they have numerical values [0;1]; [0;1]; and [0;0;1] respectively; all of which are not in descending order. Return true if it is possible to split s​​​​​​ as described above; or false otherwise. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""1234"" Output: false Explanation: There is no valid way to split s. Example 2: Input: s = ""050043"" Output: true Explanation: s can be split into [""05""; ""004""; ""3""] with numerical values [5;4;3]. The values are in descending order with adjacent values differing by 1. Example 3: Input: s = ""9080701"" Output: false Explanation: There is no valid way to split s. Constraints: 1 <= s.length <= 20 s only consists of digits."
Google,1984,Minimum Difference Between Highest and Lowest of K Scores,Easy,"Array, Two Pointers, Binary Search",You are given two non-increasing 0-indexed integer arrays nums1​​​​​​ and nums2​​​​​​. A pair of indices (i; j); where 0 <= i < nums1.length and 0 <= j < nums2.length; is valid if both i <= j and nums1[i] <= nums2[j]. The distance of the pair is j - i​​​​. Return the maximum distance of any valid pair (i; j). If there are no valid pairs; return 0. An array arr is non-increasing if arr[i-1] >= arr[i] for every 1 <= i < arr.length. Example 1: Input: nums1 = [55;30;5;4;2]; nums2 = [100;20;10;10;5] Output: 2 Explanation: The valid pairs are (0;0); (2;2); (2;3); (2;4); (3;3); (3;4); and (4;4). The maximum distance is 2 with pair (2;4). Example 2: Input: nums1 = [2;2;2]; nums2 = [10;10;1] Output: 1 Explanation: The valid pairs are (0;0); (0;1); and (1;1). The maximum distance is 1 with pair (0;1). Example 3: Input: nums1 = [30;29;19;5]; nums2 = [25;25;25;25;25] Output: 2 Explanation: The valid pairs are (2;2); (2;3); (2;4); (3;3); and (3;4). The maximum distance is 2 with pair (2;4). Constraints: 1 <= nums1.length; nums2.length <= 105 1 <= nums1[i]; nums2[j] <= 105 Both nums1 and nums2 are non-increasing.
Google,2006,Count Number of Pairs With Absolute Difference K,Easy,"Array, Binary Search, Simulation, Prefix Sum",There are n students in a class numbered from 0 to n - 1. The teacher will give each student a problem starting with the student number 0; then the student number 1; and so on until the teacher reaches the student number n - 1. After that; the teacher will restart the process; starting with the student number 0 again. You are given a 0-indexed integer array chalk and an integer k. There are initially k pieces of chalk. When the student number i is given a problem to solve; they will use chalk[i] pieces of chalk to solve that problem. However; if the current number of chalk pieces is strictly less than chalk[i]; then the student number i will be asked to replace the chalk. Return the index of the student that will replace the chalk pieces. Example 1: Input: chalk = [5;1;5]; k = 22 Output: 0 Explanation: The students go in turns as follows: - Student number 0 uses 5 chalk; so k = 17. - Student number 1 uses 1 chalk; so k = 16. - Student number 2 uses 5 chalk; so k = 11. - Student number 0 uses 5 chalk; so k = 6. - Student number 1 uses 1 chalk; so k = 5. - Student number 2 uses 5 chalk; so k = 0. Student number 0 does not have enough chalk; so they will have to replace it. Example 2: Input: chalk = [3;4;1;2]; k = 25 Output: 1 Explanation: The students go in turns as follows: - Student number 0 uses 3 chalk so k = 22. - Student number 1 uses 4 chalk so k = 18. - Student number 2 uses 1 chalk so k = 17. - Student number 3 uses 2 chalk so k = 15. - Student number 0 uses 3 chalk so k = 12. - Student number 1 uses 4 chalk so k = 8. - Student number 2 uses 1 chalk so k = 7. - Student number 3 uses 2 chalk so k = 5. - Student number 0 uses 3 chalk so k = 2. Student number 1 does not have enough chalk; so they will have to replace it. Constraints: chalk.length == n 1 <= n <= 105 1 <= chalk[i] <= 105 1 <= k <= 109
Google,2007,Find Original Array From Doubled Array,Med,"Dynamic Programming, Bit Manipulation, Graph, Bitmask",
Google,2009,Minimum Number of Operations to Make Array Continuous,Hard,"Depth-First Search, Trie",
Google,2027,Minimum Moves to Convert String,Easy,"Array, Two Pointers, String, Binary Search","You are given two strings s and p where p is a subsequence of s. You are also given a distinct 0-indexed integer array removable containing a subset of indices of s (s is also 0-indexed). You want to choose an integer k (0 <= k <= removable.length) such that; after removing k characters from s using the first k indices in removable; p is still a subsequence of s. More formally; you will mark the character at s[removable[i]] for each 0 <= i < k; then remove all marked characters and check if p is still a subsequence. Return the maximum k you can choose such that p is still a subsequence of s after the removals. A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters. Example 1: Input: s = ""abcacb""; p = ""ab""; removable = [3;1;0] Output: 2 Explanation: After removing the characters at indices 3 and 1; ""abcacb"" becomes ""accb"". ""ab"" is a subsequence of ""accb"". If we remove the characters at indices 3; 1; and 0; ""abcacb"" becomes ""ccb""; and ""ab"" is no longer a subsequence. Hence; the maximum k is 2. Example 2: Input: s = ""abcbddddd""; p = ""abcd""; removable = [3;2;1;4;5;6] Output: 1 Explanation: After removing the character at index 3; ""abcbddddd"" becomes ""abcddddd"". ""abcd"" is a subsequence of ""abcddddd"". Example 3: Input: s = ""abcab""; p = ""abc""; removable = [0;1;2;3;4] Output: 0 Explanation: If you remove the first index in the array removable; ""abc"" is no longer a subsequence. Constraints: 1 <= p.length <= s.length <= 105 0 <= removable.length < s.length 0 <= removable[i] < s.length p is a subsequence of s. s and p both consist of lowercase English letters. The elements in removable are distinct."
Google,2028,Find Missing Observations,Med,"Dynamic Programming, Memoization",There is a tournament where n players are participating. The players are standing in a single row and are numbered from 1 to n based on their initial standing position (player 1 is the first player in the row; player 2 is the second player in the row; etc.). The tournament consists of multiple rounds (starting from round number 1). In each round; the ith player from the front of the row competes against the ith player from the end of the row; and the winner advances to the next round. When the number of players is odd for the current round; the player in the middle automatically advances to the next round. For example; if the row consists of players 1; 2; 4; 6; 7 Player 1 competes against player 7. Player 2 competes against player 6. Player 4 automatically advances to the next round. After each round is over; the winners are lined back up in the row based on the original ordering assigned to them initially (ascending order). The players numbered firstPlayer and secondPlayer are the best in the tournament. They can win against any other player before they compete against each other. If any two other players compete against each other; either of them might win; and thus you may choose the outcome of this round. Given the integers n; firstPlayer; and secondPlayer; return an integer array containing two values; the earliest possible round number and the latest possible round number in which these two players will compete against each other; respectively. Example 1: Input: n = 11; firstPlayer = 2; secondPlayer = 4 Output: [3;4] Explanation: One possible scenario which leads to the earliest round number: First round: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11 Second round: 2; 3; 4; 5; 6; 11 Third round: 2; 3; 4 One possible scenario which leads to the latest round number: First round: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11 Second round: 1; 2; 3; 4; 5; 6 Third round: 1; 2; 4 Fourth round: 2; 4 Example 2: Input: n = 5; firstPlayer = 1; secondPlayer = 5 Output: [1;1] Explanation: The players numbered 1 and 5 compete in the first round. There is no way to make them compete in any other round. Constraints: 2 <= n <= 28 1 <= firstPlayer < secondPlayer <= n
Google,2127,Maximum Employees to Be Invited to a Meeting,Hard,Database,Table: Employees +-------------+----------+ | Column Name | Type | +-------------+----------+ | employee_id | int | | name | varchar | | manager_id | int | | salary | int | +-------------+----------+ In SQL; employee_id is the primary key for this table. This table contains information about the employees; their salary; and the ID of their manager. Some employees do not have a manager (manager_id is null). Find the IDs of the employees whose salary is strictly less than $30000 and whose manager left the company. When a manager leaves the company; their information is deleted from the Employees table; but the reports still have their manager_id set to the manager that left. Return the result table ordered by employee_id. The result format is in the following example. Example 1: Input: Employees table: +-------------+-----------+------------+--------+ | employee_id | name | manager_id | salary | +-------------+-----------+------------+--------+ | 3 | Mila | 9 | 60301 | | 12 | Antonella | null | 31000 | | 13 | Emery | null | 67084 | | 1 | Kalel | 11 | 21241 | | 9 | Mikaela | null | 50937 | | 11 | Joziah | 6 | 28485 | +-------------+-----------+------------+--------+ Output: +-------------+ | employee_id | +-------------+ | 11 | +-------------+ Explanation: The employees with a salary less than $30000 are 1 (Kalel) and 11 (Joziah). Kalel's manager is employee 11; who is still in the company (Joziah). Joziah's manager is employee 6; who left the company because there is no row for employee 6 as it was deleted.
Google,2239,Find Closest Number to Zero,Easy,"String, Simulation","There is an n x n grid; with the top-left cell at (0; 0) and the bottom-right cell at (n - 1; n - 1). You are given the integer n and an integer array startPos where startPos = [startrow; startcol] indicates that a robot is initially at cell (startrow; startcol). You are also given a 0-indexed string s of length m where s[i] is the ith instruction for the robot: 'L' (move left); 'R' (move right); 'U' (move up); and 'D' (move down). The robot can begin executing from any ith instruction in s. It executes the instructions one by one towards the end of s but it stops if either of these conditions is met: The next instruction will move the robot off the grid. There are no more instructions left to execute. Return an array answer of length m where answer[i] is the number of instructions the robot can execute if the robot begins executing from the ith instruction in s. Example 1: Input: n = 3; startPos = [0;1]; s = ""RRDDLU"" Output: [1;5;4;3;1;0] Explanation: Starting from startPos and beginning execution from the ith instruction: - 0th: ""RRDDLU"". Only one instruction ""R"" can be executed before it moves off the grid. - 1st: ""RDDLU"". All five instructions can be executed while it stays in the grid and ends at (1; 1). - 2nd: ""DDLU"". All four instructions can be executed while it stays in the grid and ends at (1; 0). - 3rd: ""DLU"". All three instructions can be executed while it stays in the grid and ends at (0; 0). - 4th: ""LU"". Only one instruction ""L"" can be executed before it moves off the grid. - 5th: ""U"". If moving up; it would move off the grid. Example 2: Input: n = 2; startPos = [1;1]; s = ""LURD"" Output: [4;1;0;0] Explanation: - 0th: ""LURD"". - 1st: ""URD"". - 2nd: ""RD"". - 3rd: ""D"". Example 3: Input: n = 1; startPos = [0;0]; s = ""LRUD"" Output: [0;0;0;0] Explanation: No matter which instruction the robot begins execution from; it would move off the grid. Constraints: m == s.length 1 <= n; m <= 500 startPos.length == 2 0 <= startrow; startcol < n s consists of 'L'; 'R'; 'U'; and 'D'."
Google,2296,Design a Text Editor,Hard,Database,
Google,2405,Optimal Partition of String,Med,"Hash Table, String, Greedy, Sorting, Counting",
Google,2407,Longest Increasing Subsequence II,Hard,,
Google,2463,Minimum Total Distance Traveled,Hard,"String, Sliding Window","You are given a 0-indexed string blocks of length n; where blocks[i] is either 'W' or 'B'; representing the color of the ith block. The characters 'W' and 'B' denote the colors white and black; respectively. You are also given an integer k; which is the desired number of consecutive black blocks. In one operation; you can recolor a white block such that it becomes a black block. Return the minimum number of operations needed such that there is at least one occurrence of k consecutive black blocks. Example 1: Input: blocks = ""WBBWWBBWBW""; k = 7 Output: 3 Explanation: One way to achieve 7 consecutive black blocks is to recolor the 0th; 3rd; and 4th blocks so that blocks = ""BBBBBBBWBW"". It can be shown that there is no way to achieve 7 consecutive black blocks in less than 3 operations. Therefore; we return 3. Example 2: Input: blocks = ""WBWBBBW""; k = 2 Output: 0 Explanation: No changes need to be made; since 2 consecutive black blocks already exist. Therefore; we return 0. Constraints: n == blocks.length 1 <= n <= 100 blocks[i] is either 'W' or 'B'. 1 <= k <= n"
Google,2530,Maximal Score After Applying K Operations,Med,"Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum",You are given a 0-indexed array nums comprising of n non-negative integers. In one operation; you must: Choose an integer i such that 1 <= i < n and nums[i] > 0. Decrease nums[i] by 1. Increase nums[i - 1] by 1. Return the minimum possible value of the maximum integer of nums after performing any number of operations. Example 1: Input: nums = [3;7;1;6] Output: 5 Explanation: One set of optimal operations is as follows: 1. Choose i = 1; and nums becomes [4;6;1;6]. 2. Choose i = 3; and nums becomes [4;6;2;5]. 3. Choose i = 1; and nums becomes [5;5;2;5]. The maximum integer of nums is 5. It can be shown that the maximum number cannot be less than 5. Therefore; we return 5. Example 2: Input: nums = [10;1] Output: 10 Explanation: It is optimal to leave nums as is; and since 10 is the maximum value; we return 10. Constraints: n == nums.length 2 <= n <= 105 0 <= nums[i] <= 109
Google,2601,Prime Subtraction Operation,Med,"Array, Dynamic Programming",You are given an array nums consisting of positive integers and an integer k. Partition the array into two ordered groups such that each element is in exactly one group. A partition is called great if the sum of elements of each group is greater than or equal to k. Return the number of distinct great partitions. Since the answer may be too large; return it modulo 109 + 7. Two partitions are considered distinct if some element nums[i] is in different groups in the two partitions. Example 1: Input: nums = [1;2;3;4]; k = 4 Output: 6 Explanation: The great partitions are: ([1;2;3]; [4]); ([1;3]; [2;4]); ([1;4]; [2;3]); ([2;3]; [1;4]); ([2;4]; [1;3]) and ([4]; [1;2;3]). Example 2: Input: nums = [3;3;3]; k = 4 Output: 0 Explanation: There are no great partitions for this array. Example 3: Input: nums = [6;6]; k = 2 Output: 2 Explanation: We can either put nums[0] in the first partition or in the second partition. The great partitions will be ([6]; [6]) and ([6]; [6]). Constraints: 1 <= nums.length; k <= 1000 1 <= nums[i] <= 109
Google,2621,Sleep,Easy,"Array, Math, Bit Manipulation",You are given a 0-indexed integer array nums. The effective value of three indices i; j; and k is defined as ((nums[i] | nums[j]) & nums[k]). The xor-beauty of the array is the XORing of the effective values of all the possible triplets of indices (i; j; k) where 0 <= i; j; k < n. Return the xor-beauty of nums. Note that: val1 | val2 is bitwise OR of val1 and val2. val1 & val2 is bitwise AND of val1 and val2. Example 1: Input: nums = [1;4] Output: 5 Explanation: The triplets and their corresponding effective values are listed below: - (0;0;0) with effective value ((1 | 1) & 1) = 1 - (0;0;1) with effective value ((1 | 1) & 4) = 0 - (0;1;0) with effective value ((1 | 4) & 1) = 1 - (0;1;1) with effective value ((1 | 4) & 4) = 4 - (1;0;0) with effective value ((4 | 1) & 1) = 1 - (1;0;1) with effective value ((4 | 1) & 4) = 4 - (1;1;0) with effective value ((4 | 4) & 1) = 0 - (1;1;1) with effective value ((4 | 4) & 4) = 4 Xor-beauty of array will be bitwise XOR of all beauties = 1 ^ 0 ^ 1 ^ 4 ^ 1 ^ 4 ^ 0 ^ 4 = 5. Example 2: Input: nums = [15;45;20;2;34;35;5;44;32;30] Output: 34 Explanation: The xor-beauty of the given array is 34. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 109
Google,2619,Array Prototype Last,Easy,Math,"Given four integers length; width; height; and mass; representing the dimensions and mass of a box; respectively; return a string representing the category of the box. The box is ""Bulky"" if: Any of the dimensions of the box is greater or equal to 104. Or; the volume of the box is greater or equal to 109. If the mass of the box is greater or equal to 100; it is ""Heavy"". If the box is both ""Bulky"" and ""Heavy""; then its category is ""Both"". If the box is neither ""Bulky"" nor ""Heavy""; then its category is ""Neither"". If the box is ""Bulky"" but not ""Heavy""; then its category is ""Bulky"". If the box is ""Heavy"" but not ""Bulky""; then its category is ""Heavy"". Note that the volume of the box is the product of its length; width and height. Example 1: Input: length = 1000; width = 35; height = 700; mass = 300 Output: ""Heavy"" Explanation: None of the dimensions of the box is greater or equal to 104. Its volume = 24500000 <= 109. So it cannot be categorized as ""Bulky"". However mass >= 100; so the box is ""Heavy"". Since the box is not ""Bulky"" but ""Heavy""; we return ""Heavy"". Example 2: Input: length = 200; width = 50; height = 800; mass = 50 Output: ""Neither"" Explanation: None of the dimensions of the box is greater or equal to 104. Its volume = 8 * 106 <= 109. So it cannot be categorized as ""Bulky"". Its mass is also less than 100; so it cannot be categorized as ""Heavy"" either. Since its neither of the two above categories; we return ""Neither"". Constraints: 1 <= length; width; height <= 105 1 <= mass <= 103"
Google,2633,Convert Object to JSON String,Med,"Array, Hash Table, Dynamic Programming, Counting",You are given an integer array nums and an integer k. Split the array into some number of non-empty subarrays. The cost of a split is the sum of the importance value of each subarray in the split. Let trimmed(subarray) be the version of the subarray where all numbers which appear only once are removed. For example; trimmed([3;1;2;4;3;4]) = [3;4;3;4]. The importance value of a subarray is k + trimmed(subarray).length. For example; if a subarray is [1;2;3;3;3;4;4]; then trimmed([1;2;3;3;3;4;4]) = [3;3;3;4;4].The importance value of this subarray will be k + 5. Return the minimum possible cost of a split of nums. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;2;1;2;1;3;3]; k = 2 Output: 8 Explanation: We split nums to have two subarrays: [1;2]; [1;2;1;3;3]. The importance value of [1;2] is 2 + (0) = 2. The importance value of [1;2;1;3;3] is 2 + (2 + 2) = 6. The cost of the split is 2 + 6 = 8. It can be shown that this is the minimum possible cost among all the possible splits. Example 2: Input: nums = [1;2;1;2;1]; k = 2 Output: 6 Explanation: We split nums to have two subarrays: [1;2]; [1;2;1]. The importance value of [1;2] is 2 + (0) = 2. The importance value of [1;2;1] is 2 + (2) = 4. The cost of the split is 2 + 4 = 6. It can be shown that this is the minimum possible cost among all the possible splits. Example 3: Input: nums = [1;2;1;2;1]; k = 5 Output: 10 Explanation: We split nums to have one subarray: [1;2;1;2;1]. The importance value of [1;2;1;2;1] is 5 + (3 + 2) = 10. The cost of the split is 10. It can be shown that this is the minimum possible cost among all the possible splits. Constraints: 1 <= nums.length <= 1000 0 <= nums[i] < nums.length 1 <= k <= 109
Google,2684,Maximum Number of Moves in a Grid,Med,"Array, Simulation",You are given two 0-indexed integer arrays player1 and player2; representing the number of pins that player 1 and player 2 hit in a bowling game; respectively. The bowling game consists of n turns; and the number of pins in each turn is exactly 10. Assume a player hits xi pins in the ith turn. The value of the ith turn for the player is: 2xi if the player hits 10 pins in either (i - 1)th or (i - 2)th turn. Otherwise; it is xi. The score of the player is the sum of the values of their n turns. Return 1 if the score of player 1 is more than the score of player 2; 2 if the score of player 2 is more than the score of player 1; and 0 in case of a draw. Example 1: Input: player1 = [5;10;3;2]; player2 = [6;5;7;3] Output: 1 Explanation: The score of player 1 is 5 + 10 + 2*3 + 2*2 = 25. The score of player 2 is 6 + 5 + 7 + 3 = 21. Example 2: Input: player1 = [3;5;7;6]; player2 = [8;10;10;2] Output: 2 Explanation: The score of player 1 is 3 + 5 + 7 + 6 = 21. The score of player 2 is 8 + 10 + 2*10 + 2*2 = 42. Example 3: Input: player1 = [2;3]; player2 = [4;1] Output: 0 Explanation: The score of player1 is 2 + 3 = 5. The score of player2 is 4 + 1 = 5. Example 4: Input: player1 = [1;1;1;10;10;10;10]; player2 = [10;10;10;10;1;1;1] Output: 2 Explanation: The score of player1 is 1 + 1 + 1 + 10 + 2*10 + 2*10 + 2*10 = 73. The score of player2 is 10 + 2*10 + 2*10 + 2*10 + 2*1 + 2*1 + 1 = 75. Constraints: n == player1.length == player2.length 1 <= n <= 1000 0 <= player1[i]; player2[i] <= 10
Google,2696,Minimum String Length After Removing Substrings,Easy,"Array, Hash Table, Math, Dynamic Programming, Backtracking, Sorting, Combinatorics",You are given an array nums of positive integers and a positive integer k. A subset of nums is beautiful if it does not contain two integers with an absolute difference equal to k. Return the number of non-empty beautiful subsets of the array nums. A subset of nums is an array that can be obtained by deleting some (possibly none) elements from nums. Two subsets are different if and only if the chosen indices to delete are different. Example 1: Input: nums = [2;4;6]; k = 2 Output: 4 Explanation: The beautiful subsets of the array nums are: [2]; [4]; [6]; [2; 6]. It can be proved that there are only 4 beautiful subsets in the array [2;4;6]. Example 2: Input: nums = [1]; k = 1 Output: 1 Explanation: The beautiful subset of the array nums is [1]. It can be proved that there is only 1 beautiful subset in the array [1]. Constraints: 1 <= nums.length <= 20 1 <= nums[i]; k <= 1000
Google,2699,Modify Graph Edge Weights,Hard,"Array, Two Pointers, Binary Search, Sorting",Given a 0-indexed integer array nums of size n and two integers lower and upper; return the number of fair pairs. A pair (i; j) is fair if: 0 <= i < j < n; and lower <= nums[i] + nums[j] <= upper Example 1: Input: nums = [0;1;7;4;4;5]; lower = 3; upper = 6 Output: 6 Explanation: There are 6 fair pairs: (0;3); (0;4); (0;5); (1;3); (1;4); and (1;5). Example 2: Input: nums = [1;7;9;2;5]; lower = 11; upper = 11 Output: 1 Explanation: There is a single fair pair: (2;3). Constraints: 1 <= nums.length <= 105 nums.length == n -109 <= nums[i] <= 109 -109 <= lower <= upper <= 109
Google,2800,Shortest String That Contains Three Strings,Med,"String, Stack, Simulation","You are given a string s consisting only of uppercase English letters. You can apply some operations to this string where; in one operation; you can remove any occurrence of one of the substrings ""AB"" or ""CD"" from s. Return the minimum possible length of the resulting string that you can obtain. Note that the string concatenates after removing the substring and could produce new ""AB"" or ""CD"" substrings. Example 1: Input: s = ""ABFCACDB"" Output: 2 Explanation: We can do the following operations: - Remove the substring ""ABFCACDB""; so s = ""FCACDB"". - Remove the substring ""FCACDB""; so s = ""FCAB"". - Remove the substring ""FCAB""; so s = ""FC"". So the resulting length of the string is 2. It can be shown that it is the minimum length that we can obtain. Example 2: Input: s = ""ACBBD"" Output: 5 Explanation: We cannot do any operations on the string so the length remains the same. Constraints: 1 <= s.length <= 100 s consists only of uppercase English letters."
Google,2965,Find Missing and Repeated Values,Easy,,
Google,2955,Number of Same-End Substrings,Med,Math,Initially; you have a bank account balance of 100 dollars. You are given an integer purchaseAmount representing the amount you will spend on a purchase in dollars; in other words; its price. When making the purchase; first the purchaseAmount is rounded to the nearest multiple of 10. Let us call this value roundedAmount. Then; roundedAmount dollars are removed from your bank account. Return an integer denoting your final bank account balance after this purchase. Notes: 0 is considered to be a multiple of 10 in this problem. When rounding; 5 is rounded upward (5 is rounded to 10; 15 is rounded to 20; 25 to 30; and so on). Example 1: Input: purchaseAmount = 9 Output: 90 Explanation: The nearest multiple of 10 to 9 is 10. So your account balance becomes 100 - 10 = 90. Example 2: Input: purchaseAmount = 15 Output: 80 Explanation: The nearest multiple of 10 to 15 is 20. So your account balance becomes 100 - 20 = 80. Example 3: Input: purchaseAmount = 10 Output: 90 Explanation: 10 is a multiple of 10 itself. So your account balance becomes 100 - 10 = 90. Constraints: 0 <= purchaseAmount <= 100
Google,3133,Minimum Array End,Med,,
Google,3120,Count the Number of Special Characters I,Easy,,
Google,3208,Alternating Groups II,Med,"Hash Table, Math, String, Number Theory, Prefix Sum","You are given a string s and a positive integer k. Let vowels and consonants be the number of vowels and consonants in a string. A string is beautiful if: vowels == consonants. (vowels * consonants) % k == 0; in other terms the multiplication of vowels and consonants is divisible by k. Return the number of non-empty beautiful substrings in the given string s. A substring is a contiguous sequence of characters in a string. Vowel letters in English are 'a'; 'e'; 'i'; 'o'; and 'u'. Consonant letters in English are every letter except vowels. Example 1: Input: s = ""baeyh""; k = 2 Output: 2 Explanation: There are 2 beautiful substrings in the given string. - Substring ""baeyh""; vowels = 2 ([""a"";e""]); consonants = 2 ([""y"";""h""]). You can see that string ""aeyh"" is beautiful as vowels == consonants and vowels * consonants % k == 0. - Substring ""baeyh""; vowels = 2 ([""a"";e""]); consonants = 2 ([""b"";""y""]). You can see that string ""baey"" is beautiful as vowels == consonants and vowels * consonants % k == 0. It can be shown that there are only 2 beautiful substrings in the given string. Example 2: Input: s = ""abba""; k = 1 Output: 3 Explanation: There are 3 beautiful substrings in the given string. - Substring ""abba""; vowels = 1 ([""a""]); consonants = 1 ([""b""]). - Substring ""abba""; vowels = 1 ([""a""]); consonants = 1 ([""b""]). - Substring ""abba""; vowels = 2 ([""a"";""a""]); consonants = 2 ([""b"";""b""]). It can be shown that there are only 3 beautiful substrings in the given string. Example 3: Input: s = ""bcdf""; k = 1 Output: 0 Explanation: There are no beautiful substrings in the given string. Constraints: 1 <= s.length <= 5 * 104 1 <= k <= 1000 s consists of only English lowercase letters."
Google,3275,K-th Nearest Obstacle Queries,Med,"Math, String, Greedy","You are given a string word containing distinct lowercase English letters. Telephone keypads have keys mapped with distinct collections of lowercase English letters; which can be used to form words by pushing them. For example; the key 2 is mapped with [""a"";""b"";""c""]; we need to push the key one time to type ""a""; two times to type ""b""; and three times to type ""c"" . It is allowed to remap the keys numbered 2 to 9 to distinct collections of letters. The keys can be remapped to any amount of letters; but each letter must be mapped to exactly one key. You need to find the minimum number of times the keys will be pushed to type the string word. Return the minimum number of pushes needed to type word after remapping the keys. An example mapping of letters to keys on a telephone keypad is given below. Note that 1; *; #; and 0 do not map to any letters. Example 1: Input: word = ""abcde"" Output: 5 Explanation: The remapped keypad given in the image provides the minimum cost. ""a"" -> one push on key 2 ""b"" -> one push on key 3 ""c"" -> one push on key 4 ""d"" -> one push on key 5 ""e"" -> one push on key 6 Total cost is 1 + 1 + 1 + 1 + 1 = 5. It can be shown that no other mapping can provide a lower cost. Example 2: Input: word = ""xycdefghij"" Output: 12 Explanation: The remapped keypad given in the image provides the minimum cost. ""x"" -> one push on key 2 ""y"" -> two pushes on key 2 ""c"" -> one push on key 3 ""d"" -> two pushes on key 3 ""e"" -> one push on key 4 ""f"" -> one push on key 5 ""g"" -> one push on key 6 ""h"" -> one push on key 7 ""i"" -> one push on key 8 ""j"" -> one push on key 9 Total cost is 1 + 2 + 1 + 2 + 1 + 1 + 1 + 1 + 1 + 1 = 12. It can be shown that no other mapping can provide a lower cost. Constraints: 1 <= word.length <= 26 word consists of lowercase English letters. All letters in word are distinct."
Google,3325,Count Substrings With K-Frequency Characters I,Med,"Array, Math, Geometry",There exist n rectangles in a 2D plane with edges parallel to the x and y axis. You are given two 2D integer arrays bottomLeft and topRight where bottomLeft[i] = [a_i; b_i] and topRight[i] = [c_i; d_i] represent the bottom-left and top-right coordinates of the ith rectangle; respectively. You need to find the maximum area of a square that can fit inside the intersecting region of at least two rectangles. Return 0 if such a square does not exist. Example 1: Input: bottomLeft = [[1;1];[2;2];[3;1]]; topRight = [[3;3];[4;4];[6;6]] Output: 1 Explanation: A square with side length 1 can fit inside either the intersecting region of rectangles 0 and 1 or the intersecting region of rectangles 1 and 2. Hence the maximum area is 1. It can be shown that a square with a greater side length can not fit inside any intersecting region of two rectangles. Example 2: Input: bottomLeft = [[1;1];[1;3];[1;5]]; topRight = [[5;5];[5;7];[5;9]] Output: 4 Explanation: A square with side length 2 can fit inside either the intersecting region of rectangles 0 and 1 or the intersecting region of rectangles 1 and 2. Hence the maximum area is 2 * 2 = 4. It can be shown that a square with a greater side length can not fit inside any intersecting region of two rectangles. Example 3: Input: bottomLeft = [[1;1];[2;2];[1;2]]; topRight = [[3;3];[4;4];[3;4]] Output: 1 Explanation: A square with side length 1 can fit inside the intersecting region of any two rectangles. Also; no larger square can; so the maximum area is 1. Note that the region can be formed by the intersection of more than 2 rectangles. Example 4: Input: bottomLeft = [[1;1];[3;3];[3;1]]; topRight = [[2;2];[4;4];[4;2]] Output: 0 Explanation: No pair of rectangles intersect; hence; the answer is 0. Constraints: n == bottomLeft.length == topRight.length 2 <= n <= 103 bottomLeft[i].length == topRight[i].length == 2 1 <= bottomLeft[i][0]; bottomLeft[i][1] <= 107 1 <= topRight[i][0]; topRight[i][1] <= 107 bottomLeft[i][0] < topRight[i][0] bottomLeft[i][1] < topRight[i][1]
Google,3282,Reach End of Array With Max Score,Med,Database,
Google,3248,Snake in Matrix,Easy,"Array, Two Pointers, Binary Search",You are given a 0-indexed array of positive integers nums. A subarray of nums is called incremovable if nums becomes strictly increasing on removing the subarray. For example; the subarray [3; 4] is an incremovable subarray of [5; 3; 4; 6; 7] because removing this subarray changes the array [5; 3; 4; 6; 7] to [5; 6; 7] which is strictly increasing. Return the total number of incremovable subarrays of nums. Note that an empty array is considered strictly increasing. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;2;3;4] Output: 10 Explanation: The 10 incremovable subarrays are: [1]; [2]; [3]; [4]; [1;2]; [2;3]; [3;4]; [1;2;3]; [2;3;4]; and [1;2;3;4]; because on removing any one of these subarrays nums becomes strictly increasing. Note that you cannot select an empty subarray. Example 2: Input: nums = [6;5;7;8] Output: 7 Explanation: The 7 incremovable subarrays are: [5]; [6]; [5;7]; [6;5]; [5;7;8]; [6;5;7] and [6;5;7;8]. It can be shown that there are only 7 incremovable subarrays in nums. Example 3: Input: nums = [8;7;6;6] Output: 3 Explanation: The 3 incremovable subarrays are: [8;7;6]; [7;6;6]; and [8;7;6;6]. Note that [8;7] is not an incremovable subarray because after removing [8;7] nums becomes [6;6]; which is sorted in ascending order but not strictly increasing. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 109
Google,3283,Maximum Number of Moves to Kill All Pawns,Hard,Database,
Google,3312,Sorted GCD Pair Queries,Hard,String,"You are given a 0-indexed string s typed by a user. Changing a key is defined as using a key different from the last used key. For example; s = ""ab"" has a change of a key while s = ""bBBb"" does not have any. Return the number of times the user had to change the key. Note: Modifiers like shift or caps lock won't be counted in changing the key that is if a user typed the letter 'a' and then the letter 'A' then it will not be considered as a changing of key. Example 1: Input: s = ""aAbBcC"" Output: 2 Explanation: From s[0] = 'a' to s[1] = 'A'; there is no change of key as caps lock or shift is not counted. From s[1] = 'A' to s[2] = 'b'; there is a change of key. From s[2] = 'b' to s[3] = 'B'; there is no change of key as caps lock or shift is not counted. From s[3] = 'B' to s[4] = 'c'; there is a change of key. From s[4] = 'c' to s[5] = 'C'; there is no change of key as caps lock or shift is not counted. Example 2: Input: s = ""AaAaAaaA"" Output: 0 Explanation: There is no change of key since only the letters 'a' and 'A' are pressed which does not require change of key. Constraints: 1 <= s.length <= 100 s consists of only upper case and lower case English letters."
Google,3327,Check if DFS Strings Are Palindromes,Hard,"Array, Greedy, Sliding Window, Prefix Sum",You are given a binary array nums of length n; a positive integer k and a non-negative integer maxChanges. Alice plays a game; where the goal is for Alice to pick up k ones from nums using the minimum number of moves. When the game starts; Alice picks up any index aliceIndex in the range [0; n - 1] and stands there. If nums[aliceIndex] == 1 ; Alice picks up the one and nums[aliceIndex] becomes 0(this does not count as a move). After this; Alice can make any number of moves (including zero) where in each move Alice must perform exactly one of the following actions: Select any index j != aliceIndex such that nums[j] == 0 and set nums[j] = 1. This action can be performed at most maxChanges times. Select any two adjacent indices x and y (|x - y| == 1) such that nums[x] == 1; nums[y] == 0; then swap their values (set nums[y] = 1 and nums[x] = 0). If y == aliceIndex; Alice picks up the one after this move and nums[y] becomes 0. Return the minimum number of moves required by Alice to pick exactly k ones. Example 1: Input: nums = [1;1;0;0;0;1;1;0;0;1]; k = 3; maxChanges = 1 Output: 3 Explanation: Alice can pick up 3 ones in 3 moves; if Alice performs the following actions in each move when standing at aliceIndex == 1: At the start of the game Alice picks up the one and nums[1] becomes 0. nums becomes [1;0;0;0;0;1;1;0;0;1]. Select j == 2 and perform an action of the first type. nums becomes [1;0;1;0;0;1;1;0;0;1] Select x == 2 and y == 1; and perform an action of the second type. nums becomes [1;1;0;0;0;1;1;0;0;1]. As y == aliceIndex; Alice picks up the one and nums becomes [1;0;0;0;0;1;1;0;0;1]. Select x == 0 and y == 1; and perform an action of the second type. nums becomes [0;1;0;0;0;1;1;0;0;1]. As y == aliceIndex; Alice picks up the one and nums becomes [0;0;0;0;0;1;1;0;0;1]. Note that it may be possible for Alice to pick up 3 ones using some other sequence of 3 moves. Example 2: Input: nums = [0;0;0;0]; k = 2; maxChanges = 3 Output: 4 Explanation: Alice can pick up 2 ones in 4 moves; if Alice performs the following actions in each move when standing at aliceIndex == 0: Select j == 1 and perform an action of the first type. nums becomes [0;1;0;0]. Select x == 1 and y == 0; and perform an action of the second type. nums becomes [1;0;0;0]. As y == aliceIndex; Alice picks up the one and nums becomes [0;0;0;0]. Select j == 1 again and perform an action of the first type. nums becomes [0;1;0;0]. Select x == 1 and y == 0 again; and perform an action of the second type. nums becomes [1;0;0;0]. As y == aliceIndex; Alice picks up the one and nums becomes [0;0;0;0]. Constraints: 2 <= n <= 105 0 <= nums[i] <= 1 1 <= k <= 105 0 <= maxChanges <= 105 maxChanges + sum(nums) >= k
Google,3326,Minimum Division Operations to Make Array Non Decreasing,Med,"Array, Tree, Depth-First Search",You are given an unrooted weighted tree with n vertices representing servers numbered from 0 to n - 1; an array edges where edges[i] = [ai; bi; weighti] represents a bidirectional edge between vertices ai and bi of weight weighti. You are also given an integer signalSpeed. Two servers a and b are connectable through a server c if: a < b; a != c and b != c. The distance from c to a is divisible by signalSpeed. The distance from c to b is divisible by signalSpeed. The path from c to b and the path from c to a do not share any edges. Return an integer array count of length n where count[i] is the number of server pairs that are connectable through the server i. Example 1: Input: edges = [[0;1;1];[1;2;5];[2;3;13];[3;4;9];[4;5;2]]; signalSpeed = 1 Output: [0;4;6;6;4;0] Explanation: Since signalSpeed is 1; count[c] is equal to the number of pairs of paths that start at c and do not share any edges. In the case of the given path graph; count[c] is equal to the number of servers to the left of c multiplied by the servers to the right of c. Example 2: Input: edges = [[0;6;3];[6;5;3];[0;3;1];[3;2;7];[3;1;6];[3;4;2]]; signalSpeed = 3 Output: [2;0;0;0;0;0;2] Explanation: Through server 0; there are 2 pairs of connectable servers: (4; 5) and (4; 6). Through server 6; there are 2 pairs of connectable servers: (4; 5) and (0; 5). It can be shown that no two servers are connectable through servers other than 0 and 6. Constraints: 2 <= n <= 1000 edges.length == n - 1 edges[i].length == 3 0 <= ai; bi < n edges[i] = [ai; bi; weighti] 1 <= weighti <= 106 1 <= signalSpeed <= 106 The input is generated such that edges represents a valid tree.
Amazon,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Amazon,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Amazon,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Amazon,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Amazon,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Amazon,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Amazon,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Amazon,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Amazon,621,Task Scheduler,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting","You are given an array of CPU tasks; each labeled with a letter from A to Z; and a number n. Each CPU interval can be idle or allow the completion of one task. Tasks can be completed in any order; but there's a constraint: there has to be a gap of at least n intervals between two tasks with the same label. Return the minimum number of CPU intervals required to complete all tasks. Example 1: Input: tasks = [""A"";""A"";""A"";""B"";""B"";""B""]; n = 2 Output: 8 Explanation: A possible sequence is: A -> B -> idle -> A -> B -> idle -> A -> B. After completing task A; you must wait two intervals before doing A again. The same applies to task B. In the 3rd interval; neither A nor B can be done; so you idle. By the 4th interval; you can do A again as 2 intervals have passed. Example 2: Input: tasks = [""A"";""C"";""A"";""B"";""D"";""B""]; n = 1 Output: 6 Explanation: A possible sequence is: A -> B -> C -> D -> A -> B. With a cooling interval of 1; you can repeat a task after just one other task. Example 3: Input: tasks = [""A"";""A"";""A""; ""B"";""B"";""B""]; n = 3 Output: 10 Explanation: A possible sequence is: A -> B -> idle -> idle -> A -> B -> idle -> idle -> A -> B. There are only two types of tasks; A and B; which need to be separated by 3 intervals. This leads to idling twice between repetitions of these tasks. Constraints: 1 <= tasks.length <= 104 tasks[i] is an uppercase English letter. 0 <= n <= 100"
Amazon,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Amazon,1768,Merge Strings Alternately,Easy,"Array, Math, Stack, Tree, Design, Binary Tree",
Amazon,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Amazon,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
Amazon,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Amazon,2667,Create Hello World Function,Easy,"Array, Hash Table, Math, Stack, Sliding Window",
Amazon,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Amazon,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Amazon,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
Amazon,875,Koko Eating Bananas,Med,"Array, Two Pointers, Dynamic Programming, Enumeration",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr; return the length of the longest subarray; which is a mountain. Return 0 if there is no mountain subarray. Example 1: Input: arr = [2;1;4;7;3;2;5] Output: 5 Explanation: The largest mountain is [1;4;7;3;2] which has length 5. Example 2: Input: arr = [2;2;2] Output: 0 Explanation: There is no mountain. Constraints: 1 <= arr.length <= 104 0 <= arr[i] <= 104 Follow up: Can you solve it using only one pass? Can you solve it in O(1) space?
Amazon,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Amazon,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Amazon,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
Amazon,1757,Recyclable and Low Fat Products,Easy,"Array, Dynamic Programming, Breadth-First Search",A certain bug's home is on the x-axis at position x. Help them get there from position 0. The bug jumps according to the following rules: It can jump exactly a positions forward (to the right). It can jump exactly b positions backward (to the left). It cannot jump backward twice in a row. It cannot jump to any forbidden positions. The bug may jump forward beyond its home; but it cannot jump to positions numbered with negative integers. Given an array of integers forbidden; where forbidden[i] means that the bug cannot jump to the position forbidden[i]; and integers a; b; and x; return the minimum number of jumps needed for the bug to reach its home. If there is no possible sequence of jumps that lands the bug on position x; return -1. Example 1: Input: forbidden = [14;4;18;1;15]; a = 3; b = 15; x = 9 Output: 3 Explanation: 3 jumps forward (0 -> 3 -> 6 -> 9) will get the bug home. Example 2: Input: forbidden = [8;3;16;6;12;20]; a = 15; b = 13; x = 11 Output: -1 Example 3: Input: forbidden = [1;6;2;14;5;17;4]; a = 16; b = 9; x = 7 Output: 2 Explanation: One jump forward (0 -> 16) then one jump backward (16 -> 7) will get the bug home. Constraints: 1 <= forbidden.length <= 1000 1 <= a; b; forbidden[i] <= 2000 0 <= x <= 2000 All the elements in forbidden are distinct. Position x is not forbidden.
Amazon,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Amazon,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Amazon,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Amazon,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Amazon,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Amazon,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Amazon,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Amazon,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Amazon,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Amazon,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Amazon,236,Lowest Common Ancestor of a Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",Given a binary tree; find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3. Example 2: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [1;2]; p = 1; q = 2 Output: 1 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the tree.
Amazon,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Amazon,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Amazon,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Amazon,13,Roman to Integer,Easy,"Hash Table, Math, String","Roman numerals are represented by seven different symbols: I; V; X; L; C; D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example; 2 is written as II in Roman numeral; just two ones added together. 12 is written as XII; which is simply X + II. The number 27 is written as XXVII; which is XX + V + II. Roman numerals are usually written largest to smallest from left to right. However; the numeral for four is not IIII. Instead; the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine; which is written as IX. There are six instances where subtraction is used: I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral; convert it to an integer. Example 1: Input: s = ""III"" Output: 3 Explanation: III = 3. Example 2: Input: s = ""LVIII"" Output: 58 Explanation: L = 50; V= 5; III = 3. Example 3: Input: s = ""MCMXCIV"" Output: 1994 Explanation: M = 1000; CM = 900; XC = 90 and IV = 4. Constraints: 1 <= s.length <= 15 s contains only the characters ('I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M'). It is guaranteed that s is a valid roman numeral in the range [1; 3999]."
Amazon,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Amazon,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Amazon,104,Maximum Depth of Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return its maximum depth. A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 3 Example 2: Input: root = [1;null;2] Output: 2 Constraints: The number of nodes in the tree is in the range [0; 104]. -100 <= Node.val <= 100
Amazon,128,Longest Consecutive Sequence,Med,"Array, Hash Table, Union Find",Given an unsorted array of integers nums; return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time. Example 1: Input: nums = [100;4;200;1;3;2] Output: 4 Explanation: The longest consecutive elements sequence is [1; 2; 3; 4]. Therefore its length is 4. Example 2: Input: nums = [0;3;7;2;5;8;4;6;0;1] Output: 9 Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109
Amazon,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Amazon,227,Basic Calculator II,Med,"Math, String, Stack","Given a string s which represents an expression; evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""3+2*2"" Output: 7 Example 2: Input: s = "" 3/2 "" Output: 1 Example 3: Input: s = "" 3+5 / 2 "" Output: 5 Constraints: 1 <= s.length <= 3 * 105 s consists of integers and operators ('+'; '-'; '*'; '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0; 231 - 1]. The answer is guaranteed to fit in a 32-bit integer."
Amazon,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Amazon,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
Amazon,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Amazon,1650,Lowest Common Ancestor of a Binary Tree III,Med,"Hash Table, Bit Manipulation, Tree, Depth-First Search",
Amazon,3317,Find the Number of Possible Ways for an Event,Hard,"Array, Hash Table, String, Greedy, Sorting, Counting","You are given a 0-indexed string array words having length n and containing 0-indexed strings. You are allowed to perform the following operation any number of times (including zero): Choose integers i; j; x; and y such that 0 <= i; j < n; 0 <= x < words[i].length; 0 <= y < words[j].length; and swap the characters words[i][x] and words[j][y]. Return an integer denoting the maximum number of palindromes words can contain; after performing some operations. Note: i and j may be equal during an operation. Example 1: Input: words = [""abbb"";""ba"";""aa""] Output: 3 Explanation: In this example; one way to get the maximum number of palindromes is: Choose i = 0; j = 1; x = 0; y = 0; so we swap words[0][0] and words[1][0]. words becomes [""bbbb"";""aa"";""aa""]. All strings in words are now palindromes. Hence; the maximum number of palindromes achievable is 3. Example 2: Input: words = [""abc"";""ab""] Output: 2 Explanation: In this example; one way to get the maximum number of palindromes is: Choose i = 0; j = 1; x = 1; y = 0; so we swap words[0][1] and words[1][0]. words becomes [""aac"";""bb""]. Choose i = 0; j = 0; x = 1; y = 2; so we swap words[0][1] and words[0][2]. words becomes [""aca"";""bb""]. Both strings are now palindromes. Hence; the maximum number of palindromes achievable is 2. Example 3: Input: words = [""cd"";""ef"";""a""] Output: 1 Explanation: In this example; there is no need to perform any operation. There is one palindrome in words ""a"". It can be shown that it is not possible to get more than one palindrome after any number of operations. Hence; the answer is 1. Constraints: 1 <= words.length <= 1000 1 <= words[i].length <= 100 words[i] consists only of lowercase English letters."
Amazon,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Amazon,179,Largest Number,Med,"Array, String, Greedy, Sorting","Given a list of non-negative integers nums; arrange them such that they form the largest number and return it. Since the result may be very large; so you need to return a string instead of an integer. Example 1: Input: nums = [10;2] Output: ""210"" Example 2: Input: nums = [3;30;34;5;9] Output: ""9534330"" Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 109"
Amazon,189,Rotate Array,Med,"Array, Math, Two Pointers",Given an integer array nums; rotate the array to the right by k steps; where k is non-negative. Example 1: Input: nums = [1;2;3;4;5;6;7]; k = 3 Output: [5;6;7;1;2;3;4] Explanation: rotate 1 steps to the right: [7;1;2;3;4;5;6] rotate 2 steps to the right: [6;7;1;2;3;4;5] rotate 3 steps to the right: [5;6;7;1;2;3;4] Example 2: Input: nums = [-1;-100;3;99]; k = 2 Output: [3;99;-1;-100] Explanation: rotate 1 steps to the right: [99;-1;-100;3] rotate 2 steps to the right: [3;99;-1;-100] Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 0 <= k <= 105 Follow up: Try to come up with as many solutions as you can. There are at least three different ways to solve this problem. Could you do it in-place with O(1) extra space?
Amazon,212,Word Search II,Hard,"Array, String, Backtracking, Trie, Matrix","Given an m x n board of characters and a list of strings words; return all words on the board. Each word must be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example 1: Input: board = [[""o"";""a"";""a"";""n""];[""e"";""t"";""a"";""e""];[""i"";""h"";""k"";""r""];[""i"";""f"";""l"";""v""]]; words = [""oath"";""pea"";""eat"";""rain""] Output: [""eat"";""oath""] Example 2: Input: board = [[""a"";""b""];[""c"";""d""]]; words = [""abcb""] Output: [] Constraints: m == board.length n == board[i].length 1 <= m; n <= 12 board[i][j] is a lowercase English letter. 1 <= words.length <= 3 * 104 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. All the strings of words are unique."
Amazon,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
Amazon,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
Amazon,2979,Most Expensive Item That Can Not Be Bought,Med,"Array, Hash Table, Binary Search, Dynamic Programming, Sorting",You are given an integer n representing the number of houses on a number line; numbered from 0 to n - 1. Additionally; you are given a 2D integer array offers where offers[i] = [starti; endi; goldi]; indicating that ith buyer wants to buy all the houses from starti to endi for goldi amount of gold. As a salesman; your goal is to maximize your earnings by strategically selecting and selling houses to buyers. Return the maximum amount of gold you can earn. Note that different buyers can't buy the same house; and some houses may remain unsold. Example 1: Input: n = 5; offers = [[0;0;1];[0;2;2];[1;3;2]] Output: 3 Explanation: There are 5 houses numbered from 0 to 4 and there are 3 purchase offers. We sell houses in the range [0;0] to 1st buyer for 1 gold and houses in the range [1;3] to 3rd buyer for 2 golds. It can be proven that 3 is the maximum amount of gold we can achieve. Example 2: Input: n = 5; offers = [[0;0;1];[0;2;10];[1;3;2]] Output: 10 Explanation: There are 5 houses numbered from 0 to 4 and there are 3 purchase offers. We sell houses in the range [0;2] to 2nd buyer for 10 golds. It can be proven that 10 is the maximum amount of gold we can achieve. Constraints: 1 <= n <= 105 1 <= offers.length <= 105 offers[i].length == 3 0 <= starti <= endi <= n - 1 1 <= goldi <= 103
Amazon,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Amazon,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Amazon,134,Gas Station,Med,"Array, Greedy",There are n gas stations along a circular route; where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations. Given two integer arrays gas and cost; return the starting gas station's index if you can travel around the circuit once in the clockwise direction; otherwise return -1. If there exists a solution; it is guaranteed to be unique. Example 1: Input: gas = [1;2;3;4;5]; cost = [3;4;5;1;2] Output: 3 Explanation: Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 4. Your tank = 4 - 1 + 5 = 8 Travel to station 0. Your tank = 8 - 2 + 1 = 7 Travel to station 1. Your tank = 7 - 3 + 2 = 6 Travel to station 2. Your tank = 6 - 4 + 3 = 5 Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. Therefore; return 3 as the starting index. Example 2: Input: gas = [2;3;4]; cost = [3;4;3] Output: -1 Explanation: You can't start at station 0 or 1; as there is not enough gas to travel to the next station. Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 0. Your tank = 4 - 3 + 2 = 3 Travel to station 1. Your tank = 3 - 3 + 3 = 3 You cannot travel back to station 2; as it requires 4 unit of gas but you only have 3. Therefore; you can't travel around the circuit once no matter where you start. Constraints: n == gas.length == cost.length 1 <= n <= 105 0 <= gas[i]; cost[i] <= 104
Amazon,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
Amazon,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Amazon,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
Amazon,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Amazon,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Amazon,863,All Nodes Distance K in Binary Tree,Med,"Dynamic Programming, Tree, Depth-First Search, Graph",There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Return an array answer of length n where answer[i] is the sum of the distances between the ith node in the tree and all other nodes. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;3];[2;4];[2;5]] Output: [8;12;6;10;10;10] Explanation: The tree is shown above. We can see that dist(0;1) + dist(0;2) + dist(0;3) + dist(0;4) + dist(0;5) equals 1 + 1 + 2 + 2 + 2 = 8. Hence; answer[0] = 8; and so on. Example 2: Input: n = 1; edges = [] Output: [0] Example 3: Input: n = 2; edges = [[1;0]] Output: [1;1] Constraints: 1 <= n <= 3 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n ai != bi The given input represents a valid tree.
Amazon,962,Maximum Width Ramp,Med,"String, Dynamic Programming","A binary string is monotone increasing if it consists of some number of 0's (possibly none); followed by some number of 1's (also possibly none). You are given a binary string s. You can flip s[i] changing it from 0 to 1 or from 1 to 0. Return the minimum number of flips to make s monotone increasing. Example 1: Input: s = ""00110"" Output: 1 Explanation: We flip the last digit to get 00111. Example 2: Input: s = ""010110"" Output: 2 Explanation: We flip to get 011111; or alternatively 000111. Example 3: Input: s = ""00011000"" Output: 2 Explanation: We flip to get 00000000. Constraints: 1 <= s.length <= 105 s[i] is either '0' or '1'."
Amazon,1152,Analyze User Website Visit Pattern,Med,"Greedy, Heap (Priority Queue)",
Amazon,7,Reverse Integer,Med,Math,Given a signed 32-bit integer x; return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231; 231 - 1]; then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: Input: x = 123 Output: 321 Example 2: Input: x = -123 Output: -321 Example 3: Input: x = 120 Output: 21 Constraints: -231 <= x <= 231 - 1
Amazon,12,Integer to Roman,Med,"Hash Table, Math, String","Seven different symbols represent Roman numerals with the following values: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules: If the value does not start with 4 or 9; select the symbol of the maximal value that can be subtracted from the input; append that symbol to the result; subtract its value; and convert the remainder to a Roman numeral. If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol; for example; 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV); 9 (IX); 40 (XL); 90 (XC); 400 (CD) and 900 (CM). Only powers of 10 (I; X; C; M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V); 50 (L); or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form. Given an integer; convert it to a Roman numeral. Example 1: Input: num = 3749 Output: ""MMMDCCXLIX"" Explanation: 3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M) 700 = DCC as 500 (D) + 100 (C) + 100 (C) 40 = XL as 10 (X) less of 50 (L) 9 = IX as 1 (I) less of 10 (X) Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places Example 2: Input: num = 58 Output: ""LVIII"" Explanation: 50 = L 8 = VIII Example 3: Input: num = 1994 Output: ""MCMXCIV"" Explanation: 1000 = M 900 = CM 90 = XC 4 = IV Constraints: 1 <= num <= 3999"
Amazon,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Amazon,27,Remove Element,Easy,"Array, Two Pointers",Given an integer array nums and an integer val; remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val. Consider the number of elements in nums which are not equal to val be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the elements which are not equal to val. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int val = ...; // Value to remove int[] expectedNums = [...]; // The expected answer with correct length. // It is sorted with no values equaling val. int k = removeElement(nums; val); // Calls your implementation assert k == expectedNums.length; sort(nums; 0; k); // Sort the first k elements of nums for (int i = 0; i < actualLength; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [3;2;2;3]; val = 3 Output: 2; nums = [2;2;_;_] Explanation: Your function should return k = 2; with the first two elements of nums being 2. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;1;2;2;3;0;4;2]; val = 2 Output: 5; nums = [0;1;4;0;3;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums containing 0; 0; 1; 3; and 4. Note that the five elements can be returned in any order. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 0 <= nums.length <= 100 0 <= nums[i] <= 50 0 <= val <= 100
Amazon,84,Largest Rectangle in Histogram,Hard,"Array, Stack, Monotonic Stack",Given an array of integers heights representing the histogram's bar height where the width of each bar is 1; return the area of the largest rectangle in the histogram. Example 1: Input: heights = [2;1;5;6;2;3] Output: 10 Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area; which has an area = 10 units. Example 2: Input: heights = [2;4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104
Amazon,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Amazon,135,Candy,Hard,"Array, Greedy",There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings. You are giving candies to these children subjected to the following requirements: Each child must have at least one candy. Children with a higher rating get more candies than their neighbors. Return the minimum number of candies you need to have to distribute the candies to the children. Example 1: Input: ratings = [1;0;2] Output: 5 Explanation: You can allocate to the first; second and third child with 2; 1; 2 candies respectively. Example 2: Input: ratings = [1;2;2] Output: 4 Explanation: You can allocate to the first; second and third child with 1; 2; 1 candies respectively. The third child gets 1 candy because it satisfies the above two conditions. Constraints: n == ratings.length 1 <= n <= 2 * 104 0 <= ratings[i] <= 2 * 104
Amazon,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Amazon,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Amazon,242,Valid Anagram,Easy,"Hash Table, String, Sorting","Given two strings s and t; return true if t is an anagram of s; and false otherwise. Example 1: Input: s = ""anagram""; t = ""nagaram"" Output: true Example 2: Input: s = ""rat""; t = ""car"" Output: false Constraints: 1 <= s.length; t.length <= 5 * 104 s and t consist of lowercase English letters. Follow up: What if the inputs contain Unicode characters? How would you adapt your solution to such a case?"
Amazon,273,Integer to English Words,Hard,"Math, String, Recursion","Convert a non-negative integer num to its English words representation. Example 1: Input: num = 123 Output: ""One Hundred Twenty Three"" Example 2: Input: num = 12345 Output: ""Twelve Thousand Three Hundred Forty Five"" Example 3: Input: num = 1234567 Output: ""One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"" Constraints: 0 <= num <= 231 - 1"
Amazon,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Amazon,349,Intersection of Two Arrays,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must be unique and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [9;4] Explanation: [4;9] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000
Amazon,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
Amazon,733,Flood Fill,Easy,"Array, Depth-First Search, Breadth-First Search, Matrix",You are given an image represented by an m x n grid of integers image; where image[i][j] represents the pixel value of the image. You are also given three integers sr; sc; and color. Your task is to perform a flood fill on the image starting from the pixel image[sr][sc]. To perform a flood fill: Begin with the starting pixel and change its color to color. Perform the same process for each pixel that is directly adjacent (pixels that share a side with the original pixel; either horizontally or vertically) and shares the same color as the starting pixel. Keep repeating this process by checking neighboring pixels of the updated pixels and modifying their color if it matches the original color of the starting pixel. The process stops when there are no more adjacent pixels of the original color to update. Return the modified image after performing the flood fill. Example 1: Input: image = [[1;1;1];[1;1;0];[1;0;1]]; sr = 1; sc = 1; color = 2 Output: [[2;2;2];[2;2;0];[2;0;1]] Explanation: From the center of the image with position (sr; sc) = (1; 1) (i.e.; the red pixel); all pixels connected by a path of the same color as the starting pixel (i.e.; the blue pixels) are colored with the new color. Note the bottom corner is not colored 2; because it is not horizontally or vertically connected to the starting pixel. Example 2: Input: image = [[0;0;0];[0;0;0]]; sr = 0; sc = 0; color = 0 Output: [[0;0;0];[0;0;0]] Explanation: The starting pixel is already colored with 0; which is the same as the target color. Therefore; no changes are made to the image. Constraints: m == image.length n == image[i].length 1 <= m; n <= 50 0 <= image[i][j]; color < 216 0 <= sr < m 0 <= sc < n
Amazon,1492,The kth Factor of n,Med,"Tree, Depth-First Search, Breadth-First Search",A company has n employees with a unique ID for each employee from 0 to n - 1. The head of the company is the one with headID. Each employee has one direct manager given in the manager array where manager[i] is the direct manager of the i-th employee; manager[headID] = -1. Also; it is guaranteed that the subordination relationships have a tree structure. The head of the company wants to inform all the company employees of an urgent piece of news. He will inform his direct subordinates; and they will inform their subordinates; and so on until all employees know about the urgent news. The i-th employee needs informTime[i] minutes to inform all of his direct subordinates (i.e.; After informTime[i] minutes; all his direct subordinates can start spreading the news). Return the number of minutes needed to inform all the employees about the urgent news. Example 1: Input: n = 1; headID = 0; manager = [-1]; informTime = [0] Output: 0 Explanation: The head of the company is the only employee in the company. Example 2: Input: n = 6; headID = 2; manager = [2;2;-1;2;2;2]; informTime = [0;0;1;0;0;0] Output: 1 Explanation: The head of the company with id = 2 is the direct manager of all the employees in the company and needs 1 minute to inform them all. The tree structure of the employees in the company is shown. Constraints: 1 <= n <= 105 0 <= headID < n manager.length == n 0 <= manager[i] < n manager[headID] == -1 informTime.length == n 0 <= informTime[i] <= 1000 informTime[i] == 0 if employee i has no subordinates. It is guaranteed that all the employees can be informed.
Amazon,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Amazon,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
Amazon,69,Sqrt(x),Easy,"Math, Binary Search",Given a non-negative integer x; return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. For example; do not use pow(x; 0.5) in c++ or x ** 0.5 in python. Example 1: Input: x = 4 Output: 2 Explanation: The square root of 4 is 2; so we return 2. Example 2: Input: x = 8 Output: 2 Explanation: The square root of 8 is 2.82842...; and since we round it down to the nearest integer; 2 is returned. Constraints: 0 <= x <= 231 - 1
Amazon,126,Word Ladder II,Hard,"Hash Table, String, Backtracking, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return all the shortest transformation sequences from beginWord to endWord; or an empty list if no such sequence exists. Each sequence should be returned as a list of the words [beginWord; s1; s2; ...; sk]. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: [[""hit"";""hot"";""dot"";""dog"";""cog""];[""hit"";""hot"";""lot"";""log"";""cog""]] Explanation: There are 2 shortest transformation sequences: ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> ""cog"" ""hit"" -> ""hot"" -> ""lot"" -> ""log"" -> ""cog"" Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: [] Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 5 endWord.length == beginWord.length 1 <= wordList.length <= 500 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique. The sum of all shortest transformation sequences does not exceed 105."
Amazon,143,Reorder List,Med,"Linked List, Two Pointers, Stack, Recursion",You are given the head of a singly linked-list. The list can be represented as: L0 → L1 → … → Ln - 1 → Ln Reorder the list to be on the following form: L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → … You may not modify the values in the list's nodes. Only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4] Output: [1;4;2;3] Example 2: Input: head = [1;2;3;4;5] Output: [1;5;2;4;3] Constraints: The number of nodes in the list is in the range [1; 5 * 104]. 1 <= Node.val <= 1000
Amazon,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Amazon,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Amazon,268,Missing Number,Easy,"Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting",Given an array nums containing n distinct numbers in the range [0; n]; return the only number in the range that is missing from the array. Example 1: Input: nums = [3;0;1] Output: 2 Explanation: n = 3 since there are 3 numbers; so all numbers are in the range [0;3]. 2 is the missing number in the range since it does not appear in nums. Example 2: Input: nums = [0;1] Output: 2 Explanation: n = 2 since there are 2 numbers; so all numbers are in the range [0;2]. 2 is the missing number in the range since it does not appear in nums. Example 3: Input: nums = [9;6;4;2;3;5;7;0;1] Output: 8 Explanation: n = 9 since there are 9 numbers; so all numbers are in the range [0;9]. 8 is the missing number in the range since it does not appear in nums. Constraints: n == nums.length 1 <= n <= 104 0 <= nums[i] <= n All the numbers of nums are unique. Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?
Amazon,450,Delete Node in a BST,Med,"Tree, Binary Search Tree, Binary Tree",Given a root node reference of a BST and a key; delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST. Basically; the deletion can be divided into two stages: Search for a node to remove. If the node is found; delete the node. Example 1: Input: root = [5;3;6;2;4;null;7]; key = 3 Output: [5;4;6;2;null;null;7] Explanation: Given key to delete is 3. So we find the node with value 3 and delete it. One valid answer is [5;4;6;2;null;null;7]; shown in the above BST. Please notice that another valid answer is [5;2;6;null;4;null;7] and it's also accepted. Example 2: Input: root = [5;3;6;2;4;null;7]; key = 0 Output: [5;3;6;2;4;null;7] Explanation: The tree does not contain a node with value = 0. Example 3: Input: root = []; key = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -105 <= Node.val <= 105 Each node has a unique value. root is a valid binary search tree. -105 <= key <= 105 Follow up: Could you solve it with time complexity O(height of tree)?
Amazon,567,Permutation in String,Med,"Hash Table, Two Pointers, String, Sliding Window","Given two strings s1 and s2; return true if s2 contains a permutation of s1; or false otherwise. In other words; return true if one of s1's permutations is the substring of s2. Example 1: Input: s1 = ""ab""; s2 = ""eidbaooo"" Output: true Explanation: s2 contains one permutation of s1 (""ba""). Example 2: Input: s1 = ""ab""; s2 = ""eidboaoo"" Output: false Constraints: 1 <= s1.length; s2.length <= 104 s1 and s2 consist of lowercase English letters."
Amazon,973,K Closest Points to Origin,Med,"String, Stack, Greedy, Queue","You are given two strings stamp and target. Initially; there is a string s of length target.length with all s[i] == '?'. In one turn; you can place stamp over s and replace every letter in the s with the corresponding letter from stamp. For example; if stamp = ""abc"" and target = ""abcba""; then s is ""?????"" initially. In one turn you can: place stamp at index 0 of s to obtain ""abc??""; place stamp at index 1 of s to obtain ""?abc?""; or place stamp at index 2 of s to obtain ""??abc"". Note that stamp must be fully contained in the boundaries of s in order to stamp (i.e.; you cannot place stamp at index 3 of s). We want to convert s to target using at most 10 * target.length turns. Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns; return an empty array. Example 1: Input: stamp = ""abc""; target = ""ababc"" Output: [0;2] Explanation: Initially s = ""?????"". - Place stamp at index 0 to get ""abc??"". - Place stamp at index 2 to get ""ababc"". [1;0;2] would also be accepted as an answer; as well as some other answers. Example 2: Input: stamp = ""abca""; target = ""aabcaca"" Output: [3;0;1] Explanation: Initially s = ""???????"". - Place stamp at index 3 to get ""???abca"". - Place stamp at index 0 to get ""abcabca"". - Place stamp at index 1 to get ""aabcaca"". Constraints: 1 <= stamp.length <= target.length <= 1000 stamp and target consist of lowercase English letters."
Amazon,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
Amazon,1268,Search Suggestions System,Med,Database,Table: Users +----------------+---------+ | Column Name | Type | +----------------+---------+ | user_id | int | | join_date | date | | favorite_brand | varchar | +----------------+---------+ user_id is the primary key (column with unique values) of this table. This table has the info of the users of an online shopping website where users can sell and buy items. Table: Orders +---------------+---------+ | Column Name | Type | +---------------+---------+ | order_id | int | | order_date | date | | item_id | int | | buyer_id | int | | seller_id | int | +---------------+---------+ order_id is the primary key (column with unique values) of this table. item_id is a foreign key (reference column) to the Items table. buyer_id and seller_id are foreign keys to the Users table. Table: Items +---------------+---------+ | Column Name | Type | +---------------+---------+ | item_id | int | | item_brand | varchar | +---------------+---------+ item_id is the primary key (column with unique values) of this table. Write a solution to find for each user; the join date and the number of orders they made as a buyer in 2019. Return the result table in any order. The result format is in the following example. Example 1: Input: Users table: +---------+------------+----------------+ | user_id | join_date | favorite_brand | +---------+------------+----------------+ | 1 | 2018-01-01 | Lenovo | | 2 | 2018-02-09 | Samsung | | 3 | 2018-01-19 | LG | | 4 | 2018-05-21 | HP | +---------+------------+----------------+ Orders table: +----------+------------+---------+----------+-----------+ | order_id | order_date | item_id | buyer_id | seller_id | +----------+------------+---------+----------+-----------+ | 1 | 2019-08-01 | 4 | 1 | 2 | | 2 | 2018-08-02 | 2 | 1 | 3 | | 3 | 2019-08-03 | 3 | 2 | 3 | | 4 | 2018-08-04 | 1 | 4 | 2 | | 5 | 2018-08-04 | 1 | 3 | 4 | | 6 | 2019-08-05 | 2 | 2 | 4 | +----------+------------+---------+----------+-----------+ Items table: +---------+------------+ | item_id | item_brand | +---------+------------+ | 1 | Samsung | | 2 | Lenovo | | 3 | LG | | 4 | HP | +---------+------------+ Output: +-----------+------------+----------------+ | buyer_id | join_date | orders_in_2019 | +-----------+------------+----------------+ | 1 | 2018-01-01 | 1 | | 2 | 2018-02-09 | 2 | | 3 | 2018-01-19 | 0 | | 4 | 2018-05-21 | 0 | +-----------+------------+----------------+
Amazon,2055,Plates Between Candles,Med,"Array, Hash Table, Sorting, Prefix Sum",There is a long and thin painting that can be represented by a number line. The painting was painted with multiple overlapping segments where each segment was painted with a unique color. You are given a 2D integer array segments; where segments[i] = [starti; endi; colori] represents the half-closed segment [starti; endi) with colori as the color. The colors in the overlapping segments of the painting were mixed when it was painted. When two or more colors mix; they form a new color that can be represented as a set of mixed colors. For example; if colors 2; 4; and 6 are mixed; then the resulting mixed color is {2;4;6}. For the sake of simplicity; you should only output the sum of the elements in the set rather than the full set. You want to describe the painting with the minimum number of non-overlapping half-closed segments of these mixed colors. These segments can be represented by the 2D array painting where painting[j] = [leftj; rightj; mixj] describes a half-closed segment [leftj; rightj) with the mixed color sum of mixj. For example; the painting created with segments = [[1;4;5];[1;7;7]] can be described by painting = [[1;4;12];[4;7;7]] because: [1;4) is colored {5;7} (with a sum of 12) from both the first and second segments. [4;7) is colored {7} from only the second segment. Return the 2D array painting describing the finished painting (excluding any parts that are not painted). You may return the segments in any order. A half-closed segment [a; b) is the section of the number line between points a and b including point a and not including point b. Example 1: Input: segments = [[1;4;5];[4;7;7];[1;7;9]] Output: [[1;4;14];[4;7;16]] Explanation: The painting can be described as follows: - [1;4) is colored {5;9} (with a sum of 14) from the first and third segments. - [4;7) is colored {7;9} (with a sum of 16) from the second and third segments. Example 2: Input: segments = [[1;7;9];[6;8;15];[8;10;7]] Output: [[1;6;9];[6;7;24];[7;8;15];[8;10;7]] Explanation: The painting can be described as follows: - [1;6) is colored 9 from the first segment. - [6;7) is colored {9;15} (with a sum of 24) from the first and second segments. - [7;8) is colored 15 from the second segment. - [8;10) is colored 7 from the third segment. Example 3: Input: segments = [[1;4;5];[1;4;7];[4;7;1];[4;7;11]] Output: [[1;4;12];[4;7;12]] Explanation: The painting can be described as follows: - [1;4) is colored {5;7} (with a sum of 12) from the first and second segments. - [4;7) is colored {1;11} (with a sum of 12) from the third and fourth segments. Note that returning a single segment [1;7) is incorrect because the mixed color sets are different. Constraints: 1 <= segments.length <= 2 * 104 segments[i].length == 3 1 <= starti < endi <= 105 1 <= colori <= 109 Each colori is distinct.
Amazon,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Amazon,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
Amazon,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Amazon,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Amazon,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Amazon,62,Unique Paths,Med,"Math, Dynamic Programming, Combinatorics",There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n; return the number of possible unique paths that the robot can take to reach the bottom-right corner. The test cases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: m = 3; n = 7 Output: 28 Example 2: Input: m = 3; n = 2 Output: 3 Explanation: From the top-left corner; there are a total of 3 ways to reach the bottom-right corner: 1. Right -> Down -> Down 2. Down -> Down -> Right 3. Down -> Right -> Down Constraints: 1 <= m; n <= 100
Amazon,66,Plus One,Easy,"Array, Math",You are given a large integer represented as an integer array digits; where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0's. Increment the large integer by one and return the resulting array of digits. Example 1: Input: digits = [1;2;3] Output: [1;2;4] Explanation: The array represents the integer 123. Incrementing by one gives 123 + 1 = 124. Thus; the result should be [1;2;4]. Example 2: Input: digits = [4;3;2;1] Output: [4;3;2;2] Explanation: The array represents the integer 4321. Incrementing by one gives 4321 + 1 = 4322. Thus; the result should be [4;3;2;2]. Example 3: Input: digits = [9] Output: [1;0] Explanation: The array represents the integer 9. Incrementing by one gives 9 + 1 = 10. Thus; the result should be [1;0]. Constraints: 1 <= digits.length <= 100 0 <= digits[i] <= 9 digits does not contain any leading 0's.
Amazon,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Amazon,100,Same Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the roots of two binary trees p and q; write a function to check if they are the same or not. Two binary trees are considered the same if they are structurally identical; and the nodes have the same value. Example 1: Input: p = [1;2;3]; q = [1;2;3] Output: true Example 2: Input: p = [1;2]; q = [1;null;2] Output: false Example 3: Input: p = [1;2;1]; q = [1;1;2] Output: false Constraints: The number of nodes in both trees is in the range [0; 100]. -104 <= Node.val <= 104
Amazon,102,Binary Tree Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the level order traversal of its nodes' values. (i.e.; from left to right; level by level). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[9;20];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -1000 <= Node.val <= 1000
Amazon,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Amazon,240,Search a 2D Matrix II,Med,"Array, Binary Search, Divide and Conquer, Matrix",Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. Example 1: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 5 Output: true Example 2: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 20 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= n; m <= 300 -109 <= matrix[i][j] <= 109 All the integers in each row are sorted in ascending order. All the integers in each column are sorted in ascending order. -109 <= target <= 109
Amazon,287,Find the Duplicate Number,Med,"Array, Two Pointers, Binary Search, Bit Manipulation",Given an array of integers nums containing n + 1 integers where each integer is in the range [1; n] inclusive. There is only one repeated number in nums; return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Example 1: Input: nums = [1;3;4;2;2] Output: 2 Example 2: Input: nums = [3;1;3;4;2] Output: 3 Example 3: Input: nums = [3;3;3;3;3] Output: 3 Constraints: 1 <= n <= 105 nums.length == n + 1 1 <= nums[i] <= n All the integers in nums appear only once except for precisely one integer which appears two or more times. Follow up: How can we prove that at least one duplicate number must exist in nums? Can you solve the problem in linear runtime complexity?
Amazon,348,Design Tic-Tac-Toe,Med,"Array, Hash Table, Design, Matrix, Simulation",
Amazon,437,Path Sum III,Med,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return the number of paths where the sum of the values along the path equals targetSum. The path does not need to start or end at the root or a leaf; but it must go downwards (i.e.; traveling only from parent nodes to child nodes). Example 1: Input: root = [10;5;-3;3;2;null;11;3;-2;null;1]; targetSum = 8 Output: 3 Explanation: The paths that sum to 8 are shown. Example 2: Input: root = [5;4;8;11;null;13;4;7;2;null;null;5;1]; targetSum = 22 Output: 3 Constraints: The number of nodes in the tree is in the range [0; 1000]. -109 <= Node.val <= 109 -1000 <= targetSum <= 1000
Amazon,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Amazon,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
Amazon,472,Concatenated Words,Hard,"Array, String, Dynamic Programming, Depth-First Search, Trie","Given an array of strings words (without duplicates); return all the concatenated words in the given list of words. A concatenated word is defined as a string that is comprised entirely of at least two shorter words (not necessarily distinct) in the given array. Example 1: Input: words = [""cat"";""cats"";""catsdogcats"";""dog"";""dogcatsdog"";""hippopotamuses"";""rat"";""ratcatdogcat""] Output: [""catsdogcats"";""dogcatsdog"";""ratcatdogcat""] Explanation: ""catsdogcats"" can be concatenated by ""cats""; ""dog"" and ""cats""; ""dogcatsdog"" can be concatenated by ""dog""; ""cats"" and ""dog""; ""ratcatdogcat"" can be concatenated by ""rat""; ""cat""; ""dog"" and ""cat"". Example 2: Input: words = [""cat"";""dog"";""catdog""] Output: [""catdog""] Constraints: 1 <= words.length <= 104 1 <= words[i].length <= 30 words[i] consists of only lowercase English letters. All the strings of words are unique. 1 <= sum(words[i].length) <= 105"
Amazon,496,Next Greater Element I,Easy,"Array, Hash Table, Stack, Monotonic Stack",The next greater element of some element x in an array is the first greater element that is to the right of x in the same array. You are given two distinct 0-indexed integer arrays nums1 and nums2; where nums1 is a subset of nums2. For each 0 <= i < nums1.length; find the index j such that nums1[i] == nums2[j] and determine the next greater element of nums2[j] in nums2. If there is no next greater element; then the answer for this query is -1. Return an array ans of length nums1.length such that ans[i] is the next greater element as described above. Example 1: Input: nums1 = [4;1;2]; nums2 = [1;3;4;2] Output: [-1;3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 4 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. - 1 is underlined in nums2 = [1;3;4;2]. The next greater element is 3. - 2 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. Example 2: Input: nums1 = [2;4]; nums2 = [1;2;3;4] Output: [3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 2 is underlined in nums2 = [1;2;3;4]. The next greater element is 3. - 4 is underlined in nums2 = [1;2;3;4]. There is no next greater element; so the answer is -1. Constraints: 1 <= nums1.length <= nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 104 All integers in nums1 and nums2 are unique. All the integers of nums1 also appear in nums2. Follow up: Could you find an O(nums1.length + nums2.length) solution?
Amazon,588,Design In-Memory File System,Hard,"Hash Table, String, Design, Trie, Sorting",
Amazon,632,Smallest Range Covering Elements from K Lists,Hard,"Array, Hash Table, Greedy, Sliding Window, Sorting, Heap (Priority Queue)",You have k lists of sorted integers in non-decreasing order. Find the smallest range that includes at least one number from each of the k lists. We define the range [a; b] is smaller than range [c; d] if b - a < d - c or a < c if b - a == d - c. Example 1: Input: nums = [[4;10;15;24;26];[0;9;12;20];[5;18;22;30]] Output: [20;24] Explanation: List 1: [4; 10; 15; 24;26]; 24 is in range [20;24]. List 2: [0; 9; 12; 20]; 20 is in range [20;24]. List 3: [5; 18; 22; 30]; 22 is in range [20;24]. Example 2: Input: nums = [[1;2;3];[1;2;3];[1;2;3]] Output: [1;1] Constraints: nums.length == k 1 <= k <= 3500 1 <= nums[i].length <= 50 -105 <= nums[i][j] <= 105 nums[i] is sorted in non-decreasing order.
Amazon,509,Fibonacci Number,Easy,"Tree, Binary Search Tree, Binary Tree",
Amazon,1233,Remove Sub-Folders from the Filesystem,Med,"Array, Divide and Conquer, Interactive",
Amazon,35,Search Insert Position,Easy,"Array, Binary Search",Given a sorted array of distinct integers and a target value; return the index if the target is found. If not; return the index where it would be if it were inserted in order. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [1;3;5;6]; target = 5 Output: 2 Example 2: Input: nums = [1;3;5;6]; target = 2 Output: 1 Example 3: Input: nums = [1;3;5;6]; target = 7 Output: 4 Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 nums contains distinct values sorted in ascending order. -104 <= target <= 104
Amazon,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Amazon,78,Subsets,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums of unique elements; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;3] Output: [[];[1];[2];[1;2];[3];[1;3];[2;3];[1;2;3]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10 All the numbers of nums are unique.
Amazon,92,Reverse Linked List II,Med,Linked List,Given the head of a singly linked list and two integers left and right where left <= right; reverse the nodes of the list from position left to position right; and return the reversed list. Example 1: Input: head = [1;2;3;4;5]; left = 2; right = 4 Output: [1;4;3;2;5] Example 2: Input: head = [5]; left = 1; right = 1 Output: [5] Constraints: The number of nodes in the list is n. 1 <= n <= 500 -500 <= Node.val <= 500 1 <= left <= right <= n Follow up: Could you do it in one pass?
Amazon,103,Binary Tree Zigzag Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the zigzag level order traversal of its nodes' values. (i.e.; from left to right; then right to left for the next level and alternate between). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[20;9];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100
Amazon,118,Pascal's Triangle,Easy,"Array, Dynamic Programming",Given an integer numRows; return the first numRows of Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: numRows = 5 Output: [[1];[1;1];[1;2;1];[1;3;3;1];[1;4;6;4;1]] Example 2: Input: numRows = 1 Output: [[1]] Constraints: 1 <= numRows <= 30
Amazon,125,Valid Palindrome,Easy,"Two Pointers, String","A phrase is a palindrome if; after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters; it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s; return true if it is a palindrome; or false otherwise. Example 1: Input: s = ""A man; a plan; a canal: Panama"" Output: true Explanation: ""amanaplanacanalpanama"" is a palindrome. Example 2: Input: s = ""race a car"" Output: false Explanation: ""raceacar"" is not a palindrome. Example 3: Input: s = "" "" Output: true Explanation: s is an empty string """" after removing non-alphanumeric characters. Since an empty string reads the same forward and backward; it is a palindrome. Constraints: 1 <= s.length <= 2 * 105 s consists only of printable ASCII characters."
Amazon,150,Evaluate Reverse Polish Notation,Med,"Array, Math, Stack","You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression. Return an integer that represents the value of the expression. Note that: The valid operators are '+'; '-'; '*'; and '/'. Each operand may be an integer or another expression. The division between two integers always truncates toward zero. There will not be any division by zero. The input represents a valid arithmetic expression in a reverse polish notation. The answer and all the intermediate calculations can be represented in a 32-bit integer. Example 1: Input: tokens = [""2"";""1"";""+"";""3"";""*""] Output: 9 Explanation: ((2 + 1) * 3) = 9 Example 2: Input: tokens = [""4"";""13"";""5"";""/"";""+""] Output: 6 Explanation: (4 + (13 / 5)) = 6 Example 3: Input: tokens = [""10"";""6"";""9"";""3"";""+"";""-11"";""*"";""/"";""*"";""17"";""+"";""5"";""+""] Output: 22 Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 = ((10 * (6 / (12 * -11))) + 17) + 5 = ((10 * (6 / -132)) + 17) + 5 = ((10 * 0) + 17) + 5 = (0 + 17) + 5 = 17 + 5 = 22 Constraints: 1 <= tokens.length <= 104 tokens[i] is either an operator: ""+""; ""-""; ""*""; or ""/""; or an integer in the range [-200; 200]."
Amazon,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Amazon,208,Implement Trie (Prefix Tree),Med,"Hash Table, String, Design, Trie","A trie (pronounced as ""try"") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure; such as autocomplete and spellchecker. Implement the Trie class: Trie() Initializes the trie object. void insert(String word) Inserts the string word into the trie. boolean search(String word) Returns true if the string word is in the trie (i.e.; was inserted before); and false otherwise. boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix; and false otherwise. Example 1: Input [""Trie""; ""insert""; ""search""; ""search""; ""startsWith""; ""insert""; ""search""] [[]; [""apple""]; [""apple""]; [""app""]; [""app""]; [""app""]; [""app""]] Output [null; null; true; false; true; null; true] Explanation Trie trie = new Trie(); trie.insert(""apple""); trie.search(""apple""); // return True trie.search(""app""); // return False trie.startsWith(""app""); // return True trie.insert(""app""); trie.search(""app""); // return True Constraints: 1 <= word.length; prefix.length <= 2000 word and prefix consist only of lowercase English letters. At most 3 * 104 calls in total will be made to insert; search; and startsWith."
Amazon,219,Contains Duplicate II,Easy,"Array, Hash Table, Sliding Window",Given an integer array nums and an integer k; return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k. Example 1: Input: nums = [1;2;3;1]; k = 3 Output: true Example 2: Input: nums = [1;0;1;1]; k = 1 Output: true Example 3: Input: nums = [1;2;3;1;2;3]; k = 2 Output: false Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109 0 <= k <= 105
Amazon,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Amazon,241,Different Ways to Add Parentheses,Med,"Math, String, Dynamic Programming, Recursion, Memoization","Given a string expression of numbers and operators; return all possible results from computing all the different possible ways to group numbers and operators. You may return the answer in any order. The test cases are generated such that the output values fit in a 32-bit integer and the number of different results does not exceed 104. Example 1: Input: expression = ""2-1-1"" Output: [0;2] Explanation: ((2-1)-1) = 0 (2-(1-1)) = 2 Example 2: Input: expression = ""2*3-4*5"" Output: [-34;-14;-10;-10;10] Explanation: (2*(3-(4*5))) = -34 ((2*3)-(4*5)) = -14 ((2*(3-4))*5) = -10 (2*((3-4)*5)) = -10 (((2*3)-4)*5) = 10 Constraints: 1 <= expression.length <= 20 expression consists of digits and the operator '+'; '-'; and '*'. All the integer values in the input expression are in the range [0; 99]. The integer values in the input expression do not have a leading '-' or '+' denoting the sign."
Amazon,269,Alien Dictionary,Hard,"Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort",
Amazon,485,Max Consecutive Ones,Easy,Array,Given a binary array nums; return the maximum number of consecutive 1's in the array. Example 1: Input: nums = [1;1;0;1;1;1] Output: 3 Explanation: The first two digits or the last three digits are consecutive 1s. The maximum number of consecutive 1s is 3. Example 2: Input: nums = [1;0;1;1;0;1] Output: 2 Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Amazon,584,Find Customer Referee,Easy,Database,Table: Customer +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | referee_id | int | +-------------+---------+ In SQL; id is the primary key column for this table. Each row of this table indicates the id of a customer; their name; and the id of the customer who referred them. Find the names of the customer that are not referred by the customer with id = 2. Return the result table in any order. The result format is in the following example. Example 1: Input: Customer table: +----+------+------------+ | id | name | referee_id | +----+------+------------+ | 1 | Will | null | | 2 | Jane | null | | 3 | Alex | 2 | | 4 | Bill | null | | 5 | Zack | 1 | | 6 | Mark | 2 | +----+------+------------+ Output: +------+ | name | +------+ | Will | | Jane | | Bill | | Zack | +------+
Amazon,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Amazon,746,Min Cost Climbing Stairs,Easy,"Array, Hash Table, String, Design, Trie","Design a special dictionary that searches the words in it by a prefix and a suffix. Implement the WordFilter class: WordFilter(string[] words) Initializes the object with the words in the dictionary. f(string pref; string suff) Returns the index of the word in the dictionary; which has the prefix pref and the suffix suff. If there is more than one valid index; return the largest of them. If there is no such word in the dictionary; return -1. Example 1: Input [""WordFilter""; ""f""] [[[""apple""]]; [""a""; ""e""]] Output [null; 0] Explanation WordFilter wordFilter = new WordFilter([""apple""]); wordFilter.f(""a""; ""e""); // return 0; because the word at index 0 has prefix = ""a"" and suffix = ""e"". Constraints: 1 <= words.length <= 104 1 <= words[i].length <= 7 1 <= pref.length; suff.length <= 7 words[i]; pref and suff consist of lowercase English letters only. At most 104 calls will be made to the function f."
Amazon,428,Serialize and Deserialize N-ary Tree,Hard,,
Amazon,796,Rotate String,Easy,Math,Given four integers sx; sy; tx; and ty; return true if it is possible to convert the point (sx; sy) to the point (tx; ty) through some operations; or false otherwise. The allowed operation on some point (x; y) is to convert it to either (x; x + y) or (x + y; y). Example 1: Input: sx = 1; sy = 1; tx = 3; ty = 5 Output: true Explanation: One series of moves that transforms the starting point to the target is: (1; 1) -> (1; 2) (1; 2) -> (3; 2) (3; 2) -> (3; 5) Example 2: Input: sx = 1; sy = 1; tx = 2; ty = 2 Output: false Example 3: Input: sx = 1; sy = 1; tx = 1; ty = 1 Output: true Constraints: 1 <= sx; sy; tx; ty <= 109
Amazon,706,Design HashMap,Easy,,
Amazon,912,Sort an Array,Med,"Array, Math, Binary Search, Prefix Sum, Randomized","You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index. You need to implement the function pickIndex(); which randomly picks an index in the range [0; w.length - 1] (inclusive) and returns it. The probability of picking an index i is w[i] / sum(w). For example; if w = [1; 3]; the probability of picking index 0 is 1 / (1 + 3) = 0.25 (i.e.; 25%); and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e.; 75%). Example 1: Input [""Solution"";""pickIndex""] [[[1]];[]] Output [null;0] Explanation Solution solution = new Solution([1]); solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w. Example 2: Input [""Solution"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex""] [[[1;3]];[];[];[];[];[]] Output [null;1;1;1;1;0] Explanation Solution solution = new Solution([1; 3]); solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4. solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4. Since this is a randomization problem; multiple answers are allowed. All of the following outputs can be considered correct: [null;1;1;1;1;0] [null;1;1;1;1;1] [null;1;1;1;0;0] [null;1;1;1;0;1] [null;1;0;1;0;0] ...... and so on. Constraints: 1 <= w.length <= 104 1 <= w[i] <= 105 pickIndex will be called at most 104 times."
Amazon,921,Minimum Add to Make Parentheses Valid,Med,"Array, Matrix, Simulation",You start at the cell (rStart; cStart) of an rows x cols grid facing east. The northwest corner is at the first row and column in the grid; and the southeast corner is at the last row and column. You will walk in a clockwise spiral shape to visit every position in this grid. Whenever you move outside the grid's boundary; we continue our walk outside the grid (but may return to the grid boundary later.). Eventually; we reach all rows * cols spaces of the grid. Return an array of coordinates representing the positions of the grid in the order you visited them. Example 1: Input: rows = 1; cols = 4; rStart = 0; cStart = 0 Output: [[0;0];[0;1];[0;2];[0;3]] Example 2: Input: rows = 5; cols = 6; rStart = 1; cStart = 4 Output: [[1;4];[1;5];[2;5];[2;4];[2;3];[1;3];[0;3];[0;4];[0;5];[3;5];[3;4];[3;3];[3;2];[2;2];[1;2];[0;2];[4;5];[4;4];[4;3];[4;2];[4;1];[3;1];[2;1];[1;1];[0;1];[4;0];[3;0];[2;0];[1;0];[0;0]] Constraints: 1 <= rows; cols <= 100 0 <= rStart < rows 0 <= cStart < cols
Amazon,981,Time Based Key-Value Store,Med,"Array, String","You are given an array of n strings strs; all of the same length. The strings can be arranged such that there is one on each line; making a grid. For example; strs = [""abc""; ""bce""; ""cae""] can be arranged as follows: abc bce cae You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed); columns 0 ('a'; 'b'; 'c') and 2 ('c'; 'e'; 'e') are sorted; while column 1 ('b'; 'c'; 'a') is not; so you would delete column 1. Return the number of columns that you will delete. Example 1: Input: strs = [""cba"";""daf"";""ghi""] Output: 1 Explanation: The grid looks as follows: cba daf ghi Columns 0 and 2 are sorted; but column 1 is not; so you only need to delete 1 column. Example 2: Input: strs = [""a"";""b""] Output: 0 Explanation: The grid looks as follows: a b Column 0 is the only column and is sorted; so you will not delete any columns. Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: The grid looks as follows: zyx wvu tsr All 3 columns are not sorted; so you will delete all 3. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 1000 strs[i] consists of lowercase English letters."
Amazon,1071,Greatest Common Divisor of Strings,Easy,"Array, Bit Manipulation",You are given a binary array nums (0-indexed). We define xi as the number whose binary representation is the subarray nums[0..i] (from most-significant-bit to least-significant-bit). For example; if nums = [1;0;1]; then x0 = 1; x1 = 2; and x2 = 5. Return an array of booleans answer where answer[i] is true if xi is divisible by 5. Example 1: Input: nums = [0;1;1] Output: [true;false;false] Explanation: The input numbers in binary are 0; 01; 011; which are 0; 1; and 3 in base-10. Only the first number is divisible by 5; so answer[0] is true. Example 2: Input: nums = [1;1;1] Output: [false;false;false] Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Amazon,1405,Longest Happy String,Med,Database,
Amazon,1193,Monthly Transactions I,Med,Database,
Amazon,1431,Kids With the Greatest Number of Candies,Easy,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",You are given a positive integer n representing the number of nodes of a Directed Acyclic Graph (DAG). The nodes are numbered from 0 to n - 1 (inclusive). You are also given a 2D integer array edges; where edges[i] = [fromi; toi] denotes that there is a unidirectional edge from fromi to toi in the graph. Return a list answer; where answer[i] is the list of ancestors of the ith node; sorted in ascending order. A node u is an ancestor of another node v if u can reach v via a set of edges. Example 1: Input: n = 8; edgeList = [[0;3];[0;4];[1;3];[2;4];[2;7];[3;5];[3;6];[3;7];[4;6]] Output: [[];[];[];[0;1];[0;2];[0;1;3];[0;1;2;3;4];[0;1;2;3]] Explanation: The above diagram represents the input graph. - Nodes 0; 1; and 2 do not have any ancestors. - Node 3 has two ancestors 0 and 1. - Node 4 has two ancestors 0 and 2. - Node 5 has three ancestors 0; 1; and 3. - Node 6 has five ancestors 0; 1; 2; 3; and 4. - Node 7 has four ancestors 0; 1; 2; and 3. Example 2: Input: n = 5; edgeList = [[0;1];[0;2];[0;3];[0;4];[1;2];[1;3];[1;4];[2;3];[2;4];[3;4]] Output: [[];[0];[0;1];[0;1;2];[0;1;2;3]] Explanation: The above diagram represents the input graph. - Node 0 does not have any ancestor. - Node 1 has one ancestor 0. - Node 2 has two ancestors 0 and 1. - Node 3 has three ancestors 0; 1; and 2. - Node 4 has four ancestors 0; 1; 2; and 3. Constraints: 1 <= n <= 1000 0 <= edges.length <= min(2000; n * (n - 1) / 2) edges[i].length == 2 0 <= fromi; toi <= n - 1 fromi != toi There are no duplicate edges. The graph is directed and acyclic.
Amazon,1438,Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit,Med,Database,
Amazon,1942,The Number of the Smallest Unoccupied Chair,Med,Database,Table: Employee +---------------+---------+ | Column Name | Type | +---------------+---------+ | employee_id | int | | department_id | int | | primary_flag | varchar | +---------------+---------+ (employee_id; department_id) is the primary key (combination of columns with unique values) for this table. employee_id is the id of the employee. department_id is the id of the department to which the employee belongs. primary_flag is an ENUM (category) of type ('Y'; 'N'). If the flag is 'Y'; the department is the primary department for the employee. If the flag is 'N'; the department is not the primary. Employees can belong to multiple departments. When the employee joins other departments; they need to decide which department is their primary department. Note that when an employee belongs to only one department; their primary column is 'N'. Write a solution to report all the employees with their primary department. For employees who belong to one department; report their only department. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +-------------+---------------+--------------+ | employee_id | department_id | primary_flag | +-------------+---------------+--------------+ | 1 | 1 | N | | 2 | 1 | Y | | 2 | 2 | N | | 3 | 3 | N | | 4 | 2 | N | | 4 | 3 | Y | | 4 | 4 | N | +-------------+---------------+--------------+ Output: +-------------+---------------+ | employee_id | department_id | +-------------+---------------+ | 1 | 1 | | 2 | 1 | | 3 | 3 | | 4 | 3 | +-------------+---------------+ Explanation: - The Primary department for employee 1 is 1. - The Primary department for employee 2 is 1. - The Primary department for employee 3 is 3. - The Primary department for employee 4 is 3.
Amazon,2416,Sum of Prefix Scores of Strings,Hard,"Tree, Depth-First Search, Binary Tree",You are given the root of a full binary tree with the following properties: Leaf nodes have either the value 0 or 1; where 0 represents False and 1 represents True. Non-leaf nodes have either the value 2 or 3; where 2 represents the boolean OR and 3 represents the boolean AND. The evaluation of a node is as follows: If the node is a leaf node; the evaluation is the value of the node; i.e. True or False. Otherwise; evaluate the node's two children and apply the boolean operation of its value with the children's evaluations. Return the boolean result of evaluating the root node. A full binary tree is a binary tree where each node has either 0 or 2 children. A leaf node is a node that has zero children. Example 1: Input: root = [2;1;3;null;null;0;1] Output: true Explanation: The above diagram illustrates the evaluation process. The AND node evaluates to False AND True = False. The OR node evaluates to True OR False = True. The root node evaluates to True; so we return true. Example 2: Input: root = [0] Output: false Explanation: The root node is a leaf node and it evaluates to false; so we return false. Constraints: The number of nodes in the tree is in the range [1; 1000]. 0 <= Node.val <= 3 Every node has either 0 or 2 children. Leaf nodes have a value of 0 or 1. Non-leaf nodes have a value of 2 or 3.
Amazon,2877,Create a DataFrame from List,Easy,"String, Greedy, Enumeration","Given three strings a; b; and c; your task is to find a string that has the minimum length and contains all three strings as substrings. If there are multiple such strings; return the lexicographically smallest one. Return a string denoting the answer to the problem. Notes A string a is lexicographically smaller than a string b (of the same length) if in the first position where a and b differ; string a has a letter that appears earlier in the alphabet than the corresponding letter in b. A substring is a contiguous sequence of characters within a string. Example 1: Input: a = ""abc""; b = ""bca""; c = ""aaa"" Output: ""aaabca"" Explanation: We show that ""aaabca"" contains all the given strings: a = ans[2...4]; b = ans[3..5]; c = ans[0..2]. It can be shown that the length of the resulting string would be at least 6 and ""aaabca"" is the lexicographically smallest one. Example 2: Input: a = ""ab""; b = ""ba""; c = ""aba"" Output: ""aba"" Explanation: We show that the string ""aba"" contains all the given strings: a = ans[0..1]; b = ans[1..2]; c = ans[0..2]. Since the length of c is 3; the length of the resulting string would be at least 3. It can be shown that ""aba"" is the lexicographically smallest one. Constraints: 1 <= a.length; b.length; c.length <= 100 a; b; c consist only of lowercase English letters."
Amazon,18,4Sum,Med,"Array, Two Pointers, Sorting",Given an array nums of n integers; return an array of all the unique quadruplets [nums[a]; nums[b]; nums[c]; nums[d]] such that: 0 <= a; b; c; d < n a; b; c; and d are distinct. nums[a] + nums[b] + nums[c] + nums[d] == target You may return the answer in any order. Example 1: Input: nums = [1;0;-1;0;-2;2]; target = 0 Output: [[-2;-1;1;2];[-2;0;0;2];[-1;0;0;1]] Example 2: Input: nums = [2;2;2;2;2]; target = 8 Output: [[2;2;2;2]] Constraints: 1 <= nums.length <= 200 -109 <= nums[i] <= 109 -109 <= target <= 109
Amazon,28,Find the Index of the First Occurrence in a String,Easy,"Two Pointers, String, String Matching","Given two strings needle and haystack; return the index of the first occurrence of needle in haystack; or -1 if needle is not part of haystack. Example 1: Input: haystack = ""sadbutsad""; needle = ""sad"" Output: 0 Explanation: ""sad"" occurs at index 0 and 6. The first occurrence is at index 0; so we return 0. Example 2: Input: haystack = ""leetcode""; needle = ""leeto"" Output: -1 Explanation: ""leeto"" did not occur in ""leetcode""; so we return -1. Constraints: 1 <= haystack.length; needle.length <= 104 haystack and needle consist of only lowercase English characters."
Amazon,29,Divide Two Integers,Med,"Math, Bit Manipulation",Given two integers dividend and divisor; divide two integers without using multiplication; division; and mod operator. The integer division should truncate toward zero; which means losing its fractional part. For example; 8.345 would be truncated to 8; and -2.7335 would be truncated to -2. Return the quotient after dividing dividend by divisor. Note: Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−231; 231 − 1]. For this problem; if the quotient is strictly greater than 231 - 1; then return 231 - 1; and if the quotient is strictly less than -231; then return -231. Example 1: Input: dividend = 10; divisor = 3 Output: 3 Explanation: 10/3 = 3.33333.. which is truncated to 3. Example 2: Input: dividend = 7; divisor = -3 Output: -2 Explanation: 7/-3 = -2.33333.. which is truncated to -2. Constraints: -231 <= dividend; divisor <= 231 - 1 divisor != 0
Amazon,32,Longest Valid Parentheses,Hard,"String, Dynamic Programming, Stack","Given a string containing just the characters '(' and ')'; return the length of the longest valid (well-formed) parentheses substring. Example 1: Input: s = ""(()"" Output: 2 Explanation: The longest valid parentheses substring is ""()"". Example 2: Input: s = "")()())"" Output: 4 Explanation: The longest valid parentheses substring is ""()()"". Example 3: Input: s = """" Output: 0 Constraints: 0 <= s.length <= 3 * 104 s[i] is '('; or ')'."
Amazon,51,N-Queens,Hard,"Array, Backtracking","The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n; return all distinct solutions to the n-queens puzzle. You may return the answer in any order. Each solution contains a distinct board configuration of the n-queens' placement; where 'Q' and '.' both indicate a queen and an empty space; respectively. Example 1: Input: n = 4 Output: [["".Q.."";""...Q"";""Q..."";""..Q.""];[""..Q."";""Q..."";""...Q"";"".Q..""]] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above Example 2: Input: n = 1 Output: [[""Q""]] Constraints: 1 <= n <= 9"
Amazon,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Amazon,81,Search in Rotated Sorted Array II,Med,"Array, Binary Search",There is an integer array nums sorted in non-decreasing order (not necessarily with distinct values). Before being passed to your function; nums is rotated at an unknown pivot index k (0 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;4;4;5;6;6;7] might be rotated at pivot index 5 and become [4;5;6;6;7;0;1;2;4;4]. Given the array nums after the rotation and an integer target; return true if target is in nums; or false if it is not in nums. You must decrease the overall operation steps as much as possible. Example 1: Input: nums = [2;5;6;0;0;1;2]; target = 0 Output: true Example 2: Input: nums = [2;5;6;0;0;1;2]; target = 3 Output: false Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 nums is guaranteed to be rotated at some pivot. -104 <= target <= 104 Follow up: This problem is similar to Search in Rotated Sorted Array; but nums may contain duplicates. Would this affect the runtime complexity? How and why?
Amazon,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Amazon,130,Surrounded Regions,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","You are given an m x n matrix board containing letters 'X' and 'O'; capture regions that are surrounded: Connect: A cell is connected to adjacent cells horizontally or vertically. Region: To form a region connect every 'O' cell. Surround: The region is surrounded with 'X' cells if you can connect the region with 'X' cells and none of the region cells are on the edge of the board. A surrounded region is captured by replacing all 'O's with 'X's in the input matrix board. Example 1: Input: board = [[""X"";""X"";""X"";""X""];[""X"";""O"";""O"";""X""];[""X"";""X"";""O"";""X""];[""X"";""O"";""X"";""X""]] Output: [[""X"";""X"";""X"";""X""];[""X"";""X"";""X"";""X""];[""X"";""X"";""X"";""X""];[""X"";""O"";""X"";""X""]] Explanation: In the above diagram; the bottom region is not captured because it is on the edge of the board and cannot be surrounded. Example 2: Input: board = [[""X""]] Output: [[""X""]] Constraints: m == board.length n == board[i].length 1 <= m; n <= 200 board[i][j] is 'X' or 'O'."
Amazon,136,Single Number,Easy,"Array, Bit Manipulation",Given a non-empty array of integers nums; every element appears twice except for one. Find that single one. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;1] Output: 1 Example 2: Input: nums = [4;1;2;1;2] Output: 4 Example 3: Input: nums = [1] Output: 1 Constraints: 1 <= nums.length <= 3 * 104 -3 * 104 <= nums[i] <= 3 * 104 Each element in the array appears twice except for one element which appears only once.
Amazon,145,Binary Tree Postorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the postorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [3;2;1] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [4;6;7;5;2;9;8;3;1] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of the nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Amazon,165,Compare Version Numbers,Med,"Two Pointers, String","Given two version strings; version1 and version2; compare them. A version string consists of revisions separated by dots '.'. The value of the revision is its integer conversion ignoring leading zeros. To compare version strings; compare their revision values in left-to-right order. If one of the version strings has fewer revisions; treat the missing revision values as 0. Return the following: If version1 < version2; return -1. If version1 > version2; return 1. Otherwise; return 0. Example 1: Input: version1 = ""1.2""; version2 = ""1.10"" Output: -1 Explanation: version1's second revision is ""2"" and version2's second revision is ""10"": 2 < 10; so version1 < version2. Example 2: Input: version1 = ""1.01""; version2 = ""1.001"" Output: 0 Explanation: Ignoring leading zeroes; both ""01"" and ""001"" represent the same integer ""1"". Example 3: Input: version1 = ""1.0""; version2 = ""1.0.0.0"" Output: 0 Explanation: version1 has less revisions; which means every missing revision are treated as ""0"". Constraints: 1 <= version1.length; version2.length <= 500 version1 and version2 only contain digits and '.'. version1 and version2 are valid version numbers. All the given revisions in version1 and version2 can be stored in a 32-bit integer."
Amazon,176,Second Highest Salary,Med,Database,Table: Employee +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | salary | int | +-------------+------+ id is the primary key (column with unique values) for this table. Each row of this table contains information about the salary of an employee. Write a solution to find the second highest distinct salary from the Employee table. If there is no second highest salary; return null (return None in Pandas). The result format is in the following example. Example 1: Input: Employee table: +----+--------+ | id | salary | +----+--------+ | 1 | 100 | | 2 | 200 | | 3 | 300 | +----+--------+ Output: +---------------------+ | SecondHighestSalary | +---------------------+ | 200 | +---------------------+ Example 2: Input: Employee table: +----+--------+ | id | salary | +----+--------+ | 1 | 100 | +----+--------+ Output: +---------------------+ | SecondHighestSalary | +---------------------+ | null | +---------------------+
Amazon,202,Happy Number,Easy,"Hash Table, Math, Two Pointers",Write an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer; replace the number by the sum of the squares of its digits. Repeat the process until the number equals 1 (where it will stay); or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy. Return true if n is a happy number; and false if not. Example 1: Input: n = 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1 Example 2: Input: n = 2 Output: false Constraints: 1 <= n <= 231 - 1
Amazon,205,Isomorphic Strings,Easy,"Hash Table, String","Given two strings s and t; determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character; but a character may map to itself. Example 1: Input: s = ""egg""; t = ""add"" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = ""foo""; t = ""bar"" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = ""paper""; t = ""title"" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character."
Amazon,217,Contains Duplicate,Easy,"Array, Hash Table, Sorting",Given an integer array nums; return true if any value appears at least twice in the array; and return false if every element is distinct. Example 1: Input: nums = [1;2;3;1] Output: true Explanation: The element 1 occurs at the indices 0 and 3. Example 2: Input: nums = [1;2;3;4] Output: false Explanation: All elements are distinct. Example 3: Input: nums = [1;1;1;3;3;4;3;2;4;2] Output: true Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109
Amazon,230,Kth Smallest Element in a BST,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree; and an integer k; return the kth smallest value (1-indexed) of all the values of the nodes in the tree. Example 1: Input: root = [3;1;4;null;2]; k = 1 Output: 1 Example 2: Input: root = [5;3;6;2;4;null;null;1]; k = 3 Output: 3 Constraints: The number of nodes in the tree is n. 1 <= k <= n <= 104 0 <= Node.val <= 104 Follow up: If the BST is modified often (i.e.; we can do insert and delete operations) and you need to find the kth smallest frequently; how would you optimize?
Amazon,232,Implement Queue using Stacks,Easy,"Stack, Design, Queue","Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push; peek; pop; and empty). Implement the MyQueue class: void push(int x) Pushes element x to the back of the queue. int pop() Removes the element from the front of the queue and returns it. int peek() Returns the element at the front of the queue. boolean empty() Returns true if the queue is empty; false otherwise. Notes: You must use only standard operations of a stack; which means only push to top; peek/pop from top; size; and is empty operations are valid. Depending on your language; the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack's standard operations. Example 1: Input [""MyQueue""; ""push""; ""push""; ""peek""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 1; 1; false] Explanation MyQueue myQueue = new MyQueue(); myQueue.push(1); // queue is: [1] myQueue.push(2); // queue is: [1; 2] (leftmost is front of the queue) myQueue.peek(); // return 1 myQueue.pop(); // return 1; queue is [2] myQueue.empty(); // return false Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; peek; and empty. All the calls to pop and peek are valid. Follow-up: Can you implement the queue such that each operation is amortized O(1) time complexity? In other words; performing n operations will take overall O(n) time even if one of those operations may take longer."
Amazon,344,Reverse String,Easy,"Two Pointers, String","Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory. Example 1: Input: s = [""h"";""e"";""l"";""l"";""o""] Output: [""o"";""l"";""l"";""e"";""h""] Example 2: Input: s = [""H"";""a"";""n"";""n"";""a"";""h""] Output: [""h"";""a"";""n"";""n"";""a"";""H""] Constraints: 1 <= s.length <= 105 s[i] is a printable ascii character."
Amazon,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
Amazon,417,Pacific Atlantic Water Flow,Med,"Array, Depth-First Search, Breadth-First Search, Matrix",There is an m x n rectangular island that borders both the Pacific Ocean and Atlantic Ocean. The Pacific Ocean touches the island's left and top edges; and the Atlantic Ocean touches the island's right and bottom edges. The island is partitioned into a grid of square cells. You are given an m x n integer matrix heights where heights[r][c] represents the height above sea level of the cell at coordinate (r; c). The island receives a lot of rain; and the rain water can flow to neighboring cells directly north; south; east; and west if the neighboring cell's height is less than or equal to the current cell's height. Water can flow from any cell adjacent to an ocean into the ocean. Return a 2D list of grid coordinates result where result[i] = [ri; ci] denotes that rain water can flow from cell (ri; ci) to both the Pacific and Atlantic oceans. Example 1: Input: heights = [[1;2;2;3;5];[3;2;3;4;4];[2;4;5;3;1];[6;7;1;4;5];[5;1;1;2;4]] Output: [[0;4];[1;3];[1;4];[2;2];[3;0];[3;1];[4;0]] Explanation: The following cells can flow to the Pacific and Atlantic oceans; as shown below: [0;4]: [0;4] -> Pacific Ocean [0;4] -> Atlantic Ocean [1;3]: [1;3] -> [0;3] -> Pacific Ocean [1;3] -> [1;4] -> Atlantic Ocean [1;4]: [1;4] -> [1;3] -> [0;3] -> Pacific Ocean [1;4] -> Atlantic Ocean [2;2]: [2;2] -> [1;2] -> [0;2] -> Pacific Ocean [2;2] -> [2;3] -> [2;4] -> Atlantic Ocean [3;0]: [3;0] -> Pacific Ocean [3;0] -> [4;0] -> Atlantic Ocean [3;1]: [3;1] -> [3;0] -> Pacific Ocean [3;1] -> [4;1] -> Atlantic Ocean [4;0]: [4;0] -> Pacific Ocean [4;0] -> Atlantic Ocean Note that there are other possible paths for these cells to flow to the Pacific and Atlantic oceans. Example 2: Input: heights = [[1]] Output: [[0;0]] Explanation: The water can flow from the only cell to the Pacific and Atlantic oceans. Constraints: m == heights.length n == heights[r].length 1 <= m; n <= 200 0 <= heights[r][c] <= 105
Amazon,438,Find All Anagrams in a String,Med,"Hash Table, String, Sliding Window","Given two strings s and p; return an array of all the start indices of p's anagrams in s. You may return the answer in any order. Example 1: Input: s = ""cbaebabacd""; p = ""abc"" Output: [0;6] Explanation: The substring with start index = 0 is ""cba""; which is an anagram of ""abc"". The substring with start index = 6 is ""bac""; which is an anagram of ""abc"". Example 2: Input: s = ""abab""; p = ""ab"" Output: [0;1;2] Explanation: The substring with start index = 0 is ""ab""; which is an anagram of ""ab"". The substring with start index = 1 is ""ba""; which is an anagram of ""ab"". The substring with start index = 2 is ""ab""; which is an anagram of ""ab"". Constraints: 1 <= s.length; p.length <= 3 * 104 s and p consist of lowercase English letters."
Amazon,442,Find All Duplicates in an Array,Med,"Array, Hash Table",Given an integer array nums of length n where all the integers of nums are in the range [1; n] and each integer appears at most twice; return an array of all the integers that appears twice. You must write an algorithm that runs in O(n) time and uses only constant auxiliary space; excluding the space needed to store the output Example 1: Input: nums = [4;3;2;7;8;2;3;1] Output: [2;3] Example 2: Input: nums = [1;1;2] Output: [1] Example 3: Input: nums = [1] Output: [] Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i] <= n Each element in nums appears once or twice.
Amazon,503,Next Greater Element II,Med,"Array, Stack, Monotonic Stack",Given a circular integer array nums (i.e.; the next element of nums[nums.length - 1] is nums[0]); return the next greater number for every element in nums. The next greater number of a number x is the first greater number to its traversing-order next in the array; which means you could search circularly to find its next greater number. If it doesn't exist; return -1 for this number. Example 1: Input: nums = [1;2;1] Output: [2;-1;2] Explanation: The first 1's next greater number is 2; The number 2 can't find next greater number. The second 1's next greater number needs to search circularly; which is also 2. Example 2: Input: nums = [1;2;3;4;3] Output: [2;3;4;-1;4] Constraints: 1 <= nums.length <= 104 -109 <= nums[i] <= 109
Amazon,539,Minimum Time Difference,Med,"Array, Math, String, Sorting","Given a list of 24-hour clock time points in ""HH:MM"" format; return the minimum minutes difference between any two time-points in the list. Example 1: Input: timePoints = [""23:59"";""00:00""] Output: 1 Example 2: Input: timePoints = [""00:00"";""23:59"";""00:00""] Output: 0 Constraints: 2 <= timePoints.length <= 2 * 104 timePoints[i] is in the format ""HH:MM""."
Amazon,542,01 Matrix,Med,"Array, Dynamic Programming, Breadth-First Search, Matrix",Given an m x n binary matrix mat; return the distance of the nearest 0 for each cell. The distance between two adjacent cells is 1. Example 1: Input: mat = [[0;0;0];[0;1;0];[0;0;0]] Output: [[0;0;0];[0;1;0];[0;0;0]] Example 2: Input: mat = [[0;0;0];[0;1;0];[1;1;1]] Output: [[0;0;0];[0;1;0];[1;2;1]] Constraints: m == mat.length n == mat[i].length 1 <= m; n <= 104 1 <= m * n <= 104 mat[i][j] is either 0 or 1. There is at least one 0 in mat.
Amazon,547,Number of Provinces,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",There are n cities. Some of them are connected; while some are not. If city a is connected directly with city b; and city b is connected directly with city c; then city a is connected indirectly with city c. A province is a group of directly or indirectly connected cities and no other cities outside of the group. You are given an n x n matrix isConnected where isConnected[i][j] = 1 if the ith city and the jth city are directly connected; and isConnected[i][j] = 0 otherwise. Return the total number of provinces. Example 1: Input: isConnected = [[1;1;0];[1;1;0];[0;0;1]] Output: 2 Example 2: Input: isConnected = [[1;0;0];[0;1;0];[0;0;1]] Output: 3 Constraints: 1 <= n <= 200 n == isConnected.length n == isConnected[i].length isConnected[i][j] is 1 or 0. isConnected[i][i] == 1 isConnected[i][j] == isConnected[j][i]
Amazon,670,Maximum Swap,Med,"Math, Greedy",You are given an integer num. You can swap two digits at most once to get the maximum valued number. Return the maximum valued number you can get. Example 1: Input: num = 2736 Output: 7236 Explanation: Swap the number 2 and the number 7. Example 2: Input: num = 9973 Output: 9973 Explanation: No swap. Constraints: 0 <= num <= 108
Amazon,729,My Calendar I,Med,"Array, Binary Search, Design, Segment Tree, Ordered Set","You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a double booking. A double booking happens when two events have some non-empty intersection (i.e.; some moment is common to both events.). The event can be represented as a pair of integers startTime and endTime that represents a booking on the half-open interval [startTime; endTime); the range of real numbers x such that startTime <= x < endTime. Implement the MyCalendar class: MyCalendar() Initializes the calendar object. boolean book(int startTime; int endTime) Returns true if the event can be added to the calendar successfully without causing a double booking. Otherwise; return false and do not add the event to the calendar. Example 1: Input [""MyCalendar""; ""book""; ""book""; ""book""] [[]; [10; 20]; [15; 25]; [20; 30]] Output [null; true; false; true] Explanation MyCalendar myCalendar = new MyCalendar(); myCalendar.book(10; 20); // return True myCalendar.book(15; 25); // return False; It can not be booked because time 15 is already booked by another event. myCalendar.book(20; 30); // return True; The event can be booked; as the first event takes every time less than 20; but not including 20. Constraints: 0 <= start < end <= 109 At most 1000 calls will be made to book."
Amazon,787,Cheapest Flights Within K Stops,Med,"Array, Breadth-First Search, Matrix",On an 2 x 3 board; there are five tiles labeled from 1 to 5; and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of the board is solved if and only if the board is [[1;2;3];[4;5;0]]. Given the puzzle board board; return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved; return -1. Example 1: Input: board = [[1;2;3];[4;0;5]] Output: 1 Explanation: Swap the 0 and the 5 in one move. Example 2: Input: board = [[1;2;3];[5;4;0]] Output: -1 Explanation: No number of moves will make the board solved. Example 3: Input: board = [[4;1;2];[5;0;3]] Output: 5 Explanation: 5 is the smallest number of moves that solves the board. An example path: After move 0: [[4;1;2];[5;0;3]] After move 1: [[4;1;2];[0;5;3]] After move 2: [[0;1;2];[4;5;3]] After move 3: [[1;0;2];[4;5;3]] After move 4: [[1;2;0];[4;5;3]] After move 5: [[1;2;3];[4;5;0]] Constraints: board.length == 2 board[i].length == 3 0 <= board[i][j] <= 5 Each value board[i][j] is unique.
Amazon,794,Valid Tic-Tac-Toe State,Med,"Array, Binary Search, Depth-First Search, Breadth-First Search, Union Find, Heap (Priority Queue), Matrix",You are given an n x n integer matrix grid where each value grid[i][j] represents the elevation at that point (i; j). The rain starts to fall. At time t; the depth of the water everywhere is t. You can swim from a square to another 4-directionally adjacent square if and only if the elevation of both squares individually are at most t. You can swim infinite distances in zero time. Of course; you must stay within the boundaries of the grid during your swim. Return the least time until you can reach the bottom right square (n - 1; n - 1) if you start at the top left square (0; 0). Example 1: Input: grid = [[0;2];[1;3]] Output: 3 Explanation: At time 0; you are in grid location (0; 0). You cannot go anywhere else because 4-directionally adjacent neighbors have a higher elevation than t = 0. You cannot reach point (1; 1) until time 3. When the depth of water is 3; we can swim anywhere inside the grid. Example 2: Input: grid = [[0;1;2;3;4];[24;23;22;21;5];[12;13;14;15;16];[11;17;18;19;20];[10;9;8;7;6]] Output: 16 Explanation: The final route is shown. We need to wait until time 16 so that (0; 0) and (4; 4) are connected. Constraints: n == grid.length n == grid[i].length 1 <= n <= 50 0 <= grid[i][j] < n2 Each value grid[i][j] is unique.
Amazon,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
Amazon,909,Snakes and Ladders,Med,"Array, Math, Dynamic Programming, Game Theory",Alice and Bob play a game with piles of stones. There are an even number of piles arranged in a row; and each pile has a positive integer number of stones piles[i]. The objective of the game is to end with the most stones. The total number of stones across all the piles is odd; so there are no ties. Alice and Bob take turns; with Alice starting first. Each turn; a player takes the entire pile of stones either from the beginning or from the end of the row. This continues until there are no more piles left; at which point the person with the most stones wins. Assuming Alice and Bob play optimally; return true if Alice wins the game; or false if Bob wins. Example 1: Input: piles = [5;3;4;5] Output: true Explanation: Alice starts first; and can only take the first 5 or the last 5. Say she takes the first 5; so that the row becomes [3; 4; 5]. If Bob takes 3; then the board is [4; 5]; and Alice takes 5 to win with 10 points. If Bob takes the last 5; then the board is [3; 4]; and Alice takes 4 to win with 9 points. This demonstrated that taking the first 5 was a winning move for Alice; so we return true. Example 2: Input: piles = [3;7;2;3] Output: true Constraints: 2 <= piles.length <= 500 piles.length is even. 1 <= piles[i] <= 500 sum(piles[i]) is odd.
Amazon,937,Reorder Data in Log Files,Med,"Stack, Design, Monotonic Stack, Data Stream","Design an algorithm that collects daily price quotes for some stock and returns the span of that stock's price for the current day. The span of the stock's price in one day is the maximum number of consecutive days (starting from that day and going backward) for which the stock price was less than or equal to the price of that day. For example; if the prices of the stock in the last four days is [7;2;1;2] and the price of the stock today is 2; then the span of today is 4 because starting from today; the price of the stock was less than or equal 2 for 4 consecutive days. Also; if the prices of the stock in the last four days is [7;34;1;2] and the price of the stock today is 8; then the span of today is 3 because starting from today; the price of the stock was less than or equal 8 for 3 consecutive days. Implement the StockSpanner class: StockSpanner() Initializes the object of the class. int next(int price) Returns the span of the stock's price given that today's price is price. Example 1: Input [""StockSpanner""; ""next""; ""next""; ""next""; ""next""; ""next""; ""next""; ""next""] [[]; [100]; [80]; [60]; [70]; [60]; [75]; [85]] Output [null; 1; 1; 1; 2; 1; 4; 6] Explanation StockSpanner stockSpanner = new StockSpanner(); stockSpanner.next(100); // return 1 stockSpanner.next(80); // return 1 stockSpanner.next(60); // return 1 stockSpanner.next(70); // return 2 stockSpanner.next(60); // return 1 stockSpanner.next(75); // return 4; because the last 4 prices (including today's price of 75) were less than or equal to today's price. stockSpanner.next(85); // return 6 Constraints: 1 <= price <= 105 At most 104 calls will be made to next."
Amazon,977,Squares of a Sorted Array,Easy,"String, Dynamic Programming","Given a string s; return the number of distinct non-empty subsequences of s. Since the answer may be very large; return it modulo 109 + 7. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not. Example 1: Input: s = ""abc"" Output: 7 Explanation: The 7 distinct subsequences are ""a""; ""b""; ""c""; ""ab""; ""ac""; ""bc""; and ""abc"". Example 2: Input: s = ""aba"" Output: 6 Explanation: The 6 distinct subsequences are ""a""; ""b""; ""ab""; ""aa""; ""ba""; and ""aba"". Example 3: Input: s = ""aaa"" Output: 3 Explanation: The 3 distinct subsequences are ""a""; ""aa"" and ""aaa"". Constraints: 1 <= s.length <= 2000 s consists of lowercase English letters."
Amazon,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Amazon,1010,Pairs of Songs With Total Durations Divisible by 60,Med,"Hash Table, Math, Enumeration",Given three integers x; y; and bound; return a list of all the powerful integers that have a value less than or equal to bound. An integer is powerful if it can be represented as xi + yj for some integers i >= 0 and j >= 0. You may return the answer in any order. In your answer; each value should occur at most once. Example 1: Input: x = 2; y = 3; bound = 10 Output: [2;3;4;5;7;9;10] Explanation: 2 = 20 + 30 3 = 21 + 30 4 = 20 + 31 5 = 21 + 31 7 = 22 + 31 9 = 23 + 30 10 = 20 + 32 Example 2: Input: x = 3; y = 5; bound = 15 Output: [2;4;6;8;10;14] Constraints: 1 <= x; y <= 100 0 <= bound <= 106
Amazon,1091,Shortest Path in Binary Matrix,Med,"Tree, Depth-First Search, Binary Tree",
Amazon,1331,Rank Transform of an Array,Easy,"Array, Backtracking, Matrix",In a gold mine grid of size m x n; each cell in this mine has an integer representing the amount of gold in that cell; 0 if it is empty. Return the maximum amount of gold you can collect under the conditions: Every time you are located in a cell you will collect all the gold in that cell. From your position; you can walk one step to the left; right; up; or down. You can't visit the same cell more than once. Never visit a cell with 0 gold. You can start and stop collecting gold from any position in the grid that has some gold. Example 1: Input: grid = [[0;6;0];[5;8;7];[0;9;0]] Output: 24 Explanation: [[0;6;0]; [5;8;7]; [0;9;0]] Path to get the maximum gold; 9 -> 8 -> 7. Example 2: Input: grid = [[1;0;7];[2;0;6];[3;4;5];[0;3;0];[9;0;20]] Output: 28 Explanation: [[1;0;7]; [2;0;6]; [3;4;5]; [0;3;0]; [9;0;20]] Path to get the maximum gold; 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 15 0 <= grid[i][j] <= 100 There are at most 25 cells containing gold.
Amazon,1209,Remove All Adjacent Duplicates in String II,Med,Concurrency,
Amazon,1482,Minimum Number of Days to Make m Bouquets,Med,"Array, Hash Table, Sorting, Counting",Given the array nums; for each nums[i] find out how many numbers in the array are smaller than it. That is; for each nums[i] you have to count the number of valid j's such that j != i and nums[j] < nums[i]. Return the answer in an array. Example 1: Input: nums = [8;1;2;2;3] Output: [4;0;1;1;3] Explanation: For nums[0]=8 there exist four smaller numbers than it (1; 2; 2 and 3). For nums[1]=1 does not exist any smaller number than it. For nums[2]=2 there exist one smaller number than it (1). For nums[3]=2 there exist one smaller number than it (1). For nums[4]=3 there exist three smaller numbers than it (1; 2 and 2). Example 2: Input: nums = [6;5;4;8] Output: [2;1;0;3] Example 3: Input: nums = [7;7;7;7] Output: [0;0;0;0] Constraints: 2 <= nums.length <= 500 0 <= nums[i] <= 100
Amazon,2696,Minimum String Length After Removing Substrings,Easy,"Array, Hash Table, Math, Dynamic Programming, Backtracking, Sorting, Combinatorics",You are given an array nums of positive integers and a positive integer k. A subset of nums is beautiful if it does not contain two integers with an absolute difference equal to k. Return the number of non-empty beautiful subsets of the array nums. A subset of nums is an array that can be obtained by deleting some (possibly none) elements from nums. Two subsets are different if and only if the chosen indices to delete are different. Example 1: Input: nums = [2;4;6]; k = 2 Output: 4 Explanation: The beautiful subsets of the array nums are: [2]; [4]; [6]; [2; 6]. It can be proved that there are only 4 beautiful subsets in the array [2;4;6]. Example 2: Input: nums = [1]; k = 1 Output: 1 Explanation: The beautiful subset of the array nums is [1]. It can be proved that there is only 1 beautiful subset in the array [1]. Constraints: 1 <= nums.length <= 20 1 <= nums[i]; k <= 1000
Amazon,2938,Separate Black and White Balls,Med,,
Amazon,3163,String Compression III,Med,"Array, Hash Table",You are given a 0-indexed integer array nums. The distinct count of a subarray of nums is defined as: Let nums[i..j] be a subarray of nums consisting of all the indices from i to j such that 0 <= i <= j < nums.length. Then the number of distinct values in nums[i..j] is called the distinct count of nums[i..j]. Return the sum of the squares of distinct counts of all subarrays of nums. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;2;1] Output: 15 Explanation: Six possible subarrays are: [1]: 1 distinct value [2]: 1 distinct value [1]: 1 distinct value [1;2]: 2 distinct values [2;1]: 2 distinct values [1;2;1]: 2 distinct values The sum of the squares of the distinct counts in all subarrays is equal to 12 + 12 + 12 + 22 + 22 + 22 = 15. Example 2: Input: nums = [1;1] Output: 3 Explanation: Three possible subarrays are: [1]: 1 distinct value [1]: 1 distinct value [1;1]: 1 distinct value The sum of the squares of the distinct counts in all subarrays is equal to 12 + 12 + 12 = 3. Constraints: 1 <= nums.length <= 100 1 <= nums[i] <= 100
Amazon,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Amazon,24,Swap Nodes in Pairs,Med,"Linked List, Recursion",Given a linked list; swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e.; only nodes themselves may be changed.) Example 1: Input: head = [1;2;3;4] Output: [2;1;4;3] Explanation: Example 2: Input: head = [] Output: [] Example 3: Input: head = [1] Output: [1] Example 4: Input: head = [1;2;3] Output: [2;1;3] Constraints: The number of nodes in the list is in the range [0; 100]. 0 <= Node.val <= 100
Amazon,26,Remove Duplicates from Sorted Array,Easy,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums. Consider the number of unique elements of nums to be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;2] Output: 2; nums = [1;2;_] Explanation: Your function should return k = 2; with the first two elements of nums being 1 and 2 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;2;2;3;3;4] Output: 5; nums = [0;1;2;3;4;_;_;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums being 0; 1; 2; 3; and 4 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -100 <= nums[i] <= 100 nums is sorted in non-decreasing order.
Amazon,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Amazon,38,Count and Say,Med,String,"The count-and-say sequence is a sequence of digit strings defined by the recursive formula: countAndSay(1) = ""1"" countAndSay(n) is the run-length encoding of countAndSay(n - 1). Run-length encoding (RLE) is a string compression method that works by replacing consecutive identical characters (repeated 2 or more times) with the concatenation of the character and the number marking the count of the characters (length of the run). For example; to compress the string ""3322251"" we replace ""33"" with ""23""; replace ""222"" with ""32""; replace ""5"" with ""15"" and replace ""1"" with ""11"". Thus the compressed string becomes ""23321511"". Given a positive integer n; return the nth element of the count-and-say sequence. Example 1: Input: n = 4 Output: ""1211"" Explanation: countAndSay(1) = ""1"" countAndSay(2) = RLE of ""1"" = ""11"" countAndSay(3) = RLE of ""11"" = ""21"" countAndSay(4) = RLE of ""21"" = ""1211"" Example 2: Input: n = 1 Output: ""1"" Explanation: This is the base case. Constraints: 1 <= n <= 30 Follow up: Could you solve it iteratively?"
Amazon,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
Amazon,44,Wildcard Matching,Hard,"String, Dynamic Programming, Greedy, Recursion","Given an input string (s) and a pattern (p); implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""*"" Output: true Explanation: '*' matches any sequence. Example 3: Input: s = ""cb""; p = ""?a"" Output: false Explanation: '?' matches 'c'; but the second letter is 'a'; which does not match 'b'. Constraints: 0 <= s.length; p.length <= 2000 s contains only lowercase English letters. p contains only lowercase English letters; '?' or '*'."
Amazon,61,Rotate List,Med,"Linked List, Two Pointers",Given the head of a linked list; rotate the list to the right by k places. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [4;5;1;2;3] Example 2: Input: head = [0;1;2]; k = 4 Output: [2;0;1] Constraints: The number of nodes in the list is in the range [0; 500]. -100 <= Node.val <= 100 0 <= k <= 2 * 109
Amazon,67,Add Binary,Easy,"Math, String, Bit Manipulation, Simulation","Given two binary strings a and b; return their sum as a binary string. Example 1: Input: a = ""11""; b = ""1"" Output: ""100"" Example 2: Input: a = ""1010""; b = ""1011"" Output: ""10101"" Constraints: 1 <= a.length; b.length <= 104 a and b consist only of '0' or '1' characters. Each string does not contain leading zeros except for the zero itself."
Amazon,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
Amazon,73,Set Matrix Zeroes,Med,"Array, Hash Table, Matrix",Given an m x n integer matrix matrix; if an element is 0; set its entire row and column to 0's. You must do it in place. Example 1: Input: matrix = [[1;1;1];[1;0;1];[1;1;1]] Output: [[1;0;1];[0;0;0];[1;0;1]] Example 2: Input: matrix = [[0;1;2;0];[3;4;5;2];[1;3;1;5]] Output: [[0;0;0;0];[0;4;5;0];[0;3;1;0]] Constraints: m == matrix.length n == matrix[0].length 1 <= m; n <= 200 -231 <= matrix[i][j] <= 231 - 1 Follow up: A straightforward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space; but still not the best solution. Could you devise a constant space solution?
Amazon,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Amazon,80,Remove Duplicates from Sorted Array II,Med,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same. Since it is impossible to change the length of the array in some languages; you must instead have the result be placed in the first part of the array nums. More formally; if there are k elements after removing the duplicates; then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements. Return k after placing the final result in the first k slots of nums. Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;1;2;2;3] Output: 5; nums = [1;1;2;2;3;_] Explanation: Your function should return k = 5; with the first five elements of nums being 1; 1; 2; 2 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;1;2;3;3] Output: 7; nums = [0;0;1;1;2;3;3;_;_] Explanation: Your function should return k = 7; with the first seven elements of nums being 0; 0; 1; 1; 2; 3 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -104 <= nums[i] <= 104 nums is sorted in non-decreasing order.
Amazon,83,Remove Duplicates from Sorted List,Easy,Linked List,Given the head of a sorted linked list; delete all duplicates such that each element appears only once. Return the linked list sorted as well. Example 1: Input: head = [1;1;2] Output: [1;2] Example 2: Input: head = [1;1;2;3;3] Output: [1;2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Amazon,95,Unique Binary Search Trees II,Med,"Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree",Given an integer n; return all the structurally unique BST's (binary search trees); which has exactly n nodes of unique values from 1 to n. Return the answer in any order. Example 1: Input: n = 3 Output: [[1;null;2;null;3];[1;null;3;2];[2;1;3];[3;1;null;null;2];[3;2;null;1]] Example 2: Input: n = 1 Output: [[1]] Constraints: 1 <= n <= 8
Amazon,97,Interleaving String,Med,"String, Dynamic Programming","Given strings s1; s2; and s3; find whether s3 is formed by an interleaving of s1 and s2. An interleaving of two strings s and t is a configuration where s and t are divided into n and m substrings respectively; such that: s = s1 + s2 + ... + sn t = t1 + t2 + ... + tm |n - m| <= 1 The interleaving is s1 + t1 + s2 + t2 + s3 + t3 + ... or t1 + s1 + t2 + s2 + t3 + s3 + ... Note: a + b is the concatenation of strings a and b. Example 1: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbcbcac"" Output: true Explanation: One way to obtain s3 is: Split s1 into s1 = ""aa"" + ""bc"" + ""c""; and s2 into s2 = ""dbbc"" + ""a"". Interleaving the two splits; we get ""aa"" + ""dbbc"" + ""bc"" + ""a"" + ""c"" = ""aadbbcbcac"". Since s3 can be obtained by interleaving s1 and s2; we return true. Example 2: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbbaccc"" Output: false Explanation: Notice how it is impossible to interleave s2 with any other string to obtain s3. Example 3: Input: s1 = """"; s2 = """"; s3 = """" Output: true Constraints: 0 <= s1.length; s2.length <= 100 0 <= s3.length <= 200 s1; s2; and s3 consist of lowercase English letters. Follow up: Could you solve it using only O(s2.length) additional memory space?"
Amazon,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Amazon,101,Symmetric Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; check whether it is a mirror of itself (i.e.; symmetric around its center). Example 1: Input: root = [1;2;2;3;4;4;3] Output: true Example 2: Input: root = [1;2;2;null;3;null;3] Output: false Constraints: The number of nodes in the tree is in the range [1; 1000]. -100 <= Node.val <= 100 Follow up: Could you solve it both recursively and iteratively?
Amazon,107,Binary Tree Level Order Traversal II,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the bottom-up level order traversal of its nodes' values. (i.e.; from left to right; level by level from leaf to root). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[15;7];[9;20];[3]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -1000 <= Node.val <= 1000
Amazon,110,Balanced Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given a binary tree; determine if it is height-balanced. Example 1: Input: root = [3;9;20;null;null;15;7] Output: true Example 2: Input: root = [1;2;2;3;3;null;null;4;4] Output: false Example 3: Input: root = [] Output: true Constraints: The number of nodes in the tree is in the range [0; 5000]. -104 <= Node.val <= 104
Amazon,113,Path Sum II,Med,"Backtracking, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path should be returned as a list of the node values; not node references. A root-to-leaf path is a path starting from the root and ending at any leaf node. A leaf is a node with no children. Example 1: Input: root = [5;4;8;11;null;13;4;7;2;null;null;5;1]; targetSum = 22 Output: [[5;4;11;2];[5;8;4;5]] Explanation: There are two paths whose sum equals targetSum: 5 + 4 + 11 + 2 = 22 5 + 8 + 4 + 5 = 22 Example 2: Input: root = [1;2;3]; targetSum = 5 Output: [] Example 3: Input: root = [1;2]; targetSum = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 5000]. -1000 <= Node.val <= 1000 -1000 <= targetSum <= 1000
Amazon,116,Populating Next Right Pointers in Each Node,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given a perfect binary tree where all leaves are on the same level; and every parent has two children. The binary tree has the following definition: struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;6;7] Output: [1;#;2;3;#;4;5;6;7;#] Explanation: Given the above perfect binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 212 - 1]. -1000 <= Node.val <= 1000 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Amazon,120,Triangle,Med,"Array, Dynamic Programming",Given a triangle array; return the minimum path sum from top to bottom. For each step; you may move to an adjacent number of the row below. More formally; if you are on index i on the current row; you may move to either index i or index i + 1 on the next row. Example 1: Input: triangle = [[2];[3;4];[6;5;7];[4;1;8;3]] Output: 11 Explanation: The triangle looks like: 2 3 4 6 5 7 4 1 8 3 The minimum path sum from top to bottom is 2 + 3 + 5 + 1 = 11 (underlined above). Example 2: Input: triangle = [[-10]] Output: -10 Constraints: 1 <= triangle.length <= 200 triangle[0].length == 1 triangle[i].length == triangle[i - 1].length + 1 -104 <= triangle[i][j] <= 104 Follow up: Could you do this using only O(n) extra space; where n is the total number of rows in the triangle?
Amazon,140,Word Break II,Hard,"Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization","Given a string s and a dictionary of strings wordDict; add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""catsanddog""; wordDict = [""cat"";""cats"";""and"";""sand"";""dog""] Output: [""cats and dog"";""cat sand dog""] Example 2: Input: s = ""pineapplepenapple""; wordDict = [""apple"";""pen"";""applepen"";""pine"";""pineapple""] Output: [""pine apple pen apple"";""pineapple pen apple"";""pine applepen apple""] Explanation: Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: [] Constraints: 1 <= s.length <= 20 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 10 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique. Input is generated in a way that the length of the answer doesn't exceed 105."
Amazon,141,Linked List Cycle,Easy,"Hash Table, Linked List, Two Pointers",Given head; the head of a linked list; determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise; return false. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 1st node (0-indexed). Example 2: Input: head = [1;2]; pos = 0 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 0th node. Example 3: Input: head = [1]; pos = -1 Output: false Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Amazon,148,Sort List,Med,"Linked List, Two Pointers, Divide and Conquer, Sorting, Merge Sort",Given the head of a linked list; return the list after sorting it in ascending order. Example 1: Input: head = [4;2;1;3] Output: [1;2;3;4] Example 2: Input: head = [-1;5;3;4;0] Output: [-1;0;3;4;5] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is in the range [0; 5 * 104]. -105 <= Node.val <= 105 Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?
Amazon,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
Amazon,160,Intersection of Two Linked Lists,Easy,"Hash Table, Linked List, Two Pointers",Given the heads of two singly linked-lists headA and headB; return the node at which the two lists intersect. If the two linked lists have no intersection at all; return null. For example; the following two linked lists begin to intersect at node c1: The test cases are generated such that there are no cycles anywhere in the entire linked structure. Note that the linked lists must retain their original structure after the function returns. Custom Judge: The inputs to the judge are given as follows (your program is not given these inputs): intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node. listA - The first linked list. listB - The second linked list. skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node. skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node. The judge will then create the linked structure based on these inputs and pass the two heads; headA and headB to your program. If you correctly return the intersected node; then your solution will be accepted. Example 1: Input: intersectVal = 8; listA = [4;1;8;4;5]; listB = [5;6;1;8;4;5]; skipA = 2; skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [4;1;8;4;5]. From the head of B; it reads as [5;6;1;8;4;5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words; they point to two different locations in memory; while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory. Example 2: Input: intersectVal = 2; listA = [1;9;1;2;4]; listB = [3;2;4]; skipA = 3; skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [1;9;1;2;4]. From the head of B; it reads as [3;2;4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B. Example 3: Input: intersectVal = 0; listA = [2;6;4]; listB = [1;5]; skipA = 3; skipB = 2 Output: No intersection Explanation: From the head of A; it reads as [2;6;4]. From the head of B; it reads as [1;5]. Since the two lists do not intersect; intersectVal must be 0; while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect; so return null. Constraints: The number of nodes of listA is in the m. The number of nodes of listB is in the n. 1 <= m; n <= 3 * 104 1 <= Node.val <= 105 0 <= skipA <= m 0 <= skipB <= n intersectVal is 0 if listA and listB do not intersect. intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect. Follow up: Could you write a solution that runs in O(m + n) time and use only O(1) memory?
Amazon,175,Combine Two Tables,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | personId | int | | lastName | varchar | | firstName | varchar | +-------------+---------+ personId is the primary key (column with unique values) for this table. This table contains information about the ID of some persons and their first and last names. Table: Address +-------------+---------+ | Column Name | Type | +-------------+---------+ | addressId | int | | personId | int | | city | varchar | | state | varchar | +-------------+---------+ addressId is the primary key (column with unique values) for this table. Each row of this table contains information about the city and state of one person with ID = PersonId. Write a solution to report the first name; last name; city; and state of each person in the Person table. If the address of a personId is not present in the Address table; report null instead. Return the result table in any order. The result format is in the following example. Example 1: Input: Person table: +----------+----------+-----------+ | personId | lastName | firstName | +----------+----------+-----------+ | 1 | Wang | Allen | | 2 | Alice | Bob | +----------+----------+-----------+ Address table: +-----------+----------+---------------+------------+ | addressId | personId | city | state | +-----------+----------+---------------+------------+ | 1 | 2 | New York City | New York | | 2 | 3 | Leetcode | California | +-----------+----------+---------------+------------+ Output: +-----------+----------+---------------+----------+ | firstName | lastName | city | state | +-----------+----------+---------------+----------+ | Allen | Wang | Null | Null | | Bob | Alice | New York City | New York | +-----------+----------+---------------+----------+ Explanation: There is no address in the address table for the personId = 1 so we return null in their city and state. addressId = 1 contains information about the address of personId = 2.
Amazon,181,Employees Earning More Than Their Managers,Easy,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | salary | int | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID of an employee; their name; salary; and the ID of their manager. Write a solution to find the employees who earn more than their managers. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +----+-------+--------+-----------+ | id | name | salary | managerId | +----+-------+--------+-----------+ | 1 | Joe | 70000 | 3 | | 2 | Henry | 80000 | 4 | | 3 | Sam | 60000 | Null | | 4 | Max | 90000 | Null | +----+-------+--------+-----------+ Output: +----------+ | Employee | +----------+ | Joe | +----------+ Explanation: Joe is the only employee who earns more than his manager.
Amazon,187,Repeated DNA Sequences,Med,"Hash Table, String, Bit Manipulation, Sliding Window, Rolling Hash, Hash Function","The DNA sequence is composed of a series of nucleotides abbreviated as 'A'; 'C'; 'G'; and 'T'. For example; ""ACGAATTCCG"" is a DNA sequence. When studying DNA; it is useful to identify repeated sequences within the DNA. Given a string s that represents a DNA sequence; return all the 10-letter-long sequences (substrings) that occur more than once in a DNA molecule. You may return the answer in any order. Example 1: Input: s = ""AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"" Output: [""AAAAACCCCC"";""CCCCCAAAAA""] Example 2: Input: s = ""AAAAAAAAAAAAA"" Output: [""AAAAAAAAAA""] Constraints: 1 <= s.length <= 105 s[i] is either 'A'; 'C'; 'G'; or 'T'."
Amazon,188,Best Time to Buy and Sell Stock IV,Hard,"Array, Dynamic Programming",You are given an integer array prices where prices[i] is the price of a given stock on the ith day; and an integer k. Find the maximum profit you can achieve. You may complete at most k transactions: i.e. you may buy at most k times and sell at most k times. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: k = 2; prices = [2;4;1] Output: 2 Explanation: Buy on day 1 (price = 2) and sell on day 2 (price = 4); profit = 4-2 = 2. Example 2: Input: k = 2; prices = [3;2;6;5;0;3] Output: 7 Explanation: Buy on day 2 (price = 2) and sell on day 3 (price = 6); profit = 6-2 = 4. Then buy on day 5 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Constraints: 1 <= k <= 100 1 <= prices.length <= 1000 0 <= prices[i] <= 1000
Amazon,214,Shortest Palindrome,Hard,"String, Rolling Hash, String Matching, Hash Function","You are given a string s. You can convert s to a palindrome by adding characters in front of it. Return the shortest palindrome you can find by performing this transformation. Example 1: Input: s = ""aacecaaa"" Output: ""aaacecaaa"" Example 2: Input: s = ""abcd"" Output: ""dcbabcd"" Constraints: 0 <= s.length <= 5 * 104 s consists of lowercase English letters only."
Amazon,225,Implement Stack using Queues,Easy,"Stack, Design, Queue","Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push; top; pop; and empty). Implement the MyStack class: void push(int x) Pushes element x to the top of the stack. int pop() Removes the element on the top of the stack and returns it. int top() Returns the element on the top of the stack. boolean empty() Returns true if the stack is empty; false otherwise. Notes: You must use only standard operations of a queue; which means that only push to back; peek/pop from front; size and is empty operations are valid. Depending on your language; the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations. Example 1: Input [""MyStack""; ""push""; ""push""; ""top""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 2; 2; false] Explanation MyStack myStack = new MyStack(); myStack.push(1); myStack.push(2); myStack.top(); // return 2 myStack.pop(); // return 2 myStack.empty(); // return False Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; top; and empty. All the calls to pop and top are valid. Follow-up: Can you implement the stack using only one queue?"
Amazon,229,Majority Element II,Med,"Array, Hash Table, Sorting, Counting",Given an integer array of size n; find all elements that appear more than ⌊ n/3 ⌋ times. Example 1: Input: nums = [3;2;3] Output: [3] Example 2: Input: nums = [1] Output: [1] Example 3: Input: nums = [1;2] Output: [1;2] Constraints: 1 <= nums.length <= 5 * 104 -109 <= nums[i] <= 109 Follow up: Could you solve the problem in linear time and in O(1) space?
Amazon,231,Power of Two,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of two. Otherwise; return false. An integer n is a power of two; if there exists an integer x such that n == 2x. Example 1: Input: n = 1 Output: true Explanation: 20 = 1 Example 2: Input: n = 16 Output: true Explanation: 24 = 16 Example 3: Input: n = 3 Output: false Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Amazon,234,Palindrome Linked List,Easy,"Linked List, Two Pointers, Stack, Recursion",Given the head of a singly linked list; return true if it is a palindrome or false otherwise. Example 1: Input: head = [1;2;2;1] Output: true Example 2: Input: head = [1;2] Output: false Constraints: The number of nodes in the list is in the range [1; 105]. 0 <= Node.val <= 9 Follow up: Could you do it in O(n) time and O(1) space?
Amazon,235,Lowest Common Ancestor of a Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given a binary search tree (BST); find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [2;1]; p = 2; q = 1 Output: 2 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.
Amazon,261,Graph Valid Tree,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
Amazon,274,H-Index,Med,"Array, Sorting, Counting Sort",Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper; return the researcher's h-index. According to the definition of h-index on Wikipedia: The h-index is defined as the maximum value of h such that the given researcher has published at least h papers that have each been cited at least h times. Example 1: Input: citations = [3;0;6;1;5] Output: 3 Explanation: [3;0;6;1;5] means the researcher has 5 papers in total and each of them had received 3; 0; 6; 1; 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each; their h-index is 3. Example 2: Input: citations = [1;3;1] Output: 1 Constraints: n == citations.length 1 <= n <= 5000 0 <= citations[i] <= 1000
Amazon,279,Perfect Squares,Med,"Math, Dynamic Programming, Breadth-First Search",Given an integer n; return the least number of perfect square numbers that sum to n. A perfect square is an integer that is the square of an integer; in other words; it is the product of some integer with itself. For example; 1; 4; 9; and 16 are perfect squares while 3 and 11 are not. Example 1: Input: n = 12 Output: 3 Explanation: 12 = 4 + 4 + 4. Example 2: Input: n = 13 Output: 2 Explanation: 13 = 4 + 9. Constraints: 1 <= n <= 104
Amazon,303,Range Sum Query - Immutable,Easy,"Array, Design, Prefix Sum","Given an integer array nums; handle multiple queries of the following type: Calculate the sum of the elements of nums between indices left and right inclusive where left <= right. Implement the NumArray class: NumArray(int[] nums) Initializes the object with the integer array nums. int sumRange(int left; int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]). Example 1: Input [""NumArray""; ""sumRange""; ""sumRange""; ""sumRange""] [[[-2; 0; 3; -5; 2; -1]]; [0; 2]; [2; 5]; [0; 5]] Output [null; 1; -1; -3] Explanation NumArray numArray = new NumArray([-2; 0; 3; -5; 2; -1]); numArray.sumRange(0; 2); // return (-2) + 0 + 3 = 1 numArray.sumRange(2; 5); // return 3 + (-5) + 2 + (-1) = -1 numArray.sumRange(0; 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3 Constraints: 1 <= nums.length <= 104 -105 <= nums[i] <= 105 0 <= left <= right < nums.length At most 104 calls will be made to sumRange."
Amazon,327,Count of Range Sum,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums and two integers lower and upper; return the number of range sums that lie in [lower; upper] inclusive. Range sum S(i; j) is defined as the sum of the elements in nums between indices i and j inclusive; where i <= j. Example 1: Input: nums = [-2;5;-1]; lower = -2; upper = 2 Output: 3 Explanation: The three ranges are: [0;0]; [2;2]; and [0;2] and their respective sums are: -2; -1; 2. Example 2: Input: nums = [0]; lower = 0; upper = 0 Output: 1 Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 -105 <= lower <= upper <= 105 The answer is guaranteed to fit in a 32-bit integer.
Amazon,332,Reconstruct Itinerary,Hard,"Depth-First Search, Graph, Eulerian Circuit","You are given a list of airline tickets where tickets[i] = [fromi; toi] represent the departure and the arrival airports of one flight. Reconstruct the itinerary in order and return it. All of the tickets belong to a man who departs from ""JFK""; thus; the itinerary must begin with ""JFK"". If there are multiple valid itineraries; you should return the itinerary that has the smallest lexical order when read as a single string. For example; the itinerary [""JFK""; ""LGA""] has a smaller lexical order than [""JFK""; ""LGB""]. You may assume all tickets form at least one valid itinerary. You must use all the tickets once and only once. Example 1: Input: tickets = [[""MUC"";""LHR""];[""JFK"";""MUC""];[""SFO"";""SJC""];[""LHR"";""SFO""]] Output: [""JFK"";""MUC"";""LHR"";""SFO"";""SJC""] Example 2: Input: tickets = [[""JFK"";""SFO""];[""JFK"";""ATL""];[""SFO"";""ATL""];[""ATL"";""JFK""];[""ATL"";""SFO""]] Output: [""JFK"";""ATL"";""JFK"";""SFO"";""ATL"";""SFO""] Explanation: Another possible reconstruction is [""JFK"";""SFO"";""ATL"";""JFK"";""ATL"";""SFO""] but it is larger in lexical order. Constraints: 1 <= tickets.length <= 300 tickets[i].length == 2 fromi.length == 3 toi.length == 3 fromi and toi consist of uppercase English letters. fromi != toi"
Amazon,339,Nested List Weight Sum,Med,"Depth-First Search, Breadth-First Search",
Amazon,340,Longest Substring with At Most K Distinct Characters,Med,"Hash Table, String, Sliding Window",
Amazon,383,Ransom Note,Easy,"Hash Table, String, Counting","Given two strings ransomNote and magazine; return true if ransomNote can be constructed by using the letters from magazine and false otherwise. Each letter in magazine can only be used once in ransomNote. Example 1: Input: ransomNote = ""a""; magazine = ""b"" Output: false Example 2: Input: ransomNote = ""aa""; magazine = ""ab"" Output: false Example 3: Input: ransomNote = ""aa""; magazine = ""aab"" Output: true Constraints: 1 <= ransomNote.length; magazine.length <= 105 ransomNote and magazine consist of lowercase English letters."
Amazon,386,Lexicographical Numbers,Med,"Depth-First Search, Trie",Given an integer n; return all the numbers in the range [1; n] sorted in lexicographical order. You must write an algorithm that runs in O(n) time and uses O(1) extra space. Example 1: Input: n = 13 Output: [1;10;11;12;13;2;3;4;5;6;7;8;9] Example 2: Input: n = 2 Output: [1;2] Constraints: 1 <= n <= 5 * 104
Amazon,412,Fizz Buzz,Easy,"Math, String, Simulation","Given an integer n; return a string array answer (1-indexed) where: answer[i] == ""FizzBuzz"" if i is divisible by 3 and 5. answer[i] == ""Fizz"" if i is divisible by 3. answer[i] == ""Buzz"" if i is divisible by 5. answer[i] == i (as a string) if none of the above conditions are true. Example 1: Input: n = 3 Output: [""1"";""2"";""Fizz""] Example 2: Input: n = 5 Output: [""1"";""2"";""Fizz"";""4"";""Buzz""] Example 3: Input: n = 15 Output: [""1"";""2"";""Fizz"";""4"";""Buzz"";""Fizz"";""7"";""8"";""Fizz"";""Buzz"";""11"";""Fizz"";""13"";""14"";""FizzBuzz""] Constraints: 1 <= n <= 104"
Amazon,416,Partition Equal Subset Sum,Med,"Array, Dynamic Programming",Given an integer array nums; return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise. Example 1: Input: nums = [1;5;11;5] Output: true Explanation: The array can be partitioned as [1; 5; 5] and [11]. Example 2: Input: nums = [1;2;3;5] Output: false Explanation: The array cannot be partitioned into equal sum subsets. Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 100
Amazon,424,Longest Repeating Character Replacement,Med,"Hash Table, String, Sliding Window","You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times. Return the length of the longest substring containing the same letter you can get after performing the above operations. Example 1: Input: s = ""ABAB""; k = 2 Output: 4 Explanation: Replace the two 'A's with two 'B's or vice versa. Example 2: Input: s = ""AABABBA""; k = 1 Output: 4 Explanation: Replace the one 'A' in the middle with 'B' and form ""AABBBBA"". The substring ""BBBB"" has the longest repeating letters; which is 4. There may exists other ways to achieve this answer too. Constraints: 1 <= s.length <= 105 s consists of only uppercase English letters. 0 <= k <= s.length"
Amazon,493,Reverse Pairs,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums; return the number of reverse pairs in the array. A reverse pair is a pair (i; j) where: 0 <= i < j < nums.length and nums[i] > 2 * nums[j]. Example 1: Input: nums = [1;3;2;3;1] Output: 2 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 3; nums[4] = 1; 3 > 2 * 1 Example 2: Input: nums = [2;4;3;5;1] Output: 3 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 4; nums[4] = 1; 4 > 2 * 1 (2; 4) --> nums[2] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 5; nums[4] = 1; 5 > 2 * 1 Constraints: 1 <= nums.length <= 5 * 104 -231 <= nums[i] <= 231 - 1
Amazon,1721,Swapping Nodes in a Linked List,Med,"Array, Simulation",You are the operator of a Centennial Wheel that has four gondolas; and each gondola has room for up to four people. You have the ability to rotate the gondolas counterclockwise; which costs you runningCost dollars. You are given an array customers of length n where customers[i] is the number of new customers arriving just before the ith rotation (0-indexed). This means you must rotate the wheel i times before the customers[i] customers arrive. You cannot make customers wait if there is room in the gondola. Each customer pays boardingCost dollars when they board on the gondola closest to the ground and will exit once that gondola reaches the ground again. You can stop the wheel at any time; including before serving all customers. If you decide to stop serving customers; all subsequent rotations are free in order to get all the customers down safely. Note that if there are currently more than four customers waiting at the wheel; only four will board the gondola; and the rest will wait for the next rotation. Return the minimum number of rotations you need to perform to maximize your profit. If there is no scenario where the profit is positive; return -1. Example 1: Input: customers = [8;3]; boardingCost = 5; runningCost = 6 Output: 3 Explanation: The numbers written on the gondolas are the number of people currently there. 1. 8 customers arrive; 4 board and 4 wait for the next gondola; the wheel rotates. Current profit is 4 * $5 - 1 * $6 = $14. 2. 3 customers arrive; the 4 waiting board the wheel and the other 3 wait; the wheel rotates. Current profit is 8 * $5 - 2 * $6 = $28. 3. The final 3 customers board the gondola; the wheel rotates. Current profit is 11 * $5 - 3 * $6 = $37. The highest profit was $37 after rotating the wheel 3 times. Example 2: Input: customers = [10;9;6]; boardingCost = 6; runningCost = 4 Output: 7 Explanation: 1. 10 customers arrive; 4 board and 6 wait for the next gondola; the wheel rotates. Current profit is 4 * $6 - 1 * $4 = $20. 2. 9 customers arrive; 4 board and 11 wait (2 originally waiting; 9 newly waiting); the wheel rotates. Current profit is 8 * $6 - 2 * $4 = $40. 3. The final 6 customers arrive; 4 board and 13 wait; the wheel rotates. Current profit is 12 * $6 - 3 * $4 = $60. 4. 4 board and 9 wait; the wheel rotates. Current profit is 16 * $6 - 4 * $4 = $80. 5. 4 board and 5 wait; the wheel rotates. Current profit is 20 * $6 - 5 * $4 = $100. 6. 4 board and 1 waits; the wheel rotates. Current profit is 24 * $6 - 6 * $4 = $120. 7. 1 boards; the wheel rotates. Current profit is 25 * $6 - 7 * $4 = $122. The highest profit was $122 after rotating the wheel 7 times. Example 3: Input: customers = [3;4;0;5;1]; boardingCost = 1; runningCost = 92 Output: -1 Explanation: 1. 3 customers arrive; 3 board and 0 wait; the wheel rotates. Current profit is 3 * $1 - 1 * $92 = -$89. 2. 4 customers arrive; 4 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 2 * $92 = -$177. 3. 0 customers arrive; 0 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 3 * $92 = -$269. 4. 5 customers arrive; 4 board and 1 waits; the wheel rotates. Current profit is 11 * $1 - 4 * $92 = -$357. 5. 1 customer arrives; 2 board and 0 wait; the wheel rotates. Current profit is 13 * $1 - 5 * $92 = -$447. The profit was never positive; so return -1. Constraints: n == customers.length 1 <= n <= 105 0 <= customers[i] <= 50 1 <= boardingCost; runningCost <= 100
Amazon,543,Diameter of Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them. Example 1: Input: root = [1;2;3;4;5] Output: 3 Explanation: 3 is the length of the path [4;2;1;3] or [5;2;1;3]. Example 2: Input: root = [1;2] Output: 1 Constraints: The number of nodes in the tree is in the range [1; 104]. -100 <= Node.val <= 100
Amazon,556,Next Greater Element III,Med,"Math, Two Pointers, String",Given a positive integer n; find the smallest integer which has exactly the same digits existing in the integer n and is greater in value than n. If no such positive integer exists; return -1. Note that the returned integer should fit in 32-bit integer; if there is a valid answer but it does not fit in 32-bit integer; return -1. Example 1: Input: n = 12 Output: 21 Example 2: Input: n = 21 Output: -1 Constraints: 1 <= n <= 231 - 1
Amazon,564,Find the Closest Palindrome,Hard,"Math, String","Given a string n representing an integer; return the closest integer (not including itself); which is a palindrome. If there is a tie; return the smaller one. The closest is defined as the absolute difference minimized between two integers. Example 1: Input: n = ""123"" Output: ""121"" Example 2: Input: n = ""1"" Output: ""0"" Explanation: 0 and 2 are the closest palindromes but we return the smallest which is 0. Constraints: 1 <= n.length <= 18 n consists of only digits. n does not have leading zeros. n is representing an integer in the range [1; 1018 - 1]."
Amazon,570,Managers with at Least 5 Direct Reports,Med,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | department | varchar | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the name of an employee; their department; and the id of their manager. If managerId is null; then the employee does not have a manager. No employee will be the manager of themself. Write a solution to find managers with at least five direct reports. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +-----+-------+------------+-----------+ | id | name | department | managerId | +-----+-------+------------+-----------+ | 101 | John | A | null | | 102 | Dan | A | 101 | | 103 | James | A | 101 | | 104 | Amy | A | 101 | | 105 | Anne | A | 101 | | 106 | Ron | B | 101 | +-----+-------+------------+-----------+ Output: +------+ | name | +------+ | John | +------+
Amazon,572,Subtree of Another Tree,Easy,"Tree, Depth-First Search, String Matching, Binary Tree, Hash Function",Given the roots of two binary trees root and subRoot; return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise. A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself. Example 1: Input: root = [3;4;5;1;2]; subRoot = [4;1;2] Output: true Example 2: Input: root = [3;4;5;1;2;null;null;null;null;0]; subRoot = [4;1;2] Output: false Constraints: The number of nodes in the root tree is in the range [1; 2000]. The number of nodes in the subRoot tree is in the range [1; 1000]. -104 <= root.val <= 104 -104 <= subRoot.val <= 104
Amazon,636,Exclusive Time of Functions,Med,"Array, Stack","On a single-threaded CPU; we execute a program containing n functions. Each function has a unique ID between 0 and n-1. Function calls are stored in a call stack: when a function call starts; its ID is pushed onto the stack; and when a function call ends; its ID is popped off the stack. The function whose ID is at the top of the stack is the current function being executed. Each time a function starts or ends; we write a log with the ID; whether it started or ended; and the timestamp. You are given a list logs; where logs[i] represents the ith log message formatted as a string ""{function_id}:{""start"" | ""end""}:{timestamp}"". For example; ""0:start:3"" means a function call with function ID 0 started at the beginning of timestamp 3; and ""1:end:2"" means a function call with function ID 1 ended at the end of timestamp 2. Note that a function can be called multiple times; possibly recursively. A function's exclusive time is the sum of execution times for all function calls in the program. For example; if a function is called twice; one call executing for 2 time units and another call executing for 1 time unit; the exclusive time is 2 + 1 = 3. Return the exclusive time of each function in an array; where the value at the ith index represents the exclusive time for the function with ID i. Example 1: Input: n = 2; logs = [""0:start:0"";""1:start:2"";""1:end:5"";""0:end:6""] Output: [3;4] Explanation: Function 0 starts at the beginning of time 0; then it executes 2 for units of time and reaches the end of time 1. Function 1 starts at the beginning of time 2; executes for 4 units of time; and ends at the end of time 5. Function 0 resumes execution at the beginning of time 6 and executes for 1 unit of time. So function 0 spends 2 + 1 = 3 units of total time executing; and function 1 spends 4 units of total time executing. Example 2: Input: n = 1; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""0:start:6"";""0:end:6"";""0:end:7""] Output: [8] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls itself again. Function 0 (2nd recursive call) starts at the beginning of time 6 and executes for 1 unit of time. Function 0 (initial call) resumes execution at the beginning of time 7 and executes for 1 unit of time. So function 0 spends 2 + 4 + 1 + 1 = 8 units of total time executing. Example 3: Input: n = 2; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""1:start:6"";""1:end:6"";""0:end:7""] Output: [7;1] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls function 1. Function 1 starts at the beginning of time 6; executes 1 unit of time; and ends at the end of time 6. Function 0 resumes execution at the beginning of time 6 and executes for 2 units of time. So function 0 spends 2 + 4 + 1 = 7 units of total time executing; and function 1 spends 1 unit of total time executing. Constraints: 1 <= n <= 100 1 <= logs.length <= 500 0 <= function_id < n 0 <= timestamp <= 109 No two start events will happen at the same timestamp. No two end events will happen at the same timestamp. Each function has an ""end"" log for each ""start"" log."
Amazon,680,Valid Palindrome II,Easy,"Two Pointers, String, Greedy","Given a string s; return true if the s can be palindrome after deleting at most one character from it. Example 1: Input: s = ""aba"" Output: true Example 2: Input: s = ""abca"" Output: true Explanation: You could delete the character 'c'. Example 3: Input: s = ""abc"" Output: false Constraints: 1 <= s.length <= 105 s consists of lowercase English letters."
Amazon,695,Max Area of Island,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island. Return the maximum area of an island in grid. If there is no island; return 0. Example 1: Input: grid = [[0;0;1;0;0;0;0;1;0;0;0;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;1;1;0;1;0;0;0;0;0;0;0;0];[0;1;0;0;1;1;0;0;1;0;1;0;0];[0;1;0;0;1;1;0;0;1;1;1;0;0];[0;0;0;0;0;0;0;0;0;0;1;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;0;0;0;0;0;0;1;1;0;0;0;0]] Output: 6 Explanation: The answer is not 11; because the island must be connected 4-directionally. Example 2: Input: grid = [[0;0;0;0;0;0;0;0]] Output: 0 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 50 grid[i][j] is either 0 or 1.
Amazon,752,Open the Lock,Med,"String, Bit Manipulation",
Amazon,827,Making A Large Island,Hard,"Array, Two Pointers, String","Sometimes people repeat letters to represent extra feeling. For example: ""hello"" -> ""heeellooo"" ""hi"" -> ""hiiii"" In these strings like ""heeellooo""; we have groups of adjacent letters that are all the same: ""h""; ""eee""; ""ll""; ""ooo"". You are given a string s and an array of query strings words. A query word is stretchy if it can be made to be equal to s by any number of applications of the following extension operation: choose a group consisting of characters c; and add some number of characters c to the group so that the size of the group is three or more. For example; starting with ""hello""; we could do an extension on the group ""o"" to get ""hellooo""; but we cannot get ""helloo"" since the group ""oo"" has a size less than three. Also; we could do another extension like ""ll"" -> ""lllll"" to get ""helllllooo"". If s = ""helllllooo""; then the query word ""hello"" would be stretchy because of these two extension operations: query = ""hello"" -> ""hellooo"" -> ""helllllooo"" = s. Return the number of query strings that are stretchy. Example 1: Input: s = ""heeellooo""; words = [""hello""; ""hi""; ""helo""] Output: 1 Explanation: We can extend ""e"" and ""o"" in the word ""hello"" to get ""heeellooo"". We can't extend ""helo"" to get ""heeellooo"" because the group ""ll"" is not size 3 or more. Example 2: Input: s = ""zzzzzyyyyy""; words = [""zzyy"";""zy"";""zyy""] Output: 3 Constraints: 1 <= s.length; words.length <= 100 1 <= words[i].length <= 100 s and words[i] consist of lowercase letters."
Amazon,622,Design Circular Queue,Med,,
Amazon,862,Shortest Subarray with Sum at Least K,Hard,"Array, Hash Table, String, Sorting","You are given a 0-indexed string s that you must perform k replacement operations on. The replacement operations are given as three 0-indexed parallel arrays; indices; sources; and targets; all of length k. To complete the ith replacement operation: Check if the substring sources[i] occurs at index indices[i] in the original string s. If it does not occur; do nothing. Otherwise if it does occur; replace that substring with targets[i]. For example; if s = ""abcd""; indices[i] = 0; sources[i] = ""ab""; and targets[i] = ""eee""; then the result of this replacement will be ""eeecd"". All replacement operations must occur simultaneously; meaning the replacement operations should not affect the indexing of each other. The testcases will be generated such that the replacements will not overlap. For example; a testcase with s = ""abc""; indices = [0; 1]; and sources = [""ab"";""bc""] will not be generated because the ""ab"" and ""bc"" replacements overlap. Return the resulting string after performing all replacement operations on s. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""abcd""; indices = [0; 2]; sources = [""a""; ""cd""]; targets = [""eee""; ""ffff""] Output: ""eeebffff"" Explanation: ""a"" occurs at index 0 in s; so we replace it with ""eee"". ""cd"" occurs at index 2 in s; so we replace it with ""ffff"". Example 2: Input: s = ""abcd""; indices = [0; 2]; sources = [""ab"";""ec""]; targets = [""eee"";""ffff""] Output: ""eeecd"" Explanation: ""ab"" occurs at index 0 in s; so we replace it with ""eee"". ""ec"" does not occur at index 2 in s; so we do nothing. Constraints: 1 <= s.length <= 1000 k == indices.length == sources.length == targets.length 1 <= k <= 100 0 <= indexes[i] < s.length 1 <= sources[i].length; targets[i].length <= 50 s consists of only lowercase English letters. sources[i] and targets[i] consist of only lowercase English letters."
Amazon,871,Minimum Number of Refueling Stops,Hard,"Depth-First Search, Breadth-First Search, Graph",There are n rooms labeled from 0 to n - 1 and all the rooms are locked except for room 0. Your goal is to visit all the rooms. However; you cannot enter a locked room without having its key. When you visit a room; you may find a set of distinct keys in it. Each key has a number on it; denoting which room it unlocks; and you can take all of them with you to unlock the other rooms. Given an array rooms where rooms[i] is the set of keys that you can obtain if you visited room i; return true if you can visit all the rooms; or false otherwise. Example 1: Input: rooms = [[1];[2];[3];[]] Output: true Explanation: We visit room 0 and pick up key 1. We then visit room 1 and pick up key 2. We then visit room 2 and pick up key 3. We then visit room 3. Since we were able to visit every room; we return true. Example 2: Input: rooms = [[1;3];[3;0;1];[2];[0]] Output: false Explanation: We can not enter room number 2 since the only key that unlocks it is in that room. Constraints: n == rooms.length 2 <= n <= 1000 0 <= rooms[i].length <= 1000 1 <= sum(rooms[i].length) <= 3000 0 <= rooms[i][j] < n All the values of rooms[i] are unique.
Amazon,904,Fruit Into Baskets,Med,"Tree, Depth-First Search, Binary Tree",Consider all the leaves of a binary tree; from left to right order; the values of those leaves form a leaf value sequence. For example; in the given tree above; the leaf value sequence is (6; 7; 4; 9; 8). Two binary trees are considered leaf-similar if their leaf value sequence is the same. Return true if and only if the two given trees with head nodes root1 and root2 are leaf-similar. Example 1: Input: root1 = [3;5;1;6;2;9;8;null;null;7;4]; root2 = [3;5;1;6;7;4;2;null;null;null;null;null;null;9;8] Output: true Example 2: Input: root1 = [1;2;3]; root2 = [1;3;2] Output: false Constraints: The number of nodes in each tree will be in the range [1; 200]. Both of the given trees will have values in the range [0; 200].
Amazon,934,Shortest Bridge,Med,"Array, Dynamic Programming, Bit Manipulation",Given an integer array arr; return the number of distinct bitwise ORs of all the non-empty subarrays of arr. The bitwise OR of a subarray is the bitwise OR of each integer in the subarray. The bitwise OR of a subarray of one integer is that integer. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: arr = [0] Output: 1 Explanation: There is only one possible result: 0. Example 2: Input: arr = [1;1;2] Output: 3 Explanation: The possible subarrays are [1]; [1]; [2]; [1; 1]; [1; 2]; [1; 1; 2]. These yield the results 1; 1; 2; 1; 3; 3. There are 3 unique values; so the answer is 3. Example 3: Input: arr = [1;2;4] Output: 6 Explanation: The possible results are 1; 2; 3; 4; 6; and 7. Constraints: 1 <= arr.length <= 5 * 104 0 <= arr[i] <= 109
Amazon,953,Verifying an Alien Dictionary,Easy,"Two Pointers, String","Given a string s; reverse the string according to the following rules: All the characters that are not English letters remain in the same position. All the English letters (lowercase or uppercase) should be reversed. Return s after reversing it. Example 1: Input: s = ""ab-cd"" Output: ""dc-ba"" Example 2: Input: s = ""a-bC-dEf-ghIj"" Output: ""j-Ih-gfE-dCba"" Example 3: Input: s = ""Test1ng-Leet=code-Q!"" Output: ""Qedo1ct-eeLg=ntse-T!"" Constraints: 1 <= s.length <= 100 s consists of characters with ASCII values in the range [33; 122]. s does not contain '\""' or '\\'."
Amazon,968,Binary Tree Cameras,Hard,"Array, Math, Divide and Conquer",An array nums of length n is beautiful if: nums is a permutation of the integers in the range [1; n]. For every 0 <= i < j < n; there is no index k with i < k < j where 2 * nums[k] == nums[i] + nums[j]. Given the integer n; return any beautiful array nums of length n. There will be at least one valid answer for the given n. Example 1: Input: n = 4 Output: [2;1;4;3] Example 2: Input: n = 5 Output: [3;1;2;5;4] Constraints: 1 <= n <= 1000
Amazon,1143,Longest Common Subsequence,Med,"Array, Hash Table, Binary Search, Matrix, Counting",
Amazon,1148,Article Views I,Easy,"Array, Math",Given two numbers arr1 and arr2 in base -2; return the result of adding them together. Each number is given in array format: as an array of 0s and 1s; from most significant bit to least significant bit. For example; arr = [1;1;0;1] represents the number (-2)^3 + (-2)^2 + (-2)^0 = -3. A number arr in array; format is also guaranteed to have no leading zeros: either arr == [0] or arr[0] == 1. Return the result of adding arr1 and arr2 in the same format: as an array of 0s and 1s with no leading zeros. Example 1: Input: arr1 = [1;1;1;1;1]; arr2 = [1;0;1] Output: [1;0;0;0;0] Explanation: arr1 represents 11; arr2 represents 5; the output represents 16. Example 2: Input: arr1 = [0]; arr2 = [0] Output: [0] Example 3: Input: arr1 = [0]; arr2 = [1] Output: [1] Constraints: 1 <= arr1.length; arr2.length <= 1000 arr1[i] and arr2[i] are 0 or 1 arr1 and arr2 have no leading zeros
Amazon,1174,Immediate Food Delivery II,Med,Database,Table: Product +--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | | unit_price | int | +--------------+---------+ product_id is the primary key (column with unique values) of this table. Each row of this table indicates the name and the price of each product. Table: Sales +-------------+---------+ | Column Name | Type | +-------------+---------+ | seller_id | int | | product_id | int | | buyer_id | int | | sale_date | date | | quantity | int | | price | int | +-------------+---------+ This table can have duplicate rows. product_id is a foreign key (reference column) to the Product table. Each row of this table contains some information about one sale. Write a solution to report the products that were only sold in the first quarter of 2019. That is; between 2019-01-01 and 2019-03-31 inclusive. Return the result table in any order. The result format is in the following example. Example 1: Input: Product table: +------------+--------------+------------+ | product_id | product_name | unit_price | +------------+--------------+------------+ | 1 | S8 | 1000 | | 2 | G4 | 800 | | 3 | iPhone | 1400 | +------------+--------------+------------+ Sales table: +-----------+------------+----------+------------+----------+-------+ | seller_id | product_id | buyer_id | sale_date | quantity | price | +-----------+------------+----------+------------+----------+-------+ | 1 | 1 | 1 | 2019-01-21 | 2 | 2000 | | 1 | 2 | 2 | 2019-02-17 | 1 | 800 | | 2 | 2 | 3 | 2019-06-02 | 1 | 800 | | 3 | 3 | 4 | 2019-05-13 | 2 | 2800 | +-----------+------------+----------+------------+----------+-------+ Output: +-------------+--------------+ | product_id | product_name | +-------------+--------------+ | 1 | S8 | +-------------+--------------+ Explanation: The product with id 1 was only sold in the spring of 2019. The product with id 2 was sold in the spring of 2019 but was also sold after the spring of 2019. The product with id 3 was sold after spring 2019. We return only product 1 as it is the product that was only sold in the spring of 2019.
Amazon,1429,First Unique Number,Med,"Array, Math, String, Backtracking","Given an equation; represented by words on the left side and the result on the right side. You need to check if the equation is solvable under the following rules: Each character is decoded as one digit (0 - 9). No two characters can map to the same digit. Each words[i] and result are decoded as one number without leading zeros. Sum of numbers on the left side (words) will equal to the number on the right side (result). Return true if the equation is solvable; otherwise return false. Example 1: Input: words = [""SEND"";""MORE""]; result = ""MONEY"" Output: true Explanation: Map 'S'-> 9; 'E'->5; 'N'->6; 'D'->7; 'M'->1; 'O'->0; 'R'->8; 'Y'->'2' Such that: ""SEND"" + ""MORE"" = ""MONEY"" ; 9567 + 1085 = 10652 Example 2: Input: words = [""SIX"";""SEVEN"";""SEVEN""]; result = ""TWENTY"" Output: true Explanation: Map 'S'-> 6; 'I'->5; 'X'->0; 'E'->8; 'V'->7; 'N'->2; 'T'->1; 'W'->'3'; 'Y'->4 Such that: ""SIX"" + ""SEVEN"" + ""SEVEN"" = ""TWENTY"" ; 650 + 68782 + 68782 = 138214 Example 3: Input: words = [""LEET"";""CODE""]; result = ""POINT"" Output: false Explanation: There is no possible mapping to satisfy the equation; so we return false. Note that two different characters cannot map to the same digit. Constraints: 2 <= words.length <= 5 1 <= words[i].length; result.length <= 7 words[i]; result contain only uppercase English letters. The number of different characters used in the expression is at most 10."
Amazon,1497,Check If Array Pairs Are Divisible by k,Med,"Array, Stack, Design","Design a stack that supports increment operations on its elements. Implement the CustomStack class: CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack. void push(int x) Adds x to the top of the stack if the stack has not reached the maxSize. int pop() Pops and returns the top of the stack or -1 if the stack is empty. void inc(int k; int val) Increments the bottom k elements of the stack by val. If there are less than k elements in the stack; increment all the elements in the stack. Example 1: Input [""CustomStack"";""push"";""push"";""pop"";""push"";""push"";""push"";""increment"";""increment"";""pop"";""pop"";""pop"";""pop""] [[3];[1];[2];[];[2];[3];[4];[5;100];[2;100];[];[];[];[]] Output [null;null;null;2;null;null;null;null;null;103;202;201;-1] Explanation CustomStack stk = new CustomStack(3); // Stack is Empty [] stk.push(1); // stack becomes [1] stk.push(2); // stack becomes [1; 2] stk.pop(); // return 2 --> Return top of the stack 2; stack becomes [1] stk.push(2); // stack becomes [1; 2] stk.push(3); // stack becomes [1; 2; 3] stk.push(4); // stack still [1; 2; 3]; Do not add another elements as size is 4 stk.increment(5; 100); // stack becomes [101; 102; 103] stk.increment(2; 100); // stack becomes [201; 202; 103] stk.pop(); // return 103 --> Return top of the stack 103; stack becomes [201; 202] stk.pop(); // return 202 --> Return top of the stack 202; stack becomes [201] stk.pop(); // return 201 --> Return top of the stack 201; stack becomes [] stk.pop(); // return -1 --> Stack is empty return -1. Constraints: 1 <= maxSize; x; k <= 1000 0 <= val <= 100 At most 1000 calls will be made to each method of increment; push and pop each separately."
Amazon,1552,Magnetic Force Between Two Balls,Med,"Array, Stack, Simulation","You are given an integer array target and an integer n. You have an empty stack with the two following operations: ""Push"": pushes an integer to the top of the stack. ""Pop"": removes the integer on the top of the stack. You also have a stream of the integers in the range [1; n]. Use the two stack operations to make the numbers in the stack (from the bottom to the top) equal to target. You should follow the following rules: If the stream of the integers is not empty; pick the next integer from the stream and push it to the top of the stack. If the stack is not empty; pop the integer at the top of the stack. If; at any moment; the elements in the stack (from the bottom to the top) are equal to target; do not read new integers from the stream and do not do more operations on the stack. Return the stack operations needed to build target following the mentioned rules. If there are multiple valid answers; return any of them. Example 1: Input: target = [1;3]; n = 3 Output: [""Push"";""Push"";""Pop"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Pop the integer on the top of the stack. s = [1]. Read 3 from the stream and push it to the stack. s = [1;3]. Example 2: Input: target = [1;2;3]; n = 3 Output: [""Push"";""Push"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Read 3 from the stream and push it to the stack. s = [1;2;3]. Example 3: Input: target = [1;2]; n = 4 Output: [""Push"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Since the stack (from the bottom to the top) is equal to target; we stop the stack operations. The answers that read integer 3 from the stream are not accepted. Constraints: 1 <= target.length <= 100 1 <= n <= 100 1 <= target[i] <= n target is strictly increasing."
Amazon,1590,Make Sum Divisible by P,Med,,
Amazon,1603,Design Parking System,Easy,"Array, Prefix Sum",Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]). Return the running sum of nums. Example 1: Input: nums = [1;2;3;4] Output: [1;3;6;10] Explanation: Running sum is obtained as follows: [1; 1+2; 1+2+3; 1+2+3+4]. Example 2: Input: nums = [1;1;1;1;1] Output: [1;2;3;4;5] Explanation: Running sum is obtained as follows: [1; 1+1; 1+1+1; 1+1+1+1; 1+1+1+1+1]. Example 3: Input: nums = [3;1;2;10;1] Output: [3;4;6;16;17] Constraints: 1 <= nums.length <= 1000 -10^6 <= nums[i] <= 10^6
Amazon,1731,The Number of Employees Which Report to Each Employee,Easy,"Tree, Breadth-First Search, Binary Tree",A binary tree is named Even-Odd if it meets the following conditions: The root of the binary tree is at level index 0; its children are at level index 1; their children are at level index 2; etc. For every even-indexed level; all nodes at the level have odd integer values in strictly increasing order (from left to right). For every odd-indexed level; all nodes at the level have even integer values in strictly decreasing order (from left to right). Given the root of a binary tree; return true if the binary tree is Even-Odd; otherwise return false. Example 1: Input: root = [1;10;4;3;null;7;9;12;8;6;null;null;2] Output: true Explanation: The node values on each level are: Level 0: [1] Level 1: [10;4] Level 2: [3;7;9] Level 3: [12;8;6;2] Since levels 0 and 2 are all odd and increasing and levels 1 and 3 are all even and decreasing; the tree is Even-Odd. Example 2: Input: root = [5;4;2;3;3;7] Output: false Explanation: The node values on each level are: Level 0: [5] Level 1: [4;2] Level 2: [3;3;7] Node values in level 2 must be in strictly increasing order; so the tree is not Even-Odd. Example 3: Input: root = [5;9;1;3;5;7] Output: false Explanation: Node values in the level 1 should be even integers. Constraints: The number of nodes in the tree is in the range [1; 105]. 1 <= Node.val <= 106
Amazon,2275,Largest Combination With Bitwise AND Greater Than Zero,Med,"String, Sliding Window, Rolling Hash, Hash Function","The hash of a 0-indexed string s of length k; given integers p and m; is computed using the following function: hash(s; p; m) = (val(s[0]) * p0 + val(s[1]) * p1 + ... + val(s[k-1]) * pk-1) mod m. Where val(s[i]) represents the index of s[i] in the alphabet from val('a') = 1 to val('z') = 26. You are given a string s and the integers power; modulo; k; and hashValue. Return sub; the first substring of s of length k such that hash(sub; power; modulo) == hashValue. The test cases will be generated such that an answer always exists. A substring is a contiguous non-empty sequence of characters within a string. Example 1: Input: s = ""leetcode""; power = 7; modulo = 20; k = 2; hashValue = 0 Output: ""ee"" Explanation: The hash of ""ee"" can be computed to be hash(""ee""; 7; 20) = (5 * 1 + 5 * 7) mod 20 = 40 mod 20 = 0. ""ee"" is the first substring of length 2 with hashValue 0. Hence; we return ""ee"". Example 2: Input: s = ""fbxzaad""; power = 31; modulo = 100; k = 3; hashValue = 32 Output: ""fbx"" Explanation: The hash of ""fbx"" can be computed to be hash(""fbx""; 31; 100) = (6 * 1 + 2 * 31 + 24 * 312) mod 100 = 23132 mod 100 = 32. The hash of ""bxz"" can be computed to be hash(""bxz""; 31; 100) = (2 * 1 + 24 * 31 + 26 * 312) mod 100 = 25732 mod 100 = 32. ""fbx"" is the first substring of length 3 with hashValue 32. Hence; we return ""fbx"". Note that ""bxz"" also has a hash of 32 but it appears later than ""fbx"". Constraints: 1 <= k <= s.length <= 2 * 104 1 <= power; modulo <= 109 0 <= hashValue < modulo s consists of lowercase English letters only. The test cases are generated such that an answer always exists."
Amazon,2491,Divide Players Into Teams of Equal Skill,Med,"Math, Number Theory",Given a positive integer n; return the smallest positive integer that is a multiple of both 2 and n. Example 1: Input: n = 5 Output: 10 Explanation: The smallest multiple of both 5 and 2 is 10. Example 2: Input: n = 6 Output: 6 Explanation: The smallest multiple of both 6 and 2 is 6. Note that a number is a multiple of itself. Constraints: 1 <= n <= 150
Amazon,2530,Maximal Score After Applying K Operations,Med,"Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum",You are given a 0-indexed array nums comprising of n non-negative integers. In one operation; you must: Choose an integer i such that 1 <= i < n and nums[i] > 0. Decrease nums[i] by 1. Increase nums[i - 1] by 1. Return the minimum possible value of the maximum integer of nums after performing any number of operations. Example 1: Input: nums = [3;7;1;6] Output: 5 Explanation: One set of optimal operations is as follows: 1. Choose i = 1; and nums becomes [4;6;1;6]. 2. Choose i = 3; and nums becomes [4;6;2;5]. 3. Choose i = 1; and nums becomes [5;5;2;5]. The maximum integer of nums is 5. It can be shown that the maximum number cannot be less than 5. Therefore; we return 5. Example 2: Input: nums = [10;1] Output: 10 Explanation: It is optimal to leave nums as is; and since 10 is the maximum value; we return 10. Constraints: n == nums.length 2 <= n <= 105 0 <= nums[i] <= 109
Amazon,2707,Extra Characters in a String,Med,"Array, Hash Table, Two Pointers",You are given two 2D integer arrays nums1 and nums2. nums1[i] = [idi; vali] indicate that the number with the id idi has a value equal to vali. nums2[i] = [idi; vali] indicate that the number with the id idi has a value equal to vali. Each array contains unique ids and is sorted in ascending order by id. Merge the two arrays into one array that is sorted in ascending order by id; respecting the following conditions: Only ids that appear in at least one of the two arrays should be included in the resulting array. Each id should be included only once and its value should be the sum of the values of this id in the two arrays. If the id does not exist in one of the two arrays then its value in that array is considered to be 0. Return the resulting array. The returned array must be sorted in ascending order by id. Example 1: Input: nums1 = [[1;2];[2;3];[4;5]]; nums2 = [[1;4];[3;2];[4;1]] Output: [[1;6];[2;3];[3;2];[4;6]] Explanation: The resulting array contains the following: - id = 1; the value of this id is 2 + 4 = 6. - id = 2; the value of this id is 3. - id = 3; the value of this id is 2. - id = 4; the value of this id is 5 + 1 = 6. Example 2: Input: nums1 = [[2;4];[3;6];[5;5]]; nums2 = [[1;3];[4;3]] Output: [[1;3];[2;4];[3;6];[4;3];[5;5]] Explanation: There are no common ids; so we just include each id with its value in the resulting list. Constraints: 1 <= nums1.length; nums2.length <= 200 nums1[i].length == nums2[j].length == 2 1 <= idi; vali <= 1000 Both arrays contain unique ids. Both arrays are in strictly ascending order by id.
Amazon,6,Zigzag Conversion,Med,String,"The string ""PAYPALISHIRING"" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: ""PAHNAPLSIIGYIR"" Write the code that will take a string and make this conversion given a number of rows: string convert(string s; int numRows); Example 1: Input: s = ""PAYPALISHIRING""; numRows = 3 Output: ""PAHNAPLSIIGYIR"" Example 2: Input: s = ""PAYPALISHIRING""; numRows = 4 Output: ""PINALSIGYAHRPI"" Explanation: P I N A L S I G Y A H R P I Example 3: Input: s = ""A""; numRows = 1 Output: ""A"" Constraints: 1 <= s.length <= 1000 s consists of English letters (lower-case and upper-case); ';' and '.'. 1 <= numRows <= 1000"
Amazon,8,String to Integer (atoi),Med,String,"Implement the myAtoi(string s) function; which converts a string to a 32-bit signed integer. The algorithm for myAtoi(string s) is as follows: Whitespace: Ignore any leading whitespace ("" ""). Signedness: Determine the sign by checking if the next character is '-' or '+'; assuming positivity if neither present. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read; then the result is 0. Rounding: If the integer is out of the 32-bit signed integer range [-231; 231 - 1]; then round the integer to remain in the range. Specifically; integers less than -231 should be rounded to -231; and integers greater than 231 - 1 should be rounded to 231 - 1. Return the integer as the final result. Example 1: Input: s = ""42"" Output: 42 Explanation: The underlined characters are what is read in and the caret is the current reader position. Step 1: ""42"" (no characters read because there is no leading whitespace) ^ Step 2: ""42"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""42"" (""42"" is read in) ^ Example 2: Input: s = "" -042"" Output: -42 Explanation: Step 1: "" -042"" (leading whitespace is read and ignored) ^ Step 2: "" -042"" ('-' is read; so the result should be negative) ^ Step 3: "" -042"" (""042"" is read in; leading zeros ignored in the result) ^ Example 3: Input: s = ""1337c0d3"" Output: 1337 Explanation: Step 1: ""1337c0d3"" (no characters read because there is no leading whitespace) ^ Step 2: ""1337c0d3"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""1337c0d3"" (""1337"" is read in; reading stops because the next character is a non-digit) ^ Example 4: Input: s = ""0-1"" Output: 0 Explanation: Step 1: ""0-1"" (no characters read because there is no leading whitespace) ^ Step 2: ""0-1"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""0-1"" (""0"" is read in; reading stops because the next character is a non-digit) ^ Example 5: Input: s = ""words and 987"" Output: 0 Explanation: Reading stops at the first non-digit character 'w'. Constraints: 0 <= s.length <= 200 s consists of English letters (lower-case and upper-case); digits (0-9); ' '; '+'; '-'; and '.'."
Amazon,16,3Sum Closest,Med,"Array, Two Pointers, Sorting",Given an integer array nums of length n and an integer target; find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution. Example 1: Input: nums = [-1;2;1;-4]; target = 1 Output: 2 Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2). Example 2: Input: nums = [0;0;0]; target = 1 Output: 0 Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0). Constraints: 3 <= nums.length <= 500 -1000 <= nums[i] <= 1000 -104 <= target <= 104
Amazon,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
Amazon,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Amazon,64,Minimum Path Sum,Med,"Array, Dynamic Programming, Matrix",Given a m x n grid filled with non-negative numbers; find a path from top left to bottom right; which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1;3;1];[1;5;1];[4;2;1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. Example 2: Input: grid = [[1;2;3];[4;5;6]] Output: 12 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 200 0 <= grid[i][j] <= 200
Amazon,77,Combinations,Med,Backtracking,Given two integers n and k; return all possible combinations of k numbers chosen from the range [1; n]. You may return the answer in any order. Example 1: Input: n = 4; k = 2 Output: [[1;2];[1;3];[1;4];[2;3];[2;4];[3;4]] Explanation: There are 4 choose 2 = 6 total combinations. Note that combinations are unordered; i.e.; [1;2] and [2;1] are considered to be the same combination. Example 2: Input: n = 1; k = 1 Output: [[1]] Explanation: There is 1 choose 1 = 1 total combination. Constraints: 1 <= n <= 20 1 <= k <= n
Amazon,86,Partition List,Med,"Linked List, Two Pointers",Given the head of a linked list and a value x; partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of the two partitions. Example 1: Input: head = [1;4;3;2;5;2]; x = 3 Output: [1;2;2;4;3;5] Example 2: Input: head = [2;1]; x = 2 Output: [1;2] Constraints: The number of nodes in the list is in the range [0; 200]. -100 <= Node.val <= 100 -200 <= x <= 200
Amazon,93,Restore IP Addresses,Med,"String, Backtracking","A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. For example; ""0.1.2.201"" and ""192.168.1.1"" are valid IP addresses; but ""0.011.255.245""; ""192.168.1.312"" and ""192.168@1.1"" are invalid IP addresses. Given a string s containing only digits; return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order. Example 1: Input: s = ""25525511135"" Output: [""255.255.11.135"";""255.255.111.35""] Example 2: Input: s = ""0000"" Output: [""0.0.0.0""] Example 3: Input: s = ""101023"" Output: [""1.0.10.23"";""1.0.102.3"";""10.1.0.23"";""10.10.2.3"";""101.0.2.3""] Constraints: 1 <= s.length <= 20 s consists of digits only."
Amazon,105,Construct Binary Tree from Preorder and Inorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree; construct and return the binary tree. Example 1: Input: preorder = [3;9;20;15;7]; inorder = [9;3;15;20;7] Output: [3;9;20;null;null;15;7] Example 2: Input: preorder = [-1]; inorder = [-1] Output: [-1] Constraints: 1 <= preorder.length <= 3000 inorder.length == preorder.length -3000 <= preorder[i]; inorder[i] <= 3000 preorder and inorder consist of unique values. Each value of inorder also appears in preorder. preorder is guaranteed to be the preorder traversal of the tree. inorder is guaranteed to be the inorder traversal of the tree.
Amazon,106,Construct Binary Tree from Inorder and Postorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays inorder and postorder where inorder is the inorder traversal of a binary tree and postorder is the postorder traversal of the same tree; construct and return the binary tree. Example 1: Input: inorder = [9;3;15;20;7]; postorder = [9;15;7;20;3] Output: [3;9;20;null;null;15;7] Example 2: Input: inorder = [-1]; postorder = [-1] Output: [-1] Constraints: 1 <= inorder.length <= 3000 postorder.length == inorder.length -3000 <= inorder[i]; postorder[i] <= 3000 inorder and postorder consist of unique values. Each value of postorder also appears in inorder. inorder is guaranteed to be the inorder traversal of the tree. postorder is guaranteed to be the postorder traversal of the tree.
Amazon,112,Path Sum,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum. A leaf is a node with no children. Example 1: Input: root = [5;4;8;11;null;13;4;7;2;null;null;null;1]; targetSum = 22 Output: true Explanation: The root-to-leaf path with the target sum is shown. Example 2: Input: root = [1;2;3]; targetSum = 5 Output: false Explanation: There are two root-to-leaf paths in the tree: (1 --> 2): The sum is 3. (1 --> 3): The sum is 4. There is no root-to-leaf path with sum = 5. Example 3: Input: root = []; targetSum = 0 Output: false Explanation: Since the tree is empty; there are no root-to-leaf paths. Constraints: The number of nodes in the tree is in the range [0; 5000]. -1000 <= Node.val <= 1000 -1000 <= targetSum <= 1000
Amazon,115,Distinct Subsequences,Hard,"String, Dynamic Programming","Given two strings s and t; return the number of distinct subsequences of s which equals t. The test cases are generated so that the answer fits on a 32-bit signed integer. Example 1: Input: s = ""rabbbit""; t = ""rabbit"" Output: 3 Explanation: As shown below; there are 3 ways you can generate ""rabbit"" from s. rabbbit rabbbit rabbbit Example 2: Input: s = ""babgbag""; t = ""bag"" Output: 5 Explanation: As shown below; there are 5 ways you can generate ""bag"" from s. babgbag babgbag babgbag babgbag babgbag Constraints: 1 <= s.length; t.length <= 1000 s and t consist of English letters."
Amazon,123,Best Time to Buy and Sell Stock III,Hard,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete at most two transactions. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: prices = [3;3;5;0;0;3;1;4] Output: 6 Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Then buy on day 7 (price = 1) and sell on day 8 (price = 4); profit = 4-1 = 3. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Note that you cannot buy on day 1; buy on day 2 and sell them later; as you are engaging multiple transactions at the same time. You must sell before buying again. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transaction is done; i.e. max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 105
Amazon,133,Clone Graph,Med,"Hash Table, Depth-First Search, Breadth-First Search, Graph",Given a reference of a node in a connected undirected graph. Return a deep copy (clone) of the graph. Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors. class Node { public int val; public List<Node> neighbors; } Test case format: For simplicity; each node's value is the same as the node's index (1-indexed). For example; the first node with val == 1; the second node with val == 2; and so on. The graph is represented in the test case using an adjacency list. An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph. The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph. Example 1: Input: adjList = [[2;4];[1;3];[2;4];[1;3]] Output: [[2;4];[1;3];[2;4];[1;3]] Explanation: There are 4 nodes in the graph. 1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). 3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). Example 2: Input: adjList = [[]] Output: [[]] Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors. Example 3: Input: adjList = [] Output: [] Explanation: This an empty graph; it does not have any nodes. Constraints: The number of nodes in the graph is in the range [0; 100]. 1 <= Node.val <= 100 Node.val is unique for each node. There are no repeated edges and no self-loops in the graph. The Graph is connected and all nodes can be visited starting from the given node.
Amazon,137,Single Number II,Med,"Array, Bit Manipulation",Given an integer array nums where every element appears three times except for one; which appears exactly once. Find the single element and return it. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;3;2] Output: 3 Example 2: Input: nums = [0;1;0;1;0;1;99] Output: 99 Constraints: 1 <= nums.length <= 3 * 104 -231 <= nums[i] <= 231 - 1 Each element in nums appears exactly three times except for one element which appears once.
Amazon,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Amazon,170,Two Sum III - Data structure design,Easy,"Array, Hash Table, Two Pointers, Design, Data Stream",
Amazon,173,Binary Search Tree Iterator,Med,"Stack, Tree, Design, Binary Search Tree, Binary Tree, Iterator","Implement the BSTIterator class that represents an iterator over the in-order traversal of a binary search tree (BST): BSTIterator(TreeNode root) Initializes an object of the BSTIterator class. The root of the BST is given as part of the constructor. The pointer should be initialized to a non-existent number smaller than any element in the BST. boolean hasNext() Returns true if there exists a number in the traversal to the right of the pointer; otherwise returns false. int next() Moves the pointer to the right; then returns the number at the pointer. Notice that by initializing the pointer to a non-existent smallest number; the first call to next() will return the smallest element in the BST. You may assume that next() calls will always be valid. That is; there will be at least a next number in the in-order traversal when next() is called. Example 1: Input [""BSTIterator""; ""next""; ""next""; ""hasNext""; ""next""; ""hasNext""; ""next""; ""hasNext""; ""next""; ""hasNext""] [[[7; 3; 15; null; null; 9; 20]]; []; []; []; []; []; []; []; []; []] Output [null; 3; 7; true; 9; true; 15; true; 20; false] Explanation BSTIterator bSTIterator = new BSTIterator([7; 3; 15; null; null; 9; 20]); bSTIterator.next(); // return 3 bSTIterator.next(); // return 7 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 9 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 15 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 20 bSTIterator.hasNext(); // return False Constraints: The number of nodes in the tree is in the range [1; 105]. 0 <= Node.val <= 106 At most 105 calls will be made to hasNext; and next. Follow up: Could you implement next() and hasNext() to run in average O(1) time and use O(h) memory; where h is the height of the tree?"
Amazon,183,Customers Who Never Order,Easy,Database,Table: Customers +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID and name of a customer. Table: Orders +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | customerId | int | +-------------+------+ id is the primary key (column with unique values) for this table. customerId is a foreign key (reference columns) of the ID from the Customers table. Each row of this table indicates the ID of an order and the ID of the customer who ordered it. Write a solution to find all customers who never order anything. Return the result table in any order. The result format is in the following example. Example 1: Input: Customers table: +----+-------+ | id | name | +----+-------+ | 1 | Joe | | 2 | Henry | | 3 | Sam | | 4 | Max | +----+-------+ Orders table: +----+------------+ | id | customerId | +----+------------+ | 1 | 3 | | 2 | 1 | +----+------------+ Output: +-----------+ | Customers | +-----------+ | Henry | | Max | +-----------+
Amazon,199,Binary Tree Right Side View,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; imagine yourself standing on the right side of it; return the values of the nodes you can see ordered from top to bottom. Example 1: Input: root = [1;2;3;null;5;null;4] Output: [1;3;4] Example 2: Input: root = [1;null;3] Output: [1;3] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Amazon,209,Minimum Size Subarray Sum,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of positive integers nums and a positive integer target; return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray; return 0 instead. Example 1: Input: target = 7; nums = [2;3;1;2;4;3] Output: 2 Explanation: The subarray [4;3] has the minimal length under the problem constraint. Example 2: Input: target = 4; nums = [1;4;4] Output: 1 Example 3: Input: target = 11; nums = [1;1;1;1;1;1;1;1] Output: 0 Constraints: 1 <= target <= 109 1 <= nums.length <= 105 1 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution of which the time complexity is O(n log(n)).
Amazon,211,Design Add and Search Words Data Structure,Med,"String, Depth-First Search, Design, Trie","Design a data structure that supports adding new words and finding if a string matches any previously added string. Implement the WordDictionary class: WordDictionary() Initializes the object. void addWord(word) Adds word to the data structure; it can be matched later. bool search(word) Returns true if there is any string in the data structure that matches word or false otherwise. word may contain dots '.' where dots can be matched with any letter. Example: Input [""WordDictionary"";""addWord"";""addWord"";""addWord"";""search"";""search"";""search"";""search""] [[];[""bad""];[""dad""];[""mad""];[""pad""];[""bad""];["".ad""];[""b..""]] Output [null;null;null;null;false;true;true;true] Explanation WordDictionary wordDictionary = new WordDictionary(); wordDictionary.addWord(""bad""); wordDictionary.addWord(""dad""); wordDictionary.addWord(""mad""); wordDictionary.search(""pad""); // return False wordDictionary.search(""bad""); // return True wordDictionary.search("".ad""); // return True wordDictionary.search(""b..""); // return True Constraints: 1 <= word.length <= 25 word in addWord consists of lowercase English letters. word in search consist of '.' or lowercase English letters. There will be at most 2 dots in word for search queries. At most 104 calls will be made to addWord and search."
Amazon,213,House Robber II,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile; adjacent houses have a security system connected; and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [2;3;2] Output: 3 Explanation: You cannot rob house 1 (money = 2) and then rob house 3 (money = 2); because they are adjacent houses. Example 2: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 3: Input: nums = [1;2;3] Output: 3 Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 1000
Amazon,218,The Skyline Problem,Hard,"Array, Divide and Conquer, Binary Indexed Tree, Segment Tree, Line Sweep, Heap (Priority Queue), Ordered Set","A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Given the locations and heights of all the buildings; return the skyline formed by these buildings collectively. The geometric information of each building is given in the array buildings where buildings[i] = [lefti; righti; heighti]: lefti is the x coordinate of the left edge of the ith building. righti is the x coordinate of the right edge of the ith building. heighti is the height of the ith building. You may assume all buildings are perfect rectangles grounded on an absolutely flat surface at height 0. The skyline should be represented as a list of ""key points"" sorted by their x-coordinate in the form [[x1;y1];[x2;y2];...]. Each key point is the left endpoint of some horizontal segment in the skyline except the last point in the list; which always has a y-coordinate 0 and is used to mark the skyline's termination where the rightmost building ends. Any ground between the leftmost and rightmost buildings should be part of the skyline's contour. Note: There must be no consecutive horizontal lines of equal height in the output skyline. For instance; [...;[2 3];[4 5];[7 5];[11 5];[12 7];...] is not acceptable; the three lines of height 5 should be merged into one in the final output as such: [...;[2 3];[4 5];[12 7];...] Example 1: Input: buildings = [[2;9;10];[3;7;15];[5;12;12];[15;20;10];[19;24;8]] Output: [[2;10];[3;15];[7;12];[12;0];[15;10];[20;8];[24;0]] Explanation: Figure A shows the buildings of the input. Figure B shows the skyline formed by those buildings. The red points in figure B represent the key points in the output list. Example 2: Input: buildings = [[0;2;3];[2;5;3]] Output: [[0;3];[5;0]] Constraints: 1 <= buildings.length <= 104 0 <= lefti < righti <= 231 - 1 1 <= heighti <= 231 - 1 buildings is sorted by lefti in non-decreasing order."
Amazon,228,Summary Ranges,Easy,Array,"You are given a sorted unique integer array nums. A range [a;b] is the set of all integers from a to b (inclusive). Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is; each element of nums is covered by exactly one of the ranges; and there is no integer x such that x is in one of the ranges but not in nums. Each range [a;b] in the list should be output as: ""a->b"" if a != b ""a"" if a == b Example 1: Input: nums = [0;1;2;4;5;7] Output: [""0->2"";""4->5"";""7""] Explanation: The ranges are: [0;2] --> ""0->2"" [4;5] --> ""4->5"" [7;7] --> ""7"" Example 2: Input: nums = [0;2;3;4;6;8;9] Output: [""0"";""2->4"";""6"";""8->9""] Explanation: The ranges are: [0;0] --> ""0"" [2;4] --> ""2->4"" [6;6] --> ""6"" [8;9] --> ""8->9"" Constraints: 0 <= nums.length <= 20 -231 <= nums[i] <= 231 - 1 All the values of nums are unique. nums is sorted in ascending order."
Amazon,252,Meeting Rooms,Easy,"Array, Sorting",
Amazon,271,Encode and Decode Strings,Med,"Array, String, Design",
Amazon,277,Find the Celebrity,Med,"Two Pointers, Graph, Interactive",
Amazon,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
Amazon,323,Number of Connected Components in an Undirected Graph,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
Amazon,328,Odd Even Linked List,Med,Linked List,Given the head of a singly linked list; group all the nodes with odd indices together followed by the nodes with even indices; and return the reordered list. The first node is considered odd; and the second node is even; and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input. You must solve the problem in O(1) extra space complexity and O(n) time complexity. Example 1: Input: head = [1;2;3;4;5] Output: [1;3;5;2;4] Example 2: Input: head = [2;1;3;5;6;4;7] Output: [2;3;6;7;1;5;4] Constraints: The number of nodes in the linked list is in the range [0; 104]. -106 <= Node.val <= 106
Amazon,345,Reverse Vowels of a String,Easy,"Two Pointers, String","Given a string s; reverse only all the vowels in the string and return it. The vowels are 'a'; 'e'; 'i'; 'o'; and 'u'; and they can appear in both lower and upper cases; more than once. Example 1: Input: s = ""IceCreAm"" Output: ""AceCreIm"" Explanation: The vowels in s are ['I'; 'e'; 'e'; 'A']. On reversing the vowels; s becomes ""AceCreIm"". Example 2: Input: s = ""leetcode"" Output: ""leotcede"" Constraints: 1 <= s.length <= 3 * 105 s consist of printable ASCII characters."
Amazon,346,Moving Average from Data Stream,Easy,"Array, Design, Queue, Data Stream",
Amazon,350,Intersection of Two Arrays II,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must appear as many times as it shows in both arrays and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2;2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [4;9] Explanation: [9;4] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000 Follow up: What if the given array is already sorted? How would you optimize your algorithm? What if nums1's size is small compared to nums2's size? Which algorithm is better? What if elements of nums2 are stored on disk; and the memory is limited such that you cannot load all elements into the memory at once?
Amazon,355,Design Twitter,Med,"Hash Table, Linked List, Design, Heap (Priority Queue)","Design a simplified version of Twitter where users can post tweets; follow/unfollow another user; and is able to see the 10 most recent tweets in the user's news feed. Implement the Twitter class: Twitter() Initializes your twitter object. void postTweet(int userId; int tweetId) Composes a new tweet with ID tweetId by the user userId. Each call to this function will be made with a unique tweetId. List<Integer> getNewsFeed(int userId) Retrieves the 10 most recent tweet IDs in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user themself. Tweets must be ordered from most recent to least recent. void follow(int followerId; int followeeId) The user with ID followerId started following the user with ID followeeId. void unfollow(int followerId; int followeeId) The user with ID followerId started unfollowing the user with ID followeeId. Example 1: Input [""Twitter""; ""postTweet""; ""getNewsFeed""; ""follow""; ""postTweet""; ""getNewsFeed""; ""unfollow""; ""getNewsFeed""] [[]; [1; 5]; [1]; [1; 2]; [2; 6]; [1]; [1; 2]; [1]] Output [null; null; [5]; null; null; [6; 5]; null; [5]] Explanation Twitter twitter = new Twitter(); twitter.postTweet(1; 5); // User 1 posts a new tweet (id = 5). twitter.getNewsFeed(1); // User 1's news feed should return a list with 1 tweet id -> [5]. return [5] twitter.follow(1; 2); // User 1 follows user 2. twitter.postTweet(2; 6); // User 2 posts a new tweet (id = 6). twitter.getNewsFeed(1); // User 1's news feed should return a list with 2 tweet ids -> [6; 5]. Tweet id 6 should precede tweet id 5 because it is posted after tweet id 5. twitter.unfollow(1; 2); // User 1 unfollows user 2. twitter.getNewsFeed(1); // User 1's news feed should return a list with 1 tweet id -> [5]; since user 1 is no longer following user 2. Constraints: 1 <= userId; followerId; followeeId <= 500 0 <= tweetId <= 104 All the tweets have unique IDs. At most 3 * 104 calls will be made to postTweet; getNewsFeed; follow; and unfollow."
Amazon,358,Rearrange String k Distance Apart,Hard,"Hash Table, String, Greedy, Sorting, Heap (Priority Queue), Counting",
Amazon,365,Water and Jug Problem,Med,"Math, Depth-First Search, Breadth-First Search",You are given two jugs with capacities x liters and y liters. You have an infinite water supply. Return whether the total amount of water in both jugs may reach target using the following operations: Fill either jug completely with water. Completely empty either jug. Pour water from one jug into another until the receiving jug is full; or the transferring jug is empty. Example 1: Input: x = 3; y = 5; target = 4 Output: true Explanation: Follow these steps to reach a total of 4 liters: Fill the 5-liter jug (0; 5). Pour from the 5-liter jug into the 3-liter jug; leaving 2 liters (3; 2). Empty the 3-liter jug (0; 2). Transfer the 2 liters from the 5-liter jug to the 3-liter jug (2; 0). Fill the 5-liter jug again (2; 5). Pour from the 5-liter jug into the 3-liter jug until the 3-liter jug is full. This leaves 4 liters in the 5-liter jug (3; 4). Empty the 3-liter jug. Now; you have exactly 4 liters in the 5-liter jug (0; 4). Reference: The Die Hard example. Example 2: Input: x = 2; y = 6; target = 5 Output: false Example 3: Input: x = 1; y = 2; target = 3 Output: true Explanation: Fill both jugs. The total amount of water in both jugs is equal to 3 now. Constraints: 1 <= x; y; target <= 103
Amazon,371,Sum of Two Integers,Med,"Math, Bit Manipulation",Given two integers a and b; return the sum of the two integers without using the operators + and -. Example 1: Input: a = 1; b = 2 Output: 3 Example 2: Input: a = 2; b = 3 Output: 5 Constraints: -1000 <= a; b <= 1000
Amazon,373,Find K Pairs with Smallest Sums,Med,"Array, Heap (Priority Queue)",You are given two integer arrays nums1 and nums2 sorted in non-decreasing order and an integer k. Define a pair (u; v) which consists of one element from the first array and one element from the second array. Return the k pairs (u1; v1); (u2; v2); ...; (uk; vk) with the smallest sums. Example 1: Input: nums1 = [1;7;11]; nums2 = [2;4;6]; k = 3 Output: [[1;2];[1;4];[1;6]] Explanation: The first 3 pairs are returned from the sequence: [1;2];[1;4];[1;6];[7;2];[7;4];[11;2];[7;6];[11;4];[11;6] Example 2: Input: nums1 = [1;1;2]; nums2 = [1;2;3]; k = 2 Output: [[1;1];[1;1]] Explanation: The first 2 pairs are returned from the sequence: [1;1];[1;1];[1;2];[2;1];[1;2];[2;2];[1;3];[1;3];[2;3] Constraints: 1 <= nums1.length; nums2.length <= 105 -109 <= nums1[i]; nums2[i] <= 109 nums1 and nums2 both are sorted in non-decreasing order. 1 <= k <= 104 k <= nums1.length * nums2.length
Amazon,381,Insert Delete GetRandom O(1) - Duplicates allowed,Hard,"Array, Hash Table, Math, Design, Randomized","RandomizedCollection is a data structure that contains a collection of numbers; possibly duplicates (i.e.; a multiset). It should support inserting and removing specific elements and also reporting a random element. Implement the RandomizedCollection class: RandomizedCollection() Initializes the empty RandomizedCollection object. bool insert(int val) Inserts an item val into the multiset; even if the item is already present. Returns true if the item is not present; false otherwise. bool remove(int val) Removes an item val from the multiset if present. Returns true if the item is present; false otherwise. Note that if val has multiple occurrences in the multiset; we only remove one of them. int getRandom() Returns a random element from the current multiset of elements. The probability of each element being returned is linearly related to the number of the same values the multiset contains. You must implement the functions of the class such that each function works on average O(1) time complexity. Note: The test cases are generated such that getRandom will only be called if there is at least one item in the RandomizedCollection. Example 1: Input [""RandomizedCollection""; ""insert""; ""insert""; ""insert""; ""getRandom""; ""remove""; ""getRandom""] [[]; [1]; [1]; [2]; []; [1]; []] Output [null; true; false; true; 2; true; 1] Explanation RandomizedCollection randomizedCollection = new RandomizedCollection(); randomizedCollection.insert(1); // return true since the collection does not contain 1. // Inserts 1 into the collection. randomizedCollection.insert(1); // return false since the collection contains 1. // Inserts another 1 into the collection. Collection now contains [1;1]. randomizedCollection.insert(2); // return true since the collection does not contain 2. // Inserts 2 into the collection. Collection now contains [1;1;2]. randomizedCollection.getRandom(); // getRandom should: // - return 1 with probability 2/3; or // - return 2 with probability 1/3. randomizedCollection.remove(1); // return true since the collection contains 1. // Removes 1 from the collection. Collection now contains [1;2]. randomizedCollection.getRandom(); // getRandom should return 1 or 2; both equally likely. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls in total will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Amazon,395,Longest Substring with At Least K Repeating Characters,Med,"Hash Table, String, Divide and Conquer, Sliding Window","Given a string s and an integer k; return the length of the longest substring of s such that the frequency of each character in this substring is greater than or equal to k. if no such substring exists; return 0. Example 1: Input: s = ""aaabb""; k = 3 Output: 3 Explanation: The longest substring is ""aaa""; as 'a' is repeated 3 times. Example 2: Input: s = ""ababbc""; k = 2 Output: 5 Explanation: The longest substring is ""ababb""; as 'a' is repeated 2 times and 'b' is repeated 3 times. Constraints: 1 <= s.length <= 104 s consists of only lowercase English letters. 1 <= k <= 105"
Amazon,399,Evaluate Division,Med,"Array, String, Depth-First Search, Breadth-First Search, Union Find, Graph, Shortest Path","You are given an array of variable pairs equations and an array of real numbers values; where equations[i] = [Ai; Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable. You are also given some queries; where queries[j] = [Cj; Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries. If a single answer cannot be determined; return -1.0. Note: The input is always valid. You may assume that evaluating the queries will not result in division by zero and that there is no contradiction. Note: The variables that do not occur in the list of equations are undefined; so the answer cannot be determined for them. Example 1: Input: equations = [[""a"";""b""];[""b"";""c""]]; values = [2.0;3.0]; queries = [[""a"";""c""];[""b"";""a""];[""a"";""e""];[""a"";""a""];[""x"";""x""]] Output: [6.00000;0.50000;-1.00000;1.00000;-1.00000] Explanation: Given: a / b = 2.0; b / c = 3.0 queries are: a / c = ?; b / a = ?; a / e = ?; a / a = ?; x / x = ? return: [6.0; 0.5; -1.0; 1.0; -1.0 ] note: x is undefined => -1.0 Example 2: Input: equations = [[""a"";""b""];[""b"";""c""];[""bc"";""cd""]]; values = [1.5;2.5;5.0]; queries = [[""a"";""c""];[""c"";""b""];[""bc"";""cd""];[""cd"";""bc""]] Output: [3.75000;0.40000;5.00000;0.20000] Example 3: Input: equations = [[""a"";""b""]]; values = [0.5]; queries = [[""a"";""b""];[""b"";""a""];[""a"";""c""];[""x"";""y""]] Output: [0.50000;2.00000;-1.00000;-1.00000] Constraints: 1 <= equations.length <= 20 equations[i].length == 2 1 <= Ai.length; Bi.length <= 5 values.length == equations.length 0.0 < values[i] <= 20.0 1 <= queries.length <= 20 queries[i].length == 2 1 <= Cj.length; Dj.length <= 5 Ai; Bi; Cj; Dj consist of lower case English letters and digits."
Amazon,402,Remove K Digits,Med,"String, Stack, Greedy, Monotonic Stack","Given string num representing a non-negative integer num; and an integer k; return the smallest possible integer after removing k digits from num. Example 1: Input: num = ""1432219""; k = 3 Output: ""1219"" Explanation: Remove the three digits 4; 3; and 2 to form the new number 1219 which is the smallest. Example 2: Input: num = ""10200""; k = 1 Output: ""200"" Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes. Example 3: Input: num = ""10""; k = 2 Output: ""0"" Explanation: Remove all the digits from the number and it is left with nothing which is 0. Constraints: 1 <= k <= num.length <= 105 num consists of only digits. num does not have any leading zeros except for the zero itself."
Amazon,403,Frog Jump,Hard,"Array, Dynamic Programming",A frog is crossing a river. The river is divided into some number of units; and at each unit; there may or may not exist a stone. The frog can jump on a stone; but it must not jump into the water. Given a list of stones positions (in units) in sorted ascending order; determine if the frog can cross the river by landing on the last stone. Initially; the frog is on the first stone and assumes the first jump must be 1 unit. If the frog's last jump was k units; its next jump must be either k - 1; k; or k + 1 units. The frog can only jump in the forward direction. Example 1: Input: stones = [0;1;3;5;6;8;12;17] Output: true Explanation: The frog can jump to the last stone by jumping 1 unit to the 2nd stone; then 2 units to the 3rd stone; then 2 units to the 4th stone; then 3 units to the 6th stone; 4 units to the 7th stone; and 5 units to the 8th stone. Example 2: Input: stones = [0;1;2;3;4;8;9;11] Output: false Explanation: There is no way to jump to the last stone as the gap between the 5th and 6th stone is too large. Constraints: 2 <= stones.length <= 2000 0 <= stones[i] <= 231 - 1 stones[0] == 0 stones is sorted in a strictly increasing order.
Amazon,408,Valid Word Abbreviation,Easy,"Two Pointers, String",
Amazon,410,Split Array Largest Sum,Hard,"Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum",Given an integer array nums and an integer k; split nums into k non-empty subarrays such that the largest sum of any subarray is minimized. Return the minimized largest sum of the split. A subarray is a contiguous part of the array. Example 1: Input: nums = [7;2;5;10;8]; k = 2 Output: 18 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [7;2;5] and [10;8]; where the largest sum among the two subarrays is only 18. Example 2: Input: nums = [1;2;3;4;5]; k = 2 Output: 9 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [1;2;3] and [4;5]; where the largest sum among the two subarrays is only 9. Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 106 1 <= k <= min(50; nums.length)
Amazon,415,Add Strings,Easy,"Math, String, Simulation","Given two non-negative integers; num1 and num2 represented as string; return the sum of num1 and num2 as a string. You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly. Example 1: Input: num1 = ""11""; num2 = ""123"" Output: ""134"" Example 2: Input: num1 = ""456""; num2 = ""77"" Output: ""533"" Example 3: Input: num1 = ""0""; num2 = ""0"" Output: ""0"" Constraints: 1 <= num1.length; num2.length <= 104 num1 and num2 consist of only digits. num1 and num2 don't have any leading zeros except for the zero itself."
Amazon,432,All O`one Data Structure,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure to store the strings' count with the ability to return the strings with minimum and maximum counts. Implement the AllOne class: AllOne() Initializes the object of the data structure. inc(String key) Increments the count of the string key by 1. If key does not exist in the data structure; insert it with count 1. dec(String key) Decrements the count of the string key by 1. If the count of key is 0 after the decrement; remove it from the data structure. It is guaranteed that key exists in the data structure before the decrement. getMaxKey() Returns one of the keys with the maximal count. If no element exists; return an empty string """". getMinKey() Returns one of the keys with the minimum count. If no element exists; return an empty string """". Note that each function must run in O(1) average time complexity. Example 1: Input [""AllOne""; ""inc""; ""inc""; ""getMaxKey""; ""getMinKey""; ""inc""; ""getMaxKey""; ""getMinKey""] [[]; [""hello""]; [""hello""]; []; []; [""leet""]; []; []] Output [null; null; null; ""hello""; ""hello""; null; ""hello""; ""leet""] Explanation AllOne allOne = new AllOne(); allOne.inc(""hello""); allOne.inc(""hello""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""hello"" allOne.inc(""leet""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""leet"" Constraints: 1 <= key.length <= 10 key consists of lowercase English letters. It is guaranteed that for each call to dec; key is existing in the data structure. At most 5 * 104 calls will be made to inc; dec; getMaxKey; and getMinKey."
Amazon,435,Non-overlapping Intervals,Med,"Array, Dynamic Programming, Greedy, Sorting",Given an array of intervals intervals where intervals[i] = [starti; endi]; return the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping. Note that intervals which only touch at a point are non-overlapping. For example; [1; 2] and [2; 3] are non-overlapping. Example 1: Input: intervals = [[1;2];[2;3];[3;4];[1;3]] Output: 1 Explanation: [1;3] can be removed and the rest of the intervals are non-overlapping. Example 2: Input: intervals = [[1;2];[1;2];[1;2]] Output: 2 Explanation: You need to remove two [1;2] to make the rest of the intervals non-overlapping. Example 3: Input: intervals = [[1;2];[2;3]] Output: 0 Explanation: You don't need to remove any of the intervals since they're already non-overlapping. Constraints: 1 <= intervals.length <= 105 intervals[i].length == 2 -5 * 104 <= starti < endi <= 5 * 104
Amazon,451,Sort Characters By Frequency,Med,"Hash Table, String, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given a string s; sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers; return any of them. Example 1: Input: s = ""tree"" Output: ""eert"" Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore ""eetr"" is also a valid answer. Example 2: Input: s = ""cccaaa"" Output: ""aaaccc"" Explanation: Both 'c' and 'a' appear three times; so both ""cccaaa"" and ""aaaccc"" are valid answers. Note that ""cacaca"" is incorrect; as the same characters must be together. Example 3: Input: s = ""Aabb"" Output: ""bbAa"" Explanation: ""bbaA"" is also a valid answer; but ""Aabb"" is incorrect. Note that 'A' and 'a' are treated as two different characters. Constraints: 1 <= s.length <= 5 * 105 s consists of uppercase and lowercase English letters and digits."
Amazon,486,Predict the Winner,Med,"Array, Math, Dynamic Programming, Recursion, Game Theory",You are given an integer array nums. Two players are playing a game with this array: player 1 and player 2. Player 1 and player 2 take turns; with player 1 starting first. Both players start the game with a score of 0. At each turn; the player takes one of the numbers from either end of the array (i.e.; nums[0] or nums[nums.length - 1]) which reduces the size of the array by 1. The player adds the chosen number to their score. The game ends when there are no more elements in the array. Return true if Player 1 can win the game. If the scores of both players are equal; then player 1 is still the winner; and you should also return true. You may assume that both players are playing optimally. Example 1: Input: nums = [1;5;2] Output: false Explanation: Initially; player 1 can choose between 1 and 2. If he chooses 2 (or 1); then player 2 can choose from 1 (or 2) and 5. If player 2 chooses 5; then player 1 will be left with 1 (or 2). So; final score of player 1 is 1 + 2 = 3; and player 2 is 5. Hence; player 1 will never be the winner and you need to return false. Example 2: Input: nums = [1;5;233;7] Output: true Explanation: Player 1 first chooses 1. Then player 2 has to choose between 5 and 7. No matter which number player 2 choose; player 1 can choose 233. Finally; player 1 has more score (234) than player 2 (12); so you need to return True representing player1 can win. Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 107
Amazon,490,The Maze,Med,"Array, Depth-First Search, Breadth-First Search, Matrix",
Amazon,494,Target Sum,Med,"Array, Dynamic Programming, Backtracking","You are given an integer array nums and an integer target. You want to build an expression out of nums by adding one of the symbols '+' and '-' before each integer in nums and then concatenate all the integers. For example; if nums = [2; 1]; you can add a '+' before 2 and a '-' before 1 and concatenate them to build the expression ""+2-1"". Return the number of different expressions that you can build; which evaluates to target. Example 1: Input: nums = [1;1;1;1;1]; target = 3 Output: 5 Explanation: There are 5 ways to assign symbols to make the sum of nums be target 3. -1 + 1 + 1 + 1 + 1 = 3 +1 - 1 + 1 + 1 + 1 = 3 +1 + 1 - 1 + 1 + 1 = 3 +1 + 1 + 1 - 1 + 1 = 3 +1 + 1 + 1 + 1 - 1 = 3 Example 2: Input: nums = [1]; target = 1 Output: 1 Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 1000 0 <= sum(nums[i]) <= 1000 -1000 <= target <= 1000"
Amazon,517,Super Washing Machines,Hard,"Array, Greedy",You have n super washing machines on a line. Initially; each washing machine has some dresses or is empty. For each move; you could choose any m (1 <= m <= n) washing machines; and pass one dress of each washing machine to one of its adjacent washing machines at the same time. Given an integer array machines representing the number of dresses in each washing machine from left to right on the line; return the minimum number of moves to make all the washing machines have the same number of dresses. If it is not possible to do it; return -1. Example 1: Input: machines = [1;0;5] Output: 3 Explanation: 1st move: 1 0 <-- 5 => 1 1 4 2nd move: 1 <-- 1 <-- 4 => 2 1 3 3rd move: 2 1 <-- 3 => 2 2 2 Example 2: Input: machines = [0;3;0] Output: 2 Explanation: 1st move: 0 <-- 3 0 => 1 2 0 2nd move: 1 2 --> 0 => 1 1 1 Example 3: Input: machines = [0;2;0] Output: -1 Explanation: It's impossible to make all three washing machines have the same number of dresses. Constraints: n == machines.length 1 <= n <= 104 0 <= machines[i] <= 105
Amazon,518,Coin Change II,Med,"Array, Dynamic Programming",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the number of combinations that make up that amount. If that amount of money cannot be made up by any combination of the coins; return 0. You may assume that you have an infinite number of each kind of coin. The answer is guaranteed to fit into a signed 32-bit integer. Example 1: Input: amount = 5; coins = [1;2;5] Output: 4 Explanation: there are four ways to make up the amount: 5=5 5=2+2+1 5=2+1+1+1 5=1+1+1+1+1 Example 2: Input: amount = 3; coins = [2] Output: 0 Explanation: the amount of 3 cannot be made up just with coins of 2. Example 3: Input: amount = 10; coins = [10] Output: 1 Constraints: 1 <= coins.length <= 300 1 <= coins[i] <= 5000 All the values of coins are unique. 0 <= amount <= 5000
Amazon,540,Single Element in a Sorted Array,Med,"Array, Binary Search",You are given a sorted array consisting of only integers where every element appears exactly twice; except for one element which appears exactly once. Return the single element that appears only once. Your solution must run in O(log n) time and O(1) space. Example 1: Input: nums = [1;1;2;3;3;4;4;8;8] Output: 2 Example 2: Input: nums = [3;3;7;7;10;11;11] Output: 10 Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 105
Amazon,545,Boundary of Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",
Amazon,595,Big Countries,Easy,Database,Table: World +-------------+---------+ | Column Name | Type | +-------------+---------+ | name | varchar | | continent | varchar | | area | int | | population | int | | gdp | bigint | +-------------+---------+ name is the primary key (column with unique values) for this table. Each row of this table gives information about the name of a country; the continent to which it belongs; its area; the population; and its GDP value. A country is big if: it has an area of at least three million (i.e.; 3000000 km2); or it has a population of at least twenty-five million (i.e.; 25000000). Write a solution to find the name; population; and area of the big countries. Return the result table in any order. The result format is in the following example. Example 1: Input: World table: +-------------+-----------+---------+------------+--------------+ | name | continent | area | population | gdp | +-------------+-----------+---------+------------+--------------+ | Afghanistan | Asia | 652230 | 25500100 | 20343000000 | | Albania | Europe | 28748 | 2831741 | 12960000000 | | Algeria | Africa | 2381741 | 37100000 | 188681000000 | | Andorra | Europe | 468 | 78115 | 3712000000 | | Angola | Africa | 1246700 | 20609294 | 100990000000 | +-------------+-----------+---------+------------+--------------+ Output: +-------------+------------+---------+ | name | population | area | +-------------+------------+---------+ | Afghanistan | 25500100 | 652230 | | Algeria | 37100000 | 2381741 | +-------------+------------+---------+
Amazon,605,Can Place Flowers,Easy,"Array, Greedy",You have a long flowerbed in which some of the plots are planted; and some are not. However; flowers cannot be planted in adjacent plots. Given an integer array flowerbed containing 0's and 1's; where 0 means empty and 1 means not empty; and an integer n; return true if n new flowers can be planted in the flowerbed without violating the no-adjacent-flowers rule and false otherwise. Example 1: Input: flowerbed = [1;0;0;0;1]; n = 1 Output: true Example 2: Input: flowerbed = [1;0;0;0;1]; n = 2 Output: false Constraints: 1 <= flowerbed.length <= 2 * 104 flowerbed[i] is 0 or 1. There are no two adjacent flowers in flowerbed. 0 <= n <= flowerbed.length
Amazon,647,Palindromic Substrings,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the number of palindromic substrings in it. A string is a palindrome when it reads the same backward as forward. A substring is a contiguous sequence of characters within the string. Example 1: Input: s = ""abc"" Output: 3 Explanation: Three palindromic strings: ""a""; ""b""; ""c"". Example 2: Input: s = ""aaa"" Output: 6 Explanation: Six palindromic strings: ""a""; ""a""; ""a""; ""aa""; ""aa""; ""aaa"". Constraints: 1 <= s.length <= 1000 s consists of lowercase English letters."
Amazon,658,Find K Closest Elements,Med,"Array, Two Pointers, Binary Search, Sliding Window, Sorting, Heap (Priority Queue)",Given a sorted integer array arr; two integers k and x; return the k closest integers to x in the array. The result should also be sorted in ascending order. An integer a is closer to x than an integer b if: |a - x| < |b - x|; or |a - x| == |b - x| and a < b Example 1: Input: arr = [1;2;3;4;5]; k = 4; x = 3 Output: [1;2;3;4] Example 2: Input: arr = [1;1;2;3;4;5]; k = 4; x = -1 Output: [1;1;2;3] Constraints: 1 <= k <= arr.length 1 <= arr.length <= 104 arr is sorted in ascending order. -104 <= arr[i]; x <= 104
Amazon,692,Top K Frequent Words,Med,"Hash Table, String, Trie, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given an array of strings words and an integer k; return the k most frequent strings. Return the answer sorted by the frequency from highest to lowest. Sort the words with the same frequency by their lexicographical order. Example 1: Input: words = [""i"";""love"";""leetcode"";""i"";""love"";""coding""]; k = 2 Output: [""i"";""love""] Explanation: ""i"" and ""love"" are the two most frequent words. Note that ""i"" comes before ""love"" due to a lower alphabetical order. Example 2: Input: words = [""the"";""day"";""is"";""sunny"";""the"";""the"";""the"";""sunny"";""is"";""is""]; k = 4 Output: [""the"";""is"";""sunny"";""day""] Explanation: ""the""; ""is""; ""sunny"" and ""day"" are the four most frequent words; with the number of occurrence being 4; 3; 2 and 1 respectively. Constraints: 1 <= words.length <= 500 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. k is in the range [1; The number of unique words[i]] Follow-up: Could you solve it in O(n log(k)) time and O(n) extra space?"
Amazon,713,Subarray Product Less Than K,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of integers nums and an integer k; return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k. Example 1: Input: nums = [10;5;2;6]; k = 100 Output: 8 Explanation: The 8 subarrays that have product less than 100 are: [10]; [5]; [2]; [6]; [10; 5]; [5; 2]; [2; 6]; [5; 2; 6] Note that [10; 5; 2] is not included as the product of 100 is not strictly less than k. Example 2: Input: nums = [1;2;3]; k = 0 Output: 0 Constraints: 1 <= nums.length <= 3 * 104 1 <= nums[i] <= 1000 0 <= k <= 106
Amazon,731,My Calendar II,Med,"Array, Binary Search, Design, Segment Tree, Prefix Sum, Ordered Set","You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a triple booking. A triple booking happens when three events have some non-empty intersection (i.e.; some moment is common to all the three events.). The event can be represented as a pair of integers startTime and endTime that represents a booking on the half-open interval [startTime; endTime); the range of real numbers x such that startTime <= x < endTime. Implement the MyCalendarTwo class: MyCalendarTwo() Initializes the calendar object. boolean book(int startTime; int endTime) Returns true if the event can be added to the calendar successfully without causing a triple booking. Otherwise; return false and do not add the event to the calendar. Example 1: Input [""MyCalendarTwo""; ""book""; ""book""; ""book""; ""book""; ""book""; ""book""] [[]; [10; 20]; [50; 60]; [10; 40]; [5; 15]; [5; 10]; [25; 55]] Output [null; true; true; true; false; true; true] Explanation MyCalendarTwo myCalendarTwo = new MyCalendarTwo(); myCalendarTwo.book(10; 20); // return True; The event can be booked. myCalendarTwo.book(50; 60); // return True; The event can be booked. myCalendarTwo.book(10; 40); // return True; The event can be double booked. myCalendarTwo.book(5; 15); // return False; The event cannot be booked; because it would result in a triple booking. myCalendarTwo.book(5; 10); // return True; The event can be booked; as it does not use time 10 which is already double booked. myCalendarTwo.book(25; 55); // return True; The event can be booked; as the time in [25; 40) will be double booked with the third event; the time [40; 50) will be single booked; and the time [50; 55) will be double booked with the second event. Constraints: 0 <= start < end <= 109 At most 1000 calls will be made to book."
Amazon,430,Flatten a Multilevel Doubly Linked List,Med,,
Amazon,590,N-ary Tree Postorder Traversal,Easy,,
Amazon,771,Jewels and Stones,Easy,"Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",
Amazon,780,Reaching Points,Hard,"Array, Stack, Greedy, Sorting, Monotonic Stack",You are given an integer array arr of length n that represents a permutation of the integers in the range [0; n - 1]. We split arr into some number of chunks (i.e.; partitions); and individually sort each chunk. After concatenating them; the result should equal the sorted array. Return the largest number of chunks we can make to sort the array. Example 1: Input: arr = [4;3;2;1;0] Output: 1 Explanation: Splitting into two or more chunks will not return the required result. For example; splitting into [4; 3]; [2; 1; 0] will result in [3; 4; 0; 1; 2]; which isn't sorted. Example 2: Input: arr = [1;0;2;3;4] Output: 4 Explanation: We can split into two chunks; such as [1; 0]; [2; 3; 4]. However; splitting into [1; 0]; [2]; [3]; [4] is the highest number of chunks possible. Constraints: n == arr.length 1 <= n <= 10 0 <= arr[i] < n All the elements of arr are unique.
Amazon,791,Custom Sort String,Med,"Tree, Binary Search Tree, Recursion, Binary Tree",
Amazon,802,Find Eventual Safe States,Med,"Array, Two Pointers, Binary Search, Sorting, Heap (Priority Queue)",You are given a sorted integer array arr containing 1 and prime numbers; where all the integers of arr are unique. You are also given an integer k. For every i and j where 0 <= i < j < arr.length; we consider the fraction arr[i] / arr[j]. Return the kth smallest fraction considered. Return your answer as an array of integers of size 2; where answer[0] == arr[i] and answer[1] == arr[j]. Example 1: Input: arr = [1;2;3;5]; k = 3 Output: [2;5] Explanation: The fractions to be considered in sorted order are: 1/5; 1/3; 2/5; 1/2; 3/5; and 2/3. The third fraction is 2/5. Example 2: Input: arr = [1;7]; k = 1 Output: [1;7] Constraints: 2 <= arr.length <= 1000 1 <= arr[i] <= 3 * 104 arr[0] == 1 arr[i] is a prime number for i > 0. All the numbers of arr are unique and sorted in strictly increasing order. 1 <= k <= arr.length * (arr.length - 1) / 2 Follow up: Can you solve the problem with better than O(n2) complexity?
Amazon,707,Design Linked List,Med,,
Amazon,843,Guess the Word,Hard,"Array, Hash Table, Dynamic Programming, Sorting",Given an array of unique integers; arr; where each integer arr[i] is strictly greater than 1. We make a binary tree using these integers; and each number may be used for any number of times. Each non-leaf node's value should be equal to the product of the values of its children. Return the number of binary trees we can make. The answer may be too large so return the answer modulo 109 + 7. Example 1: Input: arr = [2;4] Output: 3 Explanation: We can make these trees: [2]; [4]; [4; 2; 2] Example 2: Input: arr = [2;4;5;10] Output: 7 Explanation: We can make these trees: [2]; [4]; [5]; [10]; [4; 2; 2]; [10; 2; 5]; [10; 5; 2]. Constraints: 1 <= arr.length <= 1000 2 <= arr[i] <= 109 All the values of arr are unique.
Amazon,852,Peak Index in a Mountain Array,Med,"Array, Two Pointers, Binary Search, Sorting",There are n persons on a social media website. You are given an integer array ages where ages[i] is the age of the ith person. A Person x will not send a friend request to a person y (x != y) if any of the following conditions is true: age[y] <= 0.5 * age[x] + 7 age[y] > age[x] age[y] > 100 && age[x] < 100 Otherwise; x will send a friend request to y. Note that if x sends a request to y; y will not necessarily send a request to x. Also; a person will not send a friend request to themself. Return the total number of friend requests made. Example 1: Input: ages = [16;16] Output: 2 Explanation: 2 people friend request each other. Example 2: Input: ages = [16;17;18] Output: 2 Explanation: Friend requests are made 17 -> 16; 18 -> 17. Example 3: Input: ages = [20;30;100;110;120] Output: 3 Explanation: Friend requests are made 110 -> 100; 120 -> 110; 120 -> 100. Constraints: n == ages.length 1 <= n <= 2 * 104 1 <= ages[i] <= 120
Amazon,866,Prime Palindrome,Med,"Math, Geometry",An axis-aligned rectangle is represented as a list [x1; y1; x2; y2]; where (x1; y1) is the coordinate of its bottom-left corner; and (x2; y2) is the coordinate of its top-right corner. Its top and bottom edges are parallel to the X-axis; and its left and right edges are parallel to the Y-axis. Two rectangles overlap if the area of their intersection is positive. To be clear; two rectangles that only touch at the corner or edges do not overlap. Given two axis-aligned rectangles rec1 and rec2; return true if they overlap; otherwise return false. Example 1: Input: rec1 = [0;0;2;2]; rec2 = [1;1;3;3] Output: true Example 2: Input: rec1 = [0;0;1;1]; rec2 = [1;0;2;1] Output: false Example 3: Input: rec1 = [0;0;1;1]; rec2 = [2;2;3;3] Output: false Constraints: rec1.length == 4 rec2.length == 4 -109 <= rec1[i]; rec2[i] <= 109 rec1 and rec2 represent a valid rectangle with a non-zero area.
Amazon,874,Walking Robot Simulation,Med,"Two Pointers, String, Stack, Simulation","Given two strings s and t; return true if they are equal when both are typed into empty text editors. '#' means a backspace character. Note that after backspacing an empty text; the text will continue empty. Example 1: Input: s = ""ab#c""; t = ""ad#c"" Output: true Explanation: Both s and t become ""ac"". Example 2: Input: s = ""ab##""; t = ""c#d#"" Output: true Explanation: Both s and t become """". Example 3: Input: s = ""a#c""; t = ""b"" Output: false Explanation: s becomes ""c"" while t becomes ""b"". Constraints: 1 <= s.length; t.length <= 200 s and t only contain lowercase letters and '#' characters. Follow up: Can you solve it in O(n) time and O(1) space?"
Amazon,876,Middle of the Linked List,Easy,"Array, Hash Table, Greedy, Sorting",Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize; and consists of groupSize consecutive cards. Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize; return true if she can rearrange the cards; or false otherwise. Example 1: Input: hand = [1;2;3;6;2;3;4;7;8]; groupSize = 3 Output: true Explanation: Alice's hand can be rearranged as [1;2;3];[2;3;4];[6;7;8] Example 2: Input: hand = [1;2;3;4;5]; groupSize = 4 Output: false Explanation: Alice's hand can not be rearranged into groups of 4. Constraints: 1 <= hand.length <= 104 0 <= hand[i] <= 109 1 <= groupSize <= hand.length Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/
Amazon,884,Uncommon Words from Two Sentences,Easy,"String, Breadth-First Search","Strings s1 and s2 are k-similar (for some non-negative integer k) if we can swap the positions of two letters in s1 exactly k times so that the resulting string equals s2. Given two anagrams s1 and s2; return the smallest k for which s1 and s2 are k-similar. Example 1: Input: s1 = ""ab""; s2 = ""ba"" Output: 1 Explanation: The two string are 1-similar because we can use one swap to change s1 to s2: ""ab"" --> ""ba"". Example 2: Input: s1 = ""abc""; s2 = ""bca"" Output: 2 Explanation: The two strings are 2-similar because we can use two swaps to change s1 to s2: ""abc"" --> ""bac"" --> ""bca"". Constraints: 1 <= s1.length <= 20 s2.length == s1.length s1 and s2 contain only lowercase letters from the set {'a'; 'b'; 'c'; 'd'; 'e'; 'f'}. s2 is an anagram of s1."
Amazon,897,Increasing Order Search Tree,Easy,"Math, Number Theory",Given an integer n; return the smallest prime palindrome greater than or equal to n. An integer is prime if it has exactly two divisors: 1 and itself. Note that 1 is not a prime number. For example; 2; 3; 5; 7; 11; and 13 are all primes. An integer is a palindrome if it reads the same from left to right as it does from right to left. For example; 101 and 12321 are palindromes. The test cases are generated so that the answer always exists and is in the range [2; 2 * 108]. Example 1: Input: n = 6 Output: 7 Example 2: Input: n = 8 Output: 11 Example 3: Input: n = 13 Output: 101 Constraints: 1 <= n <= 108
Amazon,918,Maximum Sum Circular Subarray,Med,"Graph, Heap (Priority Queue), Shortest Path","You are given an undirected graph (the ""original graph"") with n nodes labeled from 0 to n - 1. You decide to subdivide each edge in the graph into a chain of nodes; with the number of new nodes varying between each edge. The graph is given as a 2D array of edges where edges[i] = [ui; vi; cnti] indicates that there is an edge between nodes ui and vi in the original graph; and cnti is the total number of new nodes that you will subdivide the edge into. Note that cnti == 0 means you will not subdivide the edge. To subdivide the edge [ui; vi]; replace it with (cnti + 1) new edges and cnti new nodes. The new nodes are x1; x2; ...; xcnti; and the new edges are [ui; x1]; [x1; x2]; [x2; x3]; ...; [xcnti-1; xcnti]; [xcnti; vi]. In this new graph; you want to know how many nodes are reachable from the node 0; where a node is reachable if the distance is maxMoves or less. Given the original graph and maxMoves; return the number of nodes that are reachable from node 0 in the new graph. Example 1: Input: edges = [[0;1;10];[0;2;1];[1;2;2]]; maxMoves = 6; n = 3 Output: 13 Explanation: The edge subdivisions are shown in the image above. The nodes that are reachable are highlighted in yellow. Example 2: Input: edges = [[0;1;4];[1;2;6];[0;2;8];[1;3;1]]; maxMoves = 10; n = 4 Output: 23 Example 3: Input: edges = [[1;2;4];[1;4;5];[1;3;1];[2;3;4];[3;4;5]]; maxMoves = 17; n = 5 Output: 1 Explanation: Node 0 is disconnected from the rest of the graph; so only node 0 is reachable. Constraints: 0 <= edges.length <= min(n * (n - 1) / 2; 104) edges[i].length == 3 0 <= ui < vi < n There are no multiple edges in the graph. 0 <= cnti <= 104 0 <= maxMoves <= 109 1 <= n <= 3000"
Amazon,919,Complete Binary Tree Inserter,Med,"Array, Math, Geometry, Matrix","You are given an n x n grid where we place some 1 x 1 x 1 cubes that are axis-aligned with the x; y; and z axes. Each value v = grid[i][j] represents a tower of v cubes placed on top of the cell (i; j). We view the projection of these cubes onto the xy; yz; and zx planes. A projection is like a shadow; that maps our 3-dimensional figure to a 2-dimensional plane. We are viewing the ""shadow"" when looking at the cubes from the top; the front; and the side. Return the total area of all three projections. Example 1: Input: grid = [[1;2];[3;4]] Output: 17 Explanation: Here are the three projections (""shadows"") of the shape made with each axis-aligned plane. Example 2: Input: grid = [[2]] Output: 5 Example 3: Input: grid = [[1;0];[0;2]] Output: 8 Constraints: n == grid.length == grid[i].length 1 <= n <= 50 0 <= grid[i][j] <= 50"
Amazon,980,Unique Paths III,Hard,"Array, String, Dynamic Programming, Bit Manipulation, Bitmask","Given an array of strings words; return the smallest string that contains each string in words as a substring. If there are multiple valid strings of the smallest length; return any of them. You may assume that no string in words is a substring of another string in words. Example 1: Input: words = [""alex"";""loves"";""leetcode""] Output: ""alexlovesleetcode"" Explanation: All permutations of ""alex"";""loves"";""leetcode"" would also be accepted. Example 2: Input: words = [""catg"";""ctaagt"";""gcta"";""ttca"";""atgcatc""] Output: ""gctaagttcatgcatc"" Constraints: 1 <= words.length <= 12 1 <= words[i].length <= 20 words[i] consists of lowercase English letters. All the strings of words are unique."
Amazon,1008,Construct Binary Search Tree from Preorder Traversal,Med,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree. We install cameras on the tree nodes where each camera at a node can monitor its parent; itself; and its immediate children. Return the minimum number of cameras needed to monitor all nodes of the tree. Example 1: Input: root = [0;0;null;0;0] Output: 1 Explanation: One camera is enough to monitor all nodes if placed as shown. Example 2: Input: root = [0;0;null;0;null;0;null;null;0] Output: 2 Explanation: At least two cameras are needed to monitor all nodes of the tree. The above image shows one of the valid configurations of camera placement. Constraints: The number of nodes in the tree is in the range [1; 1000]. Node.val == 0
Amazon,1062,Longest Repeating Substring,Med,"Array, Greedy",Given an array of integers arr; return true if we can partition the array into three non-empty parts with equal sums. Formally; we can partition the array if we can find indexes i + 1 < j with (arr[0] + arr[1] + ... + arr[i] == arr[i + 1] + arr[i + 2] + ... + arr[j - 1] == arr[j] + arr[j + 1] + ... + arr[arr.length - 1]) Example 1: Input: arr = [0;2;1;-6;6;-7;9;1;2;0;1] Output: true Explanation: 0 + 2 + 1 = -6 + 6 - 7 + 9 + 1 = 2 + 0 + 1 Example 2: Input: arr = [0;2;1;-6;6;7;9;-1;2;0;1] Output: false Example 3: Input: arr = [3;3;6;5;-2;2;5;1;-9;4] Output: true Explanation: 3 + 3 = 6 = 5 - 2 + 2 + 5 + 1 - 9 + 4 Constraints: 3 <= arr.length <= 5 * 104 -104 <= arr[i] <= 104
Amazon,1068,Product Sales Analysis I,Easy,"Math, Dynamic Programming",
Amazon,1244,Design A Leaderboard,Med,"String, Trie, Rolling Hash, Hash Function","Return the number of distinct non-empty substrings of text that can be written as the concatenation of some string with itself (i.e. it can be written as a + a where a is some string). Example 1: Input: text = ""abcabcabc"" Output: 3 Explanation: The 3 substrings are ""abcabc""; ""bcabca"" and ""cabcab"". Example 2: Input: text = ""leetcodeleetcode"" Output: 2 Explanation: The 2 substrings are ""ee"" and ""leetcodeleetcode"". Constraints: 1 <= text.length <= 2000 text has only lowercase English letters."
Amazon,550,Game Play Analysis IV,Med,"Array, Breadth-First Search, Matrix",
Amazon,1095,Find in Mountain Array,Hard,"Array, Greedy, Sorting",A company is planning to interview 2n people. Given the array costs where costs[i] = [aCosti; bCosti]; the cost of flying the ith person to city a is aCosti; and the cost of flying the ith person to city b is bCosti. Return the minimum cost to fly every person to a city such that exactly n people arrive in each city. Example 1: Input: costs = [[10;20];[30;200];[400;50];[30;20]] Output: 110 Explanation: The first person goes to city A for a cost of 10. The second person goes to city A for a cost of 30. The third person goes to city B for a cost of 50. The fourth person goes to city B for a cost of 20. The total minimum cost is 10 + 30 + 50 + 20 = 110 to have half the people interviewing in each city. Example 2: Input: costs = [[259;770];[448;54];[926;667];[184;139];[840;118];[577;469]] Output: 1859 Example 3: Input: costs = [[515;563];[451;713];[537;709];[343;819];[855;779];[457;60];[650;359];[631;42]] Output: 3086 Constraints: 2 * n == costs.length 2 <= costs.length <= 100 costs.length is even. 1 <= aCosti; bCosti <= 1000
Amazon,1164,Product Price at a Given Date,Med,"Array, Math",
Amazon,1249,Minimum Remove to Make Valid Parentheses,Med,"Array, Hash Table, Binary Search, Design","Implement a SnapshotArray that supports the following interface: SnapshotArray(int length) initializes an array-like data structure with the given length. Initially; each element equals 0. void set(index; val) sets the element at the given index to be equal to val. int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1. int get(index; snap_id) returns the value at the given index; at the time we took the snapshot with the given snap_id Example 1: Input: [""SnapshotArray"";""set"";""snap"";""set"";""get""] [[3];[0;5];[];[0;6];[0;0]] Output: [null;null;0;null;5] Explanation: SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3 snapshotArr.set(0;5); // Set array[0] = 5 snapshotArr.snap(); // Take a snapshot; return snap_id = 0 snapshotArr.set(0;6); snapshotArr.get(0;0); // Get the value of array[0] with snap_id = 0; return 5 Constraints: 1 <= length <= 5 * 104 0 <= index < length 0 <= val <= 109 0 <= snap_id < (the total number of times we call snap()) At most 5 * 104 calls will be made to set; snap; and get."
Amazon,1293,Shortest Path in a Grid with Obstacles Elimination,Hard,Array,Given an integer array arr; return true if there are three consecutive odd numbers in the array. Otherwise; return false. Example 1: Input: arr = [2;6;4;1] Output: false Explanation: There are no three consecutive odds. Example 2: Input: arr = [1;2;34;3;4;5;7;23;12] Output: true Explanation: [5;7;23] are three consecutive odds. Constraints: 1 <= arr.length <= 1000 1 <= arr[i] <= 1000
Amazon,1280,Students and Examinations,Easy,"Array, Sliding Window",
Amazon,1310,XOR Queries of a Subarray,Med,"Array, Simulation",You want to water n plants in your garden with a watering can. The plants are arranged in a row and are labeled from 0 to n - 1 from left to right where the ith plant is located at x = i. There is a river at x = -1 that you can refill your watering can at. Each plant needs a specific amount of water. You will water the plants in the following way: Water the plants in order from left to right. After watering the current plant; if you do not have enough water to completely water the next plant; return to the river to fully refill the watering can. You cannot refill the watering can early. You are initially at the river (i.e.; x = -1). It takes one step to move one unit on the x-axis. Given a 0-indexed integer array plants of n integers; where plants[i] is the amount of water the ith plant needs; and an integer capacity representing the watering can capacity; return the number of steps needed to water all the plants. Example 1: Input: plants = [2;2;3;3]; capacity = 5 Output: 14 Explanation: Start at the river with a full watering can: - Walk to plant 0 (1 step) and water it. Watering can has 3 units of water. - Walk to plant 1 (1 step) and water it. Watering can has 1 unit of water. - Since you cannot completely water plant 2; walk back to the river to refill (2 steps). - Walk to plant 2 (3 steps) and water it. Watering can has 2 units of water. - Since you cannot completely water plant 3; walk back to the river to refill (3 steps). - Walk to plant 3 (4 steps) and water it. Steps needed = 1 + 1 + 2 + 3 + 3 + 4 = 14. Example 2: Input: plants = [1;1;1;4;2;3]; capacity = 4 Output: 30 Explanation: Start at the river with a full watering can: - Water plants 0; 1; and 2 (3 steps). Return to river (3 steps). - Water plant 3 (4 steps). Return to river (4 steps). - Water plant 4 (5 steps). Return to river (5 steps). - Water plant 5 (6 steps). Steps needed = 3 + 3 + 4 + 4 + 5 + 5 + 6 = 30. Example 3: Input: plants = [7;7;7;7;7;7;7]; capacity = 8 Output: 49 Explanation: You have to refill before watering each plant. Steps needed = 1 + 1 + 2 + 2 + 3 + 3 + 4 + 4 + 5 + 5 + 6 + 6 + 7 = 49. Constraints: n == plants.length 1 <= n <= 1000 1 <= plants[i] <= 106 max(plants[i]) <= capacity <= 109
Amazon,1343,Number of Sub-arrays of Size K and Average Greater than or Equal to Threshold,Med,"Array, Dynamic Programming",A die simulator generates a random number from 1 to 6 for each roll. You introduced a constraint to the generator such that it cannot roll the number i more than rollMax[i] (1-indexed) consecutive times. Given an array of integers rollMax and an integer n; return the number of distinct sequences that can be obtained with exact n rolls. Since the answer may be too large; return it modulo 109 + 7. Two sequences are considered different if at least one element differs from each other. Example 1: Input: n = 2; rollMax = [1;1;2;2;2;3] Output: 34 Explanation: There will be 2 rolls of die; if there are no constraints on the die; there are 6 * 6 = 36 possible combinations. In this case; looking at rollMax array; the numbers 1 and 2 appear at most once consecutively; therefore sequences (1;1) and (2;2) cannot occur; so the final answer is 36-2 = 34. Example 2: Input: n = 2; rollMax = [1;1;1;1;1;1] Output: 30 Example 3: Input: n = 3; rollMax = [1;1;1;2;2;3] Output: 181 Constraints: 1 <= n <= 5000 rollMax.length == 6 1 <= rollMax[i] <= 15
Amazon,1321,Restaurant Growth,Med,"String, Binary Search, Sliding Window, Prefix Sum","You are given two strings s and t of the same length and an integer maxCost. You want to change s to t. Changing the ith character of s to ith character of t costs |s[i] - t[i]| (i.e.; the absolute difference between the ASCII values of the characters). Return the maximum length of a substring of s that can be changed to be the same as the corresponding substring of t with a cost less than or equal to maxCost. If there is no substring from s that can be changed to its corresponding substring from t; return 0. Example 1: Input: s = ""abcd""; t = ""bcdf""; maxCost = 3 Output: 3 Explanation: ""abc"" of s can change to ""bcd"". That costs 3; so the maximum length is 3. Example 2: Input: s = ""abcd""; t = ""cdef""; maxCost = 3 Output: 1 Explanation: Each character in s costs 2 to change to character in t; so the maximum length is 1. Example 3: Input: s = ""abcd""; t = ""acde""; maxCost = 0 Output: 1 Explanation: You cannot make any change; so the maximum length is 1. Constraints: 1 <= s.length <= 105 t.length == s.length 0 <= maxCost <= 106 s and t consist of only lowercase English letters."
Amazon,1347,Minimum Number of Steps to Make Two Strings Anagram,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
Amazon,1371,Find the Longest Substring Containing Vowels in Even Counts,Med,"String, Stack","Given a string s of '(' ; ')' and lowercase English characters. Your task is to remove the minimum number of parentheses ( '(' or ')'; in any positions ) so that the resulting parentheses string is valid and return any valid string. Formally; a parentheses string is valid if and only if: It is the empty string; contains only lowercase characters; or It can be written as AB (A concatenated with B); where A and B are valid strings; or It can be written as (A); where A is a valid string. Example 1: Input: s = ""lee(t(c)o)de)"" Output: ""lee(t(c)o)de"" Explanation: ""lee(t(co)de)"" ; ""lee(t(c)ode)"" would also be accepted. Example 2: Input: s = ""a)b(c)d"" Output: ""ab(c)d"" Example 3: Input: s = ""))(("" Output: """" Explanation: An empty string is also valid. Constraints: 1 <= s.length <= 105 s[i] is either '(' ; ')'; or lowercase English letter."
Amazon,1353,Maximum Number of Events That Can Be Attended,Med,"Array, Hash Table, String, Sorting","You are given a 0-indexed string array words; where words[i] consists of lowercase English letters. In one operation; select any index i such that 0 < i < words.length and words[i - 1] and words[i] are anagrams; and delete words[i] from words. Keep performing this operation as long as you can select an index that satisfies the conditions. Return words after performing all operations. It can be shown that selecting the indices for each operation in any arbitrary order will lead to the same result. An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase using all the original letters exactly once. For example; ""dacb"" is an anagram of ""abdc"". Example 1: Input: words = [""abba"";""baba"";""bbaa"";""cd"";""cd""] Output: [""abba"";""cd""] Explanation: One of the ways we can obtain the resultant array is by using the following operations: - Since words[2] = ""bbaa"" and words[1] = ""baba"" are anagrams; we choose index 2 and delete words[2]. Now words = [""abba"";""baba"";""cd"";""cd""]. - Since words[1] = ""baba"" and words[0] = ""abba"" are anagrams; we choose index 1 and delete words[1]. Now words = [""abba"";""cd"";""cd""]. - Since words[2] = ""cd"" and words[1] = ""cd"" are anagrams; we choose index 2 and delete words[2]. Now words = [""abba"";""cd""]. We can no longer perform any operations; so [""abba"";""cd""] is the final answer. Example 2: Input: words = [""a"";""b"";""c"";""d"";""e""] Output: [""a"";""b"";""c"";""d"";""e""] Explanation: No two adjacent strings in words are anagrams of each other; so no operations are performed. Constraints: 1 <= words.length <= 100 1 <= words[i].length <= 10 words[i] consists of lowercase English letters."
Amazon,1367,Linked List in Binary Tree,Med,"Array, Dynamic Programming, Sorting",Given n cuboids where the dimensions of the ith cuboid is cuboids[i] = [widthi; lengthi; heighti] (0-indexed). Choose a subset of cuboids and place them on each other. You can place cuboid i on cuboid j if widthi <= widthj and lengthi <= lengthj and heighti <= heightj. You can rearrange any cuboid's dimensions by rotating it to put it on another cuboid. Return the maximum height of the stacked cuboids. Example 1: Input: cuboids = [[50;45;20];[95;37;53];[45;23;12]] Output: 190 Explanation: Cuboid 1 is placed on the bottom with the 53x37 side facing down with height 95. Cuboid 0 is placed next with the 45x20 side facing down with height 50. Cuboid 2 is placed next with the 23x12 side facing down with height 45. The total height is 95 + 50 + 45 = 190. Example 2: Input: cuboids = [[38;25;45];[76;35;3]] Output: 76 Explanation: You can't place any of the cuboids on the other. We choose cuboid 1 and rotate it so that the 35x3 side is facing down and its height is 76. Example 3: Input: cuboids = [[7;11;17];[7;17;11];[11;7;17];[11;17;7];[17;7;11];[17;11;7]] Output: 102 Explanation: After rearranging the cuboids; you can see that all cuboids have the same dimension. You can place the 11x7 side down on all cuboids so their heights are 17. The maximum height of stacked cuboids is 6 * 17 = 102. Constraints: n == cuboids.length 1 <= n <= 100 1 <= widthi; lengthi; heighti <= 100
Amazon,1378,Replace Employee ID With The Unique Identifier,Easy,"Array, Math, Simulation",There is an m x n matrix that is initialized to all 0's. There is also a 2D array indices where each indices[i] = [ri; ci] represents a 0-indexed location to perform some increment operations on the matrix. For each location indices[i]; do both of the following: Increment all the cells on row ri. Increment all the cells on column ci. Given m; n; and indices; return the number of odd-valued cells in the matrix after applying the increment to all locations in indices. Example 1: Input: m = 2; n = 3; indices = [[0;1];[1;1]] Output: 6 Explanation: Initial matrix = [[0;0;0];[0;0;0]]. After applying first increment it becomes [[1;2;1];[0;1;0]]. The final matrix is [[1;3;1];[1;3;1]]; which contains 6 odd numbers. Example 2: Input: m = 2; n = 2; indices = [[1;1];[0;0]] Output: 0 Explanation: Final matrix = [[2;2];[2;2]]. There are no odd numbers in the final matrix. Constraints: 1 <= m; n <= 50 1 <= indices.length <= 100 0 <= ri < m 0 <= ci < n Follow up: Could you solve this in O(n + m + indices.length) time with only O(n + m) extra space?
Amazon,1410,HTML Entity Parser,Med,Concurrency,
Amazon,1464,Maximum Product of Two Elements in an Array,Easy,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue)",You are given an integer array arr. You can choose a set of integers and remove all the occurrences of these integers in the array. Return the minimum size of the set so that at least half of the integers of the array are removed. Example 1: Input: arr = [3;3;3;3;5;5;5;2;2;7] Output: 2 Explanation: Choosing {3;7} will make the new array [5;5;5;2;2] which has size 5 (i.e equal to half of the size of the old array). Possible sets of size 2 are {3;5};{3;2};{5;2}. Choosing set {2;7} is not possible as it will make the new array [3;3;3;3;5;5;5] which has a size greater than half of the size of the old array. Example 2: Input: arr = [7;7;7;7;7;7] Output: 1 Explanation: The only possible set you can choose is {7}. This will make the new array empty. Constraints: 2 <= arr.length <= 105 arr.length is even. 1 <= arr[i] <= 105
Amazon,1539,Kth Missing Positive Number,Easy,"Array, Sorting, Heap (Priority Queue)",Given a 2D integer array nums; return all elements of nums in diagonal order as shown in the below images. Example 1: Input: nums = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;4;2;7;5;3;8;6;9] Example 2: Input: nums = [[1;2;3;4;5];[6;7];[8];[9;10;11];[12;13;14;15;16]] Output: [1;6;2;8;7;3;9;4;12;10;5;13;11;14;15;16] Constraints: 1 <= nums.length <= 105 1 <= nums[i].length <= 105 1 <= sum(nums[i].length) <= 105 1 <= nums[i][j] <= 105
Amazon,1545,Find Kth Bit in Nth Binary String,Med,"Array, Dynamic Programming","Given an array of integers cost and an integer target; return the maximum integer you can paint under the following rules: The cost of painting a digit (i + 1) is given by cost[i] (0-indexed). The total cost used must be equal to target. The integer does not have 0 digits. Since the answer may be very large; return it as a string. If there is no way to paint any integer given the condition; return ""0"". Example 1: Input: cost = [4;3;2;5;6;7;2;5;5]; target = 9 Output: ""7772"" Explanation: The cost to paint the digit '7' is 2; and the digit '2' is 3. Then cost(""7772"") = 2*3+ 3*1 = 9. You could also paint ""977""; but ""7772"" is the largest number. Digit cost 1 -> 4 2 -> 3 3 -> 2 4 -> 5 5 -> 6 6 -> 7 7 -> 2 8 -> 5 9 -> 5 Example 2: Input: cost = [7;6;5;5;5;6;8;7;8]; target = 12 Output: ""85"" Explanation: The cost to paint the digit '8' is 7; and the digit '5' is 5. Then cost(""85"") = 7 + 5 = 12. Example 3: Input: cost = [2;4;6;2;4;6;4;4;4]; target = 5 Output: ""0"" Explanation: It is impossible to paint any integer with total cost equal to target. Constraints: cost.length == 9 1 <= cost[i]; target <= 5000"
Amazon,1549,The Most Recent Orders for Each Product,Med,"Array, Queue, Sliding Window, Heap (Priority Queue), Ordered Set, Monotonic Queue",Given an array of integers nums and an integer limit; return the size of the longest non-empty subarray such that the absolute difference between any two elements of this subarray is less than or equal to limit. Example 1: Input: nums = [8;2;4;7]; limit = 4 Output: 2 Explanation: All subarrays are: [8] with maximum absolute diff |8-8| = 0 <= 4. [8;2] with maximum absolute diff |8-2| = 6 > 4. [8;2;4] with maximum absolute diff |8-2| = 6 > 4. [8;2;4;7] with maximum absolute diff |8-2| = 6 > 4. [2] with maximum absolute diff |2-2| = 0 <= 4. [2;4] with maximum absolute diff |2-4| = 2 <= 4. [2;4;7] with maximum absolute diff |2-7| = 5 > 4. [4] with maximum absolute diff |4-4| = 0 <= 4. [4;7] with maximum absolute diff |4-7| = 3 <= 4. [7] with maximum absolute diff |7-7| = 0 <= 4. Therefore; the size of the longest subarray is 2. Example 2: Input: nums = [10;1;2;4;7;2]; limit = 5 Output: 4 Explanation: The subarray [2;4;7;2] is the longest since the maximum absolute diff is |2-7| = 5 <= 5. Example 3: Input: nums = [4;2;2;2;4;4;2;2]; limit = 0 Output: 3 Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 109 0 <= limit <= 109
Amazon,1593,Split a String Into the Max Number of Unique Substrings,Med,,
Amazon,1662,Check If Two String Arrays are Equivalent,Easy,"Array, Greedy, Bit Manipulation",You are given an integer array nums. You have an integer array arr of the same length with all values set to 0 initially. You also have the following modify function: You want to use the modify function to convert arr to nums using the minimum number of calls. Return the minimum number of function calls to make nums from arr. The test cases are generated so that the answer fits in a 32-bit signed integer. Example 1: Input: nums = [1;5] Output: 5 Explanation: Increment by 1 (second element): [0; 0] to get [0; 1] (1 operation). Double all the elements: [0; 1] -> [0; 2] -> [0; 4] (2 operations). Increment by 1 (both elements) [0; 4] -> [1; 4] -> [1; 5] (2 operations). Total of operations: 1 + 2 + 2 = 5. Example 2: Input: nums = [2;2] Output: 3 Explanation: Increment by 1 (both elements) [0; 0] -> [0; 1] -> [1; 1] (2 operations). Double all the elements: [1; 1] -> [2; 2] (1 operation). Total of operations: 2 + 1 = 3. Example 3: Input: nums = [4;2;5] Output: 6 Explanation: (initial)[0;0;0] -> [1;0;0] -> [1;0;1] -> [2;0;2] -> [2;1;2] -> [4;2;4] -> [4;2;5](nums). Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109
Amazon,1679,Max Number of K-Sum Pairs,Med,"Array, Two Pointers, Binary Search, Stack, Monotonic Stack",Given an integer array arr; remove a subarray (can be empty) from arr such that the remaining elements in arr are non-decreasing. Return the length of the shortest subarray to remove. A subarray is a contiguous subsequence of the array. Example 1: Input: arr = [1;2;3;10;4;2;3;5] Output: 3 Explanation: The shortest subarray we can remove is [10;4;2] of length 3. The remaining elements after that will be [1;2;3;3;5] which are sorted. Another correct solution is to remove the subarray [3;10;4]. Example 2: Input: arr = [5;4;3;2;1] Output: 4 Explanation: Since the array is strictly decreasing; we can only keep a single element. Therefore we need to remove a subarray of length 4; either [5;4;3;2] or [4;3;2;1]. Example 3: Input: arr = [1;2;3] Output: 0 Explanation: The array is already non-decreasing. We do not need to remove any elements. Constraints: 1 <= arr.length <= 105 0 <= arr[i] <= 109
Amazon,1661,Average Time of Process per Machine,Easy,Graph,Given a directed acyclic graph; with n vertices numbered from 0 to n-1; and an array edges where edges[i] = [fromi; toi] represents a directed edge from node fromi to node toi. Find the smallest set of vertices from which all nodes in the graph are reachable. It's guaranteed that a unique solution exists. Notice that you can return the vertices in any order. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;5];[3;4];[4;2]] Output: [0;3] Explanation: It's not possible to reach all the nodes from a single vertex. From 0 we can reach [0;1;2;5]. From 3 we can reach [3;4;2;5]. So we output [0;3]. Example 2: Input: n = 5; edges = [[0;1];[2;1];[3;1];[1;4];[2;4]] Output: [0;2;3] Explanation: Notice that vertices 0; 3 and 2 are not reachable from any other node; so we must include them. Also any of these vertices can reach nodes 1 and 4. Constraints: 2 <= n <= 10^5 1 <= edges.length <= min(10^5; n * (n - 1) / 2) edges[i].length == 2 0 <= fromi; toi < n All pairs (fromi; toi) are distinct.
Amazon,1689,Partitioning Into Minimum Number Of Deci-Binary Numbers,Med,"Array, Enumeration",Given an array of positive integers arr; find a pattern of length m that is repeated k or more times. A pattern is a subarray (consecutive sub-sequence) that consists of one or more values; repeated multiple times consecutively without overlapping. A pattern is defined by its length and the number of repetitions. Return true if there exists a pattern of length m that is repeated k or more times; otherwise return false. Example 1: Input: arr = [1;2;4;4;4;4]; m = 1; k = 3 Output: true Explanation: The pattern (4) of length 1 is repeated 4 consecutive times. Notice that pattern can be repeated k or more times but not less. Example 2: Input: arr = [1;2;1;2;1;1;1;3]; m = 2; k = 2 Output: true Explanation: The pattern (1;2) of length 2 is repeated 2 consecutive times. Another valid pattern (2;1) is also repeated 2 times. Example 3: Input: arr = [1;2;1;2;1;3]; m = 2; k = 3 Output: false Explanation: The pattern (1;2) is of length 2 but is repeated only 2 times. There is no pattern of length 2 that is repeated 3 or more times. Constraints: 2 <= arr.length <= 100 1 <= arr[i] <= 100 1 <= m <= 100 2 <= k <= 100
Amazon,1683,Invalid Tweets,Easy,"Array, Math, Greedy, Sorting, Game Theory",There are 3n piles of coins of varying size; you and your friends will take piles of coins as follows: In each step; you will choose any 3 piles of coins (not necessarily consecutive). Of your choice; Alice will pick the pile with the maximum number of coins. You will pick the next pile with the maximum number of coins. Your friend Bob will pick the last pile. Repeat until there are no more piles of coins. Given an array of integers piles where piles[i] is the number of coins in the ith pile. Return the maximum number of coins that you can have. Example 1: Input: piles = [2;4;1;2;7;8] Output: 9 Explanation: Choose the triplet (2; 7; 8); Alice Pick the pile with 8 coins; you the pile with 7 coins and Bob the last one. Choose the triplet (1; 2; 4); Alice Pick the pile with 4 coins; you the pile with 2 coins and Bob the last one. The maximum number of coins which you can have are: 7 + 2 = 9. On the other hand if we choose this arrangement (1; 2; 8); (2; 4; 7) you only get 2 + 4 = 6 coins which is not optimal. Example 2: Input: piles = [2;4;5] Output: 4 Example 3: Input: piles = [9;8;7;6;5;1;2;3;4] Output: 18 Constraints: 3 <= piles.length <= 105 piles.length % 3 == 0 1 <= piles[i] <= 104
Amazon,1813,Sentence Similarity III,Med,"Array, Hash Table, Sliding Window",You are given an array of positive integers nums and want to erase a subarray containing unique elements. The score you get by erasing the subarray is equal to the sum of its elements. Return the maximum score you can get by erasing exactly one subarray. An array b is called to be a subarray of a if it forms a contiguous subsequence of a; that is; if it is equal to a[l];a[l+1];...;a[r] for some (l;r). Example 1: Input: nums = [4;2;4;5;6] Output: 17 Explanation: The optimal subarray here is [2;4;5;6]. Example 2: Input: nums = [5;2;1;2;5;2;1;2;5] Output: 8 Explanation: The optimal subarray here is [5;2;1] or [1;2;5]. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 104
Amazon,1838,Frequency of the Most Frequent Element,Med,"String, Trie, Rolling Hash, Suffix Array, Hash Function",
Amazon,1882,Process Tasks Using Servers,Med,Database,Table: Employees +-------------+----------+ | Column Name | Type | +-------------+----------+ | employee_id | int | | name | varchar | | reports_to | int | | age | int | +-------------+----------+ employee_id is the column with unique values for this table. This table contains information about the employees and the id of the manager they report to. Some employees do not report to anyone (reports_to is null). For this problem; we will consider a manager an employee who has at least 1 other employee reporting to them. Write a solution to report the ids and the names of all managers; the number of employees who report directly to them; and the average age of the reports rounded to the nearest integer. Return the result table ordered by employee_id. The result format is in the following example. Example 1: Input: Employees table: +-------------+---------+------------+-----+ | employee_id | name | reports_to | age | +-------------+---------+------------+-----+ | 9 | Hercy | null | 43 | | 6 | Alice | 9 | 41 | | 4 | Bob | 9 | 36 | | 2 | Winston | null | 37 | +-------------+---------+------------+-----+ Output: +-------------+-------+---------------+-------------+ | employee_id | name | reports_count | average_age | +-------------+-------+---------------+-------------+ | 9 | Hercy | 2 | 39 | +-------------+-------+---------------+-------------+ Explanation: Hercy has 2 people report directly to him; Alice and Bob. Their average age is (41+36)/2 = 38.5; which is 39 after rounding it to the nearest integer. Example 2: Input: Employees table: +-------------+---------+------------+-----+ | employee_id | name | reports_to | age | |-------------|---------|------------|-----| | 1 | Michael | null | 45 | | 2 | Alice | 1 | 38 | | 3 | Bob | 1 | 42 | | 4 | Charlie | 2 | 34 | | 5 | David | 2 | 40 | | 6 | Eve | 3 | 37 | | 7 | Frank | null | 50 | | 8 | Grace | null | 48 | +-------------+---------+------------+-----+ Output: +-------------+---------+---------------+-------------+ | employee_id | name | reports_count | average_age | | ----------- | ------- | ------------- | ----------- | | 1 | Michael | 2 | 40 | | 2 | Alice | 2 | 37 | | 3 | Bob | 1 | 37 | +-------------+---------+---------------+-------------+
Amazon,1926,Nearest Exit from Entrance in Maze,Med,Database,
Amazon,1934,Confirmation Rate,Med,"Array, Hash Table, String","You are given a string s that contains some bracket pairs; with each pair containing a non-empty key. For example; in the string ""(name)is(age)yearsold""; there are two bracket pairs that contain the keys ""name"" and ""age"". You know the values of a wide range of keys. This is represented by a 2D string array knowledge where each knowledge[i] = [keyi; valuei] indicates that key keyi has a value of valuei. You are tasked to evaluate all of the bracket pairs. When you evaluate a bracket pair that contains some key keyi; you will: Replace keyi and the bracket pair with the key's corresponding valuei. If you do not know the value of the key; you will replace keyi and the bracket pair with a question mark ""?"" (without the quotation marks). Each key will appear at most once in your knowledge. There will not be any nested brackets in s. Return the resulting string after evaluating all of the bracket pairs. Example 1: Input: s = ""(name)is(age)yearsold""; knowledge = [[""name"";""bob""];[""age"";""two""]] Output: ""bobistwoyearsold"" Explanation: The key ""name"" has a value of ""bob""; so replace ""(name)"" with ""bob"". The key ""age"" has a value of ""two""; so replace ""(age)"" with ""two"". Example 2: Input: s = ""hi(name)""; knowledge = [[""a"";""b""]] Output: ""hi?"" Explanation: As you do not know the value of the key ""name""; replace ""(name)"" with ""?"". Example 3: Input: s = ""(a)(a)(a)aaa""; knowledge = [[""a"";""yes""]] Output: ""yesyesyesaaa"" Explanation: The same key can appear multiple times. The key ""a"" has a value of ""yes""; so replace all occurrences of ""(a)"" with ""yes"". Notice that the ""a""s not in a bracket pair are not evaluated. Constraints: 1 <= s.length <= 105 0 <= knowledge.length <= 105 knowledge[i].length == 2 1 <= keyi.length; valuei.length <= 10 s consists of lowercase English letters and round brackets '(' and ')'. Every open bracket '(' in s will have a corresponding close bracket ')'. The key in each bracket pair of s will be non-empty. There will not be any nested bracket pairs in s. keyi and valuei consist of lowercase English letters. Each keyi in knowledge is unique."
Amazon,1963,Minimum Number of Swaps to Make the String Balanced,Med,"Array, Math, Bit Manipulation",The XOR sum of a list is the bitwise XOR of all its elements. If the list only contains one element; then its XOR sum will be equal to this element. For example; the XOR sum of [1;2;3;4] is equal to 1 XOR 2 XOR 3 XOR 4 = 4; and the XOR sum of [3] is equal to 3. You are given two 0-indexed arrays arr1 and arr2 that consist only of non-negative integers. Consider the list containing the result of arr1[i] AND arr2[j] (bitwise AND) for every (i; j) pair where 0 <= i < arr1.length and 0 <= j < arr2.length. Return the XOR sum of the aforementioned list. Example 1: Input: arr1 = [1;2;3]; arr2 = [6;5] Output: 0 Explanation: The list = [1 AND 6; 1 AND 5; 2 AND 6; 2 AND 5; 3 AND 6; 3 AND 5] = [0;1;2;0;2;1]. The XOR sum = 0 XOR 1 XOR 2 XOR 0 XOR 2 XOR 1 = 0. Example 2: Input: arr1 = [12]; arr2 = [4] Output: 4 Explanation: The list = [12 AND 4] = [4]. The XOR sum = 4. Constraints: 1 <= arr1.length; arr2.length <= 105 0 <= arr1[i]; arr2[j] <= 109
Amazon,2037,Minimum Number of Moves to Seat Everyone,Easy,"Math, Enumeration",A square triple (a;b;c) is a triple where a; b; and c are integers and a2 + b2 = c2. Given an integer n; return the number of square triples such that 1 <= a; b; c <= n. Example 1: Input: n = 5 Output: 2 Explanation: The square triples are (3;4;5) and (4;3;5). Example 2: Input: n = 10 Output: 4 Explanation: The square triples are (3;4;5); (4;3;5); (6;8;10); and (8;6;10). Constraints: 1 <= n <= 250
Amazon,2028,Find Missing Observations,Med,"Dynamic Programming, Memoization",There is a tournament where n players are participating. The players are standing in a single row and are numbered from 1 to n based on their initial standing position (player 1 is the first player in the row; player 2 is the second player in the row; etc.). The tournament consists of multiple rounds (starting from round number 1). In each round; the ith player from the front of the row competes against the ith player from the end of the row; and the winner advances to the next round. When the number of players is odd for the current round; the player in the middle automatically advances to the next round. For example; if the row consists of players 1; 2; 4; 6; 7 Player 1 competes against player 7. Player 2 competes against player 6. Player 4 automatically advances to the next round. After each round is over; the winners are lined back up in the row based on the original ordering assigned to them initially (ascending order). The players numbered firstPlayer and secondPlayer are the best in the tournament. They can win against any other player before they compete against each other. If any two other players compete against each other; either of them might win; and thus you may choose the outcome of this round. Given the integers n; firstPlayer; and secondPlayer; return an integer array containing two values; the earliest possible round number and the latest possible round number in which these two players will compete against each other; respectively. Example 1: Input: n = 11; firstPlayer = 2; secondPlayer = 4 Output: [3;4] Explanation: One possible scenario which leads to the earliest round number: First round: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11 Second round: 2; 3; 4; 5; 6; 11 Third round: 2; 3; 4 One possible scenario which leads to the latest round number: First round: 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11 Second round: 1; 2; 3; 4; 5; 6 Third round: 1; 2; 4 Fourth round: 2; 4 Example 2: Input: n = 5; firstPlayer = 1; secondPlayer = 5 Output: [1;1] Explanation: The players numbered 1 and 5 compete in the first round. There is no way to make them compete in any other round. Constraints: 2 <= n <= 28 1 <= firstPlayer < secondPlayer <= n
Amazon,2035,Partition Array Into Two Arrays to Minimize Sum Difference,Hard,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given two m x n binary matrices grid1 and grid2 containing only 0's (representing water) and 1's (representing land). An island is a group of 1's connected 4-directionally (horizontal or vertical). Any cells outside of the grid are considered water cells. An island in grid2 is considered a sub-island if there is an island in grid1 that contains all the cells that make up this island in grid2. Return the number of islands in grid2 that are considered sub-islands. Example 1: Input: grid1 = [[1;1;1;0;0];[0;1;1;1;1];[0;0;0;0;0];[1;0;0;0;0];[1;1;0;1;1]]; grid2 = [[1;1;1;0;0];[0;0;1;1;1];[0;1;0;0;0];[1;0;1;1;0];[0;1;0;1;0]] Output: 3 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are three sub-islands. Example 2: Input: grid1 = [[1;0;1;0;1];[1;1;1;1;1];[0;0;0;0;0];[1;1;1;1;1];[1;0;1;0;1]]; grid2 = [[0;0;0;0;0];[1;1;1;1;1];[0;1;0;1;0];[0;1;0;1;0];[1;0;0;0;1]] Output: 2 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are two sub-islands. Constraints: m == grid1.length == grid2.length n == grid1[i].length == grid2[i].length 1 <= m; n <= 500 grid1[i][j] and grid2[i][j] are either 0 or 1.
Amazon,2049,Count Nodes With the Highest Score,Med,"Array, Greedy, Sorting",You are playing a video game where you are defending your city from a group of n monsters. You are given a 0-indexed integer array dist of size n; where dist[i] is the initial distance in kilometers of the ith monster from the city. The monsters walk toward the city at a constant speed. The speed of each monster is given to you in an integer array speed of size n; where speed[i] is the speed of the ith monster in kilometers per minute. You have a weapon that; once fully charged; can eliminate a single monster. However; the weapon takes one minute to charge. The weapon is fully charged at the very start. You lose when any monster reaches your city. If a monster reaches the city at the exact moment the weapon is fully charged; it counts as a loss; and the game ends before you can use your weapon. Return the maximum number of monsters that you can eliminate before you lose; or n if you can eliminate all the monsters before they reach the city. Example 1: Input: dist = [1;3;4]; speed = [1;1;1] Output: 3 Explanation: In the beginning; the distances of the monsters are [1;3;4]. You eliminate the first monster. After a minute; the distances of the monsters are [X;2;3]. You eliminate the second monster. After a minute; the distances of the monsters are [X;X;2]. You eliminate the third monster. All 3 monsters can be eliminated. Example 2: Input: dist = [1;1;2;3]; speed = [1;1;1;1] Output: 1 Explanation: In the beginning; the distances of the monsters are [1;1;2;3]. You eliminate the first monster. After a minute; the distances of the monsters are [X;0;1;2]; so you lose. You can only eliminate 1 monster. Example 3: Input: dist = [3;2;4]; speed = [5;3;2] Output: 1 Explanation: In the beginning; the distances of the monsters are [3;2;4]. You eliminate the first monster. After a minute; the distances of the monsters are [X;0;2]; so you lose. You can only eliminate 1 monster. Constraints: n == dist.length == speed.length 1 <= n <= 105 1 <= dist[i]; speed[i] <= 105
Amazon,2070,Most Beautiful Item for Each Query,Med,String,
Amazon,2064,Minimized Maximum of Products Distributed to Any Store,Med,Database,
Amazon,2095,Delete the Middle Node of a Linked List,Med,"Two Pointers, String, Stack, Greedy","You are given a 0-indexed string s of even length n. The string consists of exactly n / 2 opening brackets '[' and n / 2 closing brackets ']'. A string is called balanced if and only if: It is the empty string; or It can be written as AB; where both A and B are balanced strings; or It can be written as [C]; where C is a balanced string. You may swap the brackets at any two indices any number of times. Return the minimum number of swaps to make s balanced. Example 1: Input: s = ""][]["" Output: 1 Explanation: You can make the string balanced by swapping index 0 with index 3. The resulting string is ""[[]]"". Example 2: Input: s = ""]]][[["" Output: 2 Explanation: You can do the following to make the string balanced: - Swap index 0 with index 4. s = ""[]][]["". - Swap index 1 with index 5. s = ""[[][]]"". The resulting string is ""[[][]]"". Example 3: Input: s = ""[]"" Output: 0 Explanation: The string is already balanced. Constraints: n == s.length 2 <= n <= 106 n is even. s[i] is either '[' or ']'. The number of opening brackets '[' equals n / 2; and the number of closing brackets ']' equals n / 2."
Amazon,2222,Number of Ways to Select Buildings,Med,Math,"You are given two positive integers left and right with left <= right. Calculate the product of all integers in the inclusive range [left; right]. Since the product may be very large; you will abbreviate it following these steps: Count all trailing zeros in the product and remove them. Let us denote this count as C. For example; there are 3 trailing zeros in 1000; and there are 0 trailing zeros in 546. Denote the remaining number of digits in the product as d. If d > 10; then express the product as <pre>...<suf> where <pre> denotes the first 5 digits of the product; and <suf> denotes the last 5 digits of the product after removing all trailing zeros. If d <= 10; we keep it unchanged. For example; we express 1234567654321 as 12345...54321; but 1234567 is represented as 1234567. Finally; represent the product as a string ""<pre>...<suf>eC"". For example; 12345678987600000 will be represented as ""12345...89876e5"". Return a string denoting the abbreviated product of all integers in the inclusive range [left; right]. Example 1: Input: left = 1; right = 4 Output: ""24e0"" Explanation: The product is 1 × 2 × 3 × 4 = 24. There are no trailing zeros; so 24 remains the same. The abbreviation will end with ""e0"". Since the number of digits is 2; which is less than 10; we do not have to abbreviate it further. Thus; the final representation is ""24e0"". Example 2: Input: left = 2; right = 11 Output: ""399168e2"" Explanation: The product is 39916800. There are 2 trailing zeros; which we remove to get 399168. The abbreviation will end with ""e2"". The number of digits after removing the trailing zeros is 6; so we do not abbreviate it further. Hence; the abbreviated product is ""399168e2"". Example 3: Input: left = 371; right = 375 Output: ""7219856259e3"" Explanation: The product is 7219856259000. Constraints: 1 <= left <= right <= 104"
Amazon,2261,K Divisible Elements Subarrays,Med,Array,You are given a 0-indexed binary array nums of length n. nums can be divided at index i (where 0 <= i <= n) into two arrays (possibly empty) numsleft and numsright: numsleft has all the elements of nums between index 0 and i - 1 (inclusive); while numsright has all the elements of nums between index i and n - 1 (inclusive). If i == 0; numsleft is empty; while numsright has all the elements of nums. If i == n; numsleft has all the elements of nums; while numsright is empty. The division score of an index i is the sum of the number of 0's in numsleft and the number of 1's in numsright. Return all distinct indices that have the highest possible division score. You may return the answer in any order. Example 1: Input: nums = [0;0;1;0] Output: [2;4] Explanation: Division at index - 0: numsleft is []. numsright is [0;0;1;0]. The score is 0 + 1 = 1. - 1: numsleft is [0]. numsright is [0;1;0]. The score is 1 + 1 = 2. - 2: numsleft is [0;0]. numsright is [1;0]. The score is 2 + 1 = 3. - 3: numsleft is [0;0;1]. numsright is [0]. The score is 2 + 0 = 2. - 4: numsleft is [0;0;1;0]. numsright is []. The score is 3 + 0 = 3. Indices 2 and 4 both have the highest possible division score 3. Note the answer [4;2] would also be accepted. Example 2: Input: nums = [0;0;0] Output: [3] Explanation: Division at index - 0: numsleft is []. numsright is [0;0;0]. The score is 0 + 0 = 0. - 1: numsleft is [0]. numsright is [0;0]. The score is 1 + 0 = 1. - 2: numsleft is [0;0]. numsright is [0]. The score is 2 + 0 = 2. - 3: numsleft is [0;0;0]. numsright is []. The score is 3 + 0 = 3. Only index 3 has the highest possible division score 3. Example 3: Input: nums = [1;1] Output: [0] Explanation: Division at index - 0: numsleft is []. numsright is [1;1]. The score is 0 + 2 = 2. - 1: numsleft is [1]. numsright is [1]. The score is 0 + 1 = 1. - 2: numsleft is [1;1]. numsright is []. The score is 0 + 0 = 0. Only index 0 has the highest possible division score 2. Constraints: n == nums.length 1 <= n <= 105 nums[i] is either 0 or 1.
Amazon,2398,Maximum Number of Robots Within Budget,Hard,"Array, Matrix",A square matrix is said to be an X-Matrix if both of the following conditions hold: All the elements in the diagonals of the matrix are non-zero. All other elements are 0. Given a 2D integer array grid of size n x n representing a square matrix; return true if grid is an X-Matrix. Otherwise; return false. Example 1: Input: grid = [[2;0;0;1];[0;3;1;0];[0;5;2;0];[4;0;0;2]] Output: true Explanation: Refer to the diagram above. An X-Matrix should have the green elements (diagonals) be non-zero and the red elements be 0. Thus; grid is an X-Matrix. Example 2: Input: grid = [[5;7;0];[0;3;1];[0;5;0]] Output: false Explanation: Refer to the diagram above. An X-Matrix should have the green elements (diagonals) be non-zero and the red elements be 0. Thus; grid is not an X-Matrix. Constraints: n == grid.length == grid[i].length 3 <= n <= 100 0 <= grid[i][j] <= 105
Amazon,2340,Minimum Adjacent Swaps to Make a Valid Array,Med,"Hash Table, String, Dynamic Programming","The appeal of a string is the number of distinct characters found in the string. For example; the appeal of ""abbca"" is 3 because it has 3 distinct characters: 'a'; 'b'; and 'c'. Given a string s; return the total appeal of all of its substrings. A substring is a contiguous sequence of characters within a string. Example 1: Input: s = ""abbca"" Output: 28 Explanation: The following are the substrings of ""abbca"": - Substrings of length 1: ""a""; ""b""; ""b""; ""c""; ""a"" have an appeal of 1; 1; 1; 1; and 1 respectively. The sum is 5. - Substrings of length 2: ""ab""; ""bb""; ""bc""; ""ca"" have an appeal of 2; 1; 2; and 2 respectively. The sum is 7. - Substrings of length 3: ""abb""; ""bbc""; ""bca"" have an appeal of 2; 2; and 3 respectively. The sum is 7. - Substrings of length 4: ""abbc""; ""bbca"" have an appeal of 3 and 3 respectively. The sum is 6. - Substrings of length 5: ""abbca"" has an appeal of 3. The sum is 3. The total sum is 5 + 7 + 7 + 6 + 3 = 28. Example 2: Input: s = ""code"" Output: 20 Explanation: The following are the substrings of ""code"": - Substrings of length 1: ""c""; ""o""; ""d""; ""e"" have an appeal of 1; 1; 1; and 1 respectively. The sum is 4. - Substrings of length 2: ""co""; ""od""; ""de"" have an appeal of 2; 2; and 2 respectively. The sum is 6. - Substrings of length 3: ""cod""; ""ode"" have an appeal of 3 and 3 respectively. The sum is 6. - Substrings of length 4: ""code"" has an appeal of 4. The sum is 4. The total sum is 4 + 6 + 6 + 4 = 20. Constraints: 1 <= s.length <= 105 s consists of lowercase English letters."
Amazon,2405,Optimal Partition of String,Med,"Hash Table, String, Greedy, Sorting, Counting",
Amazon,2663,Lexicographically Smallest Beautiful String,Hard,"Math, Greedy",You are given an integer money denoting the amount of money (in dollars) that you have and another integer children denoting the number of children that you must distribute the money to. You have to distribute the money according to the following rules: All money must be distributed. Everyone must receive at least 1 dollar. Nobody receives 4 dollars. Return the maximum number of children who may receive exactly 8 dollars if you distribute the money according to the aforementioned rules. If there is no way to distribute the money; return -1. Example 1: Input: money = 20; children = 3 Output: 1 Explanation: The maximum number of children with 8 dollars will be 1. One of the ways to distribute the money is: - 8 dollars to the first child. - 9 dollars to the second child. - 3 dollars to the third child. It can be proven that no distribution exists such that number of children getting 8 dollars is greater than 1. Example 2: Input: money = 16; children = 2 Output: 2 Explanation: Each child can be given 8 dollars. Constraints: 1 <= money <= 200 2 <= children <= 30
Amazon,2563,Count the Number of Fair Pairs,Med,"String, Binary Search","You are given a string; message; and a positive integer; limit. You must split message into one or more parts based on limit. Each resulting part should have the suffix ""<a/b>""; where ""b"" is to be replaced with the total number of parts and ""a"" is to be replaced with the index of the part; starting from 1 and going up to b. Additionally; the length of each resulting part (including its suffix) should be equal to limit; except for the last part whose length can be at most limit. The resulting parts should be formed such that when their suffixes are removed and they are all concatenated in order; they should be equal to message. Also; the result should contain as few parts as possible. Return the parts message would be split into as an array of strings. If it is impossible to split message as required; return an empty array. Example 1: Input: message = ""this is really a very awesome message""; limit = 9 Output: [""thi<1/14>"";""s i<2/14>"";""s r<3/14>"";""eal<4/14>"";""ly <5/14>"";""a v<6/14>"";""ery<7/14>"";"" aw<8/14>"";""eso<9/14>"";""me<10/14>"";"" m<11/14>"";""es<12/14>"";""sa<13/14>"";""ge<14/14>""] Explanation: The first 9 parts take 3 characters each from the beginning of message. The next 5 parts take 2 characters each to finish splitting message. In this example; each part; including the last; has length 9. It can be shown it is not possible to split message into less than 14 parts. Example 2: Input: message = ""short message""; limit = 15 Output: [""short mess<1/2>"";""age<2/2>""] Explanation: Under the given constraints; the string can be split into two parts: - The first part comprises of the first 10 characters; and has a length 15. - The next part comprises of the last 3 characters; and has a length 8. Constraints: 1 <= message.length <= 104 message consists only of lowercase English letters and ' '. 1 <= limit <= 104"
Amazon,2601,Prime Subtraction Operation,Med,"Array, Dynamic Programming",You are given an array nums consisting of positive integers and an integer k. Partition the array into two ordered groups such that each element is in exactly one group. A partition is called great if the sum of elements of each group is greater than or equal to k. Return the number of distinct great partitions. Since the answer may be too large; return it modulo 109 + 7. Two partitions are considered distinct if some element nums[i] is in different groups in the two partitions. Example 1: Input: nums = [1;2;3;4]; k = 4 Output: 6 Explanation: The great partitions are: ([1;2;3]; [4]); ([1;3]; [2;4]); ([1;4]; [2;3]); ([2;3]; [1;4]); ([2;4]; [1;3]) and ([4]; [1;2;3]). Example 2: Input: nums = [3;3;3]; k = 4 Output: 0 Explanation: There are no great partitions for this array. Example 3: Input: nums = [6;6]; k = 2 Output: 2 Explanation: We can either put nums[0] in the first partition or in the second partition. The great partitions will be ([6]; [6]) and ([6]; [6]). Constraints: 1 <= nums.length; k <= 1000 1 <= nums[i] <= 109
Amazon,2635,Apply Transform Over Each Element in Array,Easy,"Math, Number Theory",There exists an infinitely large grid. You are currently at point (1; 1); and you need to reach the point (targetX; targetY) using a finite number of steps. In one step; you can move from point (x; y) to any one of the following points: (x; y - x) (x - y; y) (2 * x; y) (x; 2 * y) Given two integers targetX and targetY representing the X-coordinate and Y-coordinate of your final position; return true if you can reach the point from (1; 1) using some number of steps; and false otherwise. Example 1: Input: targetX = 6; targetY = 9 Output: false Explanation: It is impossible to reach (6;9) from (1;1) using any sequence of moves; so false is returned. Example 2: Input: targetX = 4; targetY = 7 Output: true Explanation: You can follow the path (1;1) -> (1;2) -> (1;4) -> (1;8) -> (1;7) -> (2;7) -> (4;7). Constraints: 1 <= targetX; targetY <= 109
Amazon,2704,To Be Or Not To Be,Easy,"Math, Greedy",You are given an integer num. You know that Bob will sneakily remap one of the 10 possible digits (0 to 9) to another digit. Return the difference between the maximum and minimum values Bob can make by remapping exactly one digit in num. Notes: When Bob remaps a digit d1 to another digit d2; Bob replaces all occurrences of d1 in num with d2. Bob can remap a digit to itself; in which case num does not change. Bob can remap different digits for obtaining minimum and maximum values respectively. The resulting number after remapping can contain leading zeroes. Example 1: Input: num = 11891 Output: 99009 Explanation: To achieve the maximum value; Bob can remap the digit 1 to the digit 9 to yield 99899. To achieve the minimum value; Bob can remap the digit 1 to the digit 0; yielding 890. The difference between these two numbers is 99009. Example 2: Input: num = 90 Output: 99 Explanation: The maximum value that can be returned by the function is 99 (if 0 is replaced by 9) and the minimum value that can be returned by the function is 0 (if 9 is replaced by 0). Thus; we return 99. Constraints: 1 <= num <= 108
Amazon,2734,Lexicographically Smallest String After Substring Operation,Med,,Write code that enhances all arrays such that you can call the array.last() method on any array and it will return the last element. If there are no elements in the array; it should return -1. You may assume the array is the output of JSON.parse. Example 1: Input: nums = [null; {}; 3] Output: 3 Explanation: Calling nums.last() should return the last element: 3. Example 2: Input: nums = [] Output: -1 Explanation: Because there are no elements; return -1. Constraints: arr is a valid JSON array 0 <= arr.length <= 1000
Amazon,2724,Sort By,Easy,"Array, Hash Table",You are given an integer array nums. You need to create a 2D array from nums satisfying the following conditions: The 2D array should contain only the elements of the array nums. Each row in the 2D array contains distinct integers. The number of rows in the 2D array should be minimal. Return the resulting array. If there are multiple answers; return any of them. Note that the 2D array can have a different number of elements on each row. Example 1: Input: nums = [1;3;4;1;2;3;1] Output: [[1;3;4;2];[1;3];[1]] Explanation: We can create a 2D array that contains the following rows: - 1;3;4;2 - 1;3 - 1 All elements of nums were used; and each row of the 2D array contains distinct integers; so it is a valid answer. It can be shown that we cannot have less than 3 rows in a valid array. Example 2: Input: nums = [1;2;3;4] Output: [[4;3;2;1]] Explanation: All elements of the array are distinct; so we can keep all of them in the first row of the 2D array. Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= nums.length
Amazon,2915,Length of the Longest Subsequence That Sums to Target,Med,"Array, Hash Table, Prefix Sum",You are given a 0-indexed integer array nums; an integer modulo; and an integer k. Your task is to find the count of subarrays that are interesting. A subarray nums[l..r] is interesting if the following condition holds: Let cnt be the number of indices i in the range [l; r] such that nums[i] % modulo == k. Then; cnt % modulo == k. Return an integer denoting the count of interesting subarrays. Note: A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [3;2;4]; modulo = 2; k = 1 Output: 3 Explanation: In this example the interesting subarrays are: The subarray nums[0..0] which is [3]. - There is only one index; i = 0; in the range [0; 0] that satisfies nums[i] % modulo == k. - Hence; cnt = 1 and cnt % modulo == k. The subarray nums[0..1] which is [3;2]. - There is only one index; i = 0; in the range [0; 1] that satisfies nums[i] % modulo == k. - Hence; cnt = 1 and cnt % modulo == k. The subarray nums[0..2] which is [3;2;4]. - There is only one index; i = 0; in the range [0; 2] that satisfies nums[i] % modulo == k. - Hence; cnt = 1 and cnt % modulo == k. It can be shown that there are no other interesting subarrays. So; the answer is 3. Example 2: Input: nums = [3;1;9;6]; modulo = 3; k = 0 Output: 2 Explanation: In this example the interesting subarrays are: The subarray nums[0..3] which is [3;1;9;6]. - There are three indices; i = 0; 2; 3; in the range [0; 3] that satisfy nums[i] % modulo == k. - Hence; cnt = 3 and cnt % modulo == k. The subarray nums[1..1] which is [1]. - There is no index; i; in the range [1; 1] that satisfies nums[i] % modulo == k. - Hence; cnt = 0 and cnt % modulo == k. It can be shown that there are no other interesting subarrays. So; the answer is 2. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 109 1 <= modulo <= 109 0 <= k < modulo
Amazon,3011,Find if Array Can Be Sorted,Med,,
Amazon,3019,Number of Changing Keys,Easy,"String, Counting","You are given a string moves of length n consisting only of characters 'L'; 'R'; and '_'. The string represents your movement on a number line starting from the origin 0. In the ith move; you can choose one of the following directions: move to the left if moves[i] = 'L' or moves[i] = '_' move to the right if moves[i] = 'R' or moves[i] = '_' Return the distance from the origin of the furthest point you can get to after n moves. Example 1: Input: moves = ""L_RL__R"" Output: 3 Explanation: The furthest point we can reach from the origin 0 is point -3 through the following sequence of moves ""LLRLLLR"". Example 2: Input: moves = ""_R__LL_"" Output: 5 Explanation: The furthest point we can reach from the origin 0 is point -5 through the following sequence of moves ""LRLLLLL"". Example 3: Input: moves = ""_______"" Output: 7 Explanation: The furthest point we can reach from the origin 0 is point 7 through the following sequence of moves ""RRRRRRR"". Constraints: 1 <= moves.length == n <= 50 moves consists only of characters 'L'; 'R' and '_'."
Amazon,3110,Score of a String,Easy,,
Amazon,3133,Minimum Array End,Med,,
Amazon,3281,Maximize Score of Numbers in Ranges,Med,Database,
Amazon,3274,Check if Two Chessboard Squares Have the Same Color,Easy,,
Amazon,3326,Minimum Division Operations to Make Array Non Decreasing,Med,"Array, Tree, Depth-First Search",You are given an unrooted weighted tree with n vertices representing servers numbered from 0 to n - 1; an array edges where edges[i] = [ai; bi; weighti] represents a bidirectional edge between vertices ai and bi of weight weighti. You are also given an integer signalSpeed. Two servers a and b are connectable through a server c if: a < b; a != c and b != c. The distance from c to a is divisible by signalSpeed. The distance from c to b is divisible by signalSpeed. The path from c to b and the path from c to a do not share any edges. Return an integer array count of length n where count[i] is the number of server pairs that are connectable through the server i. Example 1: Input: edges = [[0;1;1];[1;2;5];[2;3;13];[3;4;9];[4;5;2]]; signalSpeed = 1 Output: [0;4;6;6;4;0] Explanation: Since signalSpeed is 1; count[c] is equal to the number of pairs of paths that start at c and do not share any edges. In the case of the given path graph; count[c] is equal to the number of servers to the left of c multiplied by the servers to the right of c. Example 2: Input: edges = [[0;6;3];[6;5;3];[0;3;1];[3;2;7];[3;1;6];[3;4;2]]; signalSpeed = 3 Output: [2;0;0;0;0;0;2] Explanation: Through server 0; there are 2 pairs of connectable servers: (4; 5) and (4; 6). Through server 6; there are 2 pairs of connectable servers: (4; 5) and (0; 5). It can be shown that no two servers are connectable through servers other than 0 and 6. Constraints: 2 <= n <= 1000 edges.length == n - 1 edges[i].length == 3 0 <= ai; bi < n edges[i] = [ai; bi; weighti] 1 <= weighti <= 106 1 <= signalSpeed <= 106 The input is generated such that edges represents a valid tree.
Uber,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Uber,815,Bus Routes,Hard,Dynamic Programming,We stack glasses in a pyramid; where the first row has 1 glass; the second row has 2 glasses; and so on until the 100th row. Each glass holds one cup of champagne. Then; some champagne is poured into the first glass at the top. When the topmost glass is full; any excess liquid poured will fall equally to the glass immediately to the left and right of it. When those glasses become full; any excess champagne will fall equally to the left and right of those glasses; and so on. (A glass at the bottom row has its excess champagne fall on the floor.) For example; after one cup of champagne is poured; the top most glass is full. After two cups of champagne are poured; the two glasses on the second row are half full. After three cups of champagne are poured; those two cups become full - there are 3 full glasses total now. After four cups of champagne are poured; the third row has the middle glass half full; and the two outside glasses are a quarter full; as pictured below. Now after pouring some non-negative integer cups of champagne; return how full the jth glass in the ith row is (both i and j are 0-indexed.) Example 1: Input: poured = 1; query_row = 1; query_glass = 1 Output: 0.00000 Explanation: We poured 1 cup of champange to the top glass of the tower (which is indexed as (0; 0)). There will be no excess liquid so all the glasses under the top glass will remain empty. Example 2: Input: poured = 2; query_row = 1; query_glass = 1 Output: 0.50000 Explanation: We poured 2 cups of champange to the top glass of the tower (which is indexed as (0; 0)). There is one cup of excess liquid. The glass indexed as (1; 0) and the glass indexed as (1; 1) will share the excess liquid equally; and each will get half cup of champange. Example 3: Input: poured = 100000009; query_row = 33; query_glass = 17 Output: 1.00000 Constraints: 0 <= poured <= 109 0 <= query_glass <= query_row < 100
Uber,564,Find the Closest Palindrome,Hard,"Math, String","Given a string n representing an integer; return the closest integer (not including itself); which is a palindrome. If there is a tie; return the smaller one. The closest is defined as the absolute difference minimized between two integers. Example 1: Input: n = ""123"" Output: ""121"" Example 2: Input: n = ""1"" Output: ""0"" Explanation: 0 and 2 are the closest palindromes but we return the smallest which is 0. Constraints: 1 <= n.length <= 18 n consists of only digits. n does not have leading zeros. n is representing an integer in the range [1; 1018 - 1]."
Uber,13,Roman to Integer,Easy,"Hash Table, Math, String","Roman numerals are represented by seven different symbols: I; V; X; L; C; D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example; 2 is written as II in Roman numeral; just two ones added together. 12 is written as XII; which is simply X + II. The number 27 is written as XXVII; which is XX + V + II. Roman numerals are usually written largest to smallest from left to right. However; the numeral for four is not IIII. Instead; the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine; which is written as IX. There are six instances where subtraction is used: I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral; convert it to an integer. Example 1: Input: s = ""III"" Output: 3 Explanation: III = 3. Example 2: Input: s = ""LVIII"" Output: 58 Explanation: L = 50; V= 5; III = 3. Example 3: Input: s = ""MCMXCIV"" Output: 1994 Explanation: M = 1000; CM = 900; XC = 90 and IV = 4. Constraints: 1 <= s.length <= 15 s contains only the characters ('I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M'). It is guaranteed that s is a valid roman numeral in the range [1; 3999]."
Uber,212,Word Search II,Hard,"Array, String, Backtracking, Trie, Matrix","Given an m x n board of characters and a list of strings words; return all words on the board. Each word must be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example 1: Input: board = [[""o"";""a"";""a"";""n""];[""e"";""t"";""a"";""e""];[""i"";""h"";""k"";""r""];[""i"";""f"";""l"";""v""]]; words = [""oath"";""pea"";""eat"";""rain""] Output: [""eat"";""oath""] Example 2: Input: board = [[""a"";""b""];[""c"";""d""]]; words = [""abcb""] Output: [] Constraints: m == board.length n == board[i].length 1 <= m; n <= 12 board[i][j] is a lowercase English letter. 1 <= words.length <= 3 * 104 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. All the strings of words are unique."
Uber,1438,Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit,Med,Database,
Uber,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Uber,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Uber,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Uber,230,Kth Smallest Element in a BST,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree; and an integer k; return the kth smallest value (1-indexed) of all the values of the nodes in the tree. Example 1: Input: root = [3;1;4;null;2]; k = 1 Output: 1 Example 2: Input: root = [5;3;6;2;4;null;null;1]; k = 3 Output: 3 Constraints: The number of nodes in the tree is n. 1 <= k <= n <= 104 0 <= Node.val <= 104 Follow up: If the BST is modified often (i.e.; we can do insert and delete operations) and you need to find the kth smallest frequently; how would you optimize?
Uber,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Uber,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
Uber,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Uber,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Uber,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Uber,427,Construct Quad Tree,Med,,
Uber,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Uber,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Uber,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Uber,692,Top K Frequent Words,Med,"Hash Table, String, Trie, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given an array of strings words and an integer k; return the k most frequent strings. Return the answer sorted by the frequency from highest to lowest. Sort the words with the same frequency by their lexicographical order. Example 1: Input: words = [""i"";""love"";""leetcode"";""i"";""love"";""coding""]; k = 2 Output: [""i"";""love""] Explanation: ""i"" and ""love"" are the two most frequent words. Note that ""i"" comes before ""love"" due to a lower alphabetical order. Example 2: Input: words = [""the"";""day"";""is"";""sunny"";""the"";""the"";""the"";""sunny"";""is"";""is""]; k = 4 Output: [""the"";""is"";""sunny"";""day""] Explanation: ""the""; ""is""; ""sunny"" and ""day"" are the four most frequent words; with the number of occurrence being 4; 3; 2 and 1 respectively. Constraints: 1 <= words.length <= 500 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. k is in the range [1; The number of unique words[i]] Follow-up: Could you solve it in O(n log(k)) time and O(n) extra space?"
Uber,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Uber,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Uber,399,Evaluate Division,Med,"Array, String, Depth-First Search, Breadth-First Search, Union Find, Graph, Shortest Path","You are given an array of variable pairs equations and an array of real numbers values; where equations[i] = [Ai; Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable. You are also given some queries; where queries[j] = [Cj; Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries. If a single answer cannot be determined; return -1.0. Note: The input is always valid. You may assume that evaluating the queries will not result in division by zero and that there is no contradiction. Note: The variables that do not occur in the list of equations are undefined; so the answer cannot be determined for them. Example 1: Input: equations = [[""a"";""b""];[""b"";""c""]]; values = [2.0;3.0]; queries = [[""a"";""c""];[""b"";""a""];[""a"";""e""];[""a"";""a""];[""x"";""x""]] Output: [6.00000;0.50000;-1.00000;1.00000;-1.00000] Explanation: Given: a / b = 2.0; b / c = 3.0 queries are: a / c = ?; b / a = ?; a / e = ?; a / a = ?; x / x = ? return: [6.0; 0.5; -1.0; 1.0; -1.0 ] note: x is undefined => -1.0 Example 2: Input: equations = [[""a"";""b""];[""b"";""c""];[""bc"";""cd""]]; values = [1.5;2.5;5.0]; queries = [[""a"";""c""];[""c"";""b""];[""bc"";""cd""];[""cd"";""bc""]] Output: [3.75000;0.40000;5.00000;0.20000] Example 3: Input: equations = [[""a"";""b""]]; values = [0.5]; queries = [[""a"";""b""];[""b"";""a""];[""a"";""c""];[""x"";""y""]] Output: [0.50000;2.00000;-1.00000;-1.00000] Constraints: 1 <= equations.length <= 20 equations[i].length == 2 1 <= Ai.length; Bi.length <= 5 values.length == equations.length 0.0 < values[i] <= 20.0 1 <= queries.length <= 20 queries[i].length == 2 1 <= Cj.length; Dj.length <= 5 Ai; Bi; Cj; Dj consist of lower case English letters and digits."
Uber,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Uber,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Uber,68,Text Justification,Hard,"Array, String, Simulation","Given an array of strings words and a width maxWidth; format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is; pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words; the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text; it should be left-justified; and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = [""This""; ""is""; ""an""; ""example""; ""of""; ""text""; ""justification.""]; maxWidth = 16 Output: [ ""This is an""; ""example of text""; ""justification. "" ] Example 2: Input: words = [""What"";""must"";""be"";""acknowledgment"";""shall"";""be""]; maxWidth = 16 Output: [ ""What must be""; ""acknowledgment ""; ""shall be "" ] Explanation: Note that the last line is ""shall be "" instead of ""shall be""; because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = [""Science"";""is"";""what"";""we"";""understand"";""well"";""enough"";""to"";""explain"";""to"";""a"";""computer."";""Art"";""is"";""everything"";""else"";""we"";""do""]; maxWidth = 20 Output: [ ""Science is what we""; ""understand well""; ""enough to explain to""; ""a computer. Art is""; ""everything else we""; ""do "" ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth"
Uber,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
Uber,2468,Split Message Based on Limit,Hard,"Two Pointers, String",
Uber,7,Reverse Integer,Med,Math,Given a signed 32-bit integer x; return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231; 231 - 1]; then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: Input: x = 123 Output: 321 Example 2: Input: x = -123 Output: -321 Example 3: Input: x = 120 Output: 21 Constraints: -231 <= x <= 231 - 1
Uber,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Uber,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Uber,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Uber,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Uber,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Uber,242,Valid Anagram,Easy,"Hash Table, String, Sorting","Given two strings s and t; return true if t is an anagram of s; and false otherwise. Example 1: Input: s = ""anagram""; t = ""nagaram"" Output: true Example 2: Input: s = ""rat""; t = ""car"" Output: false Constraints: 1 <= s.length; t.length <= 5 * 104 s and t consist of lowercase English letters. Follow up: What if the inputs contain Unicode characters? How would you adapt your solution to such a case?"
Uber,1768,Merge Strings Alternately,Easy,"Array, Math, Stack, Tree, Design, Binary Tree",
Uber,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Uber,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Uber,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Uber,202,Happy Number,Easy,"Hash Table, Math, Two Pointers",Write an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer; replace the number by the sum of the squares of its digits. Repeat the process until the number equals 1 (where it will stay); or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy. Return true if n is a happy number; and false if not. Example 1: Input: n = 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1 Example 2: Input: n = 2 Output: false Constraints: 1 <= n <= 231 - 1
Uber,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Uber,217,Contains Duplicate,Easy,"Array, Hash Table, Sorting",Given an integer array nums; return true if any value appears at least twice in the array; and return false if every element is distinct. Example 1: Input: nums = [1;2;3;1] Output: true Explanation: The element 1 occurs at the indices 0 and 3. Example 2: Input: nums = [1;2;3;4] Output: false Explanation: All elements are distinct. Example 3: Input: nums = [1;1;1;3;3;4;3;2;4;2] Output: true Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109
Uber,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Uber,27,Remove Element,Easy,"Array, Two Pointers",Given an integer array nums and an integer val; remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val. Consider the number of elements in nums which are not equal to val be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the elements which are not equal to val. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int val = ...; // Value to remove int[] expectedNums = [...]; // The expected answer with correct length. // It is sorted with no values equaling val. int k = removeElement(nums; val); // Calls your implementation assert k == expectedNums.length; sort(nums; 0; k); // Sort the first k elements of nums for (int i = 0; i < actualLength; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [3;2;2;3]; val = 3 Output: 2; nums = [2;2;_;_] Explanation: Your function should return k = 2; with the first two elements of nums being 2. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;1;2;2;3;0;4;2]; val = 2 Output: 5; nums = [0;1;4;0;3;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums containing 0; 0; 1; 3; and 4. Note that the five elements can be returned in any order. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 0 <= nums.length <= 100 0 <= nums[i] <= 50 0 <= val <= 100
Uber,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Uber,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Uber,125,Valid Palindrome,Easy,"Two Pointers, String","A phrase is a palindrome if; after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters; it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s; return true if it is a palindrome; or false otherwise. Example 1: Input: s = ""A man; a plan; a canal: Panama"" Output: true Explanation: ""amanaplanacanalpanama"" is a palindrome. Example 2: Input: s = ""race a car"" Output: false Explanation: ""raceacar"" is not a palindrome. Example 3: Input: s = "" "" Output: true Explanation: s is an empty string """" after removing non-alphanumeric characters. Since an empty string reads the same forward and backward; it is a palindrome. Constraints: 1 <= s.length <= 2 * 105 s consists only of printable ASCII characters."
Uber,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
Uber,3341,Find Minimum Time to Reach Last Room I,Med,,
Uber,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Uber,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Uber,2493,Divide Nodes Into the Maximum Number of Groups,Hard,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a perfect binary tree; reverse the node values at each odd level of the tree. For example; suppose the node values at level 3 are [2;1;3;4;7;11;29;18]; then it should become [18;29;11;7;4;3;1;2]. Return the root of the reversed tree. A binary tree is perfect if all parent nodes have two children and all leaves are on the same level. The level of a node is the number of edges along the path between it and the root node. Example 1: Input: root = [2;3;5;8;13;21;34] Output: [2;5;3;8;13;21;34] Explanation: The tree has only one odd level. The nodes at level 1 are 3; 5 respectively; which are reversed and become 5; 3. Example 2: Input: root = [7;13;11] Output: [7;11;13] Explanation: The nodes at level 1 are 13; 11; which are reversed and become 11; 13. Example 3: Input: root = [0;1;2;0;0;0;0;1;1;1;1;2;2;2;2] Output: [0;2;1;0;0;0;0;2;2;2;2;1;1;1;1] Explanation: The odd levels have non-zero values. The nodes at level 1 were 1; 2; and are 2; 1 after the reversal. The nodes at level 3 were 1; 1; 1; 1; 2; 2; 2; 2; and are 2; 2; 2; 2; 1; 1; 1; 1 after the reversal. Constraints: The number of nodes in the tree is in the range [1; 214]. 0 <= Node.val <= 105 root is a perfect binary tree.
Uber,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
Uber,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Uber,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
Uber,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Uber,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Uber,269,Alien Dictionary,Hard,"Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort",
Uber,875,Koko Eating Bananas,Med,"Array, Two Pointers, Dynamic Programming, Enumeration",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr; return the length of the longest subarray; which is a mountain. Return 0 if there is no mountain subarray. Example 1: Input: arr = [2;1;4;7;3;2;5] Output: 5 Explanation: The largest mountain is [1;4;7;3;2] which has length 5. Example 2: Input: arr = [2;2;2] Output: 0 Explanation: There is no mountain. Constraints: 1 <= arr.length <= 104 0 <= arr[i] <= 104 Follow up: Can you solve it using only one pass? Can you solve it in O(1) space?
Uber,2187,Minimum Time to Complete Trips,Med,"Math, String, Dynamic Programming, Combinatorics","Given a string word; return the sum of the number of vowels ('a'; 'e'; 'i'; 'o'; and 'u') in every substring of word. A substring is a contiguous (non-empty) sequence of characters within a string. Note: Due to the large constraints; the answer may not fit in a signed 32-bit integer. Please be careful during the calculations. Example 1: Input: word = ""aba"" Output: 6 Explanation: All possible substrings are: ""a""; ""ab""; ""aba""; ""b""; ""ba""; and ""a"". - ""b"" has 0 vowels in it - ""a""; ""ab""; ""ba""; and ""a"" have 1 vowel each - ""aba"" has 2 vowels in it Hence; the total sum of vowels = 0 + 1 + 1 + 1 + 1 + 2 = 6. Example 2: Input: word = ""abc"" Output: 3 Explanation: All possible substrings are: ""a""; ""ab""; ""abc""; ""b""; ""bc""; and ""c"". - ""a""; ""ab""; and ""abc"" have 1 vowel each - ""b""; ""bc""; and ""c"" have 0 vowels each Hence; the total sum of vowels = 1 + 1 + 1 + 0 + 0 + 0 = 3. Example 3: Input: word = ""ltcd"" Output: 0 Explanation: There are no vowels in any substring of ""ltcd"". Constraints: 1 <= word.length <= 105 word consists of lowercase English letters."
Uber,69,Sqrt(x),Easy,"Math, Binary Search",Given a non-negative integer x; return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. For example; do not use pow(x; 0.5) in c++ or x ** 0.5 in python. Example 1: Input: x = 4 Output: 2 Explanation: The square root of 4 is 2; so we return 2. Example 2: Input: x = 8 Output: 2 Explanation: The square root of 8 is 2.82842...; and since we round it down to the nearest integer; 2 is returned. Constraints: 0 <= x <= 231 - 1
Uber,189,Rotate Array,Med,"Array, Math, Two Pointers",Given an integer array nums; rotate the array to the right by k steps; where k is non-negative. Example 1: Input: nums = [1;2;3;4;5;6;7]; k = 3 Output: [5;6;7;1;2;3;4] Explanation: rotate 1 steps to the right: [7;1;2;3;4;5;6] rotate 2 steps to the right: [6;7;1;2;3;4;5] rotate 3 steps to the right: [5;6;7;1;2;3;4] Example 2: Input: nums = [-1;-100;3;99]; k = 2 Output: [3;99;-1;-100] Explanation: rotate 1 steps to the right: [99;-1;-100;3] rotate 2 steps to the right: [3;99;-1;-100] Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 0 <= k <= 105 Follow up: Try to come up with as many solutions as you can. There are at least three different ways to solve this problem. Could you do it in-place with O(1) extra space?
Uber,26,Remove Duplicates from Sorted Array,Easy,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums. Consider the number of unique elements of nums to be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;2] Output: 2; nums = [1;2;_] Explanation: Your function should return k = 2; with the first two elements of nums being 1 and 2 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;2;2;3;3;4] Output: 5; nums = [0;1;2;3;4;_;_;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums being 0; 1; 2; 3; and 4 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -100 <= nums[i] <= 100 nums is sorted in non-decreasing order.
Uber,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Uber,104,Maximum Depth of Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return its maximum depth. A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 3 Example 2: Input: root = [1;null;2] Output: 2 Constraints: The number of nodes in the tree is in the range [0; 104]. -100 <= Node.val <= 100
Uber,128,Longest Consecutive Sequence,Med,"Array, Hash Table, Union Find",Given an unsorted array of integers nums; return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time. Example 1: Input: nums = [100;4;200;1;3;2] Output: 4 Explanation: The longest consecutive elements sequence is [1; 2; 3; 4]. Therefore its length is 4. Example 2: Input: nums = [0;3;7;2;5;8;4;6;0;1] Output: 9 Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109
Uber,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Uber,171,Excel Sheet Column Number,Easy,"Math, String","Given a string columnTitle that represents the column title as appears in an Excel sheet; return its corresponding column number. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: Input: columnTitle = ""A"" Output: 1 Example 2: Input: columnTitle = ""AB"" Output: 28 Example 3: Input: columnTitle = ""ZY"" Output: 701 Constraints: 1 <= columnTitle.length <= 7 columnTitle consists only of uppercase English letters. columnTitle is in the range [""A""; ""FXSHRXW""]."
Uber,305,Number of Islands II,Hard,"Array, Hash Table, Union Find",
Uber,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Uber,432,All O`one Data Structure,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure to store the strings' count with the ability to return the strings with minimum and maximum counts. Implement the AllOne class: AllOne() Initializes the object of the data structure. inc(String key) Increments the count of the string key by 1. If key does not exist in the data structure; insert it with count 1. dec(String key) Decrements the count of the string key by 1. If the count of key is 0 after the decrement; remove it from the data structure. It is guaranteed that key exists in the data structure before the decrement. getMaxKey() Returns one of the keys with the maximal count. If no element exists; return an empty string """". getMinKey() Returns one of the keys with the minimum count. If no element exists; return an empty string """". Note that each function must run in O(1) average time complexity. Example 1: Input [""AllOne""; ""inc""; ""inc""; ""getMaxKey""; ""getMinKey""; ""inc""; ""getMaxKey""; ""getMinKey""] [[]; [""hello""]; [""hello""]; []; []; [""leet""]; []; []] Output [null; null; null; ""hello""; ""hello""; null; ""hello""; ""leet""] Explanation AllOne allOne = new AllOne(); allOne.inc(""hello""); allOne.inc(""hello""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""hello"" allOne.inc(""leet""); allOne.getMaxKey(); // return ""hello"" allOne.getMinKey(); // return ""leet"" Constraints: 1 <= key.length <= 10 key consists of lowercase English letters. It is guaranteed that for each call to dec; key is existing in the data structure. At most 5 * 104 calls will be made to inc; dec; getMaxKey; and getMinKey."
Uber,733,Flood Fill,Easy,"Array, Depth-First Search, Breadth-First Search, Matrix",You are given an image represented by an m x n grid of integers image; where image[i][j] represents the pixel value of the image. You are also given three integers sr; sc; and color. Your task is to perform a flood fill on the image starting from the pixel image[sr][sc]. To perform a flood fill: Begin with the starting pixel and change its color to color. Perform the same process for each pixel that is directly adjacent (pixels that share a side with the original pixel; either horizontally or vertically) and shares the same color as the starting pixel. Keep repeating this process by checking neighboring pixels of the updated pixels and modifying their color if it matches the original color of the starting pixel. The process stops when there are no more adjacent pixels of the original color to update. Return the modified image after performing the flood fill. Example 1: Input: image = [[1;1;1];[1;1;0];[1;0;1]]; sr = 1; sc = 1; color = 2 Output: [[2;2;2];[2;2;0];[2;0;1]] Explanation: From the center of the image with position (sr; sc) = (1; 1) (i.e.; the red pixel); all pixels connected by a path of the same color as the starting pixel (i.e.; the blue pixels) are colored with the new color. Note the bottom corner is not colored 2; because it is not horizontally or vertically connected to the starting pixel. Example 2: Input: image = [[0;0;0];[0;0;0]]; sr = 0; sc = 0; color = 0 Output: [[0;0;0];[0;0;0]] Explanation: The starting pixel is already colored with 0; which is the same as the target color. Therefore; no changes are made to the image. Constraints: m == image.length n == image[i].length 1 <= m; n <= 50 0 <= image[i][j]; color < 216 0 <= sr < m 0 <= sc < n
Uber,1428,Leftmost Column with at Least a One,Med,"Array, Depth-First Search, Breadth-First Search",Given an array of non-negative integers arr; you are initially positioned at start index of the array. When you are at index i; you can jump to i + arr[i] or i - arr[i]; check if you can reach any index with value 0. Notice that you can not jump outside of the array at any time. Example 1: Input: arr = [4;2;3;0;3;1;2]; start = 5 Output: true Explanation: All possible ways to reach at index 3 with value 0 are: index 5 -> index 4 -> index 1 -> index 3 index 5 -> index 6 -> index 4 -> index 1 -> index 3 Example 2: Input: arr = [4;2;3;0;3;1;2]; start = 0 Output: true Explanation: One possible way to reach at index 3 with value 0 is: index 0 -> index 4 -> index 1 -> index 3 Example 3: Input: arr = [3;0;2;1;2]; start = 2 Output: false Explanation: There is no way to reach at index 1 with value 0. Constraints: 1 <= arr.length <= 5 * 104 0 <= arr[i] < arr.length 0 <= start < arr.length
Uber,8,String to Integer (atoi),Med,String,"Implement the myAtoi(string s) function; which converts a string to a 32-bit signed integer. The algorithm for myAtoi(string s) is as follows: Whitespace: Ignore any leading whitespace ("" ""). Signedness: Determine the sign by checking if the next character is '-' or '+'; assuming positivity if neither present. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read; then the result is 0. Rounding: If the integer is out of the 32-bit signed integer range [-231; 231 - 1]; then round the integer to remain in the range. Specifically; integers less than -231 should be rounded to -231; and integers greater than 231 - 1 should be rounded to 231 - 1. Return the integer as the final result. Example 1: Input: s = ""42"" Output: 42 Explanation: The underlined characters are what is read in and the caret is the current reader position. Step 1: ""42"" (no characters read because there is no leading whitespace) ^ Step 2: ""42"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""42"" (""42"" is read in) ^ Example 2: Input: s = "" -042"" Output: -42 Explanation: Step 1: "" -042"" (leading whitespace is read and ignored) ^ Step 2: "" -042"" ('-' is read; so the result should be negative) ^ Step 3: "" -042"" (""042"" is read in; leading zeros ignored in the result) ^ Example 3: Input: s = ""1337c0d3"" Output: 1337 Explanation: Step 1: ""1337c0d3"" (no characters read because there is no leading whitespace) ^ Step 2: ""1337c0d3"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""1337c0d3"" (""1337"" is read in; reading stops because the next character is a non-digit) ^ Example 4: Input: s = ""0-1"" Output: 0 Explanation: Step 1: ""0-1"" (no characters read because there is no leading whitespace) ^ Step 2: ""0-1"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""0-1"" (""0"" is read in; reading stops because the next character is a non-digit) ^ Example 5: Input: s = ""words and 987"" Output: 0 Explanation: Reading stops at the first non-digit character 'w'. Constraints: 0 <= s.length <= 200 s consists of English letters (lower-case and upper-case); digits (0-9); ' '; '+'; '-'; and '.'."
Uber,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Uber,35,Search Insert Position,Easy,"Array, Binary Search",Given a sorted array of distinct integers and a target value; return the index if the target is found. If not; return the index where it would be if it were inserted in order. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [1;3;5;6]; target = 5 Output: 2 Example 2: Input: nums = [1;3;5;6]; target = 2 Output: 1 Example 3: Input: nums = [1;3;5;6]; target = 7 Output: 4 Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 nums contains distinct values sorted in ascending order. -104 <= target <= 104
Uber,78,Subsets,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums of unique elements; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;3] Output: [[];[1];[2];[1;2];[3];[1;3];[2;3];[1;2;3]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10 All the numbers of nums are unique.
Uber,84,Largest Rectangle in Histogram,Hard,"Array, Stack, Monotonic Stack",Given an array of integers heights representing the histogram's bar height where the width of each bar is 1; return the area of the largest rectangle in the histogram. Example 1: Input: heights = [2;1;5;6;2;3] Output: 10 Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area; which has an area = 10 units. Example 2: Input: heights = [2;4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104
Uber,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Uber,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Uber,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Uber,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
Uber,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Uber,827,Making A Large Island,Hard,"Array, Two Pointers, String","Sometimes people repeat letters to represent extra feeling. For example: ""hello"" -> ""heeellooo"" ""hi"" -> ""hiiii"" In these strings like ""heeellooo""; we have groups of adjacent letters that are all the same: ""h""; ""eee""; ""ll""; ""ooo"". You are given a string s and an array of query strings words. A query word is stretchy if it can be made to be equal to s by any number of applications of the following extension operation: choose a group consisting of characters c; and add some number of characters c to the group so that the size of the group is three or more. For example; starting with ""hello""; we could do an extension on the group ""o"" to get ""hellooo""; but we cannot get ""helloo"" since the group ""oo"" has a size less than three. Also; we could do another extension like ""ll"" -> ""lllll"" to get ""helllllooo"". If s = ""helllllooo""; then the query word ""hello"" would be stretchy because of these two extension operations: query = ""hello"" -> ""hellooo"" -> ""helllllooo"" = s. Return the number of query strings that are stretchy. Example 1: Input: s = ""heeellooo""; words = [""hello""; ""hi""; ""helo""] Output: 1 Explanation: We can extend ""e"" and ""o"" in the word ""hello"" to get ""heeellooo"". We can't extend ""helo"" to get ""heeellooo"" because the group ""ll"" is not size 3 or more. Example 2: Input: s = ""zzzzzyyyyy""; words = [""zzyy"";""zy"";""zyy""] Output: 3 Constraints: 1 <= s.length; words.length <= 100 1 <= words[i].length <= 100 s and words[i] consist of lowercase letters."
Uber,977,Squares of a Sorted Array,Easy,"String, Dynamic Programming","Given a string s; return the number of distinct non-empty subsequences of s. Since the answer may be very large; return it modulo 109 + 7. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not. Example 1: Input: s = ""abc"" Output: 7 Explanation: The 7 distinct subsequences are ""a""; ""b""; ""c""; ""ab""; ""ac""; ""bc""; and ""abc"". Example 2: Input: s = ""aba"" Output: 6 Explanation: The 6 distinct subsequences are ""a""; ""b""; ""ab""; ""aa""; ""ba""; and ""aba"". Example 3: Input: s = ""aaa"" Output: 3 Explanation: The 3 distinct subsequences are ""a""; ""aa"" and ""aaa"". Constraints: 1 <= s.length <= 2000 s consists of lowercase English letters."
Uber,2009,Minimum Number of Operations to Make Array Continuous,Hard,"Depth-First Search, Trie",
Uber,2127,Maximum Employees to Be Invited to a Meeting,Hard,Database,Table: Employees +-------------+----------+ | Column Name | Type | +-------------+----------+ | employee_id | int | | name | varchar | | manager_id | int | | salary | int | +-------------+----------+ In SQL; employee_id is the primary key for this table. This table contains information about the employees; their salary; and the ID of their manager. Some employees do not have a manager (manager_id is null). Find the IDs of the employees whose salary is strictly less than $30000 and whose manager left the company. When a manager leaves the company; their information is deleted from the Employees table; but the reports still have their manager_id set to the manager that left. Return the result table ordered by employee_id. The result format is in the following example. Example 1: Input: Employees table: +-------------+-----------+------------+--------+ | employee_id | name | manager_id | salary | +-------------+-----------+------------+--------+ | 3 | Mila | 9 | 60301 | | 12 | Antonella | null | 31000 | | 13 | Emery | null | 67084 | | 1 | Kalel | 11 | 21241 | | 9 | Mikaela | null | 50937 | | 11 | Joziah | 6 | 28485 | +-------------+-----------+------------+--------+ Output: +-------------+ | employee_id | +-------------+ | 11 | +-------------+ Explanation: The employees with a salary less than $30000 are 1 (Kalel) and 11 (Joziah). Kalel's manager is employee 11; who is still in the company (Joziah). Joziah's manager is employee 6; who left the company because there is no row for employee 6 as it was deleted.
Uber,24,Swap Nodes in Pairs,Med,"Linked List, Recursion",Given a linked list; swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e.; only nodes themselves may be changed.) Example 1: Input: head = [1;2;3;4] Output: [2;1;4;3] Explanation: Example 2: Input: head = [] Output: [] Example 3: Input: head = [1] Output: [1] Example 4: Input: head = [1;2;3] Output: [2;1;3] Constraints: The number of nodes in the list is in the range [0; 100]. 0 <= Node.val <= 100
Uber,28,Find the Index of the First Occurrence in a String,Easy,"Two Pointers, String, String Matching","Given two strings needle and haystack; return the index of the first occurrence of needle in haystack; or -1 if needle is not part of haystack. Example 1: Input: haystack = ""sadbutsad""; needle = ""sad"" Output: 0 Explanation: ""sad"" occurs at index 0 and 6. The first occurrence is at index 0; so we return 0. Example 2: Input: haystack = ""leetcode""; needle = ""leeto"" Output: -1 Explanation: ""leeto"" did not occur in ""leetcode""; so we return -1. Constraints: 1 <= haystack.length; needle.length <= 104 haystack and needle consist of only lowercase English characters."
Uber,32,Longest Valid Parentheses,Hard,"String, Dynamic Programming, Stack","Given a string containing just the characters '(' and ')'; return the length of the longest valid (well-formed) parentheses substring. Example 1: Input: s = ""(()"" Output: 2 Explanation: The longest valid parentheses substring is ""()"". Example 2: Input: s = "")()())"" Output: 4 Explanation: The longest valid parentheses substring is ""()()"". Example 3: Input: s = """" Output: 0 Constraints: 0 <= s.length <= 3 * 104 s[i] is '('; or ')'."
Uber,102,Binary Tree Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the level order traversal of its nodes' values. (i.e.; from left to right; level by level). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[9;20];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -1000 <= Node.val <= 1000
Uber,140,Word Break II,Hard,"Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization","Given a string s and a dictionary of strings wordDict; add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""catsanddog""; wordDict = [""cat"";""cats"";""and"";""sand"";""dog""] Output: [""cats and dog"";""cat sand dog""] Example 2: Input: s = ""pineapplepenapple""; wordDict = [""apple"";""pen"";""applepen"";""pine"";""pineapple""] Output: [""pine apple pen apple"";""pineapple pen apple"";""pine applepen apple""] Explanation: Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: [] Constraints: 1 <= s.length <= 20 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 10 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique. Input is generated in a way that the length of the answer doesn't exceed 105."
Uber,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
Uber,290,Word Pattern,Easy,"Hash Table, String","Given a pattern and a string s; find if s follows the same pattern. Here follow means a full match; such that there is a bijection between a letter in pattern and a non-empty word in s. Specifically: Each letter in pattern maps to exactly one unique word in s. Each unique word in s maps to exactly one letter in pattern. No two letters map to the same word; and no two words map to the same letter. Example 1: Input: pattern = ""abba""; s = ""dog cat cat dog"" Output: true Explanation: The bijection can be established as: 'a' maps to ""dog"". 'b' maps to ""cat"". Example 2: Input: pattern = ""abba""; s = ""dog cat cat fish"" Output: false Example 3: Input: pattern = ""aaaa""; s = ""dog cat cat dog"" Output: false Constraints: 1 <= pattern.length <= 300 pattern contains only lower-case English letters. 1 <= s.length <= 3000 s contains only lowercase English letters and spaces ' '. s does not contain any leading or trailing spaces. All the words in s are separated by a single space."
Uber,337,House Robber III,Med,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",The thief has found himself a new place for his thievery again. There is only one entrance to this area; called root. Besides the root; each house has one and only one parent house. After a tour; the smart thief realized that all houses in this place form a binary tree. It will automatically contact the police if two directly-linked houses were broken into on the same night. Given the root of the binary tree; return the maximum amount of money the thief can rob without alerting the police. Example 1: Input: root = [3;2;3;null;3;null;1] Output: 7 Explanation: Maximum amount of money the thief can rob = 3 + 3 + 1 = 7. Example 2: Input: root = [3;4;5;1;3;null;1] Output: 9 Explanation: Maximum amount of money the thief can rob = 4 + 5 = 9. Constraints: The number of nodes in the tree is in the range [1; 104]. 0 <= Node.val <= 104
Uber,362,Design Hit Counter,Med,"Array, Binary Search, Design, Queue, Data Stream",
Uber,373,Find K Pairs with Smallest Sums,Med,"Array, Heap (Priority Queue)",You are given two integer arrays nums1 and nums2 sorted in non-decreasing order and an integer k. Define a pair (u; v) which consists of one element from the first array and one element from the second array. Return the k pairs (u1; v1); (u2; v2); ...; (uk; vk) with the smallest sums. Example 1: Input: nums1 = [1;7;11]; nums2 = [2;4;6]; k = 3 Output: [[1;2];[1;4];[1;6]] Explanation: The first 3 pairs are returned from the sequence: [1;2];[1;4];[1;6];[7;2];[7;4];[11;2];[7;6];[11;4];[11;6] Example 2: Input: nums1 = [1;1;2]; nums2 = [1;2;3]; k = 2 Output: [[1;1];[1;1]] Explanation: The first 2 pairs are returned from the sequence: [1;1];[1;1];[1;2];[2;1];[1;2];[2;2];[1;3];[1;3];[2;3] Constraints: 1 <= nums1.length; nums2.length <= 105 -109 <= nums1[i]; nums2[i] <= 109 nums1 and nums2 both are sorted in non-decreasing order. 1 <= k <= 104 k <= nums1.length * nums2.length
Uber,450,Delete Node in a BST,Med,"Tree, Binary Search Tree, Binary Tree",Given a root node reference of a BST and a key; delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST. Basically; the deletion can be divided into two stages: Search for a node to remove. If the node is found; delete the node. Example 1: Input: root = [5;3;6;2;4;null;7]; key = 3 Output: [5;4;6;2;null;null;7] Explanation: Given key to delete is 3. So we find the node with value 3 and delete it. One valid answer is [5;4;6;2;null;null;7]; shown in the above BST. Please notice that another valid answer is [5;2;6;null;4;null;7] and it's also accepted. Example 2: Input: root = [5;3;6;2;4;null;7]; key = 0 Output: [5;3;6;2;4;null;7] Explanation: The tree does not contain a node with value = 0. Example 3: Input: root = []; key = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -105 <= Node.val <= 105 Each node has a unique value. root is a valid binary search tree. -105 <= key <= 105 Follow up: Could you solve it with time complexity O(height of tree)?
Uber,934,Shortest Bridge,Med,"Array, Dynamic Programming, Bit Manipulation",Given an integer array arr; return the number of distinct bitwise ORs of all the non-empty subarrays of arr. The bitwise OR of a subarray is the bitwise OR of each integer in the subarray. The bitwise OR of a subarray of one integer is that integer. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: arr = [0] Output: 1 Explanation: There is only one possible result: 0. Example 2: Input: arr = [1;1;2] Output: 3 Explanation: The possible subarrays are [1]; [1]; [2]; [1; 1]; [1; 2]; [1; 1; 2]. These yield the results 1; 1; 2; 1; 3; 3. There are 3 unique values; so the answer is 3. Example 3: Input: arr = [1;2;4] Output: 6 Explanation: The possible results are 1; 2; 3; 4; 6; and 7. Constraints: 1 <= arr.length <= 5 * 104 0 <= arr[i] <= 109
Uber,1171,Remove Zero Sum Consecutive Nodes from Linked List,Med,"Array, Breadth-First Search, Matrix",Given an n x n binary matrix grid; return the length of the shortest clear path in the matrix. If there is no clear path; return -1. A clear path in a binary matrix is a path from the top-left cell (i.e.; (0; 0)) to the bottom-right cell (i.e.; (n - 1; n - 1)) such that: All the visited cells of the path are 0. All the adjacent cells of the path are 8-directionally connected (i.e.; they are different and they share an edge or a corner). The length of a clear path is the number of visited cells of this path. Example 1: Input: grid = [[0;1];[1;0]] Output: 2 Example 2: Input: grid = [[0;0;0];[1;1;0];[1;1;0]] Output: 4 Example 3: Input: grid = [[1;0;0];[1;1;0];[1;1;0]] Output: -1 Constraints: n == grid.length n == grid[i].length 1 <= n <= 100 grid[i][j] is 0 or 1
Uber,1926,Nearest Exit from Entrance in Maze,Med,Database,
Uber,2444,Count Subarrays With Fixed Bounds,Hard,"Hash Table, String, Dynamic Programming","You are given a string s consisting of lowercase letters and an integer k. We call a string t ideal if the following conditions are satisfied: t is a subsequence of the string s. The absolute difference in the alphabet order of every two adjacent letters in t is less than or equal to k. Return the length of the longest ideal string. A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters. Note that the alphabet order is not cyclic. For example; the absolute difference in the alphabet order of 'a' and 'z' is 25; not 1. Example 1: Input: s = ""acfgbd""; k = 2 Output: 4 Explanation: The longest ideal string is ""acbd"". The length of this string is 4; so 4 is returned. Note that ""acfgbd"" is not ideal because 'c' and 'f' have a difference of 3 in alphabet order. Example 2: Input: s = ""abcd""; k = 3 Output: 4 Explanation: The longest ideal string is ""abcd"". The length of this string is 4; so 4 is returned. Constraints: 1 <= s.length <= 105 0 <= k <= 25 s consists of lowercase English letters."
Uber,2828,Check if a String Is an Acronym of Words,Easy,"String, Greedy","Given a string s consisting of lowercase English letters. Perform the following operation: Select any non-empty substring then replace every letter of the substring with the preceding letter of the English alphabet. For example; 'b' is converted to 'a'; and 'a' is converted to 'z'. Return the lexicographically smallest string after performing the operation. Example 1: Input: s = ""cbabc"" Output: ""baabc"" Explanation: Perform the operation on the substring starting at index 0; and ending at index 1 inclusive. Example 2: Input: s = ""aa"" Output: ""az"" Explanation: Perform the operation on the last letter. Example 3: Input: s = ""acbbc"" Output: ""abaab"" Explanation: Perform the operation on the substring starting at index 1; and ending at index 4 inclusive. Example 4: Input: s = ""leetcode"" Output: ""kddsbncd"" Explanation: Perform the operation on the entire string. Constraints: 1 <= s.length <= 3 * 105 s consists of lowercase English letters"
Uber,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Uber,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Uber,66,Plus One,Easy,"Array, Math",You are given a large integer represented as an integer array digits; where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0's. Increment the large integer by one and return the resulting array of digits. Example 1: Input: digits = [1;2;3] Output: [1;2;4] Explanation: The array represents the integer 123. Incrementing by one gives 123 + 1 = 124. Thus; the result should be [1;2;4]. Example 2: Input: digits = [4;3;2;1] Output: [4;3;2;2] Explanation: The array represents the integer 4321. Incrementing by one gives 4321 + 1 = 4322. Thus; the result should be [4;3;2;2]. Example 3: Input: digits = [9] Output: [1;0] Explanation: The array represents the integer 9. Incrementing by one gives 9 + 1 = 10. Thus; the result should be [1;0]. Constraints: 1 <= digits.length <= 100 0 <= digits[i] <= 9 digits does not contain any leading 0's.
Uber,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Uber,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Uber,208,Implement Trie (Prefix Tree),Med,"Hash Table, String, Design, Trie","A trie (pronounced as ""try"") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure; such as autocomplete and spellchecker. Implement the Trie class: Trie() Initializes the trie object. void insert(String word) Inserts the string word into the trie. boolean search(String word) Returns true if the string word is in the trie (i.e.; was inserted before); and false otherwise. boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix; and false otherwise. Example 1: Input [""Trie""; ""insert""; ""search""; ""search""; ""startsWith""; ""insert""; ""search""] [[]; [""apple""]; [""apple""]; [""app""]; [""app""]; [""app""]; [""app""]] Output [null; null; true; false; true; null; true] Explanation Trie trie = new Trie(); trie.insert(""apple""); trie.search(""apple""); // return True trie.search(""app""); // return False trie.startsWith(""app""); // return True trie.insert(""app""); trie.search(""app""); // return True Constraints: 1 <= word.length; prefix.length <= 2000 word and prefix consist only of lowercase English letters. At most 3 * 104 calls in total will be made to insert; search; and startsWith."
Uber,218,The Skyline Problem,Hard,"Array, Divide and Conquer, Binary Indexed Tree, Segment Tree, Line Sweep, Heap (Priority Queue), Ordered Set","A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Given the locations and heights of all the buildings; return the skyline formed by these buildings collectively. The geometric information of each building is given in the array buildings where buildings[i] = [lefti; righti; heighti]: lefti is the x coordinate of the left edge of the ith building. righti is the x coordinate of the right edge of the ith building. heighti is the height of the ith building. You may assume all buildings are perfect rectangles grounded on an absolutely flat surface at height 0. The skyline should be represented as a list of ""key points"" sorted by their x-coordinate in the form [[x1;y1];[x2;y2];...]. Each key point is the left endpoint of some horizontal segment in the skyline except the last point in the list; which always has a y-coordinate 0 and is used to mark the skyline's termination where the rightmost building ends. Any ground between the leftmost and rightmost buildings should be part of the skyline's contour. Note: There must be no consecutive horizontal lines of equal height in the output skyline. For instance; [...;[2 3];[4 5];[7 5];[11 5];[12 7];...] is not acceptable; the three lines of height 5 should be merged into one in the final output as such: [...;[2 3];[4 5];[12 7];...] Example 1: Input: buildings = [[2;9;10];[3;7;15];[5;12;12];[15;20;10];[19;24;8]] Output: [[2;10];[3;15];[7;12];[12;0];[15;10];[20;8];[24;0]] Explanation: Figure A shows the buildings of the input. Figure B shows the skyline formed by those buildings. The red points in figure B represent the key points in the output list. Example 2: Input: buildings = [[0;2;3];[2;5;3]] Output: [[0;3];[5;0]] Constraints: 1 <= buildings.length <= 104 0 <= lefti < righti <= 231 - 1 1 <= heighti <= 231 - 1 buildings is sorted by lefti in non-decreasing order."
Uber,262,Trips and Users,Hard,Database,"Table: Trips +-------------+----------+ | Column Name | Type | +-------------+----------+ | id | int | | client_id | int | | driver_id | int | | city_id | int | | status | enum | | request_at | varchar | +-------------+----------+ id is the primary key (column with unique values) for this table. The table holds all taxi trips. Each trip has a unique id; while client_id and driver_id are foreign keys to the users_id at the Users table. Status is an ENUM (category) type of ('completed'; 'cancelled_by_driver'; 'cancelled_by_client'). Table: Users +-------------+----------+ | Column Name | Type | +-------------+----------+ | users_id | int | | banned | enum | | role | enum | +-------------+----------+ users_id is the primary key (column with unique values) for this table. The table holds all users. Each user has a unique users_id; and role is an ENUM type of ('client'; 'driver'; 'partner'). banned is an ENUM (category) type of ('Yes'; 'No'). The cancellation rate is computed by dividing the number of canceled (by client or driver) requests with unbanned users by the total number of requests with unbanned users on that day. Write a solution to find the cancellation rate of requests with unbanned users (both client and driver must not be banned) each day between ""2013-10-01"" and ""2013-10-03"". Round Cancellation Rate to two decimal points. Return the result table in any order. The result format is in the following example. Example 1: Input: Trips table: +----+-----------+-----------+---------+---------------------+------------+ | id | client_id | driver_id | city_id | status | request_at | +----+-----------+-----------+---------+---------------------+------------+ | 1 | 1 | 10 | 1 | completed | 2013-10-01 | | 2 | 2 | 11 | 1 | cancelled_by_driver | 2013-10-01 | | 3 | 3 | 12 | 6 | completed | 2013-10-01 | | 4 | 4 | 13 | 6 | cancelled_by_client | 2013-10-01 | | 5 | 1 | 10 | 1 | completed | 2013-10-02 | | 6 | 2 | 11 | 6 | completed | 2013-10-02 | | 7 | 3 | 12 | 6 | completed | 2013-10-02 | | 8 | 2 | 12 | 12 | completed | 2013-10-03 | | 9 | 3 | 10 | 12 | completed | 2013-10-03 | | 10 | 4 | 13 | 12 | cancelled_by_driver | 2013-10-03 | +----+-----------+-----------+---------+---------------------+------------+ Users table: +----------+--------+--------+ | users_id | banned | role | +----------+--------+--------+ | 1 | No | client | | 2 | Yes | client | | 3 | No | client | | 4 | No | client | | 10 | No | driver | | 11 | No | driver | | 12 | No | driver | | 13 | No | driver | +----------+--------+--------+ Output: +------------+-------------------+ | Day | Cancellation Rate | +------------+-------------------+ | 2013-10-01 | 0.33 | | 2013-10-02 | 0.00 | | 2013-10-03 | 0.50 | +------------+-------------------+ Explanation: On 2013-10-01: - There were 4 requests in total; 2 of which were canceled. - However; the request with Id=2 was made by a banned client (User_Id=2); so it is ignored in the calculation. - Hence there are 3 unbanned requests in total; 1 of which was canceled. - The Cancellation Rate is (1 / 3) = 0.33 On 2013-10-02: - There were 3 requests in total; 0 of which were canceled. - The request with Id=6 was made by a banned client; so it is ignored. - Hence there are 2 unbanned requests in total; 0 of which were canceled. - The Cancellation Rate is (0 / 2) = 0.00 On 2013-10-03: - There were 3 requests in total; 1 of which was canceled. - The request with Id=8 was made by a banned client; so it is ignored. - Hence there are 2 unbanned request in total; 1 of which were canceled. - The Cancellation Rate is (1 / 2) = 0.50"
Uber,535,Encode and Decode TinyURL,Med,"Hash Table, String, Design, Hash Function","Note: This is a companion problem to the System Design problem: Design TinyURL. TinyURL is a URL shortening service where you enter a URL such as https://leetcode.com/problems/design-tinyurl and it returns a short URL such as http://tinyurl.com/4e9iAk. Design a class to encode a URL and decode a tiny URL. There is no restriction on how your encode/decode algorithm should work. You just need to ensure that a URL can be encoded to a tiny URL and the tiny URL can be decoded to the original URL. Implement the Solution class: Solution() Initializes the object of the system. String encode(String longUrl) Returns a tiny URL for the given longUrl. String decode(String shortUrl) Returns the original long URL for the given shortUrl. It is guaranteed that the given shortUrl was encoded by the same object. Example 1: Input: url = ""https://leetcode.com/problems/design-tinyurl"" Output: ""https://leetcode.com/problems/design-tinyurl"" Explanation: Solution obj = new Solution(); string tiny = obj.encode(url); // returns the encoded tiny url. string ans = obj.decode(tiny); // returns the original url after decoding it. Constraints: 1 <= url.length <= 104 url is guranteed to be a valid URL."
Uber,636,Exclusive Time of Functions,Med,"Array, Stack","On a single-threaded CPU; we execute a program containing n functions. Each function has a unique ID between 0 and n-1. Function calls are stored in a call stack: when a function call starts; its ID is pushed onto the stack; and when a function call ends; its ID is popped off the stack. The function whose ID is at the top of the stack is the current function being executed. Each time a function starts or ends; we write a log with the ID; whether it started or ended; and the timestamp. You are given a list logs; where logs[i] represents the ith log message formatted as a string ""{function_id}:{""start"" | ""end""}:{timestamp}"". For example; ""0:start:3"" means a function call with function ID 0 started at the beginning of timestamp 3; and ""1:end:2"" means a function call with function ID 1 ended at the end of timestamp 2. Note that a function can be called multiple times; possibly recursively. A function's exclusive time is the sum of execution times for all function calls in the program. For example; if a function is called twice; one call executing for 2 time units and another call executing for 1 time unit; the exclusive time is 2 + 1 = 3. Return the exclusive time of each function in an array; where the value at the ith index represents the exclusive time for the function with ID i. Example 1: Input: n = 2; logs = [""0:start:0"";""1:start:2"";""1:end:5"";""0:end:6""] Output: [3;4] Explanation: Function 0 starts at the beginning of time 0; then it executes 2 for units of time and reaches the end of time 1. Function 1 starts at the beginning of time 2; executes for 4 units of time; and ends at the end of time 5. Function 0 resumes execution at the beginning of time 6 and executes for 1 unit of time. So function 0 spends 2 + 1 = 3 units of total time executing; and function 1 spends 4 units of total time executing. Example 2: Input: n = 1; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""0:start:6"";""0:end:6"";""0:end:7""] Output: [8] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls itself again. Function 0 (2nd recursive call) starts at the beginning of time 6 and executes for 1 unit of time. Function 0 (initial call) resumes execution at the beginning of time 7 and executes for 1 unit of time. So function 0 spends 2 + 4 + 1 + 1 = 8 units of total time executing. Example 3: Input: n = 2; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""1:start:6"";""1:end:6"";""0:end:7""] Output: [7;1] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls function 1. Function 1 starts at the beginning of time 6; executes 1 unit of time; and ends at the end of time 6. Function 0 resumes execution at the beginning of time 6 and executes for 2 units of time. So function 0 spends 2 + 4 + 1 = 7 units of total time executing; and function 1 spends 1 unit of total time executing. Constraints: 1 <= n <= 100 1 <= logs.length <= 500 0 <= function_id < n 0 <= timestamp <= 109 No two start events will happen at the same timestamp. No two end events will happen at the same timestamp. Each function has an ""end"" log for each ""start"" log."
Uber,648,Replace Words,Med,"Array, Hash Table, String, Trie","In English; we have a concept called root; which can be followed by some other word to form another longer word - let's call this word derivative. For example; when the root ""help"" is followed by the word ""ful""; we can form a derivative ""helpful"". Given a dictionary consisting of many roots and a sentence consisting of words separated by spaces; replace all the derivatives in the sentence with the root forming it. If a derivative can be replaced by more than one root; replace it with the root that has the shortest length. Return the sentence after the replacement. Example 1: Input: dictionary = [""cat"";""bat"";""rat""]; sentence = ""the cattle was rattled by the battery"" Output: ""the cat was rat by the bat"" Example 2: Input: dictionary = [""a"";""b"";""c""]; sentence = ""aadsfasf absbs bbab cadsfafs"" Output: ""a a b c"" Constraints: 1 <= dictionary.length <= 1000 1 <= dictionary[i].length <= 100 dictionary[i] consists of only lower-case letters. 1 <= sentence.length <= 106 sentence consists of only lower-case letters and spaces. The number of words in sentence is in the range [1; 1000] The length of each word in sentence is in the range [1; 1000] Every two consecutive words in sentence will be separated by exactly one space. sentence does not have leading or trailing spaces."
Uber,981,Time Based Key-Value Store,Med,"Array, String","You are given an array of n strings strs; all of the same length. The strings can be arranged such that there is one on each line; making a grid. For example; strs = [""abc""; ""bce""; ""cae""] can be arranged as follows: abc bce cae You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed); columns 0 ('a'; 'b'; 'c') and 2 ('c'; 'e'; 'e') are sorted; while column 1 ('b'; 'c'; 'a') is not; so you would delete column 1. Return the number of columns that you will delete. Example 1: Input: strs = [""cba"";""daf"";""ghi""] Output: 1 Explanation: The grid looks as follows: cba daf ghi Columns 0 and 2 are sorted; but column 1 is not; so you only need to delete 1 column. Example 2: Input: strs = [""a"";""b""] Output: 0 Explanation: The grid looks as follows: a b Column 0 is the only column and is sorted; so you will not delete any columns. Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: The grid looks as follows: zyx wvu tsr All 3 columns are not sorted; so you will delete all 3. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 1000 strs[i] consists of lowercase English letters."
Uber,1136,Parallel Courses,Med,Database,Table: ActorDirector +-------------+---------+ | Column Name | Type | +-------------+---------+ | actor_id | int | | director_id | int | | timestamp | int | +-------------+---------+ timestamp is the primary key (column with unique values) for this table. Write a solution to find all the pairs (actor_id; director_id) where the actor has cooperated with the director at least three times. Return the result table in any order. The result format is in the following example. Example 1: Input: ActorDirector table: +-------------+-------------+-------------+ | actor_id | director_id | timestamp | +-------------+-------------+-------------+ | 1 | 1 | 0 | | 1 | 1 | 1 | | 1 | 1 | 2 | | 1 | 2 | 3 | | 1 | 2 | 4 | | 2 | 1 | 5 | | 2 | 1 | 6 | +-------------+-------------+-------------+ Output: +-------------+-------------+ | actor_id | director_id | +-------------+-------------+ | 1 | 1 | +-------------+-------------+ Explanation: The only pair is (1; 1) where they cooperated exactly 3 times.
Uber,1385,Find the Distance Value Between Two Arrays,Easy,"Math, Dynamic Programming",
Uber,1400,Construct K Palindrome Strings,Med,"Array, Hash Table, Matrix, Simulation","Tic-tac-toe is played by two players A and B on a 3 x 3 grid. The rules of Tic-Tac-Toe are: Players take turns placing characters into empty squares ' '. The first player A always places 'X' characters; while the second player B always places 'O' characters. 'X' and 'O' characters are always placed into empty squares; never on filled ones. The game ends when there are three of the same (non-empty) character filling any row; column; or diagonal. The game also ends if all squares are non-empty. No more moves can be played if the game is over. Given a 2D integer array moves where moves[i] = [rowi; coli] indicates that the ith move will be played on grid[rowi][coli]. return the winner of the game if it exists (A or B). In case the game ends in a draw return ""Draw"". If there are still movements to play return ""Pending"". You can assume that moves is valid (i.e.; it follows the rules of Tic-Tac-Toe); the grid is initially empty; and A will play first. Example 1: Input: moves = [[0;0];[2;0];[1;1];[2;1];[2;2]] Output: ""A"" Explanation: A wins; they always play first. Example 2: Input: moves = [[0;0];[1;1];[0;1];[0;2];[1;0];[2;0]] Output: ""B"" Explanation: B wins. Example 3: Input: moves = [[0;0];[1;1];[2;0];[1;0];[1;2];[2;1];[0;1];[0;2];[2;2]] Output: ""Draw"" Explanation: The game ends in a draw since there are no moves to make. Constraints: 1 <= moves.length <= 9 moves[i].length == 2 0 <= rowi; coli <= 2 There are no repeated elements on moves. moves follow the rules of tic tac toe."
Uber,1462,Course Schedule IV,Med,Database,Table: Products +------------------+---------+ | Column Name | Type | +------------------+---------+ | product_id | int | | product_name | varchar | | product_category | varchar | +------------------+---------+ product_id is the primary key (column with unique values) for this table. This table contains data about the company's products. Table: Orders +---------------+---------+ | Column Name | Type | +---------------+---------+ | product_id | int | | order_date | date | | unit | int | +---------------+---------+ This table may have duplicate rows. product_id is a foreign key (reference column) to the Products table. unit is the number of products ordered in order_date. Write a solution to get the names of products that have at least 100 units ordered in February 2020 and their amount. Return the result table in any order. The result format is in the following example. Example 1: Input: Products table: +-------------+-----------------------+------------------+ | product_id | product_name | product_category | +-------------+-----------------------+------------------+ | 1 | Leetcode Solutions | Book | | 2 | Jewels of Stringology | Book | | 3 | HP | Laptop | | 4 | Lenovo | Laptop | | 5 | Leetcode Kit | T-shirt | +-------------+-----------------------+------------------+ Orders table: +--------------+--------------+----------+ | product_id | order_date | unit | +--------------+--------------+----------+ | 1 | 2020-02-05 | 60 | | 1 | 2020-02-10 | 70 | | 2 | 2020-01-18 | 30 | | 2 | 2020-02-11 | 80 | | 3 | 2020-02-17 | 2 | | 3 | 2020-02-24 | 3 | | 4 | 2020-03-01 | 20 | | 4 | 2020-03-04 | 30 | | 4 | 2020-03-04 | 60 | | 5 | 2020-02-25 | 50 | | 5 | 2020-02-27 | 50 | | 5 | 2020-03-01 | 50 | +--------------+--------------+----------+ Output: +--------------------+---------+ | product_name | unit | +--------------------+---------+ | Leetcode Solutions | 130 | | Leetcode Kit | 100 | +--------------------+---------+ Explanation: Products with product_id = 1 is ordered in February a total of (60 + 70) = 130. Products with product_id = 2 is ordered in February a total of 80. Products with product_id = 3 is ordered in February a total of (2 + 3) = 5. Products with product_id = 4 was not ordered in February 2020. Products with product_id = 5 is ordered in February a total of (50 + 50) = 100.
Uber,1579,Remove Max Number of Edges to Keep Graph Fully Traversable,Hard,Database,
Uber,1719,Number Of Ways To Reconstruct A Tree,Hard,"Array, Greedy, Sorting",
Uber,1705,Maximum Number of Eaten Apples,Med,"Array, Simulation",You are given a list of preferences for n friends; where n is always even. For each person i; preferences[i] contains a list of friends sorted in the order of preference. In other words; a friend earlier in the list is more preferred than a friend later in the list. Friends in each list are denoted by integers from 0 to n-1. All the friends are divided into pairs. The pairings are given in a list pairs; where pairs[i] = [xi; yi] denotes xi is paired with yi and yi is paired with xi. However; this pairing may cause some of the friends to be unhappy. A friend x is unhappy if x is paired with y and there exists a friend u who is paired with v but: x prefers u over y; and u prefers x over v. Return the number of unhappy friends. Example 1: Input: n = 4; preferences = [[1; 2; 3]; [3; 2; 0]; [3; 1; 0]; [1; 2; 0]]; pairs = [[0; 1]; [2; 3]] Output: 2 Explanation: Friend 1 is unhappy because: - 1 is paired with 0 but prefers 3 over 0; and - 3 prefers 1 over 2. Friend 3 is unhappy because: - 3 is paired with 2 but prefers 1 over 2; and - 1 prefers 3 over 0. Friends 0 and 2 are happy. Example 2: Input: n = 2; preferences = [[1]; [0]]; pairs = [[1; 0]] Output: 0 Explanation: Both friends 0 and 1 are happy. Example 3: Input: n = 4; preferences = [[1; 3; 2]; [2; 3; 0]; [1; 3; 0]; [0; 2; 1]]; pairs = [[1; 3]; [0; 2]] Output: 4 Constraints: 2 <= n <= 500 n is even. preferences.length == n preferences[i].length == n - 1 0 <= preferences[i][j] <= n - 1 preferences[i] does not contain i. All values in preferences[i] are unique. pairs.length == n/2 pairs[i].length == 2 xi != yi 0 <= xi; yi <= n - 1 Each person is contained in exactly one pair.
Uber,1757,Recyclable and Low Fat Products,Easy,"Array, Dynamic Programming, Breadth-First Search",A certain bug's home is on the x-axis at position x. Help them get there from position 0. The bug jumps according to the following rules: It can jump exactly a positions forward (to the right). It can jump exactly b positions backward (to the left). It cannot jump backward twice in a row. It cannot jump to any forbidden positions. The bug may jump forward beyond its home; but it cannot jump to positions numbered with negative integers. Given an array of integers forbidden; where forbidden[i] means that the bug cannot jump to the position forbidden[i]; and integers a; b; and x; return the minimum number of jumps needed for the bug to reach its home. If there is no possible sequence of jumps that lands the bug on position x; return -1. Example 1: Input: forbidden = [14;4;18;1;15]; a = 3; b = 15; x = 9 Output: 3 Explanation: 3 jumps forward (0 -> 3 -> 6 -> 9) will get the bug home. Example 2: Input: forbidden = [8;3;16;6;12;20]; a = 15; b = 13; x = 11 Output: -1 Example 3: Input: forbidden = [1;6;2;14;5;17;4]; a = 16; b = 9; x = 7 Output: 2 Explanation: One jump forward (0 -> 16) then one jump backward (16 -> 7) will get the bug home. Constraints: 1 <= forbidden.length <= 1000 1 <= a; b; forbidden[i] <= 2000 0 <= x <= 2000 All the elements in forbidden are distinct. Position x is not forbidden.
Uber,1961,Check If String Is a Prefix of Array,Easy,"Array, Greedy, Sorting, Counting Sort",It is a sweltering summer day; and a boy wants to buy some ice cream bars. At the store; there are n ice cream bars. You are given an array costs of length n; where costs[i] is the price of the ith ice cream bar in coins. The boy initially has coins coins to spend; and he wants to buy as many ice cream bars as possible. Note: The boy can buy the ice cream bars in any order. Return the maximum number of ice cream bars the boy can buy with coins coins. You must solve the problem by counting sort. Example 1: Input: costs = [1;3;2;4;1]; coins = 7 Output: 4 Explanation: The boy can buy ice cream bars at indices 0;1;2;4 for a total price of 1 + 3 + 2 + 1 = 7. Example 2: Input: costs = [10;6;8;7;7;8]; coins = 5 Output: 0 Explanation: The boy cannot afford any of the ice cream bars. Example 3: Input: costs = [1;6;3;1;2;5]; coins = 20 Output: 6 Explanation: The boy can buy all the ice cream bars for a total price of 1 + 6 + 3 + 1 + 2 + 5 = 18. Constraints: costs.length == n 1 <= n <= 105 1 <= costs[i] <= 105 1 <= coins <= 108
Uber,2261,K Divisible Elements Subarrays,Med,Array,You are given a 0-indexed binary array nums of length n. nums can be divided at index i (where 0 <= i <= n) into two arrays (possibly empty) numsleft and numsright: numsleft has all the elements of nums between index 0 and i - 1 (inclusive); while numsright has all the elements of nums between index i and n - 1 (inclusive). If i == 0; numsleft is empty; while numsright has all the elements of nums. If i == n; numsleft has all the elements of nums; while numsright is empty. The division score of an index i is the sum of the number of 0's in numsleft and the number of 1's in numsright. Return all distinct indices that have the highest possible division score. You may return the answer in any order. Example 1: Input: nums = [0;0;1;0] Output: [2;4] Explanation: Division at index - 0: numsleft is []. numsright is [0;0;1;0]. The score is 0 + 1 = 1. - 1: numsleft is [0]. numsright is [0;1;0]. The score is 1 + 1 = 2. - 2: numsleft is [0;0]. numsright is [1;0]. The score is 2 + 1 = 3. - 3: numsleft is [0;0;1]. numsright is [0]. The score is 2 + 0 = 2. - 4: numsleft is [0;0;1;0]. numsright is []. The score is 3 + 0 = 3. Indices 2 and 4 both have the highest possible division score 3. Note the answer [4;2] would also be accepted. Example 2: Input: nums = [0;0;0] Output: [3] Explanation: Division at index - 0: numsleft is []. numsright is [0;0;0]. The score is 0 + 0 = 0. - 1: numsleft is [0]. numsright is [0;0]. The score is 1 + 0 = 1. - 2: numsleft is [0;0]. numsright is [0]. The score is 2 + 0 = 2. - 3: numsleft is [0;0;0]. numsright is []. The score is 3 + 0 = 3. Only index 3 has the highest possible division score 3. Example 3: Input: nums = [1;1] Output: [0] Explanation: Division at index - 0: numsleft is []. numsright is [1;1]. The score is 0 + 2 = 2. - 1: numsleft is [1]. numsright is [1]. The score is 0 + 1 = 1. - 2: numsleft is [1;1]. numsright is []. The score is 0 + 0 = 0. Only index 0 has the highest possible division score 2. Constraints: n == nums.length 1 <= n <= 105 nums[i] is either 0 or 1.
Uber,2555,Maximize Win From Two Segments,Med,"Array, Hash Table, String, Design",
Uber,6,Zigzag Conversion,Med,String,"The string ""PAYPALISHIRING"" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: ""PAHNAPLSIIGYIR"" Write the code that will take a string and make this conversion given a number of rows: string convert(string s; int numRows); Example 1: Input: s = ""PAYPALISHIRING""; numRows = 3 Output: ""PAHNAPLSIIGYIR"" Example 2: Input: s = ""PAYPALISHIRING""; numRows = 4 Output: ""PINALSIGYAHRPI"" Explanation: P I N A L S I G Y A H R P I Example 3: Input: s = ""A""; numRows = 1 Output: ""A"" Constraints: 1 <= s.length <= 1000 s consists of English letters (lower-case and upper-case); ';' and '.'. 1 <= numRows <= 1000"
Uber,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
Uber,73,Set Matrix Zeroes,Med,"Array, Hash Table, Matrix",Given an m x n integer matrix matrix; if an element is 0; set its entire row and column to 0's. You must do it in place. Example 1: Input: matrix = [[1;1;1];[1;0;1];[1;1;1]] Output: [[1;0;1];[0;0;0];[1;0;1]] Example 2: Input: matrix = [[0;1;2;0];[3;4;5;2];[1;3;1;5]] Output: [[0;0;0;0];[0;4;5;0];[0;3;1;0]] Constraints: m == matrix.length n == matrix[0].length 1 <= m; n <= 200 -231 <= matrix[i][j] <= 231 - 1 Follow up: A straightforward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space; but still not the best solution. Could you devise a constant space solution?
Uber,118,Pascal's Triangle,Easy,"Array, Dynamic Programming",Given an integer numRows; return the first numRows of Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: numRows = 5 Output: [[1];[1;1];[1;2;1];[1;3;3;1];[1;4;6;4;1]] Example 2: Input: numRows = 1 Output: [[1]] Constraints: 1 <= numRows <= 30
Uber,133,Clone Graph,Med,"Hash Table, Depth-First Search, Breadth-First Search, Graph",Given a reference of a node in a connected undirected graph. Return a deep copy (clone) of the graph. Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors. class Node { public int val; public List<Node> neighbors; } Test case format: For simplicity; each node's value is the same as the node's index (1-indexed). For example; the first node with val == 1; the second node with val == 2; and so on. The graph is represented in the test case using an adjacency list. An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph. The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph. Example 1: Input: adjList = [[2;4];[1;3];[2;4];[1;3]] Output: [[2;4];[1;3];[2;4];[1;3]] Explanation: There are 4 nodes in the graph. 1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). 3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). Example 2: Input: adjList = [[]] Output: [[]] Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors. Example 3: Input: adjList = [] Output: [] Explanation: This an empty graph; it does not have any nodes. Constraints: The number of nodes in the graph is in the range [0; 100]. 1 <= Node.val <= 100 Node.val is unique for each node. There are no repeated edges and no self-loops in the graph. The Graph is connected and all nodes can be visited starting from the given node.
Uber,161,One Edit Distance,Med,"Two Pointers, String",
Uber,186,Reverse Words in a String II,Med,"Two Pointers, String",
Uber,234,Palindrome Linked List,Easy,"Linked List, Two Pointers, Stack, Recursion",Given the head of a singly linked list; return true if it is a palindrome or false otherwise. Example 1: Input: head = [1;2;2;1] Output: true Example 2: Input: head = [1;2] Output: false Constraints: The number of nodes in the list is in the range [1; 105]. 0 <= Node.val <= 9 Follow up: Could you do it in O(n) time and O(1) space?
Uber,249,Group Shifted Strings,Med,"Array, Hash Table, String",
Uber,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Uber,254,Factor Combinations,Med,Backtracking,
Uber,266,Palindrome Permutation,Easy,"Hash Table, String, Bit Manipulation",
Uber,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Uber,291,Word Pattern II,Med,"Hash Table, String, Backtracking",
Uber,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
Uber,349,Intersection of Two Arrays,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must be unique and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [9;4] Explanation: [4;9] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000
Uber,516,Longest Palindromic Subsequence,Med,"String, Dynamic Programming","Given a string s; find the longest palindromic subsequence's length in s. A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements. Example 1: Input: s = ""bbbab"" Output: 4 Explanation: One possible longest palindromic subsequence is ""bbbb"". Example 2: Input: s = ""cbbd"" Output: 2 Explanation: One possible longest palindromic subsequence is ""bb"". Constraints: 1 <= s.length <= 1000 s consists only of lowercase English letters."
Uber,690,Employee Importance,Med,"Array, Hash Table, Tree, Depth-First Search, Breadth-First Search",You have a data structure of employee information; including the employee's unique ID; importance value; and direct subordinates' IDs. You are given an array of employees employees where: employees[i].id is the ID of the ith employee. employees[i].importance is the importance value of the ith employee. employees[i].subordinates is a list of the IDs of the direct subordinates of the ith employee. Given an integer id that represents an employee's ID; return the total importance value of this employee and all their direct and indirect subordinates. Example 1: Input: employees = [[1;5;[2;3]];[2;3;[]];[3;3;[]]]; id = 1 Output: 11 Explanation: Employee 1 has an importance value of 5 and has two direct subordinates: employee 2 and employee 3. They both have an importance value of 3. Thus; the total importance value of employee 1 is 5 + 3 + 3 = 11. Example 2: Input: employees = [[1;2;[5]];[5;-3;[]]]; id = 5 Output: -3 Explanation: Employee 5 has an importance value of -3 and has no direct subordinates. Thus; the total importance value of employee 5 is -3. Constraints: 1 <= employees.length <= 2000 1 <= employees[i].id <= 2000 All employees[i].id are unique. -100 <= employees[i].importance <= 100 One employee has at most one direct leader and may have several subordinates. The IDs in employees[i].subordinates are valid IDs.
Uber,699,Falling Squares,Hard,"Array, Segment Tree, Ordered Set",There are several squares being dropped onto the X-axis of a 2D plane. You are given a 2D integer array positions where positions[i] = [lefti; sideLengthi] represents the ith square with a side length of sideLengthi that is dropped with its left edge aligned with X-coordinate lefti. Each square is dropped one at a time from a height above any landed squares. It then falls downward (negative Y direction) until it either lands on the top side of another square or on the X-axis. A square brushing the left/right side of another square does not count as landing on it. Once it lands; it freezes in place and cannot be moved. After each square is dropped; you must record the height of the current tallest stack of squares. Return an integer array ans where ans[i] represents the height described above after dropping the ith square. Example 1: Input: positions = [[1;2];[2;3];[6;1]] Output: [2;5;5] Explanation: After the first drop; the tallest stack is square 1 with a height of 2. After the second drop; the tallest stack is squares 1 and 2 with a height of 5. After the third drop; the tallest stack is still squares 1 and 2 with a height of 5. Thus; we return an answer of [2; 5; 5]. Example 2: Input: positions = [[100;100];[200;100]] Output: [100;100] Explanation: After the first drop; the tallest stack is square 1 with a height of 100. After the second drop; the tallest stack is either square 1 or square 2; both with heights of 100. Thus; we return an answer of [100; 100]. Note that square 2 only brushes the right side of square 1; which does not count as landing on it. Constraints: 1 <= positions.length <= 1000 1 <= lefti <= 108 1 <= sideLengthi <= 106
Uber,855,Exam Room,Med,"Hash Table, String, Dynamic Programming","Let's define a function countUniqueChars(s) that returns the number of unique characters in s. For example; calling countUniqueChars(s) if s = ""LEETCODE"" then ""L""; ""T""; ""C""; ""O""; ""D"" are the unique characters since they appear only once in s; therefore countUniqueChars(s) = 5. Given a string s; return the sum of countUniqueChars(t) where t is a substring of s. The test cases are generated such that the answer fits in a 32-bit integer. Notice that some substrings can be repeated so in this case you have to count the repeated ones too. Example 1: Input: s = ""ABC"" Output: 10 Explanation: All possible substrings are: ""A"";""B"";""C"";""AB"";""BC"" and ""ABC"". Every substring is composed with only unique letters. Sum of lengths of all substring is 1 + 1 + 1 + 2 + 2 + 3 = 10 Example 2: Input: s = ""ABA"" Output: 8 Explanation: The same as example 1; except countUniqueChars(""ABA"") = 1. Example 3: Input: s = ""LEETCODE"" Output: 92 Constraints: 1 <= s.length <= 105 s consists of uppercase English letters only."
Uber,710,Random Pick with Blacklist,Hard,,
Uber,959,Regions Cut By Slashes,Med,"Array, Hash Table, Two Pointers, Sorting, Counting",Given an integer array arr; and an integer target; return the number of tuples i; j; k such that i < j < k and arr[i] + arr[j] + arr[k] == target. As the answer can be very large; return it modulo 109 + 7. Example 1: Input: arr = [1;1;2;2;3;3;4;4;5;5]; target = 8 Output: 20 Explanation: Enumerating by the values (arr[i]; arr[j]; arr[k]): (1; 2; 5) occurs 8 times; (1; 3; 4) occurs 8 times; (2; 2; 4) occurs 2 times; (2; 3; 3) occurs 2 times. Example 2: Input: arr = [1;1;2;2;2;2]; target = 5 Output: 12 Explanation: arr[i] = 1; arr[j] = arr[k] = 2 occurs 12 times: We choose one 1 from [1;1] in 2 ways; and two 2s from [2;2;2;2] in 6 ways. Example 3: Input: arr = [2;1;3]; target = 6 Output: 1 Explanation: (1; 2; 3) occured one time in the array so we return 1. Constraints: 3 <= arr.length <= 3000 0 <= arr[i] <= 100 0 <= target <= 300
Uber,1064,Fixed Point,Easy,"Hash Table, Math",Given a positive integer k; you need to find the length of the smallest positive integer n such that n is divisible by k; and n only contains the digit 1. Return the length of n. If there is no such n; return -1. Note: n may not fit in a 64-bit signed integer. Example 1: Input: k = 1 Output: 1 Explanation: The smallest answer is n = 1; which has length 1. Example 2: Input: k = 2 Output: -1 Explanation: There is no such positive integer n divisible by 2. Example 3: Input: k = 3 Output: 3 Explanation: The smallest answer is n = 111; which has length 3. Constraints: 1 <= k <= 105
Uber,1039,Minimum Score Triangulation of Polygon,Med,"Array, Hash Table, Graph",In a town; there are n people labeled from 1 to n. There is a rumor that one of these people is secretly the town judge. If the town judge exists; then: The town judge trusts nobody. Everybody (except for the town judge) trusts the town judge. There is exactly one person that satisfies properties 1 and 2. You are given an array trust where trust[i] = [ai; bi] representing that the person labeled ai trusts the person labeled bi. If a trust relationship does not exist in trust array; then such a trust relationship does not exist. Return the label of the town judge if the town judge exists and can be identified; or return -1 otherwise. Example 1: Input: n = 2; trust = [[1;2]] Output: 2 Example 2: Input: n = 3; trust = [[1;3];[2;3]] Output: 3 Example 3: Input: n = 3; trust = [[1;3];[2;3];[3;1]] Output: -1 Constraints: 1 <= n <= 1000 0 <= trust.length <= 104 trust[i].length == 2 All the pairs of trust are unique. ai != bi 1 <= ai; bi <= n
Uber,1207,Unique Number of Occurrences,Easy,"Array, Hash Table, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; each node in the tree has a distinct value. After deleting all nodes with a value in to_delete; we are left with a forest (a disjoint union of trees). Return the roots of the trees in the remaining forest. You may return the result in any order. Example 1: Input: root = [1;2;3;4;5;6;7]; to_delete = [3;5] Output: [[1;2;null;4];[6];[7]] Example 2: Input: root = [1;2;4;null;3]; to_delete = [3] Output: [[1;2;4]] Constraints: The number of nodes in the given tree is at most 1000. Each node has a distinct value between 1 and 1000. to_delete.length <= 1000 to_delete contains distinct values between 1 and 1000.
Uber,1334,Find the City With the Smallest Number of Neighbors at a Threshold Distance,Med,"Math, Dynamic Programming, Greedy, Enumeration",Given two integers num and k; consider a set of positive integers with the following properties: The units digit of each integer is k. The sum of the integers is num. Return the minimum possible size of such a set; or -1 if no such set exists. Note: The set can contain multiple instances of the same integer; and the sum of an empty set is considered 0. The units digit of a number is the rightmost digit of the number. Example 1: Input: num = 58; k = 9 Output: 2 Explanation: One valid set is [9;49]; as the sum is 58 and each integer has a units digit of 9. Another valid set is [19;39]. It can be shown that 2 is the minimum possible size of a valid set. Example 2: Input: num = 37; k = 2 Output: -1 Explanation: It is not possible to obtain a sum of 37 using only integers that have a units digit of 2. Example 3: Input: num = 0; k = 7 Output: 0 Explanation: The sum of an empty set is considered 0. Constraints: 0 <= num <= 3000 0 <= k <= 9
Uber,1519,Number of Nodes in the Sub-Tree With the Same Label,Med,"Array, Greedy, Sorting",Given the array nums; obtain a subsequence of the array whose sum of elements is strictly greater than the sum of the non included elements in such subsequence. If there are multiple solutions; return the subsequence with minimum size and if there still exist multiple solutions; return the subsequence with the maximum total sum of all its elements. A subsequence of an array can be obtained by erasing some (possibly zero) elements from the array. Note that the solution with the given constraints is guaranteed to be unique. Also return the answer sorted in non-increasing order. Example 1: Input: nums = [4;3;10;9;8] Output: [10;9] Explanation: The subsequences [10;9] and [10;8] are minimal such that the sum of their elements is strictly greater than the sum of elements not included. However; the subsequence [10;9] has the maximum total sum of its elements. Example 2: Input: nums = [4;4;7;6;7] Output: [7;7;6] Explanation: The subsequence [7;7] has the sum of its elements equal to 14 which is not strictly greater than the sum of elements not included (14 = 4 + 4 + 6). Therefore; the subsequence [7;6;7] is the minimal satisfying the conditions. Note the subsequence has to be returned in non-increasing order. Constraints: 1 <= nums.length <= 500 1 <= nums[i] <= 100
Uber,1635,Hopper Company Queries I,Hard,"Array, Hash Table, Math, Counting",Given an array of integers nums; return the number of good pairs. A pair (i; j) is called good if nums[i] == nums[j] and i < j. Example 1: Input: nums = [1;2;3;1;1;3] Output: 4 Explanation: There are 4 good pairs (0;3); (0;4); (3;4); (2;5) 0-indexed. Example 2: Input: nums = [1;1;1;1] Output: 6 Explanation: Each pair in the array are good. Example 3: Input: nums = [1;2;3] Output: 0 Constraints: 1 <= nums.length <= 100 1 <= nums[i] <= 100
Uber,1645,Hopper Company Queries II,Hard,"Array, Binary Search, Bit Manipulation, Segment Tree",Winston was given the above mysterious function func. He has an integer array arr and an integer target and he wants to find the values l and r that make the value |func(arr; l; r) - target| minimum possible. Return the minimum possible value of |func(arr; l; r) - target|. Notice that func should be called with the values l and r where 0 <= l; r < arr.length. Example 1: Input: arr = [9;12;3;7;15]; target = 5 Output: 2 Explanation: Calling func with all the pairs of [l;r] = [[0;0];[1;1];[2;2];[3;3];[4;4];[0;1];[1;2];[2;3];[3;4];[0;2];[1;3];[2;4];[0;3];[1;4];[0;4]]; Winston got the following results [9;12;3;7;15;8;0;3;7;0;0;3;0;0;0]. The value closest to 5 is 7 and 3; thus the minimum difference is 2. Example 2: Input: arr = [1000000;1000000;1000000]; target = 1 Output: 999999 Explanation: Winston called the func with all possible values of [l;r] and he always got 1000000; thus the min difference is 999999. Example 3: Input: arr = [1;2;4;8;16]; target = 0 Output: 0 Constraints: 1 <= arr.length <= 105 1 <= arr[i] <= 106 0 <= target <= 107
Uber,1651,Hopper Company Queries III,Hard,"Array, String","You are given a string s and an integer array indices of the same length. The string s will be shuffled such that the character at the ith position moves to indices[i] in the shuffled string. Return the shuffled string. Example 1: Input: s = ""codeleet""; indices = [4;5;6;7;0;2;1;3] Output: ""leetcode"" Explanation: As shown; ""codeleet"" becomes ""leetcode"" after shuffling. Example 2: Input: s = ""abc""; indices = [0;1;2] Output: ""abc"" Explanation: After shuffling; each character remains in its position. Constraints: s.length == indices.length == n 1 <= n <= 100 s consists of only lowercase English letters. 0 <= indices[i] < n All values of indices are unique."
Uber,1829,Maximum XOR for Each Query,Med,"Array, Greedy, Sorting",You are assigned to put some amount of boxes onto one truck. You are given a 2D array boxTypes; where boxTypes[i] = [numberOfBoxesi; numberOfUnitsPerBoxi]: numberOfBoxesi is the number of boxes of type i. numberOfUnitsPerBoxi is the number of units in each box of the type i. You are also given an integer truckSize; which is the maximum number of boxes that can be put on the truck. You can choose any boxes to put on the truck as long as the number of boxes does not exceed truckSize. Return the maximum total number of units that can be put on the truck. Example 1: Input: boxTypes = [[1;3];[2;2];[3;1]]; truckSize = 4 Output: 8 Explanation: There are: - 1 box of the first type that contains 3 units. - 2 boxes of the second type that contain 2 units each. - 3 boxes of the third type that contain 1 unit each. You can take all the boxes of the first and second types; and one box of the third type. The total number of units will be = (1 * 3) + (2 * 2) + (1 * 1) = 8. Example 2: Input: boxTypes = [[5;10];[2;5];[4;7];[3;9]]; truckSize = 10 Output: 91 Constraints: 1 <= boxTypes.length <= 1000 1 <= numberOfBoxesi; numberOfUnitsPerBoxi <= 1000 1 <= truckSize <= 106
Uber,1818,Minimum Absolute Sum Difference,Med,"String, Stack, Greedy","You are given a string s and two integers x and y. You can perform two types of operations any number of times. Remove substring ""ab"" and gain x points. For example; when removing ""ab"" from ""cabxbae"" it becomes ""cxbae"". Remove substring ""ba"" and gain y points. For example; when removing ""ba"" from ""cabxbae"" it becomes ""cabxe"". Return the maximum points you can gain after applying the above operations on s. Example 1: Input: s = ""cdbcbbaaabab""; x = 4; y = 5 Output: 19 Explanation: - Remove the ""ba"" underlined in ""cdbcbbaaabab"". Now; s = ""cdbcbbaaab"" and 5 points are added to the score. - Remove the ""ab"" underlined in ""cdbcbbaaab"". Now; s = ""cdbcbbaa"" and 4 points are added to the score. - Remove the ""ba"" underlined in ""cdbcbbaa"". Now; s = ""cdbcba"" and 5 points are added to the score. - Remove the ""ba"" underlined in ""cdbcba"". Now; s = ""cdbc"" and 5 points are added to the score. Total score = 5 + 4 + 5 + 5 = 19. Example 2: Input: s = ""aabbaaxybbaabb""; x = 5; y = 4 Output: 20 Constraints: 1 <= s.length <= 105 1 <= x; y <= 104 s consists of lowercase English letters."
Uber,1856,Maximum Subarray Min-Product,Med,,
Uber,2307,Check for Contradictions in Equations,Hard,"Array, Math, Stack, Number Theory",You are given an array of integers nums. Perform the following steps: Find any two adjacent numbers in nums that are non-coprime. If no such numbers are found; stop the process. Otherwise; delete the two numbers and replace them with their LCM (Least Common Multiple). Repeat this process as long as you keep finding two adjacent non-coprime numbers. Return the final modified array. It can be shown that replacing adjacent non-coprime numbers in any arbitrary order will lead to the same result. The test cases are generated such that the values in the final array are less than or equal to 108. Two values x and y are non-coprime if GCD(x; y) > 1 where GCD(x; y) is the Greatest Common Divisor of x and y. Example 1: Input: nums = [6;4;3;2;7;6;2] Output: [12;7;6] Explanation: - (6; 4) are non-coprime with LCM(6; 4) = 12. Now; nums = [12;3;2;7;6;2]. - (12; 3) are non-coprime with LCM(12; 3) = 12. Now; nums = [12;2;7;6;2]. - (12; 2) are non-coprime with LCM(12; 2) = 12. Now; nums = [12;7;6;2]. - (6; 2) are non-coprime with LCM(6; 2) = 6. Now; nums = [12;7;6]. There are no more adjacent non-coprime numbers in nums. Thus; the final modified array is [12;7;6]. Note that there are other ways to obtain the same resultant array. Example 2: Input: nums = [2;2;1;1;3;3;3] Output: [2;1;1;3] Explanation: - (3; 3) are non-coprime with LCM(3; 3) = 3. Now; nums = [2;2;1;1;3;3]. - (3; 3) are non-coprime with LCM(3; 3) = 3. Now; nums = [2;2;1;1;3]. - (2; 2) are non-coprime with LCM(2; 2) = 2. Now; nums = [2;1;1;3]. There are no more adjacent non-coprime numbers in nums. Thus; the final modified array is [2;1;1;3]. Note that there are other ways to obtain the same resultant array. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105 The test cases are generated such that the values in the final array are less than or equal to 108.
Uber,1968,Array With Elements Not Equal to Average of Neighbors,Med,"Array, Math, Sorting",You want to build n new buildings in a city. The new buildings will be built in a line and are labeled from 1 to n. However; there are city restrictions on the heights of the new buildings: The height of each building must be a non-negative integer. The height of the first building must be 0. The height difference between any two adjacent buildings cannot exceed 1. Additionally; there are city restrictions on the maximum height of specific buildings. These restrictions are given as a 2D integer array restrictions where restrictions[i] = [idi; maxHeighti] indicates that building idi must have a height less than or equal to maxHeighti. It is guaranteed that each building will appear at most once in restrictions; and building 1 will not be in restrictions. Return the maximum possible height of the tallest building. Example 1: Input: n = 5; restrictions = [[2;1];[4;1]] Output: 2 Explanation: The green area in the image indicates the maximum allowed height for each building. We can build the buildings with heights [0;1;2;1;2]; and the tallest building has a height of 2. Example 2: Input: n = 6; restrictions = [] Output: 5 Explanation: The green area in the image indicates the maximum allowed height for each building. We can build the buildings with heights [0;1;2;3;4;5]; and the tallest building has a height of 5. Example 3: Input: n = 10; restrictions = [[5;3];[2;5];[7;4];[10;3]] Output: 5 Explanation: The green area in the image indicates the maximum allowed height for each building. We can build the buildings with heights [0;1;2;3;3;4;4;5;4;3]; and the tallest building has a height of 5. Constraints: 2 <= n <= 109 0 <= restrictions.length <= min(n - 1; 105) 2 <= idi <= n idi is unique. 0 <= maxHeighti <= 109
Uber,1967,Number of Strings That Appear as Substrings in Word,Easy,"String, Sliding Window","A string is considered beautiful if it satisfies the following conditions: Each of the 5 English vowels ('a'; 'e'; 'i'; 'o'; 'u') must appear at least once in it. The letters must be sorted in alphabetical order (i.e. all 'a's before 'e's; all 'e's before 'i's; etc.). For example; strings ""aeiou"" and ""aaaaaaeiiiioou"" are considered beautiful; but ""uaeio""; ""aeoiu""; and ""aaaeeeooo"" are not beautiful. Given a string word consisting of English vowels; return the length of the longest beautiful substring of word. If no such substring exists; return 0. A substring is a contiguous sequence of characters in a string. Example 1: Input: word = ""aeiaaioaaaaeiiiiouuuooaauuaeiu"" Output: 13 Explanation: The longest beautiful substring in word is ""aaaaeiiiiouuu"" of length 13. Example 2: Input: word = ""aeeeiiiioooauuuaeiou"" Output: 5 Explanation: The longest beautiful substring in word is ""aeiou"" of length 5. Example 3: Input: word = ""a"" Output: 0 Explanation: There is no beautiful substring; so return 0. Constraints: 1 <= word.length <= 5 * 105 word consists of characters 'a'; 'e'; 'i'; 'o'; and 'u'."
Uber,2035,Partition Array Into Two Arrays to Minimize Sum Difference,Hard,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given two m x n binary matrices grid1 and grid2 containing only 0's (representing water) and 1's (representing land). An island is a group of 1's connected 4-directionally (horizontal or vertical). Any cells outside of the grid are considered water cells. An island in grid2 is considered a sub-island if there is an island in grid1 that contains all the cells that make up this island in grid2. Return the number of islands in grid2 that are considered sub-islands. Example 1: Input: grid1 = [[1;1;1;0;0];[0;1;1;1;1];[0;0;0;0;0];[1;0;0;0;0];[1;1;0;1;1]]; grid2 = [[1;1;1;0;0];[0;0;1;1;1];[0;1;0;0;0];[1;0;1;1;0];[0;1;0;1;0]] Output: 3 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are three sub-islands. Example 2: Input: grid1 = [[1;0;1;0;1];[1;1;1;1;1];[0;0;0;0;0];[1;1;1;1;1];[1;0;1;0;1]]; grid2 = [[0;0;0;0;0];[1;1;1;1;1];[0;1;0;1;0];[0;1;0;1;0];[1;0;0;0;1]] Output: 2 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are two sub-islands. Constraints: m == grid1.length == grid2.length n == grid1[i].length == grid2[i].length 1 <= m; n <= 500 grid1[i][j] and grid2[i][j] are either 0 or 1.
Uber,2196,Create Binary Tree From Descriptions,Med,Linked List,You are given the head of a linked list. The nodes in the linked list are sequentially assigned to non-empty groups whose lengths form the sequence of the natural numbers (1; 2; 3; 4; ...). The length of a group is the number of nodes assigned to it. In other words; The 1st node is assigned to the first group. The 2nd and the 3rd nodes are assigned to the second group. The 4th; 5th; and 6th nodes are assigned to the third group; and so on. Note that the length of the last group may be less than or equal to 1 + the length of the second to last group. Reverse the nodes in each group with an even length; and return the head of the modified linked list. Example 1: Input: head = [5;2;6;3;9;1;7;3;8;4] Output: [5;6;2;3;9;1;4;8;3;7] Explanation: - The length of the first group is 1; which is odd; hence no reversal occurs. - The length of the second group is 2; which is even; hence the nodes are reversed. - The length of the third group is 3; which is odd; hence no reversal occurs. - The length of the last group is 4; which is even; hence the nodes are reversed. Example 2: Input: head = [1;1;0;6] Output: [1;0;1;6] Explanation: - The length of the first group is 1. No reversal occurs. - The length of the second group is 2. The nodes are reversed. - The length of the last group is 1. No reversal occurs. Example 3: Input: head = [1;1;0;6;5] Output: [1;0;1;5;6] Explanation: - The length of the first group is 1. No reversal occurs. - The length of the second group is 2. The nodes are reversed. - The length of the last group is 2. The nodes are reversed. Constraints: The number of nodes in the list is in the range [1; 105]. 0 <= Node.val <= 105
Uber,2248,Intersection of Multiple Arrays,Easy,"Array, Greedy, Sorting",A shop is selling candies at a discount. For every two candies sold; the shop gives a third candy for free. The customer can choose any candy to take away for free as long as the cost of the chosen candy is less than or equal to the minimum cost of the two candies bought. For example; if there are 4 candies with costs 1; 2; 3; and 4; and the customer buys candies with costs 2 and 3; they can take the candy with cost 1 for free; but not the candy with cost 4. Given a 0-indexed integer array cost; where cost[i] denotes the cost of the ith candy; return the minimum cost of buying all the candies. Example 1: Input: cost = [1;2;3] Output: 5 Explanation: We buy the candies with costs 2 and 3; and take the candy with cost 1 for free. The total cost of buying all candies is 2 + 3 = 5. This is the only way we can buy the candies. Note that we cannot buy candies with costs 1 and 3; and then take the candy with cost 2 for free. The cost of the free candy has to be less than or equal to the minimum cost of the purchased candies. Example 2: Input: cost = [6;5;7;9;2;2] Output: 23 Explanation: The way in which we can get the minimum cost is described below: - Buy candies with costs 9 and 7 - Take the candy with cost 6 for free - We buy candies with costs 5 and 2 - Take the last remaining candy with cost 2 for free Hence; the minimum cost to buy all candies is 9 + 7 + 5 + 2 = 23. Example 3: Input: cost = [5;5] Output: 10 Explanation: Since there are only 2 candies; we buy both of them. There is not a third candy we can take for free. Hence; the minimum cost to buy all candies is 5 + 5 = 10. Constraints: 1 <= cost.length <= 100 1 <= cost[i] <= 100
Uber,2258,Escape the Spreading Fire,Hard,Array,
Uber,2243,Calculate Digit Sum of a String,Easy,String,"Given a string s consisting of only the characters 'a' and 'b'; return true if every 'a' appears before every 'b' in the string. Otherwise; return false. Example 1: Input: s = ""aaabbb"" Output: true Explanation: The 'a's are at indices 0; 1; and 2; while the 'b's are at indices 3; 4; and 5. Hence; every 'a' appears before every 'b' and we return true. Example 2: Input: s = ""abab"" Output: false Explanation: There is an 'a' at index 2 and a 'b' at index 1. Hence; not every 'a' appears before every 'b' and we return false. Example 3: Input: s = ""bbb"" Output: true Explanation: There are no 'a's; hence; every 'a' appears before every 'b' and we return true. Constraints: 1 <= s.length <= 100 s[i] is either 'a' or 'b'."
Uber,2333,Minimum Sum of Squared Difference,Med,"Array, Binary Search, Binary Indexed Tree, Sorting",You are given a 2D integer array rectangles where rectangles[i] = [li; hi] indicates that ith rectangle has a length of li and a height of hi. You are also given a 2D integer array points where points[j] = [xj; yj] is a point with coordinates (xj; yj). The ith rectangle has its bottom-left corner point at the coordinates (0; 0) and its top-right corner point at (li; hi). Return an integer array count of length points.length where count[j] is the number of rectangles that contain the jth point. The ith rectangle contains the jth point if 0 <= xj <= li and 0 <= yj <= hi. Note that points that lie on the edges of a rectangle are also considered to be contained by that rectangle. Example 1: Input: rectangles = [[1;2];[2;3];[2;5]]; points = [[2;1];[1;4]] Output: [2;1] Explanation: The first rectangle contains no points. The second rectangle contains only the point (2; 1). The third rectangle contains the points (2; 1) and (1; 4). The number of rectangles that contain the point (2; 1) is 2. The number of rectangles that contain the point (1; 4) is 1. Therefore; we return [2; 1]. Example 2: Input: rectangles = [[1;1];[2;2];[3;3]]; points = [[1;3];[1;1]] Output: [1;3] Explanation: The first rectangle contains only the point (1; 1). The second rectangle contains only the point (1; 1). The third rectangle contains the points (1; 3) and (1; 1). The number of rectangles that contain the point (1; 3) is 1. The number of rectangles that contain the point (1; 1) is 3. Therefore; we return [1; 3]. Constraints: 1 <= rectangles.length; points.length <= 5 * 104 rectangles[i].length == points[j].length == 2 1 <= li; xj <= 109 1 <= hi; yj <= 100 All the rectangles are unique. All the points are unique.
Uber,2282,Number of People That Can Be Seen in a Grid,Med,"Array, Dynamic Programming",
Uber,2667,Create Hello World Function,Easy,"Array, Hash Table, Math, Stack, Sliding Window",
Uber,2848,Points That Intersect With Cars,Easy,"Array, Dynamic Programming, Bit Manipulation, Bitmask",You are given a 0-indexed integer array nums containing n distinct positive integers. A permutation of nums is called special if: For all indexes 0 <= i < n - 1; either nums[i] % nums[i+1] == 0 or nums[i+1] % nums[i] == 0. Return the total number of special permutations. As the answer could be large; return it modulo 109 + 7. Example 1: Input: nums = [2;3;6] Output: 2 Explanation: [3;6;2] and [2;6;3] are the two special permutations of nums. Example 2: Input: nums = [1;4;3] Output: 2 Explanation: [3;1;4] and [4;1;3] are the two special permutations of nums. Constraints: 2 <= nums.length <= 14 1 <= nums[i] <= 109
Uber,2912,Number of Ways to Reach Destination in the Grid,Hard,,
Uber,3027,Find the Number of Ways to Place People II,Hard,,
Uber,3023,Find Pattern in Infinite Stream I,Med,,
Uber,3037,Find Pattern in Infinite Stream II,Hard,,
Uber,3073,Maximum Increasing Triplet Value,Med,,DataFrame report +-------------+--------+ | Column Name | Type | +-------------+--------+ | product | object | | quarter_1 | int | | quarter_2 | int | | quarter_3 | int | | quarter_4 | int | +-------------+--------+ Write a solution to reshape the data so that each row represents sales data for a product in a specific quarter. The result format is in the following example. Example 1: Input: +-------------+-----------+-----------+-----------+-----------+ | product | quarter_1 | quarter_2 | quarter_3 | quarter_4 | +-------------+-----------+-----------+-----------+-----------+ | Umbrella | 417 | 224 | 379 | 611 | | SleepingBag | 800 | 936 | 93 | 875 | +-------------+-----------+-----------+-----------+-----------+ Output: +-------------+-----------+-------+ | product | quarter | sales | +-------------+-----------+-------+ | Umbrella | quarter_1 | 417 | | SleepingBag | quarter_1 | 800 | | Umbrella | quarter_2 | 224 | | SleepingBag | quarter_2 | 936 | | Umbrella | quarter_3 | 379 | | SleepingBag | quarter_3 | 93 | | Umbrella | quarter_4 | 611 | | SleepingBag | quarter_4 | 875 | +-------------+-----------+-------+ Explanation: The DataFrame is reshaped from wide to long format. Each row represents the sales of a product in a quarter.
Uber,3078,Match Alphanumerical Pattern in Matrix I,Med,,
Uber,3191,Minimum Operations to Make Binary Array Elements Equal to One I,Med,"Dynamic Programming, Tree, Depth-First Search",There is an undirected tree with n nodes labeled from 0 to n - 1; and rooted at node 0. You are given a 2D integer array edges of length n - 1; where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. You are also given a 0-indexed integer array values of length n; where values[i] is the value associated with the ith node. You start with a score of 0. In one operation; you can: Pick any node i. Add values[i] to your score. Set values[i] to 0. A tree is healthy if the sum of values on the path from the root to any leaf node is different than zero. Return the maximum score you can obtain after performing these operations on the tree any number of times so that it remains healthy. Example 1: Input: edges = [[0;1];[0;2];[0;3];[2;4];[4;5]]; values = [5;2;5;2;1;1] Output: 11 Explanation: We can choose nodes 1; 2; 3; 4; and 5. The value of the root is non-zero. Hence; the sum of values on the path from the root to any leaf is different than zero. Therefore; the tree is healthy and the score is values[1] + values[2] + values[3] + values[4] + values[5] = 11. It can be shown that 11 is the maximum score obtainable after any number of operations on the tree. Example 2: Input: edges = [[0;1];[0;2];[1;3];[1;4];[2;5];[2;6]]; values = [20;10;9;7;4;3;5] Output: 40 Explanation: We can choose nodes 0; 2; 3; and 4. - The sum of values on the path from 0 to 4 is equal to 10. - The sum of values on the path from 0 to 3 is equal to 10. - The sum of values on the path from 0 to 5 is equal to 3. - The sum of values on the path from 0 to 6 is equal to 5. Therefore; the tree is healthy and the score is values[0] + values[2] + values[3] + values[4] = 40. It can be shown that 40 is the maximum score obtainable after any number of operations on the tree. Constraints: 2 <= n <= 2 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n values.length == n 1 <= values[i] <= 109 The input is generated such that edges represents a valid tree.
Uber,3192,Minimum Operations to Make Binary Array Elements Equal to One II,Med,"Math, Greedy, Bit Manipulation",Given three integers a; b; and n; return the maximum value of (a XOR x) * (b XOR x) where 0 <= x < 2n. Since the answer may be too large; return it modulo 109 + 7. Note that XOR is the bitwise XOR operation. Example 1: Input: a = 12; b = 5; n = 4 Output: 98 Explanation: For x = 2; (a XOR x) = 14 and (b XOR x) = 7. Hence; (a XOR x) * (b XOR x) = 98. It can be shown that 98 is the maximum value of (a XOR x) * (b XOR x) for all 0 <= x < 2n. Example 2: Input: a = 6; b = 7 ; n = 5 Output: 930 Explanation: For x = 25; (a XOR x) = 31 and (b XOR x) = 30. Hence; (a XOR x) * (b XOR x) = 930. It can be shown that 930 is the maximum value of (a XOR x) * (b XOR x) for all 0 <= x < 2n. Example 3: Input: a = 1; b = 6; n = 3 Output: 12 Explanation: For x = 5; (a XOR x) = 4 and (b XOR x) = 3. Hence; (a XOR x) * (b XOR x) = 12. It can be shown that 12 is the maximum value of (a XOR x) * (b XOR x) for all 0 <= x < 2n. Constraints: 0 <= a; b < 250 0 <= n <= 50
Uber,3342,Find Minimum Time to Reach Last Room II,Med,,
Uber,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Uber,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Uber,58,Length of Last Word,Easy,String,"Given a string s consisting of words and spaces; return the length of the last word in the string. A word is a maximal substring consisting of non-space characters only. Example 1: Input: s = ""Hello World"" Output: 5 Explanation: The last word is ""World"" with length 5. Example 2: Input: s = "" fly me to the moon "" Output: 4 Explanation: The last word is ""moon"" with length 4. Example 3: Input: s = ""luffy is still joyboy"" Output: 6 Explanation: The last word is ""joyboy"" with length 6. Constraints: 1 <= s.length <= 104 s consists of only English letters and spaces ' '. There will be at least one word in s."
Uber,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Uber,332,Reconstruct Itinerary,Hard,"Depth-First Search, Graph, Eulerian Circuit","You are given a list of airline tickets where tickets[i] = [fromi; toi] represent the departure and the arrival airports of one flight. Reconstruct the itinerary in order and return it. All of the tickets belong to a man who departs from ""JFK""; thus; the itinerary must begin with ""JFK"". If there are multiple valid itineraries; you should return the itinerary that has the smallest lexical order when read as a single string. For example; the itinerary [""JFK""; ""LGA""] has a smaller lexical order than [""JFK""; ""LGB""]. You may assume all tickets form at least one valid itinerary. You must use all the tickets once and only once. Example 1: Input: tickets = [[""MUC"";""LHR""];[""JFK"";""MUC""];[""SFO"";""SJC""];[""LHR"";""SFO""]] Output: [""JFK"";""MUC"";""LHR"";""SFO"";""SJC""] Example 2: Input: tickets = [[""JFK"";""SFO""];[""JFK"";""ATL""];[""SFO"";""ATL""];[""ATL"";""JFK""];[""ATL"";""SFO""]] Output: [""JFK"";""ATL"";""JFK"";""SFO"";""ATL"";""SFO""] Explanation: Another possible reconstruction is [""JFK"";""SFO"";""ATL"";""JFK"";""ATL"";""SFO""] but it is larger in lexical order. Constraints: 1 <= tickets.length <= 300 tickets[i].length == 2 fromi.length == 3 toi.length == 3 fromi and toi consist of uppercase English letters. fromi != toi"
Uber,384,Shuffle an Array,Med,"Array, Math, Design, Randomized","Given an integer array nums; design an algorithm to randomly shuffle the array. All permutations of the array should be equally likely as a result of the shuffling. Implement the Solution class: Solution(int[] nums) Initializes the object with the integer array nums. int[] reset() Resets the array to its original configuration and returns it. int[] shuffle() Returns a random shuffling of the array. Example 1: Input [""Solution""; ""shuffle""; ""reset""; ""shuffle""] [[[1; 2; 3]]; []; []; []] Output [null; [3; 1; 2]; [1; 2; 3]; [1; 3; 2]] Explanation Solution solution = new Solution([1; 2; 3]); solution.shuffle(); // Shuffle the array [1;2;3] and return its result. // Any permutation of [1;2;3] must be equally likely to be returned. // Example: return [3; 1; 2] solution.reset(); // Resets the array back to its original configuration [1;2;3]. Return [1; 2; 3] solution.shuffle(); // Returns the random shuffling of array [1;2;3]. Example: return [1; 3; 2] Constraints: 1 <= nums.length <= 50 -106 <= nums[i] <= 106 All the elements of nums are unique. At most 104 calls in total will be made to reset and shuffle."
Uber,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Uber,729,My Calendar I,Med,"Array, Binary Search, Design, Segment Tree, Ordered Set","You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a double booking. A double booking happens when two events have some non-empty intersection (i.e.; some moment is common to both events.). The event can be represented as a pair of integers startTime and endTime that represents a booking on the half-open interval [startTime; endTime); the range of real numbers x such that startTime <= x < endTime. Implement the MyCalendar class: MyCalendar() Initializes the calendar object. boolean book(int startTime; int endTime) Returns true if the event can be added to the calendar successfully without causing a double booking. Otherwise; return false and do not add the event to the calendar. Example 1: Input [""MyCalendar""; ""book""; ""book""; ""book""] [[]; [10; 20]; [15; 25]; [20; 30]] Output [null; true; false; true] Explanation MyCalendar myCalendar = new MyCalendar(); myCalendar.book(10; 20); // return True myCalendar.book(15; 25); // return False; It can not be booked because time 15 is already booked by another event. myCalendar.book(20; 30); // return True; The event can be booked; as the first event takes every time less than 20; but not including 20. Constraints: 0 <= start < end <= 109 At most 1000 calls will be made to book."
Uber,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
Uber,986,Interval List Intersections,Med,"Array, String, Enumeration","Given an array arr of 4 digits; find the latest 24-hour time that can be made using each digit exactly once. 24-hour times are formatted as ""HH:MM""; where HH is between 00 and 23; and MM is between 00 and 59. The earliest 24-hour time is 00:00; and the latest is 23:59. Return the latest 24-hour time in ""HH:MM"" format. If no valid time can be made; return an empty string. Example 1: Input: arr = [1;2;3;4] Output: ""23:41"" Explanation: The valid 24-hour times are ""12:34""; ""12:43""; ""13:24""; ""13:42""; ""14:23""; ""14:32""; ""21:34""; ""21:43""; ""23:14""; and ""23:41"". Of these times; ""23:41"" is the latest. Example 2: Input: arr = [5;5;5;5] Output: """" Explanation: There are no valid 24-hour times as ""55:55"" is not valid. Constraints: arr.length == 4 0 <= arr[i] <= 9"
Uber,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Uber,2402,Meeting Rooms III,Hard,"Array, Math, Bit Manipulation",You are given a 0-indexed integer array nums. In one operation; select any non-negative integer x and an index i; then update nums[i] to be equal to nums[i] AND (nums[i] XOR x). Note that AND is the bitwise AND operation and XOR is the bitwise XOR operation. Return the maximum possible bitwise XOR of all elements of nums after applying the operation any number of times. Example 1: Input: nums = [3;2;4;6] Output: 7 Explanation: Apply the operation with x = 4 and i = 3; num[3] = 6 AND (6 XOR 4) = 6 AND 2 = 2. Now; nums = [3; 2; 4; 2] and the bitwise XOR of all the elements = 3 XOR 2 XOR 4 XOR 2 = 7. It can be shown that 7 is the maximum possible bitwise XOR. Note that other operations may be used to achieve a bitwise XOR of 7. Example 2: Input: nums = [1;2;3;9;2] Output: 11 Explanation: Apply the operation zero times. The bitwise XOR of all the elements = 1 XOR 2 XOR 3 XOR 9 XOR 2 = 11. It can be shown that 11 is the maximum possible bitwise XOR. Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 108
Uber,2508,Add Edges to Make Degrees of All Nodes Even,Hard,"Array, Matrix, Prefix Sum",You are given an m x n integer matrix grid. We define an hourglass as a part of the matrix with the following form: Return the maximum sum of the elements of an hourglass. Note that an hourglass cannot be rotated and must be entirely contained within the matrix. Example 1: Input: grid = [[6;2;1;3];[4;2;1;5];[9;2;8;7];[4;1;2;9]] Output: 30 Explanation: The cells shown above represent the hourglass with the maximum sum: 6 + 2 + 1 + 2 + 9 + 2 + 8 = 30. Example 2: Input: grid = [[1;2;3];[4;5;6];[7;8;9]] Output: 35 Explanation: There is only one hourglass in the matrix; with the sum: 1 + 2 + 3 + 5 + 7 + 8 + 9 = 35. Constraints: m == grid.length n == grid[i].length 3 <= m; n <= 150 0 <= grid[i][j] <= 106
Uber,3071,Minimum Operations to Write the Letter Y on a Grid,Med,,DataFrame customers +-------------+--------+ | Column Name | Type | +-------------+--------+ | customer_id | int | | name | object | | email | object | +-------------+--------+ There are some duplicate rows in the DataFrame based on the email column. Write a solution to remove these duplicate rows and keep only the first occurrence. The result format is in the following example. Example 1: Input: +-------------+---------+---------------------+ | customer_id | name | email | +-------------+---------+---------------------+ | 1 | Ella | emily@example.com | | 2 | David | michael@example.com | | 3 | Zachary | sarah@example.com | | 4 | Alice | john@example.com | | 5 | Finn | john@example.com | | 6 | Violet | alice@example.com | +-------------+---------+---------------------+ Output: +-------------+---------+---------------------+ | customer_id | name | email | +-------------+---------+---------------------+ | 1 | Ella | emily@example.com | | 2 | David | michael@example.com | | 3 | Zachary | sarah@example.com | | 4 | Alice | john@example.com | | 6 | Violet | alice@example.com | +-------------+---------+---------------------+ Explanation: Alic (customer_id = 4) and Finn (customer_id = 5) both use john@example.com; so only the first occurrence of this email is retained.
Uber,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
Uber,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Uber,231,Power of Two,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of two. Otherwise; return false. An integer n is a power of two; if there exists an integer x such that n == 2x. Example 1: Input: n = 1 Output: true Explanation: 20 = 1 Example 2: Input: n = 16 Output: true Explanation: 24 = 16 Example 3: Input: n = 3 Output: false Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Uber,328,Odd Even Linked List,Med,Linked List,Given the head of a singly linked list; group all the nodes with odd indices together followed by the nodes with even indices; and return the reordered list. The first node is considered odd; and the second node is even; and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input. You must solve the problem in O(1) extra space complexity and O(n) time complexity. Example 1: Input: head = [1;2;3;4;5] Output: [1;3;5;2;4] Example 2: Input: head = [2;1;3;5;6;4;7] Output: [2;3;6;7;1;5;4] Constraints: The number of nodes in the linked list is in the range [0; 104]. -106 <= Node.val <= 106
Uber,330,Patching Array,Hard,"Array, Greedy",Given a sorted integer array nums and an integer n; add/patch elements to the array such that any number in the range [1; n] inclusive can be formed by the sum of some elements in the array. Return the minimum number of patches required. Example 1: Input: nums = [1;3]; n = 6 Output: 1 Explanation: Combinations of nums are [1]; [3]; [1;3]; which form possible sums of: 1; 3; 4. Now if we add/patch 2 to nums; the combinations are: [1]; [2]; [3]; [1;3]; [2;3]; [1;2;3]. Possible sums are 1; 2; 3; 4; 5; 6; which now covers the range [1; 6]. So we only need 1 patch. Example 2: Input: nums = [1;5;10]; n = 20 Output: 2 Explanation: The two patches can be [2; 4]. Example 3: Input: nums = [1;2;2]; n = 5 Output: 0 Constraints: 1 <= nums.length <= 1000 1 <= nums[i] <= 104 nums is sorted in ascending order. 1 <= n <= 231 - 1
Uber,424,Longest Repeating Character Replacement,Med,"Hash Table, String, Sliding Window","You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times. Return the length of the longest substring containing the same letter you can get after performing the above operations. Example 1: Input: s = ""ABAB""; k = 2 Output: 4 Explanation: Replace the two 'A's with two 'B's or vice versa. Example 2: Input: s = ""AABABBA""; k = 1 Output: 4 Explanation: Replace the one 'A' in the middle with 'B' and form ""AABBBBA"". The substring ""BBBB"" has the longest repeating letters; which is 4. There may exists other ways to achieve this answer too. Constraints: 1 <= s.length <= 105 s consists of only uppercase English letters. 0 <= k <= s.length"
Uber,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Uber,490,The Maze,Med,"Array, Depth-First Search, Breadth-First Search, Matrix",
Uber,778,Swim in Rising Water,Hard,"Hash Table, String, Greedy, Sorting, Heap (Priority Queue), Counting","Given a string s; rearrange the characters of s so that any two adjacent characters are not the same. Return any possible rearrangement of s or return """" if not possible. Example 1: Input: s = ""aab"" Output: ""aba"" Example 2: Input: s = ""aaab"" Output: """" Constraints: 1 <= s.length <= 500 s consists of lowercase English letters."
Uber,2073,Time Needed to Buy Tickets,Easy,"Array, Math, Binary Search, Geometry, Enumeration",
Uber,29,Divide Two Integers,Med,"Math, Bit Manipulation",Given two integers dividend and divisor; divide two integers without using multiplication; division; and mod operator. The integer division should truncate toward zero; which means losing its fractional part. For example; 8.345 would be truncated to 8; and -2.7335 would be truncated to -2. Return the quotient after dividing dividend by divisor. Note: Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−231; 231 − 1]. For this problem; if the quotient is strictly greater than 231 - 1; then return 231 - 1; and if the quotient is strictly less than -231; then return -231. Example 1: Input: dividend = 10; divisor = 3 Output: 3 Explanation: 10/3 = 3.33333.. which is truncated to 3. Example 2: Input: dividend = 7; divisor = -3 Output: -2 Explanation: 7/-3 = -2.33333.. which is truncated to -2. Constraints: -231 <= dividend; divisor <= 231 - 1 divisor != 0
Uber,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Uber,141,Linked List Cycle,Easy,"Hash Table, Linked List, Two Pointers",Given head; the head of a linked list; determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise; return false. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 1st node (0-indexed). Example 2: Input: head = [1;2]; pos = 0 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 0th node. Example 3: Input: head = [1]; pos = -1 Output: false Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Uber,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Uber,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Uber,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Uber,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
Uber,368,Largest Divisible Subset,Med,"Array, Math, Dynamic Programming, Sorting",Given a set of distinct positive integers nums; return the largest subset answer such that every pair (answer[i]; answer[j]) of elements in this subset satisfies: answer[i] % answer[j] == 0; or answer[j] % answer[i] == 0 If there are multiple solutions; return any of them. Example 1: Input: nums = [1;2;3] Output: [1;2] Explanation: [1;3] is also accepted. Example 2: Input: nums = [1;2;4;8] Output: [1;2;4;8] Constraints: 1 <= nums.length <= 1000 1 <= nums[i] <= 2 * 109 All the integers in nums are unique.
Uber,392,Is Subsequence,Easy,"Two Pointers, String, Dynamic Programming","Given two strings s and t; return true if s is a subsequence of t; or false otherwise. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not). Example 1: Input: s = ""abc""; t = ""ahbgdc"" Output: true Example 2: Input: s = ""axc""; t = ""ahbgdc"" Output: false Constraints: 0 <= s.length <= 100 0 <= t.length <= 104 s and t consist only of lowercase English letters. Follow up: Suppose there are lots of incoming s; say s1; s2; ...; sk where k >= 109; and you want to check one by one to see if t has its subsequence. In this scenario; how would you change your code?"
Uber,503,Next Greater Element II,Med,"Array, Stack, Monotonic Stack",Given a circular integer array nums (i.e.; the next element of nums[nums.length - 1] is nums[0]); return the next greater number for every element in nums. The next greater number of a number x is the first greater number to its traversing-order next in the array; which means you could search circularly to find its next greater number. If it doesn't exist; return -1 for this number. Example 1: Input: nums = [1;2;1] Output: [2;-1;2] Explanation: The first 1's next greater number is 2; The number 2 can't find next greater number. The second 1's next greater number needs to search circularly; which is also 2. Example 2: Input: nums = [1;2;3;4;3] Output: [2;3;4;-1;4] Constraints: 1 <= nums.length <= 104 -109 <= nums[i] <= 109
Uber,540,Single Element in a Sorted Array,Med,"Array, Binary Search",You are given a sorted array consisting of only integers where every element appears exactly twice; except for one element which appears exactly once. Return the single element that appears only once. Your solution must run in O(log n) time and O(1) space. Example 1: Input: nums = [1;1;2;3;3;4;4;8;8] Output: 2 Example 2: Input: nums = [3;3;7;7;10;11;11] Output: 10 Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 105
Uber,704,Binary Search,Easy,,
Uber,1140,Stone Game II,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting",In a warehouse; there is a row of barcodes; where the ith barcode is barcodes[i]. Rearrange the barcodes so that no two adjacent barcodes are equal. You may return any answer; and it is guaranteed an answer exists. Example 1: Input: barcodes = [1;1;1;2;2;2] Output: [2;1;2;1;2;1] Example 2: Input: barcodes = [1;1;1;1;2;2;3;3] Output: [1;3;1;3;1;2;1;2] Constraints: 1 <= barcodes.length <= 10000 1 <= barcodes[i] <= 10000
Uber,1143,Longest Common Subsequence,Med,"Array, Hash Table, Binary Search, Matrix, Counting",
Uber,16,3Sum Closest,Med,"Array, Two Pointers, Sorting",Given an integer array nums of length n and an integer target; find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution. Example 1: Input: nums = [-1;2;1;-4]; target = 1 Output: 2 Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2). Example 2: Input: nums = [0;0;0]; target = 1 Output: 0 Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0). Constraints: 3 <= nums.length <= 500 -1000 <= nums[i] <= 1000 -104 <= target <= 104
Uber,18,4Sum,Med,"Array, Two Pointers, Sorting",Given an array nums of n integers; return an array of all the unique quadruplets [nums[a]; nums[b]; nums[c]; nums[d]] such that: 0 <= a; b; c; d < n a; b; c; and d are distinct. nums[a] + nums[b] + nums[c] + nums[d] == target You may return the answer in any order. Example 1: Input: nums = [1;0;-1;0;-2;2]; target = 0 Output: [[-2;-1;1;2];[-2;0;0;2];[-1;0;0;1]] Example 2: Input: nums = [2;2;2;2;2]; target = 8 Output: [[2;2;2;2]] Constraints: 1 <= nums.length <= 200 -109 <= nums[i] <= 109 -109 <= target <= 109
Uber,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Uber,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Uber,51,N-Queens,Hard,"Array, Backtracking","The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n; return all distinct solutions to the n-queens puzzle. You may return the answer in any order. Each solution contains a distinct board configuration of the n-queens' placement; where 'Q' and '.' both indicate a queen and an empty space; respectively. Example 1: Input: n = 4 Output: [["".Q.."";""...Q"";""Q..."";""..Q.""];[""..Q."";""Q..."";""...Q"";"".Q..""]] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above Example 2: Input: n = 1 Output: [[""Q""]] Constraints: 1 <= n <= 9"
Uber,67,Add Binary,Easy,"Math, String, Bit Manipulation, Simulation","Given two binary strings a and b; return their sum as a binary string. Example 1: Input: a = ""11""; b = ""1"" Output: ""100"" Example 2: Input: a = ""1010""; b = ""1011"" Output: ""10101"" Constraints: 1 <= a.length; b.length <= 104 a and b consist only of '0' or '1' characters. Each string does not contain leading zeros except for the zero itself."
Uber,94,Binary Tree Inorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the inorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [1;3;2] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [4;2;6;5;7;1;3;9;8] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Uber,143,Reorder List,Med,"Linked List, Two Pointers, Stack, Recursion",You are given the head of a singly linked-list. The list can be represented as: L0 → L1 → … → Ln - 1 → Ln Reorder the list to be on the following form: L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → … You may not modify the values in the list's nodes. Only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4] Output: [1;4;2;3] Example 2: Input: head = [1;2;3;4;5] Output: [1;5;2;4;3] Constraints: The number of nodes in the list is in the range [1; 5 * 104]. 1 <= Node.val <= 1000
Uber,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Uber,278,First Bad Version,Easy,"Binary Search, Interactive",You are a product manager and currently leading a team to develop a new product. Unfortunately; the latest version of your product fails the quality check. Since each version is developed based on the previous version; all the versions after a bad version are also bad. Suppose you have n versions [1; 2; ...; n] and you want to find out the first bad one; which causes all the following ones to be bad. You are given an API bool isBadVersion(version) which returns whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API. Example 1: Input: n = 5; bad = 4 Output: 4 Explanation: call isBadVersion(3) -> false call isBadVersion(5) -> true call isBadVersion(4) -> true Then 4 is the first bad version. Example 2: Input: n = 1; bad = 1 Output: 1 Constraints: 1 <= bad <= n <= 231 - 1
Uber,286,Walls and Gates,Med,"Array, Breadth-First Search, Matrix",
Uber,287,Find the Duplicate Number,Med,"Array, Two Pointers, Binary Search, Bit Manipulation",Given an array of integers nums containing n + 1 integers where each integer is in the range [1; n] inclusive. There is only one repeated number in nums; return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Example 1: Input: nums = [1;3;4;2;2] Output: 2 Example 2: Input: nums = [3;1;3;4;2] Output: 3 Example 3: Input: nums = [3;3;3;3;3] Output: 3 Constraints: 1 <= n <= 105 nums.length == n + 1 1 <= nums[i] <= n All the integers in nums appear only once except for precisely one integer which appears two or more times. Follow up: How can we prove that at least one duplicate number must exist in nums? Can you solve the problem in linear runtime complexity?
Uber,410,Split Array Largest Sum,Hard,"Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum",Given an integer array nums and an integer k; split nums into k non-empty subarrays such that the largest sum of any subarray is minimized. Return the minimized largest sum of the split. A subarray is a contiguous part of the array. Example 1: Input: nums = [7;2;5;10;8]; k = 2 Output: 18 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [7;2;5] and [10;8]; where the largest sum among the two subarrays is only 18. Example 2: Input: nums = [1;2;3;4;5]; k = 2 Output: 9 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [1;2;3] and [4;5]; where the largest sum among the two subarrays is only 9. Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 106 1 <= k <= min(50; nums.length)
Uber,417,Pacific Atlantic Water Flow,Med,"Array, Depth-First Search, Breadth-First Search, Matrix",There is an m x n rectangular island that borders both the Pacific Ocean and Atlantic Ocean. The Pacific Ocean touches the island's left and top edges; and the Atlantic Ocean touches the island's right and bottom edges. The island is partitioned into a grid of square cells. You are given an m x n integer matrix heights where heights[r][c] represents the height above sea level of the cell at coordinate (r; c). The island receives a lot of rain; and the rain water can flow to neighboring cells directly north; south; east; and west if the neighboring cell's height is less than or equal to the current cell's height. Water can flow from any cell adjacent to an ocean into the ocean. Return a 2D list of grid coordinates result where result[i] = [ri; ci] denotes that rain water can flow from cell (ri; ci) to both the Pacific and Atlantic oceans. Example 1: Input: heights = [[1;2;2;3;5];[3;2;3;4;4];[2;4;5;3;1];[6;7;1;4;5];[5;1;1;2;4]] Output: [[0;4];[1;3];[1;4];[2;2];[3;0];[3;1];[4;0]] Explanation: The following cells can flow to the Pacific and Atlantic oceans; as shown below: [0;4]: [0;4] -> Pacific Ocean [0;4] -> Atlantic Ocean [1;3]: [1;3] -> [0;3] -> Pacific Ocean [1;3] -> [1;4] -> Atlantic Ocean [1;4]: [1;4] -> [1;3] -> [0;3] -> Pacific Ocean [1;4] -> Atlantic Ocean [2;2]: [2;2] -> [1;2] -> [0;2] -> Pacific Ocean [2;2] -> [2;3] -> [2;4] -> Atlantic Ocean [3;0]: [3;0] -> Pacific Ocean [3;0] -> [4;0] -> Atlantic Ocean [3;1]: [3;1] -> [3;0] -> Pacific Ocean [3;1] -> [4;1] -> Atlantic Ocean [4;0]: [4;0] -> Pacific Ocean [4;0] -> Atlantic Ocean Note that there are other possible paths for these cells to flow to the Pacific and Atlantic oceans. Example 2: Input: heights = [[1]] Output: [[0;0]] Explanation: The water can flow from the only cell to the Pacific and Atlantic oceans. Constraints: m == heights.length n == heights[r].length 1 <= m; n <= 200 0 <= heights[r][c] <= 105
Uber,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
Uber,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
Uber,852,Peak Index in a Mountain Array,Med,"Array, Two Pointers, Binary Search, Sorting",There are n persons on a social media website. You are given an integer array ages where ages[i] is the age of the ith person. A Person x will not send a friend request to a person y (x != y) if any of the following conditions is true: age[y] <= 0.5 * age[x] + 7 age[y] > age[x] age[y] > 100 && age[x] < 100 Otherwise; x will send a friend request to y. Note that if x sends a request to y; y will not necessarily send a request to x. Also; a person will not send a friend request to themself. Return the total number of friend requests made. Example 1: Input: ages = [16;16] Output: 2 Explanation: 2 people friend request each other. Example 2: Input: ages = [16;17;18] Output: 2 Explanation: Friend requests are made 17 -> 16; 18 -> 17. Example 3: Input: ages = [20;30;100;110;120] Output: 3 Explanation: Friend requests are made 110 -> 100; 120 -> 110; 120 -> 100. Constraints: n == ages.length 1 <= n <= 2 * 104 1 <= ages[i] <= 120
Uber,876,Middle of the Linked List,Easy,"Array, Hash Table, Greedy, Sorting",Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize; and consists of groupSize consecutive cards. Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize; return true if she can rearrange the cards; or false otherwise. Example 1: Input: hand = [1;2;3;6;2;3;4;7;8]; groupSize = 3 Output: true Explanation: Alice's hand can be rearranged as [1;2;3];[2;3;4];[6;7;8] Example 2: Input: hand = [1;2;3;4;5]; groupSize = 4 Output: false Explanation: Alice's hand can not be rearranged into groups of 4. Constraints: 1 <= hand.length <= 104 0 <= hand[i] <= 109 1 <= groupSize <= hand.length Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/
Uber,931,Minimum Falling Path Sum,Med,"Hash Table, Stack, Design, Ordered Set","Design a stack-like data structure to push elements to the stack and pop the most frequent element from the stack. Implement the FreqStack class: FreqStack() constructs an empty frequency stack. void push(int val) pushes an integer val onto the top of the stack. int pop() removes and returns the most frequent element in the stack. If there is a tie for the most frequent element; the element closest to the stack's top is removed and returned. Example 1: Input [""FreqStack""; ""push""; ""push""; ""push""; ""push""; ""push""; ""push""; ""pop""; ""pop""; ""pop""; ""pop""] [[]; [5]; [7]; [5]; [7]; [4]; [5]; []; []; []; []] Output [null; null; null; null; null; null; null; 5; 7; 5; 4] Explanation FreqStack freqStack = new FreqStack(); freqStack.push(5); // The stack is [5] freqStack.push(7); // The stack is [5;7] freqStack.push(5); // The stack is [5;7;5] freqStack.push(7); // The stack is [5;7;5;7] freqStack.push(4); // The stack is [5;7;5;7;4] freqStack.push(5); // The stack is [5;7;5;7;4;5] freqStack.pop(); // return 5; as 5 is the most frequent. The stack becomes [5;7;5;7;4]. freqStack.pop(); // return 7; as 5 and 7 is the most frequent; but 7 is closest to the top. The stack becomes [5;7;5;4]. freqStack.pop(); // return 5; as 5 is the most frequent. The stack becomes [5;7;4]. freqStack.pop(); // return 4; as 4; 5 and 7 is the most frequent; but 4 is closest to the top. The stack becomes [5;7]. Constraints: 0 <= val <= 109 At most 2 * 104 calls will be made to push and pop. It is guaranteed that there will be at least one element in the stack before calling pop."
Uber,992,Subarrays with K Different Integers,Hard,"Array, String, Greedy","You are given an array of n strings strs; all of the same length. We may choose any deletion indices; and we delete all the characters in those indices for each string. For example; if we have strs = [""abcdef"";""uvwxyz""] and deletion indices {0; 2; 3}; then the final array after deletions is [""bef""; ""vyz""]. Suppose we chose a set of deletion indices answer such that after deletions; the final array has its elements in lexicographic order (i.e.; strs[0] <= strs[1] <= strs[2] <= ... <= strs[n - 1]). Return the minimum possible value of answer.length. Example 1: Input: strs = [""ca"";""bb"";""ac""] Output: 1 Explanation: After deleting the first column; strs = [""a""; ""b""; ""c""]. Now strs is in lexicographic order (ie. strs[0] <= strs[1] <= strs[2]). We require at least 1 deletion since initially strs was not in lexicographic order; so the answer is 1. Example 2: Input: strs = [""xc"";""yb"";""za""] Output: 0 Explanation: strs is already in lexicographic order; so we do not need to delete anything. Note that the rows of strs are not necessarily in lexicographic order: i.e.; it is NOT necessarily true that (strs[0][0] <= strs[0][1] <= ...) Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: We have to delete every column. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Uber,1353,Maximum Number of Events That Can Be Attended,Med,"Array, Hash Table, String, Sorting","You are given a 0-indexed string array words; where words[i] consists of lowercase English letters. In one operation; select any index i such that 0 < i < words.length and words[i - 1] and words[i] are anagrams; and delete words[i] from words. Keep performing this operation as long as you can select an index that satisfies the conditions. Return words after performing all operations. It can be shown that selecting the indices for each operation in any arbitrary order will lead to the same result. An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase using all the original letters exactly once. For example; ""dacb"" is an anagram of ""abdc"". Example 1: Input: words = [""abba"";""baba"";""bbaa"";""cd"";""cd""] Output: [""abba"";""cd""] Explanation: One of the ways we can obtain the resultant array is by using the following operations: - Since words[2] = ""bbaa"" and words[1] = ""baba"" are anagrams; we choose index 2 and delete words[2]. Now words = [""abba"";""baba"";""cd"";""cd""]. - Since words[1] = ""baba"" and words[0] = ""abba"" are anagrams; we choose index 1 and delete words[1]. Now words = [""abba"";""cd"";""cd""]. - Since words[2] = ""cd"" and words[1] = ""cd"" are anagrams; we choose index 2 and delete words[2]. Now words = [""abba"";""cd""]. We can no longer perform any operations; so [""abba"";""cd""] is the final answer. Example 2: Input: words = [""a"";""b"";""c"";""d"";""e""] Output: [""a"";""b"";""c"";""d"";""e""] Explanation: No two adjacent strings in words are anagrams of each other; so no operations are performed. Constraints: 1 <= words.length <= 100 1 <= words[i].length <= 10 words[i] consists of lowercase English letters."
Uber,1512,Number of Good Pairs,Easy,"Hash Table, String, Design","An underground railway system is keeping track of customer travel times between different stations. They are using this data to calculate the average time it takes to travel from one station to another. Implement the UndergroundSystem class: void checkIn(int id; string stationName; int t) A customer with a card ID equal to id; checks in at the station stationName at time t. A customer can only be checked into one place at a time. void checkOut(int id; string stationName; int t) A customer with a card ID equal to id; checks out from the station stationName at time t. double getAverageTime(string startStation; string endStation) Returns the average time it takes to travel from startStation to endStation. The average time is computed from all the previous traveling times from startStation to endStation that happened directly; meaning a check in at startStation followed by a check out from endStation. The time it takes to travel from startStation to endStation may be different from the time it takes to travel from endStation to startStation. There will be at least one customer that has traveled from startStation to endStation before getAverageTime is called. You may assume all calls to the checkIn and checkOut methods are consistent. If a customer checks in at time t1 then checks out at time t2; then t1 < t2. All events happen in chronological order. Example 1: Input [""UndergroundSystem"";""checkIn"";""checkIn"";""checkIn"";""checkOut"";""checkOut"";""checkOut"";""getAverageTime"";""getAverageTime"";""checkIn"";""getAverageTime"";""checkOut"";""getAverageTime""] [[];[45;""Leyton"";3];[32;""Paradise"";8];[27;""Leyton"";10];[45;""Waterloo"";15];[27;""Waterloo"";20];[32;""Cambridge"";22];[""Paradise"";""Cambridge""];[""Leyton"";""Waterloo""];[10;""Leyton"";24];[""Leyton"";""Waterloo""];[10;""Waterloo"";38];[""Leyton"";""Waterloo""]] Output [null;null;null;null;null;null;null;14.00000;11.00000;null;11.00000;null;12.00000] Explanation UndergroundSystem undergroundSystem = new UndergroundSystem(); undergroundSystem.checkIn(45; ""Leyton""; 3); undergroundSystem.checkIn(32; ""Paradise""; 8); undergroundSystem.checkIn(27; ""Leyton""; 10); undergroundSystem.checkOut(45; ""Waterloo""; 15); // Customer 45 ""Leyton"" -> ""Waterloo"" in 15-3 = 12 undergroundSystem.checkOut(27; ""Waterloo""; 20); // Customer 27 ""Leyton"" -> ""Waterloo"" in 20-10 = 10 undergroundSystem.checkOut(32; ""Cambridge""; 22); // Customer 32 ""Paradise"" -> ""Cambridge"" in 22-8 = 14 undergroundSystem.getAverageTime(""Paradise""; ""Cambridge""); // return 14.00000. One trip ""Paradise"" -> ""Cambridge""; (14) / 1 = 14 undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 11.00000. Two trips ""Leyton"" -> ""Waterloo""; (10 + 12) / 2 = 11 undergroundSystem.checkIn(10; ""Leyton""; 24); undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 11.00000 undergroundSystem.checkOut(10; ""Waterloo""; 38); // Customer 10 ""Leyton"" -> ""Waterloo"" in 38-24 = 14 undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 12.00000. Three trips ""Leyton"" -> ""Waterloo""; (10 + 12 + 14) / 3 = 12 Example 2: Input [""UndergroundSystem"";""checkIn"";""checkOut"";""getAverageTime"";""checkIn"";""checkOut"";""getAverageTime"";""checkIn"";""checkOut"";""getAverageTime""] [[];[10;""Leyton"";3];[10;""Paradise"";8];[""Leyton"";""Paradise""];[5;""Leyton"";10];[5;""Paradise"";16];[""Leyton"";""Paradise""];[2;""Leyton"";21];[2;""Paradise"";30];[""Leyton"";""Paradise""]] Output [null;null;null;5.00000;null;null;5.50000;null;null;6.66667] Explanation UndergroundSystem undergroundSystem = new UndergroundSystem(); undergroundSystem.checkIn(10; ""Leyton""; 3); undergroundSystem.checkOut(10; ""Paradise""; 8); // Customer 10 ""Leyton"" -> ""Paradise"" in 8-3 = 5 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 5.00000; (5) / 1 = 5 undergroundSystem.checkIn(5; ""Leyton""; 10); undergroundSystem.checkOut(5; ""Paradise""; 16); // Customer 5 ""Leyton"" -> ""Paradise"" in 16-10 = 6 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 5.50000; (5 + 6) / 2 = 5.5 undergroundSystem.checkIn(2; ""Leyton""; 21); undergroundSystem.checkOut(2; ""Paradise""; 30); // Customer 2 ""Leyton"" -> ""Paradise"" in 30-21 = 9 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 6.66667; (5 + 6 + 9) / 3 = 6.66667 Constraints: 1 <= id; t <= 106 1 <= stationName.length; startStation.length; endStation.length <= 10 All strings consist of uppercase and lowercase English letters and digits. There will be at most 2 * 104 calls in total to checkIn; checkOut; and getAverageTime. Answers within 10-5 of the actual value will be accepted."
Uber,2115,Find All Possible Recipes from Given Supplies,Med,"String, Dynamic Programming","You are given a binary string binary. A subsequence of binary is considered good if it is not empty and has no leading zeros (with the exception of ""0""). Find the number of unique good subsequences of binary. For example; if binary = ""001""; then all the good subsequences are [""0""; ""0""; ""1""]; so the unique good subsequences are ""0"" and ""1"". Note that subsequences ""00""; ""01""; and ""001"" are not good because they have leading zeros. Return the number of unique good subsequences of binary. Since the answer may be very large; return it modulo 109 + 7. A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements. Example 1: Input: binary = ""001"" Output: 2 Explanation: The good subsequences of binary are [""0""; ""0""; ""1""]. The unique good subsequences are ""0"" and ""1"". Example 2: Input: binary = ""11"" Output: 2 Explanation: The good subsequences of binary are [""1""; ""1""; ""11""]. The unique good subsequences are ""1"" and ""11"". Example 3: Input: binary = ""101"" Output: 5 Explanation: The good subsequences of binary are [""1""; ""0""; ""1""; ""10""; ""11""; ""101""]. The unique good subsequences are ""0""; ""1""; ""10""; ""11""; and ""101"". Constraints: 1 <= binary.length <= 105 binary consists of only '0's and '1's."
Uber,2251,Number of Flowers in Full Bloom,Hard,"Math, String, Dynamic Programming","Along a long library corridor; there is a line of seats and decorative plants. You are given a 0-indexed string corridor of length n consisting of letters 'S' and 'P' where each 'S' represents a seat and each 'P' represents a plant. One room divider has already been installed to the left of index 0; and another to the right of index n - 1. Additional room dividers can be installed. For each position between indices i - 1 and i (1 <= i <= n - 1); at most one divider can be installed. Divide the corridor into non-overlapping sections; where each section has exactly two seats with any number of plants. There may be multiple ways to perform the division. Two ways are different if there is a position with a room divider installed in the first way but not in the second way. Return the number of ways to divide the corridor. Since the answer may be very large; return it modulo 109 + 7. If there is no way; return 0. Example 1: Input: corridor = ""SSPPSPS"" Output: 3 Explanation: There are 3 different ways to divide the corridor. The black bars in the above image indicate the two room dividers already installed. Note that in each of the ways; each section has exactly two seats. Example 2: Input: corridor = ""PPSPSP"" Output: 1 Explanation: There is only 1 way to divide the corridor; by not installing any additional dividers. Installing any would create some section that does not have exactly two seats. Example 3: Input: corridor = ""S"" Output: 0 Explanation: There is no way to divide the corridor because there will always be a section that does not have exactly two seats. Constraints: n == corridor.length 1 <= n <= 105 corridor[i] is either 'S' or 'P'."
Uber,2235,Add Two Integers,Easy,String,"You are given a string title consisting of one or more words separated by a single space; where each word consists of English letters. Capitalize the string by changing the capitalization of each word such that: If the length of the word is 1 or 2 letters; change all letters to lowercase. Otherwise; change the first letter to uppercase and the remaining letters to lowercase. Return the capitalized title. Example 1: Input: title = ""capiTalIze tHe titLe"" Output: ""Capitalize The Title"" Explanation: Since all the words have a length of at least 3; the first letter of each word is uppercase; and the remaining letters are lowercase. Example 2: Input: title = ""First leTTeR of EACH Word"" Output: ""First Letter of Each Word"" Explanation: The word ""of"" has length 2; so it is all lowercase. The remaining words have a length of at least 3; so the first letter of each remaining word is uppercase; and the remaining letters are lowercase. Example 3: Input: title = ""i lOve leetcode"" Output: ""i Love Leetcode"" Explanation: The word ""i"" has length 1; so it is lowercase. The remaining words have a length of at least 3; so the first letter of each remaining word is uppercase; and the remaining letters are lowercase. Constraints: 1 <= title.length <= 100 title consists of words separated by a single space without any leading or trailing spaces. Each word consists of uppercase and lowercase English letters and is non-empty."
Uber,3043,Find the Length of the Longest Common Prefix,Med,"Array, Breadth-First Search, Matrix",
Uber,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
Uber,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
Uber,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Uber,57,Insert Interval,Med,Array,You are given an array of non-overlapping intervals intervals where intervals[i] = [starti; endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start; end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary). Return intervals after the insertion. Note that you don't need to modify intervals in-place. You can make a new array and return it. Example 1: Input: intervals = [[1;3];[6;9]]; newInterval = [2;5] Output: [[1;5];[6;9]] Example 2: Input: intervals = [[1;2];[3;5];[6;7];[8;10];[12;16]]; newInterval = [4;8] Output: [[1;2];[3;10];[12;16]] Explanation: Because the new interval [4;8] overlaps with [3;5];[6;7];[8;10]. Constraints: 0 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 105 intervals is sorted by starti in ascending order. newInterval.length == 2 0 <= start <= end <= 105
Uber,62,Unique Paths,Med,"Math, Dynamic Programming, Combinatorics",There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n; return the number of possible unique paths that the robot can take to reach the bottom-right corner. The test cases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: m = 3; n = 7 Output: 28 Example 2: Input: m = 3; n = 2 Output: 3 Explanation: From the top-left corner; there are a total of 3 ways to reach the bottom-right corner: 1. Right -> Down -> Down 2. Down -> Down -> Right 3. Down -> Right -> Down Constraints: 1 <= m; n <= 100
Uber,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
Uber,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Uber,123,Best Time to Buy and Sell Stock III,Hard,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete at most two transactions. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: prices = [3;3;5;0;0;3;1;4] Output: 6 Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Then buy on day 7 (price = 1) and sell on day 8 (price = 4); profit = 4-1 = 3. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Note that you cannot buy on day 1; buy on day 2 and sell them later; as you are engaging multiple transactions at the same time. You must sell before buying again. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transaction is done; i.e. max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 105
Uber,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Uber,131,Palindrome Partitioning,Med,"String, Dynamic Programming, Backtracking","Given a string s; partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s. Example 1: Input: s = ""aab"" Output: [[""a"";""a"";""b""];[""aa"";""b""]] Example 2: Input: s = ""a"" Output: [[""a""]] Constraints: 1 <= s.length <= 16 s contains only lowercase English letters."
Uber,136,Single Number,Easy,"Array, Bit Manipulation",Given a non-empty array of integers nums; every element appears twice except for one. Find that single one. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;1] Output: 1 Example 2: Input: nums = [4;1;2;1;2] Output: 4 Example 3: Input: nums = [1] Output: 1 Constraints: 1 <= nums.length <= 3 * 104 -3 * 104 <= nums[i] <= 3 * 104 Each element in the array appears twice except for one element which appears only once.
Uber,160,Intersection of Two Linked Lists,Easy,"Hash Table, Linked List, Two Pointers",Given the heads of two singly linked-lists headA and headB; return the node at which the two lists intersect. If the two linked lists have no intersection at all; return null. For example; the following two linked lists begin to intersect at node c1: The test cases are generated such that there are no cycles anywhere in the entire linked structure. Note that the linked lists must retain their original structure after the function returns. Custom Judge: The inputs to the judge are given as follows (your program is not given these inputs): intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node. listA - The first linked list. listB - The second linked list. skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node. skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node. The judge will then create the linked structure based on these inputs and pass the two heads; headA and headB to your program. If you correctly return the intersected node; then your solution will be accepted. Example 1: Input: intersectVal = 8; listA = [4;1;8;4;5]; listB = [5;6;1;8;4;5]; skipA = 2; skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [4;1;8;4;5]. From the head of B; it reads as [5;6;1;8;4;5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words; they point to two different locations in memory; while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory. Example 2: Input: intersectVal = 2; listA = [1;9;1;2;4]; listB = [3;2;4]; skipA = 3; skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [1;9;1;2;4]. From the head of B; it reads as [3;2;4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B. Example 3: Input: intersectVal = 0; listA = [2;6;4]; listB = [1;5]; skipA = 3; skipB = 2 Output: No intersection Explanation: From the head of A; it reads as [2;6;4]. From the head of B; it reads as [1;5]. Since the two lists do not intersect; intersectVal must be 0; while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect; so return null. Constraints: The number of nodes of listA is in the m. The number of nodes of listB is in the n. 1 <= m; n <= 3 * 104 1 <= Node.val <= 105 0 <= skipA <= m 0 <= skipB <= n intersectVal is 0 if listA and listB do not intersect. intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect. Follow up: Could you write a solution that runs in O(m + n) time and use only O(1) memory?
Uber,174,Dungeon Game,Hard,"Array, Dynamic Programming, Matrix",The demons had captured the princess and imprisoned her in the bottom-right corner of a dungeon. The dungeon consists of m x n rooms laid out in a 2D grid. Our valiant knight was initially positioned in the top-left room and must fight his way through dungeon to rescue the princess. The knight has an initial health point represented by a positive integer. If at any point his health point drops to 0 or below; he dies immediately. Some of the rooms are guarded by demons (represented by negative integers); so the knight loses health upon entering these rooms; other rooms are either empty (represented as 0) or contain magic orbs that increase the knight's health (represented by positive integers). To reach the princess as quickly as possible; the knight decides to move only rightward or downward in each step. Return the knight's minimum initial health so that he can rescue the princess. Note that any room can contain threats or power-ups; even the first room the knight enters and the bottom-right room where the princess is imprisoned. Example 1: Input: dungeon = [[-2;-3;3];[-5;-10;1];[10;30;-5]] Output: 7 Explanation: The initial health of the knight must be at least 7 if he follows the optimal path: RIGHT-> RIGHT -> DOWN -> DOWN. Example 2: Input: dungeon = [[0]] Output: 1 Constraints: m == dungeon.length n == dungeon[i].length 1 <= m; n <= 200 -1000 <= dungeon[i][j] <= 1000
Uber,188,Best Time to Buy and Sell Stock IV,Hard,"Array, Dynamic Programming",You are given an integer array prices where prices[i] is the price of a given stock on the ith day; and an integer k. Find the maximum profit you can achieve. You may complete at most k transactions: i.e. you may buy at most k times and sell at most k times. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: k = 2; prices = [2;4;1] Output: 2 Explanation: Buy on day 1 (price = 2) and sell on day 2 (price = 4); profit = 4-2 = 2. Example 2: Input: k = 2; prices = [3;2;6;5;0;3] Output: 7 Explanation: Buy on day 2 (price = 2) and sell on day 3 (price = 6); profit = 6-2 = 4. Then buy on day 5 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Constraints: 1 <= k <= 100 1 <= prices.length <= 1000 0 <= prices[i] <= 1000
Uber,199,Binary Tree Right Side View,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; imagine yourself standing on the right side of it; return the values of the nodes you can see ordered from top to bottom. Example 1: Input: root = [1;2;3;null;5;null;4] Output: [1;3;4] Example 2: Input: root = [1;null;3] Output: [1;3] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Uber,205,Isomorphic Strings,Easy,"Hash Table, String","Given two strings s and t; determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character; but a character may map to itself. Example 1: Input: s = ""egg""; t = ""add"" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = ""foo""; t = ""bar"" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = ""paper""; t = ""title"" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character."
Uber,312,Burst Balloons,Hard,"Array, Dynamic Programming",You are given n balloons; indexed from 0 to n - 1. Each balloon is painted with a number on it represented by an array nums. You are asked to burst all the balloons. If you burst the ith balloon; you will get nums[i - 1] * nums[i] * nums[i + 1] coins. If i - 1 or i + 1 goes out of bounds of the array; then treat it as if there is a balloon with a 1 painted on it. Return the maximum coins you can collect by bursting the balloons wisely. Example 1: Input: nums = [3;1;5;8] Output: 167 Explanation: nums = [3;1;5;8] --> [3;5;8] --> [3;8] --> [8] --> [] coins = 3*1*5 + 3*5*8 + 1*3*8 + 1*8*1 = 167 Example 2: Input: nums = [1;5] Output: 10 Constraints: n == nums.length 1 <= n <= 300 0 <= nums[i] <= 100
Uber,338,Counting Bits,Easy,"Dynamic Programming, Bit Manipulation",Given an integer n; return an array ans of length n + 1 such that for each i (0 <= i <= n); ans[i] is the number of 1's in the binary representation of i. Example 1: Input: n = 2 Output: [0;1;1] Explanation: 0 --> 0 1 --> 1 2 --> 10 Example 2: Input: n = 5 Output: [0;1;1;2;1;2] Explanation: 0 --> 0 1 --> 1 2 --> 10 3 --> 11 4 --> 100 5 --> 101 Constraints: 0 <= n <= 105 Follow up: It is very easy to come up with a solution with a runtime of O(n log n). Can you do it in linear time O(n) and possibly in a single pass? Can you do it without using any built-in function (i.e.; like __builtin_popcount in C++)?
Uber,361,Bomb Enemy,Med,"Array, Dynamic Programming, Matrix",
Uber,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
Uber,416,Partition Equal Subset Sum,Med,"Array, Dynamic Programming",Given an integer array nums; return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise. Example 1: Input: nums = [1;5;11;5] Output: true Explanation: The array can be partitioned as [1; 5; 5] and [11]. Example 2: Input: nums = [1;2;3;5] Output: false Explanation: The array cannot be partitioned into equal sum subsets. Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 100
Uber,442,Find All Duplicates in an Array,Med,"Array, Hash Table",Given an integer array nums of length n where all the integers of nums are in the range [1; n] and each integer appears at most twice; return an array of all the integers that appears twice. You must write an algorithm that runs in O(n) time and uses only constant auxiliary space; excluding the space needed to store the output Example 1: Input: nums = [4;3;2;7;8;2;3;1] Output: [2;3] Example 2: Input: nums = [1;1;2] Output: [1] Example 3: Input: nums = [1] Output: [] Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i] <= n Each element in nums appears once or twice.
Uber,451,Sort Characters By Frequency,Med,"Hash Table, String, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given a string s; sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers; return any of them. Example 1: Input: s = ""tree"" Output: ""eert"" Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore ""eetr"" is also a valid answer. Example 2: Input: s = ""cccaaa"" Output: ""aaaccc"" Explanation: Both 'c' and 'a' appear three times; so both ""cccaaa"" and ""aaaccc"" are valid answers. Note that ""cacaca"" is incorrect; as the same characters must be together. Example 3: Input: s = ""Aabb"" Output: ""bbAa"" Explanation: ""bbaA"" is also a valid answer; but ""Aabb"" is incorrect. Note that 'A' and 'a' are treated as two different characters. Constraints: 1 <= s.length <= 5 * 105 s consists of uppercase and lowercase English letters and digits."
Uber,455,Assign Cookies,Easy,"Array, Two Pointers, Greedy, Sorting",Assume you are an awesome parent and want to give your children some cookies. But; you should give each child at most one cookie. Each child i has a greed factor g[i]; which is the minimum size of a cookie that the child will be content with; and each cookie j has a size s[j]. If s[j] >= g[i]; we can assign the cookie j to the child i; and the child i will be content. Your goal is to maximize the number of your content children and output the maximum number. Example 1: Input: g = [1;2;3]; s = [1;1] Output: 1 Explanation: You have 3 children and 2 cookies. The greed factors of 3 children are 1; 2; 3. And even though you have 2 cookies; since their size is both 1; you could only make the child whose greed factor is 1 content. You need to output 1. Example 2: Input: g = [1;2]; s = [1;2;3] Output: 2 Explanation: You have 2 children and 3 cookies. The greed factors of 2 children are 1; 2. You have 3 cookies and their sizes are big enough to gratify all of the children; You need to output 2. Constraints: 1 <= g.length <= 3 * 104 0 <= s.length <= 3 * 104 1 <= g[i]; s[j] <= 231 - 1 Note: This question is the same as 2410: Maximum Matching of Players With Trainers.
Uber,465,Optimal Account Balancing,Hard,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",
Uber,493,Reverse Pairs,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums; return the number of reverse pairs in the array. A reverse pair is a pair (i; j) where: 0 <= i < j < nums.length and nums[i] > 2 * nums[j]. Example 1: Input: nums = [1;3;2;3;1] Output: 2 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 3; nums[4] = 1; 3 > 2 * 1 Example 2: Input: nums = [2;4;3;5;1] Output: 3 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 4; nums[4] = 1; 4 > 2 * 1 (2; 4) --> nums[2] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 5; nums[4] = 1; 5 > 2 * 1 Constraints: 1 <= nums.length <= 5 * 104 -231 <= nums[i] <= 231 - 1
Uber,529,Minesweeper,Med,"Array, Depth-First Search, Breadth-First Search, Matrix","Let's play the minesweeper game (Wikipedia; online game)! You are given an m x n char matrix board representing the game board where: 'M' represents an unrevealed mine; 'E' represents an unrevealed empty square; 'B' represents a revealed blank square that has no adjacent mines (i.e.; above; below; left; right; and all 4 diagonals); digit ('1' to '8') represents how many mines are adjacent to this revealed square; and 'X' represents a revealed mine. You are also given an integer array click where click = [clickr; clickc] represents the next click position among all the unrevealed squares ('M' or 'E'). Return the board after revealing this position according to the following rules: If a mine 'M' is revealed; then the game is over. You should change it to 'X'. If an empty square 'E' with no adjacent mines is revealed; then change it to a revealed blank 'B' and all of its adjacent unrevealed squares should be revealed recursively. If an empty square 'E' with at least one adjacent mine is revealed; then change it to a digit ('1' to '8') representing the number of adjacent mines. Return the board when no more squares will be revealed. Example 1: Input: board = [[""E"";""E"";""E"";""E"";""E""];[""E"";""E"";""M"";""E"";""E""];[""E"";""E"";""E"";""E"";""E""];[""E"";""E"";""E"";""E"";""E""]]; click = [3;0] Output: [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""M"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]] Example 2: Input: board = [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""M"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]]; click = [1;2] Output: [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""X"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]] Constraints: m == board.length n == board[i].length 1 <= m; n <= 50 board[i][j] is either 'M'; 'E'; 'B'; or a digit from '1' to '8'. click.length == 2 0 <= clickr < m 0 <= clickc < n board[clickr][clickc] is either 'M' or 'E'."
Uber,542,01 Matrix,Med,"Array, Dynamic Programming, Breadth-First Search, Matrix",Given an m x n binary matrix mat; return the distance of the nearest 0 for each cell. The distance between two adjacent cells is 1. Example 1: Input: mat = [[0;0;0];[0;1;0];[0;0;0]] Output: [[0;0;0];[0;1;0];[0;0;0]] Example 2: Input: mat = [[0;0;0];[0;1;0];[1;1;1]] Output: [[0;0;0];[0;1;0];[1;2;1]] Constraints: m == mat.length n == mat[i].length 1 <= m; n <= 104 1 <= m * n <= 104 mat[i][j] is either 0 or 1. There is at least one 0 in mat.
Uber,567,Permutation in String,Med,"Hash Table, Two Pointers, String, Sliding Window","Given two strings s1 and s2; return true if s2 contains a permutation of s1; or false otherwise. In other words; return true if one of s1's permutations is the substring of s2. Example 1: Input: s1 = ""ab""; s2 = ""eidbaooo"" Output: true Explanation: s2 contains one permutation of s1 (""ba""). Example 2: Input: s1 = ""ab""; s2 = ""eidboaoo"" Output: false Constraints: 1 <= s1.length; s2.length <= 104 s1 and s2 consist of lowercase English letters."
Uber,570,Managers with at Least 5 Direct Reports,Med,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | department | varchar | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the name of an employee; their department; and the id of their manager. If managerId is null; then the employee does not have a manager. No employee will be the manager of themself. Write a solution to find managers with at least five direct reports. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +-----+-------+------------+-----------+ | id | name | department | managerId | +-----+-------+------------+-----------+ | 101 | John | A | null | | 102 | Dan | A | 101 | | 103 | James | A | 101 | | 104 | Amy | A | 101 | | 105 | Anne | A | 101 | | 106 | Ron | B | 101 | +-----+-------+------------+-----------+ Output: +------+ | name | +------+ | John | +------+
Uber,588,Design In-Memory File System,Hard,"Hash Table, String, Design, Trie, Sorting",
Uber,658,Find K Closest Elements,Med,"Array, Two Pointers, Binary Search, Sliding Window, Sorting, Heap (Priority Queue)",Given a sorted integer array arr; two integers k and x; return the k closest integers to x in the array. The result should also be sorted in ascending order. An integer a is closer to x than an integer b if: |a - x| < |b - x|; or |a - x| == |b - x| and a < b Example 1: Input: arr = [1;2;3;4;5]; k = 4; x = 3 Output: [1;2;3;4] Example 2: Input: arr = [1;1;2;3;4;5]; k = 4; x = -1 Output: [1;1;2;3] Constraints: 1 <= k <= arr.length 1 <= arr.length <= 104 arr is sorted in ascending order. -104 <= arr[i]; x <= 104
Uber,678,Valid Parenthesis String,Med,"String, Dynamic Programming, Stack, Greedy","Given a string s containing only three types of characters: '('; ')' and '*'; return true if s is valid. The following rules define a valid string: Any left parenthesis '(' must have a corresponding right parenthesis ')'. Any right parenthesis ')' must have a corresponding left parenthesis '('. Left parenthesis '(' must go before the corresponding right parenthesis ')'. '*' could be treated as a single right parenthesis ')' or a single left parenthesis '(' or an empty string """". Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""(*)"" Output: true Example 3: Input: s = ""(*))"" Output: true Constraints: 1 <= s.length <= 100 s[i] is '('; ')' or '*'."
Uber,912,Sort an Array,Med,"Array, Math, Binary Search, Prefix Sum, Randomized","You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index. You need to implement the function pickIndex(); which randomly picks an index in the range [0; w.length - 1] (inclusive) and returns it. The probability of picking an index i is w[i] / sum(w). For example; if w = [1; 3]; the probability of picking index 0 is 1 / (1 + 3) = 0.25 (i.e.; 25%); and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e.; 75%). Example 1: Input [""Solution"";""pickIndex""] [[[1]];[]] Output [null;0] Explanation Solution solution = new Solution([1]); solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w. Example 2: Input [""Solution"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex""] [[[1;3]];[];[];[];[];[]] Output [null;1;1;1;1;0] Explanation Solution solution = new Solution([1; 3]); solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4. solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4. Since this is a randomization problem; multiple answers are allowed. All of the following outputs can be considered correct: [null;1;1;1;1;0] [null;1;1;1;1;1] [null;1;1;1;0;0] [null;1;1;1;0;1] [null;1;0;1;0;0] ...... and so on. Constraints: 1 <= w.length <= 104 1 <= w[i] <= 105 pickIndex will be called at most 104 times."
Uber,953,Verifying an Alien Dictionary,Easy,"Two Pointers, String","Given a string s; reverse the string according to the following rules: All the characters that are not English letters remain in the same position. All the English letters (lowercase or uppercase) should be reversed. Return s after reversing it. Example 1: Input: s = ""ab-cd"" Output: ""dc-ba"" Example 2: Input: s = ""a-bC-dEf-ghIj"" Output: ""j-Ih-gfE-dCba"" Example 3: Input: s = ""Test1ng-Leet=code-Q!"" Output: ""Qedo1ct-eeLg=ntse-T!"" Constraints: 1 <= s.length <= 100 s consists of characters with ASCII values in the range [33; 122]. s does not contain '\""' or '\\'."
Uber,974,Subarray Sums Divisible by K,Med,"Array, String, Sorting","You are given an array of logs. Each log is a space-delimited string of words; where the first word is the identifier. There are two types of logs: Letter-logs: All words (except the identifier) consist of lowercase English letters. Digit-logs: All words (except the identifier) consist of digits. Reorder these logs so that: The letter-logs come before all digit-logs. The letter-logs are sorted lexicographically by their contents. If their contents are the same; then sort them lexicographically by their identifiers. The digit-logs maintain their relative ordering. Return the final order of the logs. Example 1: Input: logs = [""dig1 8 1 5 1"";""let1 art can"";""dig2 3 6"";""let2 own kit dig"";""let3 art zero""] Output: [""let1 art can"";""let3 art zero"";""let2 own kit dig"";""dig1 8 1 5 1"";""dig2 3 6""] Explanation: The letter-log contents are all different; so their ordering is ""art can""; ""art zero""; ""own kit dig"". The digit-logs have a relative order of ""dig1 8 1 5 1""; ""dig2 3 6"". Example 2: Input: logs = [""a1 9 2 3 1"";""g1 act car"";""zo4 4 7"";""ab1 off key dog"";""a8 act zoo""] Output: [""g1 act car"";""a8 act zoo"";""ab1 off key dog"";""a1 9 2 3 1"";""zo4 4 7""] Constraints: 1 <= logs.length <= 100 3 <= logs[i].length <= 100 All the tokens of logs[i] are separated by a single space. logs[i] is guaranteed to have an identifier and at least one word after the identifier."
Uber,983,Minimum Cost For Tickets,Med,"Array, Stack, Simulation",Given two integer arrays pushed and popped each with distinct values; return true if this could have been the result of a sequence of push and pop operations on an initially empty stack; or false otherwise. Example 1: Input: pushed = [1;2;3;4;5]; popped = [4;5;3;2;1] Output: true Explanation: We might do the following sequence: push(1); push(2); push(3); push(4); pop() -> 4; push(5); pop() -> 5; pop() -> 3; pop() -> 2; pop() -> 1 Example 2: Input: pushed = [1;2;3;4;5]; popped = [4;3;5;1;2] Output: false Explanation: 1 cannot be popped before 2. Constraints: 1 <= pushed.length <= 1000 0 <= pushed[i] <= 1000 All the elements of pushed are unique. popped.length == pushed.length popped is a permutation of pushed.
Uber,1021,Remove Outermost Parentheses,Easy,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes where each node in the tree has node.val coins. There are n coins in total throughout the whole tree. In one move; we may choose two adjacent nodes and move one coin from one node to another. A move may be from parent to child; or from child to parent. Return the minimum number of moves required to make every node have exactly one coin. Example 1: Input: root = [3;0;0] Output: 2 Explanation: From the root of the tree; we move one coin to its left child; and one coin to its right child. Example 2: Input: root = [0;3;0] Output: 3 Explanation: From the left child of the root; we move two coins to the root [taking two moves]. Then; we move one coin from the root of the tree to the right child. Constraints: The number of nodes in the tree is n. 1 <= n <= 100 0 <= Node.val <= n The sum of all Node.val is n.
Uber,1489,Find Critical and Pseudo-Critical Edges in Minimum Spanning Tree,Hard,"Array, Dynamic Programming, Greedy, Heap (Priority Queue)",There is a pizza with 3n slices of varying size; you and your friends will take slices of pizza as follows: You will pick any pizza slice. Your friend Alice will pick the next slice in the anti-clockwise direction of your pick. Your friend Bob will pick the next slice in the clockwise direction of your pick. Repeat until there are no more slices of pizzas. Given an integer array slices that represent the sizes of the pizza slices in a clockwise direction; return the maximum possible sum of slice sizes that you can pick. Example 1: Input: slices = [1;2;3;4;5;6] Output: 10 Explanation: Pick pizza slice of size 4; Alice and Bob will pick slices with size 3 and 5 respectively. Then Pick slices with size 6; finally Alice and Bob will pick slice of size 2 and 1 respectively. Total = 4 + 6. Example 2: Input: slices = [8;9;8;6;1;1] Output: 16 Explanation: Pick pizza slice of size 8 in each turn. If you pick slice with size 9 your partners will pick slices of size 8. Constraints: 3 * n == slices.length 1 <= slices.length <= 500 1 <= slices[i] <= 1000
Uber,1603,Design Parking System,Easy,"Array, Prefix Sum",Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]). Return the running sum of nums. Example 1: Input: nums = [1;2;3;4] Output: [1;3;6;10] Explanation: Running sum is obtained as follows: [1; 1+2; 1+2+3; 1+2+3+4]. Example 2: Input: nums = [1;1;1;1;1] Output: [1;2;3;4;5] Explanation: Running sum is obtained as follows: [1; 1+1; 1+1+1; 1+1+1+1; 1+1+1+1+1]. Example 3: Input: nums = [3;1;2;10;1] Output: [3;4;6;16;17] Constraints: 1 <= nums.length <= 1000 -10^6 <= nums[i] <= 10^6
Uber,1752,Check if Array Is Sorted and Rotated,Easy,"Array, Hash Table, Sorting",A sequence of numbers is called arithmetic if it consists of at least two elements; and the difference between every two consecutive elements is the same. More formally; a sequence s is arithmetic if and only if s[i+1] - s[i] == s[1] - s[0] for all valid i. For example; these are arithmetic sequences: 1; 3; 5; 7; 9 7; 7; 7; 7 3; -1; -5; -9 The following sequence is not arithmetic: 1; 1; 2; 5; 7 You are given an array of n integers; nums; and two arrays of m integers each; l and r; representing the m range queries; where the ith query is the range [l[i]; r[i]]. All the arrays are 0-indexed. Return a list of boolean elements answer; where answer[i] is true if the subarray nums[l[i]]; nums[l[i]+1]; ... ; nums[r[i]] can be rearranged to form an arithmetic sequence; and false otherwise. Example 1: Input: nums = [4;6;5;9;3;7]; l = [0;0;2]; r = [2;3;5] Output: [true;false;true] Explanation: In the 0th query; the subarray is [4;6;5]. This can be rearranged as [6;5;4]; which is an arithmetic sequence. In the 1st query; the subarray is [4;6;5;9]. This cannot be rearranged as an arithmetic sequence. In the 2nd query; the subarray is [5;9;3;7]. This can be rearranged as [3;5;7;9]; which is an arithmetic sequence. Example 2: Input: nums = [-12;-9;-3;-12;-6;15;20;-25;-20;-15;-10]; l = [0;1;6;4;8;7]; r = [4;4;9;7;9;10] Output: [false;true;false;false;true;true] Constraints: n == nums.length m == l.length m == r.length 2 <= n <= 500 1 <= m <= 500 0 <= l[i] < r[i] < n -105 <= nums[i] <= 105
Uber,2385,Amount of Time for Binary Tree to Be Infected,Med,"Array, Prefix Sum",
Uber,2603,Collect Coins in a Tree,Hard,"Array, Hash Table, String, Sorting, Heap (Priority Queue)","You are given two string arrays positive_feedback and negative_feedback; containing the words denoting positive and negative feedback; respectively. Note that no word is both positive and negative. Initially every student has 0 points. Each positive word in a feedback report increases the points of a student by 3; whereas each negative word decreases the points by 1. You are given n feedback reports; represented by a 0-indexed string array report and a 0-indexed integer array student_id; where student_id[i] represents the ID of the student who has received the feedback report report[i]. The ID of each student is unique. Given an integer k; return the top k students after ranking them in non-increasing order by their points. In case more than one student has the same points; the one with the lower ID ranks higher. Example 1: Input: positive_feedback = [""smart"";""brilliant"";""studious""]; negative_feedback = [""not""]; report = [""this student is studious"";""the student is smart""]; student_id = [1;2]; k = 2 Output: [1;2] Explanation: Both the students have 1 positive feedback and 3 points but since student 1 has a lower ID he ranks higher. Example 2: Input: positive_feedback = [""smart"";""brilliant"";""studious""]; negative_feedback = [""not""]; report = [""this student is not studious"";""the student is smart""]; student_id = [1;2]; k = 2 Output: [2;1] Explanation: - The student with ID 1 has 1 positive feedback and 1 negative feedback; so he has 3-1=2 points. - The student with ID 2 has 1 positive feedback; so he has 3 points. Since student 2 has more points; [2;1] is returned. Constraints: 1 <= positive_feedback.length; negative_feedback.length <= 104 1 <= positive_feedback[i].length; negative_feedback[j].length <= 100 Both positive_feedback[i] and negative_feedback[j] consists of lowercase English letters. No word is present in both positive_feedback and negative_feedback. n == report.length == student_id.length 1 <= n <= 104 report[i] consists of lowercase English letters and spaces ' '. There is a single space between consecutive words of report[i]. 1 <= report[i].length <= 100 1 <= student_id[i] <= 109 All the values of student_id[i] are unique. 1 <= k <= n"
Uber,2958,Length of Longest Subarray With at Most K Frequency,Med,,
Uber,12,Integer to Roman,Med,"Hash Table, Math, String","Seven different symbols represent Roman numerals with the following values: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules: If the value does not start with 4 or 9; select the symbol of the maximal value that can be subtracted from the input; append that symbol to the result; subtract its value; and convert the remainder to a Roman numeral. If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol; for example; 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV); 9 (IX); 40 (XL); 90 (XC); 400 (CD) and 900 (CM). Only powers of 10 (I; X; C; M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V); 50 (L); or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form. Given an integer; convert it to a Roman numeral. Example 1: Input: num = 3749 Output: ""MMMDCCXLIX"" Explanation: 3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M) 700 = DCC as 500 (D) + 100 (C) + 100 (C) 40 = XL as 10 (X) less of 50 (L) 9 = IX as 1 (I) less of 10 (X) Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places Example 2: Input: num = 58 Output: ""LVIII"" Explanation: 50 = L 8 = VIII Example 3: Input: num = 1994 Output: ""MCMXCIV"" Explanation: 1000 = M 900 = CM 90 = XC 4 = IV Constraints: 1 <= num <= 3999"
Uber,44,Wildcard Matching,Hard,"String, Dynamic Programming, Greedy, Recursion","Given an input string (s) and a pattern (p); implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""*"" Output: true Explanation: '*' matches any sequence. Example 3: Input: s = ""cb""; p = ""?a"" Output: false Explanation: '?' matches 'c'; but the second letter is 'a'; which does not match 'b'. Constraints: 0 <= s.length; p.length <= 2000 s contains only lowercase English letters. p contains only lowercase English letters; '?' or '*'."
Uber,59,Spiral Matrix II,Med,"Array, Matrix, Simulation",Given a positive integer n; generate an n x n matrix filled with elements from 1 to n2 in spiral order. Example 1: Input: n = 3 Output: [[1;2;3];[8;9;4];[7;6;5]] Example 2: Input: n = 1 Output: [[1]] Constraints: 1 <= n <= 20
Uber,64,Minimum Path Sum,Med,"Array, Dynamic Programming, Matrix",Given a m x n grid filled with non-negative numbers; find a path from top left to bottom right; which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1;3;1];[1;5;1];[4;2;1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. Example 2: Input: grid = [[1;2;3];[4;5;6]] Output: 12 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 200 0 <= grid[i][j] <= 200
Uber,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Uber,81,Search in Rotated Sorted Array II,Med,"Array, Binary Search",There is an integer array nums sorted in non-decreasing order (not necessarily with distinct values). Before being passed to your function; nums is rotated at an unknown pivot index k (0 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;4;4;5;6;6;7] might be rotated at pivot index 5 and become [4;5;6;6;7;0;1;2;4;4]. Given the array nums after the rotation and an integer target; return true if target is in nums; or false if it is not in nums. You must decrease the overall operation steps as much as possible. Example 1: Input: nums = [2;5;6;0;0;1;2]; target = 0 Output: true Example 2: Input: nums = [2;5;6;0;0;1;2]; target = 3 Output: false Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 nums is guaranteed to be rotated at some pivot. -104 <= target <= 104 Follow up: This problem is similar to Search in Rotated Sorted Array; but nums may contain duplicates. Would this affect the runtime complexity? How and why?
Uber,83,Remove Duplicates from Sorted List,Easy,Linked List,Given the head of a sorted linked list; delete all duplicates such that each element appears only once. Return the linked list sorted as well. Example 1: Input: head = [1;1;2] Output: [1;2] Example 2: Input: head = [1;1;2;3;3] Output: [1;2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Uber,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Uber,111,Minimum Depth of Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given a binary tree; find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. Note: A leaf is a node with no children. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 2 Example 2: Input: root = [2;null;3;null;4;null;5;null;6] Output: 5 Constraints: The number of nodes in the tree is in the range [0; 105]. -1000 <= Node.val <= 1000
Uber,114,Flatten Binary Tree to Linked List,Med,"Linked List, Stack, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; flatten the tree into a ""linked list"": The ""linked list"" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. The ""linked list"" should be in the same order as a pre-order traversal of the binary tree. Example 1: Input: root = [1;2;5;3;4;null;6] Output: [1;null;2;null;3;null;4;null;5;null;6] Example 2: Input: root = [] Output: [] Example 3: Input: root = [0] Output: [0] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100 Follow up: Can you flatten the tree in-place (with O(1) extra space)?"
Uber,115,Distinct Subsequences,Hard,"String, Dynamic Programming","Given two strings s and t; return the number of distinct subsequences of s which equals t. The test cases are generated so that the answer fits on a 32-bit signed integer. Example 1: Input: s = ""rabbbit""; t = ""rabbit"" Output: 3 Explanation: As shown below; there are 3 ways you can generate ""rabbit"" from s. rabbbit rabbbit rabbbit Example 2: Input: s = ""babgbag""; t = ""bag"" Output: 5 Explanation: As shown below; there are 5 ways you can generate ""bag"" from s. babgbag babgbag babgbag babgbag babgbag Constraints: 1 <= s.length; t.length <= 1000 s and t consist of English letters."
Uber,135,Candy,Hard,"Array, Greedy",There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings. You are giving candies to these children subjected to the following requirements: Each child must have at least one candy. Children with a higher rating get more candies than their neighbors. Return the minimum number of candies you need to have to distribute the candies to the children. Example 1: Input: ratings = [1;0;2] Output: 5 Explanation: You can allocate to the first; second and third child with 2; 1; 2 candies respectively. Example 2: Input: ratings = [1;2;2] Output: 4 Explanation: You can allocate to the first; second and third child with 1; 2; 1 candies respectively. The third child gets 1 candy because it satisfies the above two conditions. Constraints: n == ratings.length 1 <= n <= 2 * 104 0 <= ratings[i] <= 2 * 104
Uber,179,Largest Number,Med,"Array, String, Greedy, Sorting","Given a list of non-negative integers nums; arrange them such that they form the largest number and return it. Since the result may be very large; so you need to return a string instead of an integer. Example 1: Input: nums = [10;2] Output: ""210"" Example 2: Input: nums = [3;30;34;5;9] Output: ""9534330"" Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 109"
Uber,180,Consecutive Numbers,Med,Database,Table: Logs +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | num | varchar | +-------------+---------+ In SQL; id is the primary key for this table. id is an autoincrement column starting from 1. Find all numbers that appear at least three times consecutively. Return the result table in any order. The result format is in the following example. Example 1: Input: Logs table: +----+-----+ | id | num | +----+-----+ | 1 | 1 | | 2 | 1 | | 3 | 1 | | 4 | 2 | | 5 | 1 | | 6 | 2 | | 7 | 2 | +----+-----+ Output: +-----------------+ | ConsecutiveNums | +-----------------+ | 1 | +-----------------+ Explanation: 1 is the only number that appears consecutively for at least three times.
Uber,181,Employees Earning More Than Their Managers,Easy,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | salary | int | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID of an employee; their name; salary; and the ID of their manager. Write a solution to find the employees who earn more than their managers. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +----+-------+--------+-----------+ | id | name | salary | managerId | +----+-------+--------+-----------+ | 1 | Joe | 70000 | 3 | | 2 | Henry | 80000 | 4 | | 3 | Sam | 60000 | Null | | 4 | Max | 90000 | Null | +----+-------+--------+-----------+ Output: +----------+ | Employee | +----------+ | Joe | +----------+ Explanation: Joe is the only employee who earns more than his manager.
Uber,209,Minimum Size Subarray Sum,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of positive integers nums and a positive integer target; return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray; return 0 instead. Example 1: Input: target = 7; nums = [2;3;1;2;4;3] Output: 2 Explanation: The subarray [4;3] has the minimal length under the problem constraint. Example 2: Input: target = 4; nums = [1;4;4] Output: 1 Example 3: Input: target = 11; nums = [1;1;1;1;1;1;1;1] Output: 0 Constraints: 1 <= target <= 109 1 <= nums.length <= 105 1 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution of which the time complexity is O(n log(n)).
Uber,213,House Robber II,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile; adjacent houses have a security system connected; and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [2;3;2] Output: 3 Explanation: You cannot rob house 1 (money = 2) and then rob house 3 (money = 2); because they are adjacent houses. Example 2: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 3: Input: nums = [1;2;3] Output: 3 Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 1000
Uber,219,Contains Duplicate II,Easy,"Array, Hash Table, Sliding Window",Given an integer array nums and an integer k; return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k. Example 1: Input: nums = [1;2;3;1]; k = 3 Output: true Example 2: Input: nums = [1;0;1;1]; k = 1 Output: true Example 3: Input: nums = [1;2;3;1;2;3]; k = 2 Output: false Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109 0 <= k <= 105
Uber,240,Search a 2D Matrix II,Med,"Array, Binary Search, Divide and Conquer, Matrix",Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. Example 1: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 5 Output: true Example 2: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 20 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= n; m <= 300 -109 <= matrix[i][j] <= 109 All the integers in each row are sorted in ascending order. All the integers in each column are sorted in ascending order. -109 <= target <= 109
Uber,246,Strobogrammatic Number,Easy,"Hash Table, Two Pointers, String",
Uber,263,Ugly Number,Easy,Math,An ugly number is a positive integer which does not have a prime factor other than 2; 3; and 5. Given an integer n; return true if n is an ugly number. Example 1: Input: n = 6 Output: true Explanation: 6 = 2 × 3 Example 2: Input: n = 1 Output: true Explanation: 1 has no prime factors. Example 3: Input: n = 14 Output: false Explanation: 14 is not ugly since it includes the prime factor 7. Constraints: -231 <= n <= 231 - 1
Uber,301,Remove Invalid Parentheses,Hard,"String, Backtracking, Breadth-First Search","Given a string s that contains parentheses and letters; remove the minimum number of invalid parentheses to make the input string valid. Return a list of unique strings that are valid with the minimum number of removals. You may return the answer in any order. Example 1: Input: s = ""()())()"" Output: [""(())()"";""()()()""] Example 2: Input: s = ""(a)())()"" Output: [""(a())()"";""(a)()()""] Example 3: Input: s = "")("" Output: [""""] Constraints: 1 <= s.length <= 25 s consists of lowercase English letters and parentheses '(' and ')'. There will be at most 20 parentheses in s."
Uber,316,Remove Duplicate Letters,Med,"String, Stack, Greedy, Monotonic Stack","Given a string s; remove duplicate letters so that every letter appears once and only once. You must make sure your result is the smallest in lexicographical order among all possible results. Example 1: Input: s = ""bcabc"" Output: ""abc"" Example 2: Input: s = ""cbacdcbc"" Output: ""acdb"" Constraints: 1 <= s.length <= 104 s consists of lowercase English letters. Note: This question is the same as 1081: https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/"
Uber,343,Integer Break,Med,"Math, Dynamic Programming",Given an integer n; break it into the sum of k positive integers; where k >= 2; and maximize the product of those integers. Return the maximum product you can get. Example 1: Input: n = 2 Output: 1 Explanation: 2 = 1 + 1; 1 × 1 = 1. Example 2: Input: n = 10 Output: 36 Explanation: 10 = 3 + 3 + 4; 3 × 3 × 4 = 36. Constraints: 2 <= n <= 58
Uber,345,Reverse Vowels of a String,Easy,"Two Pointers, String","Given a string s; reverse only all the vowels in the string and return it. The vowels are 'a'; 'e'; 'i'; 'o'; and 'u'; and they can appear in both lower and upper cases; more than once. Example 1: Input: s = ""IceCreAm"" Output: ""AceCreIm"" Explanation: The vowels in s are ['I'; 'e'; 'e'; 'A']. On reversing the vowels; s becomes ""AceCreIm"". Example 2: Input: s = ""leetcode"" Output: ""leotcede"" Constraints: 1 <= s.length <= 3 * 105 s consist of printable ASCII characters."
Uber,355,Design Twitter,Med,"Hash Table, Linked List, Design, Heap (Priority Queue)","Design a simplified version of Twitter where users can post tweets; follow/unfollow another user; and is able to see the 10 most recent tweets in the user's news feed. Implement the Twitter class: Twitter() Initializes your twitter object. void postTweet(int userId; int tweetId) Composes a new tweet with ID tweetId by the user userId. Each call to this function will be made with a unique tweetId. List<Integer> getNewsFeed(int userId) Retrieves the 10 most recent tweet IDs in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user themself. Tweets must be ordered from most recent to least recent. void follow(int followerId; int followeeId) The user with ID followerId started following the user with ID followeeId. void unfollow(int followerId; int followeeId) The user with ID followerId started unfollowing the user with ID followeeId. Example 1: Input [""Twitter""; ""postTweet""; ""getNewsFeed""; ""follow""; ""postTweet""; ""getNewsFeed""; ""unfollow""; ""getNewsFeed""] [[]; [1; 5]; [1]; [1; 2]; [2; 6]; [1]; [1; 2]; [1]] Output [null; null; [5]; null; null; [6; 5]; null; [5]] Explanation Twitter twitter = new Twitter(); twitter.postTweet(1; 5); // User 1 posts a new tweet (id = 5). twitter.getNewsFeed(1); // User 1's news feed should return a list with 1 tweet id -> [5]. return [5] twitter.follow(1; 2); // User 1 follows user 2. twitter.postTweet(2; 6); // User 2 posts a new tweet (id = 6). twitter.getNewsFeed(1); // User 1's news feed should return a list with 2 tweet ids -> [6; 5]. Tweet id 6 should precede tweet id 5 because it is posted after tweet id 5. twitter.unfollow(1; 2); // User 1 unfollows user 2. twitter.getNewsFeed(1); // User 1's news feed should return a list with 1 tweet id -> [5]; since user 1 is no longer following user 2. Constraints: 1 <= userId; followerId; followeeId <= 500 0 <= tweetId <= 104 All the tweets have unique IDs. At most 3 * 104 calls will be made to postTweet; getNewsFeed; follow; and unfollow."
Uber,371,Sum of Two Integers,Med,"Math, Bit Manipulation",Given two integers a and b; return the sum of the two integers without using the operators + and -. Example 1: Input: a = 1; b = 2 Output: 3 Example 2: Input: a = 2; b = 3 Output: 5 Constraints: -1000 <= a; b <= 1000
Uber,383,Ransom Note,Easy,"Hash Table, String, Counting","Given two strings ransomNote and magazine; return true if ransomNote can be constructed by using the letters from magazine and false otherwise. Each letter in magazine can only be used once in ransomNote. Example 1: Input: ransomNote = ""a""; magazine = ""b"" Output: false Example 2: Input: ransomNote = ""aa""; magazine = ""ab"" Output: false Example 3: Input: ransomNote = ""aa""; magazine = ""aab"" Output: true Constraints: 1 <= ransomNote.length; magazine.length <= 105 ransomNote and magazine consist of lowercase English letters."
Uber,435,Non-overlapping Intervals,Med,"Array, Dynamic Programming, Greedy, Sorting",Given an array of intervals intervals where intervals[i] = [starti; endi]; return the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping. Note that intervals which only touch at a point are non-overlapping. For example; [1; 2] and [2; 3] are non-overlapping. Example 1: Input: intervals = [[1;2];[2;3];[3;4];[1;3]] Output: 1 Explanation: [1;3] can be removed and the rest of the intervals are non-overlapping. Example 2: Input: intervals = [[1;2];[1;2];[1;2]] Output: 2 Explanation: You need to remove two [1;2] to make the rest of the intervals non-overlapping. Example 3: Input: intervals = [[1;2];[2;3]] Output: 0 Explanation: You don't need to remove any of the intervals since they're already non-overlapping. Constraints: 1 <= intervals.length <= 105 intervals[i].length == 2 -5 * 104 <= starti < endi <= 5 * 104
Uber,485,Max Consecutive Ones,Easy,Array,Given a binary array nums; return the maximum number of consecutive 1's in the array. Example 1: Input: nums = [1;1;0;1;1;1] Output: 3 Explanation: The first two digits or the last three digits are consecutive 1s. The maximum number of consecutive 1s is 3. Example 2: Input: nums = [1;0;1;1;0;1] Output: 2 Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Uber,514,Freedom Trail,Hard,"String, Dynamic Programming, Depth-First Search, Breadth-First Search","In the video game Fallout 4; the quest ""Road to Freedom"" requires players to reach a metal dial called the ""Freedom Trail Ring"" and use the dial to spell a specific keyword to open the door. Given a string ring that represents the code engraved on the outer ring and another string key that represents the keyword that needs to be spelled; return the minimum number of steps to spell all the characters in the keyword. Initially; the first character of the ring is aligned at the ""12:00"" direction. You should spell all the characters in key one by one by rotating ring clockwise or anticlockwise to make each character of the string key aligned at the ""12:00"" direction and then by pressing the center button. At the stage of rotating the ring to spell the key character key[i]: You can rotate the ring clockwise or anticlockwise by one place; which counts as one step. The final purpose of the rotation is to align one of ring's characters at the ""12:00"" direction; where this character must equal key[i]. If the character key[i] has been aligned at the ""12:00"" direction; press the center button to spell; which also counts as one step. After the pressing; you could begin to spell the next character in the key (next stage). Otherwise; you have finished all the spelling. Example 1: Input: ring = ""godding""; key = ""gd"" Output: 4 Explanation: For the first key character 'g'; since it is already in place; we just need 1 step to spell this character. For the second key character 'd'; we need to rotate the ring ""godding"" anticlockwise by two steps to make it become ""ddinggo"". Also; we need 1 more step for spelling. So the final output is 4. Example 2: Input: ring = ""godding""; key = ""godding"" Output: 13 Constraints: 1 <= ring.length; key.length <= 100 ring and key consist of only lower case English letters. It is guaranteed that key could always be spelled by rotating ring."
Uber,518,Coin Change II,Med,"Array, Dynamic Programming",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the number of combinations that make up that amount. If that amount of money cannot be made up by any combination of the coins; return 0. You may assume that you have an infinite number of each kind of coin. The answer is guaranteed to fit into a signed 32-bit integer. Example 1: Input: amount = 5; coins = [1;2;5] Output: 4 Explanation: there are four ways to make up the amount: 5=5 5=2+2+1 5=2+1+1+1 5=1+1+1+1+1 Example 2: Input: amount = 3; coins = [2] Output: 0 Explanation: the amount of 3 cannot be made up just with coins of 2. Example 3: Input: amount = 10; coins = [10] Output: 1 Constraints: 1 <= coins.length <= 300 1 <= coins[i] <= 5000 All the values of coins are unique. 0 <= amount <= 5000
Uber,525,Contiguous Array,Med,"Array, Hash Table, Prefix Sum",Given a binary array nums; return the maximum length of a contiguous subarray with an equal number of 0 and 1. Example 1: Input: nums = [0;1] Output: 2 Explanation: [0; 1] is the longest contiguous subarray with an equal number of 0 and 1. Example 2: Input: nums = [0;1;0] Output: 2 Explanation: [0; 1] (or [1; 0]) is a longest contiguous subarray with equal number of 0 and 1. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Uber,543,Diameter of Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them. Example 1: Input: root = [1;2;3;4;5] Output: 3 Explanation: 3 is the length of the path [4;2;1;3] or [5;2;1;3]. Example 2: Input: root = [1;2] Output: 1 Constraints: The number of nodes in the tree is in the range [1; 104]. -100 <= Node.val <= 100
Uber,572,Subtree of Another Tree,Easy,"Tree, Depth-First Search, String Matching, Binary Tree, Hash Function",Given the roots of two binary trees root and subRoot; return true if there is a subtree of root with the same structure and node values of subRoot and false otherwise. A subtree of a binary tree tree is a tree that consists of a node in tree and all of this node's descendants. The tree tree could also be considered as a subtree of itself. Example 1: Input: root = [3;4;5;1;2]; subRoot = [4;1;2] Output: true Example 2: Input: root = [3;4;5;1;2;null;null;null;null;0]; subRoot = [4;1;2] Output: false Constraints: The number of nodes in the root tree is in the range [1; 2000]. The number of nodes in the subRoot tree is in the range [1; 1000]. -104 <= root.val <= 104 -104 <= subRoot.val <= 104
Uber,577,Employee Bonus,Easy,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | empId | int | | name | varchar | | supervisor | int | | salary | int | +-------------+---------+ empId is the column with unique values for this table. Each row of this table indicates the name and the ID of an employee in addition to their salary and the id of their manager. Table: Bonus +-------------+------+ | Column Name | Type | +-------------+------+ | empId | int | | bonus | int | +-------------+------+ empId is the column of unique values for this table. empId is a foreign key (reference column) to empId from the Employee table. Each row of this table contains the id of an employee and their respective bonus. Write a solution to report the name and bonus amount of each employee with a bonus less than 1000. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +-------+--------+------------+--------+ | empId | name | supervisor | salary | +-------+--------+------------+--------+ | 3 | Brad | null | 4000 | | 1 | John | 3 | 1000 | | 2 | Dan | 3 | 2000 | | 4 | Thomas | 3 | 4000 | +-------+--------+------------+--------+ Bonus table: +-------+-------+ | empId | bonus | +-------+-------+ | 2 | 500 | | 4 | 2000 | +-------+-------+ Output: +------+-------+ | name | bonus | +------+-------+ | Brad | null | | John | null | | Dan | 500 | +------+-------+
Uber,584,Find Customer Referee,Easy,Database,Table: Customer +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | referee_id | int | +-------------+---------+ In SQL; id is the primary key column for this table. Each row of this table indicates the id of a customer; their name; and the id of the customer who referred them. Find the names of the customer that are not referred by the customer with id = 2. Return the result table in any order. The result format is in the following example. Example 1: Input: Customer table: +----+------+------------+ | id | name | referee_id | +----+------+------------+ | 1 | Will | null | | 2 | Jane | null | | 3 | Alex | 2 | | 4 | Bill | null | | 5 | Zack | 1 | | 6 | Mark | 2 | +----+------+------------+ Output: +------+ | name | +------+ | Will | | Jane | | Bill | | Zack | +------+
Uber,595,Big Countries,Easy,Database,Table: World +-------------+---------+ | Column Name | Type | +-------------+---------+ | name | varchar | | continent | varchar | | area | int | | population | int | | gdp | bigint | +-------------+---------+ name is the primary key (column with unique values) for this table. Each row of this table gives information about the name of a country; the continent to which it belongs; its area; the population; and its GDP value. A country is big if: it has an area of at least three million (i.e.; 3000000 km2); or it has a population of at least twenty-five million (i.e.; 25000000). Write a solution to find the name; population; and area of the big countries. Return the result table in any order. The result format is in the following example. Example 1: Input: World table: +-------------+-----------+---------+------------+--------------+ | name | continent | area | population | gdp | +-------------+-----------+---------+------------+--------------+ | Afghanistan | Asia | 652230 | 25500100 | 20343000000 | | Albania | Europe | 28748 | 2831741 | 12960000000 | | Algeria | Africa | 2381741 | 37100000 | 188681000000 | | Andorra | Europe | 468 | 78115 | 3712000000 | | Angola | Africa | 1246700 | 20609294 | 100990000000 | +-------------+-----------+---------+------------+--------------+ Output: +-------------+------------+---------+ | name | population | area | +-------------+------------+---------+ | Afghanistan | 25500100 | 652230 | | Algeria | 37100000 | 2381741 | +-------------+------------+---------+
Uber,605,Can Place Flowers,Easy,"Array, Greedy",You have a long flowerbed in which some of the plots are planted; and some are not. However; flowers cannot be planted in adjacent plots. Given an integer array flowerbed containing 0's and 1's; where 0 means empty and 1 means not empty; and an integer n; return true if n new flowers can be planted in the flowerbed without violating the no-adjacent-flowers rule and false otherwise. Example 1: Input: flowerbed = [1;0;0;0;1]; n = 1 Output: true Example 2: Input: flowerbed = [1;0;0;0;1]; n = 2 Output: false Constraints: 1 <= flowerbed.length <= 2 * 104 flowerbed[i] is 0 or 1. There are no two adjacent flowers in flowerbed. 0 <= n <= flowerbed.length
Uber,621,Task Scheduler,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting","You are given an array of CPU tasks; each labeled with a letter from A to Z; and a number n. Each CPU interval can be idle or allow the completion of one task. Tasks can be completed in any order; but there's a constraint: there has to be a gap of at least n intervals between two tasks with the same label. Return the minimum number of CPU intervals required to complete all tasks. Example 1: Input: tasks = [""A"";""A"";""A"";""B"";""B"";""B""]; n = 2 Output: 8 Explanation: A possible sequence is: A -> B -> idle -> A -> B -> idle -> A -> B. After completing task A; you must wait two intervals before doing A again. The same applies to task B. In the 3rd interval; neither A nor B can be done; so you idle. By the 4th interval; you can do A again as 2 intervals have passed. Example 2: Input: tasks = [""A"";""C"";""A"";""B"";""D"";""B""]; n = 1 Output: 6 Explanation: A possible sequence is: A -> B -> C -> D -> A -> B. With a cooling interval of 1; you can repeat a task after just one other task. Example 3: Input: tasks = [""A"";""A"";""A""; ""B"";""B"";""B""]; n = 3 Output: 10 Explanation: A possible sequence is: A -> B -> idle -> idle -> A -> B -> idle -> idle -> A -> B. There are only two types of tasks; A and B; which need to be separated by 3 intervals. This leads to idling twice between repetitions of these tasks. Constraints: 1 <= tasks.length <= 104 tasks[i] is an uppercase English letter. 0 <= n <= 100"
Uber,723,Candy Crush,Med,"Array, Two Pointers, Matrix, Simulation",
Uber,724,Find Pivot Index,Easy,"Array, Prefix Sum",Given an array of integers nums; calculate the pivot index of this array. The pivot index is the index where the sum of all the numbers strictly to the left of the index is equal to the sum of all the numbers strictly to the index's right. If the index is on the left edge of the array; then the left sum is 0 because there are no elements to the left. This also applies to the right edge of the array. Return the leftmost pivot index. If no such index exists; return -1. Example 1: Input: nums = [1;7;3;6;5;6] Output: 3 Explanation: The pivot index is 3. Left sum = nums[0] + nums[1] + nums[2] = 1 + 7 + 3 = 11 Right sum = nums[4] + nums[5] = 5 + 6 = 11 Example 2: Input: nums = [1;2;3] Output: -1 Explanation: There is no index that satisfies the conditions in the problem statement. Example 3: Input: nums = [2;1;-1] Output: 0 Explanation: The pivot index is 0. Left sum = 0 (no elements to the left of index 0) Right sum = nums[1] + nums[2] = 1 + -1 = 0 Constraints: 1 <= nums.length <= 104 -1000 <= nums[i] <= 1000 Note: This question is the same as 1991: https://leetcode.com/problems/find-the-middle-index-in-array/
Uber,737,Sentence Similarity II,Med,"Array, Hash Table, String, Depth-First Search, Breadth-First Search, Union Find",
Uber,752,Open the Lock,Med,"String, Bit Manipulation",
Uber,785,Is Graph Bipartite?,Med,"Math, String, Stack, Recursion",
Uber,791,Custom Sort String,Med,"Tree, Binary Search Tree, Recursion, Binary Tree",
Uber,792,Number of Matching Subsequences,Med,"Array, Binary Search",Given an array of integers nums which is sorted in ascending order; and an integer target; write a function to search target in nums. If target exists; then return its index. Otherwise; return -1. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [-1;0;3;5;9;12]; target = 9 Output: 4 Explanation: 9 exists in nums and its index is 4 Example 2: Input: nums = [-1;0;3;5;9;12]; target = 2 Output: -1 Explanation: 2 does not exist in nums so return -1 Constraints: 1 <= nums.length <= 104 -104 < nums[i]; target < 104 All the integers in nums are unique. nums is sorted in ascending order.
Uber,802,Find Eventual Safe States,Med,"Array, Two Pointers, Binary Search, Sorting, Heap (Priority Queue)",You are given a sorted integer array arr containing 1 and prime numbers; where all the integers of arr are unique. You are also given an integer k. For every i and j where 0 <= i < j < arr.length; we consider the fraction arr[i] / arr[j]. Return the kth smallest fraction considered. Return your answer as an array of integers of size 2; where answer[0] == arr[i] and answer[1] == arr[j]. Example 1: Input: arr = [1;2;3;5]; k = 3 Output: [2;5] Explanation: The fractions to be considered in sorted order are: 1/5; 1/3; 2/5; 1/2; 3/5; and 2/3. The third fraction is 2/5. Example 2: Input: arr = [1;7]; k = 1 Output: [1;7] Constraints: 2 <= arr.length <= 1000 1 <= arr[i] <= 3 * 104 arr[0] == 1 arr[i] is a prime number for i > 0. All the numbers of arr are unique and sorted in strictly increasing order. 1 <= k <= arr.length * (arr.length - 1) / 2 Follow up: Can you solve the problem with better than O(n2) complexity?
Uber,863,All Nodes Distance K in Binary Tree,Med,"Dynamic Programming, Tree, Depth-First Search, Graph",There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Return an array answer of length n where answer[i] is the sum of the distances between the ith node in the tree and all other nodes. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;3];[2;4];[2;5]] Output: [8;12;6;10;10;10] Explanation: The tree is shown above. We can see that dist(0;1) + dist(0;2) + dist(0;3) + dist(0;4) + dist(0;5) equals 1 + 1 + 2 + 2 + 2 = 8. Hence; answer[0] = 8; and so on. Example 2: Input: n = 1; edges = [] Output: [0] Example 3: Input: n = 2; edges = [[1;0]] Output: [1;1] Constraints: 1 <= n <= 3 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n ai != bi The given input represents a valid tree.
Uber,886,Possible Bipartition,Med,"String, Stack","Given a balanced parentheses string s; return the score of the string. The score of a balanced parentheses string is based on the following rule: ""()"" has score 1. AB has score A + B; where A and B are balanced parentheses strings. (A) has score 2 * A; where A is a balanced parentheses string. Example 1: Input: s = ""()"" Output: 1 Example 2: Input: s = ""(())"" Output: 2 Example 3: Input: s = ""()()"" Output: 2 Constraints: 2 <= s.length <= 50 s consists of only '(' and ')'. s is a balanced parentheses string."
Uber,907,Sum of Subarray Minimums,Med,"Array, Binary Search",Koko loves to eat bananas. There are n piles of bananas; the ith pile has piles[i] bananas. The guards have gone and will come back in h hours. Koko can decide her bananas-per-hour eating speed of k. Each hour; she chooses some pile of bananas and eats k bananas from that pile. If the pile has less than k bananas; she eats all of them instead and will not eat any more bananas during this hour. Koko likes to eat slowly but still wants to finish eating all the bananas before the guards return. Return the minimum integer k such that she can eat all the bananas within h hours. Example 1: Input: piles = [3;6;7;11]; h = 8 Output: 4 Example 2: Input: piles = [30;11;23;4;20]; h = 5 Output: 30 Example 3: Input: piles = [30;11;23;4;20]; h = 6 Output: 23 Constraints: 1 <= piles.length <= 104 piles.length <= h <= 109 1 <= piles[i] <= 109
Uber,509,Fibonacci Number,Easy,"Tree, Binary Search Tree, Binary Tree",
Uber,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
Uber,1152,Analyze User Website Visit Pattern,Med,"Greedy, Heap (Priority Queue)",
Uber,1092,Shortest Common Supersequence,Hard,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; find the maximum value v for which there exist different nodes a and b where v = |a.val - b.val| and a is an ancestor of b. A node a is an ancestor of b if either: any child of a is equal to b or any child of a is an ancestor of b. Example 1: Input: root = [8;3;10;1;6;null;14;null;null;4;7;13] Output: 7 Explanation: We have various ancestor-node differences; some of which are given below : |8 - 3| = 5 |3 - 7| = 4 |8 - 1| = 7 |10 - 13| = 3 Among all possible differences; the maximum value of 7 is obtained by |8 - 1| = 7. Example 2: Input: root = [1;null;2;null;0;3] Output: 3 Constraints: The number of nodes in the tree is in the range [2; 5000]. 0 <= Node.val <= 105
Uber,1108,Defanging an IP Address,Easy,"Array, Hash Table, Sorting",
Uber,1148,Article Views I,Easy,"Array, Math",Given two numbers arr1 and arr2 in base -2; return the result of adding them together. Each number is given in array format: as an array of 0s and 1s; from most significant bit to least significant bit. For example; arr = [1;1;0;1] represents the number (-2)^3 + (-2)^2 + (-2)^0 = -3. A number arr in array; format is also guaranteed to have no leading zeros: either arr == [0] or arr[0] == 1. Return the result of adding arr1 and arr2 in the same format: as an array of 0s and 1s with no leading zeros. Example 1: Input: arr1 = [1;1;1;1;1]; arr2 = [1;0;1] Output: [1;0;0;0;0] Explanation: arr1 represents 11; arr2 represents 5; the output represents 16. Example 2: Input: arr1 = [0]; arr2 = [0] Output: [0] Example 3: Input: arr1 = [0]; arr2 = [1] Output: [1] Constraints: 1 <= arr1.length; arr2.length <= 1000 arr1[i] and arr2[i] are 0 or 1 arr1 and arr2 have no leading zeros
Uber,1202,Smallest String With Swaps,Med,"Array, Dynamic Programming",
Uber,1193,Monthly Transactions I,Med,Database,
Uber,1326,Minimum Number of Taps to Open to Water a Garden,Hard,"Array, Math, Binary Search, Prefix Sum",Given an integer array nums; return the sum of floor(nums[i] / nums[j]) for all pairs of indices 0 <= i; j < nums.length in the array. Since the answer may be too large; return it modulo 109 + 7. The floor() function returns the integer part of the division. Example 1: Input: nums = [2;5;9] Output: 10 Explanation: floor(2 / 5) = floor(2 / 9) = floor(5 / 9) = 0 floor(2 / 2) = floor(5 / 5) = floor(9 / 9) = 1 floor(5 / 2) = 2 floor(9 / 2) = 4 floor(9 / 5) = 1 We calculate the floor of the division for every pair of indices in the array then sum them up. Example 2: Input: nums = [7;7;7;7;7;7;7] Output: 49 Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105
Uber,1378,Replace Employee ID With The Unique Identifier,Easy,"Array, Math, Simulation",There is an m x n matrix that is initialized to all 0's. There is also a 2D array indices where each indices[i] = [ri; ci] represents a 0-indexed location to perform some increment operations on the matrix. For each location indices[i]; do both of the following: Increment all the cells on row ri. Increment all the cells on column ci. Given m; n; and indices; return the number of odd-valued cells in the matrix after applying the increment to all locations in indices. Example 1: Input: m = 2; n = 3; indices = [[0;1];[1;1]] Output: 6 Explanation: Initial matrix = [[0;0;0];[0;0;0]]. After applying first increment it becomes [[1;2;1];[0;1;0]]. The final matrix is [[1;3;1];[1;3;1]]; which contains 6 odd numbers. Example 2: Input: m = 2; n = 2; indices = [[1;1];[0;0]] Output: 0 Explanation: Final matrix = [[2;2];[2;2]]. There are no odd numbers in the final matrix. Constraints: 1 <= m; n <= 50 1 <= indices.length <= 100 0 <= ri < m 0 <= ci < n Follow up: Could you solve this in O(n + m + indices.length) time with only O(n + m) extra space?
Uber,1539,Kth Missing Positive Number,Easy,"Array, Sorting, Heap (Priority Queue)",Given a 2D integer array nums; return all elements of nums in diagonal order as shown in the below images. Example 1: Input: nums = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;4;2;7;5;3;8;6;9] Example 2: Input: nums = [[1;2;3;4;5];[6;7];[8];[9;10;11];[12;13;14;15;16]] Output: [1;6;2;8;7;3;9;4;12;10;5;13;11;14;15;16] Constraints: 1 <= nums.length <= 105 1 <= nums[i].length <= 105 1 <= sum(nums[i].length) <= 105 1 <= nums[i][j] <= 105
Uber,1626,Best Team With No Conflicts,Med,"Array, Sorting",A sequence of numbers is called an arithmetic progression if the difference between any two consecutive elements is the same. Given an array of numbers arr; return true if the array can be rearranged to form an arithmetic progression. Otherwise; return false. Example 1: Input: arr = [3;5;1] Output: true Explanation: We can reorder the elements as [1;3;5] or [5;3;1] with differences 2 and -2 respectively; between each consecutive elements. Example 2: Input: arr = [1;2;4] Output: false Explanation: There is no way to reorder the elements to obtain an arithmetic progression. Constraints: 2 <= arr.length <= 1000 -106 <= arr[i] <= 106
Uber,1631,Path With Minimum Effort,Med,"Array, Math, Dynamic Programming, Prefix Sum",Given an array of integers arr; return the number of subarrays with an odd sum. Since the answer can be very large; return it modulo 109 + 7. Example 1: Input: arr = [1;3;5] Output: 4 Explanation: All subarrays are [[1];[1;3];[1;3;5];[3];[3;5];[5]] All sub-arrays sum are [1;4;9;3;8;5]. Odd sums are [1;9;3;5] so the answer is 4. Example 2: Input: arr = [2;4;6] Output: 0 Explanation: All subarrays are [[2];[2;4];[2;4;6];[4];[4;6];[6]] All sub-arrays sum are [2;6;12;4;10;6]. All sub-arrays have even sum and the answer is 0. Example 3: Input: arr = [1;2;3;4;5;6;7] Output: 16 Constraints: 1 <= arr.length <= 105 1 <= arr[i] <= 100
Uber,1661,Average Time of Process per Machine,Easy,Graph,Given a directed acyclic graph; with n vertices numbered from 0 to n-1; and an array edges where edges[i] = [fromi; toi] represents a directed edge from node fromi to node toi. Find the smallest set of vertices from which all nodes in the graph are reachable. It's guaranteed that a unique solution exists. Notice that you can return the vertices in any order. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;5];[3;4];[4;2]] Output: [0;3] Explanation: It's not possible to reach all the nodes from a single vertex. From 0 we can reach [0;1;2;5]. From 3 we can reach [3;4;2;5]. So we output [0;3]. Example 2: Input: n = 5; edges = [[0;1];[2;1];[3;1];[1;4];[2;4]] Output: [0;2;3] Explanation: Notice that vertices 0; 3 and 2 are not reachable from any other node; so we must include them. Also any of these vertices can reach nodes 1 and 4. Constraints: 2 <= n <= 10^5 1 <= edges.length <= min(10^5; n * (n - 1) / 2) edges[i].length == 2 0 <= fromi; toi < n All pairs (fromi; toi) are distinct.
Uber,1838,Frequency of the Most Frequent Element,Med,"String, Trie, Rolling Hash, Suffix Array, Hash Function",
Uber,1922,Count Good Numbers,Med,,
Uber,1929,Concatenation of Array,Easy,"Binary Search, Greedy",You are given three positive integers: n; index; and maxSum. You want to construct an array nums (0-indexed) that satisfies the following conditions: nums.length == n nums[i] is a positive integer where 0 <= i < n. abs(nums[i] - nums[i+1]) <= 1 where 0 <= i < n-1. The sum of all the elements of nums does not exceed maxSum. nums[index] is maximized. Return nums[index] of the constructed array. Note that abs(x) equals x if x >= 0; and -x otherwise. Example 1: Input: n = 4; index = 2; maxSum = 6 Output: 2 Explanation: nums = [1;2;2;1] is one array that satisfies all the conditions. There are no arrays that satisfy all the conditions and have nums[2] == 3; so 2 is the maximum nums[2]. Example 2: Input: n = 6; index = 1; maxSum = 10 Output: 3 Constraints: 1 <= n <= maxSum <= 109 0 <= index < n
Uber,2043,Simple Bank System,Med,"Array, Matrix, Simulation",You are given an m x n integer matrix grid​​​; where m and n are both even integers; and an integer k. The matrix is composed of several layers; which is shown in the below image; where each color is its own layer: A cyclic rotation of the matrix is done by cyclically rotating each layer in the matrix. To cyclically rotate a layer once; each element in the layer will take the place of the adjacent element in the counter-clockwise direction. An example rotation is shown below: Return the matrix after applying k cyclic rotations to it. Example 1: Input: grid = [[40;10];[30;20]]; k = 1 Output: [[10;20];[40;30]] Explanation: The figures above represent the grid at every state. Example 2: Input: grid = [[1;2;3;4];[5;6;7;8];[9;10;11;12];[13;14;15;16]]; k = 2 Output: [[3;4;8;12];[2;11;10;16];[1;7;6;15];[5;9;13;14]] Explanation: The figures above represent the grid at every state. Constraints: m == grid.length n == grid[i].length 2 <= m; n <= 50 Both m and n are even integers. 1 <= grid[i][j] <= 5000 1 <= k <= 109
Uber,2487,Remove Nodes From Linked List,Med,"Hash Table, String, Greedy","Given a string s; partition the string into one or more substrings such that the characters in each substring are unique. That is; no letter appears in a single substring more than once. Return the minimum number of substrings in such a partition. Note that each character should belong to exactly one substring in a partition. Example 1: Input: s = ""abacaba"" Output: 4 Explanation: Two possible partitions are (""a"";""ba"";""cab"";""a"") and (""ab"";""a"";""ca"";""ba""). It can be shown that 4 is the minimum number of substrings needed. Example 2: Input: s = ""ssssss"" Output: 6 Explanation: The only valid partition is (""s"";""s"";""s"";""s"";""s"";""s""). Constraints: 1 <= s.length <= 105 s consists of only English lowercase letters."
Uber,2537,Count the Number of Good Subarrays,Med,"Array, Dynamic Programming, Bit Manipulation, Bitmask",
Uber,2620,Counter,Easy,"Hash Table, Design, Queue, Counting, Data Stream","For a stream of integers; implement a data structure that checks if the last k integers parsed in the stream are equal to value. Implement the DataStream class: DataStream(int value; int k) Initializes the object with an empty integer stream and the two integers value and k. boolean consec(int num) Adds num to the stream of integers. Returns true if the last k integers are equal to value; and false otherwise. If there are less than k integers; the condition does not hold true; so returns false. Example 1: Input [""DataStream""; ""consec""; ""consec""; ""consec""; ""consec""] [[4; 3]; [4]; [4]; [4]; [3]] Output [null; false; false; true; false] Explanation DataStream dataStream = new DataStream(4; 3); //value = 4; k = 3 dataStream.consec(4); // Only 1 integer is parsed; so returns False. dataStream.consec(4); // Only 2 integers are parsed. // Since 2 is less than k; returns False. dataStream.consec(4); // The 3 integers parsed are all equal to value; so returns True. dataStream.consec(3); // The last k integers parsed in the stream are [4;4;3]. // Since 3 is not equal to value; it returns False. Constraints: 1 <= value; num <= 109 1 <= k <= 105 At most 105 calls will be made to consec."
Uber,3161,Block Placement Queries,Hard,,
Uber,63,Unique Paths II,Med,"Array, Dynamic Programming, Matrix",You are given an m x n integer array grid. There is a robot initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. An obstacle and space are marked as 1 or 0 respectively in grid. A path that the robot takes cannot include any square that is an obstacle. Return the number of possible unique paths that the robot can take to reach the bottom-right corner. The testcases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: obstacleGrid = [[0;0;0];[0;1;0];[0;0;0]] Output: 2 Explanation: There is one obstacle in the middle of the 3x3 grid above. There are two ways to reach the bottom-right corner: 1. Right -> Right -> Down -> Down 2. Down -> Down -> Right -> Right Example 2: Input: obstacleGrid = [[0;1];[0;0]] Output: 1 Constraints: m == obstacleGrid.length n == obstacleGrid[i].length 1 <= m; n <= 100 obstacleGrid[i][j] is 0 or 1.
Uber,82,Remove Duplicates from Sorted List II,Med,"Linked List, Two Pointers",Given the head of a sorted linked list; delete all nodes that have duplicate numbers; leaving only distinct numbers from the original list. Return the linked list sorted as well. Example 1: Input: head = [1;2;3;3;4;4;5] Output: [1;2;5] Example 2: Input: head = [1;1;1;2;3] Output: [2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Uber,92,Reverse Linked List II,Med,Linked List,Given the head of a singly linked list and two integers left and right where left <= right; reverse the nodes of the list from position left to position right; and return the reversed list. Example 1: Input: head = [1;2;3;4;5]; left = 2; right = 4 Output: [1;4;3;2;5] Example 2: Input: head = [5]; left = 1; right = 1 Output: [5] Constraints: The number of nodes in the list is n. 1 <= n <= 500 -500 <= Node.val <= 500 1 <= left <= right <= n Follow up: Could you do it in one pass?
Uber,95,Unique Binary Search Trees II,Med,"Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree",Given an integer n; return all the structurally unique BST's (binary search trees); which has exactly n nodes of unique values from 1 to n. Return the answer in any order. Example 1: Input: n = 3 Output: [[1;null;2;null;3];[1;null;3;2];[2;1;3];[3;1;null;null;2];[3;2;null;1]] Example 2: Input: n = 1 Output: [[1]] Constraints: 1 <= n <= 8
Uber,97,Interleaving String,Med,"String, Dynamic Programming","Given strings s1; s2; and s3; find whether s3 is formed by an interleaving of s1 and s2. An interleaving of two strings s and t is a configuration where s and t are divided into n and m substrings respectively; such that: s = s1 + s2 + ... + sn t = t1 + t2 + ... + tm |n - m| <= 1 The interleaving is s1 + t1 + s2 + t2 + s3 + t3 + ... or t1 + s1 + t2 + s2 + t3 + s3 + ... Note: a + b is the concatenation of strings a and b. Example 1: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbcbcac"" Output: true Explanation: One way to obtain s3 is: Split s1 into s1 = ""aa"" + ""bc"" + ""c""; and s2 into s2 = ""dbbc"" + ""a"". Interleaving the two splits; we get ""aa"" + ""dbbc"" + ""bc"" + ""a"" + ""c"" = ""aadbbcbcac"". Since s3 can be obtained by interleaving s1 and s2; we return true. Example 2: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbbaccc"" Output: false Explanation: Notice how it is impossible to interleave s2 with any other string to obtain s3. Example 3: Input: s1 = """"; s2 = """"; s3 = """" Output: true Constraints: 0 <= s1.length; s2.length <= 100 0 <= s3.length <= 200 s1; s2; and s3 consist of lowercase English letters. Follow up: Could you solve it using only O(s2.length) additional memory space?"
Uber,100,Same Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the roots of two binary trees p and q; write a function to check if they are the same or not. Two binary trees are considered the same if they are structurally identical; and the nodes have the same value. Example 1: Input: p = [1;2;3]; q = [1;2;3] Output: true Example 2: Input: p = [1;2]; q = [1;null;2] Output: false Example 3: Input: p = [1;2;1]; q = [1;1;2] Output: false Constraints: The number of nodes in both trees is in the range [0; 100]. -104 <= Node.val <= 104
Uber,110,Balanced Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given a binary tree; determine if it is height-balanced. Example 1: Input: root = [3;9;20;null;null;15;7] Output: true Example 2: Input: root = [1;2;2;3;3;null;null;4;4] Output: false Example 3: Input: root = [] Output: true Constraints: The number of nodes in the tree is in the range [0; 5000]. -104 <= Node.val <= 104
Uber,112,Path Sum,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return true if the tree has a root-to-leaf path such that adding up all the values along the path equals targetSum. A leaf is a node with no children. Example 1: Input: root = [5;4;8;11;null;13;4;7;2;null;null;null;1]; targetSum = 22 Output: true Explanation: The root-to-leaf path with the target sum is shown. Example 2: Input: root = [1;2;3]; targetSum = 5 Output: false Explanation: There are two root-to-leaf paths in the tree: (1 --> 2): The sum is 3. (1 --> 3): The sum is 4. There is no root-to-leaf path with sum = 5. Example 3: Input: root = []; targetSum = 0 Output: false Explanation: Since the tree is empty; there are no root-to-leaf paths. Constraints: The number of nodes in the tree is in the range [0; 5000]. -1000 <= Node.val <= 1000 -1000 <= targetSum <= 1000
Uber,134,Gas Station,Med,"Array, Greedy",There are n gas stations along a circular route; where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations. Given two integer arrays gas and cost; return the starting gas station's index if you can travel around the circuit once in the clockwise direction; otherwise return -1. If there exists a solution; it is guaranteed to be unique. Example 1: Input: gas = [1;2;3;4;5]; cost = [3;4;5;1;2] Output: 3 Explanation: Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 4. Your tank = 4 - 1 + 5 = 8 Travel to station 0. Your tank = 8 - 2 + 1 = 7 Travel to station 1. Your tank = 7 - 3 + 2 = 6 Travel to station 2. Your tank = 6 - 4 + 3 = 5 Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. Therefore; return 3 as the starting index. Example 2: Input: gas = [2;3;4]; cost = [3;4;3] Output: -1 Explanation: You can't start at station 0 or 1; as there is not enough gas to travel to the next station. Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 0. Your tank = 4 - 3 + 2 = 3 Travel to station 1. Your tank = 3 - 3 + 3 = 3 You cannot travel back to station 2; as it requires 4 unit of gas but you only have 3. Therefore; you can't travel around the circuit once no matter where you start. Constraints: n == gas.length == cost.length 1 <= n <= 105 0 <= gas[i]; cost[i] <= 104
Uber,148,Sort List,Med,"Linked List, Two Pointers, Divide and Conquer, Sorting, Merge Sort",Given the head of a linked list; return the list after sorting it in ascending order. Example 1: Input: head = [4;2;1;3] Output: [1;2;3;4] Example 2: Input: head = [-1;5;3;4;0] Output: [-1;0;3;4;5] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is in the range [0; 5 * 104]. -105 <= Node.val <= 105 Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?
Uber,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
Uber,176,Second Highest Salary,Med,Database,Table: Employee +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | salary | int | +-------------+------+ id is the primary key (column with unique values) for this table. Each row of this table contains information about the salary of an employee. Write a solution to find the second highest distinct salary from the Employee table. If there is no second highest salary; return null (return None in Pandas). The result format is in the following example. Example 1: Input: Employee table: +----+--------+ | id | salary | +----+--------+ | 1 | 100 | | 2 | 200 | | 3 | 300 | +----+--------+ Output: +---------------------+ | SecondHighestSalary | +---------------------+ | 200 | +---------------------+ Example 2: Input: Employee table: +----+--------+ | id | salary | +----+--------+ | 1 | 100 | +----+--------+ Output: +---------------------+ | SecondHighestSalary | +---------------------+ | null | +---------------------+
Uber,191,Number of 1 Bits,Easy,"Divide and Conquer, Bit Manipulation",Given a positive integer n; write a function that returns the number of set bits in its binary representation (also known as the Hamming weight). Example 1: Input: n = 11 Output: 3 Explanation: The input binary string 1011 has a total of three set bits. Example 2: Input: n = 128 Output: 1 Explanation: The input binary string 10000000 has a total of one set bit. Example 3: Input: n = 2147483645 Output: 30 Explanation: The input binary string 1111111111111111111111111111101 has a total of thirty set bits. Constraints: 1 <= n <= 231 - 1 Follow up: If this function is called many times; how would you optimize it?
Uber,197,Rising Temperature,Easy,Database,Table: Weather +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | recordDate | date | | temperature | int | +---------------+---------+ id is the column with unique values for this table. There are no different rows with the same recordDate. This table contains information about the temperature on a certain day. Write a solution to find all dates' id with higher temperatures compared to its previous dates (yesterday). Return the result table in any order. The result format is in the following example. Example 1: Input: Weather table: +----+------------+-------------+ | id | recordDate | temperature | +----+------------+-------------+ | 1 | 2015-01-01 | 10 | | 2 | 2015-01-02 | 25 | | 3 | 2015-01-03 | 20 | | 4 | 2015-01-04 | 30 | +----+------------+-------------+ Output: +----+ | id | +----+ | 2 | | 4 | +----+ Explanation: In 2015-01-02; the temperature was higher than the previous day (10 -> 25). In 2015-01-04; the temperature was higher than the previous day (20 -> 30).
Uber,214,Shortest Palindrome,Hard,"String, Rolling Hash, String Matching, Hash Function","You are given a string s. You can convert s to a palindrome by adding characters in front of it. Return the shortest palindrome you can find by performing this transformation. Example 1: Input: s = ""aacecaaa"" Output: ""aaacecaaa"" Example 2: Input: s = ""abcd"" Output: ""dcbabcd"" Constraints: 0 <= s.length <= 5 * 104 s consists of lowercase English letters only."
Uber,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Uber,232,Implement Queue using Stacks,Easy,"Stack, Design, Queue","Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push; peek; pop; and empty). Implement the MyQueue class: void push(int x) Pushes element x to the back of the queue. int pop() Removes the element from the front of the queue and returns it. int peek() Returns the element at the front of the queue. boolean empty() Returns true if the queue is empty; false otherwise. Notes: You must use only standard operations of a stack; which means only push to top; peek/pop from top; size; and is empty operations are valid. Depending on your language; the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack's standard operations. Example 1: Input [""MyQueue""; ""push""; ""push""; ""peek""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 1; 1; false] Explanation MyQueue myQueue = new MyQueue(); myQueue.push(1); // queue is: [1] myQueue.push(2); // queue is: [1; 2] (leftmost is front of the queue) myQueue.peek(); // return 1 myQueue.pop(); // return 1; queue is [2] myQueue.empty(); // return false Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; peek; and empty. All the calls to pop and peek are valid. Follow-up: Can you implement the queue such that each operation is amortized O(1) time complexity? In other words; performing n operations will take overall O(n) time even if one of those operations may take longer."
Uber,268,Missing Number,Easy,"Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting",Given an array nums containing n distinct numbers in the range [0; n]; return the only number in the range that is missing from the array. Example 1: Input: nums = [3;0;1] Output: 2 Explanation: n = 3 since there are 3 numbers; so all numbers are in the range [0;3]. 2 is the missing number in the range since it does not appear in nums. Example 2: Input: nums = [0;1] Output: 2 Explanation: n = 2 since there are 2 numbers; so all numbers are in the range [0;2]. 2 is the missing number in the range since it does not appear in nums. Example 3: Input: nums = [9;6;4;2;3;5;7;0;1] Output: 8 Explanation: n = 9 since there are 9 numbers; so all numbers are in the range [0;9]. 8 is the missing number in the range since it does not appear in nums. Constraints: n == nums.length 1 <= n <= 104 0 <= nums[i] <= n All the numbers of nums are unique. Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?
Uber,274,H-Index,Med,"Array, Sorting, Counting Sort",Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper; return the researcher's h-index. According to the definition of h-index on Wikipedia: The h-index is defined as the maximum value of h such that the given researcher has published at least h papers that have each been cited at least h times. Example 1: Input: citations = [3;0;6;1;5] Output: 3 Explanation: [3;0;6;1;5] means the researcher has 5 papers in total and each of them had received 3; 0; 6; 1; 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each; their h-index is 3. Example 2: Input: citations = [1;3;1] Output: 1 Constraints: n == citations.length 1 <= n <= 5000 0 <= citations[i] <= 1000
Uber,279,Perfect Squares,Med,"Math, Dynamic Programming, Breadth-First Search",Given an integer n; return the least number of perfect square numbers that sum to n. A perfect square is an integer that is the square of an integer; in other words; it is the product of some integer with itself. For example; 1; 4; 9; and 16 are perfect squares while 3 and 11 are not. Example 1: Input: n = 12 Output: 3 Explanation: 12 = 4 + 4 + 4. Example 2: Input: n = 13 Output: 2 Explanation: 13 = 4 + 9. Constraints: 1 <= n <= 104
Uber,303,Range Sum Query - Immutable,Easy,"Array, Design, Prefix Sum","Given an integer array nums; handle multiple queries of the following type: Calculate the sum of the elements of nums between indices left and right inclusive where left <= right. Implement the NumArray class: NumArray(int[] nums) Initializes the object with the integer array nums. int sumRange(int left; int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]). Example 1: Input [""NumArray""; ""sumRange""; ""sumRange""; ""sumRange""] [[[-2; 0; 3; -5; 2; -1]]; [0; 2]; [2; 5]; [0; 5]] Output [null; 1; -1; -3] Explanation NumArray numArray = new NumArray([-2; 0; 3; -5; 2; -1]); numArray.sumRange(0; 2); // return (-2) + 0 + 3 = 1 numArray.sumRange(2; 5); // return 3 + (-5) + 2 + (-1) = -1 numArray.sumRange(0; 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3 Constraints: 1 <= nums.length <= 104 -105 <= nums[i] <= 105 0 <= left <= right < nums.length At most 104 calls will be made to sumRange."
Uber,334,Increasing Triplet Subsequence,Med,"Array, Greedy",Given an integer array nums; return true if there exists a triple of indices (i; j; k) such that i < j < k and nums[i] < nums[j] < nums[k]. If no such indices exists; return false. Example 1: Input: nums = [1;2;3;4;5] Output: true Explanation: Any triplet where i < j < k is valid. Example 2: Input: nums = [5;4;3;2;1] Output: false Explanation: No triplet exists. Example 3: Input: nums = [2;1;5;0;4;6] Output: true Explanation: The triplet (3; 4; 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6. Constraints: 1 <= nums.length <= 5 * 105 -231 <= nums[i] <= 231 - 1 Follow up: Could you implement a solution that runs in O(n) time complexity and O(1) space complexity?
Uber,342,Power of Four,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of four. Otherwise; return false. An integer n is a power of four; if there exists an integer x such that n == 4x. Example 1: Input: n = 16 Output: true Example 2: Input: n = 5 Output: false Example 3: Input: n = 1 Output: true Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Uber,374,Guess Number Higher or Lower,Easy,"Binary Search, Interactive",We are playing the Guess Game. The game is as follows: I pick a number from 1 to n. You have to guess which number I picked. Every time you guess wrong; I will tell you whether the number I picked is higher or lower than your guess. You call a pre-defined API int guess(int num); which returns three possible results: -1: Your guess is higher than the number I picked (i.e. num > pick). 1: Your guess is lower than the number I picked (i.e. num < pick). 0: your guess is equal to the number I picked (i.e. num == pick). Return the number that I picked. Example 1: Input: n = 10; pick = 6 Output: 6 Example 2: Input: n = 1; pick = 1 Output: 1 Example 3: Input: n = 2; pick = 1 Output: 1 Constraints: 1 <= n <= 231 - 1 1 <= pick <= n
Uber,377,Combination Sum IV,Med,"Array, Dynamic Programming",Given an array of distinct integers nums and a target integer target; return the number of possible combinations that add up to target. The test cases are generated so that the answer can fit in a 32-bit integer. Example 1: Input: nums = [1;2;3]; target = 4 Output: 7 Explanation: The possible combination ways are: (1; 1; 1; 1) (1; 1; 2) (1; 2; 1) (1; 3) (2; 1; 1) (2; 2) (3; 1) Note that different sequences are counted as different combinations. Example 2: Input: nums = [9]; target = 3 Output: 0 Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 1000 All the elements of nums are unique. 1 <= target <= 1000 Follow up: What if negative numbers are allowed in the given array? How does it change the problem? What limitation we need to add to the question to allow negative numbers?
Uber,389,Find the Difference,Easy,"Hash Table, String, Bit Manipulation, Sorting","You are given two strings s and t. String t is generated by random shuffling string s and then add one more letter at a random position. Return the letter that was added to t. Example 1: Input: s = ""abcd""; t = ""abcde"" Output: ""e"" Explanation: 'e' is the letter that was added. Example 2: Input: s = """"; t = ""y"" Output: ""y"" Constraints: 0 <= s.length <= 1000 t.length == s.length + 1 s and t consist of lowercase English letters."
Uber,400,Nth Digit,Med,"Math, Binary Search",Given an integer n; return the nth digit of the infinite integer sequence [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; ...]. Example 1: Input: n = 3 Output: 3 Example 2: Input: n = 11 Output: 0 Explanation: The 11th digit of the sequence 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; ... is a 0; which is part of the number 10. Constraints: 1 <= n <= 231 - 1
Uber,401,Binary Watch,Easy,"Backtracking, Bit Manipulation","A binary watch has 4 LEDs on the top to represent the hours (0-11); and 6 LEDs on the bottom to represent the minutes (0-59). Each LED represents a zero or one; with the least significant bit on the right. For example; the below binary watch reads ""4:51"". Given an integer turnedOn which represents the number of LEDs that are currently on (ignoring the PM); return all possible times the watch could represent. You may return the answer in any order. The hour must not contain a leading zero. For example; ""01:00"" is not valid. It should be ""1:00"". The minute must consist of two digits and may contain a leading zero. For example; ""10:2"" is not valid. It should be ""10:02"". Example 1: Input: turnedOn = 1 Output: [""0:01"";""0:02"";""0:04"";""0:08"";""0:16"";""0:32"";""1:00"";""2:00"";""4:00"";""8:00""] Example 2: Input: turnedOn = 9 Output: [] Constraints: 0 <= turnedOn <= 10"
Uber,402,Remove K Digits,Med,"String, Stack, Greedy, Monotonic Stack","Given string num representing a non-negative integer num; and an integer k; return the smallest possible integer after removing k digits from num. Example 1: Input: num = ""1432219""; k = 3 Output: ""1219"" Explanation: Remove the three digits 4; 3; and 2 to form the new number 1219 which is the smallest. Example 2: Input: num = ""10200""; k = 1 Output: ""200"" Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes. Example 3: Input: num = ""10""; k = 2 Output: ""0"" Explanation: Remove all the digits from the number and it is left with nothing which is 0. Constraints: 1 <= k <= num.length <= 105 num consists of only digits. num does not have any leading zeros except for the zero itself."
Uber,403,Frog Jump,Hard,"Array, Dynamic Programming",A frog is crossing a river. The river is divided into some number of units; and at each unit; there may or may not exist a stone. The frog can jump on a stone; but it must not jump into the water. Given a list of stones positions (in units) in sorted ascending order; determine if the frog can cross the river by landing on the last stone. Initially; the frog is on the first stone and assumes the first jump must be 1 unit. If the frog's last jump was k units; its next jump must be either k - 1; k; or k + 1 units. The frog can only jump in the forward direction. Example 1: Input: stones = [0;1;3;5;6;8;12;17] Output: true Explanation: The frog can jump to the last stone by jumping 1 unit to the 2nd stone; then 2 units to the 3rd stone; then 2 units to the 4th stone; then 3 units to the 6th stone; 4 units to the 7th stone; and 5 units to the 8th stone. Example 2: Input: stones = [0;1;2;3;4;8;9;11] Output: false Explanation: There is no way to jump to the last stone as the gap between the 5th and 6th stone is too large. Constraints: 2 <= stones.length <= 2000 0 <= stones[i] <= 231 - 1 stones[0] == 0 stones is sorted in a strictly increasing order.
Uber,412,Fizz Buzz,Easy,"Math, String, Simulation","Given an integer n; return a string array answer (1-indexed) where: answer[i] == ""FizzBuzz"" if i is divisible by 3 and 5. answer[i] == ""Fizz"" if i is divisible by 3. answer[i] == ""Buzz"" if i is divisible by 5. answer[i] == i (as a string) if none of the above conditions are true. Example 1: Input: n = 3 Output: [""1"";""2"";""Fizz""] Example 2: Input: n = 5 Output: [""1"";""2"";""Fizz"";""4"";""Buzz""] Example 3: Input: n = 15 Output: [""1"";""2"";""Fizz"";""4"";""Buzz"";""Fizz"";""7"";""8"";""Fizz"";""Buzz"";""11"";""Fizz"";""13"";""14"";""FizzBuzz""] Constraints: 1 <= n <= 104"
Uber,448,Find All Numbers Disappeared in an Array,Easy,"Array, Hash Table",Given an array nums of n integers where nums[i] is in the range [1; n]; return an array of all the integers in the range [1; n] that do not appear in nums. Example 1: Input: nums = [4;3;2;7;8;2;3;1] Output: [5;6] Example 2: Input: nums = [1;1] Output: [2] Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i] <= n Follow up: Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.
Uber,459,Repeated Substring Pattern,Easy,"String, String Matching","Given a string s; check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. Example 1: Input: s = ""abab"" Output: true Explanation: It is the substring ""ab"" twice. Example 2: Input: s = ""aba"" Output: false Example 3: Input: s = ""abcabcabcabc"" Output: true Explanation: It is the substring ""abc"" four times or the substring ""abcabc"" twice. Constraints: 1 <= s.length <= 104 s consists of lowercase English letters."
Uber,473,Matchsticks to Square,Med,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",You are given an integer array matchsticks where matchsticks[i] is the length of the ith matchstick. You want to use all the matchsticks to make one square. You should not break any stick; but you can link them up; and each matchstick must be used exactly one time. Return true if you can make this square and false otherwise. Example 1: Input: matchsticks = [1;1;2;2;2] Output: true Explanation: You can form a square with length 2; one side of the square came two sticks with length 1. Example 2: Input: matchsticks = [3;3;3;3;4] Output: false Explanation: You cannot find a way to form a square with all the matchsticks. Constraints: 1 <= matchsticks.length <= 15 1 <= matchsticks[i] <= 108
Uber,474,Ones and Zeroes,Med,"Array, String, Dynamic Programming","You are given an array of binary strings strs and two integers m and n. Return the size of the largest subset of strs such that there are at most m 0's and n 1's in the subset. A set x is a subset of a set y if all elements of x are also elements of y. Example 1: Input: strs = [""10"";""0001"";""111001"";""1"";""0""]; m = 5; n = 3 Output: 4 Explanation: The largest subset with at most 5 0's and 3 1's is {""10""; ""0001""; ""1""; ""0""}; so the answer is 4. Other valid but smaller subsets include {""0001""; ""1""} and {""10""; ""1""; ""0""}. {""111001""} is an invalid subset because it contains 4 1's; greater than the maximum of 3. Example 2: Input: strs = [""10"";""0"";""1""]; m = 1; n = 1 Output: 2 Explanation: The largest subset is {""0""; ""1""}; so the answer is 2. Constraints: 1 <= strs.length <= 600 1 <= strs[i].length <= 100 strs[i] consists only of digits '0' and '1'. 1 <= m; n <= 100"
Uber,486,Predict the Winner,Med,"Array, Math, Dynamic Programming, Recursion, Game Theory",You are given an integer array nums. Two players are playing a game with this array: player 1 and player 2. Player 1 and player 2 take turns; with player 1 starting first. Both players start the game with a score of 0. At each turn; the player takes one of the numbers from either end of the array (i.e.; nums[0] or nums[nums.length - 1]) which reduces the size of the array by 1. The player adds the chosen number to their score. The game ends when there are no more elements in the array. Return true if Player 1 can win the game. If the scores of both players are equal; then player 1 is still the winner; and you should also return true. You may assume that both players are playing optimally. Example 1: Input: nums = [1;5;2] Output: false Explanation: Initially; player 1 can choose between 1 and 2. If he chooses 2 (or 1); then player 2 can choose from 1 (or 2) and 5. If player 2 chooses 5; then player 1 will be left with 1 (or 2). So; final score of player 1 is 1 + 2 = 3; and player 2 is 5. Hence; player 1 will never be the winner and you need to return false. Example 2: Input: nums = [1;5;233;7] Output: true Explanation: Player 1 first chooses 1. Then player 2 has to choose between 5 and 7. No matter which number player 2 choose; player 1 can choose 233. Finally; player 1 has more score (234) than player 2 (12); so you need to return True representing player1 can win. Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 107
Uber,496,Next Greater Element I,Easy,"Array, Hash Table, Stack, Monotonic Stack",The next greater element of some element x in an array is the first greater element that is to the right of x in the same array. You are given two distinct 0-indexed integer arrays nums1 and nums2; where nums1 is a subset of nums2. For each 0 <= i < nums1.length; find the index j such that nums1[i] == nums2[j] and determine the next greater element of nums2[j] in nums2. If there is no next greater element; then the answer for this query is -1. Return an array ans of length nums1.length such that ans[i] is the next greater element as described above. Example 1: Input: nums1 = [4;1;2]; nums2 = [1;3;4;2] Output: [-1;3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 4 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. - 1 is underlined in nums2 = [1;3;4;2]. The next greater element is 3. - 2 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. Example 2: Input: nums1 = [2;4]; nums2 = [1;2;3;4] Output: [3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 2 is underlined in nums2 = [1;2;3;4]. The next greater element is 3. - 4 is underlined in nums2 = [1;2;3;4]. There is no next greater element; so the answer is -1. Constraints: 1 <= nums1.length <= nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 104 All integers in nums1 and nums2 are unique. All the integers of nums1 also appear in nums2. Follow up: Could you find an O(nums1.length + nums2.length) solution?
Uber,501,Find Mode in Binary Search Tree,Easy,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree (BST) with duplicates; return all the mode(s) (i.e.; the most frequently occurred element) in it. If the tree has more than one mode; return them in any order. Assume a BST is defined as follows: The left subtree of a node contains only nodes with keys less than or equal to the node's key. The right subtree of a node contains only nodes with keys greater than or equal to the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [1;null;2;2] Output: [2] Example 2: Input: root = [0] Output: [0] Constraints: The number of nodes in the tree is in the range [1; 104]. -105 <= Node.val <= 105 Follow up: Could you do that without using any extra space? (Assume that the implicit stack space incurred due to recursion does not count).
Uber,523,Continuous Subarray Sum,Med,"Array, Hash Table, Math, Prefix Sum",Given an integer array nums and an integer k; return true if nums has a good subarray or false otherwise. A good subarray is a subarray where: its length is at least two; and the sum of the elements of the subarray is a multiple of k. Note that: A subarray is a contiguous part of the array. An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k. Example 1: Input: nums = [23;2;4;6;7]; k = 6 Output: true Explanation: [2; 4] is a continuous subarray of size 2 whose elements sum up to 6. Example 2: Input: nums = [23;2;6;4;7]; k = 6 Output: true Explanation: [23; 2; 6; 4; 7] is an continuous subarray of size 5 whose elements sum up to 42. 42 is a multiple of 6 because 42 = 7 * 6 and 7 is an integer. Example 3: Input: nums = [23;2;6;4;7]; k = 13 Output: false Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109 0 <= sum(nums[i]) <= 231 - 1 1 <= k <= 231 - 1
Uber,581,Shortest Unsorted Continuous Subarray,Med,"Array, Two Pointers, Stack, Greedy, Sorting, Monotonic Stack",Given an integer array nums; you need to find one continuous subarray such that if you only sort this subarray in non-decreasing order; then the whole array will be sorted in non-decreasing order. Return the shortest such subarray and output its length. Example 1: Input: nums = [2;6;4;8;10;9;15] Output: 5 Explanation: You need to sort [6; 4; 8; 10; 9] in ascending order to make the whole array sorted in ascending order. Example 2: Input: nums = [1;2;3;4] Output: 0 Example 3: Input: nums = [1] Output: 0 Constraints: 1 <= nums.length <= 104 -105 <= nums[i] <= 105 Follow up: Can you solve it in O(n) time complexity?
Uber,602,Friend Requests II: Who Has the Most Friends,Med,Database,Table: RequestAccepted +----------------+---------+ | Column Name | Type | +----------------+---------+ | requester_id | int | | accepter_id | int | | accept_date | date | +----------------+---------+ (requester_id; accepter_id) is the primary key (combination of columns with unique values) for this table. This table contains the ID of the user who sent the request; the ID of the user who received the request; and the date when the request was accepted. Write a solution to find the people who have the most friends and the most friends number. The test cases are generated so that only one person has the most friends. The result format is in the following example. Example 1: Input: RequestAccepted table: +--------------+-------------+-------------+ | requester_id | accepter_id | accept_date | +--------------+-------------+-------------+ | 1 | 2 | 2016/06/03 | | 1 | 3 | 2016/06/08 | | 2 | 3 | 2016/06/08 | | 3 | 4 | 2016/06/09 | +--------------+-------------+-------------+ Output: +----+-----+ | id | num | +----+-----+ | 3 | 3 | +----+-----+ Explanation: The person with id 3 is a friend of people 1; 2; and 4; so he has three friends in total; which is the most number than any others. Follow up: In the real world; multiple people could have the same most number of friends. Could you find all these people in this case?
Uber,607,Sales Person,Easy,Database,"Table: SalesPerson +-----------------+---------+ | Column Name | Type | +-----------------+---------+ | sales_id | int | | name | varchar | | salary | int | | commission_rate | int | | hire_date | date | +-----------------+---------+ sales_id is the primary key (column with unique values) for this table. Each row of this table indicates the name and the ID of a salesperson alongside their salary; commission rate; and hire date. Table: Company +-------------+---------+ | Column Name | Type | +-------------+---------+ | com_id | int | | name | varchar | | city | varchar | +-------------+---------+ com_id is the primary key (column with unique values) for this table. Each row of this table indicates the name and the ID of a company and the city in which the company is located. Table: Orders +-------------+------+ | Column Name | Type | +-------------+------+ | order_id | int | | order_date | date | | com_id | int | | sales_id | int | | amount | int | +-------------+------+ order_id is the primary key (column with unique values) for this table. com_id is a foreign key (reference column) to com_id from the Company table. sales_id is a foreign key (reference column) to sales_id from the SalesPerson table. Each row of this table contains information about one order. This includes the ID of the company; the ID of the salesperson; the date of the order; and the amount paid. Write a solution to find the names of all the salespersons who did not have any orders related to the company with the name ""RED"". Return the result table in any order. The result format is in the following example. Example 1: Input: SalesPerson table: +----------+------+--------+-----------------+------------+ | sales_id | name | salary | commission_rate | hire_date | +----------+------+--------+-----------------+------------+ | 1 | John | 100000 | 6 | 4/1/2006 | | 2 | Amy | 12000 | 5 | 5/1/2010 | | 3 | Mark | 65000 | 12 | 12/25/2008 | | 4 | Pam | 25000 | 25 | 1/1/2005 | | 5 | Alex | 5000 | 10 | 2/3/2007 | +----------+------+--------+-----------------+------------+ Company table: +--------+--------+----------+ | com_id | name | city | +--------+--------+----------+ | 1 | RED | Boston | | 2 | ORANGE | New York | | 3 | YELLOW | Boston | | 4 | GREEN | Austin | +--------+--------+----------+ Orders table: +----------+------------+--------+----------+--------+ | order_id | order_date | com_id | sales_id | amount | +----------+------------+--------+----------+--------+ | 1 | 1/1/2014 | 3 | 4 | 10000 | | 2 | 2/1/2014 | 4 | 5 | 5000 | | 3 | 3/1/2014 | 1 | 1 | 50000 | | 4 | 4/1/2014 | 1 | 4 | 25000 | +----------+------------+--------+----------+--------+ Output: +------+ | name | +------+ | Amy | | Mark | | Alex | +------+ Explanation: According to orders 3 and 4 in the Orders table; it is easy to tell that only salesperson John and Pam have sales to company RED; so we report all the other names in the table salesperson."
Uber,610,Triangle Judgement,Easy,Database,Table: Triangle +-------------+------+ | Column Name | Type | +-------------+------+ | x | int | | y | int | | z | int | +-------------+------+ In SQL; (x; y; z) is the primary key column for this table. Each row of this table contains the lengths of three line segments. Report for every three line segments whether they can form a triangle. Return the result table in any order. The result format is in the following example. Example 1: Input: Triangle table: +----+----+----+ | x | y | z | +----+----+----+ | 13 | 15 | 30 | | 10 | 20 | 15 | +----+----+----+ Output: +----+----+----+----------+ | x | y | z | triangle | +----+----+----+----------+ | 13 | 15 | 30 | No | | 10 | 20 | 15 | Yes | +----+----+----+----------+
Uber,611,Valid Triangle Number,Med,"Array, Two Pointers, Binary Search, Greedy, Sorting",Given an integer array nums; return the number of triplets chosen from the array that can make triangles if we take them as side lengths of a triangle. Example 1: Input: nums = [2;2;3;4] Output: 3 Explanation: Valid combinations are: 2;3;4 (using the first 2) 2;3;4 (using the second 2) 2;2;3 Example 2: Input: nums = [4;2;3;4] Output: 4 Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 1000
Uber,662,Maximum Width of Binary Tree,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the maximum width of the given tree. The maximum width of a tree is the maximum width among all levels. The width of one level is defined as the length between the end-nodes (the leftmost and rightmost non-null nodes); where the null nodes between the end-nodes that would be present in a complete binary tree extending down to that level are also counted into the length calculation. It is guaranteed that the answer will in the range of a 32-bit signed integer. Example 1: Input: root = [1;3;2;5;3;null;9] Output: 4 Explanation: The maximum width exists in the third level with length 4 (5;3;null;9). Example 2: Input: root = [1;3;2;5;null;null;9;6;null;7] Output: 7 Explanation: The maximum width exists in the fourth level with length 7 (6;null;null;null;null;null;7). Example 3: Input: root = [1;3;2;5] Output: 2 Explanation: The maximum width exists in the second level with length 2 (3;2). Constraints: The number of nodes in the tree is in the range [1; 3000]. -100 <= Node.val <= 100
Uber,680,Valid Palindrome II,Easy,"Two Pointers, String, Greedy","Given a string s; return true if the s can be palindrome after deleting at most one character from it. Example 1: Input: s = ""aba"" Output: true Example 2: Input: s = ""abca"" Output: true Explanation: You could delete the character 'c'. Example 3: Input: s = ""abc"" Output: false Constraints: 1 <= s.length <= 105 s consists of lowercase English letters."
Uber,697,Degree of an Array,Easy,"Array, Hash Table",Given a non-empty array of non-negative integers nums; the degree of this array is defined as the maximum frequency of any one of its elements. Your task is to find the smallest possible length of a (contiguous) subarray of nums; that has the same degree as nums. Example 1: Input: nums = [1;2;2;3;1] Output: 2 Explanation: The input array has a degree of 2 because both elements 1 and 2 appear twice. Of the subarrays that have the same degree: [1; 2; 2; 3; 1]; [1; 2; 2; 3]; [2; 2; 3; 1]; [1; 2; 2]; [2; 2; 3]; [2; 2] The shortest length is 2. So return 2. Example 2: Input: nums = [1;2;2;3;1;4;2] Output: 6 Explanation: The degree is 3 because the element 2 is repeated 3 times. So [2;2;3;1;4;2] is the shortest subarray; therefore returning 6. Constraints: nums.length will be between 1 and 50;000. nums[i] will be an integer between 0 and 49;999.
Uber,719,Find K-th Smallest Pair Distance,Hard,"Array, Two Pointers, Binary Search, Sorting",The distance of a pair of integers a and b is defined as the absolute difference between a and b. Given an integer array nums and an integer k; return the kth smallest distance among all the pairs nums[i] and nums[j] where 0 <= i < j < nums.length. Example 1: Input: nums = [1;3;1]; k = 1 Output: 0 Explanation: Here are all the pairs: (1;3) -> 2 (1;1) -> 0 (3;1) -> 2 Then the 1st smallest distance pair is (1;1); and its distance is 0. Example 2: Input: nums = [1;1;1]; k = 2 Output: 0 Example 3: Input: nums = [1;6;1]; k = 3 Output: 5 Constraints: n == nums.length 2 <= n <= 104 0 <= nums[i] <= 106 1 <= k <= n * (n - 1) / 2
Uber,746,Min Cost Climbing Stairs,Easy,"Array, Hash Table, String, Design, Trie","Design a special dictionary that searches the words in it by a prefix and a suffix. Implement the WordFilter class: WordFilter(string[] words) Initializes the object with the words in the dictionary. f(string pref; string suff) Returns the index of the word in the dictionary; which has the prefix pref and the suffix suff. If there is more than one valid index; return the largest of them. If there is no such word in the dictionary; return -1. Example 1: Input [""WordFilter""; ""f""] [[[""apple""]]; [""a""; ""e""]] Output [null; 0] Explanation WordFilter wordFilter = new WordFilter([""apple""]); wordFilter.f(""a""; ""e""); // return 0; because the word at index 0 has prefix = ""a"" and suffix = ""e"". Constraints: 1 <= words.length <= 104 1 <= words[i].length <= 7 1 <= pref.length; suff.length <= 7 words[i]; pref and suff consist of lowercase English letters only. At most 104 calls will be made to the function f."
Uber,773,Sliding Puzzle,Hard,"Divide and Conquer, Tree",A Binary Matrix is a matrix in which all the elements are either 0 or 1. Given quadTree1 and quadTree2. quadTree1 represents a n * n binary matrix and quadTree2 represents another n * n binary matrix. Return a Quad-Tree representing the n * n binary matrix which is the result of logical bitwise OR of the two binary matrixes represented by quadTree1 and quadTree2. Notice that you can assign the value of a node to True or False when isLeaf is False; and both are accepted in the answer. A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides; each node has two attributes: val: True if the node represents a grid of 1's or False if the node represents a grid of 0's. isLeaf: True if the node is leaf node on the tree or False if the node has the four children. class Node { public boolean val; public boolean isLeaf; public Node topLeft; public Node topRight; public Node bottomLeft; public Node bottomRight; } We can construct a Quad-Tree from a two-dimensional area using the following steps: If the current grid has the same value (i.e all 1's or all 0's) set isLeaf True and set val to the value of the grid and set the four children to Null and stop. If the current grid has different values; set isLeaf to False and set val to any value and divide the current grid into four sub-grids as shown in the photo. Recurse for each of the children with the proper sub-grid. If you want to know more about the Quad-Tree; you can refer to the wiki. Quad-Tree format: The input/output represents the serialized format of a Quad-Tree using level order traversal; where null signifies a path terminator where no node exists below. It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list [isLeaf; val]. If the value of isLeaf or val is True we represent it as 1 in the list [isLeaf; val] and if the value of isLeaf or val is False we represent it as 0. Example 1: Input: quadTree1 = [[0;1];[1;1];[1;1];[1;0];[1;0]] ; quadTree2 = [[0;1];[1;1];[0;1];[1;1];[1;0];null;null;null;null;[1;0];[1;0];[1;1];[1;1]] Output: [[0;0];[1;1];[1;1];[1;1];[1;0]] Explanation: quadTree1 and quadTree2 are shown above. You can see the binary matrix which is represented by each Quad-Tree. If we apply logical bitwise OR on the two binary matrices we get the binary matrix below which is represented by the result Quad-Tree. Notice that the binary matrices shown are only for illustration; you don't have to construct the binary matrix to get the result tree. Example 2: Input: quadTree1 = [[1;0]]; quadTree2 = [[1;0]] Output: [[1;0]] Explanation: Each tree represents a binary matrix of size 1*1. Each matrix contains only zero. The resulting matrix is of size 1*1 with also zero. Constraints: quadTree1 and quadTree2 are both valid Quad-Trees each representing a n * n grid. n == 2x where 0 <= x <= 9.
Uber,779,K-th Symbol in Grammar,Med,"Array, Stack, Greedy, Sorting, Monotonic Stack",You are given an integer array arr. We split arr into some number of chunks (i.e.; partitions); and individually sort each chunk. After concatenating them; the result should equal the sorted array. Return the largest number of chunks we can make to sort the array. Example 1: Input: arr = [5;4;3;2;1] Output: 1 Explanation: Splitting into two or more chunks will not return the required result. For example; splitting into [5; 4]; [3; 2; 1] will result in [4; 5; 1; 2; 3]; which isn't sorted. Example 2: Input: arr = [2;1;3;4;4] Output: 4 Explanation: We can split into two chunks; such as [2; 1]; [3; 4; 4]. However; splitting into [2; 1]; [3]; [4]; [4] is the highest number of chunks possible. Constraints: 1 <= arr.length <= 2000 0 <= arr[i] <= 108
Uber,801,Minimum Swaps To Make Sequences Increasing,Hard,"Depth-First Search, Breadth-First Search, Union Find, Graph",There is an undirected graph with n nodes; where each node is numbered between 0 and n - 1. You are given a 2D array graph; where graph[u] is an array of nodes that node u is adjacent to. More formally; for each v in graph[u]; there is an undirected edge between node u and node v. The graph has the following properties: There are no self-edges (graph[u] does not contain u). There are no parallel edges (graph[u] does not contain duplicate values). If v is in graph[u]; then u is in graph[v] (the graph is undirected). The graph may not be connected; meaning there may be two nodes u and v such that there is no path between them. A graph is bipartite if the nodes can be partitioned into two independent sets A and B such that every edge in the graph connects a node in set A and a node in set B. Return true if and only if it is bipartite. Example 1: Input: graph = [[1;2;3];[0;2];[0;1;3];[0;2]] Output: false Explanation: There is no way to partition the nodes into two independent sets such that every edge connects a node in one and a node in the other. Example 2: Input: graph = [[1;3];[0;2];[1;3];[0;2]] Output: true Explanation: We can partition the nodes into two sets: {0; 2} and {1; 3}. Constraints: graph.length == n 1 <= n <= 100 0 <= graph[u].length < n 0 <= graph[u][i] <= n - 1 graph[u] does not contain u. All the values of graph[u] are unique. If graph[u] contains v; then graph[v] contains u.
Uber,860,Lemonade Change,Easy,"Array, Linked List, Design, Queue","Design your implementation of the circular queue. The circular queue is a linear data structure in which the operations are performed based on FIFO (First In First Out) principle; and the last position is connected back to the first position to make a circle. It is also called ""Ring Buffer"". One of the benefits of the circular queue is that we can make use of the spaces in front of the queue. In a normal queue; once the queue becomes full; we cannot insert the next element even if there is a space in front of the queue. But using the circular queue; we can use the space to store new values. Implement the MyCircularQueue class: MyCircularQueue(k) Initializes the object with the size of the queue to be k. int Front() Gets the front item from the queue. If the queue is empty; return -1. int Rear() Gets the last item from the queue. If the queue is empty; return -1. boolean enQueue(int value) Inserts an element into the circular queue. Return true if the operation is successful. boolean deQueue() Deletes an element from the circular queue. Return true if the operation is successful. boolean isEmpty() Checks whether the circular queue is empty or not. boolean isFull() Checks whether the circular queue is full or not. You must solve the problem without using the built-in queue data structure in your programming language. Example 1: Input [""MyCircularQueue""; ""enQueue""; ""enQueue""; ""enQueue""; ""enQueue""; ""Rear""; ""isFull""; ""deQueue""; ""enQueue""; ""Rear""] [[3]; [1]; [2]; [3]; [4]; []; []; []; [4]; []] Output [null; true; true; true; false; 3; true; true; true; 4] Explanation MyCircularQueue myCircularQueue = new MyCircularQueue(3); myCircularQueue.enQueue(1); // return True myCircularQueue.enQueue(2); // return True myCircularQueue.enQueue(3); // return True myCircularQueue.enQueue(4); // return False myCircularQueue.Rear(); // return 3 myCircularQueue.isFull(); // return True myCircularQueue.deQueue(); // return True myCircularQueue.enQueue(4); // return True myCircularQueue.Rear(); // return 4 Constraints: 1 <= k <= 1000 0 <= value <= 1000 At most 3000 calls will be made to enQueue; deQueue; Front; Rear; isEmpty; and isFull."
Uber,933,Number of Recent Calls,Easy,"Stack, Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree; rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree; and every node has no left child and only one right child. Example 1: Input: root = [5;3;6;2;4;null;8;1;null;null;null;7;9] Output: [1;null;2;null;3;null;4;null;5;null;6;null;7;null;8;null;9] Example 2: Input: root = [5;1;7] Output: [1;null;5;null;7] Constraints: The number of nodes in the given tree will be in the range [1; 100]. 0 <= Node.val <= 1000
Uber,941,Valid Mountain Array,Easy,"Array, Two Pointers, Sorting",Given an integer array nums; move all the even integers at the beginning of the array followed by all the odd integers. Return any array that satisfies this condition. Example 1: Input: nums = [3;1;2;4] Output: [2;4;3;1] Explanation: The outputs [4;2;3;1]; [2;4;1;3]; and [4;2;1;3] would also be accepted. Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 5000 0 <= nums[i] <= 5000
Uber,995,Minimum Number of K Consecutive Bit Flips,Hard,,
Uber,1071,Greatest Common Divisor of Strings,Easy,"Array, Bit Manipulation",You are given a binary array nums (0-indexed). We define xi as the number whose binary representation is the subarray nums[0..i] (from most-significant-bit to least-significant-bit). For example; if nums = [1;0;1]; then x0 = 1; x1 = 2; and x2 = 5. Return an array of booleans answer where answer[i] is true if xi is divisible by 5. Example 1: Input: nums = [0;1;1] Output: [true;false;false] Explanation: The input numbers in binary are 0; 01; 011; which are 0; 1; and 3 in base-10. Only the first number is divisible by 5; so answer[0] is true. Example 2: Input: nums = [1;1;1] Output: [false;false;false] Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Uber,1068,Product Sales Analysis I,Easy,"Math, Dynamic Programming",
Uber,1291,Sequential Digits,Med,Database,
Uber,1130,Minimum Cost Tree From Leaf Values,Med,"Array, Dynamic Programming",You are given an array of integers stones where stones[i] is the weight of the ith stone. We are playing a game with the stones. On each turn; we choose any two stones and smash them together. Suppose the stones have weights x and y with x <= y. The result of this smash is: If x == y; both stones are destroyed; and If x != y; the stone of weight x is destroyed; and the stone of weight y has new weight y - x. At the end of the game; there is at most one stone left. Return the smallest possible weight of the left stone. If there are no stones left; return 0. Example 1: Input: stones = [2;7;4;1;8;1] Output: 1 Explanation: We can combine 2 and 4 to get 2; so the array converts to [2;7;1;8;1] then; we can combine 7 and 8 to get 1; so the array converts to [2;1;1;1] then; we can combine 2 and 1 to get 1; so the array converts to [1;1;1] then; we can combine 1 and 1 to get 0; so the array converts to [1]; then that's the optimal value. Example 2: Input: stones = [31;26;33;21;40] Output: 5 Constraints: 1 <= stones.length <= 30 1 <= stones[i] <= 100
Uber,1174,Immediate Food Delivery II,Med,Database,Table: Product +--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | | unit_price | int | +--------------+---------+ product_id is the primary key (column with unique values) of this table. Each row of this table indicates the name and the price of each product. Table: Sales +-------------+---------+ | Column Name | Type | +-------------+---------+ | seller_id | int | | product_id | int | | buyer_id | int | | sale_date | date | | quantity | int | | price | int | +-------------+---------+ This table can have duplicate rows. product_id is a foreign key (reference column) to the Product table. Each row of this table contains some information about one sale. Write a solution to report the products that were only sold in the first quarter of 2019. That is; between 2019-01-01 and 2019-03-31 inclusive. Return the result table in any order. The result format is in the following example. Example 1: Input: Product table: +------------+--------------+------------+ | product_id | product_name | unit_price | +------------+--------------+------------+ | 1 | S8 | 1000 | | 2 | G4 | 800 | | 3 | iPhone | 1400 | +------------+--------------+------------+ Sales table: +-----------+------------+----------+------------+----------+-------+ | seller_id | product_id | buyer_id | sale_date | quantity | price | +-----------+------------+----------+------------+----------+-------+ | 1 | 1 | 1 | 2019-01-21 | 2 | 2000 | | 1 | 2 | 2 | 2019-02-17 | 1 | 800 | | 2 | 2 | 3 | 2019-06-02 | 1 | 800 | | 3 | 3 | 4 | 2019-05-13 | 2 | 2800 | +-----------+------------+----------+------------+----------+-------+ Output: +-------------+--------------+ | product_id | product_name | +-------------+--------------+ | 1 | S8 | +-------------+--------------+ Explanation: The product with id 1 was only sold in the spring of 2019. The product with id 2 was sold in the spring of 2019 but was also sold after the spring of 2019. The product with id 3 was sold after spring 2019. We return only product 1 as it is the product that was only sold in the spring of 2019.
Uber,1235,Maximum Profit in Job Scheduling,Hard,,
Uber,1691,Maximum Height by Stacking Cuboids,Hard,"Array, Depth-First Search, Breadth-First Search, Matrix, Strongly Connected Component",You are given an m x n binary grid grid where 1 represents land and 0 represents water. An island is a maximal 4-directionally (horizontal or vertical) connected group of 1's. The grid is said to be connected if we have exactly one island; otherwise is said disconnected. In one day; we are allowed to change any single land cell (1) into a water cell (0). Return the minimum number of days to disconnect the grid. Example 1: Input: grid = [[0;1;1;0];[0;1;1;0];[0;0;0;0]] Output: 2 Explanation: We need at least 2 days to get a disconnected grid. Change land grid[1][1] and grid[0][2] to water and get 2 disconnected island. Example 2: Input: grid = [[1;1]] Output: 2 Explanation: Grid of full water is also disconnected ([[1;1]] -> [[0;0]]); 0 islands. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 30 grid[i][j] is either 0 or 1.
Uber,1280,Students and Examinations,Easy,"Array, Sliding Window",
Uber,1431,Kids With the Greatest Number of Candies,Easy,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",You are given a positive integer n representing the number of nodes of a Directed Acyclic Graph (DAG). The nodes are numbered from 0 to n - 1 (inclusive). You are also given a 2D integer array edges; where edges[i] = [fromi; toi] denotes that there is a unidirectional edge from fromi to toi in the graph. Return a list answer; where answer[i] is the list of ancestors of the ith node; sorted in ascending order. A node u is an ancestor of another node v if u can reach v via a set of edges. Example 1: Input: n = 8; edgeList = [[0;3];[0;4];[1;3];[2;4];[2;7];[3;5];[3;6];[3;7];[4;6]] Output: [[];[];[];[0;1];[0;2];[0;1;3];[0;1;2;3;4];[0;1;2;3]] Explanation: The above diagram represents the input graph. - Nodes 0; 1; and 2 do not have any ancestors. - Node 3 has two ancestors 0 and 1. - Node 4 has two ancestors 0 and 2. - Node 5 has three ancestors 0; 1; and 3. - Node 6 has five ancestors 0; 1; 2; 3; and 4. - Node 7 has four ancestors 0; 1; 2; and 3. Example 2: Input: n = 5; edgeList = [[0;1];[0;2];[0;3];[0;4];[1;2];[1;3];[1;4];[2;3];[2;4];[3;4]] Output: [[];[0];[0;1];[0;1;2];[0;1;2;3]] Explanation: The above diagram represents the input graph. - Node 0 does not have any ancestor. - Node 1 has one ancestor 0. - Node 2 has two ancestors 0 and 1. - Node 3 has three ancestors 0; 1; and 2. - Node 4 has four ancestors 0; 1; 2; and 3. Constraints: 1 <= n <= 1000 0 <= edges.length <= min(2000; n * (n - 1) / 2) edges[i].length == 2 0 <= fromi; toi <= n - 1 fromi != toi There are no duplicate edges. The graph is directed and acyclic.
Uber,1470,Shuffle the Array,Easy,"Hash Table, Binary Search, Design, Sorting, Ordered Set","A social media company is trying to monitor activity on their site by analyzing the number of tweets that occur in select periods of time. These periods can be partitioned into smaller time chunks based on a certain frequency (every minute; hour; or day). For example; the period [10; 10000] (in seconds) would be partitioned into the following time chunks with these frequencies: Every minute (60-second chunks): [10;69]; [70;129]; [130;189]; ...; [9970;10000] Every hour (3600-second chunks): [10;3609]; [3610;7209]; [7210;10000] Every day (86400-second chunks): [10;10000] Notice that the last chunk may be shorter than the specified frequency's chunk size and will always end with the end time of the period (10000 in the above example). Design and implement an API to help the company with their analysis. Implement the TweetCounts class: TweetCounts() Initializes the TweetCounts object. void recordTweet(String tweetName; int time) Stores the tweetName at the recorded time (in seconds). List<Integer> getTweetCountsPerFrequency(String freq; String tweetName; int startTime; int endTime) Returns a list of integers representing the number of tweets with tweetName in each time chunk for the given period of time [startTime; endTime] (in seconds) and frequency freq. freq is one of ""minute""; ""hour""; or ""day"" representing a frequency of every minute; hour; or day respectively. Example: Input [""TweetCounts"";""recordTweet"";""recordTweet"";""recordTweet"";""getTweetCountsPerFrequency"";""getTweetCountsPerFrequency"";""recordTweet"";""getTweetCountsPerFrequency""] [[];[""tweet3"";0];[""tweet3"";60];[""tweet3"";10];[""minute"";""tweet3"";0;59];[""minute"";""tweet3"";0;60];[""tweet3"";120];[""hour"";""tweet3"";0;210]] Output [null;null;null;null;[2];[2;1];null;[4]] Explanation TweetCounts tweetCounts = new TweetCounts(); tweetCounts.recordTweet(""tweet3""; 0); // New tweet ""tweet3"" at time 0 tweetCounts.recordTweet(""tweet3""; 60); // New tweet ""tweet3"" at time 60 tweetCounts.recordTweet(""tweet3""; 10); // New tweet ""tweet3"" at time 10 tweetCounts.getTweetCountsPerFrequency(""minute""; ""tweet3""; 0; 59); // return [2]; chunk [0;59] had 2 tweets tweetCounts.getTweetCountsPerFrequency(""minute""; ""tweet3""; 0; 60); // return [2;1]; chunk [0;59] had 2 tweets; chunk [60;60] had 1 tweet tweetCounts.recordTweet(""tweet3""; 120); // New tweet ""tweet3"" at time 120 tweetCounts.getTweetCountsPerFrequency(""hour""; ""tweet3""; 0; 210); // return [4]; chunk [0;210] had 4 tweets Constraints: 0 <= time; startTime; endTime <= 109 0 <= endTime - startTime <= 104 There will be at most 104 calls in total to recordTweet and getTweetCountsPerFrequency."
Uber,1480,Running Sum of 1d Array,Easy,Database,"Table: Movies +---------------+---------+ | Column Name | Type | +---------------+---------+ | movie_id | int | | title | varchar | +---------------+---------+ movie_id is the primary key (column with unique values) for this table. title is the name of the movie. Table: Users +---------------+---------+ | Column Name | Type | +---------------+---------+ | user_id | int | | name | varchar | +---------------+---------+ user_id is the primary key (column with unique values) for this table. The column 'name' has unique values. Table: MovieRating +---------------+---------+ | Column Name | Type | +---------------+---------+ | movie_id | int | | user_id | int | | rating | int | | created_at | date | +---------------+---------+ (movie_id; user_id) is the primary key (column with unique values) for this table. This table contains the rating of a movie by a user in their review. created_at is the user's review date. Write a solution to: Find the name of the user who has rated the greatest number of movies. In case of a tie; return the lexicographically smaller user name. Find the movie name with the highest average rating in February 2020. In case of a tie; return the lexicographically smaller movie name. The result format is in the following example. Example 1: Input: Movies table: +-------------+--------------+ | movie_id | title | +-------------+--------------+ | 1 | Avengers | | 2 | Frozen 2 | | 3 | Joker | +-------------+--------------+ Users table: +-------------+--------------+ | user_id | name | +-------------+--------------+ | 1 | Daniel | | 2 | Monica | | 3 | Maria | | 4 | James | +-------------+--------------+ MovieRating table: +-------------+--------------+--------------+-------------+ | movie_id | user_id | rating | created_at | +-------------+--------------+--------------+-------------+ | 1 | 1 | 3 | 2020-01-12 | | 1 | 2 | 4 | 2020-02-11 | | 1 | 3 | 2 | 2020-02-12 | | 1 | 4 | 1 | 2020-01-01 | | 2 | 1 | 5 | 2020-02-17 | | 2 | 2 | 2 | 2020-02-01 | | 2 | 3 | 2 | 2020-03-01 | | 3 | 1 | 3 | 2020-02-22 | | 3 | 2 | 4 | 2020-02-25 | +-------------+--------------+--------------+-------------+ Output: +--------------+ | results | +--------------+ | Daniel | | Frozen 2 | +--------------+ Explanation: Daniel and Monica have rated 3 movies (""Avengers""; ""Frozen 2"" and ""Joker"") but Daniel is smaller lexicographically. Frozen 2 and Joker have a rating average of 3.5 in February but Frozen 2 is smaller lexicographically."
Uber,1515,Best Position for a Service Centre,Hard,"Math, Greedy",Given an integer k; return the minimum number of Fibonacci numbers whose sum is equal to k. The same Fibonacci number can be used multiple times. The Fibonacci numbers are defined as: F1 = 1 F2 = 1 Fn = Fn-1 + Fn-2 for n > 2. It is guaranteed that for the given constraints we can always find such Fibonacci numbers that sum up to k. Example 1: Input: k = 7 Output: 2 Explanation: The Fibonacci numbers are: 1; 1; 2; 3; 5; 8; 13; ... For k = 7 we can use 2 + 5 = 7. Example 2: Input: k = 10 Output: 2 Explanation: For k = 10 we can use 2 + 8 = 10. Example 3: Input: k = 19 Output: 3 Explanation: For k = 19 we can use 1 + 5 + 13 = 19. Constraints: 1 <= k <= 109
Uber,1547,Minimum Cost to Cut a Stick,Hard,"Array, Hash Table, String","You are given the array paths; where paths[i] = [cityAi; cityBi] means there exists a direct path going from cityAi to cityBi. Return the destination city; that is; the city without any path outgoing to another city. It is guaranteed that the graph of paths forms a line without any loop; therefore; there will be exactly one destination city. Example 1: Input: paths = [[""London"";""New York""];[""New York"";""Lima""];[""Lima"";""Sao Paulo""]] Output: ""Sao Paulo"" Explanation: Starting at ""London"" city you will reach ""Sao Paulo"" city which is the destination city. Your trip consist of: ""London"" -> ""New York"" -> ""Lima"" -> ""Sao Paulo"". Example 2: Input: paths = [[""B"";""C""];[""D"";""B""];[""C"";""A""]] Output: ""A"" Explanation: All possible trips are: ""D"" -> ""B"" -> ""C"" -> ""A"". ""B"" -> ""C"" -> ""A"". ""C"" -> ""A"". ""A"". Clearly the destination city is ""A"". Example 3: Input: paths = [[""A"";""Z""]] Output: ""Z"" Constraints: 1 <= paths.length <= 100 paths[i].length == 2 1 <= cityAi.length; cityBi.length <= 10 cityAi != cityBi All strings consist of lowercase and uppercase English letters and the space character."
Uber,1572,Matrix Diagonal Sum,Easy,"Array, Design, Matrix","Implement the class SubrectangleQueries which receives a rows x cols rectangle as a matrix of integers in the constructor and supports two methods: 1. updateSubrectangle(int row1; int col1; int row2; int col2; int newValue) Updates all values with newValue in the subrectangle whose upper left coordinate is (row1;col1) and bottom right coordinate is (row2;col2). 2. getValue(int row; int col) Returns the current value of the coordinate (row;col) from the rectangle. Example 1: Input [""SubrectangleQueries"";""getValue"";""updateSubrectangle"";""getValue"";""getValue"";""updateSubrectangle"";""getValue"";""getValue""] [[[[1;2;1];[4;3;4];[3;2;1];[1;1;1]]];[0;2];[0;0;3;2;5];[0;2];[3;1];[3;0;3;2;10];[3;1];[0;2]] Output [null;1;null;5;5;null;10;5] Explanation SubrectangleQueries subrectangleQueries = new SubrectangleQueries([[1;2;1];[4;3;4];[3;2;1];[1;1;1]]); // The initial rectangle (4x3) looks like: // 1 2 1 // 4 3 4 // 3 2 1 // 1 1 1 subrectangleQueries.getValue(0; 2); // return 1 subrectangleQueries.updateSubrectangle(0; 0; 3; 2; 5); // After this update the rectangle looks like: // 5 5 5 // 5 5 5 // 5 5 5 // 5 5 5 subrectangleQueries.getValue(0; 2); // return 5 subrectangleQueries.getValue(3; 1); // return 5 subrectangleQueries.updateSubrectangle(3; 0; 3; 2; 10); // After this update the rectangle looks like: // 5 5 5 // 5 5 5 // 5 5 5 // 10 10 10 subrectangleQueries.getValue(3; 1); // return 10 subrectangleQueries.getValue(0; 2); // return 5 Example 2: Input [""SubrectangleQueries"";""getValue"";""updateSubrectangle"";""getValue"";""getValue"";""updateSubrectangle"";""getValue""] [[[[1;1;1];[2;2;2];[3;3;3]]];[0;0];[0;0;2;2;100];[0;0];[2;2];[1;1;2;2;20];[2;2]] Output [null;1;null;100;100;null;20] Explanation SubrectangleQueries subrectangleQueries = new SubrectangleQueries([[1;1;1];[2;2;2];[3;3;3]]); subrectangleQueries.getValue(0; 0); // return 1 subrectangleQueries.updateSubrectangle(0; 0; 2; 2; 100); subrectangleQueries.getValue(0; 0); // return 100 subrectangleQueries.getValue(2; 2); // return 100 subrectangleQueries.updateSubrectangle(1; 1; 2; 2; 20); subrectangleQueries.getValue(2; 2); // return 20 Constraints: There will be at most 500 operations considering both methods: updateSubrectangle and getValue. 1 <= rows; cols <= 100 rows == rectangle.length cols == rectangle[i].length 0 <= row1 <= row2 < rows 0 <= col1 <= col2 < cols 1 <= newValue; rectangle[i][j] <= 10^9 0 <= row < rows 0 <= col < cols"
Uber,1581,Customer Who Visited but Did Not Make Any Transactions,Easy,"Array, Two Pointers, Sorting",Given an array of integers arr and an integer k. A value arr[i] is said to be stronger than a value arr[j] if |arr[i] - m| > |arr[j] - m| where m is the median of the array. If |arr[i] - m| == |arr[j] - m|; then arr[i] is said to be stronger than arr[j] if arr[i] > arr[j]. Return a list of the strongest k values in the array. return the answer in any arbitrary order. Median is the middle value in an ordered integer list. More formally; if the length of the list is n; the median is the element in position ((n - 1) / 2) in the sorted list (0-indexed). For arr = [6; -3; 7; 2; 11]; n = 5 and the median is obtained by sorting the array arr = [-3; 2; 6; 7; 11] and the median is arr[m] where m = ((5 - 1) / 2) = 2. The median is 6. For arr = [-7; 22; 17; 3]; n = 4 and the median is obtained by sorting the array arr = [-7; 3; 17; 22] and the median is arr[m] where m = ((4 - 1) / 2) = 1. The median is 3. Example 1: Input: arr = [1;2;3;4;5]; k = 2 Output: [5;1] Explanation: Median is 3; the elements of the array sorted by the strongest are [5;1;4;2;3]. The strongest 2 elements are [5; 1]. [1; 5] is also accepted answer. Please note that although |5 - 3| == |1 - 3| but 5 is stronger than 1 because 5 > 1. Example 2: Input: arr = [1;1;3;5;5]; k = 2 Output: [5;5] Explanation: Median is 3; the elements of the array sorted by the strongest are [5;5;1;1;3]. The strongest 2 elements are [5; 5]. Example 3: Input: arr = [6;7;11;7;6;8]; k = 5 Output: [11;8;6;6;7] Explanation: Median is 7; the elements of the array sorted by the strongest are [11;8;6;6;7;7]. Any permutation of [11;8;6;6;7] is accepted. Constraints: 1 <= arr.length <= 105 -105 <= arr[i] <= 105 1 <= k <= arr.length
Uber,1684,Count the Number of Consistent Strings,Easy,"Array, Hash Table, Binary Search, Simulation","Given an array arr that represents a permutation of numbers from 1 to n. You have a binary string of size n that initially has all its bits set to zero. At each step i (assuming both the binary string and arr are 1-indexed) from 1 to n; the bit at position arr[i] is set to 1. You are also given an integer m. Find the latest step at which there exists a group of ones of length m. A group of ones is a contiguous substring of 1's such that it cannot be extended in either direction. Return the latest step at which there exists a group of ones of length exactly m. If no such group exists; return -1. Example 1: Input: arr = [3;5;1;2;4]; m = 1 Output: 4 Explanation: Step 1: ""00100""; groups: [""1""] Step 2: ""00101""; groups: [""1""; ""1""] Step 3: ""10101""; groups: [""1""; ""1""; ""1""] Step 4: ""11101""; groups: [""111""; ""1""] Step 5: ""11111""; groups: [""11111""] The latest step at which there exists a group of size 1 is step 4. Example 2: Input: arr = [3;1;5;4;2]; m = 2 Output: -1 Explanation: Step 1: ""00100""; groups: [""1""] Step 2: ""10100""; groups: [""1""; ""1""] Step 3: ""10101""; groups: [""1""; ""1""; ""1""] Step 4: ""10111""; groups: [""1""; ""111""] Step 5: ""11111""; groups: [""11111""] No group of size 2 exists during any step. Constraints: n == arr.length 1 <= m <= n <= 105 1 <= arr[i] <= n All integers in arr are distinct."
Uber,1672,Richest Customer Wealth,Easy,"Array, Binary Search, Interactive",
Uber,1878,Get Biggest Three Rhombus Sums in a Grid,Med,Array,Given an array nums; return true if the array was originally sorted in non-decreasing order; then rotated some number of positions (including zero). Otherwise; return false. There may be duplicates in the original array. Note: An array A rotated by x positions results in an array B of the same length such that A[i] == B[(i+x) % A.length]; where % is the modulo operation. Example 1: Input: nums = [3;4;5;1;2] Output: true Explanation: [1;2;3;4;5] is the original sorted array. You can rotate the array by x = 3 positions to begin on the the element of value 3: [3;4;5;1;2]. Example 2: Input: nums = [2;1;3;4] Output: false Explanation: There is no sorted array once rotated that can make nums. Example 3: Input: nums = [1;2;3] Output: true Explanation: [1;2;3] is the original sorted array. You can rotate the array by x = 0 positions (i.e. no rotation) to make nums. Constraints: 1 <= nums.length <= 100 1 <= nums[i] <= 100
Uber,1921,Eliminate Maximum Number of Monsters,Med,,
Uber,2008,Maximum Earnings From Taxi,Med,"Math, String, Dynamic Programming, Stack","You are given a valid boolean expression as a string expression consisting of the characters '1';'0';'&' (bitwise AND operator);'|' (bitwise OR operator);'('; and ')'. For example; ""()1|1"" and ""(1)&()"" are not valid while ""1""; ""(((1))|(0))""; and ""1|(0&(1))"" are valid expressions. Return the minimum cost to change the final value of the expression. For example; if expression = ""1|1|(0&0)&1""; its value is 1|1|(0&0)&1 = 1|1|0&1 = 1|0&1 = 1&1 = 1. We want to apply operations so that the new expression evaluates to 0. The cost of changing the final value of an expression is the number of operations performed on the expression. The types of operations are described as follows: Turn a '1' into a '0'. Turn a '0' into a '1'. Turn a '&' into a '|'. Turn a '|' into a '&'. Note: '&' does not take precedence over '|' in the order of calculation. Evaluate parentheses first; then in left-to-right order. Example 1: Input: expression = ""1&(0|1)"" Output: 1 Explanation: We can turn ""1&(0|1)"" into ""1&(0&1)"" by changing the '|' to a '&' using 1 operation. The new expression evaluates to 0. Example 2: Input: expression = ""(0&0)&(0&0&0)"" Output: 3 Explanation: We can turn ""(0&0)&(0&0&0)"" into ""(0|1)|(0&0&0)"" using 3 operations. The new expression evaluates to 1. Example 3: Input: expression = ""(0|(1|0&1))"" Output: 1 Explanation: We can turn ""(0|(1|0&1))"" into ""(0|(0|0&1))"" using 1 operation. The new expression evaluates to 0. Constraints: 1 <= expression.length <= 105 expression only contains '1';'0';'&';'|';'('; and ')' All parentheses are properly matched. There will be no empty parentheses (i.e: ""()"" is not a substring of expression)."
Uber,2163,Minimum Difference in Sums After Removal of Elements,Hard,"Array, Hash Table, String, Counting","A distinct string is a string that is present only once in an array. Given an array of strings arr; and an integer k; return the kth distinct string present in arr. If there are fewer than k distinct strings; return an empty string """". Note that the strings are considered in the order in which they appear in the array. Example 1: Input: arr = [""d"";""b"";""c"";""b"";""c"";""a""]; k = 2 Output: ""a"" Explanation: The only distinct strings in arr are ""d"" and ""a"". ""d"" appears 1st; so it is the 1st distinct string. ""a"" appears 2nd; so it is the 2nd distinct string. Since k == 2; ""a"" is returned. Example 2: Input: arr = [""aaa"";""aa"";""a""]; k = 1 Output: ""aaa"" Explanation: All strings in arr are distinct; so the 1st string ""aaa"" is returned. Example 3: Input: arr = [""a"";""b"";""a""]; k = 3 Output: """" Explanation: The only distinct string is ""b"". Since there are fewer than 3 distinct strings; we return an empty string """". Constraints: 1 <= k <= arr.length <= 1000 1 <= arr[i].length <= 5 arr[i] consists of lowercase English letters."
Uber,2149,Rearrange Array Elements by Sign,Med,"Math, String, Greedy, Game Theory","There are n pieces arranged in a line; and each piece is colored either by 'A' or by 'B'. You are given a string colors of length n where colors[i] is the color of the ith piece. Alice and Bob are playing a game where they take alternating turns removing pieces from the line. In this game; Alice moves first. Alice is only allowed to remove a piece colored 'A' if both its neighbors are also colored 'A'. She is not allowed to remove pieces that are colored 'B'. Bob is only allowed to remove a piece colored 'B' if both its neighbors are also colored 'B'. He is not allowed to remove pieces that are colored 'A'. Alice and Bob cannot remove pieces from the edge of the line. If a player cannot make a move on their turn; that player loses and the other player wins. Assuming Alice and Bob play optimally; return true if Alice wins; or return false if Bob wins. Example 1: Input: colors = ""AAABABB"" Output: true Explanation: AAABABB -> AABABB Alice moves first. She removes the second 'A' from the left since that is the only 'A' whose neighbors are both 'A'. Now it's Bob's turn. Bob cannot make a move on his turn since there are no 'B's whose neighbors are both 'B'. Thus; Alice wins; so return true. Example 2: Input: colors = ""AA"" Output: false Explanation: Alice has her turn first. There are only two 'A's and both are on the edge of the line; so she cannot move on her turn. Thus; Bob wins; so return false. Example 3: Input: colors = ""ABBBBBBBAAA"" Output: false Explanation: ABBBBBBBAAA -> ABBBBBBBAA Alice moves first. Her only option is to remove the second to last 'A' from the right. ABBBBBBBAA -> ABBBBBBAA Next is Bob's turn. He has many options for which 'B' piece to remove. He can pick any. On Alice's second turn; she has no more pieces that she can remove. Thus; Bob wins; so return false. Constraints: 1 <= colors.length <= 105 colors consists of only the letters 'A' and 'B'"
Uber,2158,Amount of New Area Painted Each Day,Hard,Database,
Uber,2365,Task Scheduler II,Med,String,"Given a string s and a character letter; return the percentage of characters in s that equal letter rounded down to the nearest whole percent. Example 1: Input: s = ""foobar""; letter = ""o"" Output: 33 Explanation: The percentage of characters in s that equal the letter 'o' is 2 / 6 * 100% = 33% when rounded down; so we return 33. Example 2: Input: s = ""jjjj""; letter = ""k"" Output: 0 Explanation: The percentage of characters in s that equal the letter 'k' is 0%; so we return 0. Constraints: 1 <= s.length <= 100 s consists of lowercase English letters. letter is a lowercase English letter."
Uber,2418,Sort the People,Easy,"Array, Binary Search, Greedy, Sorting, Heap (Priority Queue)",You are given two positive 0-indexed integer arrays nums1 and nums2; both of length n. The sum of squared difference of arrays nums1 and nums2 is defined as the sum of (nums1[i] - nums2[i])2 for each 0 <= i < n. You are also given two positive integers k1 and k2. You can modify any of the elements of nums1 by +1 or -1 at most k1 times. Similarly; you can modify any of the elements of nums2 by +1 or -1 at most k2 times. Return the minimum sum of squared difference after modifying array nums1 at most k1 times and modifying array nums2 at most k2 times. Note: You are allowed to modify the array elements to become negative integers. Example 1: Input: nums1 = [1;2;3;4]; nums2 = [2;10;20;19]; k1 = 0; k2 = 0 Output: 579 Explanation: The elements in nums1 and nums2 cannot be modified because k1 = 0 and k2 = 0. The sum of square difference will be: (1 - 2)2 + (2 - 10)2 + (3 - 20)2 + (4 - 19)2 = 579. Example 2: Input: nums1 = [1;4;10;12]; nums2 = [5;8;6;9]; k1 = 1; k2 = 1 Output: 43 Explanation: One way to obtain the minimum sum of square difference is: - Increase nums1[0] once. - Increase nums2[2] once. The minimum of the sum of square difference will be: (2 - 5)2 + (4 - 8)2 + (10 - 7)2 + (12 - 9)2 = 43. Note that; there are other ways to obtain the minimum of the sum of square difference; but there is no way to obtain a sum smaller than 43. Constraints: n == nums1.length == nums2.length 1 <= n <= 105 0 <= nums1[i]; nums2[i] <= 105 0 <= k1; k2 <= 109
Uber,2483,Minimum Penalty for a Shop,Med,"Array, Hash Table, Simulation",You are given a 0-indexed array of positive integers tasks; representing tasks that need to be completed in order; where tasks[i] represents the type of the ith task. You are also given a positive integer space; which represents the minimum number of days that must pass after the completion of a task before another task of the same type can be performed. Each day; until all tasks have been completed; you must either: Complete the next task from tasks; or Take a break. Return the minimum number of days needed to complete all tasks. Example 1: Input: tasks = [1;2;1;2;3;1]; space = 3 Output: 9 Explanation: One way to complete all tasks in 9 days is as follows: Day 1: Complete the 0th task. Day 2: Complete the 1st task. Day 3: Take a break. Day 4: Take a break. Day 5: Complete the 2nd task. Day 6: Complete the 3rd task. Day 7: Take a break. Day 8: Complete the 4th task. Day 9: Complete the 5th task. It can be shown that the tasks cannot be completed in less than 9 days. Example 2: Input: tasks = [5;8;8;5]; space = 2 Output: 6 Explanation: One way to complete all tasks in 6 days is as follows: Day 1: Complete the 0th task. Day 2: Complete the 1st task. Day 3: Take a break. Day 4: Take a break. Day 5: Complete the 2nd task. Day 6: Complete the 3rd task. It can be shown that the tasks cannot be completed in less than 6 days. Constraints: 1 <= tasks.length <= 105 1 <= tasks[i] <= 109 1 <= space <= tasks.length
Uber,2551,Put Marbles in Bags,Hard,"Array, Two Pointers, Simulation",You are given a 0-indexed array nums of size n consisting of non-negative integers. You need to apply n - 1 operations to this array where; in the ith operation (0-indexed); you will apply the following on the ith element of nums: If nums[i] == nums[i + 1]; then multiply nums[i] by 2 and set nums[i + 1] to 0. Otherwise; you skip this operation. After performing all the operations; shift all the 0's to the end of the array. For example; the array [1;0;2;0;0;1] after shifting all its 0's to the end; is [1;2;1;0;0;0]. Return the resulting array. Note that the operations are applied sequentially; not all at once. Example 1: Input: nums = [1;2;2;1;1;0] Output: [1;4;2;0;0;0] Explanation: We do the following operations: - i = 0: nums[0] and nums[1] are not equal; so we skip this operation. - i = 1: nums[1] and nums[2] are equal; we multiply nums[1] by 2 and change nums[2] to 0. The array becomes [1;4;0;1;1;0]. - i = 2: nums[2] and nums[3] are not equal; so we skip this operation. - i = 3: nums[3] and nums[4] are equal; we multiply nums[3] by 2 and change nums[4] to 0. The array becomes [1;4;0;2;0;0]. - i = 4: nums[4] and nums[5] are equal; we multiply nums[4] by 2 and change nums[5] to 0. The array becomes [1;4;0;2;0;0]. After that; we shift the 0's to the end; which gives the array [1;4;2;0;0;0]. Example 2: Input: nums = [0;1] Output: [1;0] Explanation: No operation can be applied; we just shift the 0 to the end. Constraints: 2 <= nums.length <= 2000 0 <= nums[i] <= 1000
Uber,2610,Convert an Array Into a 2D Array With Conditions,Med,"Math, Number Theory",Given two positive integers left and right; find the two integers num1 and num2 such that: left <= num1 < num2 <= right . num1 and num2 are both prime numbers. num2 - num1 is the minimum amongst all other pairs satisfying the above conditions. Return the positive integer array ans = [num1; num2]. If there are multiple pairs satisfying these conditions; return the one with the minimum num1 value or [-1; -1] if such numbers do not exist. A number greater than 1 is called prime if it is only divisible by 1 and itself. Example 1: Input: left = 10; right = 19 Output: [11;13] Explanation: The prime numbers between 10 and 19 are 11; 13; 17; and 19. The closest gap between any pair is 2; which can be achieved by [11;13] or [17;19]. Since 11 is smaller than 17; we return the first pair. Example 2: Input: left = 4; right = 6 Output: [-1;-1] Explanation: There exists only one prime number in the given range; so the conditions cannot be satisfied. Constraints: 1 <= left <= right <= 106
Uber,2741,Special Permutations,Med,,Given an array of functions [f1; f2; f3; ...; fn]; return a new function fn that is the function composition of the array of functions. The function composition of [f(x); g(x); h(x)] is fn(x) = f(g(h(x))). The function composition of an empty list of functions is the identity function f(x) = x. You may assume each function in the array accepts one integer as input and returns one integer as output. Example 1: Input: functions = [x => x + 1; x => x * x; x => 2 * x]; x = 4 Output: 65 Explanation: Evaluating from right to left ... Starting with x = 4. 2 * (4) = 8 (8) * (8) = 64 (64) + 1 = 65 Example 2: Input: functions = [x => 10 * x; x => 10 * x; x => 10 * x]; x = 1 Output: 1000 Explanation: Evaluating from right to left ... 10 * (1) = 10 10 * (10) = 100 10 * (100) = 1000 Example 3: Input: functions = []; x = 42 Output: 42 Explanation: The composition of zero functions is the identity function Constraints: -1000 <= x <= 1000 0 <= functions.length <= 1000 all functions accept and return a single integer
Uber,2817,Minimum Absolute Difference Between Elements With Constraint,Med,"String, Dynamic Programming, Greedy","You are given a 0-indexed binary string s of length n on which you can apply two types of operations: Choose an index i and invert all characters from index 0 to index i (both inclusive); with a cost of i + 1 Choose an index i and invert all characters from index i to index n - 1 (both inclusive); with a cost of n - i Return the minimum cost to make all characters of the string equal. Invert a character means if its value is '0' it becomes '1' and vice-versa. Example 1: Input: s = ""0011"" Output: 2 Explanation: Apply the second operation with i = 2 to obtain s = ""0000"" for a cost of 2. It can be shown that 2 is the minimum cost to make all characters equal. Example 2: Input: s = ""010101"" Output: 9 Explanation: Apply the first operation with i = 2 to obtain s = ""101101"" for a cost of 3. Apply the first operation with i = 1 to obtain s = ""011101"" for a cost of 2. Apply the first operation with i = 0 to obtain s = ""111101"" for a cost of 1. Apply the second operation with i = 4 to obtain s = ""111110"" for a cost of 2. Apply the second operation with i = 5 to obtain s = ""111111"" for a cost of 1. The total cost to make all characters equal is 9. It can be shown that 9 is the minimum cost to make all characters equal. Constraints: 1 <= s.length == n <= 105 s[i] is either '0' or '1'"
Uber,2877,Create a DataFrame from List,Easy,"String, Greedy, Enumeration","Given three strings a; b; and c; your task is to find a string that has the minimum length and contains all three strings as substrings. If there are multiple such strings; return the lexicographically smallest one. Return a string denoting the answer to the problem. Notes A string a is lexicographically smaller than a string b (of the same length) if in the first position where a and b differ; string a has a letter that appears earlier in the alphabet than the corresponding letter in b. A substring is a contiguous sequence of characters within a string. Example 1: Input: a = ""abc""; b = ""bca""; c = ""aaa"" Output: ""aaabca"" Explanation: We show that ""aaabca"" contains all the given strings: a = ans[2...4]; b = ans[3..5]; c = ans[0..2]. It can be shown that the length of the resulting string would be at least 6 and ""aaabca"" is the lexicographically smallest one. Example 2: Input: a = ""ab""; b = ""ba""; c = ""aba"" Output: ""aba"" Explanation: We show that the string ""aba"" contains all the given strings: a = ans[0..1]; b = ans[1..2]; c = ans[0..2]. Since the length of c is 3; the length of the resulting string would be at least 3. It can be shown that ""aba"" is the lexicographically smallest one. Constraints: 1 <= a.length; b.length; c.length <= 100 a; b; c consist only of lowercase English letters."
Uber,43,Multiply Strings,Med,"Math, String, Simulation","Given two non-negative integers num1 and num2 represented as strings; return the product of num1 and num2; also represented as a string. Note: You must not use any built-in BigInteger library or convert the inputs to integer directly. Example 1: Input: num1 = ""2""; num2 = ""3"" Output: ""6"" Example 2: Input: num1 = ""123""; num2 = ""456"" Output: ""56088"" Constraints: 1 <= num1.length; num2.length <= 200 num1 and num2 consist of digits only. Both num1 and num2 do not contain any leading zero; except the number 0 itself."
Uber,60,Permutation Sequence,Hard,"Math, Recursion","The set [1; 2; 3; ...; n] contains a total of n! unique permutations. By listing and labeling all of the permutations in order; we get the following sequence for n = 3: ""123"" ""132"" ""213"" ""231"" ""312"" ""321"" Given n and k; return the kth permutation sequence. Example 1: Input: n = 3; k = 3 Output: ""213"" Example 2: Input: n = 4; k = 9 Output: ""2314"" Example 3: Input: n = 3; k = 1 Output: ""123"" Constraints: 1 <= n <= 9 1 <= k <= n!"
Uber,71,Simplify Path,Med,"String, Stack","You are given an absolute path for a Unix-style file system; which always begins with a slash '/'. Your task is to transform this absolute path into its simplified canonical path. The rules of a Unix-style file system are as follows: A single period '.' represents the current directory. A double period '..' represents the previous/parent directory. Multiple consecutive slashes such as '//' and '///' are treated as a single slash '/'. Any sequence of periods that does not match the rules above should be treated as a valid directory or file name. For example; '...' and '....' are valid directory or file names. The simplified canonical path should follow these rules: The path must start with a single slash '/'. Directories within the path must be separated by exactly one slash '/'. The path must not end with a slash '/'; unless it is the root directory. The path must not have any single or double periods ('.' and '..') used to denote current or parent directories. Return the simplified canonical path. Example 1: Input: path = ""/home/"" Output: ""/home"" Explanation: The trailing slash should be removed. Example 2: Input: path = ""/home//foo/"" Output: ""/home/foo"" Explanation: Multiple consecutive slashes are replaced by a single one. Example 3: Input: path = ""/home/user/Documents/../Pictures"" Output: ""/home/user/Pictures"" Explanation: A double period "".."" refers to the directory up a level (the parent directory). Example 4: Input: path = ""/../"" Output: ""/"" Explanation: Going one level up from the root directory is not possible. Example 5: Input: path = ""/.../a/../b/c/../d/./"" Output: ""/.../b/d"" Explanation: ""..."" is a valid name for a directory in this problem. Constraints: 1 <= path.length <= 3000 path consists of English letters; digits; period '.'; slash '/' or '_'. path is a valid absolute Unix path."
Uber,77,Combinations,Med,Backtracking,Given two integers n and k; return all possible combinations of k numbers chosen from the range [1; n]. You may return the answer in any order. Example 1: Input: n = 4; k = 2 Output: [[1;2];[1;3];[1;4];[2;3];[2;4];[3;4]] Explanation: There are 4 choose 2 = 6 total combinations. Note that combinations are unordered; i.e.; [1;2] and [2;1] are considered to be the same combination. Example 2: Input: n = 1; k = 1 Output: [[1]] Explanation: There is 1 choose 1 = 1 total combination. Constraints: 1 <= n <= 20 1 <= k <= n
Uber,80,Remove Duplicates from Sorted Array II,Med,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same. Since it is impossible to change the length of the array in some languages; you must instead have the result be placed in the first part of the array nums. More formally; if there are k elements after removing the duplicates; then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements. Return k after placing the final result in the first k slots of nums. Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;1;2;2;3] Output: 5; nums = [1;1;2;2;3;_] Explanation: Your function should return k = 5; with the first five elements of nums being 1; 1; 2; 2 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;1;2;3;3] Output: 7; nums = [0;0;1;1;2;3;3;_;_] Explanation: Your function should return k = 7; with the first seven elements of nums being 0; 0; 1; 1; 2; 3 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -104 <= nums[i] <= 104 nums is sorted in non-decreasing order.
Uber,85,Maximal Rectangle,Hard,"Array, Dynamic Programming, Stack, Matrix, Monotonic Stack","Given a rows x cols binary matrix filled with 0's and 1's; find the largest rectangle containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 6 Explanation: The maximal rectangle is shown in the above picture. Example 2: Input: matrix = [[""0""]] Output: 0 Example 3: Input: matrix = [[""1""]] Output: 1 Constraints: rows == matrix.length cols == matrix[i].length 1 <= row; cols <= 200 matrix[i][j] is '0' or '1'."
Uber,90,Subsets II,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums that may contain duplicates; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;2] Output: [[];[1];[1;2];[1;2;2];[2];[2;2]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10
Uber,101,Symmetric Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; check whether it is a mirror of itself (i.e.; symmetric around its center). Example 1: Input: root = [1;2;2;3;4;4;3] Output: true Example 2: Input: root = [1;2;2;null;3;null;3] Output: false Constraints: The number of nodes in the tree is in the range [1; 1000]. -100 <= Node.val <= 100 Follow up: Could you solve it both recursively and iteratively?
Uber,103,Binary Tree Zigzag Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the zigzag level order traversal of its nodes' values. (i.e.; from left to right; then right to left for the next level and alternate between). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[20;9];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100
Uber,105,Construct Binary Tree from Preorder and Inorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree; construct and return the binary tree. Example 1: Input: preorder = [3;9;20;15;7]; inorder = [9;3;15;20;7] Output: [3;9;20;null;null;15;7] Example 2: Input: preorder = [-1]; inorder = [-1] Output: [-1] Constraints: 1 <= preorder.length <= 3000 inorder.length == preorder.length -3000 <= preorder[i]; inorder[i] <= 3000 preorder and inorder consist of unique values. Each value of inorder also appears in preorder. preorder is guaranteed to be the preorder traversal of the tree. inorder is guaranteed to be the inorder traversal of the tree.
Uber,109,Convert Sorted List to Binary Search Tree,Med,"Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree",Given the head of a singly linked list where elements are sorted in ascending order; convert it to a height-balanced binary search tree. Example 1: Input: head = [-10;-3;0;5;9] Output: [0;-3;9;-10;null;5] Explanation: One possible answer is [0;-3;9;-10;null;5]; which represents the shown height balanced BST. Example 2: Input: head = [] Output: [] Constraints: The number of nodes in head is in the range [0; 2 * 104]. -105 <= Node.val <= 105
Uber,120,Triangle,Med,"Array, Dynamic Programming",Given a triangle array; return the minimum path sum from top to bottom. For each step; you may move to an adjacent number of the row below. More formally; if you are on index i on the current row; you may move to either index i or index i + 1 on the next row. Example 1: Input: triangle = [[2];[3;4];[6;5;7];[4;1;8;3]] Output: 11 Explanation: The triangle looks like: 2 3 4 6 5 7 4 1 8 3 The minimum path sum from top to bottom is 2 + 3 + 5 + 1 = 11 (underlined above). Example 2: Input: triangle = [[-10]] Output: -10 Constraints: 1 <= triangle.length <= 200 triangle[0].length == 1 triangle[i].length == triangle[i - 1].length + 1 -104 <= triangle[i][j] <= 104 Follow up: Could you do this using only O(n) extra space; where n is the total number of rows in the triangle?
Uber,126,Word Ladder II,Hard,"Hash Table, String, Backtracking, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return all the shortest transformation sequences from beginWord to endWord; or an empty list if no such sequence exists. Each sequence should be returned as a list of the words [beginWord; s1; s2; ...; sk]. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: [[""hit"";""hot"";""dot"";""dog"";""cog""];[""hit"";""hot"";""lot"";""log"";""cog""]] Explanation: There are 2 shortest transformation sequences: ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> ""cog"" ""hit"" -> ""hot"" -> ""lot"" -> ""log"" -> ""cog"" Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: [] Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 5 endWord.length == beginWord.length 1 <= wordList.length <= 500 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique. The sum of all shortest transformation sequences does not exceed 105."
Uber,149,Max Points on a Line,Hard,"Array, Hash Table, Math, Geometry",Given an array of points where points[i] = [xi; yi] represents a point on the X-Y plane; return the maximum number of points that lie on the same straight line. Example 1: Input: points = [[1;1];[2;2];[3;3]] Output: 3 Example 2: Input: points = [[1;1];[3;2];[5;3];[4;1];[2;3];[1;4]] Output: 4 Constraints: 1 <= points.length <= 300 points[i].length == 2 -104 <= xi; yi <= 104 All the points are unique.
Uber,150,Evaluate Reverse Polish Notation,Med,"Array, Math, Stack","You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression. Return an integer that represents the value of the expression. Note that: The valid operators are '+'; '-'; '*'; and '/'. Each operand may be an integer or another expression. The division between two integers always truncates toward zero. There will not be any division by zero. The input represents a valid arithmetic expression in a reverse polish notation. The answer and all the intermediate calculations can be represented in a 32-bit integer. Example 1: Input: tokens = [""2"";""1"";""+"";""3"";""*""] Output: 9 Explanation: ((2 + 1) * 3) = 9 Example 2: Input: tokens = [""4"";""13"";""5"";""/"";""+""] Output: 6 Explanation: (4 + (13 / 5)) = 6 Example 3: Input: tokens = [""10"";""6"";""9"";""3"";""+"";""-11"";""*"";""/"";""*"";""17"";""+"";""5"";""+""] Output: 22 Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 = ((10 * (6 / (12 * -11))) + 17) + 5 = ((10 * (6 / -132)) + 17) + 5 = ((10 * 0) + 17) + 5 = (0 + 17) + 5 = 17 + 5 = 22 Constraints: 1 <= tokens.length <= 104 tokens[i] is either an operator: ""+""; ""-""; ""*""; or ""/""; or an integer in the range [-200; 200]."
Uber,168,Excel Sheet Column Title,Easy,"Math, String","Given an integer columnNumber; return its corresponding column title as it appears in an Excel sheet. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: Input: columnNumber = 1 Output: ""A"" Example 2: Input: columnNumber = 28 Output: ""AB"" Example 3: Input: columnNumber = 701 Output: ""ZY"" Constraints: 1 <= columnNumber <= 231 - 1"
Uber,173,Binary Search Tree Iterator,Med,"Stack, Tree, Design, Binary Search Tree, Binary Tree, Iterator","Implement the BSTIterator class that represents an iterator over the in-order traversal of a binary search tree (BST): BSTIterator(TreeNode root) Initializes an object of the BSTIterator class. The root of the BST is given as part of the constructor. The pointer should be initialized to a non-existent number smaller than any element in the BST. boolean hasNext() Returns true if there exists a number in the traversal to the right of the pointer; otherwise returns false. int next() Moves the pointer to the right; then returns the number at the pointer. Notice that by initializing the pointer to a non-existent smallest number; the first call to next() will return the smallest element in the BST. You may assume that next() calls will always be valid. That is; there will be at least a next number in the in-order traversal when next() is called. Example 1: Input [""BSTIterator""; ""next""; ""next""; ""hasNext""; ""next""; ""hasNext""; ""next""; ""hasNext""; ""next""; ""hasNext""] [[[7; 3; 15; null; null; 9; 20]]; []; []; []; []; []; []; []; []; []] Output [null; 3; 7; true; 9; true; 15; true; 20; false] Explanation BSTIterator bSTIterator = new BSTIterator([7; 3; 15; null; null; 9; 20]); bSTIterator.next(); // return 3 bSTIterator.next(); // return 7 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 9 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 15 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 20 bSTIterator.hasNext(); // return False Constraints: The number of nodes in the tree is in the range [1; 105]. 0 <= Node.val <= 106 At most 105 calls will be made to hasNext; and next. Follow up: Could you implement next() and hasNext() to run in average O(1) time and use O(h) memory; where h is the height of the tree?"
Uber,175,Combine Two Tables,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | personId | int | | lastName | varchar | | firstName | varchar | +-------------+---------+ personId is the primary key (column with unique values) for this table. This table contains information about the ID of some persons and their first and last names. Table: Address +-------------+---------+ | Column Name | Type | +-------------+---------+ | addressId | int | | personId | int | | city | varchar | | state | varchar | +-------------+---------+ addressId is the primary key (column with unique values) for this table. Each row of this table contains information about the city and state of one person with ID = PersonId. Write a solution to report the first name; last name; city; and state of each person in the Person table. If the address of a personId is not present in the Address table; report null instead. Return the result table in any order. The result format is in the following example. Example 1: Input: Person table: +----------+----------+-----------+ | personId | lastName | firstName | +----------+----------+-----------+ | 1 | Wang | Allen | | 2 | Alice | Bob | +----------+----------+-----------+ Address table: +-----------+----------+---------------+------------+ | addressId | personId | city | state | +-----------+----------+---------------+------------+ | 1 | 2 | New York City | New York | | 2 | 3 | Leetcode | California | +-----------+----------+---------------+------------+ Output: +-----------+----------+---------------+----------+ | firstName | lastName | city | state | +-----------+----------+---------------+----------+ | Allen | Wang | Null | Null | | Bob | Alice | New York City | New York | +-----------+----------+---------------+----------+ Explanation: There is no address in the address table for the personId = 1 so we return null in their city and state. addressId = 1 contains information about the address of personId = 2.
Uber,178,Rank Scores,Med,Database,Table: Scores +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | score | decimal | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table contains the score of a game. Score is a floating point value with two decimal places. Write a solution to find the rank of the scores. The ranking should be calculated according to the following rules: The scores should be ranked from the highest to the lowest. If there is a tie between two scores; both should have the same ranking. After a tie; the next ranking number should be the next consecutive integer value. In other words; there should be no holes between ranks. Return the result table ordered by score in descending order. The result format is in the following example. Example 1: Input: Scores table: +----+-------+ | id | score | +----+-------+ | 1 | 3.50 | | 2 | 3.65 | | 3 | 4.00 | | 4 | 3.85 | | 5 | 4.00 | | 6 | 3.65 | +----+-------+ Output: +-------+------+ | score | rank | +-------+------+ | 4.00 | 1 | | 4.00 | 1 | | 3.85 | 2 | | 3.65 | 3 | | 3.65 | 3 | | 3.50 | 4 | +-------+------+
Uber,182,Duplicate Emails,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | email | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table contains an email. The emails will not contain uppercase letters. Write a solution to report all the duplicate emails. Note that it's guaranteed that the email field is not NULL. Return the result table in any order. The result format is in the following example. Example 1: Input: Person table: +----+---------+ | id | email | +----+---------+ | 1 | a@b.com | | 2 | c@d.com | | 3 | a@b.com | +----+---------+ Output: +---------+ | Email | +---------+ | a@b.com | +---------+ Explanation: a@b.com is repeated two times.
Uber,185,Department Top Three Salaries,Hard,Database,Table: Employee +--------------+---------+ | Column Name | Type | +--------------+---------+ | id | int | | name | varchar | | salary | int | | departmentId | int | +--------------+---------+ id is the primary key (column with unique values) for this table. departmentId is a foreign key (reference column) of the ID from the Department table. Each row of this table indicates the ID; name; and salary of an employee. It also contains the ID of their department. Table: Department +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID of a department and its name. A company's executives are interested in seeing who earns the most money in each of the company's departments. A high earner in a department is an employee who has a salary in the top three unique salaries for that department. Write a solution to find the employees who are high earners in each of the departments. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +----+-------+--------+--------------+ | id | name | salary | departmentId | +----+-------+--------+--------------+ | 1 | Joe | 85000 | 1 | | 2 | Henry | 80000 | 2 | | 3 | Sam | 60000 | 2 | | 4 | Max | 90000 | 1 | | 5 | Janet | 69000 | 1 | | 6 | Randy | 85000 | 1 | | 7 | Will | 70000 | 1 | +----+-------+--------+--------------+ Department table: +----+-------+ | id | name | +----+-------+ | 1 | IT | | 2 | Sales | +----+-------+ Output: +------------+----------+--------+ | Department | Employee | Salary | +------------+----------+--------+ | IT | Max | 90000 | | IT | Joe | 85000 | | IT | Randy | 85000 | | IT | Will | 70000 | | Sales | Henry | 80000 | | Sales | Sam | 60000 | +------------+----------+--------+ Explanation: In the IT department: - Max earns the highest unique salary - Both Randy and Joe earn the second-highest unique salary - Will earns the third-highest unique salary In the Sales department: - Henry earns the highest salary - Sam earns the second-highest salary - There is no third-highest salary as there are only two employees
Uber,196,Delete Duplicate Emails,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | email | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table contains an email. The emails will not contain uppercase letters. Write a solution to delete all duplicate emails; keeping only one unique email with the smallest id. For SQL users; please note that you are supposed to write a DELETE statement and not a SELECT one. For Pandas users; please note that you are supposed to modify Person in place. After running your script; the answer shown is the Person table. The driver will first compile and run your piece of code and then show the Person table. The final order of the Person table does not matter. The result format is in the following example. Example 1: Input: Person table: +----+------------------+ | id | email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | | 3 | john@example.com | +----+------------------+ Output: +----+------------------+ | id | email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | +----+------------------+ Explanation: john@example.com is repeated two times. We keep the row with the smallest Id = 1.
Uber,201,Bitwise AND of Numbers Range,Med,Bit Manipulation,Given two integers left and right that represent the range [left; right]; return the bitwise AND of all numbers in this range; inclusive. Example 1: Input: left = 5; right = 7 Output: 4 Example 2: Input: left = 0; right = 0 Output: 0 Example 3: Input: left = 1; right = 2147483647 Output: 0 Constraints: 0 <= left <= right <= 231 - 1
Uber,203,Remove Linked List Elements,Easy,"Linked List, Recursion",Given the head of a linked list and an integer val; remove all the nodes of the linked list that has Node.val == val; and return the new head. Example 1: Input: head = [1;2;6;3;4;5;6]; val = 6 Output: [1;2;3;4;5] Example 2: Input: head = []; val = 1 Output: [] Example 3: Input: head = [7;7;7;7]; val = 7 Output: [] Constraints: The number of nodes in the list is in the range [0; 104]. 1 <= Node.val <= 50 0 <= val <= 50
Uber,220,Contains Duplicate III,Hard,"Array, Sliding Window, Sorting, Bucket Sort, Ordered Set",You are given an integer array nums and two integers indexDiff and valueDiff. Find a pair of indices (i; j) such that: i != j; abs(i - j) <= indexDiff. abs(nums[i] - nums[j]) <= valueDiff; and Return true if such pair exists or false otherwise. Example 1: Input: nums = [1;2;3;1]; indexDiff = 3; valueDiff = 0 Output: true Explanation: We can choose (i; j) = (0; 3). We satisfy the three conditions: i != j --> 0 != 3 abs(i - j) <= indexDiff --> abs(0 - 3) <= 3 abs(nums[i] - nums[j]) <= valueDiff --> abs(1 - 1) <= 0 Example 2: Input: nums = [1;5;9;1;5;9]; indexDiff = 2; valueDiff = 3 Output: false Explanation: After trying all the possible pairs (i; j); we cannot satisfy the three conditions; so we return false. Constraints: 2 <= nums.length <= 105 -109 <= nums[i] <= 109 1 <= indexDiff <= nums.length 0 <= valueDiff <= 109
Uber,226,Invert Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; invert the tree; and return its root. Example 1: Input: root = [4;2;7;1;3;6;9] Output: [4;7;2;9;6;3;1] Example 2: Input: root = [2;1;3] Output: [2;3;1] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Uber,228,Summary Ranges,Easy,Array,"You are given a sorted unique integer array nums. A range [a;b] is the set of all integers from a to b (inclusive). Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is; each element of nums is covered by exactly one of the ranges; and there is no integer x such that x is in one of the ranges but not in nums. Each range [a;b] in the list should be output as: ""a->b"" if a != b ""a"" if a == b Example 1: Input: nums = [0;1;2;4;5;7] Output: [""0->2"";""4->5"";""7""] Explanation: The ranges are: [0;2] --> ""0->2"" [4;5] --> ""4->5"" [7;7] --> ""7"" Example 2: Input: nums = [0;2;3;4;6;8;9] Output: [""0"";""2->4"";""6"";""8->9""] Explanation: The ranges are: [0;0] --> ""0"" [2;4] --> ""2->4"" [6;6] --> ""6"" [8;9] --> ""8->9"" Constraints: 0 <= nums.length <= 20 -231 <= nums[i] <= 231 - 1 All the values of nums are unique. nums is sorted in ascending order."
Uber,229,Majority Element II,Med,"Array, Hash Table, Sorting, Counting",Given an integer array of size n; find all elements that appear more than ⌊ n/3 ⌋ times. Example 1: Input: nums = [3;2;3] Output: [3] Example 2: Input: nums = [1] Output: [1] Example 3: Input: nums = [1;2] Output: [1;2] Constraints: 1 <= nums.length <= 5 * 104 -109 <= nums[i] <= 109 Follow up: Could you solve the problem in linear time and in O(1) space?
Uber,233,Number of Digit One,Hard,"Math, Dynamic Programming, Recursion",Given an integer n; count the total number of digit 1 appearing in all non-negative integers less than or equal to n. Example 1: Input: n = 13 Output: 6 Example 2: Input: n = 0 Output: 0 Constraints: 0 <= n <= 109
Uber,247,Strobogrammatic Number II,Med,"Array, String, Recursion",
Uber,252,Meeting Rooms,Easy,"Array, Sorting",
Uber,256,Paint House,Med,"Array, Dynamic Programming",
Uber,258,Add Digits,Easy,"Math, Simulation, Number Theory",Given an integer num; repeatedly add all its digits until the result has only one digit; and return it. Example 1: Input: num = 38 Output: 2 Explanation: The process is 38 --> 3 + 8 --> 11 11 --> 1 + 1 --> 2 Since 2 has only one digit; return it. Example 2: Input: num = 0 Output: 0 Constraints: 0 <= num <= 231 - 1 Follow up: Could you do it without any loop/recursion in O(1) runtime?
Uber,264,Ugly Number II,Med,"Hash Table, Math, Dynamic Programming, Heap (Priority Queue)",An ugly number is a positive integer whose prime factors are limited to 2; 3; and 5. Given an integer n; return the nth ugly number. Example 1: Input: n = 10 Output: 12 Explanation: [1; 2; 3; 4; 5; 6; 8; 9; 10; 12] is the sequence of the first 10 ugly numbers. Example 2: Input: n = 1 Output: 1 Explanation: 1 has no prime factors; therefore all of its prime factors are limited to 2; 3; and 5. Constraints: 1 <= n <= 1690
Uber,315,Count of Smaller Numbers After Self,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums; return an integer array counts where counts[i] is the number of smaller elements to the right of nums[i]. Example 1: Input: nums = [5;2;6;1] Output: [2;1;1;0] Explanation: To the right of 5 there are 2 smaller elements (2 and 1). To the right of 2 there is only 1 smaller element (1). To the right of 6 there is 1 smaller element (1). To the right of 1 there is 0 smaller element. Example 2: Input: nums = [-1] Output: [0] Example 3: Input: nums = [-1;-1] Output: [0;0] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104
Uber,319,Bulb Switcher,Med,"Math, Brainteaser",There are n bulbs that are initially off. You first turn on all the bulbs; then you turn off every second bulb. On the third round; you toggle every third bulb (turning on if it's off or turning off if it's on). For the ith round; you toggle every i bulb. For the nth round; you only toggle the last bulb. Return the number of bulbs that are on after n rounds. Example 1: Input: n = 3 Output: 1 Explanation: At first; the three bulbs are [off; off; off]. After the first round; the three bulbs are [on; on; on]. After the second round; the three bulbs are [on; off; on]. After the third round; the three bulbs are [on; off; off]. So you should return 1 because there is only one bulb is on. Example 2: Input: n = 0 Output: 0 Example 3: Input: n = 1 Output: 1 Constraints: 0 <= n <= 109
Uber,344,Reverse String,Easy,"Two Pointers, String","Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory. Example 1: Input: s = [""h"";""e"";""l"";""l"";""o""] Output: [""o"";""l"";""l"";""e"";""h""] Example 2: Input: s = [""H"";""a"";""n"";""n"";""a"";""h""] Output: [""h"";""a"";""n"";""n"";""a"";""H""] Constraints: 1 <= s.length <= 105 s[i] is a printable ascii character."
Uber,354,Russian Doll Envelopes,Hard,"Array, Binary Search, Dynamic Programming, Sorting",You are given a 2D array of integers envelopes where envelopes[i] = [wi; hi] represents the width and the height of an envelope. One envelope can fit into another if and only if both the width and height of one envelope are greater than the other envelope's width and height. Return the maximum number of envelopes you can Russian doll (i.e.; put one inside the other). Note: You cannot rotate an envelope. Example 1: Input: envelopes = [[5;4];[6;4];[6;7];[2;3]] Output: 3 Explanation: The maximum number of envelopes you can Russian doll is 3 ([2;3] => [5;4] => [6;7]). Example 2: Input: envelopes = [[1;1];[1;1];[1;1]] Output: 1 Constraints: 1 <= envelopes.length <= 105 envelopes[i].length == 2 1 <= wi; hi <= 105
Uber,378,Kth Smallest Element in a Sorted Matrix,Med,"Array, Binary Search, Sorting, Heap (Priority Queue), Matrix",Given an n x n matrix where each of the rows and columns is sorted in ascending order; return the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order; not the kth distinct element. You must find a solution with a memory complexity better than O(n2). Example 1: Input: matrix = [[1;5;9];[10;11;13];[12;13;15]]; k = 8 Output: 13 Explanation: The elements in the matrix are [1;5;9;10;11;12;13;13;15]; and the 8th smallest number is 13 Example 2: Input: matrix = [[-5]]; k = 1 Output: -5 Constraints: n == matrix.length == matrix[i].length 1 <= n <= 300 -109 <= matrix[i][j] <= 109 All the rows and columns of matrix are guaranteed to be sorted in non-decreasing order. 1 <= k <= n2 Follow up: Could you solve the problem with a constant memory (i.e.; O(1) memory complexity)? Could you solve the problem in O(n) time complexity? The solution may be too advanced for an interview but you may find reading this paper fun.
Uber,386,Lexicographical Numbers,Med,"Depth-First Search, Trie",Given an integer n; return all the numbers in the range [1; n] sorted in lexicographical order. You must write an algorithm that runs in O(n) time and uses O(1) extra space. Example 1: Input: n = 13 Output: [1;10;11;12;13;2;3;4;5;6;7;8;9] Example 2: Input: n = 2 Output: [1;2] Constraints: 1 <= n <= 5 * 104
Uber,390,Elimination Game,Med,"Math, Recursion",You have a list arr of all integers in the range [1; n] sorted in a strictly increasing order. Apply the following algorithm on arr: Starting from left to right; remove the first number and every other number afterward until you reach the end of the list. Repeat the previous step again; but this time from right to left; remove the rightmost number and every other number from the remaining numbers. Keep repeating the steps again; alternating left to right and right to left; until a single number remains. Given the integer n; return the last number that remains in arr. Example 1: Input: n = 9 Output: 6 Explanation: arr = [1; 2; 3; 4; 5; 6; 7; 8; 9] arr = [2; 4; 6; 8] arr = [2; 6] arr = [6] Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 109
Uber,404,Sum of Left Leaves,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the sum of all left leaves. A leaf is a node with no children. A left leaf is a leaf that is the left child of another node. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 24 Explanation: There are two left leaves in the binary tree; with values 9 and 15 respectively. Example 2: Input: root = [1] Output: 0 Constraints: The number of nodes in the tree is in the range [1; 1000]. -1000 <= Node.val <= 1000
Uber,414,Third Maximum Number,Easy,"Array, Sorting",Given an integer array nums; return the third distinct maximum number in this array. If the third maximum does not exist; return the maximum number. Example 1: Input: nums = [3;2;1] Output: 1 Explanation: The first distinct maximum is 3. The second distinct maximum is 2. The third distinct maximum is 1. Example 2: Input: nums = [1;2] Output: 2 Explanation: The first distinct maximum is 2. The second distinct maximum is 1. The third distinct maximum does not exist; so the maximum (2) is returned instead. Example 3: Input: nums = [2;2;3;1] Output: 1 Explanation: The first distinct maximum is 3. The second distinct maximum is 2 (both 2's are counted together since they have the same value). The third distinct maximum is 1. Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Can you find an O(n) solution?
Uber,445,Add Two Numbers II,Med,"Linked List, Math, Stack",You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [7;2;4;3]; l2 = [5;6;4] Output: [7;8;0;7] Example 2: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [8;0;7] Example 3: Input: l1 = [0]; l2 = [0] Output: [0] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros. Follow up: Could you solve it without reversing the input lists?
Uber,456,132 Pattern,Med,"Array, Binary Search, Stack, Monotonic Stack, Ordered Set",Given an array of n integers nums; a 132 pattern is a subsequence of three integers nums[i]; nums[j] and nums[k] such that i < j < k and nums[i] < nums[k] < nums[j]. Return true if there is a 132 pattern in nums; otherwise; return false. Example 1: Input: nums = [1;2;3;4] Output: false Explanation: There is no 132 pattern in the sequence. Example 2: Input: nums = [3;1;4;2] Output: true Explanation: There is a 132 pattern in the sequence: [1; 4; 2]. Example 3: Input: nums = [-1;3;2;0] Output: true Explanation: There are three 132 patterns in the sequence: [-1; 3; 2]; [-1; 3; 0] and [-1; 2; 0]. Constraints: n == nums.length 1 <= n <= 2 * 105 -109 <= nums[i] <= 109
Uber,464,Can I Win,Med,"Math, Dynamic Programming, Bit Manipulation, Memoization, Game Theory, Bitmask","In the ""100 game"" two players take turns adding; to a running total; any integer from 1 to 10. The player who first causes the running total to reach or exceed 100 wins. What if we change the game so that players cannot re-use integers? For example; two players might take turns drawing from a common pool of numbers from 1 to 15 without replacement until they reach a total >= 100. Given two integers maxChoosableInteger and desiredTotal; return true if the first player to move can force a win; otherwise; return false. Assume both players play optimally. Example 1: Input: maxChoosableInteger = 10; desiredTotal = 11 Output: false Explanation: No matter which integer the first player choose; the first player will lose. The first player can choose an integer from 1 up to 10. If the first player choose 1; the second player can only choose integers from 2 up to 10. The second player will win by choosing 10 and get a total = 11; which is >= desiredTotal. Same with other integers chosen by the first player; the second player will always win. Example 2: Input: maxChoosableInteger = 10; desiredTotal = 0 Output: true Example 3: Input: maxChoosableInteger = 10; desiredTotal = 1 Output: true Constraints: 1 <= maxChoosableInteger <= 20 0 <= desiredTotal <= 300"
Uber,500,Keyboard Row,Easy,"Array, Hash Table, String","Given an array of strings words; return the words that can be typed using letters of the alphabet on only one row of American keyboard like the image below. Note that the strings are case-insensitive; both lowercased and uppercased of the same letter are treated as if they are at the same row. In the American keyboard: the first row consists of the characters ""qwertyuiop""; the second row consists of the characters ""asdfghjkl""; and the third row consists of the characters ""zxcvbnm"". Example 1: Input: words = [""Hello"";""Alaska"";""Dad"";""Peace""] Output: [""Alaska"";""Dad""] Explanation: Both ""a"" and ""A"" are in the 2nd row of the American keyboard due to case insensitivity. Example 2: Input: words = [""omk""] Output: [] Example 3: Input: words = [""adsdf"";""sfd""] Output: [""adsdf"";""sfd""] Constraints: 1 <= words.length <= 20 1 <= words[i].length <= 100 words[i] consists of English letters (both lowercase and uppercase)."
Uber,508,Most Frequent Subtree Sum,Med,"Hash Table, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the most frequent subtree sum. If there is a tie; return all the values with the highest frequency in any order. The subtree sum of a node is defined as the sum of all the node values formed by the subtree rooted at that node (including the node itself). Example 1: Input: root = [5;2;-3] Output: [2;-3;4] Example 2: Input: root = [5;2;-5] Output: [2] Constraints: The number of nodes in the tree is in the range [1; 104]. -105 <= Node.val <= 105
Uber,1721,Swapping Nodes in a Linked List,Med,"Array, Simulation",You are the operator of a Centennial Wheel that has four gondolas; and each gondola has room for up to four people. You have the ability to rotate the gondolas counterclockwise; which costs you runningCost dollars. You are given an array customers of length n where customers[i] is the number of new customers arriving just before the ith rotation (0-indexed). This means you must rotate the wheel i times before the customers[i] customers arrive. You cannot make customers wait if there is room in the gondola. Each customer pays boardingCost dollars when they board on the gondola closest to the ground and will exit once that gondola reaches the ground again. You can stop the wheel at any time; including before serving all customers. If you decide to stop serving customers; all subsequent rotations are free in order to get all the customers down safely. Note that if there are currently more than four customers waiting at the wheel; only four will board the gondola; and the rest will wait for the next rotation. Return the minimum number of rotations you need to perform to maximize your profit. If there is no scenario where the profit is positive; return -1. Example 1: Input: customers = [8;3]; boardingCost = 5; runningCost = 6 Output: 3 Explanation: The numbers written on the gondolas are the number of people currently there. 1. 8 customers arrive; 4 board and 4 wait for the next gondola; the wheel rotates. Current profit is 4 * $5 - 1 * $6 = $14. 2. 3 customers arrive; the 4 waiting board the wheel and the other 3 wait; the wheel rotates. Current profit is 8 * $5 - 2 * $6 = $28. 3. The final 3 customers board the gondola; the wheel rotates. Current profit is 11 * $5 - 3 * $6 = $37. The highest profit was $37 after rotating the wheel 3 times. Example 2: Input: customers = [10;9;6]; boardingCost = 6; runningCost = 4 Output: 7 Explanation: 1. 10 customers arrive; 4 board and 6 wait for the next gondola; the wheel rotates. Current profit is 4 * $6 - 1 * $4 = $20. 2. 9 customers arrive; 4 board and 11 wait (2 originally waiting; 9 newly waiting); the wheel rotates. Current profit is 8 * $6 - 2 * $4 = $40. 3. The final 6 customers arrive; 4 board and 13 wait; the wheel rotates. Current profit is 12 * $6 - 3 * $4 = $60. 4. 4 board and 9 wait; the wheel rotates. Current profit is 16 * $6 - 4 * $4 = $80. 5. 4 board and 5 wait; the wheel rotates. Current profit is 20 * $6 - 5 * $4 = $100. 6. 4 board and 1 waits; the wheel rotates. Current profit is 24 * $6 - 6 * $4 = $120. 7. 1 boards; the wheel rotates. Current profit is 25 * $6 - 7 * $4 = $122. The highest profit was $122 after rotating the wheel 7 times. Example 3: Input: customers = [3;4;0;5;1]; boardingCost = 1; runningCost = 92 Output: -1 Explanation: 1. 3 customers arrive; 3 board and 0 wait; the wheel rotates. Current profit is 3 * $1 - 1 * $92 = -$89. 2. 4 customers arrive; 4 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 2 * $92 = -$177. 3. 0 customers arrive; 0 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 3 * $92 = -$269. 4. 5 customers arrive; 4 board and 1 waits; the wheel rotates. Current profit is 11 * $1 - 4 * $92 = -$357. 5. 1 customer arrives; 2 board and 0 wait; the wheel rotates. Current profit is 13 * $1 - 5 * $92 = -$447. The profit was never positive; so return -1. Constraints: n == customers.length 1 <= n <= 105 0 <= customers[i] <= 50 1 <= boardingCost; runningCost <= 100
Uber,532,K-diff Pairs in an Array,Med,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given an array of integers nums and an integer k; return the number of unique k-diff pairs in the array. A k-diff pair is an integer pair (nums[i]; nums[j]); where the following are true: 0 <= i; j < nums.length i != j |nums[i] - nums[j]| == k Notice that |val| denotes the absolute value of val. Example 1: Input: nums = [3;1;4;1;5]; k = 2 Output: 2 Explanation: There are two 2-diff pairs in the array; (1; 3) and (3; 5). Although we have two 1s in the input; we should only return the number of unique pairs. Example 2: Input: nums = [1;2;3;4;5]; k = 1 Output: 4 Explanation: There are four 1-diff pairs in the array; (1; 2); (2; 3); (3; 4) and (4; 5). Example 3: Input: nums = [1;3;1;5;4]; k = 0 Output: 1 Explanation: There is one 0-diff pair in the array; (1; 1). Constraints: 1 <= nums.length <= 104 -107 <= nums[i] <= 107 0 <= k <= 107
Uber,545,Boundary of Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",
Uber,546,Remove Boxes,Hard,"Array, Dynamic Programming, Memoization",You are given several boxes with different colors represented by different positive numbers. You may experience several rounds to remove boxes until there is no box left. Each time you can choose some continuous boxes with the same color (i.e.; composed of k boxes; k >= 1); remove them and get k * k points. Return the maximum points you can get. Example 1: Input: boxes = [1;3;2;2;2;3;4;3;1] Output: 23 Explanation: [1; 3; 2; 2; 2; 3; 4; 3; 1] ----> [1; 3; 3; 4; 3; 1] (3*3=9 points) ----> [1; 3; 3; 3; 1] (1*1=1 points) ----> [1; 1] (3*3=9 points) ----> [] (2*2=4 points) Example 2: Input: boxes = [1;1;1] Output: 9 Example 3: Input: boxes = [1] Output: 1 Constraints: 1 <= boxes.length <= 100 1 <= boxes[i] <= 100
Uber,585,Investments in 2016,Med,Database,Table: Insurance +-------------+-------+ | Column Name | Type | +-------------+-------+ | pid | int | | tiv_2015 | float | | tiv_2016 | float | | lat | float | | lon | float | +-------------+-------+ pid is the primary key (column with unique values) for this table. Each row of this table contains information about one policy where: pid is the policyholder's policy ID. tiv_2015 is the total investment value in 2015 and tiv_2016 is the total investment value in 2016. lat is the latitude of the policy holder's city. It's guaranteed that lat is not NULL. lon is the longitude of the policy holder's city. It's guaranteed that lon is not NULL. Write a solution to report the sum of all total investment values in 2016 tiv_2016; for all policyholders who: have the same tiv_2015 value as one or more other policyholders; and are not located in the same city as any other policyholder (i.e.; the (lat; lon) attribute pairs must be unique). Round tiv_2016 to two decimal places. The result format is in the following example. Example 1: Input: Insurance table: +-----+----------+----------+-----+-----+ | pid | tiv_2015 | tiv_2016 | lat | lon | +-----+----------+----------+-----+-----+ | 1 | 10 | 5 | 10 | 10 | | 2 | 20 | 20 | 20 | 20 | | 3 | 10 | 30 | 20 | 20 | | 4 | 10 | 40 | 40 | 40 | +-----+----------+----------+-----+-----+ Output: +----------+ | tiv_2016 | +----------+ | 45.00 | +----------+ Explanation: The first record in the table; like the last record; meets both of the two criteria. The tiv_2015 value 10 is the same as the third and fourth records; and its location is unique. The second record does not meet any of the two criteria. Its tiv_2015 is not like any other policyholders and its location is the same as the third record; which makes the third record fail; too. So; the result is the sum of tiv_2016 of the first and last record; which is 45.
Uber,596,Classes More Than 5 Students,Easy,Database,Table: Courses +-------------+---------+ | Column Name | Type | +-------------+---------+ | student | varchar | | class | varchar | +-------------+---------+ (student; class) is the primary key (combination of columns with unique values) for this table. Each row of this table indicates the name of a student and the class in which they are enrolled. Write a solution to find all the classes that have at least five students. Return the result table in any order. The result format is in the following example. Example 1: Input: Courses table: +---------+----------+ | student | class | +---------+----------+ | A | Math | | B | English | | C | Math | | D | Biology | | E | Math | | F | Computer | | G | Math | | H | Math | | I | Math | +---------+----------+ Output: +---------+ | class | +---------+ | Math | +---------+ Explanation: - Math has 6 students; so we include it. - English has 1 student; so we do not include it. - Biology has 1 student; so we do not include it. - Computer has 1 student; so we do not include it.
Uber,608,Tree Node,Med,Database,"Table: Tree +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | p_id | int | +-------------+------+ id is the column with unique values for this table. Each row of this table contains information about the id of a node and the id of its parent node in a tree. The given structure is always a valid tree. Each node in the tree can be one of three types: ""Leaf"": if the node is a leaf node. ""Root"": if the node is the root of the tree. ""Inner"": If the node is neither a leaf node nor a root node. Write a solution to report the type of each node in the tree. Return the result table in any order. The result format is in the following example. Example 1: Input: Tree table: +----+------+ | id | p_id | +----+------+ | 1 | null | | 2 | 1 | | 3 | 1 | | 4 | 2 | | 5 | 2 | +----+------+ Output: +----+-------+ | id | type | +----+-------+ | 1 | Root | | 2 | Inner | | 3 | Leaf | | 4 | Leaf | | 5 | Leaf | +----+-------+ Explanation: Node 1 is the root node because its parent node is null and it has child nodes 2 and 3. Node 2 is an inner node because it has parent node 1 and child node 4 and 5. Nodes 3; 4; and 5 are leaf nodes because they have parent nodes and they do not have child nodes. Example 2: Input: Tree table: +----+------+ | id | p_id | +----+------+ | 1 | null | +----+------+ Output: +----+-------+ | id | type | +----+-------+ | 1 | Root | +----+-------+ Explanation: If there is only one node on the tree; you only need to output its root attributes. Note: This question is the same as 3054: Binary Tree Nodes."
Uber,617,Merge Two Binary Trees,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given two binary trees root1 and root2. Imagine that when you put one of them to cover the other; some nodes of the two trees are overlapped while the others are not. You need to merge the two trees into a new binary tree. The merge rule is that if two nodes overlap; then sum node values up as the new value of the merged node. Otherwise; the NOT null node will be used as the node of the new tree. Return the merged tree. Note: The merging process must start from the root nodes of both trees. Example 1: Input: root1 = [1;3;2;5]; root2 = [2;1;3;null;4;null;7] Output: [3;4;5;5;4;null;7] Example 2: Input: root1 = [1]; root2 = [1;2] Output: [2;2] Constraints: The number of nodes in both trees is in the range [0; 2000]. -104 <= Node.val <= 104
Uber,620,Not Boring Movies,Easy,Database,"Table: Cinema +----------------+----------+ | Column Name | Type | +----------------+----------+ | id | int | | movie | varchar | | description | varchar | | rating | float | +----------------+----------+ id is the primary key (column with unique values) for this table. Each row contains information about the name of a movie; its genre; and its rating. rating is a 2 decimal places float in the range [0; 10] Write a solution to report the movies with an odd-numbered ID and a description that is not ""boring"". Return the result table ordered by rating in descending order. The result format is in the following example. Example 1: Input: Cinema table: +----+------------+-------------+--------+ | id | movie | description | rating | +----+------------+-------------+--------+ | 1 | War | great 3D | 8.9 | | 2 | Science | fiction | 8.5 | | 3 | irish | boring | 6.2 | | 4 | Ice song | Fantacy | 8.6 | | 5 | House card | Interesting | 9.1 | +----+------------+-------------+--------+ Output: +----+------------+-------------+--------+ | id | movie | description | rating | +----+------------+-------------+--------+ | 5 | House card | Interesting | 9.1 | | 1 | War | great 3D | 8.9 | +----+------------+-------------+--------+ Explanation: We have three movies with odd-numbered IDs: 1; 3; and 5. The movie with ID = 3 is boring so we do not include it in the answer."
Uber,626,Exchange Seats,Med,Database,Table: Seat +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | student | varchar | +-------------+---------+ id is the primary key (unique value) column for this table. Each row of this table indicates the name and the ID of a student. The ID sequence always starts from 1 and increments continuously. Write a solution to swap the seat id of every two consecutive students. If the number of students is odd; the id of the last student is not swapped. Return the result table ordered by id in ascending order. The result format is in the following example. Example 1: Input: Seat table: +----+---------+ | id | student | +----+---------+ | 1 | Abbot | | 2 | Doris | | 3 | Emerson | | 4 | Green | | 5 | Jeames | +----+---------+ Output: +----+---------+ | id | student | +----+---------+ | 1 | Doris | | 2 | Abbot | | 3 | Green | | 4 | Emerson | | 5 | Jeames | +----+---------+ Explanation: Note that if the number of students is odd; there is no need to change the last one's seat.
Uber,628,Maximum Product of Three Numbers,Easy,"Array, Math, Sorting",Given an integer array nums; find three numbers whose product is maximum and return the maximum product. Example 1: Input: nums = [1;2;3] Output: 6 Example 2: Input: nums = [1;2;3;4] Output: 24 Example 3: Input: nums = [-1;-2;-3] Output: -6 Constraints: 3 <= nums.length <= 104 -1000 <= nums[i] <= 1000
Uber,629,K Inverse Pairs Array,Hard,Dynamic Programming,For an integer array nums; an inverse pair is a pair of integers [i; j] where 0 <= i < j < nums.length and nums[i] > nums[j]. Given two integers n and k; return the number of different arrays consisting of numbers from 1 to n such that there are exactly k inverse pairs. Since the answer can be huge; return it modulo 109 + 7. Example 1: Input: n = 3; k = 0 Output: 1 Explanation: Only the array [1;2;3] which consists of numbers from 1 to 3 has exactly 0 inverse pairs. Example 2: Input: n = 3; k = 1 Output: 2 Explanation: The array [1;3;2] and [2;1;3] have exactly 1 inverse pair. Constraints: 1 <= n <= 1000 0 <= k <= 1000
Uber,642,Design Search Autocomplete System,Hard,"String, Depth-First Search, Design, Trie, Sorting, Heap (Priority Queue), Data Stream",
Uber,646,Maximum Length of Pair Chain,Med,"Array, Dynamic Programming, Greedy, Sorting",You are given an array of n pairs pairs where pairs[i] = [lefti; righti] and lefti < righti. A pair p2 = [c; d] follows a pair p1 = [a; b] if b < c. A chain of pairs can be formed in this fashion. Return the length longest chain which can be formed. You do not need to use up all the given intervals. You can select pairs in any order. Example 1: Input: pairs = [[1;2];[2;3];[3;4]] Output: 2 Explanation: The longest chain is [1;2] -> [3;4]. Example 2: Input: pairs = [[1;2];[7;8];[4;5]] Output: 3 Explanation: The longest chain is [1;2] -> [4;5] -> [7;8]. Constraints: n == pairs.length 1 <= n <= 1000 -1000 <= lefti < righti <= 1000
Uber,647,Palindromic Substrings,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the number of palindromic substrings in it. A string is a palindrome when it reads the same backward as forward. A substring is a contiguous sequence of characters within the string. Example 1: Input: s = ""abc"" Output: 3 Explanation: Three palindromic strings: ""a""; ""b""; ""c"". Example 2: Input: s = ""aaa"" Output: 6 Explanation: Six palindromic strings: ""a""; ""a""; ""a""; ""aa""; ""aa""; ""aaa"". Constraints: 1 <= s.length <= 1000 s consists of lowercase English letters."
Uber,664,Strange Printer,Hard,"String, Dynamic Programming","There is a strange printer with the following two special properties: The printer can only print a sequence of the same character each time. At each turn; the printer can print new characters starting from and ending at any place and will cover the original existing characters. Given a string s; return the minimum number of turns the printer needed to print it. Example 1: Input: s = ""aaabbb"" Output: 2 Explanation: Print ""aaa"" first and then print ""bbb"". Example 2: Input: s = ""aba"" Output: 2 Explanation: Print ""aaa"" first and then print ""b"" from the second place of the string; which will cover the existing character 'a'. Constraints: 1 <= s.length <= 100 s consists of lowercase English letters."
Uber,686,Repeated String Match,Med,"String, String Matching","Given two strings a and b; return the minimum number of times you should repeat string a so that string b is a substring of it. If it is impossible for b​​​​​​ to be a substring of a after repeating it; return -1. Notice: string ""abc"" repeated 0 times is """"; repeated 1 time is ""abc"" and repeated 2 times is ""abcabc"". Example 1: Input: a = ""abcd""; b = ""cdabcdab"" Output: 3 Explanation: We return 3 because by repeating a three times ""abcdabcdabcd""; b is a substring of it. Example 2: Input: a = ""a""; b = ""aa"" Output: 2 Constraints: 1 <= a.length; b.length <= 104 a and b consist of lowercase English letters."
Uber,695,Max Area of Island,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island. Return the maximum area of an island in grid. If there is no island; return 0. Example 1: Input: grid = [[0;0;1;0;0;0;0;1;0;0;0;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;1;1;0;1;0;0;0;0;0;0;0;0];[0;1;0;0;1;1;0;0;1;0;1;0;0];[0;1;0;0;1;1;0;0;1;1;1;0;0];[0;0;0;0;0;0;0;0;0;0;1;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;0;0;0;0;0;0;1;1;0;0;0;0]] Output: 6 Explanation: The answer is not 11; because the island must be connected 4-directionally. Example 2: Input: grid = [[0;0;0;0;0;0;0;0]] Output: 0 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 50 grid[i][j] is either 0 or 1.
Uber,715,Range Module,Hard,"Design, Segment Tree, Ordered Set","A Range Module is a module that tracks ranges of numbers. Design a data structure to track the ranges represented as half-open intervals and query about them. A half-open interval [left; right) denotes all the real numbers x where left <= x < right. Implement the RangeModule class: RangeModule() Initializes the object of the data structure. void addRange(int left; int right) Adds the half-open interval [left; right); tracking every real number in that interval. Adding an interval that partially overlaps with currently tracked numbers should add any numbers in the interval [left; right) that are not already tracked. boolean queryRange(int left; int right) Returns true if every real number in the interval [left; right) is currently being tracked; and false otherwise. void removeRange(int left; int right) Stops tracking every real number currently being tracked in the half-open interval [left; right). Example 1: Input [""RangeModule""; ""addRange""; ""removeRange""; ""queryRange""; ""queryRange""; ""queryRange""] [[]; [10; 20]; [14; 16]; [10; 14]; [13; 15]; [16; 17]] Output [null; null; null; true; false; true] Explanation RangeModule rangeModule = new RangeModule(); rangeModule.addRange(10; 20); rangeModule.removeRange(14; 16); rangeModule.queryRange(10; 14); // return True;(Every number in [10; 14) is being tracked) rangeModule.queryRange(13; 15); // return False;(Numbers like 14; 14.03; 14.17 in [13; 15) are not being tracked) rangeModule.queryRange(16; 17); // return True; (The number 16 in [16; 17) is still being tracked; despite the remove operation) Constraints: 1 <= left < right <= 109 At most 104 calls will be made to addRange; queryRange; and removeRange."
Uber,725,Split Linked List in Parts,Med,Linked List,Given the head of a singly linked list and an integer k; split the linked list into k consecutive linked list parts. The length of each part should be as equal as possible: no two parts should have a size differing by more than one. This may lead to some parts being null. The parts should be in the order of occurrence in the input list; and parts occurring earlier should always have a size greater than or equal to parts occurring later. Return an array of the k parts. Example 1: Input: head = [1;2;3]; k = 5 Output: [[1];[2];[3];[];[]] Explanation: The first element output[0] has output[0].val = 1; output[0].next = null. The last element output[4] is null; but its string representation as a ListNode is []. Example 2: Input: head = [1;2;3;4;5;6;7;8;9;10]; k = 3 Output: [[1;2;3;4];[5;6;7];[8;9;10]] Explanation: The input has been split into consecutive parts with size difference at most 1; and earlier parts are a larger size than the later parts. Constraints: The number of nodes in the list is in the range [0; 1000]. 0 <= Node.val <= 1000 1 <= k <= 50
Uber,731,My Calendar II,Med,"Array, Binary Search, Design, Segment Tree, Prefix Sum, Ordered Set","You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a triple booking. A triple booking happens when three events have some non-empty intersection (i.e.; some moment is common to all the three events.). The event can be represented as a pair of integers startTime and endTime that represents a booking on the half-open interval [startTime; endTime); the range of real numbers x such that startTime <= x < endTime. Implement the MyCalendarTwo class: MyCalendarTwo() Initializes the calendar object. boolean book(int startTime; int endTime) Returns true if the event can be added to the calendar successfully without causing a triple booking. Otherwise; return false and do not add the event to the calendar. Example 1: Input [""MyCalendarTwo""; ""book""; ""book""; ""book""; ""book""; ""book""; ""book""] [[]; [10; 20]; [50; 60]; [10; 40]; [5; 15]; [5; 10]; [25; 55]] Output [null; true; true; true; false; true; true] Explanation MyCalendarTwo myCalendarTwo = new MyCalendarTwo(); myCalendarTwo.book(10; 20); // return True; The event can be booked. myCalendarTwo.book(50; 60); // return True; The event can be booked. myCalendarTwo.book(10; 40); // return True; The event can be double booked. myCalendarTwo.book(5; 15); // return False; The event cannot be booked; because it would result in a triple booking. myCalendarTwo.book(5; 10); // return True; The event can be booked; as it does not use time 10 which is already double booked. myCalendarTwo.book(25; 55); // return True; The event can be booked; as the time in [25; 40) will be double booked with the third event; the time [40; 50) will be single booked; and the time [50; 55) will be double booked with the second event. Constraints: 0 <= start < end <= 109 At most 1000 calls will be made to book."
Uber,741,Cherry Pickup,Hard,"Array, Dynamic Programming, Matrix",You are given an n x n grid representing a field of cherries; each cell is one of three possible integers. 0 means the cell is empty; so you can pass through; 1 means the cell contains a cherry that you can pick up and pass through; or -1 means the cell contains a thorn that blocks your way. Return the maximum number of cherries you can collect by following the rules below: Starting at the position (0; 0) and reaching (n - 1; n - 1) by moving right or down through valid path cells (cells with value 0 or 1). After reaching (n - 1; n - 1); returning to (0; 0) by moving left or up through valid path cells. When passing through a path cell containing a cherry; you pick it up; and the cell becomes an empty cell 0. If there is no valid path between (0; 0) and (n - 1; n - 1); then no cherries can be collected. Example 1: Input: grid = [[0;1;-1];[1;0;-1];[1;1;1]] Output: 5 Explanation: The player started at (0; 0) and went down; down; right right to reach (2; 2). 4 cherries were picked up during this single trip; and the matrix becomes [[0;1;-1];[0;0;-1];[0;0;0]]. Then; the player went left; up; up; left to return home; picking up one more cherry. The total number of cherries picked up is 5; and this is the maximum possible. Example 2: Input: grid = [[1;1;-1];[1;-1;1];[-1;1;1]] Output: 0 Constraints: n == grid.length n == grid[i].length 1 <= n <= 50 grid[i][j] is -1; 0; or 1. grid[0][0] != -1 grid[n - 1][n - 1] != -1
Uber,747,Largest Number At Least Twice of Others,Easy,"Array, Dynamic Programming",You are given an integer array cost where cost[i] is the cost of ith step on a staircase. Once you pay the cost; you can either climb one or two steps. You can either start from the step with index 0; or the step with index 1. Return the minimum cost to reach the top of the floor. Example 1: Input: cost = [10;15;20] Output: 15 Explanation: You will start at index 1. - Pay 15 and climb two steps to reach the top. The total cost is 15. Example 2: Input: cost = [1;100;1;1;1;100;1;1;100;1] Output: 6 Explanation: You will start at index 0. - Pay 1 and climb two steps to reach index 2. - Pay 1 and climb two steps to reach index 4. - Pay 1 and climb two steps to reach index 6. - Pay 1 and climb one step to reach index 7. - Pay 1 and climb two steps to reach index 9. - Pay 1 and climb one step to reach the top. The total cost is 6. Constraints: 2 <= cost.length <= 1000 0 <= cost[i] <= 999
Uber,757,Set Intersection Size At Least Two,Hard,"Bit Manipulation, Depth-First Search, Breadth-First Search","You are stacking blocks to form a pyramid. Each block has a color; which is represented by a single letter. Each row of blocks contains one less block than the row beneath it and is centered on top. To make the pyramid aesthetically pleasing; there are only specific triangular patterns that are allowed. A triangular pattern consists of a single block stacked on top of two blocks. The patterns are given as a list of three-letter strings allowed; where the first two characters of a pattern represent the left and right bottom blocks respectively; and the third character is the top block. For example; ""ABC"" represents a triangular pattern with a 'C' block stacked on top of an 'A' (left) and 'B' (right) block. Note that this is different from ""BAC"" where 'B' is on the left bottom and 'A' is on the right bottom. You start with a bottom row of blocks bottom; given as a single string; that you must use as the base of the pyramid. Given bottom and allowed; return true if you can build the pyramid all the way to the top such that every triangular pattern in the pyramid is in allowed; or false otherwise. Example 1: Input: bottom = ""BCD""; allowed = [""BCC"";""CDE"";""CEA"";""FFF""] Output: true Explanation: The allowed triangular patterns are shown on the right. Starting from the bottom (level 3); we can build ""CE"" on level 2 and then build ""A"" on level 1. There are three triangular patterns in the pyramid; which are ""BCC""; ""CDE""; and ""CEA"". All are allowed. Example 2: Input: bottom = ""AAAA""; allowed = [""AAB"";""AAC"";""BCD"";""BBE"";""DEF""] Output: false Explanation: The allowed triangular patterns are shown on the right. Starting from the bottom (level 4); there are multiple ways to build level 3; but trying all the possibilites; you will get always stuck before building level 1. Constraints: 2 <= bottom.length <= 6 0 <= allowed.length <= 216 allowed[i].length == 3 The letters in all input strings are from the set {'A'; 'B'; 'C'; 'D'; 'E'; 'F'}. All the values of allowed are unique."
Uber,764,Largest Plus Sign,Med,"Tree, Breadth-First Search",Given an n-ary tree; return the level order traversal of its nodes' values. Nary-Tree input serialization is represented in their level order traversal; each group of children is separated by the null value (See examples). Example 1: Input: root = [1;null;3;2;4;null;5;6] Output: [[1];[3;2;4];[5;6]] Example 2: Input: root = [1;null;2;3;4;5;null;null;6;7;null;8;null;9;10;null;null;11;null;12;null;13;null;null;14] Output: [[1];[2;3;4;5];[6;7;8;9;10];[11;12;13];[14]] Constraints: The height of the n-ary tree is less than or equal to 1000 The total number of nodes is between [0; 104]
Uber,771,Jewels and Stones,Easy,"Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",
Uber,703,Kth Largest Element in a Stream,Easy,,
Uber,780,Reaching Points,Hard,"Array, Stack, Greedy, Sorting, Monotonic Stack",You are given an integer array arr of length n that represents a permutation of the integers in the range [0; n - 1]. We split arr into some number of chunks (i.e.; partitions); and individually sort each chunk. After concatenating them; the result should equal the sorted array. Return the largest number of chunks we can make to sort the array. Example 1: Input: arr = [4;3;2;1;0] Output: 1 Explanation: Splitting into two or more chunks will not return the required result. For example; splitting into [4; 3]; [2; 1; 0] will result in [3; 4; 0; 1; 2]; which isn't sorted. Example 2: Input: arr = [1;0;2;3;4] Output: 4 Explanation: We can split into two chunks; such as [1; 0]; [2; 3; 4]. However; splitting into [1; 0]; [2]; [3]; [4] is the highest number of chunks possible. Constraints: n == arr.length 1 <= n <= 10 0 <= arr[i] < n All the elements of arr are unique.
Uber,784,Letter Case Permutation,Med,"Tree, Binary Search Tree, Binary Tree",You are given the root node of a binary search tree (BST) and a value to insert into the tree. Return the root node of the BST after the insertion. It is guaranteed that the new value does not exist in the original BST. Notice that there may exist multiple valid ways for the insertion; as long as the tree remains a BST after insertion. You can return any of them. Example 1: Input: root = [4;2;7;1;3]; val = 5 Output: [4;2;7;1;3;5] Explanation: Another accepted tree is: Example 2: Input: root = [40;20;60;10;30;50;70]; val = 25 Output: [40;20;60;10;30;50;70;null;null;25] Example 3: Input: root = [4;2;7;1;3;null;null;null;null;null;null]; val = 5 Output: [4;2;7;1;3;5] Constraints: The number of nodes in the tree will be in the range [0; 104]. -108 <= Node.val <= 108 All the values Node.val are unique. -108 <= val <= 108 It's guaranteed that val does not exist in the original BST.
Uber,787,Cheapest Flights Within K Stops,Med,"Array, Breadth-First Search, Matrix",On an 2 x 3 board; there are five tiles labeled from 1 to 5; and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of the board is solved if and only if the board is [[1;2;3];[4;5;0]]. Given the puzzle board board; return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved; return -1. Example 1: Input: board = [[1;2;3];[4;0;5]] Output: 1 Explanation: Swap the 0 and the 5 in one move. Example 2: Input: board = [[1;2;3];[5;4;0]] Output: -1 Explanation: No number of moves will make the board solved. Example 3: Input: board = [[4;1;2];[5;0;3]] Output: 5 Explanation: 5 is the smallest number of moves that solves the board. An example path: After move 0: [[4;1;2];[5;0;3]] After move 1: [[4;1;2];[0;5;3]] After move 2: [[0;1;2];[4;5;3]] After move 3: [[1;0;2];[4;5;3]] After move 4: [[1;2;0];[4;5;3]] After move 5: [[1;2;3];[4;5;0]] Constraints: board.length == 2 board[i].length == 3 0 <= board[i][j] <= 5 Each value board[i][j] is unique.
Uber,795,Number of Subarrays with Bounded Maximum,Med,"Math, Bit Manipulation, Recursion",We build a table of n rows (1-indexed). We start by writing 0 in the 1st row. Now in every subsequent row; we look at the previous row and replace each occurrence of 0 with 01; and each occurrence of 1 with 10. For example; for n = 3; the 1st row is 0; the 2nd row is 01; and the 3rd row is 0110. Given two integer n and k; return the kth (1-indexed) symbol in the nth row of a table of n rows. Example 1: Input: n = 1; k = 1 Output: 0 Explanation: row 1: 0 Example 2: Input: n = 2; k = 1 Output: 0 Explanation: row 1: 0 row 2: 01 Example 3: Input: n = 2; k = 2 Output: 1 Explanation: row 1: 0 row 2: 01 Constraints: 1 <= n <= 30 1 <= k <= 2n - 1
Uber,809,Expressive Words,Med,"Math, Binary Search",Let f(x) be the number of zeroes at the end of x!. Recall that x! = 1 * 2 * 3 * ... * x and by convention; 0! = 1. For example; f(3) = 0 because 3! = 6 has no zeroes at the end; while f(11) = 2 because 11! = 39916800 has two zeroes at the end. Given an integer k; return the number of non-negative integers x have the property that f(x) = k. Example 1: Input: k = 0 Output: 5 Explanation: 0!; 1!; 2!; 3!; and 4! end with k = 0 zeroes. Example 2: Input: k = 5 Output: 0 Explanation: There is no x such that x! ends in k = 5 zeroes. Example 3: Input: k = 3 Output: 5 Constraints: 0 <= k <= 109
Uber,813,Largest Sum of Averages,Med,"Backtracking, Depth-First Search, Breadth-First Search, Graph",Given a directed acyclic graph (DAG) of n nodes labeled from 0 to n - 1; find all possible paths from node 0 to node n - 1 and return them in any order. The graph is given as follows: graph[i] is a list of all nodes you can visit from node i (i.e.; there is a directed edge from node i to node graph[i][j]). Example 1: Input: graph = [[1;2];[3];[3];[]] Output: [[0;1;3];[0;2;3]] Explanation: There are two paths: 0 -> 1 -> 3 and 0 -> 2 -> 3. Example 2: Input: graph = [[4;3;1];[3;2;4];[3];[4];[]] Output: [[0;4];[0;3;4];[0;1;3;4];[0;1;2;3;4];[0;1;4]] Constraints: n == graph.length 2 <= n <= 15 0 <= graph[i][j] < n graph[i][j] != i (i.e.; there will be no self-loops). All the elements of graph[i] are unique. The input graph is guaranteed to be a DAG.
Uber,832,Flipping an Image,Easy,"Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; return the same tree where every subtree (of the given tree) not containing a 1 has been removed. A subtree of a node node is node plus every node that is a descendant of node. Example 1: Input: root = [1;null;0;0;1] Output: [1;null;0;null;1] Explanation: Only the red nodes satisfy the property ""every subtree not containing a 1"". The diagram on the right represents the answer. Example 2: Input: root = [1;0;1;0;0;0;1] Output: [1;null;1;null;1] Example 3: Input: root = [1;1;0;1;1;0;1;0] Output: [1;1;0;1;1;null;1] Constraints: The number of nodes in the tree is in the range [1; 200]. Node.val is either 0 or 1."
Uber,851,Loud and Rich,Med,String,"You are given a string sentence that consist of words separated by spaces. Each word consists of lowercase and uppercase letters only. We would like to convert the sentence to ""Goat Latin"" (a made-up language similar to Pig Latin.) The rules of Goat Latin are as follows: If a word begins with a vowel ('a'; 'e'; 'i'; 'o'; or 'u'); append ""ma"" to the end of the word. For example; the word ""apple"" becomes ""applema"". If a word begins with a consonant (i.e.; not a vowel); remove the first letter and append it to the end; then add ""ma"". For example; the word ""goat"" becomes ""oatgma"". Add one letter 'a' to the end of each word per its word index in the sentence; starting with 1. For example; the first word gets ""a"" added to the end; the second word gets ""aa"" added to the end; and so on. Return the final sentence representing the conversion from sentence to Goat Latin. Example 1: Input: sentence = ""I speak Goat Latin"" Output: ""Imaa peaksmaaa oatGmaaaa atinLmaaaaa"" Example 2: Input: sentence = ""The quick brown fox jumped over the lazy dog"" Output: ""heTmaa uickqmaaa rownbmaaaa oxfmaaaaa umpedjmaaaaaa overmaaaaaaa hetmaaaaaaaa azylmaaaaaaaaa ogdmaaaaaaaaaa"" Constraints: 1 <= sentence.length <= 150 sentence consists of English letters and spaces. sentence has no leading or trailing spaces. All the words in sentence are separated by a single space."
Uber,864,Shortest Path to Get All Keys,Hard,"Array, Matrix",You are given two images; img1 and img2; represented as binary; square matrices of size n x n. A binary matrix has only 0s and 1s as values. We translate one image however we choose by sliding all the 1 bits left; right; up; and/or down any number of units. We then place it on top of the other image. We can then calculate the overlap by counting the number of positions that have a 1 in both images. Note also that a translation does not include any kind of rotation. Any 1 bits that are translated outside of the matrix borders are erased. Return the largest possible overlap. Example 1: Input: img1 = [[1;1;0];[0;1;0];[0;1;0]]; img2 = [[0;0;0];[0;1;1];[0;0;1]] Output: 3 Explanation: We translate img1 to right by 1 unit and down by 1 unit. The number of positions that have a 1 in both images is 3 (shown in red). Example 2: Input: img1 = [[1]]; img2 = [[1]] Output: 1 Example 3: Input: img1 = [[0]]; img2 = [[0]] Output: 0 Constraints: n == img1.length == img1[i].length n == img2.length == img2[i].length 1 <= n <= 30 img1[i][j] is either 0 or 1. img2[i][j] is either 0 or 1.
Uber,877,Stone Game,Med,"Dynamic Programming, Bit Manipulation, Breadth-First Search, Graph, Bitmask",You have an undirected; connected graph of n nodes labeled from 0 to n - 1. You are given an array graph where graph[i] is a list of all the nodes connected with node i by an edge. Return the length of the shortest path that visits every node. You may start and stop at any node; you may revisit nodes multiple times; and you may reuse edges. Example 1: Input: graph = [[1;2;3];[0];[0];[0]] Output: 4 Explanation: One possible path is [1;0;2;0;3] Example 2: Input: graph = [[1];[0;2;4];[1;3;4];[2];[1;2]] Output: 4 Explanation: One possible path is [0;1;4;2;3] Constraints: n == graph.length 1 <= n <= 12 0 <= graph[i].length < n graph[i] does not contain i. If graph[a] contains b; then graph[b] contains a. The input graph is always connected.
Uber,879,Profitable Schemes,Hard,Array,You are given an array representing a row of seats where seats[i] = 1 represents a person sitting in the ith seat; and seats[i] = 0 represents that the ith seat is empty (0-indexed). There is at least one empty seat; and at least one person sitting. Alex wants to sit in the seat such that the distance between him and the closest person to him is maximized. Return that maximum distance to the closest person. Example 1: Input: seats = [1;0;0;0;1;0;1] Output: 2 Explanation: If Alex sits in the second open seat (i.e. seats[2]); then the closest person has distance 2. If Alex sits in any other open seat; the closest person has distance 1. Thus; the maximum distance to the closest person is 2. Example 2: Input: seats = [1;0;0;0] Output: 3 Explanation: If Alex sits in the last seat (i.e. seats[3]); the closest person is 3 seats away. This is the maximum distance possible; so the answer is 3. Example 3: Input: seats = [0;1] Output: 1 Constraints: 2 <= seats.length <= 2 * 104 seats[i] is 0 or 1. At least one seat is empty. At least one seat is occupied.
Uber,881,Boats to Save People,Med,"Array, Depth-First Search, Graph, Topological Sort",There is a group of n people labeled from 0 to n - 1 where each person has a different amount of money and a different level of quietness. You are given an array richer where richer[i] = [ai; bi] indicates that ai has more money than bi and an integer array quiet where quiet[i] is the quietness of the ith person. All the given data in richer are logically correct (i.e.; the data will not lead you to a situation where x is richer than y and y is richer than x at the same time). Return an integer array answer where answer[x] = y if y is the least quiet person (that is; the person y with the smallest value of quiet[y]) among all people who definitely have equal to or more money than the person x. Example 1: Input: richer = [[1;0];[2;1];[3;1];[3;7];[4;3];[5;3];[6;3]]; quiet = [3;2;5;4;6;1;7;0] Output: [5;5;2;5;4;5;6;7] Explanation: answer[0] = 5. Person 5 has more money than 3; which has more money than 1; which has more money than 0. The only person who is quieter (has lower quiet[x]) is person 7; but it is not clear if they have more money than person 0. answer[7] = 7. Among all people that definitely have equal to or more money than person 7 (which could be persons 3; 4; 5; 6; or 7); the person who is the quietest (has lower quiet[x]) is person 7. The other answers can be filled out with similar reasoning. Example 2: Input: richer = []; quiet = [0] Output: [0] Constraints: n == quiet.length 1 <= n <= 500 0 <= quiet[i] < n All the values of quiet are unique. 0 <= richer.length <= n * (n - 1) / 2 0 <= ai; bi < n ai != bi All the pairs of richer are unique. The observations in richer are all logically consistent.
Uber,887,Super Egg Drop,Hard,"Array, Greedy, Sorting, Heap (Priority Queue)",There are n workers. You are given two integer arrays quality and wage where quality[i] is the quality of the ith worker and wage[i] is the minimum wage expectation for the ith worker. We want to hire exactly k workers to form a paid group. To hire a group of k workers; we must pay them according to the following rules: Every worker in the paid group must be paid at least their minimum wage expectation. In the group; each worker's pay must be directly proportional to their quality. This means if a worker’s quality is double that of another worker in the group; then they must be paid twice as much as the other worker. Given the integer k; return the least amount of money needed to form a paid group satisfying the above conditions. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: quality = [10;20;5]; wage = [70;50;30]; k = 2 Output: 105.00000 Explanation: We pay 70 to 0th worker and 35 to 2nd worker. Example 2: Input: quality = [3;1;10;10;1]; wage = [4;8;2;2;7]; k = 3 Output: 30.66667 Explanation: We pay 4 to 0th worker; 13.33333 to 2nd and 3rd workers separately. Constraints: n == quality.length == wage.length 1 <= k <= n <= 104 1 <= quality[i]; wage[i] <= 104
Uber,888,Fair Candy Swap,Easy,"Math, Geometry, Number Theory",There is a special square room with mirrors on each of the four walls. Except for the southwest corner; there are receptors on each of the remaining corners; numbered 0; 1; and 2. The square room has walls of length p and a laser ray from the southwest corner first meets the east wall at a distance q from the 0th receptor. Given the two integers p and q; return the number of the receptor that the ray meets first. The test cases are guaranteed so that the ray will meet a receptor eventually. Example 1: Input: p = 2; q = 1 Output: 2 Explanation: The ray meets receptor 2 the first time it gets reflected back to the left wall. Example 2: Input: p = 3; q = 1 Output: 1 Constraints: 1 <= q <= p <= 1000
Uber,896,Monotonic Array,Easy,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; the depth of each node is the shortest distance to the root. Return the smallest subtree such that it contains all the deepest nodes in the original tree. A node is called the deepest if it has the largest depth possible among any node in the entire tree. The subtree of a node is a tree consisting of that node; plus the set of all descendants of that node. Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4] Output: [2;7;4] Explanation: We return the node with value 2; colored in yellow in the diagram. The nodes coloured in blue are the deepest nodes of the tree. Notice that nodes 5; 3 and 2 contain the deepest nodes in the tree but node 2 is the smallest subtree among them; so we return it. Example 2: Input: root = [1] Output: [1] Explanation: The root is the deepest node in the tree. Example 3: Input: root = [0;1;3;null;2] Output: [2] Explanation: The deepest node in the tree is 2; the valid subtrees are the subtrees of nodes 2; 1 and 0 but the subtree of node 2 is the smallest. Constraints: The number of nodes in the tree will be in the range [1; 500]. 0 <= Node.val <= 500 The values of the nodes in the tree are unique. Note: This question is the same as 1123: https://leetcode.com/problems/lowest-common-ancestor-of-deepest-leaves/
Uber,917,Reverse Only Letters,Easy,"Array, Two Pointers, Greedy, Sorting",You are given an array people where people[i] is the weight of the ith person; and an infinite number of boats where each boat can carry a maximum weight of limit. Each boat carries at most two people at the same time; provided the sum of the weight of those people is at most limit. Return the minimum number of boats to carry every given person. Example 1: Input: people = [1;2]; limit = 3 Output: 1 Explanation: 1 boat (1; 2) Example 2: Input: people = [3;2;2;1]; limit = 3 Output: 3 Explanation: 3 boats (1; 2); (2) and (3) Example 3: Input: people = [3;5;3;4]; limit = 5 Output: 4 Explanation: 4 boats (3); (3); (4); (5) Constraints: 1 <= people.length <= 5 * 104 1 <= people[i] <= limit <= 3 * 104
Uber,919,Complete Binary Tree Inserter,Med,"Array, Math, Geometry, Matrix","You are given an n x n grid where we place some 1 x 1 x 1 cubes that are axis-aligned with the x; y; and z axes. Each value v = grid[i][j] represents a tower of v cubes placed on top of the cell (i; j). We view the projection of these cubes onto the xy; yz; and zx planes. A projection is like a shadow; that maps our 3-dimensional figure to a 2-dimensional plane. We are viewing the ""shadow"" when looking at the cubes from the top; the front; and the side. Return the total area of all three projections. Example 1: Input: grid = [[1;2];[3;4]] Output: 17 Explanation: Here are the three projections (""shadows"") of the shape made with each axis-aligned plane. Example 2: Input: grid = [[2]] Output: 5 Example 3: Input: grid = [[1;0];[0;2]] Output: 8 Constraints: n == grid.length == grid[i].length 1 <= n <= 50 0 <= grid[i][j] <= 50"
Uber,929,Unique Email Addresses,Easy,"Array, Hash Table, String, Sorting","You are given an array of strings of the same length words. In one move; you can swap any two even indexed characters or any two odd indexed characters of a string words[i]. Two strings words[i] and words[j] are special-equivalent if after any number of moves; words[i] == words[j]. For example; words[i] = ""zzxy"" and words[j] = ""xyzz"" are special-equivalent because we may make the moves ""zzxy"" -> ""xzzy"" -> ""xyzz"". A group of special-equivalent strings from words is a non-empty subset of words such that: Every pair of strings in the group are special equivalent; and The group is the largest size possible (i.e.; there is not a string words[i] not in the group such that words[i] is special-equivalent to every string in the group). Return the number of groups of special-equivalent strings from words. Example 1: Input: words = [""abcd"";""cdab"";""cbad"";""xyzz"";""zzxy"";""zzyx""] Output: 3 Explanation: One group is [""abcd""; ""cdab""; ""cbad""]; since they are all pairwise special equivalent; and none of the other strings is all pairwise special equivalent to these. The other two groups are [""xyzz""; ""zzxy""] and [""zzyx""]. Note that in particular; ""zzxy"" is not special equivalent to ""zzyx"". Example 2: Input: words = [""abc"";""acb"";""bac"";""bca"";""cab"";""cba""] Output: 3 Constraints: 1 <= words.length <= 1000 1 <= words[i].length <= 20 words[i] consist of lowercase English letters. All the strings are of the same length."
Uber,930,Binary Subarrays With Sum,Med,"Dynamic Programming, Tree, Recursion, Memoization, Binary Tree",Given an integer n; return a list of all possible full binary trees with n nodes. Each node of each tree in the answer must have Node.val == 0. Each element of the answer is the root node of one possible tree. You may return the final list of trees in any order. A full binary tree is a binary tree where each node has exactly 0 or 2 children. Example 1: Input: n = 7 Output: [[0;0;0;null;null;0;0;null;null;0;0];[0;0;0;null;null;0;0;0;0];[0;0;0;0;0;0;0];[0;0;0;0;0;null;null;null;null;0;0];[0;0;0;0;0;null;null;0;0]] Example 2: Input: n = 3 Output: [[0;0;0]] Constraints: 1 <= n <= 20
Uber,940,Distinct Subsequences II,Hard,"Array, Hash Table, Sliding Window",You are visiting a farm that has a single row of fruit trees arranged from left to right. The trees are represented by an integer array fruits where fruits[i] is the type of fruit the ith tree produces. You want to collect as much fruit as possible. However; the owner has some strict rules that you must follow: You only have two baskets; and each basket can only hold a single type of fruit. There is no limit on the amount of fruit each basket can hold. Starting from any tree of your choice; you must pick exactly one fruit from every tree (including the start tree) while moving to the right. The picked fruits must fit in one of your baskets. Once you reach a tree with fruit that cannot fit in your baskets; you must stop. Given the integer array fruits; return the maximum number of fruits you can pick. Example 1: Input: fruits = [1;2;1] Output: 3 Explanation: We can pick from all 3 trees. Example 2: Input: fruits = [0;1;2;2] Output: 3 Explanation: We can pick from trees [1;2;2]. If we had started at the first tree; we would only pick from trees [0;1]. Example 3: Input: fruits = [1;2;3;2;2] Output: 4 Explanation: We can pick from trees [2;3;2;2]. If we had started at the first tree; we would only pick from trees [1;2]. Constraints: 1 <= fruits.length <= 105 0 <= fruits[i] < fruits.length
Uber,948,Bag of Tokens,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort",Given an array of integers nums; sort the array in ascending order and return it. You must solve the problem without using any built-in functions in O(nlog(n)) time complexity and with the smallest space complexity possible. Example 1: Input: nums = [5;2;3;1] Output: [1;2;3;5] Explanation: After sorting the array; the positions of some numbers are not changed (for example; 2 and 3); while the positions of other numbers are changed (for example; 1 and 5). Example 2: Input: nums = [5;1;1;2;0;0] Output: [0;0;1;1;2;5] Explanation: Note that the values of nums are not necessairly unique. Constraints: 1 <= nums.length <= 5 * 104 -5 * 104 <= nums[i] <= 5 * 104
Uber,956,Tallest Billboard,Hard,"Math, Dynamic Programming, Combinatorics",Your music player contains n different songs. You want to listen to goal songs (not necessarily different) during your trip. To avoid boredom; you will create a playlist so that: Every song is played at least once. A song can only be played again only if k other songs have been played. Given n; goal; and k; return the number of possible playlists that you can create. Since the answer can be very large; return it modulo 109 + 7. Example 1: Input: n = 3; goal = 3; k = 1 Output: 6 Explanation: There are 6 possible playlists: [1; 2; 3]; [1; 3; 2]; [2; 1; 3]; [2; 3; 1]; [3; 1; 2]; and [3; 2; 1]. Example 2: Input: n = 2; goal = 3; k = 0 Output: 6 Explanation: There are 6 possible playlists: [1; 1; 2]; [1; 2; 1]; [2; 1; 1]; [2; 2; 1]; [2; 1; 2]; and [1; 2; 2]. Example 3: Input: n = 2; goal = 3; k = 1 Output: 2 Explanation: There are 2 possible playlists: [1; 2; 1] and [2; 1; 2]. Constraints: 0 <= k < n <= goal <= 100
Uber,976,Largest Perimeter Triangle,Easy,"Array, Hash Table, Math, Geometry, Sorting",You are given an array of points in the X-Y plane points where points[i] = [xi; yi]. Return the minimum area of a rectangle formed from these points; with sides parallel to the X and Y axes. If there is not any such rectangle; return 0. Example 1: Input: points = [[1;1];[1;3];[3;1];[3;3];[2;2]] Output: 4 Example 2: Input: points = [[1;1];[1;3];[3;1];[3;3];[4;1];[4;3]] Output: 2 Constraints: 1 <= points.length <= 500 points[i].length == 2 0 <= xi; yi <= 4 * 104 All the given points are unique.
Uber,997,Find the Town Judge,Easy,,
Uber,1002,Find Common Characters,Easy,"Array, Stack, Monotonic Stack",A ramp in an integer array nums is a pair (i; j) for which i < j and nums[i] <= nums[j]. The width of such a ramp is j - i. Given an integer array nums; return the maximum width of a ramp in nums. If there is no ramp in nums; return 0. Example 1: Input: nums = [6;0;8;2;1;5] Output: 4 Explanation: The maximum width ramp is achieved at (i; j) = (1; 5): nums[1] = 0 and nums[5] = 5. Example 2: Input: nums = [9;8;1;0;1;9;4;0;4;1] Output: 7 Explanation: The maximum width ramp is achieved at (i; j) = (2; 9): nums[2] = 1 and nums[9] = 1. Constraints: 2 <= nums.length <= 5 * 104 0 <= nums[i] <= 5 * 104
Uber,1009,Complement of Base 10 Integer,Easy,"Array, Two Pointers, Greedy, Sorting",Given an array of integers arr; sort the array by performing a series of pancake flips. In one pancake flip we do the following steps: Choose an integer k where 1 <= k <= arr.length. Reverse the sub-array arr[0...k-1] (0-indexed). For example; if arr = [3;2;1;4] and we performed a pancake flip choosing k = 3; we reverse the sub-array [3;2;1]; so arr = [1;2;3;4] after the pancake flip at k = 3. Return an array of the k-values corresponding to a sequence of pancake flips that sort arr. Any valid answer that sorts the array within 10 * arr.length flips will be judged as correct. Example 1: Input: arr = [3;2;4;1] Output: [4;2;4;3] Explanation: We perform 4 pancake flips; with k values 4; 2; 4; and 3. Starting state: arr = [3; 2; 4; 1] After 1st flip (k = 4): arr = [1; 4; 2; 3] After 2nd flip (k = 2): arr = [4; 1; 2; 3] After 3rd flip (k = 4): arr = [3; 2; 1; 4] After 4th flip (k = 3): arr = [1; 2; 3; 4]; which is sorted. Example 2: Input: arr = [1;2;3] Output: [] Explanation: The input is already sorted; so there is no need to flip anything. Note that other answers; such as [3; 3]; would also be accepted. Constraints: 1 <= arr.length <= 100 1 <= arr[i] <= arr.length All integers in arr are unique (i.e. arr is a permutation of the integers from 1 to arr.length).
Uber,1020,Number of Enclaves,Med,"Array, Dynamic Programming, Sliding Window",Given an integer array arr; return the length of a maximum size turbulent subarray of arr. A subarray is turbulent if the comparison sign flips between each adjacent pair of elements in the subarray. More formally; a subarray [arr[i]; arr[i + 1]; ...; arr[j]] of arr is said to be turbulent if and only if: For i <= k < j: arr[k] > arr[k + 1] when k is odd; and arr[k] < arr[k + 1] when k is even. Or; for i <= k < j: arr[k] > arr[k + 1] when k is even; and arr[k] < arr[k + 1] when k is odd. Example 1: Input: arr = [9;4;2;10;7;8;8;1;9] Output: 5 Explanation: arr[1] > arr[2] < arr[3] > arr[4] < arr[5] Example 2: Input: arr = [4;8;12;16] Output: 2 Example 3: Input: arr = [100] Output: 1 Constraints: 1 <= arr.length <= 4 * 104 0 <= arr[i] <= 109
Uber,1027,Longest Arithmetic Subsequence,Med,"Array, Simulation",You are given an integer array nums and an array queries where queries[i] = [vali; indexi]. For each query i; first; apply nums[indexi] = nums[indexi] + vali; then print the sum of the even values of nums. Return an integer array answer where answer[i] is the answer to the ith query. Example 1: Input: nums = [1;2;3;4]; queries = [[1;0];[-3;1];[-4;0];[2;3]] Output: [8;6;2;4] Explanation: At the beginning; the array is [1;2;3;4]. After adding 1 to nums[0]; the array is [2;2;3;4]; and the sum of even values is 2 + 2 + 4 = 8. After adding -3 to nums[1]; the array is [2;-1;3;4]; and the sum of even values is 2 + 4 = 6. After adding -4 to nums[0]; the array is [-2;-1;3;4]; and the sum of even values is -2 + 4 = 2. After adding 2 to nums[3]; the array is [-2;-1;3;6]; and the sum of even values is -2 + 6 = 4. Example 2: Input: nums = [1]; queries = [[4;0]] Output: [0] Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 1 <= queries.length <= 104 -104 <= vali <= 104 0 <= indexi < nums.length
Uber,1160,Find Words That Can Be Formed by Characters,Easy,"Hash Table, String, Backtracking, Counting","You have n tiles; where each tile has one letter tiles[i] printed on it. Return the number of possible non-empty sequences of letters you can make using the letters printed on those tiles. Example 1: Input: tiles = ""AAB"" Output: 8 Explanation: The possible sequences are ""A""; ""B""; ""AA""; ""AB""; ""BA""; ""AAB""; ""ABA""; ""BAA"". Example 2: Input: tiles = ""AAABBC"" Output: 188 Example 3: Input: tiles = ""V"" Output: 1 Constraints: 1 <= tiles.length <= 7 tiles consists of uppercase English letters."
Uber,1162,As Far from Land as Possible,Med,Database,
Uber,1044,Longest Duplicate Substring,Hard,"Array, Hash Table, String","Given a string array words; return an array of all characters that show up in all strings within the words (including duplicates). You may return the answer in any order. Example 1: Input: words = [""bella"";""label"";""roller""] Output: [""e"";""l"";""l""] Example 2: Input: words = [""cool"";""lock"";""cook""] Output: [""c"";""o""] Constraints: 1 <= words.length <= 100 1 <= words[i].length <= 100 words[i] consists of lowercase English letters."
Uber,1046,Last Stone Weight,Easy,"Array, Binary Search, Sliding Window, Prefix Sum",Given a binary array nums and an integer k; return the maximum number of consecutive 1's in the array if you can flip at most k 0's. Example 1: Input: nums = [1;1;1;0;0;0;1;1;1;1;0]; k = 2 Output: 6 Explanation: [1;1;1;0;0;1;1;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Example 2: Input: nums = [0;0;1;1;0;0;1;1;1;0;1;1;0;0;0;1;1;1;1]; k = 3 Output: 10 Explanation: [0;0;1;1;1;1;1;1;1;1;1;1;0;0;0;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1. 0 <= k <= nums.length
Uber,1047,Remove All Adjacent Duplicates In String,Easy,"Array, Greedy, Sorting",Given an integer array nums and an integer k; modify the array in the following way: choose an index i and replace nums[i] with -nums[i]. You should apply this process exactly k times. You may choose the same index i multiple times. Return the largest possible sum of the array after modifying it in this way. Example 1: Input: nums = [4;2;3]; k = 1 Output: 5 Explanation: Choose index 1 and nums becomes [4;-2;3]. Example 2: Input: nums = [3;-1;0;2]; k = 3 Output: 6 Explanation: Choose indices (1; 2; 2) and nums becomes [3;1;0;2]. Example 3: Input: nums = [2;-3;-1;5;-4]; k = 2 Output: 13 Explanation: Choose indices (1; 4) and nums becomes [2;3;-1;5;4]. Constraints: 1 <= nums.length <= 104 -100 <= nums[i] <= 100 1 <= k <= 104
Uber,1045,Customers Who Bought All Products,Med,"String, Stack","Given a string s; determine if it is valid. A string s is valid if; starting with an empty string t = """"; you can transform t into s after performing the following operation any number of times: Insert string ""abc"" into any position in t. More formally; t becomes tleft + ""abc"" + tright; where t == tleft + tright. Note that tleft and tright may be empty. Return true if s is a valid string; otherwise; return false. Example 1: Input: s = ""aabcbc"" Output: true Explanation: """" -> ""abc"" -> ""aabcbc"" Thus; ""aabcbc"" is valid. Example 2: Input: s = ""abcabcababcc"" Output: true Explanation: """" -> ""abc"" -> ""abcabc"" -> ""abcabcabc"" -> ""abcabcababcc"" Thus; ""abcabcababcc"" is valid. Example 3: Input: s = ""abccba"" Output: false Explanation: It is impossible to get ""abccba"" using the operation. Constraints: 1 <= s.length <= 2 * 104 s consists of letters 'a'; 'b'; and 'c'"
Uber,1229,Meeting Scheduler,Med,"Breadth-First Search, Graph",You are given an integer n; the number of nodes in a directed graph where the nodes are labeled from 0 to n - 1. Each edge is red or blue in this graph; and there could be self-edges and parallel edges. You are given two arrays redEdges and blueEdges where: redEdges[i] = [ai; bi] indicates that there is a directed red edge from node ai to node bi in the graph; and blueEdges[j] = [uj; vj] indicates that there is a directed blue edge from node uj to node vj in the graph. Return an array answer of length n; where each answer[x] is the length of the shortest path from node 0 to node x such that the edge colors alternate along the path; or -1 if such a path does not exist. Example 1: Input: n = 3; redEdges = [[0;1];[1;2]]; blueEdges = [] Output: [0;1;-1] Example 2: Input: n = 3; redEdges = [[0;1]]; blueEdges = [[2;1]] Output: [0;1;-1] Constraints: 1 <= n <= 100 0 <= redEdges.length; blueEdges.length <= 400 redEdges[i].length == blueEdges[j].length == 2 0 <= ai; bi; uj; vj < n
Uber,1089,Duplicate Zeros,Easy,String,
Uber,1091,Shortest Path in Binary Matrix,Med,"Tree, Depth-First Search, Binary Tree",
Uber,550,Game Play Analysis IV,Med,"Array, Breadth-First Search, Matrix",
Uber,1313,Decompress Run-Length Encoded List,Easy,"Math, Dynamic Programming, Tree, Graph, Topological Sort, Combinatorics",You are an ant tasked with adding n new rooms numbered 0 to n-1 to your colony. You are given the expansion plan as a 0-indexed integer array of length n; prevRoom; where prevRoom[i] indicates that you must build room prevRoom[i] before building room i; and these two rooms must be connected directly. Room 0 is already built; so prevRoom[0] = -1. The expansion plan is given such that once all the rooms are built; every room will be reachable from room 0. You can only build one room at a time; and you can travel freely between rooms you have already built only if they are connected. You can choose to build any room as long as its previous room is already built. Return the number of different orders you can build all the rooms in. Since the answer may be large; return it modulo 109 + 7. Example 1: Input: prevRoom = [-1;0;1] Output: 1 Explanation: There is only one way to build the additional rooms: 0 → 1 → 2 Example 2: Input: prevRoom = [-1;0;0;1;2] Output: 6 Explanation: The 6 ways are: 0 → 1 → 3 → 2 → 4 0 → 2 → 4 → 1 → 3 0 → 1 → 2 → 3 → 4 0 → 1 → 2 → 4 → 3 0 → 2 → 1 → 3 → 4 0 → 2 → 1 → 4 → 3 Constraints: n == prevRoom.length 2 <= n <= 105 prevRoom[0] == -1 0 <= prevRoom[i] < n for all 1 <= i < n Every room is reachable from room 0 once all the rooms are built.
Uber,1141,User Activity for the Past 30 Days I,Easy,"Array, Greedy, Sorting",
Uber,1186,Maximum Subarray Sum with One Deletion,Med,Concurrency,"There are two kinds of threads: oxygen and hydrogen. Your goal is to group these threads to form water molecules. There is a barrier where each thread has to wait until a complete molecule can be formed. Hydrogen and oxygen threads will be given releaseHydrogen and releaseOxygen methods respectively; which will allow them to pass the barrier. These threads should pass the barrier in groups of three; and they must immediately bond with each other to form a water molecule. You must guarantee that all the threads from one molecule bond before any other threads from the next molecule do. In other words: If an oxygen thread arrives at the barrier when no hydrogen threads are present; it must wait for two hydrogen threads. If a hydrogen thread arrives at the barrier when no other threads are present; it must wait for an oxygen thread and another hydrogen thread. We do not have to worry about matching the threads up explicitly; the threads do not necessarily know which other threads they are paired up with. The key is that threads pass the barriers in complete sets; thus; if we examine the sequence of threads that bind and divide them into groups of three; each group should contain one oxygen and two hydrogen threads. Write synchronization code for oxygen and hydrogen molecules that enforces these constraints. Example 1: Input: water = ""HOH"" Output: ""HHO"" Explanation: ""HOH"" and ""OHH"" are also valid answers. Example 2: Input: water = ""OOHHHH"" Output: ""HHOHHO"" Explanation: ""HOHHHO""; ""OHHHHO""; ""HHOHOH""; ""HOHHOH""; ""OHHHOH""; ""HHOOHH""; ""HOHOHH"" and ""OHHOHH"" are also valid answers. Constraints: 3 * n == water.length 1 <= n <= 20 water[i] is either 'H' or 'O'. There will be exactly 2 * n 'H' in water. There will be exactly n 'O' in water."
Uber,1200,Minimum Absolute Difference,Easy,Array,
Uber,1204,Last Person to Fit in the Bus,Med,Database,
Uber,1248,Count Number of Nice Subarrays,Med,"Tree, Depth-First Search, Binary Tree",Two players play a turn based game on a binary tree. We are given the root of this binary tree; and the number of nodes n in the tree. n is odd; and each node has a distinct value from 1 to n. Initially; the first player names a value x with 1 <= x <= n; and the second player names a value y with 1 <= y <= n and y != x. The first player colors the node with value x red; and the second player colors the node with value y blue. Then; the players take turns starting with the first player. In each turn; that player chooses a node of their color (red if player 1; blue if player 2) and colors an uncolored neighbor of the chosen node (either the left child; right child; or parent of the chosen node.) If (and only if) a player cannot choose such a node in this way; they must pass their turn. If both players pass their turn; the game ends; and the winner is the player that colored more nodes. You are the second player. If it is possible to choose such a y to ensure you win the game; return true. If it is not possible; return false. Example 1: Input: root = [1;2;3;4;5;6;7;8;9;10;11]; n = 11; x = 3 Output: true Explanation: The second player can choose the node with value 2. Example 2: Input: root = [1;2;3]; n = 3; x = 1 Output: false Constraints: The number of nodes in the tree is n. 1 <= x <= n <= 100 n is odd. 1 <= Node.val <= n All the values of the tree are unique.
Uber,2218,Maximum Value of K Coins From Piles,Hard,Graph,
Uber,1266,Minimum Time Visiting All Points,Easy,,
Uber,1277,Count Square Submatrices with All Ones,Med,"Array, Dynamic Programming, Greedy","Given an array of digits digits; return the largest multiple of three that can be formed by concatenating some of the given digits in any order. If there is no answer return an empty string. Since the answer may not fit in an integer data type; return the answer as a string. Note that the returning answer must not contain unnecessary leading zeros. Example 1: Input: digits = [8;1;9] Output: ""981"" Example 2: Input: digits = [8;6;7;1;0] Output: ""8760"" Example 3: Input: digits = [1] Output: """" Constraints: 1 <= digits.length <= 104 0 <= digits[i] <= 9"
Uber,1295,Find Numbers with Even Number of Digits,Easy,"Math, Binary Search",In a garden represented as an infinite 2D grid; there is an apple tree planted at every integer coordinate. The apple tree planted at an integer coordinate (i; j) has |i| + |j| apples growing on it. You will buy an axis-aligned square plot of land that is centered at (0; 0). Given an integer neededApples; return the minimum perimeter of a plot such that at least neededApples apples are inside or on the perimeter of that plot. The value of |x| is defined as: x if x >= 0 -x if x < 0 Example 1: Input: neededApples = 1 Output: 8 Explanation: A square plot of side length 1 does not contain any apples. However; a square plot of side length 2 has 12 apples inside (as depicted in the image above). The perimeter is 2 * 4 = 8. Example 2: Input: neededApples = 13 Output: 16 Example 3: Input: neededApples = 1000000000 Output: 5040 Constraints: 1 <= neededApples <= 1015
Uber,1319,Number of Operations to Make Network Connected,Med,"Array, Hash Table",Given an array of integers arr; return true if the number of occurrences of each value in the array is unique or false otherwise. Example 1: Input: arr = [1;2;2;1;1;3] Output: true Explanation: The value 1 has 3 occurrences; 2 has 2 and 3 has 1. No two values have the same number of occurrences. Example 2: Input: arr = [1;2] Output: false Example 3: Input: arr = [-3;0;1;-3;1;1;1;-3;10;0] Output: true Constraints: 1 <= arr.length <= 1000 -1000 <= arr[i] <= 1000
Uber,1321,Restaurant Growth,Med,"String, Binary Search, Sliding Window, Prefix Sum","You are given two strings s and t of the same length and an integer maxCost. You want to change s to t. Changing the ith character of s to ith character of t costs |s[i] - t[i]| (i.e.; the absolute difference between the ASCII values of the characters). Return the maximum length of a substring of s that can be changed to be the same as the corresponding substring of t with a cost less than or equal to maxCost. If there is no substring from s that can be changed to its corresponding substring from t; return 0. Example 1: Input: s = ""abcd""; t = ""bcdf""; maxCost = 3 Output: 3 Explanation: ""abc"" of s can change to ""bcd"". That costs 3; so the maximum length is 3. Example 2: Input: s = ""abcd""; t = ""cdef""; maxCost = 3 Output: 1 Explanation: Each character in s costs 2 to change to character in t; so the maximum length is 1. Example 3: Input: s = ""abcd""; t = ""acde""; maxCost = 0 Output: 1 Explanation: You cannot make any change; so the maximum length is 1. Constraints: 1 <= s.length <= 105 t.length == s.length 0 <= maxCost <= 106 s and t consist of only lowercase English letters."
Uber,1356,Sort Integers by The Number of 1 Bits,Easy,"Two Pointers, String, Greedy, Binary Indexed Tree","You are given a string s consisting only of lowercase English letters. In one move; you can select any two adjacent characters of s and swap them. Return the minimum number of moves needed to make s a palindrome. Note that the input will be generated such that s can always be converted to a palindrome. Example 1: Input: s = ""aabb"" Output: 2 Explanation: We can obtain two palindromes from s; ""abba"" and ""baab"". - We can obtain ""abba"" from s in 2 moves: ""aabb"" -> ""abab"" -> ""abba"". - We can obtain ""baab"" from s in 2 moves: ""aabb"" -> ""abab"" -> ""baab"". Thus; the minimum number of moves needed to make s a palindrome is 2. Example 2: Input: s = ""letelt"" Output: 2 Explanation: One of the palindromes we can obtain from s in 2 moves is ""lettel"". One of the ways we can obtain it is ""letelt"" -> ""letetl"" -> ""lettel"". Other palindromes such as ""tleelt"" can also be obtained in 2 moves. It can be shown that it is not possible to obtain a palindrome in less than 2 moves. Constraints: 1 <= s.length <= 2000 s consists only of lowercase English letters. s can be converted to a palindrome using a finite number of moves."
Uber,1338,Reduce Array Size to The Half,Med,Database,Table: Queries +-------------+---------+ | Column Name | Type | +-------------+---------+ | query_name | varchar | | result | varchar | | position | int | | rating | int | +-------------+---------+ This table may have duplicate rows. This table contains information collected from some queries on a database. The position column has a value from 1 to 500. The rating column has a value from 1 to 5. Query with rating less than 3 is a poor query. We define query quality as: The average of the ratio between query rating and its position. We also define poor query percentage as: The percentage of all queries with rating less than 3. Write a solution to find each query_name; the quality and poor_query_percentage. Both quality and poor_query_percentage should be rounded to 2 decimal places. Return the result table in any order. The result format is in the following example. Example 1: Input: Queries table: +------------+-------------------+----------+--------+ | query_name | result | position | rating | +------------+-------------------+----------+--------+ | Dog | Golden Retriever | 1 | 5 | | Dog | German Shepherd | 2 | 5 | | Dog | Mule | 200 | 1 | | Cat | Shirazi | 5 | 2 | | Cat | Siamese | 3 | 3 | | Cat | Sphynx | 7 | 4 | +------------+-------------------+----------+--------+ Output: +------------+---------+-----------------------+ | query_name | quality | poor_query_percentage | +------------+---------+-----------------------+ | Dog | 2.50 | 33.33 | | Cat | 0.66 | 33.33 | +------------+---------+-----------------------+ Explanation: Dog queries quality is ((5 / 1) + (5 / 2) + (1 / 200)) / 3 = 2.50 Dog queries poor_ query_percentage is (1 / 3) * 100 = 33.33 Cat queries quality equals ((2 / 5) + (3 / 3) + (4 / 7)) / 3 = 0.66 Cat queries poor_ query_percentage is (1 / 3) * 100 = 33.33
Uber,1373,Maximum Sum BST in Binary Tree,Hard,,
Uber,1365,How Many Numbers Are Smaller Than the Current Number,Easy,,
Uber,1376,Time Needed to Inform All Employees,Med,"Array, Dynamic Programming, Memoization",You are given two integers m and n that represent the height and width of a rectangular piece of wood. You are also given a 2D integer array prices; where prices[i] = [hi; wi; pricei] indicates you can sell a rectangular piece of wood of height hi and width wi for pricei dollars. To cut a piece of wood; you must make a vertical or horizontal cut across the entire height or width of the piece to split it into two smaller pieces. After cutting a piece of wood into some number of smaller pieces; you can sell pieces according to prices. You may sell multiple pieces of the same shape; and you do not have to sell all the shapes. The grain of the wood makes a difference; so you cannot rotate a piece to swap its height and width. Return the maximum money you can earn after cutting an m x n piece of wood. Note that you can cut the piece of wood as many times as you want. Example 1: Input: m = 3; n = 5; prices = [[1;4;2];[2;2;7];[2;1;3]] Output: 19 Explanation: The diagram above shows a possible scenario. It consists of: - 2 pieces of wood shaped 2 x 2; selling for a price of 2 * 7 = 14. - 1 piece of wood shaped 2 x 1; selling for a price of 1 * 3 = 3. - 1 piece of wood shaped 1 x 4; selling for a price of 1 * 2 = 2. This obtains a total of 14 + 3 + 2 = 19 money earned. It can be shown that 19 is the maximum amount of money that can be earned. Example 2: Input: m = 4; n = 6; prices = [[3;2;10];[1;4;2];[4;1;3]] Output: 32 Explanation: The diagram above shows a possible scenario. It consists of: - 3 pieces of wood shaped 3 x 2; selling for a price of 3 * 10 = 30. - 1 piece of wood shaped 1 x 4; selling for a price of 1 * 2 = 2. This obtains a total of 30 + 2 = 32 money earned. It can be shown that 32 is the maximum amount of money that can be earned. Notice that we cannot rotate the 1 x 4 piece of wood to obtain a 4 x 1 piece of wood. Constraints: 1 <= m; n <= 200 1 <= prices.length <= 2 * 104 prices[i].length == 3 1 <= hi <= m 1 <= wi <= n 1 <= pricei <= 106 All the shapes of wood (hi; wi) are pairwise distinct.
Uber,1389,Create Target Array in the Given Order,Easy,"Array, Breadth-First Search, Heap (Priority Queue), Matrix","A storekeeper is a game in which the player pushes boxes around in a warehouse trying to get them to target locations. The game is represented by an m x n grid of characters grid where each element is a wall; floor; or box. Your task is to move the box 'B' to the target position 'T' under the following rules: The character 'S' represents the player. The player can move up; down; left; right in grid if it is a floor (empty cell). The character '.' represents the floor which means a free cell to walk. The character '#' represents the wall which means an obstacle (impossible to walk there). There is only one box 'B' and one target cell 'T' in the grid. The box can be moved to an adjacent free cell by standing next to the box and then moving in the direction of the box. This is a push. The player cannot walk through the box. Return the minimum number of pushes to move the box to the target. If there is no way to reach the target; return -1. Example 1: Input: grid = [[""#"";""#"";""#"";""#"";""#"";""#""]; [""#"";""T"";""#"";""#"";""#"";""#""]; [""#"";""."";""."";""B"";""."";""#""]; [""#"";""."";""#"";""#"";""."";""#""]; [""#"";""."";""."";""."";""S"";""#""]; [""#"";""#"";""#"";""#"";""#"";""#""]] Output: 3 Explanation: We return only the number of times the box is pushed. Example 2: Input: grid = [[""#"";""#"";""#"";""#"";""#"";""#""]; [""#"";""T"";""#"";""#"";""#"";""#""]; [""#"";""."";""."";""B"";""."";""#""]; [""#"";""#"";""#"";""#"";""."";""#""]; [""#"";""."";""."";""."";""S"";""#""]; [""#"";""#"";""#"";""#"";""#"";""#""]] Output: -1 Example 3: Input: grid = [[""#"";""#"";""#"";""#"";""#"";""#""]; [""#"";""T"";""."";""."";""#"";""#""]; [""#"";""."";""#"";""B"";""."";""#""]; [""#"";""."";""."";""."";""."";""#""]; [""#"";""."";""."";""."";""S"";""#""]; [""#"";""#"";""#"";""#"";""#"";""#""]] Output: 5 Explanation: push the box down; left; left; up and up. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 20 grid contains only characters '.'; '#'; 'S'; 'T'; or 'B'. There is only one character 'S'; 'B'; and 'T' in the grid."
Uber,1395,Count Number of Teams,Med,"Array, Math, Geometry",On a 2D plane; there are n points with integer coordinates points[i] = [xi; yi]. Return the minimum time in seconds to visit all the points in the order given by points. You can move according to these rules: In 1 second; you can either: move vertically by one unit; move horizontally by one unit; or move diagonally sqrt(2) units (in other words; move one unit vertically then one unit horizontally in 1 second). You have to visit the points in the same order as they appear in the array. You are allowed to pass through points that appear later in the order; but these do not count as visits. Example 1: Input: points = [[1;1];[3;4];[-1;0]] Output: 7 Explanation: One optimal path is [1;1] -> [2;2] -> [3;3] -> [3;4] -> [2;3] -> [1;2] -> [0;1] -> [-1;0] Time from [1;1] to [3;4] = 3 seconds Time from [3;4] to [-1;0] = 4 seconds Total time = 7 seconds Example 2: Input: points = [[3;2];[-2;2]] Output: 5 Constraints: points.length == n 1 <= n <= 100 points[i].length == 2 -1000 <= points[i][0]; points[i][1] <= 1000
Uber,1463,Cherry Pickup II,Hard,"Array, Binary Search, Sorting, Heap (Priority Queue), Matrix",You are given an m x n binary matrix mat of 1's (representing soldiers) and 0's (representing civilians). The soldiers are positioned in front of the civilians. That is; all the 1's will appear to the left of all the 0's in each row. A row i is weaker than a row j if one of the following is true: The number of soldiers in row i is less than the number of soldiers in row j. Both rows have the same number of soldiers and i < j. Return the indices of the k weakest rows in the matrix ordered from weakest to strongest. Example 1: Input: mat = [[1;1;0;0;0]; [1;1;1;1;0]; [1;0;0;0;0]; [1;1;0;0;0]; [1;1;1;1;1]]; k = 3 Output: [2;0;3] Explanation: The number of soldiers in each row is: - Row 0: 2 - Row 1: 4 - Row 2: 1 - Row 3: 2 - Row 4: 5 The rows ordered from weakest to strongest are [2;0;3;1;4]. Example 2: Input: mat = [[1;0;0;0]; [1;1;1;1]; [1;0;0;0]; [1;0;0;0]]; k = 2 Output: [0;2] Explanation: The number of soldiers in each row is: - Row 0: 1 - Row 1: 4 - Row 2: 1 - Row 3: 1 The rows ordered from weakest to strongest are [0;2;3;1]. Constraints: m == mat.length n == mat[i].length 2 <= n; m <= 100 1 <= k <= m matrix[i][j] is either 0 or 1.
Uber,1472,Design Browser History,Med,"Hash Table, String, Counting","You are given a string s. Reorder the string using the following algorithm: Remove the smallest character from s and append it to the result. Remove the smallest character from s that is greater than the last appended character; and append it to the result. Repeat step 2 until no more characters can be removed. Remove the largest character from s and append it to the result. Remove the largest character from s that is smaller than the last appended character; and append it to the result. Repeat step 5 until no more characters can be removed. Repeat steps 1 through 6 until all characters from s have been removed. If the smallest or largest character appears more than once; you may choose any occurrence to append to the result. Return the resulting string after reordering s using this algorithm. Example 1: Input: s = ""aaaabbbbcccc"" Output: ""abccbaabccba"" Explanation: After steps 1; 2 and 3 of the first iteration; result = ""abc"" After steps 4; 5 and 6 of the first iteration; result = ""abccba"" First iteration is done. Now s = ""aabbcc"" and we go back to step 1 After steps 1; 2 and 3 of the second iteration; result = ""abccbaabc"" After steps 4; 5 and 6 of the second iteration; result = ""abccbaabccba"" Example 2: Input: s = ""rat"" Output: ""art"" Explanation: The word ""rat"" becomes ""art"" after re-ordering it with the mentioned algorithm. Constraints: 1 <= s.length <= 500 s consists of only lowercase English letters."
Uber,1491,Average Salary Excluding the Minimum and Maximum Salary,Easy,Array,"You have a 1-indexed binary string of length n where all the bits are 0 initially. We will flip all the bits of this binary string (i.e.; change them from 0 to 1) one by one. You are given a 1-indexed integer array flips where flips[i] indicates that the bit at index i will be flipped in the ith step. A binary string is prefix-aligned if; after the ith step; all the bits in the inclusive range [1; i] are ones and all the other bits are zeros. Return the number of times the binary string is prefix-aligned during the flipping process. Example 1: Input: flips = [3;2;4;1;5] Output: 2 Explanation: The binary string is initially ""00000"". After applying step 1: The string becomes ""00100""; which is not prefix-aligned. After applying step 2: The string becomes ""01100""; which is not prefix-aligned. After applying step 3: The string becomes ""01110""; which is not prefix-aligned. After applying step 4: The string becomes ""11110""; which is prefix-aligned. After applying step 5: The string becomes ""11111""; which is prefix-aligned. We can see that the string was prefix-aligned 2 times; so we return 2. Example 2: Input: flips = [4;1;2;3] Output: 1 Explanation: The binary string is initially ""0000"". After applying step 1: The string becomes ""0001""; which is not prefix-aligned. After applying step 2: The string becomes ""1001""; which is not prefix-aligned. After applying step 3: The string becomes ""1101""; which is not prefix-aligned. After applying step 4: The string becomes ""1111""; which is prefix-aligned. We can see that the string was prefix-aligned 1 time; so we return 1. Constraints: n == flips.length 1 <= n <= 5 * 104 flips is a permutation of the integers in the range [1; n]."
Uber,1481,Least Number of Unique Integers after K Removals,Med,Database,
Uber,1502,Can Make Arithmetic Progression From Sequence,Easy,"Hash Table, String, Greedy, Counting","Given a string s and an integer k; return true if you can use all the characters in s to construct k palindrome strings or false otherwise. Example 1: Input: s = ""annabelle""; k = 2 Output: true Explanation: You can construct two palindromes using all characters in s. Some possible constructions ""anna"" + ""elble""; ""anbna"" + ""elle""; ""anellena"" + ""b"" Example 2: Input: s = ""leetcode""; k = 3 Output: false Explanation: It is impossible to construct 3 palindromes using all the characters of s. Example 3: Input: s = ""true""; k = 4 Output: true Explanation: The only possible solution is to put each character in a separate string. Constraints: 1 <= s.length <= 105 s consists of lowercase English letters. 1 <= k <= 105"
Uber,1552,Magnetic Force Between Two Balls,Med,"Array, Stack, Simulation","You are given an integer array target and an integer n. You have an empty stack with the two following operations: ""Push"": pushes an integer to the top of the stack. ""Pop"": removes the integer on the top of the stack. You also have a stream of the integers in the range [1; n]. Use the two stack operations to make the numbers in the stack (from the bottom to the top) equal to target. You should follow the following rules: If the stream of the integers is not empty; pick the next integer from the stream and push it to the top of the stack. If the stack is not empty; pop the integer at the top of the stack. If; at any moment; the elements in the stack (from the bottom to the top) are equal to target; do not read new integers from the stream and do not do more operations on the stack. Return the stack operations needed to build target following the mentioned rules. If there are multiple valid answers; return any of them. Example 1: Input: target = [1;3]; n = 3 Output: [""Push"";""Push"";""Pop"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Pop the integer on the top of the stack. s = [1]. Read 3 from the stream and push it to the stack. s = [1;3]. Example 2: Input: target = [1;2;3]; n = 3 Output: [""Push"";""Push"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Read 3 from the stream and push it to the stack. s = [1;2;3]. Example 3: Input: target = [1;2]; n = 4 Output: [""Push"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Since the stack (from the bottom to the top) is equal to target; we stop the stack operations. The answers that read integer 3 from the stream are not accepted. Constraints: 1 <= target.length <= 100 1 <= n <= 100 1 <= target[i] <= n target is strictly increasing."
Uber,1584,Min Cost to Connect All Points,Med,"Array, Sorting",You are given an array of unique integers salary where salary[i] is the salary of the ith employee. Return the average salary of employees excluding the minimum and maximum salary. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: salary = [4000;3000;1000;2000] Output: 2500.00000 Explanation: Minimum salary and maximum salary are 1000 and 4000 respectively. Average salary excluding minimum and maximum salary is (2000+3000) / 2 = 2500 Example 2: Input: salary = [1000;2000;3000] Output: 2000.00000 Explanation: Minimum salary and maximum salary are 1000 and 3000 respectively. Average salary excluding minimum and maximum salary is (2000) / 1 = 2000 Constraints: 3 <= salary.length <= 100 1000 <= salary[i] <= 106 All the integers of salary are unique.
Uber,1611,Minimum One Bit Operations to Make Integers Zero,Hard,"Array, Hash Table, String","Given an array of strings names of size n. You will create n folders in your file system such that; at the ith minute; you will create a folder with the name names[i]. Since two files cannot have the same name; if you enter a folder name that was previously used; the system will have a suffix addition to its name in the form of (k); where; k is the smallest positive integer such that the obtained name remains unique. Return an array of strings of length n where ans[i] is the actual name the system will assign to the ith folder when you create it. Example 1: Input: names = [""pes"";""fifa"";""gta"";""pes(2019)""] Output: [""pes"";""fifa"";""gta"";""pes(2019)""] Explanation: Let's see how the file system creates folder names: ""pes"" --> not assigned before; remains ""pes"" ""fifa"" --> not assigned before; remains ""fifa"" ""gta"" --> not assigned before; remains ""gta"" ""pes(2019)"" --> not assigned before; remains ""pes(2019)"" Example 2: Input: names = [""gta"";""gta(1)"";""gta"";""avalon""] Output: [""gta"";""gta(1)"";""gta(2)"";""avalon""] Explanation: Let's see how the file system creates folder names: ""gta"" --> not assigned before; remains ""gta"" ""gta(1)"" --> not assigned before; remains ""gta(1)"" ""gta"" --> the name is reserved; system adds (k); since ""gta(1)"" is also reserved; systems put k = 2. it becomes ""gta(2)"" ""avalon"" --> not assigned before; remains ""avalon"" Example 3: Input: names = [""onepiece"";""onepiece(1)"";""onepiece(2)"";""onepiece(3)"";""onepiece""] Output: [""onepiece"";""onepiece(1)"";""onepiece(2)"";""onepiece(3)"";""onepiece(4)""] Explanation: When the last folder is created; the smallest positive valid k is 4; and it becomes ""onepiece(4)"". Constraints: 1 <= names.length <= 5 * 104 1 <= names[i].length <= 20 names[i] consists of lowercase English letters; digits; and/or round brackets."
Uber,1642,Furthest Building You Can Reach,Med,"Math, Simulation",There are numBottles water bottles that are initially full of water. You can exchange numExchange empty water bottles from the market with one full water bottle. The operation of drinking a full water bottle turns it into an empty bottle. Given the two integers numBottles and numExchange; return the maximum number of water bottles you can drink. Example 1: Input: numBottles = 9; numExchange = 3 Output: 13 Explanation: You can exchange 3 empty bottles to get 1 full water bottle. Number of water bottles you can drink: 9 + 3 + 1 = 13. Example 2: Input: numBottles = 15; numExchange = 4 Output: 19 Explanation: You can exchange 4 empty bottles to get 1 full water bottle. Number of water bottles you can drink: 15 + 3 + 1 = 19. Constraints: 1 <= numBottles <= 100 2 <= numExchange <= 100
Uber,1669,Merge In Between Linked Lists,Med,"Array, Dynamic Programming, Sorting",Given a wooden stick of length n units. The stick is labelled from 0 to n. For example; a stick of length 6 is labelled as follows: Given an integer array cuts where cuts[i] denotes a position you should perform a cut at. You should perform the cuts in order; you can change the order of the cuts as you wish. The cost of one cut is the length of the stick to be cut; the total cost is the sum of costs of all cuts. When you cut a stick; it will be split into two smaller sticks (i.e. the sum of their lengths is the length of the stick before the cut). Please refer to the first example for a better explanation. Return the minimum total cost of the cuts. Example 1: Input: n = 7; cuts = [1;3;4;5] Output: 16 Explanation: Using cuts order = [1; 3; 4; 5] as in the input leads to the following scenario: The first cut is done to a rod of length 7 so the cost is 7. The second cut is done to a rod of length 6 (i.e. the second part of the first cut); the third is done to a rod of length 4 and the last cut is to a rod of length 3. The total cost is 7 + 6 + 4 + 3 = 20. Rearranging the cuts to be [3; 5; 1; 4] for example will lead to a scenario with total cost = 16 (as shown in the example photo 7 + 4 + 3 + 2 = 16). Example 2: Input: n = 9; cuts = [5;6;1;4;2] Output: 22 Explanation: If you try the given cuts ordering the cost will be 25. There are much ordering with total cost <= 25; for example; the order [4; 6; 5; 2; 1] has total cost = 22 which is the minimum possible. Constraints: 2 <= n <= 106 1 <= cuts.length <= min(n - 1; 100) 1 <= cuts[i] <= n - 1 All the integers in cuts array are distinct.
Uber,1662,Check If Two String Arrays are Equivalent,Easy,"Array, Greedy, Bit Manipulation",You are given an integer array nums. You have an integer array arr of the same length with all values set to 0 initially. You also have the following modify function: You want to use the modify function to convert arr to nums using the minimum number of calls. Return the minimum number of function calls to make nums from arr. The test cases are generated so that the answer fits in a 32-bit signed integer. Example 1: Input: nums = [1;5] Output: 5 Explanation: Increment by 1 (second element): [0; 0] to get [0; 1] (1 operation). Double all the elements: [0; 1] -> [0; 2] -> [0; 4] (2 operations). Increment by 1 (both elements) [0; 4] -> [1; 4] -> [1; 5] (2 operations). Total of operations: 1 + 2 + 2 = 5. Example 2: Input: nums = [2;2] Output: 3 Explanation: Increment by 1 (both elements) [0; 0] -> [0; 1] -> [1; 1] (2 operations). Double all the elements: [1; 1] -> [2; 2] (1 operation). Total of operations: 2 + 1 = 3. Example 3: Input: nums = [4;2;5] Output: 6 Explanation: (initial)[0;0;0] -> [1;0;0] -> [1;0;1] -> [2;0;2] -> [2;1;2] -> [4;2;4] -> [4;2;5](nums). Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109
Uber,1685,Sum of Absolute Differences in a Sorted Array,Med,"Array, Math, Dynamic Programming, Game Theory",There are several stones arranged in a row; and each stone has an associated value which is an integer given in the array stoneValue. In each round of the game; Alice divides the row into two non-empty rows (i.e. left row and right row); then Bob calculates the value of each row which is the sum of the values of all the stones in this row. Bob throws away the row which has the maximum value; and Alice's score increases by the value of the remaining row. If the value of the two rows are equal; Bob lets Alice decide which row will be thrown away. The next round starts with the remaining row. The game ends when there is only one stone remaining. Alice's is initially zero. Return the maximum score that Alice can obtain. Example 1: Input: stoneValue = [6;2;3;4;5;5] Output: 18 Explanation: In the first round; Alice divides the row to [6;2;3]; [4;5;5]. The left row has the value 11 and the right row has value 14. Bob throws away the right row and Alice's score is now 11. In the second round Alice divides the row to [6]; [2;3]. This time Bob throws away the left row and Alice's score becomes 16 (11 + 5). The last round Alice has only one choice to divide the row which is [2]; [3]. Bob throws away the right row and Alice's score is now 18 (16 + 2). The game ends because only one stone is remaining in the row. Example 2: Input: stoneValue = [7;7;7;7;7;7;7] Output: 28 Example 3: Input: stoneValue = [4] Output: 0 Constraints: 1 <= stoneValue.length <= 500 1 <= stoneValue[i] <= 106
Uber,1673,Find the Most Competitive Subsequence,Med,,
Uber,1716,Calculate Money in Leetcode Bank,Easy,"Array, Dynamic Programming, Matrix",You are given a m x n matrix grid. Initially; you are located at the top-left corner (0; 0); and in each step; you can only move right or down in the matrix. Among all possible paths starting from the top-left corner (0; 0) and ending in the bottom-right corner (m - 1; n - 1); find the path with the maximum non-negative product. The product of a path is the product of all integers in the grid cells visited along the path. Return the maximum non-negative product modulo 109 + 7. If the maximum product is negative; return -1. Notice that the modulo is performed after getting the maximum product. Example 1: Input: grid = [[-1;-2;-3];[-2;-3;-3];[-3;-3;-2]] Output: -1 Explanation: It is not possible to get non-negative product in the path from (0; 0) to (2; 2); so return -1. Example 2: Input: grid = [[1;-2;1];[1;-2;1];[3;-4;1]] Output: 8 Explanation: Maximum non-negative product is shown (1 * 1 * -2 * -4 * 1 = 8). Example 3: Input: grid = [[1;3];[0;-4]] Output: 0 Explanation: Maximum non-negative product is shown (1 * 0 * -4 = 0). Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 15 -4 <= grid[i][j] <= 4
Uber,1727,Largest Submatrix With Rearrangements,Med,"Array, Math, Dynamic Programming, Graph, Topological Sort, Memoization, Matrix, Game Theory","A game is played by a cat and a mouse named Cat and Mouse. The environment is represented by a grid of size rows x cols; where each element is a wall; floor; player (Cat; Mouse); or food. Players are represented by the characters 'C'(Cat);'M'(Mouse). Floors are represented by the character '.' and can be walked on. Walls are represented by the character '#' and cannot be walked on. Food is represented by the character 'F' and can be walked on. There is only one of each character 'C'; 'M'; and 'F' in grid. Mouse and Cat play according to the following rules: Mouse moves first; then they take turns to move. During each turn; Cat and Mouse can jump in one of the four directions (left; right; up; down). They cannot jump over the wall nor outside of the grid. catJump; mouseJump are the maximum lengths Cat and Mouse can jump at a time; respectively. Cat and Mouse can jump less than the maximum length. Staying in the same position is allowed. Mouse can jump over Cat. The game can end in 4 ways: If Cat occupies the same position as Mouse; Cat wins. If Cat reaches the food first; Cat wins. If Mouse reaches the food first; Mouse wins. If Mouse cannot get to the food within 1000 turns; Cat wins. Given a rows x cols matrix grid and two integers catJump and mouseJump; return true if Mouse can win the game if both Cat and Mouse play optimally; otherwise return false. Example 1: Input: grid = [""####F"";""#C..."";""M....""]; catJump = 1; mouseJump = 2 Output: true Explanation: Cat cannot catch Mouse on its turn nor can it get the food before Mouse. Example 2: Input: grid = [""M.C...F""]; catJump = 1; mouseJump = 4 Output: true Example 3: Input: grid = [""M.C...F""]; catJump = 1; mouseJump = 3 Output: false Constraints: rows == grid.length cols = grid[i].length 1 <= rows; cols <= 8 grid[i][j] consist only of characters 'C'; 'M'; 'F'; '.'; and '#'. There is only one of each character 'C'; 'M'; and 'F' in grid. 1 <= catJump; mouseJump <= 8"
Uber,1743,Restore the Array From Adjacent Pairs,Med,"Hash Table, String, Dynamic Programming, Enumeration","Given two strings s and t; find the number of ways you can choose a non-empty substring of s and replace a single character by a different character such that the resulting substring is a substring of t. In other words; find the number of substrings in s that differ from some substring in t by exactly one character. For example; the underlined substrings in ""computer"" and ""computation"" only differ by the 'e'/'a'; so this is a valid way. Return the number of substrings that satisfy the condition above. A substring is a contiguous sequence of characters within a string. Example 1: Input: s = ""aba""; t = ""baba"" Output: 6 Explanation: The following are the pairs of substrings from s and t that differ by exactly 1 character: (""aba""; ""baba"") (""aba""; ""baba"") (""aba""; ""baba"") (""aba""; ""baba"") (""aba""; ""baba"") (""aba""; ""baba"") The underlined portions are the substrings that are chosen from s and t. ​​Example 2: Input: s = ""ab""; t = ""bb"" Output: 3 Explanation: The following are the pairs of substrings from s and t that differ by 1 character: (""ab""; ""bb"") (""ab""; ""bb"") (""ab""; ""bb"") ​​​​The underlined portions are the substrings that are chosen from s and t. Constraints: 1 <= s.length; t.length <= 100 s and t consist of lowercase English letters only."
Uber,1766,Tree of Coprimes,Hard,"Array, Binary Search, Dynamic Programming, Greedy",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array nums​​​; return the minimum number of elements to remove to make nums​​​ a mountain array. Example 1: Input: nums = [1;3;1] Output: 0 Explanation: The array itself is a mountain array so we do not need to remove any elements. Example 2: Input: nums = [2;1;1;5;6;2;3;1] Output: 3 Explanation: One solution is to remove the elements at indices 0; 1; and 5; making the array nums = [1;5;6;3;1]. Constraints: 3 <= nums.length <= 1000 1 <= nums[i] <= 109 It is guaranteed that you can make a mountain array out of nums.
Uber,1729,Find Followers Count,Easy,"Stack, Tree, Design, Binary Search Tree, Binary Tree, Iterator",
Uber,1755,Closest Subsequence Sum,Hard,"Array, Sliding Window",You have a bomb to defuse; and your time is running out! Your informer will provide you with a circular array code of length of n and a key k. To decrypt the code; you must replace every number. All the numbers are replaced simultaneously. If k > 0; replace the ith number with the sum of the next k numbers. If k < 0; replace the ith number with the sum of the previous k numbers. If k == 0; replace the ith number with 0. As code is circular; the next element of code[n-1] is code[0]; and the previous element of code[0] is code[n-1]. Given the circular array code and an integer key k; return the decrypted code to defuse the bomb! Example 1: Input: code = [5;7;1;4]; k = 3 Output: [12;10;16;13] Explanation: Each number is replaced by the sum of the next 3 numbers. The decrypted code is [7+1+4; 1+4+5; 4+5+7; 5+7+1]. Notice that the numbers wrap around. Example 2: Input: code = [1;2;3;4]; k = 0 Output: [0;0;0;0] Explanation: When k is zero; the numbers are replaced by 0. Example 3: Input: code = [2;4;9;3]; k = -2 Output: [12;5;6;13] Explanation: The decrypted code is [3+9; 2+3; 4+2; 9+4]. Notice that the numbers wrap around again. If k is negative; the sum is of the previous numbers. Constraints: n == code.length 1 <= n <= 100 1 <= code[i] <= 100 -(n - 1) <= k <= n - 1
Uber,1814,Count Nice Pairs in an Array,Med,"Array, Dynamic Programming, Queue, Heap (Priority Queue), Monotonic Queue",You are given a 0-indexed integer array nums and an integer k. You are initially standing at index 0. In one move; you can jump at most k steps forward without going outside the boundaries of the array. That is; you can jump from index i to any index in the range [i + 1; min(n - 1; i + k)] inclusive. You want to reach the last index of the array (index n - 1). Your score is the sum of all nums[j] for each index j you visited in the array. Return the maximum score you can get. Example 1: Input: nums = [1;-1;-2;4;-7;3]; k = 2 Output: 7 Explanation: You can choose your jumps forming the subsequence [1;-1;4;3] (underlined above). The sum is 7. Example 2: Input: nums = [10;-5;-2;4;0;3]; k = 3 Output: 17 Explanation: You can choose your jumps forming the subsequence [10;4;3] (underlined above). The sum is 17. Example 3: Input: nums = [1;-5;-20;4;-1;3;-6;-3]; k = 2 Output: 0 Constraints: 1 <= nums.length; k <= 105 -104 <= nums[i] <= 104
Uber,1802,Maximum Value at a Given Index in a Bounded Array,Med,"Array, Stack, Queue, Simulation",The school cafeteria offers circular and square sandwiches at lunch break; referred to by numbers 0 and 1 respectively. All students stand in a queue. Each student either prefers square or circular sandwiches. The number of sandwiches in the cafeteria is equal to the number of students. The sandwiches are placed in a stack. At each step: If the student at the front of the queue prefers the sandwich on the top of the stack; they will take it and leave the queue. Otherwise; they will leave it and go to the queue's end. This continues until none of the queue students want to take the top sandwich and are thus unable to eat. You are given two integer arrays students and sandwiches where sandwiches[i] is the type of the i​​​​​​th sandwich in the stack (i = 0 is the top of the stack) and students[j] is the preference of the j​​​​​​th student in the initial queue (j = 0 is the front of the queue). Return the number of students that are unable to eat. Example 1: Input: students = [1;1;0;0]; sandwiches = [0;1;0;1] Output: 0 Explanation: - Front student leaves the top sandwich and returns to the end of the line making students = [1;0;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;0;1;1]. - Front student takes the top sandwich and leaves the line making students = [0;1;1] and sandwiches = [1;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [1;1;0]. - Front student takes the top sandwich and leaves the line making students = [1;0] and sandwiches = [0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;1]. - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = [1]. - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = []. Hence all students are able to eat. Example 2: Input: students = [1;1;1;0;0;1]; sandwiches = [1;0;0;0;1;1] Output: 3 Constraints: 1 <= students.length; sandwiches.length <= 100 students.length == sandwiches.length sandwiches[i] is 0 or 1. students[i] is 0 or 1.
Uber,1820,Maximum Number of Accepted Invitations,Med,"Tree, Graph",You are given an array pairs; where pairs[i] = [xi; yi]; and: There are no duplicates. xi < yi Let ways be the number of rooted trees that satisfy the following conditions: The tree consists of nodes whose values appeared in pairs. A pair [xi; yi] exists in pairs if and only if xi is an ancestor of yi or yi is an ancestor of xi. Note: the tree does not have to be a binary tree. Two ways are considered to be different if there is at least one node that has different parents in both ways. Return: 0 if ways == 0 1 if ways == 1 2 if ways > 1 A rooted tree is a tree that has a single root node; and all edges are oriented to be outgoing from the root. An ancestor of a node is any node on the path from the root to that node (excluding the node itself). The root has no ancestors. Example 1: Input: pairs = [[1;2];[2;3]] Output: 1 Explanation: There is exactly one valid rooted tree; which is shown in the above figure. Example 2: Input: pairs = [[1;2];[2;3];[1;3]] Output: 2 Explanation: There are multiple valid rooted trees. Three of them are shown in the above figures. Example 3: Input: pairs = [[1;2];[2;3];[2;4];[1;5]] Output: 0 Explanation: There are no valid rooted trees. Constraints: 1 <= pairs.length <= 105 1 <= xi < yi <= 500 The elements in pairs are unique.
Uber,1877,Minimize Maximum Pair Sum in Array,Med,Database,Table: Followers +-------------+------+ | Column Name | Type | +-------------+------+ | user_id | int | | follower_id | int | +-------------+------+ (user_id; follower_id) is the primary key (combination of columns with unique values) for this table. This table contains the IDs of a user and a follower in a social media app where the follower follows the user. Write a solution that will; for each user; return the number of followers. Return the result table ordered by user_id in ascending order. The result format is in the following example. Example 1: Input: Followers table: +---------+-------------+ | user_id | follower_id | +---------+-------------+ | 0 | 1 | | 1 | 0 | | 2 | 0 | | 2 | 1 | +---------+-------------+ Output: +---------+----------------+ | user_id | followers_count| +---------+----------------+ | 0 | 1 | | 1 | 1 | | 2 | 2 | +---------+----------------+ Explanation: The followers of 0 are {1} The followers of 1 are {0} The followers of 2 are {0;1}
Uber,1842,Next Palindrome Using Same Digits,Hard,Database,
Uber,1912,Design Movie Rental System,Hard,"Dynamic Programming, Graph, Topological Sort, Heap (Priority Queue), Shortest Path",There is an undirected weighted connected graph. You are given a positive integer n which denotes that the graph has n nodes labeled from 1 to n; and an array edges where each edges[i] = [ui; vi; weighti] denotes that there is an edge between nodes ui and vi with weight equal to weighti. A path from node start to node end is a sequence of nodes [z0; z1; z2; ...; zk] such that z0 = start and zk = end and there is an edge between zi and zi+1 where 0 <= i <= k-1. The distance of a path is the sum of the weights on the edges of the path. Let distanceToLastNode(x) denote the shortest distance of a path between node n and node x. A restricted path is a path that also satisfies that distanceToLastNode(zi) > distanceToLastNode(zi+1) where 0 <= i <= k-1. Return the number of restricted paths from node 1 to node n. Since that number may be too large; return it modulo 109 + 7. Example 1: Input: n = 5; edges = [[1;2;3];[1;3;3];[2;3;1];[1;4;2];[5;2;2];[3;5;1];[5;4;10]] Output: 3 Explanation: Each circle contains the node number in black and its distanceToLastNode value in blue. The three restricted paths are: 1) 1 --> 2 --> 5 2) 1 --> 2 --> 3 --> 5 3) 1 --> 3 --> 5 Example 2: Input: n = 7; edges = [[1;3;1];[4;1;2];[7;3;4];[2;5;3];[5;6;1];[6;7;2];[7;5;3];[2;6;4]] Output: 1 Explanation: Each circle contains the node number in black and its distanceToLastNode value in blue. The only restricted path is 1 --> 3 --> 7. Constraints: 1 <= n <= 2 * 104 n - 1 <= edges.length <= 4 * 104 edges[i].length == 3 1 <= ui; vi <= n ui != vi 1 <= weighti <= 105 There is at most one edge between any two nodes. There is at least one path between any two nodes.
Uber,1920,Build Array from Permutation,Easy,"Math, String","You are given coordinates; a string that represents the coordinates of a square of the chessboard. Below is a chessboard for your reference. Return true if the square is white; and false if the square is black. The coordinate will always represent a valid chessboard square. The coordinate will always have the letter first; and the number second. Example 1: Input: coordinates = ""a1"" Output: false Explanation: From the chessboard above; the square with coordinates ""a1"" is black; so return false. Example 2: Input: coordinates = ""h3"" Output: true Explanation: From the chessboard above; the square with coordinates ""h3"" is white; so return true. Example 3: Input: coordinates = ""c7"" Output: false Constraints: coordinates.length == 2 'a' <= coordinates[0] <= 'h' '1' <= coordinates[1] <= '8'"
Uber,1930,Unique Length-3 Palindromic Subsequences,Med,"Array, Greedy, Sorting",You are given an integer array coins of length n which represents the n coins that you own. The value of the ith coin is coins[i]. You can make some value x if you can choose some of your n coins such that their values sum up to x. Return the maximum number of consecutive integer values that you can make with your coins starting from and including 0. Note that you may have multiple coins of the same value. Example 1: Input: coins = [1;3] Output: 2 Explanation: You can make the following values: - 0: take [] - 1: take [1] You can make 2 consecutive integer values starting from 0. Example 2: Input: coins = [1;1;1;4] Output: 8 Explanation: You can make the following values: - 0: take [] - 1: take [1] - 2: take [1;1] - 3: take [1;1;1] - 4: take [4] - 5: take [4;1] - 6: take [4;1;1] - 7: take [4;1;1;1] You can make 8 consecutive integer values starting from 0. Example 3: Input: coins = [1;4;10;3;1] Output: 20 Constraints: coins.length == n 1 <= n <= 4 * 104 1 <= coins[i] <= 4 * 104
Uber,2021,Brightest Position on Street,Med,"String, Stack, Simulation","Given two strings s and part; perform the following operation on s until all occurrences of the substring part are removed: Find the leftmost occurrence of the substring part and remove it from s. Return s after removing all occurrences of part. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""daabcbaabcbc""; part = ""abc"" Output: ""dab"" Explanation: The following operations are done: - s = ""daabcbaabcbc""; remove ""abc"" starting at index 2; so s = ""dabaabcbc"". - s = ""dabaabcbc""; remove ""abc"" starting at index 4; so s = ""dababc"". - s = ""dababc""; remove ""abc"" starting at index 3; so s = ""dab"". Now s has no occurrences of ""abc"". Example 2: Input: s = ""axxxxyyyyb""; part = ""xy"" Output: ""ab"" Explanation: The following operations are done: - s = ""axxxxyyyyb""; remove ""xy"" starting at index 4 so s = ""axxxyyyb"". - s = ""axxxyyyb""; remove ""xy"" starting at index 3 so s = ""axxyyb"". - s = ""axxyyb""; remove ""xy"" starting at index 2 so s = ""axyb"". - s = ""axyb""; remove ""xy"" starting at index 1 so s = ""ab"". Now s has no occurrences of ""xy"". Constraints: 1 <= s.length <= 1000 1 <= part.length <= 1000 s​​​​​​ and part consists of lowercase English letters."
Uber,1934,Confirmation Rate,Med,"Array, Hash Table, String","You are given a string s that contains some bracket pairs; with each pair containing a non-empty key. For example; in the string ""(name)is(age)yearsold""; there are two bracket pairs that contain the keys ""name"" and ""age"". You know the values of a wide range of keys. This is represented by a 2D string array knowledge where each knowledge[i] = [keyi; valuei] indicates that key keyi has a value of valuei. You are tasked to evaluate all of the bracket pairs. When you evaluate a bracket pair that contains some key keyi; you will: Replace keyi and the bracket pair with the key's corresponding valuei. If you do not know the value of the key; you will replace keyi and the bracket pair with a question mark ""?"" (without the quotation marks). Each key will appear at most once in your knowledge. There will not be any nested brackets in s. Return the resulting string after evaluating all of the bracket pairs. Example 1: Input: s = ""(name)is(age)yearsold""; knowledge = [[""name"";""bob""];[""age"";""two""]] Output: ""bobistwoyearsold"" Explanation: The key ""name"" has a value of ""bob""; so replace ""(name)"" with ""bob"". The key ""age"" has a value of ""two""; so replace ""(age)"" with ""two"". Example 2: Input: s = ""hi(name)""; knowledge = [[""a"";""b""]] Output: ""hi?"" Explanation: As you do not know the value of the key ""name""; replace ""(name)"" with ""?"". Example 3: Input: s = ""(a)(a)(a)aaa""; knowledge = [[""a"";""yes""]] Output: ""yesyesyesaaa"" Explanation: The same key can appear multiple times. The key ""a"" has a value of ""yes""; so replace all occurrences of ""(a)"" with ""yes"". Notice that the ""a""s not in a bracket pair are not evaluated. Constraints: 1 <= s.length <= 105 0 <= knowledge.length <= 105 knowledge[i].length == 2 1 <= keyi.length; valuei.length <= 10 s consists of lowercase English letters and round brackets '(' and ')'. Every open bracket '(' in s will have a corresponding close bracket ')'. The key in each bracket pair of s will be non-empty. There will not be any nested bracket pairs in s. keyi and valuei consist of lowercase English letters. Each keyi in knowledge is unique."
Uber,1991,Find the Middle Index in Array,Easy,Database,
Uber,2024,Maximize the Confusion of an Exam,Med,Database,Table: Employees +-------------+---------+ | Column Name | Type | +-------------+---------+ | employee_id | int | | name | varchar | | salary | int | +-------------+---------+ employee_id is the primary key (column with unique values) for this table. Each row of this table indicates the employee ID; employee name; and salary. Write a solution to calculate the bonus of each employee. The bonus of an employee is 100% of their salary if the ID of the employee is an odd number and the employee's name does not start with the character 'M'. The bonus of an employee is 0 otherwise. Return the result table ordered by employee_id. The result format is in the following example. Example 1: Input: Employees table: +-------------+---------+--------+ | employee_id | name | salary | +-------------+---------+--------+ | 2 | Meir | 3000 | | 3 | Michael | 3800 | | 7 | Addilyn | 7400 | | 8 | Juan | 6100 | | 9 | Kannon | 7700 | +-------------+---------+--------+ Output: +-------------+-------+ | employee_id | bonus | +-------------+-------+ | 2 | 0 | | 3 | 0 | | 7 | 7400 | | 8 | 0 | | 9 | 7700 | +-------------+-------+ Explanation: The employees with IDs 2 and 8 get 0 bonus because they have an even employee_id. The employee with ID 3 gets 0 bonus because their name starts with 'M'. The rest of the employees get a 100% bonus.
Uber,2101,Detonate the Maximum Bombs,Med,"Array, Binary Search, Depth-First Search, Breadth-First Search, Union Find, Matrix",There is a 1-based binary matrix where 0 represents land and 1 represents water. You are given integers row and col representing the number of rows and columns in the matrix; respectively. Initially on day 0; the entire matrix is land. However; each day a new cell becomes flooded with water. You are given a 1-based 2D array cells; where cells[i] = [ri; ci] represents that on the ith day; the cell on the rith row and cith column (1-based coordinates) will be covered with water (i.e.; changed to 1). You want to find the last day that it is possible to walk from the top to the bottom by only walking on land cells. You can start from any cell in the top row and end at any cell in the bottom row. You can only travel in the four cardinal directions (left; right; up; and down). Return the last day where it is possible to walk from the top to the bottom by only walking on land cells. Example 1: Input: row = 2; col = 2; cells = [[1;1];[2;1];[1;2];[2;2]] Output: 2 Explanation: The above image depicts how the matrix changes each day starting from day 0. The last day where it is possible to cross from top to bottom is on day 2. Example 2: Input: row = 2; col = 2; cells = [[1;1];[1;2];[2;1];[2;2]] Output: 1 Explanation: The above image depicts how the matrix changes each day starting from day 0. The last day where it is possible to cross from top to bottom is on day 1. Example 3: Input: row = 3; col = 3; cells = [[1;2];[2;1];[3;3];[2;2];[1;1];[1;3];[2;3];[3;2];[3;1]] Output: 3 Explanation: The above image depicts how the matrix changes each day starting from day 0. The last day where it is possible to cross from top to bottom is on day 3. Constraints: 2 <= row; col <= 2 * 104 4 <= row * col <= 2 * 104 cells.length == row * col 1 <= ri <= row 1 <= ci <= col All the values of cells are unique.
Uber,2095,Delete the Middle Node of a Linked List,Med,"Two Pointers, String, Stack, Greedy","You are given a 0-indexed string s of even length n. The string consists of exactly n / 2 opening brackets '[' and n / 2 closing brackets ']'. A string is called balanced if and only if: It is the empty string; or It can be written as AB; where both A and B are balanced strings; or It can be written as [C]; where C is a balanced string. You may swap the brackets at any two indices any number of times. Return the minimum number of swaps to make s balanced. Example 1: Input: s = ""][]["" Output: 1 Explanation: You can make the string balanced by swapping index 0 with index 3. The resulting string is ""[[]]"". Example 2: Input: s = ""]]][[["" Output: 2 Explanation: You can do the following to make the string balanced: - Swap index 0 with index 4. s = ""[]][]["". - Swap index 1 with index 5. s = ""[[][]]"". The resulting string is ""[[][]]"". Example 3: Input: s = ""[]"" Output: 0 Explanation: The string is already balanced. Constraints: n == s.length 2 <= n <= 106 n is even. s[i] is either '[' or ']'. The number of opening brackets '[' equals n / 2; and the number of closing brackets ']' equals n / 2."
Uber,2130,Maximum Twin Sum of a Linked List,Med,"String, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask","Given a string s; find two disjoint palindromic subsequences of s such that the product of their lengths is maximized. The two subsequences are disjoint if they do not both pick a character at the same index. Return the maximum possible product of the lengths of the two palindromic subsequences. A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters. A string is palindromic if it reads the same forward and backward. Example 1: Input: s = ""leetcodecom"" Output: 9 Explanation: An optimal solution is to choose ""ete"" for the 1st subsequence and ""cdc"" for the 2nd subsequence. The product of their lengths is: 3 * 3 = 9. Example 2: Input: s = ""bb"" Output: 1 Explanation: An optimal solution is to choose ""b"" (the first character) for the 1st subsequence and ""b"" (the second character) for the 2nd subsequence. The product of their lengths is: 1 * 1 = 1. Example 3: Input: s = ""accbcaxxcxx"" Output: 25 Explanation: An optimal solution is to choose ""accca"" for the 1st subsequence and ""xxcxx"" for the 2nd subsequence. The product of their lengths is: 5 * 5 = 25. Constraints: 2 <= s.length <= 12 s consists of lowercase English letters only."
Uber,2336,Smallest Number in Infinite Set,Med,Database,
Uber,2367,Number of Arithmetic Triplets,Easy,"Array, Math, Geometry, Sorting, Number Theory",You are given a 2D integer array stockPrices where stockPrices[i] = [dayi; pricei] indicates the price of the stock on day dayi is pricei. A line chart is created from the array by plotting the points on an XY plane with the X-axis representing the day and the Y-axis representing the price and connecting adjacent points. One such example is shown below: Return the minimum number of lines needed to represent the line chart. Example 1: Input: stockPrices = [[1;7];[2;6];[3;5];[4;4];[5;4];[6;3];[7;2];[8;1]] Output: 3 Explanation: The diagram above represents the input; with the X-axis representing the day and Y-axis representing the price. The following 3 lines can be drawn to represent the line chart: - Line 1 (in red) from (1;7) to (4;4) passing through (1;7); (2;6); (3;5); and (4;4). - Line 2 (in blue) from (4;4) to (5;4). - Line 3 (in green) from (5;4) to (8;1) passing through (5;4); (6;3); (7;2); and (8;1). It can be shown that it is not possible to represent the line chart using less than 3 lines. Example 2: Input: stockPrices = [[3;4];[1;2];[7;8];[2;3]] Output: 1 Explanation: As shown in the diagram above; the line chart can be represented with a single line. Constraints: 1 <= stockPrices.length <= 105 stockPrices[i].length == 2 1 <= dayi; pricei <= 109 All dayi are distinct.
Uber,2413,Smallest Even Multiple,Easy,"Hash Table, Design, Heap (Priority Queue), Ordered Set","You have a set which contains all positive integers [1; 2; 3; 4; 5; ...]. Implement the SmallestInfiniteSet class: SmallestInfiniteSet() Initializes the SmallestInfiniteSet object to contain all positive integers. int popSmallest() Removes and returns the smallest integer contained in the infinite set. void addBack(int num) Adds a positive integer num back into the infinite set; if it is not already in the infinite set. Example 1: Input [""SmallestInfiniteSet""; ""addBack""; ""popSmallest""; ""popSmallest""; ""popSmallest""; ""addBack""; ""popSmallest""; ""popSmallest""; ""popSmallest""] [[]; [2]; []; []; []; [1]; []; []; []] Output [null; null; 1; 2; 3; null; 1; 4; 5] Explanation SmallestInfiniteSet smallestInfiniteSet = new SmallestInfiniteSet(); smallestInfiniteSet.addBack(2); // 2 is already in the set; so no change is made. smallestInfiniteSet.popSmallest(); // return 1; since 1 is the smallest number; and remove it from the set. smallestInfiniteSet.popSmallest(); // return 2; and remove it from the set. smallestInfiniteSet.popSmallest(); // return 3; and remove it from the set. smallestInfiniteSet.addBack(1); // 1 is added back to the set. smallestInfiniteSet.popSmallest(); // return 1; since 1 was added back to the set and // is the smallest number; and remove it from the set. smallestInfiniteSet.popSmallest(); // return 4; and remove it from the set. smallestInfiniteSet.popSmallest(); // return 5; and remove it from the set. Constraints: 1 <= num <= 1000 At most 1000 calls will be made in total to popSmallest and addBack."
Uber,2491,Divide Players Into Teams of Equal Skill,Med,"Math, Number Theory",Given a positive integer n; return the smallest positive integer that is a multiple of both 2 and n. Example 1: Input: n = 5 Output: 10 Explanation: The smallest multiple of both 5 and 2 is 10. Example 2: Input: n = 6 Output: 6 Explanation: The smallest multiple of both 6 and 2 is 6. Note that a number is a multiple of itself. Constraints: 1 <= n <= 150
Uber,2542,Maximum Subsequence Score,Med,"Array, Math",Given an integer array nums of positive integers; return the average value of all even integers that are divisible by 3. Note that the average of n elements is the sum of the n elements divided by n and rounded down to the nearest integer. Example 1: Input: nums = [1;3;6;10;12;15] Output: 9 Explanation: 6 and 12 are even numbers that are divisible by 3. (6 + 12) / 2 = 9. Example 2: Input: nums = [1;2;4;7;10] Output: 0 Explanation: There is no single number that satisfies the requirement; so return 0. Constraints: 1 <= nums.length <= 1000 1 <= nums[i] <= 1000
Uber,2601,Prime Subtraction Operation,Med,"Array, Dynamic Programming",You are given an array nums consisting of positive integers and an integer k. Partition the array into two ordered groups such that each element is in exactly one group. A partition is called great if the sum of elements of each group is greater than or equal to k. Return the number of distinct great partitions. Since the answer may be too large; return it modulo 109 + 7. Two partitions are considered distinct if some element nums[i] is in different groups in the two partitions. Example 1: Input: nums = [1;2;3;4]; k = 4 Output: 6 Explanation: The great partitions are: ([1;2;3]; [4]); ([1;3]; [2;4]); ([1;4]; [2;3]); ([2;3]; [1;4]); ([2;4]; [1;3]) and ([4]; [1;2;3]). Example 2: Input: nums = [3;3;3]; k = 4 Output: 0 Explanation: There are no great partitions for this array. Example 3: Input: nums = [6;6]; k = 2 Output: 2 Explanation: We can either put nums[0] in the first partition or in the second partition. The great partitions will be ([6]; [6]) and ([6]; [6]). Constraints: 1 <= nums.length; k <= 1000 1 <= nums[i] <= 109
Uber,2616,Minimize the Maximum Difference of Pairs,Med,"Array, Greedy, Heap (Priority Queue)",You are given a 0-indexed integer array nums and an integer k. You have a starting score of 0. In one operation: choose an index i such that 0 <= i < nums.length; increase your score by nums[i]; and replace nums[i] with ceil(nums[i] / 3). Return the maximum possible score you can attain after applying exactly k operations. The ceiling function ceil(val) is the least integer greater than or equal to val. Example 1: Input: nums = [10;10;10;10;10]; k = 5 Output: 50 Explanation: Apply the operation to each array element exactly once. The final score is 10 + 10 + 10 + 10 + 10 = 50. Example 2: Input: nums = [1;10;3;3;3]; k = 3 Output: 17 Explanation: You can do the following operations: Operation 1: Select i = 1; so nums becomes [1;4;3;3;3]. Your score increases by 10. Operation 2: Select i = 1; so nums becomes [1;2;3;3;3]. Your score increases by 4. Operation 3: Select i = 2; so nums becomes [1;2;1;3;3]. Your score increases by 3. The final score is 10 + 4 + 3 = 17. Constraints: 1 <= nums.length; k <= 105 1 <= nums[i] <= 109
Uber,2623,Memoize,Med,"Tree, Depth-First Search, Graph, Trie",
Uber,2629,Function Composition,Easy,"Hash Table, Math, String, Prefix Sum",
Uber,2707,Extra Characters in a String,Med,"Array, Hash Table, Two Pointers",You are given two 2D integer arrays nums1 and nums2. nums1[i] = [idi; vali] indicate that the number with the id idi has a value equal to vali. nums2[i] = [idi; vali] indicate that the number with the id idi has a value equal to vali. Each array contains unique ids and is sorted in ascending order by id. Merge the two arrays into one array that is sorted in ascending order by id; respecting the following conditions: Only ids that appear in at least one of the two arrays should be included in the resulting array. Each id should be included only once and its value should be the sum of the values of this id in the two arrays. If the id does not exist in one of the two arrays then its value in that array is considered to be 0. Return the resulting array. The returned array must be sorted in ascending order by id. Example 1: Input: nums1 = [[1;2];[2;3];[4;5]]; nums2 = [[1;4];[3;2];[4;1]] Output: [[1;6];[2;3];[3;2];[4;6]] Explanation: The resulting array contains the following: - id = 1; the value of this id is 2 + 4 = 6. - id = 2; the value of this id is 3. - id = 3; the value of this id is 2. - id = 4; the value of this id is 5 + 1 = 6. Example 2: Input: nums1 = [[2;4];[3;6];[5;5]]; nums2 = [[1;3];[4;3]] Output: [[1;3];[2;4];[3;6];[4;3];[5;5]] Explanation: There are no common ids; so we just include each id with its value in the resulting list. Constraints: 1 <= nums1.length; nums2.length <= 200 nums1[i].length == nums2[j].length == 2 1 <= idi; vali <= 1000 Both arrays contain unique ids. Both arrays are in strictly ascending order by id.
Uber,2648,Generate Fibonacci Sequence,Easy,"Array, Dynamic Programming",There is a test that has n types of questions. You are given an integer target and a 0-indexed 2D integer array types where types[i] = [counti; marksi] indicates that there are counti questions of the ith type; and each one of them is worth marksi points. Return the number of ways you can earn exactly target points in the exam. Since the answer may be too large; return it modulo 109 + 7. Note that questions of the same type are indistinguishable. For example; if there are 3 questions of the same type; then solving the 1st and 2nd questions is the same as solving the 1st and 3rd questions; or the 2nd and 3rd questions. Example 1: Input: target = 6; types = [[6;1];[3;2];[2;3]] Output: 7 Explanation: You can earn 6 points in one of the seven ways: - Solve 6 questions of the 0th type: 1 + 1 + 1 + 1 + 1 + 1 = 6 - Solve 4 questions of the 0th type and 1 question of the 1st type: 1 + 1 + 1 + 1 + 2 = 6 - Solve 2 questions of the 0th type and 2 questions of the 1st type: 1 + 1 + 2 + 2 = 6 - Solve 3 questions of the 0th type and 1 question of the 2nd type: 1 + 1 + 1 + 3 = 6 - Solve 1 question of the 0th type; 1 question of the 1st type and 1 question of the 2nd type: 1 + 2 + 3 = 6 - Solve 3 questions of the 1st type: 2 + 2 + 2 = 6 - Solve 2 questions of the 2nd type: 3 + 3 = 6 Example 2: Input: target = 5; types = [[50;1];[50;2];[50;5]] Output: 4 Explanation: You can earn 5 points in one of the four ways: - Solve 5 questions of the 0th type: 1 + 1 + 1 + 1 + 1 = 5 - Solve 3 questions of the 0th type and 1 question of the 1st type: 1 + 1 + 1 + 2 = 5 - Solve 1 questions of the 0th type and 2 questions of the 1st type: 1 + 2 + 2 = 5 - Solve 1 question of the 2nd type: 5 Example 3: Input: target = 18; types = [[6;1];[3;2];[2;3]] Output: 1 Explanation: You can only earn 18 points by answering all questions. Constraints: 1 <= target <= 1000 n == types.length 1 <= n <= 50 types[i].length == 2 1 <= counti; marksi <= 50
Uber,2742,Painting the Walls,Hard,,"Write code that enhances all arrays such that you can call the array.groupBy(fn) method on any array and it will return a grouped version of the array. A grouped array is an object where each key is the output of fn(arr[i]) and each value is an array containing all items in the original array which generate that key. The provided callback fn will accept an item in the array and return a string key. The order of each value list should be the order the items appear in the array. Any order of keys is acceptable. Please solve it without lodash's _.groupBy function. Example 1: Input: array = [ {""id"":""1""}; {""id"":""1""}; {""id"":""2""} ]; fn = function (item) { return item.id; } Output: { ""1"": [{""id"": ""1""}; {""id"": ""1""}]; ""2"": [{""id"": ""2""}] } Explanation: Output is from array.groupBy(fn). The selector function gets the ""id"" out of each item in the array. There are two objects with an ""id"" of 1. Both of those objects are put in the first array. There is one object with an ""id"" of 2. That object is put in the second array. Example 2: Input: array = [ [1; 2; 3]; [1; 3; 5]; [1; 5; 9] ] fn = function (list) { return String(list[0]); } Output: { ""1"": [[1; 2; 3]; [1; 3; 5]; [1; 5; 9]] } Explanation: The array can be of any type. In this case; the selector function defines the key as being the first element in the array. All the arrays have 1 as their first element so they are grouped together. { ""1"": [[1; 2; 3]; [1; 3; 5]; [1; 5; 9]] } Example 3: Input: array = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10] fn = function (n) { return String(n > 5); } Output: { ""true"": [6; 7; 8; 9; 10]; ""false"": [1; 2; 3; 4; 5] } Explanation: The selector function splits the array by whether each number is greater than 5. Constraints: 0 <= array.length <= 105 fn returns a string"
Uber,2831,Find the Longest Equal Subarray,Med,"Array, Hash Table, Math, Counting, Number Theory",You are given a 0-indexed integer array nums. A pair of indices i; j where 0 <= i < j < nums.length is called beautiful if the first digit of nums[i] and the last digit of nums[j] are coprime. Return the total number of beautiful pairs in nums. Two integers x and y are coprime if there is no integer greater than 1 that divides both of them. In other words; x and y are coprime if gcd(x; y) == 1; where gcd(x; y) is the greatest common divisor of x and y. Example 1: Input: nums = [2;5;1;4] Output: 5 Explanation: There are 5 beautiful pairs in nums: When i = 0 and j = 1: the first digit of nums[0] is 2; and the last digit of nums[1] is 5. We can confirm that 2 and 5 are coprime; since gcd(2;5) == 1. When i = 0 and j = 2: the first digit of nums[0] is 2; and the last digit of nums[2] is 1. Indeed; gcd(2;1) == 1. When i = 1 and j = 2: the first digit of nums[1] is 5; and the last digit of nums[2] is 1. Indeed; gcd(5;1) == 1. When i = 1 and j = 3: the first digit of nums[1] is 5; and the last digit of nums[3] is 4. Indeed; gcd(5;4) == 1. When i = 2 and j = 3: the first digit of nums[2] is 1; and the last digit of nums[3] is 4. Indeed; gcd(1;4) == 1. Thus; we return 5. Example 2: Input: nums = [11;21;12] Output: 2 Explanation: There are 2 beautiful pairs: When i = 0 and j = 1: the first digit of nums[0] is 1; and the last digit of nums[1] is 1. Indeed; gcd(1;1) == 1. When i = 0 and j = 2: the first digit of nums[0] is 1; and the last digit of nums[2] is 2. Indeed; gcd(1;2) == 1. Thus; we return 2. Constraints: 2 <= nums.length <= 100 1 <= nums[i] <= 9999 nums[i] % 10 != 0
Uber,2723,Add Two Promises,Easy,String,"You are given a binary string s consisting only of zeroes and ones. A substring of s is considered balanced if all zeroes are before ones and the number of zeroes is equal to the number of ones inside the substring. Notice that the empty substring is considered a balanced substring. Return the length of the longest balanced substring of s. A substring is a contiguous sequence of characters within a string. Example 1: Input: s = ""01000111"" Output: 6 Explanation: The longest balanced substring is ""000111""; which has length 6. Example 2: Input: s = ""00111"" Output: 4 Explanation: The longest balanced substring is ""0011""; which has length 4. Example 3: Input: s = ""111"" Output: 0 Explanation: There is no balanced substring except the empty substring; so the answer is 0. Constraints: 1 <= s.length <= 50 '0' <= s[i] <= '1'"
Uber,2762,Continuous Subarrays,Med,,"Write a class that allows getting and setting key-value pairs; however a time until expiration is associated with each key. The class has three public methods: set(key; value; duration): accepts an integer key; an integer value; and a duration in milliseconds. Once the duration has elapsed; the key should be inaccessible. The method should return true if the same un-expired key already exists and false otherwise. Both the value and duration should be overwritten if the key already exists. get(key): if an un-expired key exists; it should return the associated value. Otherwise it should return -1. count(): returns the count of un-expired keys. Example 1: Input: actions = [""TimeLimitedCache""; ""set""; ""get""; ""count""; ""get""] values = [[]; [1; 42; 100]; [1]; []; [1]] timeDelays = [0; 0; 50; 50; 150] Output: [null; false; 42; 1; -1] Explanation: At t=0; the cache is constructed. At t=0; a key-value pair (1: 42) is added with a time limit of 100ms. The value doesn't exist so false is returned. At t=50; key=1 is requested and the value of 42 is returned. At t=50; count() is called and there is one active key in the cache. At t=100; key=1 expires. At t=150; get(1) is called but -1 is returned because the cache is empty. Example 2: Input: actions = [""TimeLimitedCache""; ""set""; ""set""; ""get""; ""get""; ""get""; ""count""] values = [[]; [1; 42; 50]; [1; 50; 100]; [1]; [1]; [1]; []] timeDelays = [0; 0; 40; 50; 120; 200; 250] Output: [null; false; true; 50; 50; -1; 0] Explanation: At t=0; the cache is constructed. At t=0; a key-value pair (1: 42) is added with a time limit of 50ms. The value doesn't exist so false is returned. At t=40; a key-value pair (1: 50) is added with a time limit of 100ms. A non-expired value already existed so true is returned and the old value was overwritten. At t=50; get(1) is called which returned 50. At t=120; get(1) is called which returned 50. At t=140; key=1 expires. At t=200; get(1) is called but the cache is empty so -1 is returned. At t=250; count() returns 0 because the cache is empty. Constraints: 0 <= key; value <= 109 0 <= duration <= 1000 1 <= actions.length <= 100 actions.length === values.length actions.length === timeDelays.length 0 <= timeDelays[i] <= 1450 actions[i] is one of ""TimeLimitedCache""; ""set""; ""get"" and ""count"" First action is always ""TimeLimitedCache"" and must be executed immediately; with a 0-millisecond delay"
Uber,2798,Number of Employees Who Met the Target,Easy,,Given an array arr and a chunk size size; return a chunked array. A chunked array contains the original elements in arr; but consists of subarrays each of length size. The length of the last subarray may be less than size if arr.length is not evenly divisible by size. You may assume the array is the output of JSON.parse. In other words; it is valid JSON. Please solve it without using lodash's _.chunk function. Example 1: Input: arr = [1;2;3;4;5]; size = 1 Output: [[1];[2];[3];[4];[5]] Explanation: The arr has been split into subarrays each with 1 element. Example 2: Input: arr = [1;9;6;3;2]; size = 3 Output: [[1;9;6];[3;2]] Explanation: The arr has been split into subarrays with 3 elements. However; only two elements are left for the 2nd subarray. Example 3: Input: arr = [8;5;3;2;6]; size = 6 Output: [[8;5;3;2;6]] Explanation: Size is greater than arr.length thus all elements are in the first subarray. Example 4: Input: arr = []; size = 1 Output: [] Explanation: There are no elements to be chunked so an empty array is returned. Constraints: arr is a valid JSON array 2 <= JSON.stringify(arr).length <= 105 1 <= size <= arr.length + 1
Uber,2781,Length of the Longest Valid Substring,Hard,,
Uber,2883,Drop Missing Data,Easy,"Hash Table, String, Dynamic Programming, Backtracking","Given a binary string s; partition the string into one or more substrings such that each substring is beautiful. A string is beautiful if: It doesn't contain leading zeros. It's the binary representation of a number that is a power of 5. Return the minimum number of substrings in such partition. If it is impossible to partition the string s into beautiful substrings; return -1. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""1011"" Output: 2 Explanation: We can paritition the given string into [""101""; ""1""]. - The string ""101"" does not contain leading zeros and is the binary representation of integer 51 = 5. - The string ""1"" does not contain leading zeros and is the binary representation of integer 50 = 1. It can be shown that 2 is the minimum number of beautiful substrings that s can be partitioned into. Example 2: Input: s = ""111"" Output: 3 Explanation: We can paritition the given string into [""1""; ""1""; ""1""]. - The string ""1"" does not contain leading zeros and is the binary representation of integer 50 = 1. It can be shown that 3 is the minimum number of beautiful substrings that s can be partitioned into. Example 3: Input: s = ""0"" Output: -1 Explanation: We can not partition the given string into beautiful substrings. Constraints: 1 <= s.length <= 15 s[i] is either '0' or '1'."
Uber,2858,Minimum Edge Reversals So Every Node Is Reachable,Hard,,"Given two arrays arr1 and arr2; return a new array joinedArray. All the objects in each of the two inputs arrays will contain an id field that has an integer value. joinedArray is an array formed by merging arr1 and arr2 based on their id key. The length of joinedArray should be the length of unique values of id. The returned array should be sorted in ascending order based on the id key. If a given id exists in one array but not the other; the single object with that id should be included in the result array without modification. If two objects share an id; their properties should be merged into a single object: If a key only exists in one object; that single key-value pair should be included in the object. If a key is included in both objects; the value in the object from arr2 should override the value from arr1. Example 1: Input: arr1 = [ {""id"": 1; ""x"": 1}; {""id"": 2; ""x"": 9} ]; arr2 = [ {""id"": 3; ""x"": 5} ] Output: [ {""id"": 1; ""x"": 1}; {""id"": 2; ""x"": 9}; {""id"": 3; ""x"": 5} ] Explanation: There are no duplicate ids so arr1 is simply concatenated with arr2. Example 2: Input: arr1 = [ {""id"": 1; ""x"": 2; ""y"": 3}; {""id"": 2; ""x"": 3; ""y"": 6} ]; arr2 = [ {""id"": 2; ""x"": 10; ""y"": 20}; {""id"": 3; ""x"": 0; ""y"": 0} ] Output: [ {""id"": 1; ""x"": 2; ""y"": 3}; {""id"": 2; ""x"": 10; ""y"": 20}; {""id"": 3; ""x"": 0; ""y"": 0} ] Explanation: The two objects with id=1 and id=3 are included in the result array without modifiction. The two objects with id=2 are merged together. The keys from arr2 override the values in arr1. Example 3: Input: arr1 = [ {""id"": 1; ""b"": {""b"": 94};""v"": [4; 3]; ""y"": 48} ] arr2 = [ {""id"": 1; ""b"": {""c"": 84}; ""v"": [1; 3]} ] Output: [ {""id"": 1; ""b"": {""c"": 84}; ""v"": [1; 3]; ""y"": 48} ] Explanation: The two objects with id=1 are merged together. For the keys ""b"" and ""v"" the values from arr2 are used. Since the key ""y"" only exists in arr1; that value is taken form arr1. Constraints: arr1 and arr2 are valid JSON arrays Each object in arr1 and arr2 has a unique integer id key 2 <= JSON.stringify(arr1).length <= 106 2 <= JSON.stringify(arr2).length <= 106"
Uber,2914,Minimum Number of Changes to Make Binary String Beautiful,Med,"Array, Binary Search, Breadth-First Search, Union Find, Matrix",You are given a 0-indexed 2D matrix grid of size n x n; where (r; c) represents: A cell containing a thief if grid[r][c] = 1 An empty cell if grid[r][c] = 0 You are initially positioned at cell (0; 0). In one move; you can move to any adjacent cell in the grid; including cells containing thieves. The safeness factor of a path on the grid is defined as the minimum manhattan distance from any cell in the path to any thief in the grid. Return the maximum safeness factor of all paths leading to cell (n - 1; n - 1). An adjacent cell of cell (r; c); is one of the cells (r; c + 1); (r; c - 1); (r + 1; c) and (r - 1; c) if it exists. The Manhattan distance between two cells (a; b) and (x; y) is equal to |a - x| + |b - y|; where |val| denotes the absolute value of val. Example 1: Input: grid = [[1;0;0];[0;0;0];[0;0;1]] Output: 0 Explanation: All paths from (0; 0) to (n - 1; n - 1) go through the thieves in cells (0; 0) and (n - 1; n - 1). Example 2: Input: grid = [[0;0;1];[0;0;0];[0;0;0]] Output: 2 Explanation: The path depicted in the picture above has a safeness factor of 2 since: - The closest cell of the path to the thief at cell (0; 2) is cell (0; 0). The distance between them is | 0 - 0 | + | 0 - 2 | = 2. It can be shown that there are no other paths with a higher safeness factor. Example 3: Input: grid = [[0;0;0;1];[0;0;0;0];[0;0;0;0];[1;0;0;0]] Output: 2 Explanation: The path depicted in the picture above has a safeness factor of 2 since: - The closest cell of the path to the thief at cell (0; 3) is cell (1; 2). The distance between them is | 0 - 1 | + | 3 - 2 | = 2. - The closest cell of the path to the thief at cell (3; 0) is cell (3; 2). The distance between them is | 3 - 3 | + | 0 - 2 | = 2. It can be shown that there are no other paths with a higher safeness factor. Constraints: 1 <= grid.length == n <= 400 grid[i].length == n grid[i][j] is either 0 or 1. There is at least one thief in the grid.
Uber,2925,Maximum Score After Applying Operations on a Tree,Med,,
Uber,3042,Count Prefix and Suffix Pairs I,Easy,,
Apple,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Apple,1207,Unique Number of Occurrences,Easy,"Array, Hash Table, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; each node in the tree has a distinct value. After deleting all nodes with a value in to_delete; we are left with a forest (a disjoint union of trees). Return the roots of the trees in the remaining forest. You may return the result in any order. Example 1: Input: root = [1;2;3;4;5;6;7]; to_delete = [3;5] Output: [[1;2;null;4];[6];[7]] Example 2: Input: root = [1;2;4;null;3]; to_delete = [3] Output: [[1;2;4]] Constraints: The number of nodes in the given tree is at most 1000. Each node has a distinct value between 1 and 1000. to_delete.length <= 1000 to_delete contains distinct values between 1 and 1000.
Apple,13,Roman to Integer,Easy,"Hash Table, Math, String","Roman numerals are represented by seven different symbols: I; V; X; L; C; D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example; 2 is written as II in Roman numeral; just two ones added together. 12 is written as XII; which is simply X + II. The number 27 is written as XXVII; which is XX + V + II. Roman numerals are usually written largest to smallest from left to right. However; the numeral for four is not IIII. Instead; the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine; which is written as IX. There are six instances where subtraction is used: I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral; convert it to an integer. Example 1: Input: s = ""III"" Output: 3 Explanation: III = 3. Example 2: Input: s = ""LVIII"" Output: 58 Explanation: L = 50; V= 5; III = 3. Example 3: Input: s = ""MCMXCIV"" Output: 1994 Explanation: M = 1000; CM = 900; XC = 90 and IV = 4. Constraints: 1 <= s.length <= 15 s contains only the characters ('I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M'). It is guaranteed that s is a valid roman numeral in the range [1; 3999]."
Apple,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Apple,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Apple,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Apple,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Apple,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Apple,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Apple,7,Reverse Integer,Med,Math,Given a signed 32-bit integer x; return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231; 231 - 1]; then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: Input: x = 123 Output: 321 Example 2: Input: x = -123 Output: -321 Example 3: Input: x = 120 Output: 21 Constraints: -231 <= x <= 231 - 1
Apple,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Apple,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Apple,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Apple,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
Apple,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Apple,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Apple,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Apple,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Apple,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Apple,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Apple,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Apple,189,Rotate Array,Med,"Array, Math, Two Pointers",Given an integer array nums; rotate the array to the right by k steps; where k is non-negative. Example 1: Input: nums = [1;2;3;4;5;6;7]; k = 3 Output: [5;6;7;1;2;3;4] Explanation: rotate 1 steps to the right: [7;1;2;3;4;5;6] rotate 2 steps to the right: [6;7;1;2;3;4;5] rotate 3 steps to the right: [5;6;7;1;2;3;4] Example 2: Input: nums = [-1;-100;3;99]; k = 2 Output: [3;99;-1;-100] Explanation: rotate 1 steps to the right: [99;-1;-100;3] rotate 2 steps to the right: [3;99;-1;-100] Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 0 <= k <= 105 Follow up: Try to come up with as many solutions as you can. There are at least three different ways to solve this problem. Could you do it in-place with O(1) extra space?
Apple,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
Apple,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Apple,118,Pascal's Triangle,Easy,"Array, Dynamic Programming",Given an integer numRows; return the first numRows of Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: numRows = 5 Output: [[1];[1;1];[1;2;1];[1;3;3;1];[1;4;6;4;1]] Example 2: Input: numRows = 1 Output: [[1]] Constraints: 1 <= numRows <= 30
Apple,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Apple,2667,Create Hello World Function,Easy,"Array, Hash Table, Math, Stack, Sliding Window",
Apple,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Apple,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Apple,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Apple,26,Remove Duplicates from Sorted Array,Easy,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums. Consider the number of unique elements of nums to be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;2] Output: 2; nums = [1;2;_] Explanation: Your function should return k = 2; with the first two elements of nums being 1 and 2 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;2;2;3;3;4] Output: 5; nums = [0;1;2;3;4;_;_;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums being 0; 1; 2; 3; and 4 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -100 <= nums[i] <= 100 nums is sorted in non-decreasing order.
Apple,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Apple,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Apple,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Apple,69,Sqrt(x),Easy,"Math, Binary Search",Given a non-negative integer x; return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. For example; do not use pow(x; 0.5) in c++ or x ** 0.5 in python. Example 1: Input: x = 4 Output: 2 Explanation: The square root of 4 is 2; so we return 2. Example 2: Input: x = 8 Output: 2 Explanation: The square root of 8 is 2.82842...; and since we round it down to the nearest integer; 2 is returned. Constraints: 0 <= x <= 231 - 1
Apple,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Apple,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Apple,125,Valid Palindrome,Easy,"Two Pointers, String","A phrase is a palindrome if; after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters; it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s; return true if it is a palindrome; or false otherwise. Example 1: Input: s = ""A man; a plan; a canal: Panama"" Output: true Explanation: ""amanaplanacanalpanama"" is a palindrome. Example 2: Input: s = ""race a car"" Output: false Explanation: ""raceacar"" is not a palindrome. Example 3: Input: s = "" "" Output: true Explanation: s is an empty string """" after removing non-alphanumeric characters. Since an empty string reads the same forward and backward; it is a palindrome. Constraints: 1 <= s.length <= 2 * 105 s consists only of printable ASCII characters."
Apple,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Apple,217,Contains Duplicate,Easy,"Array, Hash Table, Sorting",Given an integer array nums; return true if any value appears at least twice in the array; and return false if every element is distinct. Example 1: Input: nums = [1;2;3;1] Output: true Explanation: The element 1 occurs at the indices 0 and 3. Example 2: Input: nums = [1;2;3;4] Output: false Explanation: All elements are distinct. Example 3: Input: nums = [1;1;1;3;3;4;3;2;4;2] Output: true Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109
Apple,242,Valid Anagram,Easy,"Hash Table, String, Sorting","Given two strings s and t; return true if t is an anagram of s; and false otherwise. Example 1: Input: s = ""anagram""; t = ""nagaram"" Output: true Example 2: Input: s = ""rat""; t = ""car"" Output: false Constraints: 1 <= s.length; t.length <= 5 * 104 s and t consist of lowercase English letters. Follow up: What if the inputs contain Unicode characters? How would you adapt your solution to such a case?"
Apple,1768,Merge Strings Alternately,Easy,"Array, Math, Stack, Tree, Design, Binary Tree",
Apple,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Apple,191,Number of 1 Bits,Easy,"Divide and Conquer, Bit Manipulation",Given a positive integer n; write a function that returns the number of set bits in its binary representation (also known as the Hamming weight). Example 1: Input: n = 11 Output: 3 Explanation: The input binary string 1011 has a total of three set bits. Example 2: Input: n = 128 Output: 1 Explanation: The input binary string 10000000 has a total of one set bit. Example 3: Input: n = 2147483645 Output: 30 Explanation: The input binary string 1111111111111111111111111111101 has a total of thirty set bits. Constraints: 1 <= n <= 231 - 1 Follow up: If this function is called many times; how would you optimize it?
Apple,28,Find the Index of the First Occurrence in a String,Easy,"Two Pointers, String, String Matching","Given two strings needle and haystack; return the index of the first occurrence of needle in haystack; or -1 if needle is not part of haystack. Example 1: Input: haystack = ""sadbutsad""; needle = ""sad"" Output: 0 Explanation: ""sad"" occurs at index 0 and 6. The first occurrence is at index 0; so we return 0. Example 2: Input: haystack = ""leetcode""; needle = ""leeto"" Output: -1 Explanation: ""leeto"" did not occur in ""leetcode""; so we return -1. Constraints: 1 <= haystack.length; needle.length <= 104 haystack and needle consist of only lowercase English characters."
Apple,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Apple,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Apple,35,Search Insert Position,Easy,"Array, Binary Search",Given a sorted array of distinct integers and a target value; return the index if the target is found. If not; return the index where it would be if it were inserted in order. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [1;3;5;6]; target = 5 Output: 2 Example 2: Input: nums = [1;3;5;6]; target = 2 Output: 1 Example 3: Input: nums = [1;3;5;6]; target = 7 Output: 4 Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 nums contains distinct values sorted in ascending order. -104 <= target <= 104
Apple,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Apple,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Apple,190,Reverse Bits,Easy,"Divide and Conquer, Bit Manipulation",Reverse bits of a given 32 bits unsigned integer. Note: Note that in some languages; such as Java; there is no unsigned integer type. In this case; both input and output will be given as a signed integer type. They should not affect your implementation; as the integer's internal binary representation is the same; whether it is signed or unsigned. In Java; the compiler represents the signed integers using 2's complement notation. Therefore; in Example 2 above; the input represents the signed integer -3 and the output represents the signed integer -1073741825. Example 1: Input: n = 00000010100101000001111010011100 Output: 964176192 (00111001011110000010100101000000) Explanation: The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596; so return 964176192 which its binary representation is 00111001011110000010100101000000. Example 2: Input: n = 11111111111111111111111111111101 Output: 3221225471 (10111111111111111111111111111111) Explanation: The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293; so return 3221225471 which its binary representation is 10111111111111111111111111111111. Constraints: The input must be a binary string of length 32 Follow up: If this function is called many times; how would you optimize it?
Apple,27,Remove Element,Easy,"Array, Two Pointers",Given an integer array nums and an integer val; remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val. Consider the number of elements in nums which are not equal to val be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the elements which are not equal to val. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int val = ...; // Value to remove int[] expectedNums = [...]; // The expected answer with correct length. // It is sorted with no values equaling val. int k = removeElement(nums; val); // Calls your implementation assert k == expectedNums.length; sort(nums; 0; k); // Sort the first k elements of nums for (int i = 0; i < actualLength; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [3;2;2;3]; val = 3 Output: 2; nums = [2;2;_;_] Explanation: Your function should return k = 2; with the first two elements of nums being 2. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;1;2;2;3;0;4;2]; val = 2 Output: 5; nums = [0;1;4;0;3;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums containing 0; 0; 1; 3; and 4. Note that the five elements can be returned in any order. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 0 <= nums.length <= 100 0 <= nums[i] <= 50 0 <= val <= 100
Apple,84,Largest Rectangle in Histogram,Hard,"Array, Stack, Monotonic Stack",Given an array of integers heights representing the histogram's bar height where the width of each bar is 1; return the area of the largest rectangle in the histogram. Example 1: Input: heights = [2;1;5;6;2;3] Output: 10 Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area; which has an area = 10 units. Example 2: Input: heights = [2;4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104
Apple,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Apple,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Apple,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Apple,349,Intersection of Two Arrays,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must be unique and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [9;4] Explanation: [4;9] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000
Apple,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Apple,2235,Add Two Integers,Easy,String,"You are given a string title consisting of one or more words separated by a single space; where each word consists of English letters. Capitalize the string by changing the capitalization of each word such that: If the length of the word is 1 or 2 letters; change all letters to lowercase. Otherwise; change the first letter to uppercase and the remaining letters to lowercase. Return the capitalized title. Example 1: Input: title = ""capiTalIze tHe titLe"" Output: ""Capitalize The Title"" Explanation: Since all the words have a length of at least 3; the first letter of each word is uppercase; and the remaining letters are lowercase. Example 2: Input: title = ""First leTTeR of EACH Word"" Output: ""First Letter of Each Word"" Explanation: The word ""of"" has length 2; so it is all lowercase. The remaining words have a length of at least 3; so the first letter of each remaining word is uppercase; and the remaining letters are lowercase. Example 3: Input: title = ""i lOve leetcode"" Output: ""i Love Leetcode"" Explanation: The word ""i"" has length 1; so it is lowercase. The remaining words have a length of at least 3; so the first letter of each remaining word is uppercase; and the remaining letters are lowercase. Constraints: 1 <= title.length <= 100 title consists of words separated by a single space without any leading or trailing spaces. Each word consists of uppercase and lowercase English letters and is non-empty."
Apple,67,Add Binary,Easy,"Math, String, Bit Manipulation, Simulation","Given two binary strings a and b; return their sum as a binary string. Example 1: Input: a = ""11""; b = ""1"" Output: ""100"" Example 2: Input: a = ""1010""; b = ""1011"" Output: ""10101"" Constraints: 1 <= a.length; b.length <= 104 a and b consist only of '0' or '1' characters. Each string does not contain leading zeros except for the zero itself."
Apple,128,Longest Consecutive Sequence,Med,"Array, Hash Table, Union Find",Given an unsorted array of integers nums; return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time. Example 1: Input: nums = [100;4;200;1;3;2] Output: 4 Explanation: The longest consecutive elements sequence is [1; 2; 3; 4]. Therefore its length is 4. Example 2: Input: nums = [0;3;7;2;5;8;4;6;0;1] Output: 9 Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109
Apple,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
Apple,234,Palindrome Linked List,Easy,"Linked List, Two Pointers, Stack, Recursion",Given the head of a singly linked list; return true if it is a palindrome or false otherwise. Example 1: Input: head = [1;2;2;1] Output: true Example 2: Input: head = [1;2] Output: false Constraints: The number of nodes in the list is in the range [1; 105]. 0 <= Node.val <= 9 Follow up: Could you do it in O(n) time and O(1) space?
Apple,18,4Sum,Med,"Array, Two Pointers, Sorting",Given an array nums of n integers; return an array of all the unique quadruplets [nums[a]; nums[b]; nums[c]; nums[d]] such that: 0 <= a; b; c; d < n a; b; c; and d are distinct. nums[a] + nums[b] + nums[c] + nums[d] == target You may return the answer in any order. Example 1: Input: nums = [1;0;-1;0;-2;2]; target = 0 Output: [[-2;-1;1;2];[-2;0;0;2];[-1;0;0;1]] Example 2: Input: nums = [2;2;2;2;2]; target = 8 Output: [[2;2;2;2]] Constraints: 1 <= nums.length <= 200 -109 <= nums[i] <= 109 -109 <= target <= 109
Apple,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
Apple,202,Happy Number,Easy,"Hash Table, Math, Two Pointers",Write an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer; replace the number by the sum of the squares of its digits. Repeat the process until the number equals 1 (where it will stay); or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy. Return true if n is a happy number; and false if not. Example 1: Input: n = 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1 Example 2: Input: n = 2 Output: false Constraints: 1 <= n <= 231 - 1
Apple,287,Find the Duplicate Number,Med,"Array, Two Pointers, Binary Search, Bit Manipulation",Given an array of integers nums containing n + 1 integers where each integer is in the range [1; n] inclusive. There is only one repeated number in nums; return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Example 1: Input: nums = [1;3;4;2;2] Output: 2 Example 2: Input: nums = [3;1;3;4;2] Output: 3 Example 3: Input: nums = [3;3;3;3;3] Output: 3 Constraints: 1 <= n <= 105 nums.length == n + 1 1 <= nums[i] <= n All the integers in nums appear only once except for precisely one integer which appears two or more times. Follow up: How can we prove that at least one duplicate number must exist in nums? Can you solve the problem in linear runtime complexity?
Apple,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Apple,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Apple,136,Single Number,Easy,"Array, Bit Manipulation",Given a non-empty array of integers nums; every element appears twice except for one. Find that single one. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;1] Output: 1 Example 2: Input: nums = [4;1;2;1;2] Output: 4 Example 3: Input: nums = [1] Output: 1 Constraints: 1 <= nums.length <= 3 * 104 -3 * 104 <= nums[i] <= 3 * 104 Each element in the array appears twice except for one element which appears only once.
Apple,273,Integer to English Words,Hard,"Math, String, Recursion","Convert a non-negative integer num to its English words representation. Example 1: Input: num = 123 Output: ""One Hundred Twenty Three"" Example 2: Input: num = 12345 Output: ""Twelve Thousand Three Hundred Forty Five"" Example 3: Input: num = 1234567 Output: ""One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"" Constraints: 0 <= num <= 231 - 1"
Apple,875,Koko Eating Bananas,Med,"Array, Two Pointers, Dynamic Programming, Enumeration",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr; return the length of the longest subarray; which is a mountain. Return 0 if there is no mountain subarray. Example 1: Input: arr = [2;1;4;7;3;2;5] Output: 5 Explanation: The largest mountain is [1;4;7;3;2] which has length 5. Example 2: Input: arr = [2;2;2] Output: 0 Explanation: There is no mountain. Constraints: 1 <= arr.length <= 104 0 <= arr[i] <= 104 Follow up: Can you solve it using only one pass? Can you solve it in O(1) space?
Apple,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Apple,101,Symmetric Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; check whether it is a mirror of itself (i.e.; symmetric around its center). Example 1: Input: root = [1;2;2;3;4;4;3] Output: true Example 2: Input: root = [1;2;2;null;3;null;3] Output: false Constraints: The number of nodes in the tree is in the range [1; 1000]. -100 <= Node.val <= 100 Follow up: Could you solve it both recursively and iteratively?
Apple,102,Binary Tree Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the level order traversal of its nodes' values. (i.e.; from left to right; level by level). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[9;20];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -1000 <= Node.val <= 1000
Apple,104,Maximum Depth of Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return its maximum depth. A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 3 Example 2: Input: root = [1;null;2] Output: 2 Constraints: The number of nodes in the tree is in the range [0; 104]. -100 <= Node.val <= 100
Apple,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Apple,236,Lowest Common Ancestor of a Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",Given a binary tree; find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3. Example 2: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [1;2]; p = 1; q = 2 Output: 1 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the tree.
Apple,240,Search a 2D Matrix II,Med,"Array, Binary Search, Divide and Conquer, Matrix",Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. Example 1: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 5 Output: true Example 2: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 20 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= n; m <= 300 -109 <= matrix[i][j] <= 109 All the integers in each row are sorted in ascending order. All the integers in each column are sorted in ascending order. -109 <= target <= 109
Apple,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Apple,165,Compare Version Numbers,Med,"Two Pointers, String","Given two version strings; version1 and version2; compare them. A version string consists of revisions separated by dots '.'. The value of the revision is its integer conversion ignoring leading zeros. To compare version strings; compare their revision values in left-to-right order. If one of the version strings has fewer revisions; treat the missing revision values as 0. Return the following: If version1 < version2; return -1. If version1 > version2; return 1. Otherwise; return 0. Example 1: Input: version1 = ""1.2""; version2 = ""1.10"" Output: -1 Explanation: version1's second revision is ""2"" and version2's second revision is ""10"": 2 < 10; so version1 < version2. Example 2: Input: version1 = ""1.01""; version2 = ""1.001"" Output: 0 Explanation: Ignoring leading zeroes; both ""01"" and ""001"" represent the same integer ""1"". Example 3: Input: version1 = ""1.0""; version2 = ""1.0.0.0"" Output: 0 Explanation: version1 has less revisions; which means every missing revision are treated as ""0"". Constraints: 1 <= version1.length; version2.length <= 500 version1 and version2 only contain digits and '.'. version1 and version2 are valid version numbers. All the given revisions in version1 and version2 can be stored in a 32-bit integer."
Apple,876,Middle of the Linked List,Easy,"Array, Hash Table, Greedy, Sorting",Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize; and consists of groupSize consecutive cards. Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize; return true if she can rearrange the cards; or false otherwise. Example 1: Input: hand = [1;2;3;6;2;3;4;7;8]; groupSize = 3 Output: true Explanation: Alice's hand can be rearranged as [1;2;3];[2;3;4];[6;7;8] Example 2: Input: hand = [1;2;3;4;5]; groupSize = 4 Output: false Explanation: Alice's hand can not be rearranged into groups of 4. Constraints: 1 <= hand.length <= 104 0 <= hand[i] <= 109 1 <= groupSize <= hand.length Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/
Apple,509,Fibonacci Number,Easy,"Tree, Binary Search Tree, Binary Tree",
Apple,1757,Recyclable and Low Fat Products,Easy,"Array, Dynamic Programming, Breadth-First Search",A certain bug's home is on the x-axis at position x. Help them get there from position 0. The bug jumps according to the following rules: It can jump exactly a positions forward (to the right). It can jump exactly b positions backward (to the left). It cannot jump backward twice in a row. It cannot jump to any forbidden positions. The bug may jump forward beyond its home; but it cannot jump to positions numbered with negative integers. Given an array of integers forbidden; where forbidden[i] means that the bug cannot jump to the position forbidden[i]; and integers a; b; and x; return the minimum number of jumps needed for the bug to reach its home. If there is no possible sequence of jumps that lands the bug on position x; return -1. Example 1: Input: forbidden = [14;4;18;1;15]; a = 3; b = 15; x = 9 Output: 3 Explanation: 3 jumps forward (0 -> 3 -> 6 -> 9) will get the bug home. Example 2: Input: forbidden = [8;3;16;6;12;20]; a = 15; b = 13; x = 11 Output: -1 Example 3: Input: forbidden = [1;6;2;14;5;17;4]; a = 16; b = 9; x = 7 Output: 2 Explanation: One jump forward (0 -> 16) then one jump backward (16 -> 7) will get the bug home. Constraints: 1 <= forbidden.length <= 1000 1 <= a; b; forbidden[i] <= 2000 0 <= x <= 2000 All the elements in forbidden are distinct. Position x is not forbidden.
Apple,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
Apple,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Apple,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Apple,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Apple,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Apple,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Apple,149,Max Points on a Line,Hard,"Array, Hash Table, Math, Geometry",Given an array of points where points[i] = [xi; yi] represents a point on the X-Y plane; return the maximum number of points that lie on the same straight line. Example 1: Input: points = [[1;1];[2;2];[3;3]] Output: 3 Example 2: Input: points = [[1;1];[3;2];[5;3];[4;1];[2;3];[1;4]] Output: 4 Constraints: 1 <= points.length <= 300 points[i].length == 2 -104 <= xi; yi <= 104 All the points are unique.
Apple,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Apple,167,Two Sum II - Input Array Is Sorted,Med,"Array, Two Pointers, Binary Search",Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order; find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 1 <= index1 < index2 <= numbers.length. Return the indices of the two numbers; index1 and index2; added by one as an integer array [index1; index2] of length 2. The tests are generated such that there is exactly one solution. You may not use the same element twice. Your solution must use only constant extra space. Example 1: Input: numbers = [2;7;11;15]; target = 9 Output: [1;2] Explanation: The sum of 2 and 7 is 9. Therefore; index1 = 1; index2 = 2. We return [1; 2]. Example 2: Input: numbers = [2;3;4]; target = 6 Output: [1;3] Explanation: The sum of 2 and 4 is 6. Therefore index1 = 1; index2 = 3. We return [1; 3]. Example 3: Input: numbers = [-1;0]; target = -1 Output: [1;2] Explanation: The sum of -1 and 0 is -1. Therefore index1 = 1; index2 = 2. We return [1; 2]. Constraints: 2 <= numbers.length <= 3 * 104 -1000 <= numbers[i] <= 1000 numbers is sorted in non-decreasing order. -1000 <= target <= 1000 The tests are generated such that there is exactly one solution.
Apple,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Apple,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
Apple,704,Binary Search,Easy,,
Apple,1480,Running Sum of 1d Array,Easy,Database,"Table: Movies +---------------+---------+ | Column Name | Type | +---------------+---------+ | movie_id | int | | title | varchar | +---------------+---------+ movie_id is the primary key (column with unique values) for this table. title is the name of the movie. Table: Users +---------------+---------+ | Column Name | Type | +---------------+---------+ | user_id | int | | name | varchar | +---------------+---------+ user_id is the primary key (column with unique values) for this table. The column 'name' has unique values. Table: MovieRating +---------------+---------+ | Column Name | Type | +---------------+---------+ | movie_id | int | | user_id | int | | rating | int | | created_at | date | +---------------+---------+ (movie_id; user_id) is the primary key (column with unique values) for this table. This table contains the rating of a movie by a user in their review. created_at is the user's review date. Write a solution to: Find the name of the user who has rated the greatest number of movies. In case of a tie; return the lexicographically smaller user name. Find the movie name with the highest average rating in February 2020. In case of a tie; return the lexicographically smaller movie name. The result format is in the following example. Example 1: Input: Movies table: +-------------+--------------+ | movie_id | title | +-------------+--------------+ | 1 | Avengers | | 2 | Frozen 2 | | 3 | Joker | +-------------+--------------+ Users table: +-------------+--------------+ | user_id | name | +-------------+--------------+ | 1 | Daniel | | 2 | Monica | | 3 | Maria | | 4 | James | +-------------+--------------+ MovieRating table: +-------------+--------------+--------------+-------------+ | movie_id | user_id | rating | created_at | +-------------+--------------+--------------+-------------+ | 1 | 1 | 3 | 2020-01-12 | | 1 | 2 | 4 | 2020-02-11 | | 1 | 3 | 2 | 2020-02-12 | | 1 | 4 | 1 | 2020-01-01 | | 2 | 1 | 5 | 2020-02-17 | | 2 | 2 | 2 | 2020-02-01 | | 2 | 3 | 2 | 2020-03-01 | | 3 | 1 | 3 | 2020-02-22 | | 3 | 2 | 4 | 2020-02-25 | +-------------+--------------+--------------+-------------+ Output: +--------------+ | results | +--------------+ | Daniel | | Frozen 2 | +--------------+ Explanation: Daniel and Monica have rated 3 movies (""Avengers""; ""Frozen 2"" and ""Joker"") but Daniel is smaller lexicographically. Frozen 2 and Joker have a rating average of 3.5 in February but Frozen 2 is smaller lexicographically."
Apple,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
Apple,66,Plus One,Easy,"Array, Math",You are given a large integer represented as an integer array digits; where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0's. Increment the large integer by one and return the resulting array of digits. Example 1: Input: digits = [1;2;3] Output: [1;2;4] Explanation: The array represents the integer 123. Incrementing by one gives 123 + 1 = 124. Thus; the result should be [1;2;4]. Example 2: Input: digits = [4;3;2;1] Output: [4;3;2;2] Explanation: The array represents the integer 4321. Incrementing by one gives 4321 + 1 = 4322. Thus; the result should be [4;3;2;2]. Example 3: Input: digits = [9] Output: [1;0] Explanation: The array represents the integer 9. Incrementing by one gives 9 + 1 = 10. Thus; the result should be [1;0]. Constraints: 1 <= digits.length <= 100 0 <= digits[i] <= 9 digits does not contain any leading 0's.
Apple,97,Interleaving String,Med,"String, Dynamic Programming","Given strings s1; s2; and s3; find whether s3 is formed by an interleaving of s1 and s2. An interleaving of two strings s and t is a configuration where s and t are divided into n and m substrings respectively; such that: s = s1 + s2 + ... + sn t = t1 + t2 + ... + tm |n - m| <= 1 The interleaving is s1 + t1 + s2 + t2 + s3 + t3 + ... or t1 + s1 + t2 + s2 + t3 + s3 + ... Note: a + b is the concatenation of strings a and b. Example 1: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbcbcac"" Output: true Explanation: One way to obtain s3 is: Split s1 into s1 = ""aa"" + ""bc"" + ""c""; and s2 into s2 = ""dbbc"" + ""a"". Interleaving the two splits; we get ""aa"" + ""dbbc"" + ""bc"" + ""a"" + ""c"" = ""aadbbcbcac"". Since s3 can be obtained by interleaving s1 and s2; we return true. Example 2: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbbaccc"" Output: false Explanation: Notice how it is impossible to interleave s2 with any other string to obtain s3. Example 3: Input: s1 = """"; s2 = """"; s3 = """" Output: true Constraints: 0 <= s1.length; s2.length <= 100 0 <= s3.length <= 200 s1; s2; and s3 consist of lowercase English letters. Follow up: Could you solve it using only O(s2.length) additional memory space?"
Apple,219,Contains Duplicate II,Easy,"Array, Hash Table, Sliding Window",Given an integer array nums and an integer k; return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k. Example 1: Input: nums = [1;2;3;1]; k = 3 Output: true Example 2: Input: nums = [1;0;1;1]; k = 1 Output: true Example 3: Input: nums = [1;2;3;1;2;3]; k = 2 Output: false Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109 0 <= k <= 105
Apple,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Apple,237,Delete Node in a Linked List,Med,Linked List,There is a singly-linked list head and we want to delete a node node in it. You are given the node to be deleted node. You will not be given access to the first node of head. All the values of the linked list are unique; and it is guaranteed that the given node node is not the last node in the linked list. Delete the given node. Note that by deleting the node; we do not mean removing it from memory. We mean: The value of the given node should not exist in the linked list. The number of nodes in the linked list should decrease by one. All the values before node should be in the same order. All the values after node should be in the same order. Custom testing: For the input; you should provide the entire linked list head and the node to be given node. node should not be the last node of the list and should be an actual node in the list. We will build the linked list and pass the node to your function. The output will be the entire list after calling your function. Example 1: Input: head = [4;5;1;9]; node = 5 Output: [4;1;9] Explanation: You are given the second node with value 5; the linked list should become 4 -> 1 -> 9 after calling your function. Example 2: Input: head = [4;5;1;9]; node = 1 Output: [4;5;9] Explanation: You are given the third node with value 1; the linked list should become 4 -> 5 -> 9 after calling your function. Constraints: The number of the nodes in the given list is in the range [2; 1000]. -1000 <= Node.val <= 1000 The value of each node in the list is unique. The node to be deleted is in the list and is not a tail node.
Apple,257,Binary Tree Paths,Easy,"String, Backtracking, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; return all root-to-leaf paths in any order. A leaf is a node with no children. Example 1: Input: root = [1;2;3;null;5] Output: [""1->2->5"";""1->3""] Example 2: Input: root = [1] Output: [""1""] Constraints: The number of nodes in the tree is in the range [1; 100]. -100 <= Node.val <= 100"
Apple,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
Apple,73,Set Matrix Zeroes,Med,"Array, Hash Table, Matrix",Given an m x n integer matrix matrix; if an element is 0; set its entire row and column to 0's. You must do it in place. Example 1: Input: matrix = [[1;1;1];[1;0;1];[1;1;1]] Output: [[1;0;1];[0;0;0];[1;0;1]] Example 2: Input: matrix = [[0;1;2;0];[3;4;5;2];[1;3;1;5]] Output: [[0;0;0;0];[0;4;5;0];[0;3;1;0]] Constraints: m == matrix.length n == matrix[0].length 1 <= m; n <= 200 -231 <= matrix[i][j] <= 231 - 1 Follow up: A straightforward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space; but still not the best solution. Could you devise a constant space solution?
Apple,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Apple,205,Isomorphic Strings,Easy,"Hash Table, String","Given two strings s and t; determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character; but a character may map to itself. Example 1: Input: s = ""egg""; t = ""add"" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = ""foo""; t = ""bar"" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = ""paper""; t = ""title"" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character."
Apple,231,Power of Two,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of two. Otherwise; return false. An integer n is a power of two; if there exists an integer x such that n == 2x. Example 1: Input: n = 1 Output: true Explanation: 20 = 1 Example 2: Input: n = 16 Output: true Explanation: 24 = 16 Example 3: Input: n = 3 Output: false Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Apple,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
Apple,279,Perfect Squares,Med,"Math, Dynamic Programming, Breadth-First Search",Given an integer n; return the least number of perfect square numbers that sum to n. A perfect square is an integer that is the square of an integer; in other words; it is the product of some integer with itself. For example; 1; 4; 9; and 16 are perfect squares while 3 and 11 are not. Example 1: Input: n = 12 Output: 3 Explanation: 12 = 4 + 4 + 4. Example 2: Input: n = 13 Output: 2 Explanation: 13 = 4 + 9. Constraints: 1 <= n <= 104
Apple,412,Fizz Buzz,Easy,"Math, String, Simulation","Given an integer n; return a string array answer (1-indexed) where: answer[i] == ""FizzBuzz"" if i is divisible by 3 and 5. answer[i] == ""Fizz"" if i is divisible by 3. answer[i] == ""Buzz"" if i is divisible by 5. answer[i] == i (as a string) if none of the above conditions are true. Example 1: Input: n = 3 Output: [""1"";""2"";""Fizz""] Example 2: Input: n = 5 Output: [""1"";""2"";""Fizz"";""4"";""Buzz""] Example 3: Input: n = 15 Output: [""1"";""2"";""Fizz"";""4"";""Buzz"";""Fizz"";""7"";""8"";""Fizz"";""Buzz"";""11"";""Fizz"";""13"";""14"";""FizzBuzz""] Constraints: 1 <= n <= 104"
Apple,1071,Greatest Common Divisor of Strings,Easy,"Array, Bit Manipulation",You are given a binary array nums (0-indexed). We define xi as the number whose binary representation is the subarray nums[0..i] (from most-significant-bit to least-significant-bit). For example; if nums = [1;0;1]; then x0 = 1; x1 = 2; and x2 = 5. Return an array of booleans answer where answer[i] is true if xi is divisible by 5. Example 1: Input: nums = [0;1;1] Output: [true;false;false] Explanation: The input numbers in binary are 0; 01; 011; which are 0; 1; and 3 in base-10. Only the first number is divisible by 5; so answer[0] is true. Example 2: Input: nums = [1;1;1] Output: [false;false;false] Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Apple,29,Divide Two Integers,Med,"Math, Bit Manipulation",Given two integers dividend and divisor; divide two integers without using multiplication; division; and mod operator. The integer division should truncate toward zero; which means losing its fractional part. For example; 8.345 would be truncated to 8; and -2.7335 would be truncated to -2. Return the quotient after dividing dividend by divisor. Note: Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−231; 231 − 1]. For this problem; if the quotient is strictly greater than 231 - 1; then return 231 - 1; and if the quotient is strictly less than -231; then return -231. Example 1: Input: dividend = 10; divisor = 3 Output: 3 Explanation: 10/3 = 3.33333.. which is truncated to 3. Example 2: Input: dividend = 7; divisor = -3 Output: -2 Explanation: 7/-3 = -2.33333.. which is truncated to -2. Constraints: -231 <= dividend; divisor <= 231 - 1 divisor != 0
Apple,57,Insert Interval,Med,Array,You are given an array of non-overlapping intervals intervals where intervals[i] = [starti; endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start; end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary). Return intervals after the insertion. Note that you don't need to modify intervals in-place. You can make a new array and return it. Example 1: Input: intervals = [[1;3];[6;9]]; newInterval = [2;5] Output: [[1;5];[6;9]] Example 2: Input: intervals = [[1;2];[3;5];[6;7];[8;10];[12;16]]; newInterval = [4;8] Output: [[1;2];[3;10];[12;16]] Explanation: Because the new interval [4;8] overlaps with [3;5];[6;7];[8;10]. Constraints: 0 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 105 intervals is sorted by starti in ascending order. newInterval.length == 2 0 <= start <= end <= 105
Apple,92,Reverse Linked List II,Med,Linked List,Given the head of a singly linked list and two integers left and right where left <= right; reverse the nodes of the list from position left to position right; and return the reversed list. Example 1: Input: head = [1;2;3;4;5]; left = 2; right = 4 Output: [1;4;3;2;5] Example 2: Input: head = [5]; left = 1; right = 1 Output: [5] Constraints: The number of nodes in the list is n. 1 <= n <= 500 -500 <= Node.val <= 500 1 <= left <= right <= n Follow up: Could you do it in one pass?
Apple,204,Count Primes,Med,"Array, Math, Enumeration, Number Theory",Given an integer n; return the number of prime numbers that are strictly less than n. Example 1: Input: n = 10 Output: 4 Explanation: There are 4 prime numbers less than 10; they are 2; 3; 5; 7. Example 2: Input: n = 0 Output: 0 Example 3: Input: n = 1 Output: 0 Constraints: 0 <= n <= 5 * 106
Apple,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
Apple,345,Reverse Vowels of a String,Easy,"Two Pointers, String","Given a string s; reverse only all the vowels in the string and return it. The vowels are 'a'; 'e'; 'i'; 'o'; and 'u'; and they can appear in both lower and upper cases; more than once. Example 1: Input: s = ""IceCreAm"" Output: ""AceCreIm"" Explanation: The vowels in s are ['I'; 'e'; 'e'; 'A']. On reversing the vowels; s becomes ""AceCreIm"". Example 2: Input: s = ""leetcode"" Output: ""leotcede"" Constraints: 1 <= s.length <= 3 * 105 s consist of printable ASCII characters."
Apple,383,Ransom Note,Easy,"Hash Table, String, Counting","Given two strings ransomNote and magazine; return true if ransomNote can be constructed by using the letters from magazine and false otherwise. Each letter in magazine can only be used once in ransomNote. Example 1: Input: ransomNote = ""a""; magazine = ""b"" Output: false Example 2: Input: ransomNote = ""aa""; magazine = ""ab"" Output: false Example 3: Input: ransomNote = ""aa""; magazine = ""aab"" Output: true Constraints: 1 <= ransomNote.length; magazine.length <= 105 ransomNote and magazine consist of lowercase English letters."
Apple,455,Assign Cookies,Easy,"Array, Two Pointers, Greedy, Sorting",Assume you are an awesome parent and want to give your children some cookies. But; you should give each child at most one cookie. Each child i has a greed factor g[i]; which is the minimum size of a cookie that the child will be content with; and each cookie j has a size s[j]. If s[j] >= g[i]; we can assign the cookie j to the child i; and the child i will be content. Your goal is to maximize the number of your content children and output the maximum number. Example 1: Input: g = [1;2;3]; s = [1;1] Output: 1 Explanation: You have 3 children and 2 cookies. The greed factors of 3 children are 1; 2; 3. And even though you have 2 cookies; since their size is both 1; you could only make the child whose greed factor is 1 content. You need to output 1. Example 2: Input: g = [1;2]; s = [1;2;3] Output: 2 Explanation: You have 2 children and 3 cookies. The greed factors of 2 children are 1; 2. You have 3 cookies and their sizes are big enough to gratify all of the children; You need to output 2. Constraints: 1 <= g.length <= 3 * 104 0 <= s.length <= 3 * 104 1 <= g[i]; s[j] <= 231 - 1 Note: This question is the same as 2410: Maximum Matching of Players With Trainers.
Apple,1672,Richest Customer Wealth,Easy,"Array, Binary Search, Interactive",
Apple,8,String to Integer (atoi),Med,String,"Implement the myAtoi(string s) function; which converts a string to a 32-bit signed integer. The algorithm for myAtoi(string s) is as follows: Whitespace: Ignore any leading whitespace ("" ""). Signedness: Determine the sign by checking if the next character is '-' or '+'; assuming positivity if neither present. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read; then the result is 0. Rounding: If the integer is out of the 32-bit signed integer range [-231; 231 - 1]; then round the integer to remain in the range. Specifically; integers less than -231 should be rounded to -231; and integers greater than 231 - 1 should be rounded to 231 - 1. Return the integer as the final result. Example 1: Input: s = ""42"" Output: 42 Explanation: The underlined characters are what is read in and the caret is the current reader position. Step 1: ""42"" (no characters read because there is no leading whitespace) ^ Step 2: ""42"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""42"" (""42"" is read in) ^ Example 2: Input: s = "" -042"" Output: -42 Explanation: Step 1: "" -042"" (leading whitespace is read and ignored) ^ Step 2: "" -042"" ('-' is read; so the result should be negative) ^ Step 3: "" -042"" (""042"" is read in; leading zeros ignored in the result) ^ Example 3: Input: s = ""1337c0d3"" Output: 1337 Explanation: Step 1: ""1337c0d3"" (no characters read because there is no leading whitespace) ^ Step 2: ""1337c0d3"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""1337c0d3"" (""1337"" is read in; reading stops because the next character is a non-digit) ^ Example 4: Input: s = ""0-1"" Output: 0 Explanation: Step 1: ""0-1"" (no characters read because there is no leading whitespace) ^ Step 2: ""0-1"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""0-1"" (""0"" is read in; reading stops because the next character is a non-digit) ^ Example 5: Input: s = ""words and 987"" Output: 0 Explanation: Reading stops at the first non-digit character 'w'. Constraints: 0 <= s.length <= 200 s consists of English letters (lower-case and upper-case); digits (0-9); ' '; '+'; '-'; and '.'."
Apple,44,Wildcard Matching,Hard,"String, Dynamic Programming, Greedy, Recursion","Given an input string (s) and a pattern (p); implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""*"" Output: true Explanation: '*' matches any sequence. Example 3: Input: s = ""cb""; p = ""?a"" Output: false Explanation: '?' matches 'c'; but the second letter is 'a'; which does not match 'b'. Constraints: 0 <= s.length; p.length <= 2000 s contains only lowercase English letters. p contains only lowercase English letters; '?' or '*'."
Apple,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Apple,83,Remove Duplicates from Sorted List,Easy,Linked List,Given the head of a sorted linked list; delete all duplicates such that each element appears only once. Return the linked list sorted as well. Example 1: Input: head = [1;1;2] Output: [1;2] Example 2: Input: head = [1;1;2;3;3] Output: [1;2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Apple,94,Binary Tree Inorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the inorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [1;3;2] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [4;2;6;5;7;1;3;9;8] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Apple,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Apple,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Apple,278,First Bad Version,Easy,"Binary Search, Interactive",You are a product manager and currently leading a team to develop a new product. Unfortunately; the latest version of your product fails the quality check. Since each version is developed based on the previous version; all the versions after a bad version are also bad. Suppose you have n versions [1; 2; ...; n] and you want to find out the first bad one; which causes all the following ones to be bad. You are given an API bool isBadVersion(version) which returns whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API. Example 1: Input: n = 5; bad = 4 Output: 4 Explanation: call isBadVersion(3) -> false call isBadVersion(5) -> true call isBadVersion(4) -> true Then 4 is the first bad version. Example 2: Input: n = 1; bad = 1 Output: 1 Constraints: 1 <= bad <= n <= 231 - 1
Apple,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Apple,328,Odd Even Linked List,Med,Linked List,Given the head of a singly linked list; group all the nodes with odd indices together followed by the nodes with even indices; and return the reordered list. The first node is considered odd; and the second node is even; and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input. You must solve the problem in O(1) extra space complexity and O(n) time complexity. Example 1: Input: head = [1;2;3;4;5] Output: [1;3;5;2;4] Example 2: Input: head = [2;1;3;5;6;4;7] Output: [2;3;6;7;1;5;4] Constraints: The number of nodes in the linked list is in the range [0; 104]. -106 <= Node.val <= 106
Apple,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
Apple,463,Island Perimeter,Easy,"Array, Depth-First Search, Breadth-First Search, Matrix","You are given row x col grid representing a map where grid[i][j] = 1 represents land and grid[i][j] = 0 represents water. Grid cells are connected horizontally/vertically (not diagonally). The grid is completely surrounded by water; and there is exactly one island (i.e.; one or more connected land cells). The island doesn't have ""lakes""; meaning the water inside isn't connected to the water around the island. One cell is a square with side length 1. The grid is rectangular; width and height don't exceed 100. Determine the perimeter of the island. Example 1: Input: grid = [[0;1;0;0];[1;1;1;0];[0;1;0;0];[1;1;0;0]] Output: 16 Explanation: The perimeter is the 16 yellow stripes in the image above. Example 2: Input: grid = [[1]] Output: 4 Example 3: Input: grid = [[1;0]] Output: 4 Constraints: row == grid.length col == grid[i].length 1 <= row; col <= 100 grid[i][j] is 0 or 1. There is exactly one island in grid."
Apple,540,Single Element in a Sorted Array,Med,"Array, Binary Search",You are given a sorted array consisting of only integers where every element appears exactly twice; except for one element which appears exactly once. Return the single element that appears only once. Your solution must run in O(log n) time and O(1) space. Example 1: Input: nums = [1;1;2;3;3;4;4;8;8] Output: 2 Example 2: Input: nums = [3;3;7;7;10;11;11] Output: 10 Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 105
Apple,543,Diameter of Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them. Example 1: Input: root = [1;2;3;4;5] Output: 3 Explanation: 3 is the length of the path [4;2;1;3] or [5;2;1;3]. Example 2: Input: root = [1;2] Output: 1 Constraints: The number of nodes in the tree is in the range [1; 104]. -100 <= Node.val <= 100
Apple,584,Find Customer Referee,Easy,Database,Table: Customer +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | referee_id | int | +-------------+---------+ In SQL; id is the primary key column for this table. Each row of this table indicates the id of a customer; their name; and the id of the customer who referred them. Find the names of the customer that are not referred by the customer with id = 2. Return the result table in any order. The result format is in the following example. Example 1: Input: Customer table: +----+------+------------+ | id | name | referee_id | +----+------+------------+ | 1 | Will | null | | 2 | Jane | null | | 3 | Alex | 2 | | 4 | Bill | null | | 5 | Zack | 1 | | 6 | Mark | 2 | +----+------+------------+ Output: +------+ | name | +------+ | Will | | Jane | | Bill | | Zack | +------+
Apple,595,Big Countries,Easy,Database,Table: World +-------------+---------+ | Column Name | Type | +-------------+---------+ | name | varchar | | continent | varchar | | area | int | | population | int | | gdp | bigint | +-------------+---------+ name is the primary key (column with unique values) for this table. Each row of this table gives information about the name of a country; the continent to which it belongs; its area; the population; and its GDP value. A country is big if: it has an area of at least three million (i.e.; 3000000 km2); or it has a population of at least twenty-five million (i.e.; 25000000). Write a solution to find the name; population; and area of the big countries. Return the result table in any order. The result format is in the following example. Example 1: Input: World table: +-------------+-----------+---------+------------+--------------+ | name | continent | area | population | gdp | +-------------+-----------+---------+------------+--------------+ | Afghanistan | Asia | 652230 | 25500100 | 20343000000 | | Albania | Europe | 28748 | 2831741 | 12960000000 | | Algeria | Africa | 2381741 | 37100000 | 188681000000 | | Andorra | Europe | 468 | 78115 | 3712000000 | | Angola | Africa | 1246700 | 20609294 | 100990000000 | +-------------+-----------+---------+------------+--------------+ Output: +-------------+------------+---------+ | name | population | area | +-------------+------------+---------+ | Afghanistan | 25500100 | 652230 | | Algeria | 37100000 | 2381741 | +-------------+------------+---------+
Apple,680,Valid Palindrome II,Easy,"Two Pointers, String, Greedy","Given a string s; return true if the s can be palindrome after deleting at most one character from it. Example 1: Input: s = ""aba"" Output: true Example 2: Input: s = ""abca"" Output: true Explanation: You could delete the character 'c'. Example 3: Input: s = ""abc"" Output: false Constraints: 1 <= s.length <= 105 s consists of lowercase English letters."
Apple,721,Accounts Merge,Med,"Array, Hash Table, String, Depth-First Search, Breadth-First Search, Union Find, Sorting","Given a list of accounts where each element accounts[i] is a list of strings; where the first element accounts[i][0] is a name; and the rest of the elements are emails representing emails of the account. Now; we would like to merge these accounts. Two accounts definitely belong to the same person if there is some common email to both accounts. Note that even if two accounts have the same name; they may belong to different people as people could have the same name. A person can have any number of accounts initially; but all of their accounts definitely have the same name. After merging the accounts; return the accounts in the following format: the first element of each account is the name; and the rest of the elements are emails in sorted order. The accounts themselves can be returned in any order. Example 1: Input: accounts = [[""John"";""johnsmith@mail.com"";""john_newyork@mail.com""];[""John"";""johnsmith@mail.com"";""john00@mail.com""];[""Mary"";""mary@mail.com""];[""John"";""johnnybravo@mail.com""]] Output: [[""John"";""john00@mail.com"";""john_newyork@mail.com"";""johnsmith@mail.com""];[""Mary"";""mary@mail.com""];[""John"";""johnnybravo@mail.com""]] Explanation: The first and second John's are the same person as they have the common email ""johnsmith@mail.com"". The third John and Mary are different people as none of their email addresses are used by other accounts. We could return these lists in any order; for example the answer [['Mary'; 'mary@mail.com']; ['John'; 'johnnybravo@mail.com']; ['John'; 'john00@mail.com'; 'john_newyork@mail.com'; 'johnsmith@mail.com']] would still be accepted. Example 2: Input: accounts = [[""Gabe"";""Gabe0@m.co"";""Gabe3@m.co"";""Gabe1@m.co""];[""Kevin"";""Kevin3@m.co"";""Kevin5@m.co"";""Kevin0@m.co""];[""Ethan"";""Ethan5@m.co"";""Ethan4@m.co"";""Ethan0@m.co""];[""Hanzo"";""Hanzo3@m.co"";""Hanzo1@m.co"";""Hanzo0@m.co""];[""Fern"";""Fern5@m.co"";""Fern1@m.co"";""Fern0@m.co""]] Output: [[""Ethan"";""Ethan0@m.co"";""Ethan4@m.co"";""Ethan5@m.co""];[""Gabe"";""Gabe0@m.co"";""Gabe1@m.co"";""Gabe3@m.co""];[""Hanzo"";""Hanzo0@m.co"";""Hanzo1@m.co"";""Hanzo3@m.co""];[""Kevin"";""Kevin0@m.co"";""Kevin3@m.co"";""Kevin5@m.co""];[""Fern"";""Fern0@m.co"";""Fern1@m.co"";""Fern5@m.co""]] Constraints: 1 <= accounts.length <= 1000 2 <= accounts[i].length <= 10 1 <= accounts[i][j].length <= 30 accounts[i][0] consists of English letters. accounts[i][j] (for j > 0) is a valid email."
Apple,796,Rotate String,Easy,Math,Given four integers sx; sy; tx; and ty; return true if it is possible to convert the point (sx; sy) to the point (tx; ty) through some operations; or false otherwise. The allowed operation on some point (x; y) is to convert it to either (x; x + y) or (x + y; y). Example 1: Input: sx = 1; sy = 1; tx = 3; ty = 5 Output: true Explanation: One series of moves that transforms the starting point to the target is: (1; 1) -> (1; 2) (1; 2) -> (3; 2) (3; 2) -> (3; 5) Example 2: Input: sx = 1; sy = 1; tx = 2; ty = 2 Output: false Example 3: Input: sx = 1; sy = 1; tx = 1; ty = 1 Output: true Constraints: 1 <= sx; sy; tx; ty <= 109
Apple,622,Design Circular Queue,Med,,
Apple,1275,Find Winner on a Tic Tac Toe Game,Easy,"Tree, Depth-First Search, Breadth-First Search, Union Find, Graph, Binary Tree",You have n binary tree nodes numbered from 0 to n - 1 where node i has two children leftChild[i] and rightChild[i]; return true if and only if all the given nodes form exactly one valid binary tree. If node i has no left child then leftChild[i] will equal -1; similarly for the right child. Note that the nodes have no values and that we only use the node numbers in this problem. Example 1: Input: n = 4; leftChild = [1;-1;3;-1]; rightChild = [2;-1;-1;-1] Output: true Example 2: Input: n = 4; leftChild = [1;-1;3;-1]; rightChild = [2;3;-1;-1] Output: false Example 3: Input: n = 2; leftChild = [1;0]; rightChild = [-1;-1] Output: false Constraints: n == leftChild.length == rightChild.length 1 <= n <= 104 -1 <= leftChild[i]; rightChild[i] <= n - 1
Apple,2023,Number of Pairs of Strings With Concatenation Equal to Target,Med,"Array, Hash Table, Design, Heap (Priority Queue), Ordered Set","You have a movie renting company consisting of n shops. You want to implement a renting system that supports searching for; booking; and returning movies. The system should also support generating a report of the currently rented movies. Each movie is given as a 2D integer array entries where entries[i] = [shopi; moviei; pricei] indicates that there is a copy of movie moviei at shop shopi with a rental price of pricei. Each shop carries at most one copy of a movie moviei. The system should support the following functions: Search: Finds the cheapest 5 shops that have an unrented copy of a given movie. The shops should be sorted by price in ascending order; and in case of a tie; the one with the smaller shopi should appear first. If there are less than 5 matching shops; then all of them should be returned. If no shop has an unrented copy; then an empty list should be returned. Rent: Rents an unrented copy of a given movie from a given shop. Drop: Drops off a previously rented copy of a given movie at a given shop. Report: Returns the cheapest 5 rented movies (possibly of the same movie ID) as a 2D list res where res[j] = [shopj; moviej] describes that the jth cheapest rented movie moviej was rented from the shop shopj. The movies in res should be sorted by price in ascending order; and in case of a tie; the one with the smaller shopj should appear first; and if there is still tie; the one with the smaller moviej should appear first. If there are fewer than 5 rented movies; then all of them should be returned. If no movies are currently being rented; then an empty list should be returned. Implement the MovieRentingSystem class: MovieRentingSystem(int n; int[][] entries) Initializes the MovieRentingSystem object with n shops and the movies in entries. List<Integer> search(int movie) Returns a list of shops that have an unrented copy of the given movie as described above. void rent(int shop; int movie) Rents the given movie from the given shop. void drop(int shop; int movie) Drops off a previously rented movie at the given shop. List<List<Integer>> report() Returns a list of cheapest rented movies as described above. Note: The test cases will be generated such that rent will only be called if the shop has an unrented copy of the movie; and drop will only be called if the shop had previously rented out the movie. Example 1: Input [""MovieRentingSystem""; ""search""; ""rent""; ""rent""; ""report""; ""drop""; ""search""] [[3; [[0; 1; 5]; [0; 2; 6]; [0; 3; 7]; [1; 1; 4]; [1; 2; 7]; [2; 1; 5]]]; [1]; [0; 1]; [1; 2]; []; [1; 2]; [2]] Output [null; [1; 0; 2]; null; null; [[0; 1]; [1; 2]]; null; [0; 1]] Explanation MovieRentingSystem movieRentingSystem = new MovieRentingSystem(3; [[0; 1; 5]; [0; 2; 6]; [0; 3; 7]; [1; 1; 4]; [1; 2; 7]; [2; 1; 5]]); movieRentingSystem.search(1); // return [1; 0; 2]; Movies of ID 1 are unrented at shops 1; 0; and 2. Shop 1 is cheapest; shop 0 and 2 are the same price; so order by shop number. movieRentingSystem.rent(0; 1); // Rent movie 1 from shop 0. Unrented movies at shop 0 are now [2;3]. movieRentingSystem.rent(1; 2); // Rent movie 2 from shop 1. Unrented movies at shop 1 are now [1]. movieRentingSystem.report(); // return [[0; 1]; [1; 2]]. Movie 1 from shop 0 is cheapest; followed by movie 2 from shop 1. movieRentingSystem.drop(1; 2); // Drop off movie 2 at shop 1. Unrented movies at shop 1 are now [1;2]. movieRentingSystem.search(2); // return [0; 1]. Movies of ID 2 are unrented at shops 0 and 1. Shop 0 is cheapest; followed by shop 1. Constraints: 1 <= n <= 3 * 105 1 <= entries.length <= 105 0 <= shopi < n 1 <= moviei; pricei <= 104 Each shop carries at most one copy of a movie moviei. At most 105 calls in total will be made to search; rent; drop and report."
Apple,6,Zigzag Conversion,Med,String,"The string ""PAYPALISHIRING"" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: ""PAHNAPLSIIGYIR"" Write the code that will take a string and make this conversion given a number of rows: string convert(string s; int numRows); Example 1: Input: s = ""PAYPALISHIRING""; numRows = 3 Output: ""PAHNAPLSIIGYIR"" Example 2: Input: s = ""PAYPALISHIRING""; numRows = 4 Output: ""PINALSIGYAHRPI"" Explanation: P I N A L S I G Y A H R P I Example 3: Input: s = ""A""; numRows = 1 Output: ""A"" Constraints: 1 <= s.length <= 1000 s consists of English letters (lower-case and upper-case); ';' and '.'. 1 <= numRows <= 1000"
Apple,51,N-Queens,Hard,"Array, Backtracking","The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n; return all distinct solutions to the n-queens puzzle. You may return the answer in any order. Each solution contains a distinct board configuration of the n-queens' placement; where 'Q' and '.' both indicate a queen and an empty space; respectively. Example 1: Input: n = 4 Output: [["".Q.."";""...Q"";""Q..."";""..Q.""];[""..Q."";""Q..."";""...Q"";"".Q..""]] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above Example 2: Input: n = 1 Output: [[""Q""]] Constraints: 1 <= n <= 9"
Apple,78,Subsets,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums of unique elements; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;3] Output: [[];[1];[2];[1;2];[3];[1;3];[2;3];[1;2;3]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10 All the numbers of nums are unique.
Apple,131,Palindrome Partitioning,Med,"String, Dynamic Programming, Backtracking","Given a string s; partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s. Example 1: Input: s = ""aab"" Output: [[""a"";""a"";""b""];[""aa"";""b""]] Example 2: Input: s = ""a"" Output: [[""a""]] Constraints: 1 <= s.length <= 16 s contains only lowercase English letters."
Apple,143,Reorder List,Med,"Linked List, Two Pointers, Stack, Recursion",You are given the head of a singly linked-list. The list can be represented as: L0 → L1 → … → Ln - 1 → Ln Reorder the list to be on the following form: L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → … You may not modify the values in the list's nodes. Only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4] Output: [1;4;2;3] Example 2: Input: head = [1;2;3;4;5] Output: [1;5;2;4;3] Constraints: The number of nodes in the list is in the range [1; 5 * 104]. 1 <= Node.val <= 1000
Apple,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Apple,235,Lowest Common Ancestor of a Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given a binary search tree (BST); find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [2;1]; p = 2; q = 1 Output: 2 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.
Apple,284,Peeking Iterator,Med,"Array, Design, Iterator","Design an iterator that supports the peek operation on an existing iterator in addition to the hasNext and the next operations. Implement the PeekingIterator class: PeekingIterator(Iterator<int> nums) Initializes the object with the given integer iterator iterator. int next() Returns the next element in the array and moves the pointer to the next element. boolean hasNext() Returns true if there are still elements in the array. int peek() Returns the next element in the array without moving the pointer. Note: Each language may have a different implementation of the constructor and Iterator; but they all support the int next() and boolean hasNext() functions. Example 1: Input [""PeekingIterator""; ""next""; ""peek""; ""next""; ""next""; ""hasNext""] [[[1; 2; 3]]; []; []; []; []; []] Output [null; 1; 2; 2; 3; false] Explanation PeekingIterator peekingIterator = new PeekingIterator([1; 2; 3]); // [1;2;3] peekingIterator.next(); // return 1; the pointer moves to the next element [1;2;3]. peekingIterator.peek(); // return 2; the pointer does not move [1;2;3]. peekingIterator.next(); // return 2; the pointer moves to the next element [1;2;3] peekingIterator.next(); // return 3; the pointer moves to the next element [1;2;3] peekingIterator.hasNext(); // return False Constraints: 1 <= nums.length <= 1000 1 <= nums[i] <= 1000 All the calls to next and peek are valid. At most 1000 calls will be made to next; hasNext; and peek. Follow up: How would you extend your design to be generic and work with all types; not just integer?"
Apple,344,Reverse String,Easy,"Two Pointers, String","Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory. Example 1: Input: s = [""h"";""e"";""l"";""l"";""o""] Output: [""o"";""l"";""l"";""e"";""h""] Example 2: Input: s = [""H"";""a"";""n"";""n"";""a"";""h""] Output: [""h"";""a"";""n"";""n"";""a"";""H""] Constraints: 1 <= s.length <= 105 s[i] is a printable ascii character."
Apple,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Apple,424,Longest Repeating Character Replacement,Med,"Hash Table, String, Sliding Window","You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times. Return the length of the longest substring containing the same letter you can get after performing the above operations. Example 1: Input: s = ""ABAB""; k = 2 Output: 4 Explanation: Replace the two 'A's with two 'B's or vice versa. Example 2: Input: s = ""AABABBA""; k = 1 Output: 4 Explanation: Replace the one 'A' in the middle with 'B' and form ""AABBBBA"". The substring ""BBBB"" has the longest repeating letters; which is 4. There may exists other ways to achieve this answer too. Constraints: 1 <= s.length <= 105 s consists of only uppercase English letters. 0 <= k <= s.length"
Apple,496,Next Greater Element I,Easy,"Array, Hash Table, Stack, Monotonic Stack",The next greater element of some element x in an array is the first greater element that is to the right of x in the same array. You are given two distinct 0-indexed integer arrays nums1 and nums2; where nums1 is a subset of nums2. For each 0 <= i < nums1.length; find the index j such that nums1[i] == nums2[j] and determine the next greater element of nums2[j] in nums2. If there is no next greater element; then the answer for this query is -1. Return an array ans of length nums1.length such that ans[i] is the next greater element as described above. Example 1: Input: nums1 = [4;1;2]; nums2 = [1;3;4;2] Output: [-1;3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 4 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. - 1 is underlined in nums2 = [1;3;4;2]. The next greater element is 3. - 2 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. Example 2: Input: nums1 = [2;4]; nums2 = [1;2;3;4] Output: [3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 2 is underlined in nums2 = [1;2;3;4]. The next greater element is 3. - 4 is underlined in nums2 = [1;2;3;4]. There is no next greater element; so the answer is -1. Constraints: 1 <= nums1.length <= nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 104 All integers in nums1 and nums2 are unique. All the integers of nums1 also appear in nums2. Follow up: Could you find an O(nums1.length + nums2.length) solution?
Apple,565,Array Nesting,Med,"Array, Depth-First Search",You are given an integer array nums of length n where nums is a permutation of the numbers in the range [0; n - 1]. You should build a set s[k] = {nums[k]; nums[nums[k]]; nums[nums[nums[k]]]; ... } subjected to the following rule: The first element in s[k] starts with the selection of the element nums[k] of index = k. The next element in s[k] should be nums[nums[k]]; and then nums[nums[nums[k]]]; and so on. We stop adding right before a duplicate element occurs in s[k]. Return the longest length of a set s[k]. Example 1: Input: nums = [5;4;0;3;1;6;2] Output: 4 Explanation: nums[0] = 5; nums[1] = 4; nums[2] = 0; nums[3] = 3; nums[4] = 1; nums[5] = 6; nums[6] = 2. One of the longest sets s[k]: s[0] = {nums[0]; nums[5]; nums[6]; nums[2]} = {5; 6; 2; 0} Example 2: Input: nums = [0;1;2] Output: 1 Constraints: 1 <= nums.length <= 105 0 <= nums[i] < nums.length All the values of nums are unique.
Apple,733,Flood Fill,Easy,"Array, Depth-First Search, Breadth-First Search, Matrix",You are given an image represented by an m x n grid of integers image; where image[i][j] represents the pixel value of the image. You are also given three integers sr; sc; and color. Your task is to perform a flood fill on the image starting from the pixel image[sr][sc]. To perform a flood fill: Begin with the starting pixel and change its color to color. Perform the same process for each pixel that is directly adjacent (pixels that share a side with the original pixel; either horizontally or vertically) and shares the same color as the starting pixel. Keep repeating this process by checking neighboring pixels of the updated pixels and modifying their color if it matches the original color of the starting pixel. The process stops when there are no more adjacent pixels of the original color to update. Return the modified image after performing the flood fill. Example 1: Input: image = [[1;1;1];[1;1;0];[1;0;1]]; sr = 1; sc = 1; color = 2 Output: [[2;2;2];[2;2;0];[2;0;1]] Explanation: From the center of the image with position (sr; sc) = (1; 1) (i.e.; the red pixel); all pixels connected by a path of the same color as the starting pixel (i.e.; the blue pixels) are colored with the new color. Note the bottom corner is not colored 2; because it is not horizontally or vertically connected to the starting pixel. Example 2: Input: image = [[0;0;0];[0;0;0]]; sr = 0; sc = 0; color = 0 Output: [[0;0;0];[0;0;0]] Explanation: The starting pixel is already colored with 0; which is the same as the target color. Therefore; no changes are made to the image. Constraints: m == image.length n == image[i].length 1 <= m; n <= 50 0 <= image[i][j]; color < 216 0 <= sr < m 0 <= sc < n
Apple,706,Design HashMap,Easy,,
Apple,907,Sum of Subarray Minimums,Med,"Array, Binary Search",Koko loves to eat bananas. There are n piles of bananas; the ith pile has piles[i] bananas. The guards have gone and will come back in h hours. Koko can decide her bananas-per-hour eating speed of k. Each hour; she chooses some pile of bananas and eats k bananas from that pile. If the pile has less than k bananas; she eats all of them instead and will not eat any more bananas during this hour. Koko likes to eat slowly but still wants to finish eating all the bananas before the guards return. Return the minimum integer k such that she can eat all the bananas within h hours. Example 1: Input: piles = [3;6;7;11]; h = 8 Output: 4 Example 2: Input: piles = [30;11;23;4;20]; h = 5 Output: 30 Example 3: Input: piles = [30;11;23;4;20]; h = 6 Output: 23 Constraints: 1 <= piles.length <= 104 piles.length <= h <= 109 1 <= piles[i] <= 109
Apple,977,Squares of a Sorted Array,Easy,"String, Dynamic Programming","Given a string s; return the number of distinct non-empty subsequences of s. Since the answer may be very large; return it modulo 109 + 7. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not. Example 1: Input: s = ""abc"" Output: 7 Explanation: The 7 distinct subsequences are ""a""; ""b""; ""c""; ""ab""; ""ac""; ""bc""; and ""abc"". Example 2: Input: s = ""aba"" Output: 6 Explanation: The 6 distinct subsequences are ""a""; ""b""; ""ab""; ""aa""; ""ba""; and ""aba"". Example 3: Input: s = ""aaa"" Output: 3 Explanation: The 3 distinct subsequences are ""a""; ""aa"" and ""aaa"". Constraints: 1 <= s.length <= 2000 s consists of lowercase English letters."
Apple,996,Number of Squareful Arrays,Hard,,
Apple,2397,Maximum Rows Covered by Columns,Med,Dynamic Programming,There is a street with n * 2 plots; where there are n plots on each side of the street. The plots on each side are numbered from 1 to n. On each plot; a house can be placed. Return the number of ways houses can be placed such that no two houses are adjacent to each other on the same side of the street. Since the answer may be very large; return it modulo 109 + 7. Note that if a house is placed on the ith plot on one side of the street; a house can also be placed on the ith plot on the other side of the street. Example 1: Input: n = 1 Output: 4 Explanation: Possible arrangements: 1. All plots are empty. 2. A house is placed on one side of the street. 3. A house is placed on the other side of the street. 4. Two houses are placed; one on each side of the street. Example 2: Input: n = 2 Output: 9 Explanation: The 9 possible arrangements are shown in the diagram above. Constraints: 1 <= n <= 104
Apple,2972,Count the Number of Incremovable Subarrays II,Hard,,
Apple,2970,Count the Number of Incremovable Subarrays I,Easy,,
Apple,3030,Find the Grid of Region Average,Med,"Math, String, Bit Manipulation",
Apple,38,Count and Say,Med,String,"The count-and-say sequence is a sequence of digit strings defined by the recursive formula: countAndSay(1) = ""1"" countAndSay(n) is the run-length encoding of countAndSay(n - 1). Run-length encoding (RLE) is a string compression method that works by replacing consecutive identical characters (repeated 2 or more times) with the concatenation of the character and the number marking the count of the characters (length of the run). For example; to compress the string ""3322251"" we replace ""33"" with ""23""; replace ""222"" with ""32""; replace ""5"" with ""15"" and replace ""1"" with ""11"". Thus the compressed string becomes ""23321511"". Given a positive integer n; return the nth element of the count-and-say sequence. Example 1: Input: n = 4 Output: ""1211"" Explanation: countAndSay(1) = ""1"" countAndSay(2) = RLE of ""1"" = ""11"" countAndSay(3) = RLE of ""11"" = ""21"" countAndSay(4) = RLE of ""21"" = ""1211"" Example 2: Input: n = 1 Output: ""1"" Explanation: This is the base case. Constraints: 1 <= n <= 30 Follow up: Could you solve it iteratively?"
Apple,62,Unique Paths,Med,"Math, Dynamic Programming, Combinatorics",There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n; return the number of possible unique paths that the robot can take to reach the bottom-right corner. The test cases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: m = 3; n = 7 Output: 28 Example 2: Input: m = 3; n = 2 Output: 3 Explanation: From the top-left corner; there are a total of 3 ways to reach the bottom-right corner: 1. Right -> Down -> Down 2. Down -> Down -> Right 3. Down -> Right -> Down Constraints: 1 <= m; n <= 100
Apple,64,Minimum Path Sum,Med,"Array, Dynamic Programming, Matrix",Given a m x n grid filled with non-negative numbers; find a path from top left to bottom right; which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1;3;1];[1;5;1];[4;2;1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. Example 2: Input: grid = [[1;2;3];[4;5;6]] Output: 12 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 200 0 <= grid[i][j] <= 200
Apple,81,Search in Rotated Sorted Array II,Med,"Array, Binary Search",There is an integer array nums sorted in non-decreasing order (not necessarily with distinct values). Before being passed to your function; nums is rotated at an unknown pivot index k (0 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;4;4;5;6;6;7] might be rotated at pivot index 5 and become [4;5;6;6;7;0;1;2;4;4]. Given the array nums after the rotation and an integer target; return true if target is in nums; or false if it is not in nums. You must decrease the overall operation steps as much as possible. Example 1: Input: nums = [2;5;6;0;0;1;2]; target = 0 Output: true Example 2: Input: nums = [2;5;6;0;0;1;2]; target = 3 Output: false Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 nums is guaranteed to be rotated at some pivot. -104 <= target <= 104 Follow up: This problem is similar to Search in Rotated Sorted Array; but nums may contain duplicates. Would this affect the runtime complexity? How and why?
Apple,110,Balanced Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given a binary tree; determine if it is height-balanced. Example 1: Input: root = [3;9;20;null;null;15;7] Output: true Example 2: Input: root = [1;2;2;3;3;null;null;4;4] Output: false Example 3: Input: root = [] Output: true Constraints: The number of nodes in the tree is in the range [0; 5000]. -104 <= Node.val <= 104
Apple,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
Apple,141,Linked List Cycle,Easy,"Hash Table, Linked List, Two Pointers",Given head; the head of a linked list; determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise; return false. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 1st node (0-indexed). Example 2: Input: head = [1;2]; pos = 0 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 0th node. Example 3: Input: head = [1]; pos = -1 Output: false Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Apple,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
Apple,213,House Robber II,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile; adjacent houses have a security system connected; and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [2;3;2] Output: 3 Explanation: You cannot rob house 1 (money = 2) and then rob house 3 (money = 2); because they are adjacent houses. Example 2: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 3: Input: nums = [1;2;3] Output: 3 Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 1000
Apple,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Apple,341,Flatten Nested List Iterator,Med,"Stack, Tree, Depth-First Search, Design, Queue, Iterator",You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it. Implement the NestedIterator class: NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList. int next() Returns the next integer in the nested list. boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise. Your code will be tested with the following pseudocode: initialize iterator with nestedList res = [] while iterator.hasNext() append iterator.next() to the end of res return res If res matches the expected flattened list; then your code will be judged as correct. Example 1: Input: nestedList = [[1;1];2;[1;1]] Output: [1;1;2;1;1] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;1;2;1;1]. Example 2: Input: nestedList = [1;[4;[6]]] Output: [1;4;6] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;4;6]. Constraints: 1 <= nestedList.length <= 500 The values of the integers in the nested list is in the range [-106; 106].
Apple,451,Sort Characters By Frequency,Med,"Hash Table, String, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given a string s; sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers; return any of them. Example 1: Input: s = ""tree"" Output: ""eert"" Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore ""eetr"" is also a valid answer. Example 2: Input: s = ""cccaaa"" Output: ""aaaccc"" Explanation: Both 'c' and 'a' appear three times; so both ""cccaaa"" and ""aaaccc"" are valid answers. Note that ""cacaca"" is incorrect; as the same characters must be together. Example 3: Input: s = ""Aabb"" Output: ""bbAa"" Explanation: ""bbaA"" is also a valid answer; but ""Aabb"" is incorrect. Note that 'A' and 'a' are treated as two different characters. Constraints: 1 <= s.length <= 5 * 105 s consists of uppercase and lowercase English letters and digits."
Apple,456,132 Pattern,Med,"Array, Binary Search, Stack, Monotonic Stack, Ordered Set",Given an array of n integers nums; a 132 pattern is a subsequence of three integers nums[i]; nums[j] and nums[k] such that i < j < k and nums[i] < nums[k] < nums[j]. Return true if there is a 132 pattern in nums; otherwise; return false. Example 1: Input: nums = [1;2;3;4] Output: false Explanation: There is no 132 pattern in the sequence. Example 2: Input: nums = [3;1;4;2] Output: true Explanation: There is a 132 pattern in the sequence: [1; 4; 2]. Example 3: Input: nums = [-1;3;2;0] Output: true Explanation: There are three 132 patterns in the sequence: [-1; 3; 2]; [-1; 3; 0] and [-1; 2; 0]. Constraints: n == nums.length 1 <= n <= 2 * 105 -109 <= nums[i] <= 109
Apple,542,01 Matrix,Med,"Array, Dynamic Programming, Breadth-First Search, Matrix",Given an m x n binary matrix mat; return the distance of the nearest 0 for each cell. The distance between two adjacent cells is 1. Example 1: Input: mat = [[0;0;0];[0;1;0];[0;0;0]] Output: [[0;0;0];[0;1;0];[0;0;0]] Example 2: Input: mat = [[0;0;0];[0;1;0];[1;1;1]] Output: [[0;0;0];[0;1;0];[1;2;1]] Constraints: m == mat.length n == mat[i].length 1 <= m; n <= 104 1 <= m * n <= 104 mat[i][j] is either 0 or 1. There is at least one 0 in mat.
Apple,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Apple,852,Peak Index in a Mountain Array,Med,"Array, Two Pointers, Binary Search, Sorting",There are n persons on a social media website. You are given an integer array ages where ages[i] is the age of the ith person. A Person x will not send a friend request to a person y (x != y) if any of the following conditions is true: age[y] <= 0.5 * age[x] + 7 age[y] > age[x] age[y] > 100 && age[x] < 100 Otherwise; x will send a friend request to y. Note that if x sends a request to y; y will not necessarily send a request to x. Also; a person will not send a friend request to themself. Return the total number of friend requests made. Example 1: Input: ages = [16;16] Output: 2 Explanation: 2 people friend request each other. Example 2: Input: ages = [16;17;18] Output: 2 Explanation: Friend requests are made 17 -> 16; 18 -> 17. Example 3: Input: ages = [20;30;100;110;120] Output: 3 Explanation: Friend requests are made 110 -> 100; 120 -> 110; 120 -> 100. Constraints: n == ages.length 1 <= n <= 2 * 104 1 <= ages[i] <= 120
Apple,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
Apple,912,Sort an Array,Med,"Array, Math, Binary Search, Prefix Sum, Randomized","You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index. You need to implement the function pickIndex(); which randomly picks an index in the range [0; w.length - 1] (inclusive) and returns it. The probability of picking an index i is w[i] / sum(w). For example; if w = [1; 3]; the probability of picking index 0 is 1 / (1 + 3) = 0.25 (i.e.; 25%); and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e.; 75%). Example 1: Input [""Solution"";""pickIndex""] [[[1]];[]] Output [null;0] Explanation Solution solution = new Solution([1]); solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w. Example 2: Input [""Solution"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex""] [[[1;3]];[];[];[];[];[]] Output [null;1;1;1;1;0] Explanation Solution solution = new Solution([1; 3]); solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4. solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4. Since this is a randomization problem; multiple answers are allowed. All of the following outputs can be considered correct: [null;1;1;1;1;0] [null;1;1;1;1;1] [null;1;1;1;0;0] [null;1;1;1;0;1] [null;1;0;1;0;0] ...... and so on. Constraints: 1 <= w.length <= 104 1 <= w[i] <= 105 pickIndex will be called at most 104 times."
Apple,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Apple,1581,Customer Who Visited but Did Not Make Any Transactions,Easy,"Array, Two Pointers, Sorting",Given an array of integers arr and an integer k. A value arr[i] is said to be stronger than a value arr[j] if |arr[i] - m| > |arr[j] - m| where m is the median of the array. If |arr[i] - m| == |arr[j] - m|; then arr[i] is said to be stronger than arr[j] if arr[i] > arr[j]. Return a list of the strongest k values in the array. return the answer in any arbitrary order. Median is the middle value in an ordered integer list. More formally; if the length of the list is n; the median is the element in position ((n - 1) / 2) in the sorted list (0-indexed). For arr = [6; -3; 7; 2; 11]; n = 5 and the median is obtained by sorting the array arr = [-3; 2; 6; 7; 11] and the median is arr[m] where m = ((5 - 1) / 2) = 2. The median is 6. For arr = [-7; 22; 17; 3]; n = 4 and the median is obtained by sorting the array arr = [-7; 3; 17; 22] and the median is arr[m] where m = ((4 - 1) / 2) = 1. The median is 3. Example 1: Input: arr = [1;2;3;4;5]; k = 2 Output: [5;1] Explanation: Median is 3; the elements of the array sorted by the strongest are [5;1;4;2;3]. The strongest 2 elements are [5; 1]. [1; 5] is also accepted answer. Please note that although |5 - 3| == |1 - 3| but 5 is stronger than 1 because 5 > 1. Example 2: Input: arr = [1;1;3;5;5]; k = 2 Output: [5;5] Explanation: Median is 3; the elements of the array sorted by the strongest are [5;5;1;1;3]. The strongest 2 elements are [5; 5]. Example 3: Input: arr = [6;7;11;7;6;8]; k = 5 Output: [11;8;6;6;7] Explanation: Median is 7; the elements of the array sorted by the strongest are [11;8;6;6;7;7]. Any permutation of [11;8;6;6;7] is accepted. Constraints: 1 <= arr.length <= 105 -105 <= arr[i] <= 105 1 <= k <= arr.length
Apple,1642,Furthest Building You Can Reach,Med,"Math, Simulation",There are numBottles water bottles that are initially full of water. You can exchange numExchange empty water bottles from the market with one full water bottle. The operation of drinking a full water bottle turns it into an empty bottle. Given the two integers numBottles and numExchange; return the maximum number of water bottles you can drink. Example 1: Input: numBottles = 9; numExchange = 3 Output: 13 Explanation: You can exchange 3 empty bottles to get 1 full water bottle. Number of water bottles you can drink: 9 + 3 + 1 = 13. Example 2: Input: numBottles = 15; numExchange = 4 Output: 19 Explanation: You can exchange 4 empty bottles to get 1 full water bottle. Number of water bottles you can drink: 15 + 3 + 1 = 19. Constraints: 1 <= numBottles <= 100 2 <= numExchange <= 100
Apple,2149,Rearrange Array Elements by Sign,Med,"Math, String, Greedy, Game Theory","There are n pieces arranged in a line; and each piece is colored either by 'A' or by 'B'. You are given a string colors of length n where colors[i] is the color of the ith piece. Alice and Bob are playing a game where they take alternating turns removing pieces from the line. In this game; Alice moves first. Alice is only allowed to remove a piece colored 'A' if both its neighbors are also colored 'A'. She is not allowed to remove pieces that are colored 'B'. Bob is only allowed to remove a piece colored 'B' if both its neighbors are also colored 'B'. He is not allowed to remove pieces that are colored 'A'. Alice and Bob cannot remove pieces from the edge of the line. If a player cannot make a move on their turn; that player loses and the other player wins. Assuming Alice and Bob play optimally; return true if Alice wins; or return false if Bob wins. Example 1: Input: colors = ""AAABABB"" Output: true Explanation: AAABABB -> AABABB Alice moves first. She removes the second 'A' from the left since that is the only 'A' whose neighbors are both 'A'. Now it's Bob's turn. Bob cannot make a move on his turn since there are no 'B's whose neighbors are both 'B'. Thus; Alice wins; so return true. Example 2: Input: colors = ""AA"" Output: false Explanation: Alice has her turn first. There are only two 'A's and both are on the edge of the line; so she cannot move on her turn. Thus; Bob wins; so return false. Example 3: Input: colors = ""ABBBBBBBAAA"" Output: false Explanation: ABBBBBBBAAA -> ABBBBBBBAA Alice moves first. Her only option is to remove the second to last 'A' from the right. ABBBBBBBAA -> ABBBBBBAA Next is Bob's turn. He has many options for which 'B' piece to remove. He can pick any. On Alice's second turn; she has no more pieces that she can remove. Thus; Bob wins; so return false. Constraints: 1 <= colors.length <= 105 colors consists of only the letters 'A' and 'B'"
Apple,24,Swap Nodes in Pairs,Med,"Linked List, Recursion",Given a linked list; swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e.; only nodes themselves may be changed.) Example 1: Input: head = [1;2;3;4] Output: [2;1;4;3] Explanation: Example 2: Input: head = [] Output: [] Example 3: Input: head = [1] Output: [1] Example 4: Input: head = [1;2;3] Output: [2;1;3] Constraints: The number of nodes in the list is in the range [0; 100]. 0 <= Node.val <= 100
Apple,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Apple,32,Longest Valid Parentheses,Hard,"String, Dynamic Programming, Stack","Given a string containing just the characters '(' and ')'; return the length of the longest valid (well-formed) parentheses substring. Example 1: Input: s = ""(()"" Output: 2 Explanation: The longest valid parentheses substring is ""()"". Example 2: Input: s = "")()())"" Output: 4 Explanation: The longest valid parentheses substring is ""()()"". Example 3: Input: s = """" Output: 0 Constraints: 0 <= s.length <= 3 * 104 s[i] is '('; or ')'."
Apple,61,Rotate List,Med,"Linked List, Two Pointers",Given the head of a linked list; rotate the list to the right by k places. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [4;5;1;2;3] Example 2: Input: head = [0;1;2]; k = 4 Output: [2;0;1] Constraints: The number of nodes in the list is in the range [0; 500]. -100 <= Node.val <= 100 0 <= k <= 2 * 109
Apple,71,Simplify Path,Med,"String, Stack","You are given an absolute path for a Unix-style file system; which always begins with a slash '/'. Your task is to transform this absolute path into its simplified canonical path. The rules of a Unix-style file system are as follows: A single period '.' represents the current directory. A double period '..' represents the previous/parent directory. Multiple consecutive slashes such as '//' and '///' are treated as a single slash '/'. Any sequence of periods that does not match the rules above should be treated as a valid directory or file name. For example; '...' and '....' are valid directory or file names. The simplified canonical path should follow these rules: The path must start with a single slash '/'. Directories within the path must be separated by exactly one slash '/'. The path must not end with a slash '/'; unless it is the root directory. The path must not have any single or double periods ('.' and '..') used to denote current or parent directories. Return the simplified canonical path. Example 1: Input: path = ""/home/"" Output: ""/home"" Explanation: The trailing slash should be removed. Example 2: Input: path = ""/home//foo/"" Output: ""/home/foo"" Explanation: Multiple consecutive slashes are replaced by a single one. Example 3: Input: path = ""/home/user/Documents/../Pictures"" Output: ""/home/user/Pictures"" Explanation: A double period "".."" refers to the directory up a level (the parent directory). Example 4: Input: path = ""/../"" Output: ""/"" Explanation: Going one level up from the root directory is not possible. Example 5: Input: path = ""/.../a/../b/c/../d/./"" Output: ""/.../b/d"" Explanation: ""..."" is a valid name for a directory in this problem. Constraints: 1 <= path.length <= 3000 path consists of English letters; digits; period '.'; slash '/' or '_'. path is a valid absolute Unix path."
Apple,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Apple,142,Linked List Cycle II,Med,"Hash Table, Linked List, Two Pointers",Given the head of a linked list; return the node where the cycle begins. If there is no cycle; return null. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to (0-indexed). It is -1 if there is no cycle. Note that pos is not passed as a parameter. Do not modify the linked list. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: tail connects to node index 1 Explanation: There is a cycle in the linked list; where tail connects to the second node. Example 2: Input: head = [1;2]; pos = 0 Output: tail connects to node index 0 Explanation: There is a cycle in the linked list; where tail connects to the first node. Example 3: Input: head = [1]; pos = -1 Output: no cycle Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Apple,148,Sort List,Med,"Linked List, Two Pointers, Divide and Conquer, Sorting, Merge Sort",Given the head of a linked list; return the list after sorting it in ascending order. Example 1: Input: head = [4;2;1;3] Output: [1;2;3;4] Example 2: Input: head = [-1;5;3;4;0] Output: [-1;0;3;4;5] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is in the range [0; 5 * 104]. -105 <= Node.val <= 105 Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?
Apple,348,Design Tic-Tac-Toe,Med,"Array, Hash Table, Design, Matrix, Simulation",
Apple,442,Find All Duplicates in an Array,Med,"Array, Hash Table",Given an integer array nums of length n where all the integers of nums are in the range [1; n] and each integer appears at most twice; return an array of all the integers that appears twice. You must write an algorithm that runs in O(n) time and uses only constant auxiliary space; excluding the space needed to store the output Example 1: Input: nums = [4;3;2;7;8;2;3;1] Output: [2;3] Example 2: Input: nums = [1;1;2] Output: [1] Example 3: Input: nums = [1] Output: [] Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i] <= n Each element in nums appears once or twice.
Apple,643,Maximum Average Subarray I,Easy,"Array, Sliding Window",You are given an integer array nums consisting of n elements; and an integer k. Find a contiguous subarray whose length is equal to k that has the maximum average value and return this value. Any answer with a calculation error less than 10-5 will be accepted. Example 1: Input: nums = [1;12;-5;-6;50;3]; k = 4 Output: 12.75000 Explanation: Maximum average is (12 - 5 - 6 + 50) / 4 = 51 / 4 = 12.75 Example 2: Input: nums = [5]; k = 1 Output: 5.00000 Constraints: n == nums.length 1 <= k <= n <= 105 -104 <= nums[i] <= 104
Apple,662,Maximum Width of Binary Tree,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the maximum width of the given tree. The maximum width of a tree is the maximum width among all levels. The width of one level is defined as the length between the end-nodes (the leftmost and rightmost non-null nodes); where the null nodes between the end-nodes that would be present in a complete binary tree extending down to that level are also counted into the length calculation. It is guaranteed that the answer will in the range of a 32-bit signed integer. Example 1: Input: root = [1;3;2;5;3;null;9] Output: 4 Explanation: The maximum width exists in the third level with length 4 (5;3;null;9). Example 2: Input: root = [1;3;2;5;null;null;9;6;null;7] Output: 7 Explanation: The maximum width exists in the fourth level with length 7 (6;null;null;null;null;null;7). Example 3: Input: root = [1;3;2;5] Output: 2 Explanation: The maximum width exists in the second level with length 2 (3;2). Constraints: The number of nodes in the tree is in the range [1; 3000]. -100 <= Node.val <= 100
Apple,678,Valid Parenthesis String,Med,"String, Dynamic Programming, Stack, Greedy","Given a string s containing only three types of characters: '('; ')' and '*'; return true if s is valid. The following rules define a valid string: Any left parenthesis '(' must have a corresponding right parenthesis ')'. Any right parenthesis ')' must have a corresponding left parenthesis '('. Left parenthesis '(' must go before the corresponding right parenthesis ')'. '*' could be treated as a single right parenthesis ')' or a single left parenthesis '(' or an empty string """". Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""(*)"" Output: true Example 3: Input: s = ""(*))"" Output: true Constraints: 1 <= s.length <= 100 s[i] is '('; ')' or '*'."
Apple,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
Apple,1095,Find in Mountain Array,Hard,"Array, Greedy, Sorting",A company is planning to interview 2n people. Given the array costs where costs[i] = [aCosti; bCosti]; the cost of flying the ith person to city a is aCosti; and the cost of flying the ith person to city b is bCosti. Return the minimum cost to fly every person to a city such that exactly n people arrive in each city. Example 1: Input: costs = [[10;20];[30;200];[400;50];[30;20]] Output: 110 Explanation: The first person goes to city A for a cost of 10. The second person goes to city A for a cost of 30. The third person goes to city B for a cost of 50. The fourth person goes to city B for a cost of 20. The total minimum cost is 10 + 30 + 50 + 20 = 110 to have half the people interviewing in each city. Example 2: Input: costs = [[259;770];[448;54];[926;667];[184;139];[840;118];[577;469]] Output: 1859 Example 3: Input: costs = [[515;563];[451;713];[537;709];[343;819];[855;779];[457;60];[650;359];[631;42]] Output: 3086 Constraints: 2 * n == costs.length 2 <= costs.length <= 100 costs.length is even. 1 <= aCosti; bCosti <= 1000
Apple,1148,Article Views I,Easy,"Array, Math",Given two numbers arr1 and arr2 in base -2; return the result of adding them together. Each number is given in array format: as an array of 0s and 1s; from most significant bit to least significant bit. For example; arr = [1;1;0;1] represents the number (-2)^3 + (-2)^2 + (-2)^0 = -3. A number arr in array; format is also guaranteed to have no leading zeros: either arr == [0] or arr[0] == 1. Return the result of adding arr1 and arr2 in the same format: as an array of 0s and 1s with no leading zeros. Example 1: Input: arr1 = [1;1;1;1;1]; arr2 = [1;0;1] Output: [1;0;0;0;0] Explanation: arr1 represents 11; arr2 represents 5; the output represents 16. Example 2: Input: arr1 = [0]; arr2 = [0] Output: [0] Example 3: Input: arr1 = [0]; arr2 = [1] Output: [1] Constraints: 1 <= arr1.length; arr2.length <= 1000 arr1[i] and arr2[i] are 0 or 1 arr1 and arr2 have no leading zeros
Apple,12,Integer to Roman,Med,"Hash Table, Math, String","Seven different symbols represent Roman numerals with the following values: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules: If the value does not start with 4 or 9; select the symbol of the maximal value that can be subtracted from the input; append that symbol to the result; subtract its value; and convert the remainder to a Roman numeral. If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol; for example; 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV); 9 (IX); 40 (XL); 90 (XC); 400 (CD) and 900 (CM). Only powers of 10 (I; X; C; M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V); 50 (L); or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form. Given an integer; convert it to a Roman numeral. Example 1: Input: num = 3749 Output: ""MMMDCCXLIX"" Explanation: 3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M) 700 = DCC as 500 (D) + 100 (C) + 100 (C) 40 = XL as 10 (X) less of 50 (L) 9 = IX as 1 (I) less of 10 (X) Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places Example 2: Input: num = 58 Output: ""LVIII"" Explanation: 50 = L 8 = VIII Example 3: Input: num = 1994 Output: ""MCMXCIV"" Explanation: 1000 = M 900 = CM 90 = XC 4 = IV Constraints: 1 <= num <= 3999"
Apple,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Apple,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Apple,134,Gas Station,Med,"Array, Greedy",There are n gas stations along a circular route; where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations. Given two integer arrays gas and cost; return the starting gas station's index if you can travel around the circuit once in the clockwise direction; otherwise return -1. If there exists a solution; it is guaranteed to be unique. Example 1: Input: gas = [1;2;3;4;5]; cost = [3;4;5;1;2] Output: 3 Explanation: Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 4. Your tank = 4 - 1 + 5 = 8 Travel to station 0. Your tank = 8 - 2 + 1 = 7 Travel to station 1. Your tank = 7 - 3 + 2 = 6 Travel to station 2. Your tank = 6 - 4 + 3 = 5 Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. Therefore; return 3 as the starting index. Example 2: Input: gas = [2;3;4]; cost = [3;4;3] Output: -1 Explanation: You can't start at station 0 or 1; as there is not enough gas to travel to the next station. Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 0. Your tank = 4 - 3 + 2 = 3 Travel to station 1. Your tank = 3 - 3 + 3 = 3 You cannot travel back to station 2; as it requires 4 unit of gas but you only have 3. Therefore; you can't travel around the circuit once no matter where you start. Constraints: n == gas.length == cost.length 1 <= n <= 105 0 <= gas[i]; cost[i] <= 104
Apple,168,Excel Sheet Column Title,Easy,"Math, String","Given an integer columnNumber; return its corresponding column title as it appears in an Excel sheet. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: Input: columnNumber = 1 Output: ""A"" Example 2: Input: columnNumber = 28 Output: ""AB"" Example 3: Input: columnNumber = 701 Output: ""ZY"" Constraints: 1 <= columnNumber <= 231 - 1"
Apple,179,Largest Number,Med,"Array, String, Greedy, Sorting","Given a list of non-negative integers nums; arrange them such that they form the largest number and return it. Since the result may be very large; so you need to return a string instead of an integer. Example 1: Input: nums = [10;2] Output: ""210"" Example 2: Input: nums = [3;30;34;5;9] Output: ""9534330"" Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 109"
Apple,218,The Skyline Problem,Hard,"Array, Divide and Conquer, Binary Indexed Tree, Segment Tree, Line Sweep, Heap (Priority Queue), Ordered Set","A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Given the locations and heights of all the buildings; return the skyline formed by these buildings collectively. The geometric information of each building is given in the array buildings where buildings[i] = [lefti; righti; heighti]: lefti is the x coordinate of the left edge of the ith building. righti is the x coordinate of the right edge of the ith building. heighti is the height of the ith building. You may assume all buildings are perfect rectangles grounded on an absolutely flat surface at height 0. The skyline should be represented as a list of ""key points"" sorted by their x-coordinate in the form [[x1;y1];[x2;y2];...]. Each key point is the left endpoint of some horizontal segment in the skyline except the last point in the list; which always has a y-coordinate 0 and is used to mark the skyline's termination where the rightmost building ends. Any ground between the leftmost and rightmost buildings should be part of the skyline's contour. Note: There must be no consecutive horizontal lines of equal height in the output skyline. For instance; [...;[2 3];[4 5];[7 5];[11 5];[12 7];...] is not acceptable; the three lines of height 5 should be merged into one in the final output as such: [...;[2 3];[4 5];[12 7];...] Example 1: Input: buildings = [[2;9;10];[3;7;15];[5;12;12];[15;20;10];[19;24;8]] Output: [[2;10];[3;15];[7;12];[12;0];[15;10];[20;8];[24;0]] Explanation: Figure A shows the buildings of the input. Figure B shows the skyline formed by those buildings. The red points in figure B represent the key points in the output list. Example 2: Input: buildings = [[0;2;3];[2;5;3]] Output: [[0;3];[5;0]] Constraints: 1 <= buildings.length <= 104 0 <= lefti < righti <= 231 - 1 1 <= heighti <= 231 - 1 buildings is sorted by lefti in non-decreasing order."
Apple,290,Word Pattern,Easy,"Hash Table, String","Given a pattern and a string s; find if s follows the same pattern. Here follow means a full match; such that there is a bijection between a letter in pattern and a non-empty word in s. Specifically: Each letter in pattern maps to exactly one unique word in s. Each unique word in s maps to exactly one letter in pattern. No two letters map to the same word; and no two words map to the same letter. Example 1: Input: pattern = ""abba""; s = ""dog cat cat dog"" Output: true Explanation: The bijection can be established as: 'a' maps to ""dog"". 'b' maps to ""cat"". Example 2: Input: pattern = ""abba""; s = ""dog cat cat fish"" Output: false Example 3: Input: pattern = ""aaaa""; s = ""dog cat cat dog"" Output: false Constraints: 1 <= pattern.length <= 300 pattern contains only lower-case English letters. 1 <= s.length <= 3000 s contains only lowercase English letters and spaces ' '. s does not contain any leading or trailing spaces. All the words in s are separated by a single space."
Apple,362,Design Hit Counter,Med,"Array, Binary Search, Design, Queue, Data Stream",
Apple,367,Valid Perfect Square,Easy,"Math, Binary Search",Given a positive integer num; return true if num is a perfect square or false otherwise. A perfect square is an integer that is the square of an integer. In other words; it is the product of some integer with itself. You must not use any built-in library function; such as sqrt. Example 1: Input: num = 16 Output: true Explanation: We return true because 4 * 4 = 16 and 4 is an integer. Example 2: Input: num = 14 Output: false Explanation: We return false because 3.742 * 3.742 = 14 and 3.742 is not an integer. Constraints: 1 <= num <= 231 - 1
Apple,416,Partition Equal Subset Sum,Med,"Array, Dynamic Programming",Given an integer array nums; return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise. Example 1: Input: nums = [1;5;11;5] Output: true Explanation: The array can be partitioned as [1; 5; 5] and [11]. Example 2: Input: nums = [1;2;3;5] Output: false Explanation: The array cannot be partitioned into equal sum subsets. Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 100
Apple,438,Find All Anagrams in a String,Med,"Hash Table, String, Sliding Window","Given two strings s and p; return an array of all the start indices of p's anagrams in s. You may return the answer in any order. Example 1: Input: s = ""cbaebabacd""; p = ""abc"" Output: [0;6] Explanation: The substring with start index = 0 is ""cba""; which is an anagram of ""abc"". The substring with start index = 6 is ""bac""; which is an anagram of ""abc"". Example 2: Input: s = ""abab""; p = ""ab"" Output: [0;1;2] Explanation: The substring with start index = 0 is ""ab""; which is an anagram of ""ab"". The substring with start index = 1 is ""ba""; which is an anagram of ""ab"". The substring with start index = 2 is ""ab""; which is an anagram of ""ab"". Constraints: 1 <= s.length; p.length <= 3 * 104 s and p consist of lowercase English letters."
Apple,503,Next Greater Element II,Med,"Array, Stack, Monotonic Stack",Given a circular integer array nums (i.e.; the next element of nums[nums.length - 1] is nums[0]); return the next greater number for every element in nums. The next greater number of a number x is the first greater number to its traversing-order next in the array; which means you could search circularly to find its next greater number. If it doesn't exist; return -1 for this number. Example 1: Input: nums = [1;2;1] Output: [2;-1;2] Explanation: The first 1's next greater number is 2; The number 2 can't find next greater number. The second 1's next greater number needs to search circularly; which is also 2. Example 2: Input: nums = [1;2;3;4;3] Output: [2;3;4;-1;4] Constraints: 1 <= nums.length <= 104 -109 <= nums[i] <= 109
Apple,605,Can Place Flowers,Easy,"Array, Greedy",You have a long flowerbed in which some of the plots are planted; and some are not. However; flowers cannot be planted in adjacent plots. Given an integer array flowerbed containing 0's and 1's; where 0 means empty and 1 means not empty; and an integer n; return true if n new flowers can be planted in the flowerbed without violating the no-adjacent-flowers rule and false otherwise. Example 1: Input: flowerbed = [1;0;0;0;1]; n = 1 Output: true Example 2: Input: flowerbed = [1;0;0;0;1]; n = 2 Output: false Constraints: 1 <= flowerbed.length <= 2 * 104 flowerbed[i] is 0 or 1. There are no two adjacent flowers in flowerbed. 0 <= n <= flowerbed.length
Apple,713,Subarray Product Less Than K,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of integers nums and an integer k; return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k. Example 1: Input: nums = [10;5;2;6]; k = 100 Output: 8 Explanation: The 8 subarrays that have product less than 100 are: [10]; [5]; [2]; [6]; [10; 5]; [5; 2]; [2; 6]; [5; 2; 6] Note that [10; 5; 2] is not included as the product of 100 is not strictly less than k. Example 2: Input: nums = [1;2;3]; k = 0 Output: 0 Constraints: 1 <= nums.length <= 3 * 104 1 <= nums[i] <= 1000 0 <= k <= 106
Apple,714,Best Time to Buy and Sell Stock with Transaction Fee,Med,"Array, Dynamic Programming, Greedy",You are given an array prices where prices[i] is the price of a given stock on the ith day; and an integer fee representing a transaction fee. Find the maximum profit you can achieve. You may complete as many transactions as you like; but you need to pay the transaction fee for each transaction. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). The transaction fee is only charged once for each stock purchase and sale. Example 1: Input: prices = [1;3;2;8;4;9]; fee = 2 Output: 8 Explanation: The maximum profit can be achieved by: - Buying at prices[0] = 1 - Selling at prices[3] = 8 - Buying at prices[4] = 4 - Selling at prices[5] = 9 The total profit is ((8 - 1) - 2) + ((9 - 4) - 2) = 8. Example 2: Input: prices = [1;3;7;5;10;3]; fee = 3 Output: 6 Constraints: 1 <= prices.length <= 5 * 104 1 <= prices[i] < 5 * 104 0 <= fee < 5 * 104
Apple,740,Delete and Earn,Med,"Array, Hash Table, Dynamic Programming",You are given an integer array nums. You want to maximize the number of points you get by performing the following operation any number of times: Pick any nums[i] and delete it to earn nums[i] points. Afterwards; you must delete every element equal to nums[i] - 1 and every element equal to nums[i] + 1. Return the maximum number of points you can earn by applying the above operation some number of times. Example 1: Input: nums = [3;4;2] Output: 6 Explanation: You can perform the following operations: - Delete 4 to earn 4 points. Consequently; 3 is also deleted. nums = [2]. - Delete 2 to earn 2 points. nums = []. You earn a total of 6 points. Example 2: Input: nums = [2;2;3;3;3;4] Output: 9 Explanation: You can perform the following operations: - Delete a 3 to earn 3 points. All 2's and 4's are also deleted. nums = [3;3]. - Delete a 3 again to earn 3 points. nums = [3]. - Delete a 3 once more to earn 3 points. nums = []. You earn a total of 9 points. Constraints: 1 <= nums.length <= 2 * 104 1 <= nums[i] <= 104
Apple,1344,Angle Between Hands of a Clock,Med,"Array, Hash Table",Given an array nums of positive integers; return the longest possible length of an array prefix of nums; such that it is possible to remove exactly one element from this prefix so that every number that has appeared in it will have the same number of occurrences. If after removing one element there are no remaining elements; it's still considered that every appeared number has the same number of ocurrences (0). Example 1: Input: nums = [2;2;1;1;5;3;3;5] Output: 7 Explanation: For the subarray [2;2;1;1;5;3;3] of length 7; if we remove nums[4] = 5; we will get [2;2;1;1;3;3]; so that each number will appear exactly twice. Example 2: Input: nums = [1;1;1;2;2;2;3;3;3;4;4;4;5] Output: 13 Constraints: 2 <= nums.length <= 105 1 <= nums[i] <= 105
Apple,1732,Find the Highest Altitude,Easy,"Dynamic Programming, Bit Manipulation, Memoization","Given an integer n; you must transform it into 0 using the following operations any number of times: Change the rightmost (0th) bit in the binary representation of n. Change the ith bit in the binary representation of n if the (i-1)th bit is set to 1 and the (i-2)th through 0th bits are set to 0. Return the minimum number of operations to transform n into 0. Example 1: Input: n = 3 Output: 2 Explanation: The binary representation of 3 is ""11"". ""11"" -> ""01"" with the 2nd operation since the 0th bit is 1. ""01"" -> ""00"" with the 1st operation. Example 2: Input: n = 6 Output: 4 Explanation: The binary representation of 6 is ""110"". ""110"" -> ""010"" with the 2nd operation since the 1st bit is 1 and 0th through 0th bits are 0. ""010"" -> ""011"" with the 1st operation. ""011"" -> ""001"" with the 2nd operation since the 0th bit is 1. ""001"" -> ""000"" with the 1st operation. Constraints: 0 <= n <= 109"
Apple,1802,Maximum Value at a Given Index in a Bounded Array,Med,"Array, Stack, Queue, Simulation",The school cafeteria offers circular and square sandwiches at lunch break; referred to by numbers 0 and 1 respectively. All students stand in a queue. Each student either prefers square or circular sandwiches. The number of sandwiches in the cafeteria is equal to the number of students. The sandwiches are placed in a stack. At each step: If the student at the front of the queue prefers the sandwich on the top of the stack; they will take it and leave the queue. Otherwise; they will leave it and go to the queue's end. This continues until none of the queue students want to take the top sandwich and are thus unable to eat. You are given two integer arrays students and sandwiches where sandwiches[i] is the type of the i​​​​​​th sandwich in the stack (i = 0 is the top of the stack) and students[j] is the preference of the j​​​​​​th student in the initial queue (j = 0 is the front of the queue). Return the number of students that are unable to eat. Example 1: Input: students = [1;1;0;0]; sandwiches = [0;1;0;1] Output: 0 Explanation: - Front student leaves the top sandwich and returns to the end of the line making students = [1;0;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;0;1;1]. - Front student takes the top sandwich and leaves the line making students = [0;1;1] and sandwiches = [1;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [1;1;0]. - Front student takes the top sandwich and leaves the line making students = [1;0] and sandwiches = [0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;1]. - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = [1]. - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = []. Hence all students are able to eat. Example 2: Input: students = [1;1;1;0;0;1]; sandwiches = [1;0;0;0;1;1] Output: 3 Constraints: 1 <= students.length; sandwiches.length <= 100 students.length == sandwiches.length sandwiches[i] is 0 or 1. students[i] is 0 or 1.
Apple,1838,Frequency of the Most Frequent Element,Med,"String, Trie, Rolling Hash, Suffix Array, Hash Function",
Apple,43,Multiply Strings,Med,"Math, String, Simulation","Given two non-negative integers num1 and num2 represented as strings; return the product of num1 and num2; also represented as a string. Note: You must not use any built-in BigInteger library or convert the inputs to integer directly. Example 1: Input: num1 = ""2""; num2 = ""3"" Output: ""6"" Example 2: Input: num1 = ""123""; num2 = ""456"" Output: ""56088"" Constraints: 1 <= num1.length; num2.length <= 200 num1 and num2 consist of digits only. Both num1 and num2 do not contain any leading zero; except the number 0 itself."
Apple,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
Apple,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Apple,77,Combinations,Med,Backtracking,Given two integers n and k; return all possible combinations of k numbers chosen from the range [1; n]. You may return the answer in any order. Example 1: Input: n = 4; k = 2 Output: [[1;2];[1;3];[1;4];[2;3];[2;4];[3;4]] Explanation: There are 4 choose 2 = 6 total combinations. Note that combinations are unordered; i.e.; [1;2] and [2;1] are considered to be the same combination. Example 2: Input: n = 1; k = 1 Output: [[1]] Explanation: There is 1 choose 1 = 1 total combination. Constraints: 1 <= n <= 20 1 <= k <= n
Apple,80,Remove Duplicates from Sorted Array II,Med,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same. Since it is impossible to change the length of the array in some languages; you must instead have the result be placed in the first part of the array nums. More formally; if there are k elements after removing the duplicates; then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements. Return k after placing the final result in the first k slots of nums. Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;1;2;2;3] Output: 5; nums = [1;1;2;2;3;_] Explanation: Your function should return k = 5; with the first five elements of nums being 1; 1; 2; 2 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;1;2;3;3] Output: 7; nums = [0;0;1;1;2;3;3;_;_] Explanation: Your function should return k = 7; with the first seven elements of nums being 0; 0; 1; 1; 2; 3 and 3 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -104 <= nums[i] <= 104 nums is sorted in non-decreasing order.
Apple,86,Partition List,Med,"Linked List, Two Pointers",Given the head of a linked list and a value x; partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of the two partitions. Example 1: Input: head = [1;4;3;2;5;2]; x = 3 Output: [1;2;2;4;3;5] Example 2: Input: head = [2;1]; x = 2 Output: [1;2] Constraints: The number of nodes in the list is in the range [0; 200]. -100 <= Node.val <= 100 -200 <= x <= 200
Apple,95,Unique Binary Search Trees II,Med,"Dynamic Programming, Backtracking, Tree, Binary Search Tree, Binary Tree",Given an integer n; return all the structurally unique BST's (binary search trees); which has exactly n nodes of unique values from 1 to n. Return the answer in any order. Example 1: Input: n = 3 Output: [[1;null;2;null;3];[1;null;3;2];[2;1;3];[3;1;null;null;2];[3;2;null;1]] Example 2: Input: n = 1 Output: [[1]] Constraints: 1 <= n <= 8
Apple,137,Single Number II,Med,"Array, Bit Manipulation",Given an integer array nums where every element appears three times except for one; which appears exactly once. Find the single element and return it. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;3;2] Output: 3 Example 2: Input: nums = [0;1;0;1;0;1;99] Output: 99 Constraints: 1 <= nums.length <= 3 * 104 -231 <= nums[i] <= 231 - 1 Each element in nums appears exactly three times except for one element which appears once.
Apple,175,Combine Two Tables,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | personId | int | | lastName | varchar | | firstName | varchar | +-------------+---------+ personId is the primary key (column with unique values) for this table. This table contains information about the ID of some persons and their first and last names. Table: Address +-------------+---------+ | Column Name | Type | +-------------+---------+ | addressId | int | | personId | int | | city | varchar | | state | varchar | +-------------+---------+ addressId is the primary key (column with unique values) for this table. Each row of this table contains information about the city and state of one person with ID = PersonId. Write a solution to report the first name; last name; city; and state of each person in the Person table. If the address of a personId is not present in the Address table; report null instead. Return the result table in any order. The result format is in the following example. Example 1: Input: Person table: +----------+----------+-----------+ | personId | lastName | firstName | +----------+----------+-----------+ | 1 | Wang | Allen | | 2 | Alice | Bob | +----------+----------+-----------+ Address table: +-----------+----------+---------------+------------+ | addressId | personId | city | state | +-----------+----------+---------------+------------+ | 1 | 2 | New York City | New York | | 2 | 3 | Leetcode | California | +-----------+----------+---------------+------------+ Output: +-----------+----------+---------------+----------+ | firstName | lastName | city | state | +-----------+----------+---------------+----------+ | Allen | Wang | Null | Null | | Bob | Alice | New York City | New York | +-----------+----------+---------------+----------+ Explanation: There is no address in the address table for the personId = 1 so we return null in their city and state. addressId = 1 contains information about the address of personId = 2.
Apple,227,Basic Calculator II,Med,"Math, String, Stack","Given a string s which represents an expression; evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""3+2*2"" Output: 7 Example 2: Input: s = "" 3/2 "" Output: 1 Example 3: Input: s = "" 3+5 / 2 "" Output: 5 Constraints: 1 <= s.length <= 3 * 105 s consists of integers and operators ('+'; '-'; '*'; '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0; 231 - 1]. The answer is guaranteed to fit in a 32-bit integer."
Apple,230,Kth Smallest Element in a BST,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree; and an integer k; return the kth smallest value (1-indexed) of all the values of the nodes in the tree. Example 1: Input: root = [3;1;4;null;2]; k = 1 Output: 1 Example 2: Input: root = [5;3;6;2;4;null;null;1]; k = 3 Output: 3 Constraints: The number of nodes in the tree is n. 1 <= k <= n <= 104 0 <= Node.val <= 104 Follow up: If the BST is modified often (i.e.; we can do insert and delete operations) and you need to find the kth smallest frequently; how would you optimize?
Apple,268,Missing Number,Easy,"Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting",Given an array nums containing n distinct numbers in the range [0; n]; return the only number in the range that is missing from the array. Example 1: Input: nums = [3;0;1] Output: 2 Explanation: n = 3 since there are 3 numbers; so all numbers are in the range [0;3]. 2 is the missing number in the range since it does not appear in nums. Example 2: Input: nums = [0;1] Output: 2 Explanation: n = 2 since there are 2 numbers; so all numbers are in the range [0;2]. 2 is the missing number in the range since it does not appear in nums. Example 3: Input: nums = [9;6;4;2;3;5;7;0;1] Output: 8 Explanation: n = 9 since there are 9 numbers; so all numbers are in the range [0;9]. 8 is the missing number in the range since it does not appear in nums. Constraints: n == nums.length 1 <= n <= 104 0 <= nums[i] <= n All the numbers of nums are unique. Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?
Apple,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
Apple,334,Increasing Triplet Subsequence,Med,"Array, Greedy",Given an integer array nums; return true if there exists a triple of indices (i; j; k) such that i < j < k and nums[i] < nums[j] < nums[k]. If no such indices exists; return false. Example 1: Input: nums = [1;2;3;4;5] Output: true Explanation: Any triplet where i < j < k is valid. Example 2: Input: nums = [5;4;3;2;1] Output: false Explanation: No triplet exists. Example 3: Input: nums = [2;1;5;0;4;6] Output: true Explanation: The triplet (3; 4; 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6. Constraints: 1 <= nums.length <= 5 * 105 -231 <= nums[i] <= 231 - 1 Follow up: Could you implement a solution that runs in O(n) time complexity and O(1) space complexity?
Apple,343,Integer Break,Med,"Math, Dynamic Programming",Given an integer n; break it into the sum of k positive integers; where k >= 2; and maximize the product of those integers. Return the maximum product you can get. Example 1: Input: n = 2 Output: 1 Explanation: 2 = 1 + 1; 1 × 1 = 1. Example 2: Input: n = 10 Output: 36 Explanation: 10 = 3 + 3 + 4; 3 × 3 × 4 = 36. Constraints: 2 <= n <= 58
Apple,368,Largest Divisible Subset,Med,"Array, Math, Dynamic Programming, Sorting",Given a set of distinct positive integers nums; return the largest subset answer such that every pair (answer[i]; answer[j]) of elements in this subset satisfies: answer[i] % answer[j] == 0; or answer[j] % answer[i] == 0 If there are multiple solutions; return any of them. Example 1: Input: nums = [1;2;3] Output: [1;2] Explanation: [1;3] is also accepted. Example 2: Input: nums = [1;2;4;8] Output: [1;2;4;8] Constraints: 1 <= nums.length <= 1000 1 <= nums[i] <= 2 * 109 All the integers in nums are unique.
Apple,389,Find the Difference,Easy,"Hash Table, String, Bit Manipulation, Sorting","You are given two strings s and t. String t is generated by random shuffling string s and then add one more letter at a random position. Return the letter that was added to t. Example 1: Input: s = ""abcd""; t = ""abcde"" Output: ""e"" Explanation: 'e' is the letter that was added. Example 2: Input: s = """"; t = ""y"" Output: ""y"" Constraints: 0 <= s.length <= 1000 t.length == s.length + 1 s and t consist of lowercase English letters."
Apple,410,Split Array Largest Sum,Hard,"Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum",Given an integer array nums and an integer k; split nums into k non-empty subarrays such that the largest sum of any subarray is minimized. Return the minimized largest sum of the split. A subarray is a contiguous part of the array. Example 1: Input: nums = [7;2;5;10;8]; k = 2 Output: 18 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [7;2;5] and [10;8]; where the largest sum among the two subarrays is only 18. Example 2: Input: nums = [1;2;3;4;5]; k = 2 Output: 9 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [1;2;3] and [4;5]; where the largest sum among the two subarrays is only 9. Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 106 1 <= k <= min(50; nums.length)
Apple,486,Predict the Winner,Med,"Array, Math, Dynamic Programming, Recursion, Game Theory",You are given an integer array nums. Two players are playing a game with this array: player 1 and player 2. Player 1 and player 2 take turns; with player 1 starting first. Both players start the game with a score of 0. At each turn; the player takes one of the numbers from either end of the array (i.e.; nums[0] or nums[nums.length - 1]) which reduces the size of the array by 1. The player adds the chosen number to their score. The game ends when there are no more elements in the array. Return true if Player 1 can win the game. If the scores of both players are equal; then player 1 is still the winner; and you should also return true. You may assume that both players are playing optimally. Example 1: Input: nums = [1;5;2] Output: false Explanation: Initially; player 1 can choose between 1 and 2. If he chooses 2 (or 1); then player 2 can choose from 1 (or 2) and 5. If player 2 chooses 5; then player 1 will be left with 1 (or 2). So; final score of player 1 is 1 + 2 = 3; and player 2 is 5. Hence; player 1 will never be the winner and you need to return false. Example 2: Input: nums = [1;5;233;7] Output: true Explanation: Player 1 first chooses 1. Then player 2 has to choose between 5 and 7. No matter which number player 2 choose; player 1 can choose 233. Finally; player 1 has more score (234) than player 2 (12); so you need to return True representing player1 can win. Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 107
Apple,567,Permutation in String,Med,"Hash Table, Two Pointers, String, Sliding Window","Given two strings s1 and s2; return true if s2 contains a permutation of s1; or false otherwise. In other words; return true if one of s1's permutations is the substring of s2. Example 1: Input: s1 = ""ab""; s2 = ""eidbaooo"" Output: true Explanation: s2 contains one permutation of s1 (""ba""). Example 2: Input: s1 = ""ab""; s2 = ""eidboaoo"" Output: false Constraints: 1 <= s1.length; s2.length <= 104 s1 and s2 consist of lowercase English letters."
Apple,621,Task Scheduler,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting","You are given an array of CPU tasks; each labeled with a letter from A to Z; and a number n. Each CPU interval can be idle or allow the completion of one task. Tasks can be completed in any order; but there's a constraint: there has to be a gap of at least n intervals between two tasks with the same label. Return the minimum number of CPU intervals required to complete all tasks. Example 1: Input: tasks = [""A"";""A"";""A"";""B"";""B"";""B""]; n = 2 Output: 8 Explanation: A possible sequence is: A -> B -> idle -> A -> B -> idle -> A -> B. After completing task A; you must wait two intervals before doing A again. The same applies to task B. In the 3rd interval; neither A nor B can be done; so you idle. By the 4th interval; you can do A again as 2 intervals have passed. Example 2: Input: tasks = [""A"";""C"";""A"";""B"";""D"";""B""]; n = 1 Output: 6 Explanation: A possible sequence is: A -> B -> C -> D -> A -> B. With a cooling interval of 1; you can repeat a task after just one other task. Example 3: Input: tasks = [""A"";""A"";""A""; ""B"";""B"";""B""]; n = 3 Output: 10 Explanation: A possible sequence is: A -> B -> idle -> idle -> A -> B -> idle -> idle -> A -> B. There are only two types of tasks; A and B; which need to be separated by 3 intervals. This leads to idling twice between repetitions of these tasks. Constraints: 1 <= tasks.length <= 104 tasks[i] is an uppercase English letter. 0 <= n <= 100"
Apple,628,Maximum Product of Three Numbers,Easy,"Array, Math, Sorting",Given an integer array nums; find three numbers whose product is maximum and return the maximum product. Example 1: Input: nums = [1;2;3] Output: 6 Example 2: Input: nums = [1;2;3;4] Output: 24 Example 3: Input: nums = [-1;-2;-3] Output: -6 Constraints: 3 <= nums.length <= 104 -1000 <= nums[i] <= 1000
Apple,647,Palindromic Substrings,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the number of palindromic substrings in it. A string is a palindrome when it reads the same backward as forward. A substring is a contiguous sequence of characters within the string. Example 1: Input: s = ""abc"" Output: 3 Explanation: Three palindromic strings: ""a""; ""b""; ""c"". Example 2: Input: s = ""aaa"" Output: 6 Explanation: Six palindromic strings: ""a""; ""a""; ""a""; ""aa""; ""aa""; ""aaa"". Constraints: 1 <= s.length <= 1000 s consists of lowercase English letters."
Apple,867,Transpose Matrix,Easy,"Math, Dynamic Programming, Sliding Window, Probability and Statistics","Alice plays the following game; loosely based on the card game ""21"". Alice starts with 0 points and draws numbers while she has less than k points. During each draw; she gains an integer number of points randomly from the range [1; maxPts]; where maxPts is an integer. Each draw is independent and the outcomes have equal probabilities. Alice stops drawing numbers when she gets k or more points. Return the probability that Alice has n or fewer points. Answers within 10-5 of the actual answer are considered accepted. Example 1: Input: n = 10; k = 1; maxPts = 10 Output: 1.00000 Explanation: Alice gets a single card; then stops. Example 2: Input: n = 6; k = 1; maxPts = 10 Output: 0.60000 Explanation: Alice gets a single card; then stops. In 6 out of 10 possibilities; she is at or below 6 points. Example 3: Input: n = 21; k = 17; maxPts = 10 Output: 0.73278 Constraints: 0 <= k <= n <= 104 1 <= maxPts <= 104"
Apple,905,Sort Array By Parity,Easy,"Array, Hash Table, Dynamic Programming",A sequence x1; x2; ...; xn is Fibonacci-like if: n >= 3 xi + xi+1 == xi+2 for all i + 2 <= n Given a strictly increasing array arr of positive integers forming a sequence; return the length of the longest Fibonacci-like subsequence of arr. If one does not exist; return 0. A subsequence is derived from another sequence arr by deleting any number of elements (including none) from arr; without changing the order of the remaining elements. For example; [3; 5; 8] is a subsequence of [3; 4; 5; 6; 7; 8]. Example 1: Input: arr = [1;2;3;4;5;6;7;8] Output: 5 Explanation: The longest subsequence that is fibonacci-like: [1;2;3;5;8]. Example 2: Input: arr = [1;3;7;11;12;14;18] Output: 3 Explanation: The longest subsequence that is fibonacci-like: [1;11;12]; [3;11;14] or [7;11;18]. Constraints: 3 <= arr.length <= 1000 1 <= arr[i] < arr[i + 1] <= 109
Apple,909,Snakes and Ladders,Med,"Array, Math, Dynamic Programming, Game Theory",Alice and Bob play a game with piles of stones. There are an even number of piles arranged in a row; and each pile has a positive integer number of stones piles[i]. The objective of the game is to end with the most stones. The total number of stones across all the piles is odd; so there are no ties. Alice and Bob take turns; with Alice starting first. Each turn; a player takes the entire pile of stones either from the beginning or from the end of the row. This continues until there are no more piles left; at which point the person with the most stones wins. Assuming Alice and Bob play optimally; return true if Alice wins the game; or false if Bob wins. Example 1: Input: piles = [5;3;4;5] Output: true Explanation: Alice starts first; and can only take the first 5 or the last 5. Say she takes the first 5; so that the row becomes [3; 4; 5]. If Bob takes 3; then the board is [4; 5]; and Alice takes 5 to win with 10 points. If Bob takes the last 5; then the board is [3; 4]; and Alice takes 4 to win with 9 points. This demonstrated that taking the first 5 was a winning move for Alice; so we return true. Example 2: Input: piles = [3;7;2;3] Output: true Constraints: 2 <= piles.length <= 500 piles.length is even. 1 <= piles[i] <= 500 sum(piles[i]) is odd.
Apple,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
Apple,1047,Remove All Adjacent Duplicates In String,Easy,"Array, Greedy, Sorting",Given an integer array nums and an integer k; modify the array in the following way: choose an index i and replace nums[i] with -nums[i]. You should apply this process exactly k times. You may choose the same index i multiple times. Return the largest possible sum of the array after modifying it in this way. Example 1: Input: nums = [4;2;3]; k = 1 Output: 5 Explanation: Choose index 1 and nums becomes [4;-2;3]. Example 2: Input: nums = [3;-1;0;2]; k = 3 Output: 6 Explanation: Choose indices (1; 2; 2) and nums becomes [3;1;0;2]. Example 3: Input: nums = [2;-3;-1;5;-4]; k = 2 Output: 13 Explanation: Choose indices (1; 4) and nums becomes [2;3;-1;5;4]. Constraints: 1 <= nums.length <= 104 -100 <= nums[i] <= 100 1 <= k <= 104
Apple,1232,Check If It Is a Straight Line,Easy,"Array, Binary Search, Sorting",Given an integer array arr and a target value target; return the integer value such that when we change all the integers larger than value in the given array to be equal to value; the sum of the array gets as close as possible (in absolute difference) to target. In case of a tie; return the minimum such integer. Notice that the answer is not neccesarilly a number from arr. Example 1: Input: arr = [4;9;3]; target = 10 Output: 3 Explanation: When using 3 arr converts to [3; 3; 3] which sums 9 and that's the optimal answer. Example 2: Input: arr = [2;3;5]; target = 10 Output: 5 Example 3: Input: arr = [60864;25176;27249;21296;20204]; target = 56803 Output: 11361 Constraints: 1 <= arr.length <= 104 1 <= arr[i]; target <= 105
Apple,1352,Product of the Last K Numbers,Med,"Array, Binary Search, Dynamic Programming, Sorting",We have n jobs; where every job is scheduled to be done from startTime[i] to endTime[i]; obtaining a profit of profit[i]. You're given the startTime; endTime and profit arrays; return the maximum profit you can take such that there are no two jobs in the subset with overlapping time range. If you choose a job that ends at time X you will be able to start another job that starts at time X. Example 1: Input: startTime = [1;2;3;3]; endTime = [3;4;5;6]; profit = [50;10;40;70] Output: 120 Explanation: The subset chosen is the first and fourth job. Time range [1-3]+[3-6] ; we get profit of 120 = 50 + 70. Example 2: Input: startTime = [1;2;3;4;6]; endTime = [3;5;10;6;9]; profit = [20;20;100;70;60] Output: 150 Explanation: The subset chosen is the first; fourth and fifth job. Profit obtained 150 = 20 + 70 + 60. Example 3: Input: startTime = [1;1;1]; endTime = [2;3;4]; profit = [5;6;4] Output: 6 Constraints: 1 <= startTime.length == endTime.length == profit.length <= 5 * 104 1 <= startTime[i] < endTime[i] <= 109 1 <= profit[i] <= 104
Apple,1470,Shuffle the Array,Easy,"Hash Table, Binary Search, Design, Sorting, Ordered Set","A social media company is trying to monitor activity on their site by analyzing the number of tweets that occur in select periods of time. These periods can be partitioned into smaller time chunks based on a certain frequency (every minute; hour; or day). For example; the period [10; 10000] (in seconds) would be partitioned into the following time chunks with these frequencies: Every minute (60-second chunks): [10;69]; [70;129]; [130;189]; ...; [9970;10000] Every hour (3600-second chunks): [10;3609]; [3610;7209]; [7210;10000] Every day (86400-second chunks): [10;10000] Notice that the last chunk may be shorter than the specified frequency's chunk size and will always end with the end time of the period (10000 in the above example). Design and implement an API to help the company with their analysis. Implement the TweetCounts class: TweetCounts() Initializes the TweetCounts object. void recordTweet(String tweetName; int time) Stores the tweetName at the recorded time (in seconds). List<Integer> getTweetCountsPerFrequency(String freq; String tweetName; int startTime; int endTime) Returns a list of integers representing the number of tweets with tweetName in each time chunk for the given period of time [startTime; endTime] (in seconds) and frequency freq. freq is one of ""minute""; ""hour""; or ""day"" representing a frequency of every minute; hour; or day respectively. Example: Input [""TweetCounts"";""recordTweet"";""recordTweet"";""recordTweet"";""getTweetCountsPerFrequency"";""getTweetCountsPerFrequency"";""recordTweet"";""getTweetCountsPerFrequency""] [[];[""tweet3"";0];[""tweet3"";60];[""tweet3"";10];[""minute"";""tweet3"";0;59];[""minute"";""tweet3"";0;60];[""tweet3"";120];[""hour"";""tweet3"";0;210]] Output [null;null;null;null;[2];[2;1];null;[4]] Explanation TweetCounts tweetCounts = new TweetCounts(); tweetCounts.recordTweet(""tweet3""; 0); // New tweet ""tweet3"" at time 0 tweetCounts.recordTweet(""tweet3""; 60); // New tweet ""tweet3"" at time 60 tweetCounts.recordTweet(""tweet3""; 10); // New tweet ""tweet3"" at time 10 tweetCounts.getTweetCountsPerFrequency(""minute""; ""tweet3""; 0; 59); // return [2]; chunk [0;59] had 2 tweets tweetCounts.getTweetCountsPerFrequency(""minute""; ""tweet3""; 0; 60); // return [2;1]; chunk [0;59] had 2 tweets; chunk [60;60] had 1 tweet tweetCounts.recordTweet(""tweet3""; 120); // New tweet ""tweet3"" at time 120 tweetCounts.getTweetCountsPerFrequency(""hour""; ""tweet3""; 0; 210); // return [4]; chunk [0;210] had 4 tweets Constraints: 0 <= time; startTime; endTime <= 109 0 <= endTime - startTime <= 104 There will be at most 104 calls in total to recordTweet and getTweetCountsPerFrequency."
Apple,1512,Number of Good Pairs,Easy,"Hash Table, String, Design","An underground railway system is keeping track of customer travel times between different stations. They are using this data to calculate the average time it takes to travel from one station to another. Implement the UndergroundSystem class: void checkIn(int id; string stationName; int t) A customer with a card ID equal to id; checks in at the station stationName at time t. A customer can only be checked into one place at a time. void checkOut(int id; string stationName; int t) A customer with a card ID equal to id; checks out from the station stationName at time t. double getAverageTime(string startStation; string endStation) Returns the average time it takes to travel from startStation to endStation. The average time is computed from all the previous traveling times from startStation to endStation that happened directly; meaning a check in at startStation followed by a check out from endStation. The time it takes to travel from startStation to endStation may be different from the time it takes to travel from endStation to startStation. There will be at least one customer that has traveled from startStation to endStation before getAverageTime is called. You may assume all calls to the checkIn and checkOut methods are consistent. If a customer checks in at time t1 then checks out at time t2; then t1 < t2. All events happen in chronological order. Example 1: Input [""UndergroundSystem"";""checkIn"";""checkIn"";""checkIn"";""checkOut"";""checkOut"";""checkOut"";""getAverageTime"";""getAverageTime"";""checkIn"";""getAverageTime"";""checkOut"";""getAverageTime""] [[];[45;""Leyton"";3];[32;""Paradise"";8];[27;""Leyton"";10];[45;""Waterloo"";15];[27;""Waterloo"";20];[32;""Cambridge"";22];[""Paradise"";""Cambridge""];[""Leyton"";""Waterloo""];[10;""Leyton"";24];[""Leyton"";""Waterloo""];[10;""Waterloo"";38];[""Leyton"";""Waterloo""]] Output [null;null;null;null;null;null;null;14.00000;11.00000;null;11.00000;null;12.00000] Explanation UndergroundSystem undergroundSystem = new UndergroundSystem(); undergroundSystem.checkIn(45; ""Leyton""; 3); undergroundSystem.checkIn(32; ""Paradise""; 8); undergroundSystem.checkIn(27; ""Leyton""; 10); undergroundSystem.checkOut(45; ""Waterloo""; 15); // Customer 45 ""Leyton"" -> ""Waterloo"" in 15-3 = 12 undergroundSystem.checkOut(27; ""Waterloo""; 20); // Customer 27 ""Leyton"" -> ""Waterloo"" in 20-10 = 10 undergroundSystem.checkOut(32; ""Cambridge""; 22); // Customer 32 ""Paradise"" -> ""Cambridge"" in 22-8 = 14 undergroundSystem.getAverageTime(""Paradise""; ""Cambridge""); // return 14.00000. One trip ""Paradise"" -> ""Cambridge""; (14) / 1 = 14 undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 11.00000. Two trips ""Leyton"" -> ""Waterloo""; (10 + 12) / 2 = 11 undergroundSystem.checkIn(10; ""Leyton""; 24); undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 11.00000 undergroundSystem.checkOut(10; ""Waterloo""; 38); // Customer 10 ""Leyton"" -> ""Waterloo"" in 38-24 = 14 undergroundSystem.getAverageTime(""Leyton""; ""Waterloo""); // return 12.00000. Three trips ""Leyton"" -> ""Waterloo""; (10 + 12 + 14) / 3 = 12 Example 2: Input [""UndergroundSystem"";""checkIn"";""checkOut"";""getAverageTime"";""checkIn"";""checkOut"";""getAverageTime"";""checkIn"";""checkOut"";""getAverageTime""] [[];[10;""Leyton"";3];[10;""Paradise"";8];[""Leyton"";""Paradise""];[5;""Leyton"";10];[5;""Paradise"";16];[""Leyton"";""Paradise""];[2;""Leyton"";21];[2;""Paradise"";30];[""Leyton"";""Paradise""]] Output [null;null;null;5.00000;null;null;5.50000;null;null;6.66667] Explanation UndergroundSystem undergroundSystem = new UndergroundSystem(); undergroundSystem.checkIn(10; ""Leyton""; 3); undergroundSystem.checkOut(10; ""Paradise""; 8); // Customer 10 ""Leyton"" -> ""Paradise"" in 8-3 = 5 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 5.00000; (5) / 1 = 5 undergroundSystem.checkIn(5; ""Leyton""; 10); undergroundSystem.checkOut(5; ""Paradise""; 16); // Customer 5 ""Leyton"" -> ""Paradise"" in 16-10 = 6 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 5.50000; (5 + 6) / 2 = 5.5 undergroundSystem.checkIn(2; ""Leyton""; 21); undergroundSystem.checkOut(2; ""Paradise""; 30); // Customer 2 ""Leyton"" -> ""Paradise"" in 30-21 = 9 undergroundSystem.getAverageTime(""Leyton""; ""Paradise""); // return 6.66667; (5 + 6 + 9) / 3 = 6.66667 Constraints: 1 <= id; t <= 106 1 <= stationName.length; startStation.length; endStation.length <= 10 All strings consist of uppercase and lowercase English letters and digits. There will be at most 2 * 104 calls in total to checkIn; checkOut; and getAverageTime. Answers within 10-5 of the actual value will be accepted."
Apple,1913,Maximum Product Difference Between Two Pairs,Easy,"Array, Dynamic Programming, Bit Manipulation",You are given an array nums​​​ and an integer k​​​​​. The XOR of a segment [left; right] where left <= right is the XOR of all the elements with indices between left and right; inclusive: nums[left] XOR nums[left+1] XOR ... XOR nums[right]. Return the minimum number of elements to change in the array such that the XOR of all segments of size k​​​​​​ is equal to zero. Example 1: Input: nums = [1;2;0;3;0]; k = 1 Output: 3 Explanation: Modify the array from [1;2;0;3;0] to from [0;0;0;0;0]. Example 2: Input: nums = [3;4;5;2;1;7;3;4;7]; k = 3 Output: 3 Explanation: Modify the array from [3;4;5;2;1;7;3;4;7] to [3;4;7;3;4;7;3;4;7]. Example 3: Input: nums = [1;2;4;1;2;5;1;2;6]; k = 3 Output: 3 Explanation: Modify the array from [1;2;4;1;2;5;1;2;6] to [1;2;3;1;2;3;1;2;3]. Constraints: 1 <= k <= nums.length <= 2000 ​​​​​​0 <= nums[i] < 210
Apple,2620,Counter,Easy,"Hash Table, Design, Queue, Counting, Data Stream","For a stream of integers; implement a data structure that checks if the last k integers parsed in the stream are equal to value. Implement the DataStream class: DataStream(int value; int k) Initializes the object with an empty integer stream and the two integers value and k. boolean consec(int num) Adds num to the stream of integers. Returns true if the last k integers are equal to value; and false otherwise. If there are less than k integers; the condition does not hold true; so returns false. Example 1: Input [""DataStream""; ""consec""; ""consec""; ""consec""; ""consec""] [[4; 3]; [4]; [4]; [4]; [3]] Output [null; false; false; true; false] Explanation DataStream dataStream = new DataStream(4; 3); //value = 4; k = 3 dataStream.consec(4); // Only 1 integer is parsed; so returns False. dataStream.consec(4); // Only 2 integers are parsed. // Since 2 is less than k; returns False. dataStream.consec(4); // The 3 integers parsed are all equal to value; so returns True. dataStream.consec(3); // The last k integers parsed in the stream are [4;4;3]. // Since 3 is not equal to value; it returns False. Constraints: 1 <= value; num <= 109 1 <= k <= 105 At most 105 calls will be made to consec."
Apple,3074,Apple Redistribution into Boxes,Easy,,DataFrame students +-------------+--------+ | Column Name | Type | +-------------+--------+ | student_id | int | | name | object | | age | int | +-------------+--------+ Write a solution to select the name and age of the student with student_id = 101. The result format is in the following example. Example 1: Input: +------------+---------+-----+ | student_id | name | age | +------------+---------+-----+ | 101 | Ulysses | 13 | | 53 | William | 10 | | 128 | Henry | 6 | | 3 | Henry | 11 | +------------+---------+-----+ Output: +---------+-----+ | name | age | +---------+-----+ | Ulysses | 13 | +---------+-----+ Explanation: Student Ulysses has student_id = 101; we select the name and age.
Apple,16,3Sum Closest,Med,"Array, Two Pointers, Sorting",Given an integer array nums of length n and an integer target; find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution. Example 1: Input: nums = [-1;2;1;-4]; target = 1 Output: 2 Explanation: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2). Example 2: Input: nums = [0;0;0]; target = 1 Output: 0 Explanation: The sum that is closest to the target is 0. (0 + 0 + 0 = 0). Constraints: 3 <= nums.length <= 500 -1000 <= nums[i] <= 1000 -104 <= target <= 104
Apple,58,Length of Last Word,Easy,String,"Given a string s consisting of words and spaces; return the length of the last word in the string. A word is a maximal substring consisting of non-space characters only. Example 1: Input: s = ""Hello World"" Output: 5 Explanation: The last word is ""World"" with length 5. Example 2: Input: s = "" fly me to the moon "" Output: 4 Explanation: The last word is ""moon"" with length 4. Example 3: Input: s = ""luffy is still joyboy"" Output: 6 Explanation: The last word is ""joyboy"" with length 6. Constraints: 1 <= s.length <= 104 s consists of only English letters and spaces ' '. There will be at least one word in s."
Apple,68,Text Justification,Hard,"Array, String, Simulation","Given an array of strings words and a width maxWidth; format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is; pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words; the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text; it should be left-justified; and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = [""This""; ""is""; ""an""; ""example""; ""of""; ""text""; ""justification.""]; maxWidth = 16 Output: [ ""This is an""; ""example of text""; ""justification. "" ] Example 2: Input: words = [""What"";""must"";""be"";""acknowledgment"";""shall"";""be""]; maxWidth = 16 Output: [ ""What must be""; ""acknowledgment ""; ""shall be "" ] Explanation: Note that the last line is ""shall be "" instead of ""shall be""; because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = [""Science"";""is"";""what"";""we"";""understand"";""well"";""enough"";""to"";""explain"";""to"";""a"";""computer."";""Art"";""is"";""everything"";""else"";""we"";""do""]; maxWidth = 20 Output: [ ""Science is what we""; ""understand well""; ""enough to explain to""; ""a computer. Art is""; ""everything else we""; ""do "" ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth"
Apple,85,Maximal Rectangle,Hard,"Array, Dynamic Programming, Stack, Matrix, Monotonic Stack","Given a rows x cols binary matrix filled with 0's and 1's; find the largest rectangle containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 6 Explanation: The maximal rectangle is shown in the above picture. Example 2: Input: matrix = [[""0""]] Output: 0 Example 3: Input: matrix = [[""1""]] Output: 1 Constraints: rows == matrix.length cols == matrix[i].length 1 <= row; cols <= 200 matrix[i][j] is '0' or '1'."
Apple,105,Construct Binary Tree from Preorder and Inorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree; construct and return the binary tree. Example 1: Input: preorder = [3;9;20;15;7]; inorder = [9;3;15;20;7] Output: [3;9;20;null;null;15;7] Example 2: Input: preorder = [-1]; inorder = [-1] Output: [-1] Constraints: 1 <= preorder.length <= 3000 inorder.length == preorder.length -3000 <= preorder[i]; inorder[i] <= 3000 preorder and inorder consist of unique values. Each value of inorder also appears in preorder. preorder is guaranteed to be the preorder traversal of the tree. inorder is guaranteed to be the inorder traversal of the tree.
Apple,108,Convert Sorted Array to Binary Search Tree,Easy,"Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree",Given an integer array nums where the elements are sorted in ascending order; convert it to a height-balanced binary search tree. Example 1: Input: nums = [-10;-3;0;5;9] Output: [0;-3;9;-10;null;5] Explanation: [0;-10;5;null;-3;null;9] is also accepted: Example 2: Input: nums = [1;3] Output: [3;1] Explanation: [1;null;3] and [3;1] are both height-balanced BSTs. Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 nums is sorted in a strictly increasing order.
Apple,120,Triangle,Med,"Array, Dynamic Programming",Given a triangle array; return the minimum path sum from top to bottom. For each step; you may move to an adjacent number of the row below. More formally; if you are on index i on the current row; you may move to either index i or index i + 1 on the next row. Example 1: Input: triangle = [[2];[3;4];[6;5;7];[4;1;8;3]] Output: 11 Explanation: The triangle looks like: 2 3 4 6 5 7 4 1 8 3 The minimum path sum from top to bottom is 2 + 3 + 5 + 1 = 11 (underlined above). Example 2: Input: triangle = [[-10]] Output: -10 Constraints: 1 <= triangle.length <= 200 triangle[0].length == 1 triangle[i].length == triangle[i - 1].length + 1 -104 <= triangle[i][j] <= 104 Follow up: Could you do this using only O(n) extra space; where n is the total number of rows in the triangle?
Apple,208,Implement Trie (Prefix Tree),Med,"Hash Table, String, Design, Trie","A trie (pronounced as ""try"") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure; such as autocomplete and spellchecker. Implement the Trie class: Trie() Initializes the trie object. void insert(String word) Inserts the string word into the trie. boolean search(String word) Returns true if the string word is in the trie (i.e.; was inserted before); and false otherwise. boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix; and false otherwise. Example 1: Input [""Trie""; ""insert""; ""search""; ""search""; ""startsWith""; ""insert""; ""search""] [[]; [""apple""]; [""apple""]; [""app""]; [""app""]; [""app""]; [""app""]] Output [null; null; true; false; true; null; true] Explanation Trie trie = new Trie(); trie.insert(""apple""); trie.search(""apple""); // return True trie.search(""app""); // return False trie.startsWith(""app""); // return True trie.insert(""app""); trie.search(""app""); // return True Constraints: 1 <= word.length; prefix.length <= 2000 word and prefix consist only of lowercase English letters. At most 3 * 104 calls in total will be made to insert; search; and startsWith."
Apple,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Apple,226,Invert Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; invert the tree; and return its root. Example 1: Input: root = [4;2;7;1;3;6;9] Output: [4;7;2;9;6;3;1] Example 2: Input: root = [2;1;3] Output: [2;3;1] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Apple,229,Majority Element II,Med,"Array, Hash Table, Sorting, Counting",Given an integer array of size n; find all elements that appear more than ⌊ n/3 ⌋ times. Example 1: Input: nums = [3;2;3] Output: [3] Example 2: Input: nums = [1] Output: [1] Example 3: Input: nums = [1;2] Output: [1;2] Constraints: 1 <= nums.length <= 5 * 104 -109 <= nums[i] <= 109 Follow up: Could you solve the problem in linear time and in O(1) space?
Apple,232,Implement Queue using Stacks,Easy,"Stack, Design, Queue","Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push; peek; pop; and empty). Implement the MyQueue class: void push(int x) Pushes element x to the back of the queue. int pop() Removes the element from the front of the queue and returns it. int peek() Returns the element at the front of the queue. boolean empty() Returns true if the queue is empty; false otherwise. Notes: You must use only standard operations of a stack; which means only push to top; peek/pop from top; size; and is empty operations are valid. Depending on your language; the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack's standard operations. Example 1: Input [""MyQueue""; ""push""; ""push""; ""peek""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 1; 1; false] Explanation MyQueue myQueue = new MyQueue(); myQueue.push(1); // queue is: [1] myQueue.push(2); // queue is: [1; 2] (leftmost is front of the queue) myQueue.peek(); // return 1 myQueue.pop(); // return 1; queue is [2] myQueue.empty(); // return false Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; peek; and empty. All the calls to pop and peek are valid. Follow-up: Can you implement the queue such that each operation is amortized O(1) time complexity? In other words; performing n operations will take overall O(n) time even if one of those operations may take longer."
Apple,263,Ugly Number,Easy,Math,An ugly number is a positive integer which does not have a prime factor other than 2; 3; and 5. Given an integer n; return true if n is an ugly number. Example 1: Input: n = 6 Output: true Explanation: 6 = 2 × 3 Example 2: Input: n = 1 Output: true Explanation: 1 has no prime factors. Example 3: Input: n = 14 Output: false Explanation: 14 is not ugly since it includes the prime factor 7. Constraints: -231 <= n <= 231 - 1
Apple,274,H-Index,Med,"Array, Sorting, Counting Sort",Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper; return the researcher's h-index. According to the definition of h-index on Wikipedia: The h-index is defined as the maximum value of h such that the given researcher has published at least h papers that have each been cited at least h times. Example 1: Input: citations = [3;0;6;1;5] Output: 3 Explanation: [3;0;6;1;5] means the researcher has 5 papers in total and each of them had received 3; 0; 6; 1; 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each; their h-index is 3. Example 2: Input: citations = [1;3;1] Output: 1 Constraints: n == citations.length 1 <= n <= 5000 0 <= citations[i] <= 1000
Apple,315,Count of Smaller Numbers After Self,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums; return an integer array counts where counts[i] is the number of smaller elements to the right of nums[i]. Example 1: Input: nums = [5;2;6;1] Output: [2;1;1;0] Explanation: To the right of 5 there are 2 smaller elements (2 and 1). To the right of 2 there is only 1 smaller element (1). To the right of 6 there is 1 smaller element (1). To the right of 1 there is 0 smaller element. Example 2: Input: nums = [-1] Output: [0] Example 3: Input: nums = [-1;-1] Output: [0;0] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104
Apple,392,Is Subsequence,Easy,"Two Pointers, String, Dynamic Programming","Given two strings s and t; return true if s is a subsequence of t; or false otherwise. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not). Example 1: Input: s = ""abc""; t = ""ahbgdc"" Output: true Example 2: Input: s = ""axc""; t = ""ahbgdc"" Output: false Constraints: 0 <= s.length <= 100 0 <= t.length <= 104 s and t consist only of lowercase English letters. Follow up: Suppose there are lots of incoming s; say s1; s2; ...; sk where k >= 109; and you want to check one by one to see if t has its subsequence. In this scenario; how would you change your code?"
Apple,400,Nth Digit,Med,"Math, Binary Search",Given an integer n; return the nth digit of the infinite integer sequence [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; ...]. Example 1: Input: n = 3 Output: 3 Example 2: Input: n = 11 Output: 0 Explanation: The 11th digit of the sequence 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; ... is a 0; which is part of the number 10. Constraints: 1 <= n <= 231 - 1
Apple,437,Path Sum III,Med,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return the number of paths where the sum of the values along the path equals targetSum. The path does not need to start or end at the root or a leaf; but it must go downwards (i.e.; traveling only from parent nodes to child nodes). Example 1: Input: root = [10;5;-3;3;2;null;11;3;-2;null;1]; targetSum = 8 Output: 3 Explanation: The paths that sum to 8 are shown. Example 2: Input: root = [5;4;8;11;null;13;4;7;2;null;null;5;1]; targetSum = 22 Output: 3 Constraints: The number of nodes in the tree is in the range [0; 1000]. -109 <= Node.val <= 109 -1000 <= targetSum <= 1000
Apple,446,Arithmetic Slices II - Subsequence,Hard,"Array, Dynamic Programming",Given an integer array nums; return the number of all the arithmetic subsequences of nums. A sequence of numbers is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same. For example; [1; 3; 5; 7; 9]; [7; 7; 7; 7]; and [3; -1; -5; -9] are arithmetic sequences. For example; [1; 1; 2; 5; 7] is not an arithmetic sequence. A subsequence of an array is a sequence that can be formed by removing some elements (possibly none) of the array. For example; [2;5;10] is a subsequence of [1;2;1;2;4;1;5;10]. The test cases are generated so that the answer fits in 32-bit integer. Example 1: Input: nums = [2;4;6;8;10] Output: 7 Explanation: All arithmetic subsequence slices are: [2;4;6] [4;6;8] [6;8;10] [2;4;6;8] [4;6;8;10] [2;4;6;8;10] [2;6;10] Example 2: Input: nums = [7;7;7;7;7] Output: 16 Explanation: Any subsequence of this array is arithmetic. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1
Apple,452,Minimum Number of Arrows to Burst Balloons,Med,"Array, Greedy, Sorting",There are some spherical balloons taped onto a flat wall that represents the XY-plane. The balloons are represented as a 2D integer array points where points[i] = [xstart; xend] denotes a balloon whose horizontal diameter stretches between xstart and xend. You do not know the exact y-coordinates of the balloons. Arrows can be shot up directly vertically (in the positive y-direction) from different points along the x-axis. A balloon with xstart and xend is burst by an arrow shot at x if xstart <= x <= xend. There is no limit to the number of arrows that can be shot. A shot arrow keeps traveling up infinitely; bursting any balloons in its path. Given the array points; return the minimum number of arrows that must be shot to burst all balloons. Example 1: Input: points = [[10;16];[2;8];[1;6];[7;12]] Output: 2 Explanation: The balloons can be burst by 2 arrows: - Shoot an arrow at x = 6; bursting the balloons [2;8] and [1;6]. - Shoot an arrow at x = 11; bursting the balloons [10;16] and [7;12]. Example 2: Input: points = [[1;2];[3;4];[5;6];[7;8]] Output: 4 Explanation: One arrow needs to be shot for each balloon for a total of 4 arrows. Example 3: Input: points = [[1;2];[2;3];[3;4];[4;5]] Output: 2 Explanation: The balloons can be burst by 2 arrows: - Shoot an arrow at x = 2; bursting the balloons [1;2] and [2;3]. - Shoot an arrow at x = 4; bursting the balloons [3;4] and [4;5]. Constraints: 1 <= points.length <= 105 points[i].length == 2 -231 <= xstart < xend <= 231 - 1
Apple,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
Apple,493,Reverse Pairs,Hard,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",Given an integer array nums; return the number of reverse pairs in the array. A reverse pair is a pair (i; j) where: 0 <= i < j < nums.length and nums[i] > 2 * nums[j]. Example 1: Input: nums = [1;3;2;3;1] Output: 2 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 3; nums[4] = 1; 3 > 2 * 1 Example 2: Input: nums = [2;4;3;5;1] Output: 3 Explanation: The reverse pairs are: (1; 4) --> nums[1] = 4; nums[4] = 1; 4 > 2 * 1 (2; 4) --> nums[2] = 3; nums[4] = 1; 3 > 2 * 1 (3; 4) --> nums[3] = 5; nums[4] = 1; 5 > 2 * 1 Constraints: 1 <= nums.length <= 5 * 104 -231 <= nums[i] <= 231 - 1
Apple,570,Managers with at Least 5 Direct Reports,Med,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | department | varchar | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the name of an employee; their department; and the id of their manager. If managerId is null; then the employee does not have a manager. No employee will be the manager of themself. Write a solution to find managers with at least five direct reports. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +-----+-------+------------+-----------+ | id | name | department | managerId | +-----+-------+------------+-----------+ | 101 | John | A | null | | 102 | Dan | A | 101 | | 103 | James | A | 101 | | 104 | Amy | A | 101 | | 105 | Anne | A | 101 | | 106 | Ron | B | 101 | +-----+-------+------------+-----------+ Output: +------+ | name | +------+ | John | +------+
Apple,646,Maximum Length of Pair Chain,Med,"Array, Dynamic Programming, Greedy, Sorting",You are given an array of n pairs pairs where pairs[i] = [lefti; righti] and lefti < righti. A pair p2 = [c; d] follows a pair p1 = [a; b] if b < c. A chain of pairs can be formed in this fashion. Return the length longest chain which can be formed. You do not need to use up all the given intervals. You can select pairs in any order. Example 1: Input: pairs = [[1;2];[2;3];[3;4]] Output: 2 Explanation: The longest chain is [1;2] -> [3;4]. Example 2: Input: pairs = [[1;2];[7;8];[4;5]] Output: 3 Explanation: The longest chain is [1;2] -> [4;5] -> [7;8]. Constraints: n == pairs.length 1 <= n <= 1000 -1000 <= lefti < righti <= 1000
Apple,768,Max Chunks To Make Sorted II,Hard,"Hash Table, Two Pointers, String, Greedy","You are given a string s. We want to partition the string into as many parts as possible so that each letter appears in at most one part. Note that the partition is done so that after concatenating all the parts in order; the resultant string should be s. Return a list of integers representing the size of these parts. Example 1: Input: s = ""ababcbacadefegdehijhklij"" Output: [9;7;8] Explanation: The partition is ""ababcbaca""; ""defegde""; ""hijhklij"". This is a partition so that each letter appears in at most one part. A partition like ""ababcbacadefegde""; ""hijhklij"" is incorrect; because it splits s into less parts. Example 2: Input: s = ""eccbbbbdec"" Output: [10] Constraints: 1 <= s.length <= 500 s consists of lowercase English letters."
Apple,771,Jewels and Stones,Easy,"Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",
Apple,703,Kth Largest Element in a Stream,Easy,,
Apple,787,Cheapest Flights Within K Stops,Med,"Array, Breadth-First Search, Matrix",On an 2 x 3 board; there are five tiles labeled from 1 to 5; and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of the board is solved if and only if the board is [[1;2;3];[4;5;0]]. Given the puzzle board board; return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved; return -1. Example 1: Input: board = [[1;2;3];[4;0;5]] Output: 1 Explanation: Swap the 0 and the 5 in one move. Example 2: Input: board = [[1;2;3];[5;4;0]] Output: -1 Explanation: No number of moves will make the board solved. Example 3: Input: board = [[4;1;2];[5;0;3]] Output: 5 Explanation: 5 is the smallest number of moves that solves the board. An example path: After move 0: [[4;1;2];[5;0;3]] After move 1: [[4;1;2];[0;5;3]] After move 2: [[0;1;2];[4;5;3]] After move 3: [[1;0;2];[4;5;3]] After move 4: [[1;2;0];[4;5;3]] After move 5: [[1;2;3];[4;5;0]] Constraints: board.length == 2 board[i].length == 3 0 <= board[i][j] <= 5 Each value board[i][j] is unique.
Apple,790,Domino and Tromino Tiling,Med,"Array, Math",You are given an integer array nums of length n which represents a permutation of all the integers in the range [0; n - 1]. The number of global inversions is the number of the different pairs (i; j) where: 0 <= i < j < n nums[i] > nums[j] The number of local inversions is the number of indices i where: 0 <= i < n - 1 nums[i] > nums[i + 1] Return true if the number of global inversions is equal to the number of local inversions. Example 1: Input: nums = [1;0;2] Output: true Explanation: There is 1 global inversion and 1 local inversion. Example 2: Input: nums = [1;2;0] Output: false Explanation: There are 2 global inversions and 1 local inversion. Constraints: n == nums.length 1 <= n <= 105 0 <= nums[i] < n All the integers of nums are unique. nums is a permutation of all the numbers in the range [0; n - 1].
Apple,863,All Nodes Distance K in Binary Tree,Med,"Dynamic Programming, Tree, Depth-First Search, Graph",There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Return an array answer of length n where answer[i] is the sum of the distances between the ith node in the tree and all other nodes. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;3];[2;4];[2;5]] Output: [8;12;6;10;10;10] Explanation: The tree is shown above. We can see that dist(0;1) + dist(0;2) + dist(0;3) + dist(0;4) + dist(0;5) equals 1 + 1 + 2 + 2 + 2 = 8. Hence; answer[0] = 8; and so on. Example 2: Input: n = 1; edges = [] Output: [0] Example 3: Input: n = 2; edges = [[1;0]] Output: [1;1] Constraints: 1 <= n <= 3 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n ai != bi The given input represents a valid tree.
Apple,938,Range Sum of BST,Easy,"Array, Math, String, Binary Search, Dynamic Programming","Given an array of digits which is sorted in non-decreasing order. You can write numbers using each digits[i] as many times as we want. For example; if digits = ['1';'3';'5']; we may write numbers such as '13'; '551'; and '1351315'. Return the number of positive integers that can be generated that are less than or equal to a given integer n. Example 1: Input: digits = [""1"";""3"";""5"";""7""]; n = 100 Output: 20 Explanation: The 20 numbers that can be written are: 1; 3; 5; 7; 11; 13; 15; 17; 31; 33; 35; 37; 51; 53; 55; 57; 71; 73; 75; 77. Example 2: Input: digits = [""1"";""4"";""9""]; n = 1000000000 Output: 29523 Explanation: We can write 3 one digit numbers; 9 two digit numbers; 27 three digit numbers; 81 four digit numbers; 243 five digit numbers; 729 six digit numbers; 2187 seven digit numbers; 6561 eight digit numbers; and 19683 nine digit numbers. In total; this is 29523 integers that can be written using the digits array. Example 3: Input: digits = [""7""]; n = 8 Output: 1 Constraints: 1 <= digits.length <= 9 digits[i].length == 1 digits[i] is a digit from '1' to '9'. All the values in digits are unique. digits is sorted in non-decreasing order. 1 <= n <= 109"
Apple,948,Bag of Tokens,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Merge Sort, Bucket Sort, Radix Sort, Counting Sort",Given an array of integers nums; sort the array in ascending order and return it. You must solve the problem without using any built-in functions in O(nlog(n)) time complexity and with the smallest space complexity possible. Example 1: Input: nums = [5;2;3;1] Output: [1;2;3;5] Explanation: After sorting the array; the positions of some numbers are not changed (for example; 2 and 3); while the positions of other numbers are changed (for example; 1 and 5). Example 2: Input: nums = [5;1;1;2;0;0] Output: [0;0;1;1;2;5] Explanation: Note that the values of nums are not necessairly unique. Constraints: 1 <= nums.length <= 5 * 104 -5 * 104 <= nums[i] <= 5 * 104
Apple,974,Subarray Sums Divisible by K,Med,"Array, String, Sorting","You are given an array of logs. Each log is a space-delimited string of words; where the first word is the identifier. There are two types of logs: Letter-logs: All words (except the identifier) consist of lowercase English letters. Digit-logs: All words (except the identifier) consist of digits. Reorder these logs so that: The letter-logs come before all digit-logs. The letter-logs are sorted lexicographically by their contents. If their contents are the same; then sort them lexicographically by their identifiers. The digit-logs maintain their relative ordering. Return the final order of the logs. Example 1: Input: logs = [""dig1 8 1 5 1"";""let1 art can"";""dig2 3 6"";""let2 own kit dig"";""let3 art zero""] Output: [""let1 art can"";""let3 art zero"";""let2 own kit dig"";""dig1 8 1 5 1"";""dig2 3 6""] Explanation: The letter-log contents are all different; so their ordering is ""art can""; ""art zero""; ""own kit dig"". The digit-logs have a relative order of ""dig1 8 1 5 1""; ""dig2 3 6"". Example 2: Input: logs = [""a1 9 2 3 1"";""g1 act car"";""zo4 4 7"";""ab1 off key dog"";""a8 act zoo""] Output: [""g1 act car"";""a8 act zoo"";""ab1 off key dog"";""a1 9 2 3 1"";""zo4 4 7""] Constraints: 1 <= logs.length <= 100 3 <= logs[i].length <= 100 All the tokens of logs[i] are separated by a single space. logs[i] is guaranteed to have an identifier and at least one word after the identifier."
Apple,981,Time Based Key-Value Store,Med,"Array, String","You are given an array of n strings strs; all of the same length. The strings can be arranged such that there is one on each line; making a grid. For example; strs = [""abc""; ""bce""; ""cae""] can be arranged as follows: abc bce cae You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed); columns 0 ('a'; 'b'; 'c') and 2 ('c'; 'e'; 'e') are sorted; while column 1 ('b'; 'c'; 'a') is not; so you would delete column 1. Return the number of columns that you will delete. Example 1: Input: strs = [""cba"";""daf"";""ghi""] Output: 1 Explanation: The grid looks as follows: cba daf ghi Columns 0 and 2 are sorted; but column 1 is not; so you only need to delete 1 column. Example 2: Input: strs = [""a"";""b""] Output: 0 Explanation: The grid looks as follows: a b Column 0 is the only column and is sorted; so you will not delete any columns. Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: The grid looks as follows: zyx wvu tsr All 3 columns are not sorted; so you will delete all 3. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 1000 strs[i] consists of lowercase English letters."
Apple,987,Vertical Order Traversal of a Binary Tree,Hard,"Array, Queue, Sorting, Simulation",You are given an integer array deck. There is a deck of cards where every card has a unique integer. The integer on the ith card is deck[i]. You can order the deck in any order you want. Initially; all the cards start face down (unrevealed) in one deck. You will do the following steps repeatedly until all cards are revealed: Take the top card of the deck; reveal it; and take it out of the deck. If there are still cards in the deck then put the next top card of the deck at the bottom of the deck. If there are still unrevealed cards; go back to step 1. Otherwise; stop. Return an ordering of the deck that would reveal the cards in increasing order. Note that the first entry in the answer is considered to be the top of the deck. Example 1: Input: deck = [17;13;11;2;3;5;7] Output: [2;13;3;11;5;17;7] Explanation: We get the deck in the order [17;13;11;2;3;5;7] (this order does not matter); and reorder it. After reordering; the deck starts as [2;13;3;11;5;17;7]; where 2 is the top of the deck. We reveal 2; and move 13 to the bottom. The deck is now [3;11;5;17;7;13]. We reveal 3; and move 11 to the bottom. The deck is now [5;17;7;13;11]. We reveal 5; and move 17 to the bottom. The deck is now [7;13;11;17]. We reveal 7; and move 13 to the bottom. The deck is now [11;17;13]. We reveal 11; and move 17 to the bottom. The deck is now [13;17]. We reveal 13; and move 17 to the bottom. The deck is now [17]. We reveal 17. Since all the cards revealed are in increasing order; the answer is correct. Example 2: Input: deck = [1;1000] Output: [1;1000] Constraints: 1 <= deck.length <= 1000 1 <= deck[i] <= 106 All the values of deck are unique.
Apple,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Apple,1009,Complement of Base 10 Integer,Easy,"Array, Two Pointers, Greedy, Sorting",Given an array of integers arr; sort the array by performing a series of pancake flips. In one pancake flip we do the following steps: Choose an integer k where 1 <= k <= arr.length. Reverse the sub-array arr[0...k-1] (0-indexed). For example; if arr = [3;2;1;4] and we performed a pancake flip choosing k = 3; we reverse the sub-array [3;2;1]; so arr = [1;2;3;4] after the pancake flip at k = 3. Return an array of the k-values corresponding to a sequence of pancake flips that sort arr. Any valid answer that sorts the array within 10 * arr.length flips will be judged as correct. Example 1: Input: arr = [3;2;4;1] Output: [4;2;4;3] Explanation: We perform 4 pancake flips; with k values 4; 2; 4; and 3. Starting state: arr = [3; 2; 4; 1] After 1st flip (k = 4): arr = [1; 4; 2; 3] After 2nd flip (k = 2): arr = [4; 1; 2; 3] After 3rd flip (k = 4): arr = [3; 2; 1; 4] After 4th flip (k = 3): arr = [1; 2; 3; 4]; which is sorted. Example 2: Input: arr = [1;2;3] Output: [] Explanation: The input is already sorted; so there is no need to flip anything. Note that other answers; such as [3; 3]; would also be accepted. Constraints: 1 <= arr.length <= 100 1 <= arr[i] <= arr.length All integers in arr are unique (i.e. arr is a permutation of the integers from 1 to arr.length).
Apple,511,Game Play Analysis I,Easy,"Graph, Topological Sort",
Apple,1287,Element Appearing More Than 25% In Sorted Array,Easy,Array,A bus has n stops numbered from 0 to n - 1 that form a circle. We know the distance between all pairs of neighboring stops where distance[i] is the distance between the stops number i and (i + 1) % n. The bus goes along both directions i.e. clockwise and counterclockwise. Return the shortest distance between the given start and destination stops. Example 1: Input: distance = [1;2;3;4]; start = 0; destination = 1 Output: 1 Explanation: Distance between 0 and 1 is 1 or 9; minimum is 1. Example 2: Input: distance = [1;2;3;4]; start = 0; destination = 2 Output: 3 Explanation: Distance between 0 and 2 is 3 or 7; minimum is 3. Example 3: Input: distance = [1;2;3;4]; start = 0; destination = 3 Output: 4 Explanation: Distance between 0 and 3 is 6 or 4; minimum is 4. Constraints: 1 <= n <= 10^4 distance.length == n 0 <= start; destination < n 0 <= distance[i] <= 10^4
Apple,1146,Snapshot Array,Med,"Math, String","For two strings s and t; we say ""t divides s"" if and only if s = t + t + t + ... + t + t (i.e.; t is concatenated with itself one or more times). Given two strings str1 and str2; return the largest string x such that x divides both str1 and str2. Example 1: Input: str1 = ""ABCABC""; str2 = ""ABC"" Output: ""ABC"" Example 2: Input: str1 = ""ABABAB""; str2 = ""ABAB"" Output: ""AB"" Example 3: Input: str1 = ""LEET""; str2 = ""CODE"" Output: """" Constraints: 1 <= str1.length; str2.length <= 1000 str1 and str2 consist of English uppercase letters."
Apple,1164,Product Price at a Given Date,Med,"Array, Math",
Apple,1235,Maximum Profit in Job Scheduling,Hard,,
Apple,1431,Kids With the Greatest Number of Candies,Easy,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",You are given a positive integer n representing the number of nodes of a Directed Acyclic Graph (DAG). The nodes are numbered from 0 to n - 1 (inclusive). You are also given a 2D integer array edges; where edges[i] = [fromi; toi] denotes that there is a unidirectional edge from fromi to toi in the graph. Return a list answer; where answer[i] is the list of ancestors of the ith node; sorted in ascending order. A node u is an ancestor of another node v if u can reach v via a set of edges. Example 1: Input: n = 8; edgeList = [[0;3];[0;4];[1;3];[2;4];[2;7];[3;5];[3;6];[3;7];[4;6]] Output: [[];[];[];[0;1];[0;2];[0;1;3];[0;1;2;3;4];[0;1;2;3]] Explanation: The above diagram represents the input graph. - Nodes 0; 1; and 2 do not have any ancestors. - Node 3 has two ancestors 0 and 1. - Node 4 has two ancestors 0 and 2. - Node 5 has three ancestors 0; 1; and 3. - Node 6 has five ancestors 0; 1; 2; 3; and 4. - Node 7 has four ancestors 0; 1; 2; and 3. Example 2: Input: n = 5; edgeList = [[0;1];[0;2];[0;3];[0;4];[1;2];[1;3];[1;4];[2;3];[2;4];[3;4]] Output: [[];[0];[0;1];[0;1;2];[0;1;2;3]] Explanation: The above diagram represents the input graph. - Node 0 does not have any ancestor. - Node 1 has one ancestor 0. - Node 2 has two ancestors 0 and 1. - Node 3 has three ancestors 0; 1; and 2. - Node 4 has four ancestors 0; 1; 2; and 3. Constraints: 1 <= n <= 1000 0 <= edges.length <= min(2000; n * (n - 1) / 2) edges[i].length == 2 0 <= fromi; toi <= n - 1 fromi != toi There are no duplicate edges. The graph is directed and acyclic.
Apple,1572,Matrix Diagonal Sum,Easy,"Array, Design, Matrix","Implement the class SubrectangleQueries which receives a rows x cols rectangle as a matrix of integers in the constructor and supports two methods: 1. updateSubrectangle(int row1; int col1; int row2; int col2; int newValue) Updates all values with newValue in the subrectangle whose upper left coordinate is (row1;col1) and bottom right coordinate is (row2;col2). 2. getValue(int row; int col) Returns the current value of the coordinate (row;col) from the rectangle. Example 1: Input [""SubrectangleQueries"";""getValue"";""updateSubrectangle"";""getValue"";""getValue"";""updateSubrectangle"";""getValue"";""getValue""] [[[[1;2;1];[4;3;4];[3;2;1];[1;1;1]]];[0;2];[0;0;3;2;5];[0;2];[3;1];[3;0;3;2;10];[3;1];[0;2]] Output [null;1;null;5;5;null;10;5] Explanation SubrectangleQueries subrectangleQueries = new SubrectangleQueries([[1;2;1];[4;3;4];[3;2;1];[1;1;1]]); // The initial rectangle (4x3) looks like: // 1 2 1 // 4 3 4 // 3 2 1 // 1 1 1 subrectangleQueries.getValue(0; 2); // return 1 subrectangleQueries.updateSubrectangle(0; 0; 3; 2; 5); // After this update the rectangle looks like: // 5 5 5 // 5 5 5 // 5 5 5 // 5 5 5 subrectangleQueries.getValue(0; 2); // return 5 subrectangleQueries.getValue(3; 1); // return 5 subrectangleQueries.updateSubrectangle(3; 0; 3; 2; 10); // After this update the rectangle looks like: // 5 5 5 // 5 5 5 // 5 5 5 // 10 10 10 subrectangleQueries.getValue(3; 1); // return 10 subrectangleQueries.getValue(0; 2); // return 5 Example 2: Input [""SubrectangleQueries"";""getValue"";""updateSubrectangle"";""getValue"";""getValue"";""updateSubrectangle"";""getValue""] [[[[1;1;1];[2;2;2];[3;3;3]]];[0;0];[0;0;2;2;100];[0;0];[2;2];[1;1;2;2;20];[2;2]] Output [null;1;null;100;100;null;20] Explanation SubrectangleQueries subrectangleQueries = new SubrectangleQueries([[1;1;1];[2;2;2];[3;3;3]]); subrectangleQueries.getValue(0; 0); // return 1 subrectangleQueries.updateSubrectangle(0; 0; 2; 2; 100); subrectangleQueries.getValue(0; 0); // return 100 subrectangleQueries.getValue(2; 2); // return 100 subrectangleQueries.updateSubrectangle(1; 1; 2; 2; 20); subrectangleQueries.getValue(2; 2); // return 20 Constraints: There will be at most 500 operations considering both methods: updateSubrectangle and getValue. 1 <= rows; cols <= 100 rows == rectangle.length cols == rectangle[i].length 0 <= row1 <= row2 < rows 0 <= col1 <= col2 < cols 1 <= newValue; rectangle[i][j] <= 10^9 0 <= row < rows 0 <= col < cols"
Apple,1675,Minimize Deviation in Array,Hard,"Array, Binary Search, Sorting",In the universe Earth C-137; Rick discovered a special form of magnetic force between two balls if they are put in his new invented basket. Rick has n empty baskets; the ith basket is at position[i]; Morty has m balls and needs to distribute the balls into the baskets such that the minimum magnetic force between any two balls is maximum. Rick stated that magnetic force between two different balls at positions x and y is |x - y|. Given the integer array position and the integer m. Return the required force. Example 1: Input: position = [1;2;3;4;7]; m = 3 Output: 3 Explanation: Distributing the 3 balls into baskets 1; 4 and 7 will make the magnetic force between ball pairs [3; 3; 6]. The minimum magnetic force is 3. We cannot achieve a larger minimum magnetic force than 3. Example 2: Input: position = [5;4;3;2;1;1000000000]; m = 2 Output: 999999999 Explanation: We can use baskets 1 and 1000000000. Constraints: n == position.length 2 <= n <= 105 1 <= position[i] <= 109 All integers in position are distinct. 2 <= m <= position.length
Apple,1922,Count Good Numbers,Med,,
Apple,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
Apple,82,Remove Duplicates from Sorted List II,Med,"Linked List, Two Pointers",Given the head of a sorted linked list; delete all nodes that have duplicate numbers; leaving only distinct numbers from the original list. Return the linked list sorted as well. Example 1: Input: head = [1;2;3;3;4;4;5] Output: [1;2;5] Example 2: Input: head = [1;1;1;2;3] Output: [2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Apple,99,Recover Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",You are given the root of a binary search tree (BST); where the values of exactly two nodes of the tree were swapped by mistake. Recover the tree without changing its structure. Example 1: Input: root = [1;3;null;null;2] Output: [3;1;null;null;2] Explanation: 3 cannot be a left child of 1 because 3 > 1. Swapping 1 and 3 makes the BST valid. Example 2: Input: root = [3;1;4;null;null;2] Output: [2;1;4;null;null;3] Explanation: 2 cannot be in the right subtree of 3 because 2 < 3. Swapping 2 and 3 makes the BST valid. Constraints: The number of nodes in the tree is in the range [2; 1000]. -231 <= Node.val <= 231 - 1 Follow up: A solution using O(n) space is pretty straight-forward. Could you devise a constant O(1) space solution?
Apple,160,Intersection of Two Linked Lists,Easy,"Hash Table, Linked List, Two Pointers",Given the heads of two singly linked-lists headA and headB; return the node at which the two lists intersect. If the two linked lists have no intersection at all; return null. For example; the following two linked lists begin to intersect at node c1: The test cases are generated such that there are no cycles anywhere in the entire linked structure. Note that the linked lists must retain their original structure after the function returns. Custom Judge: The inputs to the judge are given as follows (your program is not given these inputs): intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node. listA - The first linked list. listB - The second linked list. skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node. skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node. The judge will then create the linked structure based on these inputs and pass the two heads; headA and headB to your program. If you correctly return the intersected node; then your solution will be accepted. Example 1: Input: intersectVal = 8; listA = [4;1;8;4;5]; listB = [5;6;1;8;4;5]; skipA = 2; skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [4;1;8;4;5]. From the head of B; it reads as [5;6;1;8;4;5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words; they point to two different locations in memory; while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory. Example 2: Input: intersectVal = 2; listA = [1;9;1;2;4]; listB = [3;2;4]; skipA = 3; skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [1;9;1;2;4]. From the head of B; it reads as [3;2;4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B. Example 3: Input: intersectVal = 0; listA = [2;6;4]; listB = [1;5]; skipA = 3; skipB = 2 Output: No intersection Explanation: From the head of A; it reads as [2;6;4]. From the head of B; it reads as [1;5]. Since the two lists do not intersect; intersectVal must be 0; while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect; so return null. Constraints: The number of nodes of listA is in the m. The number of nodes of listB is in the n. 1 <= m; n <= 3 * 104 1 <= Node.val <= 105 0 <= skipA <= m 0 <= skipB <= n intersectVal is 0 if listA and listB do not intersect. intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect. Follow up: Could you write a solution that runs in O(m + n) time and use only O(1) memory?
Apple,182,Duplicate Emails,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | email | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table contains an email. The emails will not contain uppercase letters. Write a solution to report all the duplicate emails. Note that it's guaranteed that the email field is not NULL. Return the result table in any order. The result format is in the following example. Example 1: Input: Person table: +----+---------+ | id | email | +----+---------+ | 1 | a@b.com | | 2 | c@d.com | | 3 | a@b.com | +----+---------+ Output: +---------+ | Email | +---------+ | a@b.com | +---------+ Explanation: a@b.com is repeated two times.
Apple,185,Department Top Three Salaries,Hard,Database,Table: Employee +--------------+---------+ | Column Name | Type | +--------------+---------+ | id | int | | name | varchar | | salary | int | | departmentId | int | +--------------+---------+ id is the primary key (column with unique values) for this table. departmentId is a foreign key (reference column) of the ID from the Department table. Each row of this table indicates the ID; name; and salary of an employee. It also contains the ID of their department. Table: Department +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID of a department and its name. A company's executives are interested in seeing who earns the most money in each of the company's departments. A high earner in a department is an employee who has a salary in the top three unique salaries for that department. Write a solution to find the employees who are high earners in each of the departments. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +----+-------+--------+--------------+ | id | name | salary | departmentId | +----+-------+--------+--------------+ | 1 | Joe | 85000 | 1 | | 2 | Henry | 80000 | 2 | | 3 | Sam | 60000 | 2 | | 4 | Max | 90000 | 1 | | 5 | Janet | 69000 | 1 | | 6 | Randy | 85000 | 1 | | 7 | Will | 70000 | 1 | +----+-------+--------+--------------+ Department table: +----+-------+ | id | name | +----+-------+ | 1 | IT | | 2 | Sales | +----+-------+ Output: +------------+----------+--------+ | Department | Employee | Salary | +------------+----------+--------+ | IT | Max | 90000 | | IT | Joe | 85000 | | IT | Randy | 85000 | | IT | Will | 70000 | | Sales | Henry | 80000 | | Sales | Sam | 60000 | +------------+----------+--------+ Explanation: In the IT department: - Max earns the highest unique salary - Both Randy and Joe earn the second-highest unique salary - Will earns the third-highest unique salary In the Sales department: - Henry earns the highest salary - Sam earns the second-highest salary - There is no third-highest salary as there are only two employees
Apple,186,Reverse Words in a String II,Med,"Two Pointers, String",
Apple,188,Best Time to Buy and Sell Stock IV,Hard,"Array, Dynamic Programming",You are given an integer array prices where prices[i] is the price of a given stock on the ith day; and an integer k. Find the maximum profit you can achieve. You may complete at most k transactions: i.e. you may buy at most k times and sell at most k times. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: k = 2; prices = [2;4;1] Output: 2 Explanation: Buy on day 1 (price = 2) and sell on day 2 (price = 4); profit = 4-2 = 2. Example 2: Input: k = 2; prices = [3;2;6;5;0;3] Output: 7 Explanation: Buy on day 2 (price = 2) and sell on day 3 (price = 6); profit = 6-2 = 4. Then buy on day 5 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Constraints: 1 <= k <= 100 1 <= prices.length <= 1000 0 <= prices[i] <= 1000
Apple,197,Rising Temperature,Easy,Database,Table: Weather +---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | recordDate | date | | temperature | int | +---------------+---------+ id is the column with unique values for this table. There are no different rows with the same recordDate. This table contains information about the temperature on a certain day. Write a solution to find all dates' id with higher temperatures compared to its previous dates (yesterday). Return the result table in any order. The result format is in the following example. Example 1: Input: Weather table: +----+------------+-------------+ | id | recordDate | temperature | +----+------------+-------------+ | 1 | 2015-01-01 | 10 | | 2 | 2015-01-02 | 25 | | 3 | 2015-01-03 | 20 | | 4 | 2015-01-04 | 30 | +----+------------+-------------+ Output: +----+ | id | +----+ | 2 | | 4 | +----+ Explanation: In 2015-01-02; the temperature was higher than the previous day (10 -> 25). In 2015-01-04; the temperature was higher than the previous day (20 -> 30).
Apple,212,Word Search II,Hard,"Array, String, Backtracking, Trie, Matrix","Given an m x n board of characters and a list of strings words; return all words on the board. Each word must be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example 1: Input: board = [[""o"";""a"";""a"";""n""];[""e"";""t"";""a"";""e""];[""i"";""h"";""k"";""r""];[""i"";""f"";""l"";""v""]]; words = [""oath"";""pea"";""eat"";""rain""] Output: [""eat"";""oath""] Example 2: Input: board = [[""a"";""b""];[""c"";""d""]]; words = [""abcb""] Output: [] Constraints: m == board.length n == board[i].length 1 <= m; n <= 12 board[i][j] is a lowercase English letter. 1 <= words.length <= 3 * 104 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. All the strings of words are unique."
Apple,223,Rectangle Area,Med,"Math, Geometry",Given the coordinates of two rectilinear rectangles in a 2D plane; return the total area covered by the two rectangles. The first rectangle is defined by its bottom-left corner (ax1; ay1) and its top-right corner (ax2; ay2). The second rectangle is defined by its bottom-left corner (bx1; by1) and its top-right corner (bx2; by2). Example 1: Input: ax1 = -3; ay1 = 0; ax2 = 3; ay2 = 4; bx1 = 0; by1 = -1; bx2 = 9; by2 = 2 Output: 45 Example 2: Input: ax1 = -2; ay1 = -2; ax2 = 2; ay2 = 2; bx1 = -2; by1 = -2; bx2 = 2; by2 = 2 Output: 16 Constraints: -104 <= ax1 <= ax2 <= 104 -104 <= ay1 <= ay2 <= 104 -104 <= bx1 <= bx2 <= 104 -104 <= by1 <= by2 <= 104
Apple,252,Meeting Rooms,Easy,"Array, Sorting",
Apple,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
Apple,314,Binary Tree Vertical Order Traversal,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Sorting, Binary Tree",
Apple,319,Bulb Switcher,Med,"Math, Brainteaser",There are n bulbs that are initially off. You first turn on all the bulbs; then you turn off every second bulb. On the third round; you toggle every third bulb (turning on if it's off or turning off if it's on). For the ith round; you toggle every i bulb. For the nth round; you only toggle the last bulb. Return the number of bulbs that are on after n rounds. Example 1: Input: n = 3 Output: 1 Explanation: At first; the three bulbs are [off; off; off]. After the first round; the three bulbs are [on; on; on]. After the second round; the three bulbs are [on; off; on]. After the third round; the three bulbs are [on; off; off]. So you should return 1 because there is only one bulb is on. Example 2: Input: n = 0 Output: 0 Example 3: Input: n = 1 Output: 1 Constraints: 0 <= n <= 109
Apple,342,Power of Four,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of four. Otherwise; return false. An integer n is a power of four; if there exists an integer x such that n == 4x. Example 1: Input: n = 16 Output: true Example 2: Input: n = 5 Output: false Example 3: Input: n = 1 Output: true Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Apple,350,Intersection of Two Arrays II,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must appear as many times as it shows in both arrays and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2;2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [4;9] Explanation: [9;4] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000 Follow up: What if the given array is already sorted? How would you optimize your algorithm? What if nums1's size is small compared to nums2's size? Which algorithm is better? What if elements of nums2 are stored on disk; and the memory is limited such that you cannot load all elements into the memory at once?
Apple,355,Design Twitter,Med,"Hash Table, Linked List, Design, Heap (Priority Queue)","Design a simplified version of Twitter where users can post tweets; follow/unfollow another user; and is able to see the 10 most recent tweets in the user's news feed. Implement the Twitter class: Twitter() Initializes your twitter object. void postTweet(int userId; int tweetId) Composes a new tweet with ID tweetId by the user userId. Each call to this function will be made with a unique tweetId. List<Integer> getNewsFeed(int userId) Retrieves the 10 most recent tweet IDs in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user themself. Tweets must be ordered from most recent to least recent. void follow(int followerId; int followeeId) The user with ID followerId started following the user with ID followeeId. void unfollow(int followerId; int followeeId) The user with ID followerId started unfollowing the user with ID followeeId. Example 1: Input [""Twitter""; ""postTweet""; ""getNewsFeed""; ""follow""; ""postTweet""; ""getNewsFeed""; ""unfollow""; ""getNewsFeed""] [[]; [1; 5]; [1]; [1; 2]; [2; 6]; [1]; [1; 2]; [1]] Output [null; null; [5]; null; null; [6; 5]; null; [5]] Explanation Twitter twitter = new Twitter(); twitter.postTweet(1; 5); // User 1 posts a new tweet (id = 5). twitter.getNewsFeed(1); // User 1's news feed should return a list with 1 tweet id -> [5]. return [5] twitter.follow(1; 2); // User 1 follows user 2. twitter.postTweet(2; 6); // User 2 posts a new tweet (id = 6). twitter.getNewsFeed(1); // User 1's news feed should return a list with 2 tweet ids -> [6; 5]. Tweet id 6 should precede tweet id 5 because it is posted after tweet id 5. twitter.unfollow(1; 2); // User 1 unfollows user 2. twitter.getNewsFeed(1); // User 1's news feed should return a list with 1 tweet id -> [5]; since user 1 is no longer following user 2. Constraints: 1 <= userId; followerId; followeeId <= 500 0 <= tweetId <= 104 All the tweets have unique IDs. At most 3 * 104 calls will be made to postTweet; getNewsFeed; follow; and unfollow."
Apple,357,Count Numbers with Unique Digits,Med,"Math, Dynamic Programming, Backtracking",Given an integer n; return the count of all numbers with unique digits; x; where 0 <= x < 10n. Example 1: Input: n = 2 Output: 91 Explanation: The answer should be the total numbers in the range of 0 ≤ x < 100; excluding 11;22;33;44;55;66;77;88;99 Example 2: Input: n = 0 Output: 1 Constraints: 0 <= n <= 8
Apple,395,Longest Substring with At Least K Repeating Characters,Med,"Hash Table, String, Divide and Conquer, Sliding Window","Given a string s and an integer k; return the length of the longest substring of s such that the frequency of each character in this substring is greater than or equal to k. if no such substring exists; return 0. Example 1: Input: s = ""aaabb""; k = 3 Output: 3 Explanation: The longest substring is ""aaa""; as 'a' is repeated 3 times. Example 2: Input: s = ""ababbc""; k = 2 Output: 5 Explanation: The longest substring is ""ababb""; as 'a' is repeated 2 times and 'b' is repeated 3 times. Constraints: 1 <= s.length <= 104 s consists of only lowercase English letters. 1 <= k <= 105"
Apple,399,Evaluate Division,Med,"Array, String, Depth-First Search, Breadth-First Search, Union Find, Graph, Shortest Path","You are given an array of variable pairs equations and an array of real numbers values; where equations[i] = [Ai; Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable. You are also given some queries; where queries[j] = [Cj; Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries. If a single answer cannot be determined; return -1.0. Note: The input is always valid. You may assume that evaluating the queries will not result in division by zero and that there is no contradiction. Note: The variables that do not occur in the list of equations are undefined; so the answer cannot be determined for them. Example 1: Input: equations = [[""a"";""b""];[""b"";""c""]]; values = [2.0;3.0]; queries = [[""a"";""c""];[""b"";""a""];[""a"";""e""];[""a"";""a""];[""x"";""x""]] Output: [6.00000;0.50000;-1.00000;1.00000;-1.00000] Explanation: Given: a / b = 2.0; b / c = 3.0 queries are: a / c = ?; b / a = ?; a / e = ?; a / a = ?; x / x = ? return: [6.0; 0.5; -1.0; 1.0; -1.0 ] note: x is undefined => -1.0 Example 2: Input: equations = [[""a"";""b""];[""b"";""c""];[""bc"";""cd""]]; values = [1.5;2.5;5.0]; queries = [[""a"";""c""];[""c"";""b""];[""bc"";""cd""];[""cd"";""bc""]] Output: [3.75000;0.40000;5.00000;0.20000] Example 3: Input: equations = [[""a"";""b""]]; values = [0.5]; queries = [[""a"";""b""];[""b"";""a""];[""a"";""c""];[""x"";""y""]] Output: [0.50000;2.00000;-1.00000;-1.00000] Constraints: 1 <= equations.length <= 20 equations[i].length == 2 1 <= Ai.length; Bi.length <= 5 values.length == equations.length 0.0 < values[i] <= 20.0 1 <= queries.length <= 20 queries[i].length == 2 1 <= Cj.length; Dj.length <= 5 Ai; Bi; Cj; Dj consist of lower case English letters and digits."
Apple,402,Remove K Digits,Med,"String, Stack, Greedy, Monotonic Stack","Given string num representing a non-negative integer num; and an integer k; return the smallest possible integer after removing k digits from num. Example 1: Input: num = ""1432219""; k = 3 Output: ""1219"" Explanation: Remove the three digits 4; 3; and 2 to form the new number 1219 which is the smallest. Example 2: Input: num = ""10200""; k = 1 Output: ""200"" Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes. Example 3: Input: num = ""10""; k = 2 Output: ""0"" Explanation: Remove all the digits from the number and it is left with nothing which is 0. Constraints: 1 <= k <= num.length <= 105 num consists of only digits. num does not have any leading zeros except for the zero itself."
Apple,403,Frog Jump,Hard,"Array, Dynamic Programming",A frog is crossing a river. The river is divided into some number of units; and at each unit; there may or may not exist a stone. The frog can jump on a stone; but it must not jump into the water. Given a list of stones positions (in units) in sorted ascending order; determine if the frog can cross the river by landing on the last stone. Initially; the frog is on the first stone and assumes the first jump must be 1 unit. If the frog's last jump was k units; its next jump must be either k - 1; k; or k + 1 units. The frog can only jump in the forward direction. Example 1: Input: stones = [0;1;3;5;6;8;12;17] Output: true Explanation: The frog can jump to the last stone by jumping 1 unit to the 2nd stone; then 2 units to the 3rd stone; then 2 units to the 4th stone; then 3 units to the 6th stone; 4 units to the 7th stone; and 5 units to the 8th stone. Example 2: Input: stones = [0;1;2;3;4;8;9;11] Output: false Explanation: There is no way to jump to the last stone as the gap between the 5th and 6th stone is too large. Constraints: 2 <= stones.length <= 2000 0 <= stones[i] <= 231 - 1 stones[0] == 0 stones is sorted in a strictly increasing order.
Apple,407,Trapping Rain Water II,Hard,"Array, Breadth-First Search, Heap (Priority Queue), Matrix",Given an m x n integer matrix heightMap representing the height of each unit cell in a 2D elevation map; return the volume of water it can trap after raining. Example 1: Input: heightMap = [[1;4;3;1;3;2];[3;2;1;3;2;4];[2;3;3;2;3;1]] Output: 4 Explanation: After the rain; water is trapped between the blocks. We have two small ponds 1 and 3 units trapped. The total volume of water trapped is 4. Example 2: Input: heightMap = [[3;3;3;3;3];[3;2;2;2;3];[3;2;1;2;3];[3;2;2;2;3];[3;3;3;3;3]] Output: 10 Constraints: m == heightMap.length n == heightMap[i].length 1 <= m; n <= 200 0 <= heightMap[i][j] <= 2 * 104
Apple,408,Valid Word Abbreviation,Easy,"Two Pointers, String",
Apple,417,Pacific Atlantic Water Flow,Med,"Array, Depth-First Search, Breadth-First Search, Matrix",There is an m x n rectangular island that borders both the Pacific Ocean and Atlantic Ocean. The Pacific Ocean touches the island's left and top edges; and the Atlantic Ocean touches the island's right and bottom edges. The island is partitioned into a grid of square cells. You are given an m x n integer matrix heights where heights[r][c] represents the height above sea level of the cell at coordinate (r; c). The island receives a lot of rain; and the rain water can flow to neighboring cells directly north; south; east; and west if the neighboring cell's height is less than or equal to the current cell's height. Water can flow from any cell adjacent to an ocean into the ocean. Return a 2D list of grid coordinates result where result[i] = [ri; ci] denotes that rain water can flow from cell (ri; ci) to both the Pacific and Atlantic oceans. Example 1: Input: heights = [[1;2;2;3;5];[3;2;3;4;4];[2;4;5;3;1];[6;7;1;4;5];[5;1;1;2;4]] Output: [[0;4];[1;3];[1;4];[2;2];[3;0];[3;1];[4;0]] Explanation: The following cells can flow to the Pacific and Atlantic oceans; as shown below: [0;4]: [0;4] -> Pacific Ocean [0;4] -> Atlantic Ocean [1;3]: [1;3] -> [0;3] -> Pacific Ocean [1;3] -> [1;4] -> Atlantic Ocean [1;4]: [1;4] -> [1;3] -> [0;3] -> Pacific Ocean [1;4] -> Atlantic Ocean [2;2]: [2;2] -> [1;2] -> [0;2] -> Pacific Ocean [2;2] -> [2;3] -> [2;4] -> Atlantic Ocean [3;0]: [3;0] -> Pacific Ocean [3;0] -> [4;0] -> Atlantic Ocean [3;1]: [3;1] -> [3;0] -> Pacific Ocean [3;1] -> [4;1] -> Atlantic Ocean [4;0]: [4;0] -> Pacific Ocean [4;0] -> Atlantic Ocean Note that there are other possible paths for these cells to flow to the Pacific and Atlantic oceans. Example 2: Input: heights = [[1]] Output: [[0;0]] Explanation: The water can flow from the only cell to the Pacific and Atlantic oceans. Constraints: m == heights.length n == heights[r].length 1 <= m; n <= 200 0 <= heights[r][c] <= 105
Apple,420,Strong Password Checker,Hard,"String, Greedy, Heap (Priority Queue)","A password is considered strong if the below conditions are all met: It has at least 6 characters and at most 20 characters. It contains at least one lowercase letter; at least one uppercase letter; and at least one digit. It does not contain three repeating characters in a row (i.e.; ""Baaabb0"" is weak; but ""Baaba0"" is strong). Given a string password; return the minimum number of steps required to make password strong. if password is already strong; return 0. In one step; you can: Insert one character to password; Delete one character from password; or Replace one character of password with another character. Example 1: Input: password = ""a"" Output: 5 Example 2: Input: password = ""aA1"" Output: 3 Example 3: Input: password = ""1337C0d3"" Output: 0 Constraints: 1 <= password.length <= 50 password consists of letters; digits; dot '.' or exclamation mark '!'."
Apple,459,Repeated Substring Pattern,Easy,"String, String Matching","Given a string s; check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. Example 1: Input: s = ""abab"" Output: true Explanation: It is the substring ""ab"" twice. Example 2: Input: s = ""aba"" Output: false Example 3: Input: s = ""abcabcabcabc"" Output: true Explanation: It is the substring ""abc"" four times or the substring ""abcabc"" twice. Constraints: 1 <= s.length <= 104 s consists of lowercase English letters."
Apple,468,Validate IP Address,Med,String,"Given a string queryIP; return ""IPv4"" if IP is a valid IPv4 address; ""IPv6"" if IP is a valid IPv6 address or ""Neither"" if IP is not a correct IP of any type. A valid IPv4 address is an IP in the form ""x1.x2.x3.x4"" where 0 <= xi <= 255 and xi cannot contain leading zeros. For example; ""192.168.1.1"" and ""192.168.1.0"" are valid IPv4 addresses while ""192.168.01.1""; ""192.168.1.00""; and ""192.168@1.1"" are invalid IPv4 addresses. A valid IPv6 address is an IP in the form ""x1:x2:x3:x4:x5:x6:x7:x8"" where: 1 <= xi.length <= 4 xi is a hexadecimal string which may contain digits; lowercase English letter ('a' to 'f') and upper-case English letters ('A' to 'F'). Leading zeros are allowed in xi. For example; ""2001:0db8:85a3:0000:0000:8a2e:0370:7334"" and ""2001:db8:85a3:0:0:8A2E:0370:7334"" are valid IPv6 addresses; while ""2001:0db8:85a3::8A2E:037j:7334"" and ""02001:0db8:85a3:0000:0000:8a2e:0370:7334"" are invalid IPv6 addresses. Example 1: Input: queryIP = ""172.16.254.1"" Output: ""IPv4"" Explanation: This is a valid IPv4 address; return ""IPv4"". Example 2: Input: queryIP = ""2001:0db8:85a3:0:0:8A2E:0370:7334"" Output: ""IPv6"" Explanation: This is a valid IPv6 address; return ""IPv6"". Example 3: Input: queryIP = ""256.256.256.256"" Output: ""Neither"" Explanation: This is neither a IPv4 address nor a IPv6 address. Constraints: queryIP consists only of English letters; digits and the characters '.' and ':'."
Apple,485,Max Consecutive Ones,Easy,Array,Given a binary array nums; return the maximum number of consecutive 1's in the array. Example 1: Input: nums = [1;1;0;1;1;1] Output: 3 Explanation: The first two digits or the last three digits are consecutive 1s. The maximum number of consecutive 1s is 3. Example 2: Input: nums = [1;0;1;1;0;1] Output: 2 Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Apple,518,Coin Change II,Med,"Array, Dynamic Programming",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the number of combinations that make up that amount. If that amount of money cannot be made up by any combination of the coins; return 0. You may assume that you have an infinite number of each kind of coin. The answer is guaranteed to fit into a signed 32-bit integer. Example 1: Input: amount = 5; coins = [1;2;5] Output: 4 Explanation: there are four ways to make up the amount: 5=5 5=2+2+1 5=2+1+1+1 5=1+1+1+1+1 Example 2: Input: amount = 3; coins = [2] Output: 0 Explanation: the amount of 3 cannot be made up just with coins of 2. Example 3: Input: amount = 10; coins = [10] Output: 1 Constraints: 1 <= coins.length <= 300 1 <= coins[i] <= 5000 All the values of coins are unique. 0 <= amount <= 5000
Apple,525,Contiguous Array,Med,"Array, Hash Table, Prefix Sum",Given a binary array nums; return the maximum length of a contiguous subarray with an equal number of 0 and 1. Example 1: Input: nums = [0;1] Output: 2 Explanation: [0; 1] is the longest contiguous subarray with an equal number of 0 and 1. Example 2: Input: nums = [0;1;0] Output: 2 Explanation: [0; 1] (or [1; 0]) is a longest contiguous subarray with equal number of 0 and 1. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Apple,545,Boundary of Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",
Apple,561,Array Partition,Easy,"Array, Greedy, Sorting, Counting Sort",Given an integer array nums of 2n integers; group these integers into n pairs (a1; b1); (a2; b2); ...; (an; bn) such that the sum of min(ai; bi) for all i is maximized. Return the maximized sum. Example 1: Input: nums = [1;4;3;2] Output: 4 Explanation: All possible pairings (ignoring the ordering of elements) are: 1. (1; 4); (2; 3) -> min(1; 4) + min(2; 3) = 1 + 2 = 3 2. (1; 3); (2; 4) -> min(1; 3) + min(2; 4) = 1 + 2 = 3 3. (1; 2); (3; 4) -> min(1; 2) + min(3; 4) = 1 + 3 = 4 So the maximum possible sum is 4. Example 2: Input: nums = [6;2;6;5;1;2] Output: 9 Explanation: The optimal pairing is (2; 1); (2; 5); (6; 6). min(2; 1) + min(2; 5) + min(6; 6) = 1 + 2 + 6 = 9. Constraints: 1 <= n <= 104 nums.length == 2 * n -104 <= nums[i] <= 104
Apple,617,Merge Two Binary Trees,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given two binary trees root1 and root2. Imagine that when you put one of them to cover the other; some nodes of the two trees are overlapped while the others are not. You need to merge the two trees into a new binary tree. The merge rule is that if two nodes overlap; then sum node values up as the new value of the merged node. Otherwise; the NOT null node will be used as the node of the new tree. Return the merged tree. Note: The merging process must start from the root nodes of both trees. Example 1: Input: root1 = [1;3;2;5]; root2 = [2;1;3;null;4;null;7] Output: [3;4;5;5;4;null;7] Example 2: Input: root1 = [1]; root2 = [1;2] Output: [2;2] Constraints: The number of nodes in both trees is in the range [0; 2000]. -104 <= Node.val <= 104
Apple,658,Find K Closest Elements,Med,"Array, Two Pointers, Binary Search, Sliding Window, Sorting, Heap (Priority Queue)",Given a sorted integer array arr; two integers k and x; return the k closest integers to x in the array. The result should also be sorted in ascending order. An integer a is closer to x than an integer b if: |a - x| < |b - x|; or |a - x| == |b - x| and a < b Example 1: Input: arr = [1;2;3;4;5]; k = 4; x = 3 Output: [1;2;3;4] Example 2: Input: arr = [1;1;2;3;4;5]; k = 4; x = -1 Output: [1;1;2;3] Constraints: 1 <= k <= arr.length 1 <= arr.length <= 104 arr is sorted in ascending order. -104 <= arr[i]; x <= 104
Apple,682,Baseball Game,Easy,"Array, Stack, Simulation","You are keeping the scores for a baseball game with strange rules. At the beginning of the game; you start with an empty record. You are given a list of strings operations; where operations[i] is the ith operation you must apply to the record and is one of the following: An integer x. Record a new score of x. '+'. Record a new score that is the sum of the previous two scores. 'D'. Record a new score that is the double of the previous score. 'C'. Invalidate the previous score; removing it from the record. Return the sum of all the scores on the record after applying all the operations. The test cases are generated such that the answer and all intermediate calculations fit in a 32-bit integer and that all operations are valid. Example 1: Input: ops = [""5"";""2"";""C"";""D"";""+""] Output: 30 Explanation: ""5"" - Add 5 to the record; record is now [5]. ""2"" - Add 2 to the record; record is now [5; 2]. ""C"" - Invalidate and remove the previous score; record is now [5]. ""D"" - Add 2 * 5 = 10 to the record; record is now [5; 10]. ""+"" - Add 5 + 10 = 15 to the record; record is now [5; 10; 15]. The total sum is 5 + 10 + 15 = 30. Example 2: Input: ops = [""5"";""-2"";""4"";""C"";""D"";""9"";""+"";""+""] Output: 27 Explanation: ""5"" - Add 5 to the record; record is now [5]. ""-2"" - Add -2 to the record; record is now [5; -2]. ""4"" - Add 4 to the record; record is now [5; -2; 4]. ""C"" - Invalidate and remove the previous score; record is now [5; -2]. ""D"" - Add 2 * -2 = -4 to the record; record is now [5; -2; -4]. ""9"" - Add 9 to the record; record is now [5; -2; -4; 9]. ""+"" - Add -4 + 9 = 5 to the record; record is now [5; -2; -4; 9; 5]. ""+"" - Add 9 + 5 = 14 to the record; record is now [5; -2; -4; 9; 5; 14]. The total sum is 5 + -2 + -4 + 9 + 5 + 14 = 27. Example 3: Input: ops = [""1"";""C""] Output: 0 Explanation: ""1"" - Add 1 to the record; record is now [1]. ""C"" - Invalidate and remove the previous score; record is now []. Since the record is empty; the total sum is 0. Constraints: 1 <= operations.length <= 1000 operations[i] is ""C""; ""D""; ""+""; or a string representing an integer in the range [-3 * 104; 3 * 104]. For operation ""+""; there will always be at least two previous scores on the record. For operations ""C"" and ""D""; there will always be at least one previous score on the record."
Apple,692,Top K Frequent Words,Med,"Hash Table, String, Trie, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given an array of strings words and an integer k; return the k most frequent strings. Return the answer sorted by the frequency from highest to lowest. Sort the words with the same frequency by their lexicographical order. Example 1: Input: words = [""i"";""love"";""leetcode"";""i"";""love"";""coding""]; k = 2 Output: [""i"";""love""] Explanation: ""i"" and ""love"" are the two most frequent words. Note that ""i"" comes before ""love"" due to a lower alphabetical order. Example 2: Input: words = [""the"";""day"";""is"";""sunny"";""the"";""the"";""the"";""sunny"";""is"";""is""]; k = 4 Output: [""the"";""is"";""sunny"";""day""] Explanation: ""the""; ""is""; ""sunny"" and ""day"" are the four most frequent words; with the number of occurrence being 4; 3; 2 and 1 respectively. Constraints: 1 <= words.length <= 500 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. k is in the range [1; The number of unique words[i]] Follow-up: Could you solve it in O(n log(k)) time and O(n) extra space?"
Apple,726,Number of Atoms,Hard,"Hash Table, String, Stack, Sorting","Given a string formula representing a chemical formula; return the count of each atom. The atomic element always starts with an uppercase character; then zero or more lowercase letters; representing the name. One or more digits representing that element's count may follow if the count is greater than 1. If the count is 1; no digits will follow. For example; ""H2O"" and ""H2O2"" are possible; but ""H1O2"" is impossible. Two formulas are concatenated together to produce another formula. For example; ""H2O2He3Mg4"" is also a formula. A formula placed in parentheses; and a count (optionally added) is also a formula. For example; ""(H2O2)"" and ""(H2O2)3"" are formulas. Return the count of all elements as a string in the following form: the first name (in sorted order); followed by its count (if that count is more than 1); followed by the second name (in sorted order); followed by its count (if that count is more than 1); and so on. The test cases are generated so that all the values in the output fit in a 32-bit integer. Example 1: Input: formula = ""H2O"" Output: ""H2O"" Explanation: The count of elements are {'H': 2; 'O': 1}. Example 2: Input: formula = ""Mg(OH)2"" Output: ""H2MgO2"" Explanation: The count of elements are {'H': 2; 'Mg': 1; 'O': 2}. Example 3: Input: formula = ""K4(ON(SO3)2)2"" Output: ""K4N2O14S4"" Explanation: The count of elements are {'K': 4; 'N': 2; 'O': 14; 'S': 4}. Constraints: 1 <= formula.length <= 1000 formula consists of English letters; digits; '('; and ')'. formula is always valid."
Apple,430,Flatten a Multilevel Doubly Linked List,Med,,
Apple,700,Search in a Binary Search Tree,Easy,,
Apple,778,Swim in Rising Water,Hard,"Hash Table, String, Greedy, Sorting, Heap (Priority Queue), Counting","Given a string s; rearrange the characters of s so that any two adjacent characters are not the same. Return any possible rearrangement of s or return """" if not possible. Example 1: Input: s = ""aab"" Output: ""aba"" Example 2: Input: s = ""aaab"" Output: """" Constraints: 1 <= s.length <= 500 s consists of lowercase English letters."
Apple,781,Rabbits in Forest,Med,"Hash Table, Math, String, Stack, Recursion","Given an expression such as expression = ""e + 8 - a + 5"" and an evaluation map such as {""e"": 1} (given in terms of evalvars = [""e""] and evalints = [1]); return a list of tokens representing the simplified expression; such as [""-1*a"";""14""] An expression alternates chunks and symbols; with a space separating each chunk and symbol. A chunk is either an expression in parentheses; a variable; or a non-negative integer. A variable is a string of lowercase letters (not including digits.) Note that variables can be multiple letters; and note that variables never have a leading coefficient or unary operator like ""2x"" or ""-x"". Expressions are evaluated in the usual order: brackets first; then multiplication; then addition and subtraction. For example; expression = ""1 + 2 * 3"" has an answer of [""7""]. The format of the output is as follows: For each term of free variables with a non-zero coefficient; we write the free variables within a term in sorted order lexicographically. For example; we would never write a term like ""b*a*c""; only ""a*b*c"". Terms have degrees equal to the number of free variables being multiplied; counting multiplicity. We write the largest degree terms of our answer first; breaking ties by lexicographic order ignoring the leading coefficient of the term. For example; ""a*a*b*c"" has degree 4. The leading coefficient of the term is placed directly to the left with an asterisk separating it from the variables (if they exist.) A leading coefficient of 1 is still printed. An example of a well-formatted answer is [""-2*a*a*a""; ""3*a*a*b""; ""3*b*b""; ""4*a""; ""5*c""; ""-6""]. Terms (including constant terms) with coefficient 0 are not included. For example; an expression of ""0"" has an output of []. Note: You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Example 1: Input: expression = ""e + 8 - a + 5""; evalvars = [""e""]; evalints = [1] Output: [""-1*a"";""14""] Example 2: Input: expression = ""e - 8 + temperature - pressure""; evalvars = [""e""; ""temperature""]; evalints = [1; 12] Output: [""-1*pressure"";""5""] Example 3: Input: expression = ""(e + 8) * (e - 8)""; evalvars = []; evalints = [] Output: [""1*e*e"";""-64""] Constraints: 1 <= expression.length <= 250 expression consists of lowercase English letters; digits; '+'; '-'; '*'; '('; ')'; ' '. expression does not contain any leading or trailing spaces. All the tokens in expression are separated by a single space. 0 <= evalvars.length <= 100 1 <= evalvars[i].length <= 20 evalvars[i] consists of lowercase English letters. evalints.length == evalvars.length -100 <= evalints[i] <= 100"
Apple,785,Is Graph Bipartite?,Med,"Math, String, Stack, Recursion",
Apple,808,Soup Servings,Med,"Array, Hash Table, String, Binary Search, Dynamic Programming, Trie, Sorting","Given a string s and an array of strings words; return the number of words[i] that is a subsequence of s. A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters. For example; ""ace"" is a subsequence of ""abcde"". Example 1: Input: s = ""abcde""; words = [""a"";""bb"";""acd"";""ace""] Output: 3 Explanation: There are three strings in words that are a subsequence of s: ""a""; ""acd""; ""ace"". Example 2: Input: s = ""dsahjpjauf""; words = [""ahjpjau"";""ja"";""ahbwzgqnuk"";""tnmlanowax""] Output: 2 Constraints: 1 <= s.length <= 5 * 104 1 <= words.length <= 5000 1 <= words[i].length <= 50 s and words[i] consist of only lowercase English letters."
Apple,839,Similar String Groups,Hard,"Array, Hash Table, String, Trie","A valid encoding of an array of words is any reference string s and array of indices indices such that: words.length == indices.length The reference string s ends with the '#' character. For each index indices[i]; the substring of s starting from indices[i] and up to (but not including) the next '#' character is equal to words[i]. Given an array of words; return the length of the shortest reference string s possible of any valid encoding of words. Example 1: Input: words = [""time""; ""me""; ""bell""] Output: 10 Explanation: A valid encoding would be s = ""time#bell#"" and indices = [0; 2; 5]. words[0] = ""time""; the substring of s starting from indices[0] = 0 to the next '#' is underlined in ""time#bell#"" words[1] = ""me""; the substring of s starting from indices[1] = 2 to the next '#' is underlined in ""time#bell#"" words[2] = ""bell""; the substring of s starting from indices[2] = 5 to the next '#' is underlined in ""time#bell#"" Example 2: Input: words = [""t""] Output: 2 Explanation: A valid encoding would be s = ""t#"" and indices = [0]. Constraints: 1 <= words.length <= 2000 1 <= words[i].length <= 7 words[i] consists of only lowercase letters."
Apple,844,Backspace String Compare,Easy,,
Apple,853,Car Fleet,Med,"Array, Two Pointers, Binary Search, Greedy, Sorting",You have n jobs and m workers. You are given three arrays: difficulty; profit; and worker where: difficulty[i] and profit[i] are the difficulty and the profit of the ith job; and worker[j] is the ability of jth worker (i.e.; the jth worker can only complete a job with difficulty at most worker[j]). Every worker can be assigned at most one job; but one job can be completed multiple times. For example; if three workers attempt the same job that pays $1; then the total profit will be $3. If a worker cannot complete any job; their profit is $0. Return the maximum profit we can achieve after assigning the workers to the jobs. Example 1: Input: difficulty = [2;4;6;8;10]; profit = [10;20;30;40;50]; worker = [4;5;6;7] Output: 100 Explanation: Workers are assigned jobs of difficulty [4;4;6;6] and they get a profit of [20;20;30;30] separately. Example 2: Input: difficulty = [85;47;57]; profit = [24;66;99]; worker = [40;25;25] Output: 0 Constraints: n == difficulty.length n == profit.length m == worker.length 1 <= n; m <= 104 1 <= difficulty[i]; profit[i]; worker[i] <= 105
Apple,887,Super Egg Drop,Hard,"Array, Greedy, Sorting, Heap (Priority Queue)",There are n workers. You are given two integer arrays quality and wage where quality[i] is the quality of the ith worker and wage[i] is the minimum wage expectation for the ith worker. We want to hire exactly k workers to form a paid group. To hire a group of k workers; we must pay them according to the following rules: Every worker in the paid group must be paid at least their minimum wage expectation. In the group; each worker's pay must be directly proportional to their quality. This means if a worker’s quality is double that of another worker in the group; then they must be paid twice as much as the other worker. Given the integer k; return the least amount of money needed to form a paid group satisfying the above conditions. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: quality = [10;20;5]; wage = [70;50;30]; k = 2 Output: 105.00000 Explanation: We pay 70 to 0th worker and 35 to 2nd worker. Example 2: Input: quality = [3;1;10;10;1]; wage = [4;8;2;2;7]; k = 3 Output: 30.66667 Explanation: We pay 4 to 0th worker; 13.33333 to 2nd and 3rd workers separately. Constraints: n == quality.length == wage.length 1 <= k <= n <= 104 1 <= quality[i]; wage[i] <= 104
Apple,894,All Possible Full Binary Trees,Med,"Array, Hash Table, Math, Binary Search, Sorting, Randomized","You are given an integer n and an array of unique integers blacklist. Design an algorithm to pick a random integer in the range [0; n - 1] that is not in blacklist. Any integer that is in the mentioned range and not in blacklist should be equally likely to be returned. Optimize your algorithm such that it minimizes the number of calls to the built-in random function of your language. Implement the Solution class: Solution(int n; int[] blacklist) Initializes the object with the integer n and the blacklisted integers blacklist. int pick() Returns a random integer in the range [0; n - 1] and not in blacklist. Example 1: Input [""Solution""; ""pick""; ""pick""; ""pick""; ""pick""; ""pick""; ""pick""; ""pick""] [[7; [2; 3; 5]]; []; []; []; []; []; []; []] Output [null; 0; 4; 1; 6; 1; 0; 4] Explanation Solution solution = new Solution(7; [2; 3; 5]); solution.pick(); // return 0; any integer from [0;1;4;6] should be ok. Note that for every call of pick; // 0; 1; 4; and 6 must be equally likely to be returned (i.e.; with probability 1/4). solution.pick(); // return 4 solution.pick(); // return 1 solution.pick(); // return 6 solution.pick(); // return 1 solution.pick(); // return 0 solution.pick(); // return 4 Constraints: 1 <= n <= 109 0 <= blacklist.length <= min(105; n - 1) 0 <= blacklist[i] < n All the values of blacklist are unique. At most 2 * 104 calls will be made to pick."
Apple,930,Binary Subarrays With Sum,Med,"Dynamic Programming, Tree, Recursion, Memoization, Binary Tree",Given an integer n; return a list of all possible full binary trees with n nodes. Each node of each tree in the answer must have Node.val == 0. Each element of the answer is the root node of one possible tree. You may return the final list of trees in any order. A full binary tree is a binary tree where each node has exactly 0 or 2 children. Example 1: Input: n = 7 Output: [[0;0;0;null;null;0;0;null;null;0;0];[0;0;0;null;null;0;0;0;0];[0;0;0;0;0;0;0];[0;0;0;0;0;null;null;null;null;0;0];[0;0;0;0;0;null;null;0;0]] Example 2: Input: n = 3 Output: [[0;0;0]] Constraints: 1 <= n <= 20
Apple,973,K Closest Points to Origin,Med,"String, Stack, Greedy, Queue","You are given two strings stamp and target. Initially; there is a string s of length target.length with all s[i] == '?'. In one turn; you can place stamp over s and replace every letter in the s with the corresponding letter from stamp. For example; if stamp = ""abc"" and target = ""abcba""; then s is ""?????"" initially. In one turn you can: place stamp at index 0 of s to obtain ""abc??""; place stamp at index 1 of s to obtain ""?abc?""; or place stamp at index 2 of s to obtain ""??abc"". Note that stamp must be fully contained in the boundaries of s in order to stamp (i.e.; you cannot place stamp at index 3 of s). We want to convert s to target using at most 10 * target.length turns. Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns; return an empty array. Example 1: Input: stamp = ""abc""; target = ""ababc"" Output: [0;2] Explanation: Initially s = ""?????"". - Place stamp at index 0 to get ""abc??"". - Place stamp at index 2 to get ""ababc"". [1;0;2] would also be accepted as an answer; as well as some other answers. Example 2: Input: stamp = ""abca""; target = ""aabcaca"" Output: [3;0;1] Explanation: Initially s = ""???????"". - Place stamp at index 3 to get ""???abca"". - Place stamp at index 0 to get ""abcabca"". - Place stamp at index 1 to get ""aabcaca"". Constraints: 1 <= stamp.length <= target.length <= 1000 stamp and target consist of lowercase English letters."
Apple,1043,Partition Array for Maximum Sum,Med,"Array, Hash Table",There is a 2D grid of size n x n where each cell of this grid has a lamp that is initially turned off. You are given a 2D array of lamp positions lamps; where lamps[i] = [rowi; coli] indicates that the lamp at grid[rowi][coli] is turned on. Even if the same lamp is listed more than once; it is turned on. When a lamp is turned on; it illuminates its cell and all other cells in the same row; column; or diagonal. You are also given another 2D array queries; where queries[j] = [rowj; colj]. For the jth query; determine whether grid[rowj][colj] is illuminated or not. After answering the jth query; turn off the lamp at grid[rowj][colj] and its 8 adjacent lamps if they exist. A lamp is adjacent if its cell shares either a side or corner with grid[rowj][colj]. Return an array of integers ans; where ans[j] should be 1 if the cell in the jth query was illuminated; or 0 if the lamp was not. Example 1: Input: n = 5; lamps = [[0;0];[4;4]]; queries = [[1;1];[1;0]] Output: [1;0] Explanation: We have the initial grid with all lamps turned off. In the above picture we see the grid after turning on the lamp at grid[0][0] then turning on the lamp at grid[4][4]. The 0th query asks if the lamp at grid[1][1] is illuminated or not (the blue square). It is illuminated; so set ans[0] = 1. Then; we turn off all lamps in the red square. The 1st query asks if the lamp at grid[1][0] is illuminated or not (the blue square). It is not illuminated; so set ans[1] = 0. Then; we turn off all lamps in the red rectangle. Example 2: Input: n = 5; lamps = [[0;0];[4;4]]; queries = [[1;1];[1;1]] Output: [1;1] Example 3: Input: n = 5; lamps = [[0;0];[0;4]]; queries = [[0;4];[0;1];[1;4]] Output: [1;1;0] Constraints: 1 <= n <= 109 0 <= lamps.length <= 20000 0 <= queries.length <= 20000 lamps[i].length == 2 0 <= rowi; coli < n queries[j].length == 2 0 <= rowj; colj < n
Apple,1048,Longest String Chain,Med,"Math, Stack, Simulation",The factorial of a positive integer n is the product of all positive integers less than or equal to n. For example; factorial(10) = 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1. We make a clumsy factorial using the integers in decreasing order by swapping out the multiply operations for a fixed rotation of operations with multiply '*'; divide '/'; add '+'; and subtract '-' in this order. For example; clumsy(10) = 10 * 9 / 8 + 7 - 6 * 5 / 4 + 3 - 2 * 1. However; these operations are still applied using the usual order of operations of arithmetic. We do all multiplication and division steps before any addition or subtraction steps; and multiplication and division steps are processed left to right. Additionally; the division that we use is floor division such that 10 * 9 / 8 = 90 / 8 = 11. Given an integer n; return the clumsy factorial of n. Example 1: Input: n = 4 Output: 7 Explanation: 7 = 4 * 3 / 2 + 1 Example 2: Input: n = 10 Output: 12 Explanation: 12 = 10 * 9 / 8 + 7 - 6 * 5 / 4 + 3 - 2 * 1 Constraints: 1 <= n <= 104
Apple,1115,Print FooBar Alternately,Med,"Array, Math, Geometry",Given an array points where points[i] = [xi; yi] represents a point on the X-Y plane; return true if these points are a boomerang. A boomerang is a set of three points that are all distinct and not in a straight line. Example 1: Input: points = [[1;1];[2;3];[3;2]] Output: true Example 2: Input: points = [[1;1];[2;2];[3;3]] Output: false Constraints: points.length == 3 points[i].length == 2 0 <= xi; yi <= 100
Apple,1291,Sequential Digits,Med,Database,
Apple,1143,Longest Common Subsequence,Med,"Array, Hash Table, Binary Search, Matrix, Counting",
Apple,1174,Immediate Food Delivery II,Med,Database,Table: Product +--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | | unit_price | int | +--------------+---------+ product_id is the primary key (column with unique values) of this table. Each row of this table indicates the name and the price of each product. Table: Sales +-------------+---------+ | Column Name | Type | +-------------+---------+ | seller_id | int | | product_id | int | | buyer_id | int | | sale_date | date | | quantity | int | | price | int | +-------------+---------+ This table can have duplicate rows. product_id is a foreign key (reference column) to the Product table. Each row of this table contains some information about one sale. Write a solution to report the products that were only sold in the first quarter of 2019. That is; between 2019-01-01 and 2019-03-31 inclusive. Return the result table in any order. The result format is in the following example. Example 1: Input: Product table: +------------+--------------+------------+ | product_id | product_name | unit_price | +------------+--------------+------------+ | 1 | S8 | 1000 | | 2 | G4 | 800 | | 3 | iPhone | 1400 | +------------+--------------+------------+ Sales table: +-----------+------------+----------+------------+----------+-------+ | seller_id | product_id | buyer_id | sale_date | quantity | price | +-----------+------------+----------+------------+----------+-------+ | 1 | 1 | 1 | 2019-01-21 | 2 | 2000 | | 1 | 2 | 2 | 2019-02-17 | 1 | 800 | | 2 | 2 | 3 | 2019-06-02 | 1 | 800 | | 3 | 3 | 4 | 2019-05-13 | 2 | 2800 | +-----------+------------+----------+------------+----------+-------+ Output: +-------------+--------------+ | product_id | product_name | +-------------+--------------+ | 1 | S8 | +-------------+--------------+ Explanation: The product with id 1 was only sold in the spring of 2019. The product with id 2 was sold in the spring of 2019 but was also sold after the spring of 2019. The product with id 3 was sold after spring 2019. We return only product 1 as it is the product that was only sold in the spring of 2019.
Apple,1218,Longest Arithmetic Subsequence of Given Difference,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the lowest common ancestor of its deepest leaves. Recall that: The node of a binary tree is a leaf if and only if it has no children The depth of the root of the tree is 0. if the depth of a node is d; the depth of each of its children is d + 1. The lowest common ancestor of a set S of nodes; is the node A with the largest depth such that every node in S is in the subtree with root A. Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4] Output: [2;7;4] Explanation: We return the node with value 2; colored in yellow in the diagram. The nodes coloured in blue are the deepest leaf-nodes of the tree. Note that nodes 6; 0; and 8 are also leaf nodes; but the depth of them is 2; but the depth of nodes 7 and 4 is 3. Example 2: Input: root = [1] Output: [1] Explanation: The root is the deepest node in the tree; and it's the lca of itself. Example 3: Input: root = [0;1;3;null;2] Output: [2] Explanation: The deepest leaf node in the tree is 2; the lca of one node is itself. Constraints: The number of nodes in the tree will be in the range [1; 1000]. 0 <= Node.val <= 1000 The values of the nodes in the tree are unique. Note: This question is the same as 865: https://leetcode.com/problems/smallest-subtree-with-all-the-deepest-nodes/
Apple,1249,Minimum Remove to Make Valid Parentheses,Med,"Array, Hash Table, Binary Search, Design","Implement a SnapshotArray that supports the following interface: SnapshotArray(int length) initializes an array-like data structure with the given length. Initially; each element equals 0. void set(index; val) sets the element at the given index to be equal to val. int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1. int get(index; snap_id) returns the value at the given index; at the time we took the snapshot with the given snap_id Example 1: Input: [""SnapshotArray"";""set"";""snap"";""set"";""get""] [[3];[0;5];[];[0;6];[0;0]] Output: [null;null;0;null;5] Explanation: SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3 snapshotArr.set(0;5); // Set array[0] = 5 snapshotArr.snap(); // Take a snapshot; return snap_id = 0 snapshotArr.set(0;6); snapshotArr.get(0;0); // Get the value of array[0] with snap_id = 0; return 5 Constraints: 1 <= length <= 5 * 104 0 <= index < length 0 <= val <= 109 0 <= snap_id < (the total number of times we call snap()) At most 5 * 104 calls will be made to set; snap; and get."
Apple,1251,Average Selling Price,Easy,"Two Pointers, String, Dynamic Programming, Greedy, Rolling Hash, Hash Function","You are given a string text. You should split it to k substrings (subtext1; subtext2; ...; subtextk) such that: subtexti is a non-empty string. The concatenation of all the substrings is equal to text (i.e.; subtext1 + subtext2 + ... + subtextk == text). subtexti == subtextk - i + 1 for all valid values of i (i.e.; 1 <= i <= k). Return the largest possible value of k. Example 1: Input: text = ""ghiabcdefhelloadamhelloabcdefghi"" Output: 7 Explanation: We can split the string on ""(ghi)(abcdef)(hello)(adam)(hello)(abcdef)(ghi)"". Example 2: Input: text = ""merchant"" Output: 1 Explanation: We can split the string on ""(merchant)"". Example 3: Input: text = ""antaprezatepzapreanta"" Output: 11 Explanation: We can split the string on ""(a)(nt)(a)(pre)(za)(tep)(za)(pre)(a)(nt)(a)"". Constraints: 1 <= text.length <= 1000 text consists only of lowercase English characters."
Apple,1268,Search Suggestions System,Med,Database,Table: Users +----------------+---------+ | Column Name | Type | +----------------+---------+ | user_id | int | | join_date | date | | favorite_brand | varchar | +----------------+---------+ user_id is the primary key (column with unique values) of this table. This table has the info of the users of an online shopping website where users can sell and buy items. Table: Orders +---------------+---------+ | Column Name | Type | +---------------+---------+ | order_id | int | | order_date | date | | item_id | int | | buyer_id | int | | seller_id | int | +---------------+---------+ order_id is the primary key (column with unique values) of this table. item_id is a foreign key (reference column) to the Items table. buyer_id and seller_id are foreign keys to the Users table. Table: Items +---------------+---------+ | Column Name | Type | +---------------+---------+ | item_id | int | | item_brand | varchar | +---------------+---------+ item_id is the primary key (column with unique values) of this table. Write a solution to find for each user; the join date and the number of orders they made as a buyer in 2019. Return the result table in any order. The result format is in the following example. Example 1: Input: Users table: +---------+------------+----------------+ | user_id | join_date | favorite_brand | +---------+------------+----------------+ | 1 | 2018-01-01 | Lenovo | | 2 | 2018-02-09 | Samsung | | 3 | 2018-01-19 | LG | | 4 | 2018-05-21 | HP | +---------+------------+----------------+ Orders table: +----------+------------+---------+----------+-----------+ | order_id | order_date | item_id | buyer_id | seller_id | +----------+------------+---------+----------+-----------+ | 1 | 2019-08-01 | 4 | 1 | 2 | | 2 | 2018-08-02 | 2 | 1 | 3 | | 3 | 2019-08-03 | 3 | 2 | 3 | | 4 | 2018-08-04 | 1 | 4 | 2 | | 5 | 2018-08-04 | 1 | 3 | 4 | | 6 | 2019-08-05 | 2 | 2 | 4 | +----------+------------+---------+----------+-----------+ Items table: +---------+------------+ | item_id | item_brand | +---------+------------+ | 1 | Samsung | | 2 | Lenovo | | 3 | LG | | 4 | HP | +---------+------------+ Output: +-----------+------------+----------------+ | buyer_id | join_date | orders_in_2019 | +-----------+------------+----------------+ | 1 | 2018-01-01 | 1 | | 2 | 2018-02-09 | 2 | | 3 | 2018-01-19 | 0 | | 4 | 2018-05-21 | 0 | +-----------+------------+----------------+
Apple,1282,Group the People Given the Group Size They Belong To,Med,"Array, Hash Table, String, Bit Manipulation, Trie","With respect to a given puzzle string; a word is valid if both the following conditions are satisfied: word contains the first letter of puzzle. For each letter in word; that letter is in puzzle. For example; if the puzzle is ""abcdefg""; then valid words are ""faced""; ""cabbage""; and ""baggage""; while invalid words are ""beefed"" (does not include 'a') and ""based"" (includes 's' which is not in the puzzle). Return an array answer; where answer[i] is the number of words in the given word list words that is valid with respect to the puzzle puzzles[i]. Example 1: Input: words = [""aaaa"";""asas"";""able"";""ability"";""actt"";""actor"";""access""]; puzzles = [""aboveyz"";""abrodyz"";""abslute"";""absoryz"";""actresz"";""gaswxyz""] Output: [1;1;3;2;4;0] Explanation: 1 valid word for ""aboveyz"" : ""aaaa"" 1 valid word for ""abrodyz"" : ""aaaa"" 3 valid words for ""abslute"" : ""aaaa""; ""asas""; ""able"" 2 valid words for ""absoryz"" : ""aaaa""; ""asas"" 4 valid words for ""actresz"" : ""aaaa""; ""asas""; ""actt""; ""access"" There are no valid words for ""gaswxyz"" cause none of the words in the list contains letter 'g'. Example 2: Input: words = [""apple"";""pleas"";""please""]; puzzles = [""aelwxyz"";""aelpxyz"";""aelpsxy"";""saelpxy"";""xaelpsy""] Output: [0;1;3;2;0] Constraints: 1 <= words.length <= 105 4 <= words[i].length <= 50 1 <= puzzles.length <= 104 puzzles[i].length == 7 words[i] and puzzles[i] consist of lowercase English letters. Each puzzles[i] does not contain repeated characters."
Apple,1280,Students and Examinations,Easy,"Array, Sliding Window",
Apple,1326,Minimum Number of Taps to Open to Water a Garden,Hard,"Array, Math, Binary Search, Prefix Sum",Given an integer array nums; return the sum of floor(nums[i] / nums[j]) for all pairs of indices 0 <= i; j < nums.length in the array. Since the answer may be too large; return it modulo 109 + 7. The floor() function returns the integer part of the division. Example 1: Input: nums = [2;5;9] Output: 10 Explanation: floor(2 / 5) = floor(2 / 9) = floor(5 / 9) = 0 floor(2 / 2) = floor(5 / 5) = floor(9 / 9) = 1 floor(5 / 2) = 2 floor(9 / 2) = 4 floor(9 / 5) = 1 We calculate the floor of the division for every pair of indices in the array then sum them up. Example 2: Input: nums = [7;7;7;7;7;7;7] Output: 49 Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105
Apple,1493,Longest Subarray of 1's After Deleting One Element,Med,"Tree, Depth-First Search, Breadth-First Search, Graph",Given an undirected tree consisting of n vertices numbered from 1 to n. A frog starts jumping from vertex 1. In one second; the frog jumps from its current vertex to another unvisited vertex if they are directly connected. The frog can not jump back to a visited vertex. In case the frog can jump to several vertices; it jumps randomly to one of them with the same probability. Otherwise; when the frog can not jump to any unvisited vertex; it jumps forever on the same vertex. The edges of the undirected tree are given in the array edges; where edges[i] = [ai; bi] means that exists an edge connecting the vertices ai and bi. Return the probability that after t seconds the frog is on the vertex target. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: n = 7; edges = [[1;2];[1;3];[1;7];[2;4];[2;6];[3;5]]; t = 2; target = 4 Output: 0.16666666666666666 Explanation: The figure above shows the given graph. The frog starts at vertex 1; jumping with 1/3 probability to the vertex 2 after second 1 and then jumping with 1/2 probability to vertex 4 after second 2. Thus the probability for the frog is on the vertex 4 after 2 seconds is 1/3 * 1/2 = 1/6 = 0.16666666666666666. Example 2: Input: n = 7; edges = [[1;2];[1;3];[1;7];[2;4];[2;6];[3;5]]; t = 1; target = 7 Output: 0.3333333333333333 Explanation: The figure above shows the given graph. The frog starts at vertex 1; jumping with 1/3 = 0.3333333333333333 probability to the vertex 7 after second 1. Constraints: 1 <= n <= 100 edges.length == n - 1 edges[i].length == 2 1 <= ai; bi <= n 1 <= t <= 50 1 <= target <= n
Apple,1547,Minimum Cost to Cut a Stick,Hard,"Array, Hash Table, String","You are given the array paths; where paths[i] = [cityAi; cityBi] means there exists a direct path going from cityAi to cityBi. Return the destination city; that is; the city without any path outgoing to another city. It is guaranteed that the graph of paths forms a line without any loop; therefore; there will be exactly one destination city. Example 1: Input: paths = [[""London"";""New York""];[""New York"";""Lima""];[""Lima"";""Sao Paulo""]] Output: ""Sao Paulo"" Explanation: Starting at ""London"" city you will reach ""Sao Paulo"" city which is the destination city. Your trip consist of: ""London"" -> ""New York"" -> ""Lima"" -> ""Sao Paulo"". Example 2: Input: paths = [[""B"";""C""];[""D"";""B""];[""C"";""A""]] Output: ""A"" Explanation: All possible trips are: ""D"" -> ""B"" -> ""C"" -> ""A"". ""B"" -> ""C"" -> ""A"". ""C"" -> ""A"". ""A"". Clearly the destination city is ""A"". Example 3: Input: paths = [[""A"";""Z""]] Output: ""Z"" Constraints: 1 <= paths.length <= 100 paths[i].length == 2 1 <= cityAi.length; cityBi.length <= 10 cityAi != cityBi All strings consist of lowercase and uppercase English letters and the space character."
Apple,1615,Maximal Network Rank,Med,"Array, Two Pointers, Binary Search, Sorting",You are given the array nums consisting of n positive integers. You computed the sum of all non-empty continuous subarrays from the array and then sorted them in non-decreasing order; creating a new array of n * (n + 1) / 2 numbers. Return the sum of the numbers from index left to index right (indexed from 1); inclusive; in the new array. Since the answer can be a huge number return it modulo 109 + 7. Example 1: Input: nums = [1;2;3;4]; n = 4; left = 1; right = 5 Output: 13 Explanation: All subarray sums are 1; 3; 6; 10; 2; 5; 9; 3; 7; 4. After sorting them in non-decreasing order we have the new array [1; 2; 3; 3; 4; 5; 6; 7; 9; 10]. The sum of the numbers from index le = 1 to ri = 5 is 1 + 2 + 3 + 3 + 4 = 13. Example 2: Input: nums = [1;2;3;4]; n = 4; left = 3; right = 4 Output: 6 Explanation: The given array is the same as example 1. We have the new array [1; 2; 3; 3; 4; 5; 6; 7; 9; 10]. The sum of the numbers from index le = 3 to ri = 4 is 3 + 3 = 6. Example 3: Input: nums = [1;2;3;4]; n = 4; left = 1; right = 10 Output: 50 Constraints: n == nums.length 1 <= nums.length <= 1000 1 <= nums[i] <= 100 1 <= left <= right <= n * (n + 1) / 2
Apple,1657,Determine if Two Strings Are Close,Med,"Array, Simulation",Given an integer array arr of distinct integers and an integer k. A game will be played between the first two elements of the array (i.e. arr[0] and arr[1]). In each round of the game; we compare arr[0] with arr[1]; the larger integer wins and remains at position 0; and the smaller integer moves to the end of the array. The game ends when an integer wins k consecutive rounds. Return the integer which will win the game. It is guaranteed that there will be a winner of the game. Example 1: Input: arr = [2;1;3;5;4;6;7]; k = 2 Output: 5 Explanation: Let's see the rounds of the game: Round | arr | winner | win_count 1 | [2;1;3;5;4;6;7] | 2 | 1 2 | [2;3;5;4;6;7;1] | 3 | 1 3 | [3;5;4;6;7;1;2] | 5 | 1 4 | [5;4;6;7;1;2;3] | 5 | 2 So we can see that 4 rounds will be played and 5 is the winner because it wins 2 consecutive games. Example 2: Input: arr = [3;2;1]; k = 10 Output: 3 Explanation: 3 will win the first 10 rounds consecutively. Constraints: 2 <= arr.length <= 105 1 <= arr[i] <= 106 arr contains distinct integers. 1 <= k <= 109
Apple,1661,Average Time of Process per Machine,Easy,Graph,Given a directed acyclic graph; with n vertices numbered from 0 to n-1; and an array edges where edges[i] = [fromi; toi] represents a directed edge from node fromi to node toi. Find the smallest set of vertices from which all nodes in the graph are reachable. It's guaranteed that a unique solution exists. Notice that you can return the vertices in any order. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;5];[3;4];[4;2]] Output: [0;3] Explanation: It's not possible to reach all the nodes from a single vertex. From 0 we can reach [0;1;2;5]. From 3 we can reach [3;4;2;5]. So we output [0;3]. Example 2: Input: n = 5; edges = [[0;1];[2;1];[3;1];[1;4];[2;4]] Output: [0;2;3] Explanation: Notice that vertices 0; 3 and 2 are not reachable from any other node; so we must include them. Also any of these vertices can reach nodes 1 and 4. Constraints: 2 <= n <= 10^5 1 <= edges.length <= min(10^5; n * (n - 1) / 2) edges[i].length == 2 0 <= fromi; toi < n All pairs (fromi; toi) are distinct.
Apple,1773,Count Items Matching a Rule,Easy,Database,Table: Users +-------------+---------+ | Column Name | Type | +-------------+---------+ | user_id | int | | user_name | varchar | +-------------+---------+ user_id is the primary key (column with unique values) for this table. Each row of this table contains the name and the id of a user. Table: Register +-------------+---------+ | Column Name | Type | +-------------+---------+ | contest_id | int | | user_id | int | +-------------+---------+ (contest_id; user_id) is the primary key (combination of columns with unique values) for this table. Each row of this table contains the id of a user and the contest they registered into. Write a solution to find the percentage of the users registered in each contest rounded to two decimals. Return the result table ordered by percentage in descending order. In case of a tie; order it by contest_id in ascending order. The result format is in the following example. Example 1: Input: Users table: +---------+-----------+ | user_id | user_name | +---------+-----------+ | 6 | Alice | | 2 | Bob | | 7 | Alex | +---------+-----------+ Register table: +------------+---------+ | contest_id | user_id | +------------+---------+ | 215 | 6 | | 209 | 2 | | 208 | 2 | | 210 | 6 | | 208 | 6 | | 209 | 7 | | 209 | 6 | | 215 | 7 | | 208 | 7 | | 210 | 2 | | 207 | 2 | | 210 | 7 | +------------+---------+ Output: +------------+------------+ | contest_id | percentage | +------------+------------+ | 208 | 100.0 | | 209 | 100.0 | | 210 | 100.0 | | 215 | 66.67 | | 207 | 33.33 | +------------+------------+ Explanation: All the users registered in contests 208; 209; and 210. The percentage is 100% and we sort them in the answer table by contest_id in ascending order. Alice and Alex registered in contest 215 and the percentage is ((2/3) * 100) = 66.67% Bob registered in contest 207 and the percentage is ((1/3) * 100) = 33.33%
Apple,1793,Maximum Score of a Good Subarray,Hard,"Array, Hash Table, Prefix Sum",You are given an integer array nums of even length n and an integer limit. In one move; you can replace any integer from nums with another integer between 1 and limit; inclusive. The array nums is complementary if for all indices i (0-indexed); nums[i] + nums[n - 1 - i] equals the same number. For example; the array [1;2;3;4] is complementary because for all indices i; nums[i] + nums[n - 1 - i] = 5. Return the minimum number of moves required to make nums complementary. Example 1: Input: nums = [1;2;4;3]; limit = 4 Output: 1 Explanation: In 1 move; you can change nums to [1;2;2;3] (underlined elements are changed). nums[0] + nums[3] = 1 + 3 = 4. nums[1] + nums[2] = 2 + 2 = 4. nums[2] + nums[1] = 2 + 2 = 4. nums[3] + nums[0] = 3 + 1 = 4. Therefore; nums[i] + nums[n-1-i] = 4 for every i; so nums is complementary. Example 2: Input: nums = [1;2;2;1]; limit = 2 Output: 2 Explanation: In 2 moves; you can change nums to [2;2;2;2]. You cannot change any number to 3 since 3 > limit. Example 3: Input: nums = [1;2;1;2]; limit = 2 Output: 0 Explanation: nums is already complementary. Constraints: n == nums.length 2 <= n <= 105 1 <= nums[i] <= limit <= 105 n is even.
Apple,1857,Largest Color Value in a Directed Graph,Hard,,
Apple,1920,Build Array from Permutation,Easy,"Math, String","You are given coordinates; a string that represents the coordinates of a square of the chessboard. Below is a chessboard for your reference. Return true if the square is white; and false if the square is black. The coordinate will always represent a valid chessboard square. The coordinate will always have the letter first; and the number second. Example 1: Input: coordinates = ""a1"" Output: false Explanation: From the chessboard above; the square with coordinates ""a1"" is black; so return false. Example 2: Input: coordinates = ""h3"" Output: true Explanation: From the chessboard above; the square with coordinates ""h3"" is white; so return true. Example 3: Input: coordinates = ""c7"" Output: false Constraints: coordinates.length == 2 'a' <= coordinates[0] <= 'h' '1' <= coordinates[1] <= '8'"
Apple,2090,K Radius Subarray Averages,Med,"Dynamic Programming, Graph, Topological Sort, Shortest Path",You are in a city that consists of n intersections numbered from 0 to n - 1 with bi-directional roads between some intersections. The inputs are generated such that you can reach any intersection from any other intersection and that there is at most one road between any two intersections. You are given an integer n and a 2D integer array roads where roads[i] = [ui; vi; timei] means that there is a road between intersections ui and vi that takes timei minutes to travel. You want to know in how many ways you can travel from intersection 0 to intersection n - 1 in the shortest amount of time. Return the number of ways you can arrive at your destination in the shortest amount of time. Since the answer may be large; return it modulo 109 + 7. Example 1: Input: n = 7; roads = [[0;6;7];[0;1;2];[1;2;3];[1;3;3];[6;3;3];[3;5;1];[6;5;1];[2;5;1];[0;4;5];[4;6;2]] Output: 4 Explanation: The shortest amount of time it takes to go from intersection 0 to intersection 6 is 7 minutes. The four ways to get there in 7 minutes are: - 0 ➝ 6 - 0 ➝ 4 ➝ 6 - 0 ➝ 1 ➝ 2 ➝ 5 ➝ 6 - 0 ➝ 1 ➝ 3 ➝ 5 ➝ 6 Example 2: Input: n = 2; roads = [[1;0;10]] Output: 1 Explanation: There is only one way to go from intersection 0 to intersection 1; and it takes 10 minutes. Constraints: 1 <= n <= 200 n - 1 <= roads.length <= n * (n - 1) / 2 roads[i].length == 3 0 <= ui; vi <= n - 1 1 <= timei <= 109 ui != vi There is at most one road connecting any two intersections. You can reach any intersection from any other intersection.
Apple,2187,Minimum Time to Complete Trips,Med,"Math, String, Dynamic Programming, Combinatorics","Given a string word; return the sum of the number of vowels ('a'; 'e'; 'i'; 'o'; and 'u') in every substring of word. A substring is a contiguous (non-empty) sequence of characters within a string. Note: Due to the large constraints; the answer may not fit in a signed 32-bit integer. Please be careful during the calculations. Example 1: Input: word = ""aba"" Output: 6 Explanation: All possible substrings are: ""a""; ""ab""; ""aba""; ""b""; ""ba""; and ""a"". - ""b"" has 0 vowels in it - ""a""; ""ab""; ""ba""; and ""a"" have 1 vowel each - ""aba"" has 2 vowels in it Hence; the total sum of vowels = 0 + 1 + 1 + 1 + 1 + 2 = 6. Example 2: Input: word = ""abc"" Output: 3 Explanation: All possible substrings are: ""a""; ""ab""; ""abc""; ""b""; ""bc""; and ""c"". - ""a""; ""ab""; and ""abc"" have 1 vowel each - ""b""; ""bc""; and ""c"" have 0 vowels each Hence; the total sum of vowels = 1 + 1 + 1 + 0 + 0 + 0 = 3. Example 3: Input: word = ""ltcd"" Output: 0 Explanation: There are no vowels in any substring of ""ltcd"". Constraints: 1 <= word.length <= 105 word consists of lowercase English letters."
Apple,2236,Root Equals Sum of Children,Easy,"Linked List, Two Pointers, Stack",In a linked list of size n; where n is even; the ith node (0-indexed) of the linked list is known as the twin of the (n-1-i)th node; if 0 <= i <= (n / 2) - 1. For example; if n = 4; then node 0 is the twin of node 3; and node 1 is the twin of node 2. These are the only nodes with twins for n = 4. The twin sum is defined as the sum of a node and its twin. Given the head of a linked list with even length; return the maximum twin sum of the linked list. Example 1: Input: head = [5;4;2;1] Output: 6 Explanation: Nodes 0 and 1 are the twins of nodes 3 and 2; respectively. All have twin sum = 6. There are no other nodes with twins in the linked list. Thus; the maximum twin sum of the linked list is 6. Example 2: Input: head = [4;2;2;3] Output: 7 Explanation: The nodes with twins present in this linked list are: - Node 0 is the twin of node 3 having a twin sum of 4 + 3 = 7. - Node 1 is the twin of node 2 having a twin sum of 2 + 2 = 4. Thus; the maximum twin sum of the linked list is max(7; 4) = 7. Example 3: Input: head = [1;100000] Output: 100001 Explanation: There is only one node with a twin in the linked list having twin sum of 1 + 100000 = 100001. Constraints: The number of nodes in the list is an even integer in the range [2; 105]. 1 <= Node.val <= 105
Apple,2352,Equal Row and Column Pairs,Med,"Array, Greedy, Design","There is an ATM machine that stores banknotes of 5 denominations: 20; 50; 100; 200; and 500 dollars. Initially the ATM is empty. The user can use the machine to deposit or withdraw any amount of money. When withdrawing; the machine prioritizes using banknotes of larger values. For example; if you want to withdraw $300 and there are 2 $50 banknotes; 1 $100 banknote; and 1 $200 banknote; then the machine will use the $100 and $200 banknotes. However; if you try to withdraw $600 and there are 3 $200 banknotes and 1 $500 banknote; then the withdraw request will be rejected because the machine will first try to use the $500 banknote and then be unable to use banknotes to complete the remaining $100. Note that the machine is not allowed to use the $200 banknotes instead of the $500 banknote. Implement the ATM class: ATM() Initializes the ATM object. void deposit(int[] banknotesCount) Deposits new banknotes in the order $20; $50; $100; $200; and $500. int[] withdraw(int amount) Returns an array of length 5 of the number of banknotes that will be handed to the user in the order $20; $50; $100; $200; and $500; and update the number of banknotes in the ATM after withdrawing. Returns [-1] if it is not possible (do not withdraw any banknotes in this case). Example 1: Input [""ATM""; ""deposit""; ""withdraw""; ""deposit""; ""withdraw""; ""withdraw""] [[]; [[0;0;1;2;1]]; [600]; [[0;1;0;1;1]]; [600]; [550]] Output [null; null; [0;0;1;0;1]; null; [-1]; [0;1;0;0;1]] Explanation ATM atm = new ATM(); atm.deposit([0;0;1;2;1]); // Deposits 1 $100 banknote; 2 $200 banknotes; // and 1 $500 banknote. atm.withdraw(600); // Returns [0;0;1;0;1]. The machine uses 1 $100 banknote // and 1 $500 banknote. The banknotes left over in the // machine are [0;0;0;2;0]. atm.deposit([0;1;0;1;1]); // Deposits 1 $50; $200; and $500 banknote. // The banknotes in the machine are now [0;1;0;3;1]. atm.withdraw(600); // Returns [-1]. The machine will try to use a $500 banknote // and then be unable to complete the remaining $100; // so the withdraw request will be rejected. // Since the request is rejected; the number of banknotes // in the machine is not modified. atm.withdraw(550); // Returns [0;1;0;0;1]. The machine uses 1 $50 banknote // and 1 $500 banknote. Constraints: banknotesCount.length == 5 0 <= banknotesCount[i] <= 109 1 <= amount <= 109 At most 5000 calls in total will be made to withdraw and deposit. At least one call will be made to each function withdraw and deposit. Sum of banknotesCount[i] in all deposits doesn't exceed 109"
Apple,2413,Smallest Even Multiple,Easy,"Hash Table, Design, Heap (Priority Queue), Ordered Set","You have a set which contains all positive integers [1; 2; 3; 4; 5; ...]. Implement the SmallestInfiniteSet class: SmallestInfiniteSet() Initializes the SmallestInfiniteSet object to contain all positive integers. int popSmallest() Removes and returns the smallest integer contained in the infinite set. void addBack(int num) Adds a positive integer num back into the infinite set; if it is not already in the infinite set. Example 1: Input [""SmallestInfiniteSet""; ""addBack""; ""popSmallest""; ""popSmallest""; ""popSmallest""; ""addBack""; ""popSmallest""; ""popSmallest""; ""popSmallest""] [[]; [2]; []; []; []; [1]; []; []; []] Output [null; null; 1; 2; 3; null; 1; 4; 5] Explanation SmallestInfiniteSet smallestInfiniteSet = new SmallestInfiniteSet(); smallestInfiniteSet.addBack(2); // 2 is already in the set; so no change is made. smallestInfiniteSet.popSmallest(); // return 1; since 1 is the smallest number; and remove it from the set. smallestInfiniteSet.popSmallest(); // return 2; and remove it from the set. smallestInfiniteSet.popSmallest(); // return 3; and remove it from the set. smallestInfiniteSet.addBack(1); // 1 is added back to the set. smallestInfiniteSet.popSmallest(); // return 1; since 1 was added back to the set and // is the smallest number; and remove it from the set. smallestInfiniteSet.popSmallest(); // return 4; and remove it from the set. smallestInfiniteSet.popSmallest(); // return 5; and remove it from the set. Constraints: 1 <= num <= 1000 At most 1000 calls will be made in total to popSmallest and addBack."
Apple,2439,Minimize Maximum of Array,Med,"Depth-First Search, Graph, Topological Sort",You are given a directed graph of n nodes numbered from 0 to n - 1; where each node has at most one outgoing edge. The graph is represented with a given 0-indexed array edges of size n; indicating that there is a directed edge from node i to node edges[i]. If there is no outgoing edge from node i; then edges[i] == -1. Return the length of the longest cycle in the graph. If no cycle exists; return -1. A cycle is a path that starts and ends at the same node. Example 1: Input: edges = [3;3;4;2;3] Output: 3 Explanation: The longest cycle in the graph is the cycle: 2 -> 4 -> 3 -> 2. The length of this cycle is 3; so 3 is returned. Example 2: Input: edges = [2;-1;3;1] Output: -1 Explanation: There are no cycles in this graph. Constraints: n == edges.length 2 <= n <= 105 -1 <= edges[i] < n edges[i] != i
Apple,2485,Find the Pivot Integer,Easy,"Array, Stack, Sorting, Monotonic Stack",
Apple,2742,Painting the Walls,Hard,,"Write code that enhances all arrays such that you can call the array.groupBy(fn) method on any array and it will return a grouped version of the array. A grouped array is an object where each key is the output of fn(arr[i]) and each value is an array containing all items in the original array which generate that key. The provided callback fn will accept an item in the array and return a string key. The order of each value list should be the order the items appear in the array. Any order of keys is acceptable. Please solve it without lodash's _.groupBy function. Example 1: Input: array = [ {""id"":""1""}; {""id"":""1""}; {""id"":""2""} ]; fn = function (item) { return item.id; } Output: { ""1"": [{""id"": ""1""}; {""id"": ""1""}]; ""2"": [{""id"": ""2""}] } Explanation: Output is from array.groupBy(fn). The selector function gets the ""id"" out of each item in the array. There are two objects with an ""id"" of 1. Both of those objects are put in the first array. There is one object with an ""id"" of 2. That object is put in the second array. Example 2: Input: array = [ [1; 2; 3]; [1; 3; 5]; [1; 5; 9] ] fn = function (list) { return String(list[0]); } Output: { ""1"": [[1; 2; 3]; [1; 3; 5]; [1; 5; 9]] } Explanation: The array can be of any type. In this case; the selector function defines the key as being the first element in the array. All the arrays have 1 as their first element so they are grouped together. { ""1"": [[1; 2; 3]; [1; 3; 5]; [1; 5; 9]] } Example 3: Input: array = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10] fn = function (n) { return String(n > 5); } Output: { ""true"": [6; 7; 8; 9; 10]; ""false"": [1; 2; 3; 4; 5] } Explanation: The selector function splits the array by whether each number is greater than 5. Constraints: 0 <= array.length <= 105 fn returns a string"
Apple,2703,Return Length of Arguments Passed,Easy,"Array, Segment Tree",You are given two 0-indexed arrays nums1 and nums2 and a 2D array queries of queries. There are three types of queries: For a query of type 1; queries[i] = [1; l; r]. Flip the values from 0 to 1 and from 1 to 0 in nums1 from index l to index r. Both l and r are 0-indexed. For a query of type 2; queries[i] = [2; p; 0]. For every index 0 <= i < n; set nums2[i] = nums2[i] + nums1[i] * p. For a query of type 3; queries[i] = [3; 0; 0]. Find the sum of the elements in nums2. Return an array containing all the answers to the third type queries. Example 1: Input: nums1 = [1;0;1]; nums2 = [0;0;0]; queries = [[1;1;1];[2;1;0];[3;0;0]] Output: [3] Explanation: After the first query nums1 becomes [1;1;1]. After the second query; nums2 becomes [1;1;1]; so the answer to the third query is 3. Thus; [3] is returned. Example 2: Input: nums1 = [1]; nums2 = [5]; queries = [[2;0;0];[3;0;0]] Output: [5] Explanation: After the first query; nums2 remains [5]; so the answer to the second query is 5. Thus; [5] is returned. Constraints: 1 <= nums1.length;nums2.length <= 105 nums1.length = nums2.length 1 <= queries.length <= 105 queries[i].length = 3 0 <= l <= r <= nums1.length - 1 0 <= p <= 106 0 <= nums1[i] <= 1 0 <= nums2[i] <= 109
Apple,2877,Create a DataFrame from List,Easy,"String, Greedy, Enumeration","Given three strings a; b; and c; your task is to find a string that has the minimum length and contains all three strings as substrings. If there are multiple such strings; return the lexicographically smallest one. Return a string denoting the answer to the problem. Notes A string a is lexicographically smaller than a string b (of the same length) if in the first position where a and b differ; string a has a letter that appears earlier in the alphabet than the corresponding letter in b. A substring is a contiguous sequence of characters within a string. Example 1: Input: a = ""abc""; b = ""bca""; c = ""aaa"" Output: ""aaabca"" Explanation: We show that ""aaabca"" contains all the given strings: a = ans[2...4]; b = ans[3..5]; c = ans[0..2]. It can be shown that the length of the resulting string would be at least 6 and ""aaabca"" is the lexicographically smallest one. Example 2: Input: a = ""ab""; b = ""ba""; c = ""aba"" Output: ""aba"" Explanation: We show that the string ""aba"" contains all the given strings: a = ans[0..1]; b = ans[1..2]; c = ans[0..2]. Since the length of c is 3; the length of the resulting string would be at least 3. It can be shown that ""aba"" is the lexicographically smallest one. Constraints: 1 <= a.length; b.length; c.length <= 100 a; b; c consist only of lowercase English letters."
Apple,2870,Minimum Number of Operations to Make Array Empty,Med,"Array, Enumeration",You are given a 0-indexed integer array nums. A subarray s of length m is called alternating if: m is greater than 1. s1 = s0 + 1. The 0-indexed subarray s looks like [s0; s1; s0; s1;...;s(m-1) % 2]. In other words; s1 - s0 = 1; s2 - s1 = -1; s3 - s2 = 1; s4 - s3 = -1; and so on up to s[m - 1] - s[m - 2] = (-1)m. Return the maximum length of all alternating subarrays present in nums or -1 if no such subarray exists. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [2;3;4;3;4] Output: 4 Explanation: The alternating subarrays are [2; 3]; [3;4]; [3;4;3]; and [3;4;3;4]. The longest of these is [3;4;3;4]; which is of length 4. Example 2: Input: nums = [4;5;6] Output: 2 Explanation: [4;5] and [5;6] are the only two alternating subarrays. They are both of length 2. Constraints: 2 <= nums.length <= 100 1 <= nums[i] <= 104
Apple,2962,Count Subarrays Where Max Element Appears at Least K Times,Med,,
Apple,3040,Maximum Number of Operations With the Same Score II,Med,,
Apple,30,Substring with Concatenation of All Words,Hard,"Hash Table, String, Sliding Window","You are given a string s and an array of strings words. All the strings of words are of the same length. A concatenated string is a string that exactly contains all the strings of any permutation of words concatenated. For example; if words = [""ab"";""cd"";""ef""]; then ""abcdef""; ""abefcd""; ""cdabef""; ""cdefab""; ""efabcd""; and ""efcdab"" are all concatenated strings. ""acdbef"" is not a concatenated string because it is not the concatenation of any permutation of words. Return an array of the starting indices of all the concatenated substrings in s. You can return the answer in any order. Example 1: Input: s = ""barfoothefoobarman""; words = [""foo"";""bar""] Output: [0;9] Explanation: The substring starting at 0 is ""barfoo"". It is the concatenation of [""bar"";""foo""] which is a permutation of words. The substring starting at 9 is ""foobar"". It is the concatenation of [""foo"";""bar""] which is a permutation of words. Example 2: Input: s = ""wordgoodgoodgoodbestword""; words = [""word"";""good"";""best"";""word""] Output: [] Explanation: There is no concatenated substring. Example 3: Input: s = ""barfoofoobarthefoobarman""; words = [""bar"";""foo"";""the""] Output: [6;9;12] Explanation: The substring starting at 6 is ""foobarthe"". It is the concatenation of [""foo"";""bar"";""the""]. The substring starting at 9 is ""barthefoo"". It is the concatenation of [""bar"";""the"";""foo""]. The substring starting at 12 is ""thefoobar"". It is the concatenation of [""the"";""foo"";""bar""]. Constraints: 1 <= s.length <= 104 1 <= words.length <= 5000 1 <= words[i].length <= 30 s and words[i] consist of lowercase English letters."
Apple,65,Valid Number,Hard,String,"Given a string s; return whether s is a valid number. For example; all the following are valid numbers: ""2""; ""0089""; ""-0.1""; ""+3.14""; ""4.""; ""-.9""; ""2e10""; ""-90E3""; ""3e+7""; ""+6e-1""; ""53.5e93""; ""-123.456e789""; while the following are not valid numbers: ""abc""; ""1a""; ""1e""; ""e3""; ""99e2.5""; ""--6""; ""-+3""; ""95a54e53"". Formally; a valid number is defined using one of the following definitions: An integer number followed by an optional exponent. A decimal number followed by an optional exponent. An integer number is defined with an optional sign '-' or '+' followed by digits. A decimal number is defined with an optional sign '-' or '+' followed by one of the following definitions: Digits followed by a dot '.'. Digits followed by a dot '.' followed by digits. A dot '.' followed by digits. An exponent is defined with an exponent notation 'e' or 'E' followed by an integer number. The digits are defined as one or more digits. Example 1: Input: s = ""0"" Output: true Example 2: Input: s = ""e"" Output: false Example 3: Input: s = ""."" Output: false Constraints: 1 <= s.length <= 20 s consists of only English letters (both uppercase and lowercase); digits (0-9); plus '+'; minus '-'; or dot '.'."
Apple,90,Subsets II,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums that may contain duplicates; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;2] Output: [[];[1];[1;2];[1;2;2];[2];[2;2]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10
Apple,93,Restore IP Addresses,Med,"String, Backtracking","A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. For example; ""0.1.2.201"" and ""192.168.1.1"" are valid IP addresses; but ""0.011.255.245""; ""192.168.1.312"" and ""192.168@1.1"" are invalid IP addresses. Given a string s containing only digits; return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order. Example 1: Input: s = ""25525511135"" Output: [""255.255.11.135"";""255.255.111.35""] Example 2: Input: s = ""0000"" Output: [""0.0.0.0""] Example 3: Input: s = ""101023"" Output: [""1.0.10.23"";""1.0.102.3"";""10.1.0.23"";""10.10.2.3"";""101.0.2.3""] Constraints: 1 <= s.length <= 20 s consists of digits only."
Apple,96,Unique Binary Search Trees,Med,"Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree",Given an integer n; return the number of structurally unique BST's (binary search trees) which has exactly n nodes of unique values from 1 to n. Example 1: Input: n = 3 Output: 5 Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 19
Apple,100,Same Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the roots of two binary trees p and q; write a function to check if they are the same or not. Two binary trees are considered the same if they are structurally identical; and the nodes have the same value. Example 1: Input: p = [1;2;3]; q = [1;2;3] Output: true Example 2: Input: p = [1;2]; q = [1;null;2] Output: false Example 3: Input: p = [1;2;1]; q = [1;1;2] Output: false Constraints: The number of nodes in both trees is in the range [0; 100]. -104 <= Node.val <= 104
Apple,111,Minimum Depth of Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given a binary tree; find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. Note: A leaf is a node with no children. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 2 Example 2: Input: root = [2;null;3;null;4;null;5;null;6] Output: 5 Constraints: The number of nodes in the tree is in the range [0; 105]. -1000 <= Node.val <= 1000
Apple,116,Populating Next Right Pointers in Each Node,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given a perfect binary tree where all leaves are on the same level; and every parent has two children. The binary tree has the following definition: struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;6;7] Output: [1;#;2;3;#;4;5;6;7;#] Explanation: Given the above perfect binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 212 - 1]. -1000 <= Node.val <= 1000 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Apple,119,Pascal's Triangle II,Easy,"Array, Dynamic Programming",Given an integer rowIndex; return the rowIndexth (0-indexed) row of the Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: rowIndex = 3 Output: [1;3;3;1] Example 2: Input: rowIndex = 0 Output: [1] Example 3: Input: rowIndex = 1 Output: [1;1] Constraints: 0 <= rowIndex <= 33 Follow up: Could you optimize your algorithm to use only O(rowIndex) extra space?
Apple,130,Surrounded Regions,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","You are given an m x n matrix board containing letters 'X' and 'O'; capture regions that are surrounded: Connect: A cell is connected to adjacent cells horizontally or vertically. Region: To form a region connect every 'O' cell. Surround: The region is surrounded with 'X' cells if you can connect the region with 'X' cells and none of the region cells are on the edge of the board. A surrounded region is captured by replacing all 'O's with 'X's in the input matrix board. Example 1: Input: board = [[""X"";""X"";""X"";""X""];[""X"";""O"";""O"";""X""];[""X"";""X"";""O"";""X""];[""X"";""O"";""X"";""X""]] Output: [[""X"";""X"";""X"";""X""];[""X"";""X"";""X"";""X""];[""X"";""X"";""X"";""X""];[""X"";""O"";""X"";""X""]] Explanation: In the above diagram; the bottom region is not captured because it is on the edge of the board and cannot be surrounded. Example 2: Input: board = [[""X""]] Output: [[""X""]] Constraints: m == board.length n == board[i].length 1 <= m; n <= 200 board[i][j] is 'X' or 'O'."
Apple,144,Binary Tree Preorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the preorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [1;2;3] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [1;2;4;5;6;7;3;8;9] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Apple,150,Evaluate Reverse Polish Notation,Med,"Array, Math, Stack","You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression. Return an integer that represents the value of the expression. Note that: The valid operators are '+'; '-'; '*'; and '/'. Each operand may be an integer or another expression. The division between two integers always truncates toward zero. There will not be any division by zero. The input represents a valid arithmetic expression in a reverse polish notation. The answer and all the intermediate calculations can be represented in a 32-bit integer. Example 1: Input: tokens = [""2"";""1"";""+"";""3"";""*""] Output: 9 Explanation: ((2 + 1) * 3) = 9 Example 2: Input: tokens = [""4"";""13"";""5"";""/"";""+""] Output: 6 Explanation: (4 + (13 / 5)) = 6 Example 3: Input: tokens = [""10"";""6"";""9"";""3"";""+"";""-11"";""*"";""/"";""*"";""17"";""+"";""5"";""+""] Output: 22 Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 = ((10 * (6 / (12 * -11))) + 17) + 5 = ((10 * (6 / -132)) + 17) + 5 = ((10 * 0) + 17) + 5 = (0 + 17) + 5 = 17 + 5 = 22 Constraints: 1 <= tokens.length <= 104 tokens[i] is either an operator: ""+""; ""-""; ""*""; or ""/""; or an integer in the range [-200; 200]."
Apple,154,Find Minimum in Rotated Sorted Array II,Hard,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;4;4;5;6;7] might become: [4;5;6;7;0;1;4] if it was rotated 4 times. [0;1;4;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums that may contain duplicates; return the minimum element of this array. You must decrease the overall operation steps as much as possible. Example 1: Input: nums = [1;3;5] Output: 1 Example 2: Input: nums = [2;2;2;0;1] Output: 0 Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 nums is sorted and rotated between 1 and n times. Follow up: This problem is similar to Find Minimum in Rotated Sorted Array; but nums may contain duplicates. Would this affect the runtime complexity? How and why?
Apple,176,Second Highest Salary,Med,Database,Table: Employee +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | salary | int | +-------------+------+ id is the primary key (column with unique values) for this table. Each row of this table contains information about the salary of an employee. Write a solution to find the second highest distinct salary from the Employee table. If there is no second highest salary; return null (return None in Pandas). The result format is in the following example. Example 1: Input: Employee table: +----+--------+ | id | salary | +----+--------+ | 1 | 100 | | 2 | 200 | | 3 | 300 | +----+--------+ Output: +---------------------+ | SecondHighestSalary | +---------------------+ | 200 | +---------------------+ Example 2: Input: Employee table: +----+--------+ | id | salary | +----+--------+ | 1 | 100 | +----+--------+ Output: +---------------------+ | SecondHighestSalary | +---------------------+ | null | +---------------------+
Apple,196,Delete Duplicate Emails,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | email | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table contains an email. The emails will not contain uppercase letters. Write a solution to delete all duplicate emails; keeping only one unique email with the smallest id. For SQL users; please note that you are supposed to write a DELETE statement and not a SELECT one. For Pandas users; please note that you are supposed to modify Person in place. After running your script; the answer shown is the Person table. The driver will first compile and run your piece of code and then show the Person table. The final order of the Person table does not matter. The result format is in the following example. Example 1: Input: Person table: +----+------------------+ | id | email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | | 3 | john@example.com | +----+------------------+ Output: +----+------------------+ | id | email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | +----+------------------+ Explanation: john@example.com is repeated two times. We keep the row with the smallest Id = 1.
Apple,201,Bitwise AND of Numbers Range,Med,Bit Manipulation,Given two integers left and right that represent the range [left; right]; return the bitwise AND of all numbers in this range; inclusive. Example 1: Input: left = 5; right = 7 Output: 4 Example 2: Input: left = 0; right = 0 Output: 0 Example 3: Input: left = 1; right = 2147483647 Output: 0 Constraints: 0 <= left <= right <= 231 - 1
Apple,203,Remove Linked List Elements,Easy,"Linked List, Recursion",Given the head of a linked list and an integer val; remove all the nodes of the linked list that has Node.val == val; and return the new head. Example 1: Input: head = [1;2;6;3;4;5;6]; val = 6 Output: [1;2;3;4;5] Example 2: Input: head = []; val = 1 Output: [] Example 3: Input: head = [7;7;7;7]; val = 7 Output: [] Constraints: The number of nodes in the list is in the range [0; 104]. 1 <= Node.val <= 50 0 <= val <= 50
Apple,211,Design Add and Search Words Data Structure,Med,"String, Depth-First Search, Design, Trie","Design a data structure that supports adding new words and finding if a string matches any previously added string. Implement the WordDictionary class: WordDictionary() Initializes the object. void addWord(word) Adds word to the data structure; it can be matched later. bool search(word) Returns true if there is any string in the data structure that matches word or false otherwise. word may contain dots '.' where dots can be matched with any letter. Example: Input [""WordDictionary"";""addWord"";""addWord"";""addWord"";""search"";""search"";""search"";""search""] [[];[""bad""];[""dad""];[""mad""];[""pad""];[""bad""];["".ad""];[""b..""]] Output [null;null;null;null;false;true;true;true] Explanation WordDictionary wordDictionary = new WordDictionary(); wordDictionary.addWord(""bad""); wordDictionary.addWord(""dad""); wordDictionary.addWord(""mad""); wordDictionary.search(""pad""); // return False wordDictionary.search(""bad""); // return True wordDictionary.search("".ad""); // return True wordDictionary.search(""b..""); // return True Constraints: 1 <= word.length <= 25 word in addWord consists of lowercase English letters. word in search consist of '.' or lowercase English letters. There will be at most 2 dots in word for search queries. At most 104 calls will be made to addWord and search."
Apple,214,Shortest Palindrome,Hard,"String, Rolling Hash, String Matching, Hash Function","You are given a string s. You can convert s to a palindrome by adding characters in front of it. Return the shortest palindrome you can find by performing this transformation. Example 1: Input: s = ""aacecaaa"" Output: ""aaacecaaa"" Example 2: Input: s = ""abcd"" Output: ""dcbabcd"" Constraints: 0 <= s.length <= 5 * 104 s consists of lowercase English letters only."
Apple,216,Combination Sum III,Med,"Array, Backtracking",Find all valid combinations of k numbers that sum up to n such that the following conditions are true: Only numbers 1 through 9 are used. Each number is used at most once. Return a list of all possible valid combinations. The list must not contain the same combination twice; and the combinations may be returned in any order. Example 1: Input: k = 3; n = 7 Output: [[1;2;4]] Explanation: 1 + 2 + 4 = 7 There are no other valid combinations. Example 2: Input: k = 3; n = 9 Output: [[1;2;6];[1;3;5];[2;3;4]] Explanation: 1 + 2 + 6 = 9 1 + 3 + 5 = 9 2 + 3 + 4 = 9 There are no other valid combinations. Example 3: Input: k = 4; n = 1 Output: [] Explanation: There are no valid combinations. Using 4 different numbers in the range [1;9]; the smallest sum we can get is 1+2+3+4 = 10 and since 10 > 1; there are no valid combination. Constraints: 2 <= k <= 9 1 <= n <= 60
Apple,222,Count Complete Tree Nodes,Easy,"Binary Search, Bit Manipulation, Tree, Binary Tree",Given the root of a complete binary tree; return the number of the nodes in the tree. According to Wikipedia; every level; except possibly the last; is completely filled in a complete binary tree; and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h. Design an algorithm that runs in less than O(n) time complexity. Example 1: Input: root = [1;2;3;4;5;6] Output: 6 Example 2: Input: root = [] Output: 0 Example 3: Input: root = [1] Output: 1 Constraints: The number of nodes in the tree is in the range [0; 5 * 104]. 0 <= Node.val <= 5 * 104 The tree is guaranteed to be complete.
Apple,225,Implement Stack using Queues,Easy,"Stack, Design, Queue","Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push; top; pop; and empty). Implement the MyStack class: void push(int x) Pushes element x to the top of the stack. int pop() Removes the element on the top of the stack and returns it. int top() Returns the element on the top of the stack. boolean empty() Returns true if the stack is empty; false otherwise. Notes: You must use only standard operations of a queue; which means that only push to back; peek/pop from front; size and is empty operations are valid. Depending on your language; the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations. Example 1: Input [""MyStack""; ""push""; ""push""; ""top""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 2; 2; false] Explanation MyStack myStack = new MyStack(); myStack.push(1); myStack.push(2); myStack.top(); // return 2 myStack.pop(); // return 2 myStack.empty(); // return False Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; top; and empty. All the calls to pop and top are valid. Follow-up: Can you implement the stack using only one queue?"
Apple,233,Number of Digit One,Hard,"Math, Dynamic Programming, Recursion",Given an integer n; count the total number of digit 1 appearing in all non-negative integers less than or equal to n. Example 1: Input: n = 13 Output: 6 Example 2: Input: n = 0 Output: 0 Constraints: 0 <= n <= 109
Apple,310,Minimum Height Trees,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",A tree is an undirected graph in which any two vertices are connected by exactly one path. In other words; any connected graph without simple cycles is a tree. Given a tree of n nodes labelled from 0 to n - 1; and an array of n - 1 edges where edges[i] = [ai; bi] indicates that there is an undirected edge between the two nodes ai and bi in the tree; you can choose any node of the tree as the root. When you select a node x as the root; the result tree has height h. Among all possible rooted trees; those with minimum height (i.e. min(h)) are called minimum height trees (MHTs). Return a list of all MHTs' root labels. You can return the answer in any order. The height of a rooted tree is the number of edges on the longest downward path between the root and a leaf. Example 1: Input: n = 4; edges = [[1;0];[1;2];[1;3]] Output: [1] Explanation: As shown; the height of the tree is 1 when the root is the node with label 1 which is the only MHT. Example 2: Input: n = 6; edges = [[3;0];[3;1];[3;2];[3;4];[5;4]] Output: [3;4] Constraints: 1 <= n <= 2 * 104 edges.length == n - 1 0 <= ai; bi < n ai != bi All the pairs (ai; bi) are distinct. The given input is guaranteed to be a tree and there will be no repeated edges.
Apple,316,Remove Duplicate Letters,Med,"String, Stack, Greedy, Monotonic Stack","Given a string s; remove duplicate letters so that every letter appears once and only once. You must make sure your result is the smallest in lexicographical order among all possible results. Example 1: Input: s = ""bcabc"" Output: ""abc"" Example 2: Input: s = ""cbacdcbc"" Output: ""acdb"" Constraints: 1 <= s.length <= 104 s consists of lowercase English letters. Note: This question is the same as 1081: https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/"
Apple,339,Nested List Weight Sum,Med,"Depth-First Search, Breadth-First Search",
Apple,371,Sum of Two Integers,Med,"Math, Bit Manipulation",Given two integers a and b; return the sum of the two integers without using the operators + and -. Example 1: Input: a = 1; b = 2 Output: 3 Example 2: Input: a = 2; b = 3 Output: 5 Constraints: -1000 <= a; b <= 1000
Apple,415,Add Strings,Easy,"Math, String, Simulation","Given two non-negative integers; num1 and num2 represented as string; return the sum of num1 and num2 as a string. You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly. Example 1: Input: num1 = ""11""; num2 = ""123"" Output: ""134"" Example 2: Input: num1 = ""456""; num2 = ""77"" Output: ""533"" Example 3: Input: num1 = ""0""; num2 = ""0"" Output: ""0"" Constraints: 1 <= num1.length; num2.length <= 104 num1 and num2 consist of only digits. num1 and num2 don't have any leading zeros except for the zero itself."
Apple,435,Non-overlapping Intervals,Med,"Array, Dynamic Programming, Greedy, Sorting",Given an array of intervals intervals where intervals[i] = [starti; endi]; return the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping. Note that intervals which only touch at a point are non-overlapping. For example; [1; 2] and [2; 3] are non-overlapping. Example 1: Input: intervals = [[1;2];[2;3];[3;4];[1;3]] Output: 1 Explanation: [1;3] can be removed and the rest of the intervals are non-overlapping. Example 2: Input: intervals = [[1;2];[1;2];[1;2]] Output: 2 Explanation: You need to remove two [1;2] to make the rest of the intervals non-overlapping. Example 3: Input: intervals = [[1;2];[2;3]] Output: 0 Explanation: You don't need to remove any of the intervals since they're already non-overlapping. Constraints: 1 <= intervals.length <= 105 intervals[i].length == 2 -5 * 104 <= starti < endi <= 5 * 104
Apple,441,Arranging Coins,Easy,"Math, Binary Search",You have n coins and you want to build a staircase with these coins. The staircase consists of k rows where the ith row has exactly i coins. The last row of the staircase may be incomplete. Given the integer n; return the number of complete rows of the staircase you will build. Example 1: Input: n = 5 Output: 2 Explanation: Because the 3rd row is incomplete; we return 2. Example 2: Input: n = 8 Output: 3 Explanation: Because the 4th row is incomplete; we return 3. Constraints: 1 <= n <= 231 - 1
Apple,445,Add Two Numbers II,Med,"Linked List, Math, Stack",You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [7;2;4;3]; l2 = [5;6;4] Output: [7;8;0;7] Example 2: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [8;0;7] Example 3: Input: l1 = [0]; l2 = [0] Output: [0] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros. Follow up: Could you solve it without reversing the input lists?
Apple,448,Find All Numbers Disappeared in an Array,Easy,"Array, Hash Table",Given an array nums of n integers where nums[i] is in the range [1; n]; return an array of all the integers in the range [1; n] that do not appear in nums. Example 1: Input: nums = [4;3;2;7;8;2;3;1] Output: [5;6] Example 2: Input: nums = [1;1] Output: [2] Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i] <= n Follow up: Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.
Apple,450,Delete Node in a BST,Med,"Tree, Binary Search Tree, Binary Tree",Given a root node reference of a BST and a key; delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST. Basically; the deletion can be divided into two stages: Search for a node to remove. If the node is found; delete the node. Example 1: Input: root = [5;3;6;2;4;null;7]; key = 3 Output: [5;4;6;2;null;null;7] Explanation: Given key to delete is 3. So we find the node with value 3 and delete it. One valid answer is [5;4;6;2;null;null;7]; shown in the above BST. Please notice that another valid answer is [5;2;6;null;4;null;7] and it's also accepted. Example 2: Input: root = [5;3;6;2;4;null;7]; key = 0 Output: [5;3;6;2;4;null;7] Explanation: The tree does not contain a node with value = 0. Example 3: Input: root = []; key = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -105 <= Node.val <= 105 Each node has a unique value. root is a valid binary search tree. -105 <= key <= 105 Follow up: Could you solve it with time complexity O(height of tree)?
Apple,472,Concatenated Words,Hard,"Array, String, Dynamic Programming, Depth-First Search, Trie","Given an array of strings words (without duplicates); return all the concatenated words in the given list of words. A concatenated word is defined as a string that is comprised entirely of at least two shorter words (not necessarily distinct) in the given array. Example 1: Input: words = [""cat"";""cats"";""catsdogcats"";""dog"";""dogcatsdog"";""hippopotamuses"";""rat"";""ratcatdogcat""] Output: [""catsdogcats"";""dogcatsdog"";""ratcatdogcat""] Explanation: ""catsdogcats"" can be concatenated by ""cats""; ""dog"" and ""cats""; ""dogcatsdog"" can be concatenated by ""dog""; ""cats"" and ""dog""; ""ratcatdogcat"" can be concatenated by ""rat""; ""cat""; ""dog"" and ""cat"". Example 2: Input: words = [""cat"";""dog"";""catdog""] Output: [""catdog""] Constraints: 1 <= words.length <= 104 1 <= words[i].length <= 30 words[i] consists of only lowercase English letters. All the strings of words are unique. 1 <= sum(words[i].length) <= 105"
Apple,475,Heaters,Med,"Array, Two Pointers, Binary Search, Sorting",Winter is coming! During the contest; your first job is to design a standard heater with a fixed warm radius to warm all the houses. Every house can be warmed; as long as the house is within the heater's warm radius range. Given the positions of houses and heaters on a horizontal line; return the minimum radius standard of heaters so that those heaters could cover all houses. Notice that all the heaters follow your radius standard; and the warm radius will the same. Example 1: Input: houses = [1;2;3]; heaters = [2] Output: 1 Explanation: The only heater was placed in the position 2; and if we use the radius 1 standard; then all the houses can be warmed. Example 2: Input: houses = [1;2;3;4]; heaters = [1;4] Output: 1 Explanation: The two heaters were placed at positions 1 and 4. We need to use a radius 1 standard; then all the houses can be warmed. Example 3: Input: houses = [1;5]; heaters = [2] Output: 3 Constraints: 1 <= houses.length; heaters.length <= 3 * 104 1 <= houses[i]; heaters[i] <= 109
Apple,494,Target Sum,Med,"Array, Dynamic Programming, Backtracking","You are given an integer array nums and an integer target. You want to build an expression out of nums by adding one of the symbols '+' and '-' before each integer in nums and then concatenate all the integers. For example; if nums = [2; 1]; you can add a '+' before 2 and a '-' before 1 and concatenate them to build the expression ""+2-1"". Return the number of different expressions that you can build; which evaluates to target. Example 1: Input: nums = [1;1;1;1;1]; target = 3 Output: 5 Explanation: There are 5 ways to assign symbols to make the sum of nums be target 3. -1 + 1 + 1 + 1 + 1 = 3 +1 - 1 + 1 + 1 + 1 = 3 +1 + 1 - 1 + 1 + 1 = 3 +1 + 1 + 1 - 1 + 1 = 3 +1 + 1 + 1 + 1 - 1 = 3 Example 2: Input: nums = [1]; target = 1 Output: 1 Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 1000 0 <= sum(nums[i]) <= 1000 -1000 <= target <= 1000"
Apple,504,Base 7,Easy,Math,"Given an integer num; return a string of its base 7 representation. Example 1: Input: num = 100 Output: ""202"" Example 2: Input: num = -7 Output: ""-10"" Constraints: -107 <= num <= 107"
Apple,523,Continuous Subarray Sum,Med,"Array, Hash Table, Math, Prefix Sum",Given an integer array nums and an integer k; return true if nums has a good subarray or false otherwise. A good subarray is a subarray where: its length is at least two; and the sum of the elements of the subarray is a multiple of k. Note that: A subarray is a contiguous part of the array. An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k. Example 1: Input: nums = [23;2;4;6;7]; k = 6 Output: true Explanation: [2; 4] is a continuous subarray of size 2 whose elements sum up to 6. Example 2: Input: nums = [23;2;6;4;7]; k = 6 Output: true Explanation: [23; 2; 6; 4; 7] is an continuous subarray of size 5 whose elements sum up to 42. 42 is a multiple of 6 because 42 = 7 * 6 and 7 is an integer. Example 3: Input: nums = [23;2;6;4;7]; k = 13 Output: false Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109 0 <= sum(nums[i]) <= 231 - 1 1 <= k <= 231 - 1
Apple,532,K-diff Pairs in an Array,Med,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given an array of integers nums and an integer k; return the number of unique k-diff pairs in the array. A k-diff pair is an integer pair (nums[i]; nums[j]); where the following are true: 0 <= i; j < nums.length i != j |nums[i] - nums[j]| == k Notice that |val| denotes the absolute value of val. Example 1: Input: nums = [3;1;4;1;5]; k = 2 Output: 2 Explanation: There are two 2-diff pairs in the array; (1; 3) and (3; 5). Although we have two 1s in the input; we should only return the number of unique pairs. Example 2: Input: nums = [1;2;3;4;5]; k = 1 Output: 4 Explanation: There are four 1-diff pairs in the array; (1; 2); (2; 3); (3; 4) and (4; 5). Example 3: Input: nums = [1;3;1;5;4]; k = 0 Output: 1 Explanation: There is one 0-diff pair in the array; (1; 1). Constraints: 1 <= nums.length <= 104 -107 <= nums[i] <= 107 0 <= k <= 107
Apple,538,Convert BST to Greater Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a Binary Search Tree (BST); convert it to a Greater Tree such that every key of the original BST is changed to the original key plus the sum of all keys greater than the original key in BST. As a reminder; a binary search tree is a tree that satisfies these constraints: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [4;1;6;0;2;5;7;null;null;null;3;null;null;null;8] Output: [30;36;21;36;35;26;15;null;null;null;33;null;null;null;8] Example 2: Input: root = [0;null;1] Output: [1;null;1] Constraints: The number of nodes in the tree is in the range [0; 104]. -104 <= Node.val <= 104 All the values in the tree are unique. root is guaranteed to be a valid binary search tree. Note: This question is the same as 1038: https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/
Apple,557,Reverse Words in a String III,Easy,"Two Pointers, String","Given a string s; reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order. Example 1: Input: s = ""Let's take LeetCode contest"" Output: ""s'teL ekat edoCteeL tsetnoc"" Example 2: Input: s = ""Mr Ding"" Output: ""rM gniD"" Constraints: 1 <= s.length <= 5 * 104 s contains printable ASCII characters. s does not contain any leading or trailing spaces. There is at least one word in s. All the words in s are separated by a single space."
Apple,588,Design In-Memory File System,Hard,"Hash Table, String, Design, Trie, Sorting",
Apple,602,Friend Requests II: Who Has the Most Friends,Med,Database,Table: RequestAccepted +----------------+---------+ | Column Name | Type | +----------------+---------+ | requester_id | int | | accepter_id | int | | accept_date | date | +----------------+---------+ (requester_id; accepter_id) is the primary key (combination of columns with unique values) for this table. This table contains the ID of the user who sent the request; the ID of the user who received the request; and the date when the request was accepted. Write a solution to find the people who have the most friends and the most friends number. The test cases are generated so that only one person has the most friends. The result format is in the following example. Example 1: Input: RequestAccepted table: +--------------+-------------+-------------+ | requester_id | accepter_id | accept_date | +--------------+-------------+-------------+ | 1 | 2 | 2016/06/03 | | 1 | 3 | 2016/06/08 | | 2 | 3 | 2016/06/08 | | 3 | 4 | 2016/06/09 | +--------------+-------------+-------------+ Output: +----+-----+ | id | num | +----+-----+ | 3 | 3 | +----+-----+ Explanation: The person with id 3 is a friend of people 1; 2; and 4; so he has three friends in total; which is the most number than any others. Follow up: In the real world; multiple people could have the same most number of friends. Could you find all these people in this case?
Apple,610,Triangle Judgement,Easy,Database,Table: Triangle +-------------+------+ | Column Name | Type | +-------------+------+ | x | int | | y | int | | z | int | +-------------+------+ In SQL; (x; y; z) is the primary key column for this table. Each row of this table contains the lengths of three line segments. Report for every three line segments whether they can form a triangle. Return the result table in any order. The result format is in the following example. Example 1: Input: Triangle table: +----+----+----+ | x | y | z | +----+----+----+ | 13 | 15 | 30 | | 10 | 20 | 15 | +----+----+----+ Output: +----+----+----+----------+ | x | y | z | triangle | +----+----+----+----------+ | 13 | 15 | 30 | No | | 10 | 20 | 15 | Yes | +----+----+----+----------+
Apple,642,Design Search Autocomplete System,Hard,"String, Depth-First Search, Design, Trie, Sorting, Heap (Priority Queue), Data Stream",
Apple,645,Set Mismatch,Easy,"Array, Hash Table, Bit Manipulation, Sorting",You have a set of integers s; which originally contains all the numbers from 1 to n. Unfortunately; due to some error; one of the numbers in s got duplicated to another number in the set; which results in repetition of one number and loss of another number. You are given an integer array nums representing the data status of this set after the error. Find the number that occurs twice and the number that is missing and return them in the form of an array. Example 1: Input: nums = [1;2;2;4] Output: [2;3] Example 2: Input: nums = [1;1] Output: [1;2] Constraints: 2 <= nums.length <= 104 1 <= nums[i] <= 104
Apple,649,Dota2 Senate,Med,"String, Greedy, Queue","In the world of Dota2; there are two parties: the Radiant and the Dire. The Dota2 senate consists of senators coming from two parties. Now the Senate wants to decide on a change in the Dota2 game. The voting for this change is a round-based procedure. In each round; each senator can exercise one of the two rights: Ban one senator's right: A senator can make another senator lose all his rights in this and all the following rounds. Announce the victory: If this senator found the senators who still have rights to vote are all from the same party; he can announce the victory and decide on the change in the game. Given a string senate representing each senator's party belonging. The character 'R' and 'D' represent the Radiant party and the Dire party. Then if there are n senators; the size of the given string will be n. The round-based procedure starts from the first senator to the last senator in the given order. This procedure will last until the end of voting. All the senators who have lost their rights will be skipped during the procedure. Suppose every senator is smart enough and will play the best strategy for his own party. Predict which party will finally announce the victory and change the Dota2 game. The output should be ""Radiant"" or ""Dire"". Example 1: Input: senate = ""RD"" Output: ""Radiant"" Explanation: The first senator comes from Radiant and he can just ban the next senator's right in round 1. And the second senator can't exercise any rights anymore since his right has been banned. And in round 2; the first senator can just announce the victory since he is the only guy in the senate who can vote. Example 2: Input: senate = ""RDD"" Output: ""Dire"" Explanation: The first senator comes from Radiant and he can just ban the next senator's right in round 1. And the second senator can't exercise any rights anymore since his right has been banned. And the third senator comes from Dire and he can ban the first senator's right in round 1. And in round 2; the third senator can just announce the victory since he is the only guy in the senate who can vote. Constraints: n == senate.length 1 <= n <= 104 senate[i] is either 'R' or 'D'."
Apple,653,Two Sum IV - Input is a BST,Easy,"Hash Table, Two Pointers, Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree and an integer k; return true if there exist two elements in the BST such that their sum is equal to k; or false otherwise. Example 1: Input: root = [5;3;6;2;4;null;7]; k = 9 Output: true Example 2: Input: root = [5;3;6;2;4;null;7]; k = 28 Output: false Constraints: The number of nodes in the tree is in the range [1; 104]. -104 <= Node.val <= 104 root is guaranteed to be a valid binary search tree. -105 <= k <= 105
Apple,664,Strange Printer,Hard,"String, Dynamic Programming","There is a strange printer with the following two special properties: The printer can only print a sequence of the same character each time. At each turn; the printer can print new characters starting from and ending at any place and will cover the original existing characters. Given a string s; return the minimum number of turns the printer needed to print it. Example 1: Input: s = ""aaabbb"" Output: 2 Explanation: Print ""aaa"" first and then print ""bbb"". Example 2: Input: s = ""aba"" Output: 2 Explanation: Print ""aaa"" first and then print ""b"" from the second place of the string; which will cover the existing character 'a'. Constraints: 1 <= s.length <= 100 s consists of lowercase English letters."
Apple,688,Knight Probability in Chessboard,Med,Dynamic Programming,On an n x n chessboard; a knight starts at the cell (row; column) and attempts to make exactly k moves. The rows and columns are 0-indexed; so the top-left cell is (0; 0); and the bottom-right cell is (n - 1; n - 1). A chess knight has eight possible moves it can make; as illustrated below. Each move is two cells in a cardinal direction; then one cell in an orthogonal direction. Each time the knight is to move; it chooses one of eight possible moves uniformly at random (even if the piece would go off the chessboard) and moves there. The knight continues moving until it has made exactly k moves or has moved off the chessboard. Return the probability that the knight remains on the board after it has stopped moving. Example 1: Input: n = 3; k = 2; row = 0; column = 0 Output: 0.06250 Explanation: There are two moves (to (1;2); (2;1)) that will keep the knight on the board. From each of those positions; there are also two moves that will keep the knight on the board. The total probability the knight stays on the board is 0.0625. Example 2: Input: n = 1; k = 0; row = 0; column = 0 Output: 1.00000 Constraints: 1 <= n <= 25 0 <= k <= 100 0 <= row; column <= n - 1
Apple,698,Partition to K Equal Sum Subsets,Med,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Memoization, Bitmask",Given an integer array nums and an integer k; return true if it is possible to divide this array into k non-empty subsets whose sums are all equal. Example 1: Input: nums = [4;3;2;3;5;2;1]; k = 4 Output: true Explanation: It is possible to divide it into 4 subsets (5); (1; 4); (2;3); (2;3) with equal sums. Example 2: Input: nums = [1;2;3;4]; k = 3 Output: false Constraints: 1 <= k <= nums.length <= 16 1 <= nums[i] <= 104 The frequency of each element is in the range [1; 4].
Apple,779,K-th Symbol in Grammar,Med,"Array, Stack, Greedy, Sorting, Monotonic Stack",You are given an integer array arr. We split arr into some number of chunks (i.e.; partitions); and individually sort each chunk. After concatenating them; the result should equal the sorted array. Return the largest number of chunks we can make to sort the array. Example 1: Input: arr = [5;4;3;2;1] Output: 1 Explanation: Splitting into two or more chunks will not return the required result. For example; splitting into [5; 4]; [3; 2; 1] will result in [4; 5; 1; 2; 3]; which isn't sorted. Example 2: Input: arr = [2;1;3;4;4] Output: 4 Explanation: We can split into two chunks; such as [2; 1]; [3; 4; 4]. However; splitting into [2; 1]; [3]; [4]; [4] is the highest number of chunks possible. Constraints: 1 <= arr.length <= 2000 0 <= arr[i] <= 108
Apple,791,Custom Sort String,Med,"Tree, Binary Search Tree, Recursion, Binary Tree",
Apple,705,Design HashSet,Easy,,
Apple,707,Design Linked List,Med,,
Apple,881,Boats to Save People,Med,"Array, Depth-First Search, Graph, Topological Sort",There is a group of n people labeled from 0 to n - 1 where each person has a different amount of money and a different level of quietness. You are given an array richer where richer[i] = [ai; bi] indicates that ai has more money than bi and an integer array quiet where quiet[i] is the quietness of the ith person. All the given data in richer are logically correct (i.e.; the data will not lead you to a situation where x is richer than y and y is richer than x at the same time). Return an integer array answer where answer[x] = y if y is the least quiet person (that is; the person y with the smallest value of quiet[y]) among all people who definitely have equal to or more money than the person x. Example 1: Input: richer = [[1;0];[2;1];[3;1];[3;7];[4;3];[5;3];[6;3]]; quiet = [3;2;5;4;6;1;7;0] Output: [5;5;2;5;4;5;6;7] Explanation: answer[0] = 5. Person 5 has more money than 3; which has more money than 1; which has more money than 0. The only person who is quieter (has lower quiet[x]) is person 7; but it is not clear if they have more money than person 0. answer[7] = 7. Among all people that definitely have equal to or more money than person 7 (which could be persons 3; 4; 5; 6; or 7); the person who is the quietest (has lower quiet[x]) is person 7. The other answers can be filled out with similar reasoning. Example 2: Input: richer = []; quiet = [0] Output: [0] Constraints: n == quiet.length 1 <= n <= 500 0 <= quiet[i] < n All the values of quiet are unique. 0 <= richer.length <= n * (n - 1) / 2 0 <= ai; bi < n ai != bi All the pairs of richer are unique. The observations in richer are all logically consistent.
Apple,885,Spiral Matrix III,Med,"Design, Heap (Priority Queue), Ordered Set","There is an exam room with n seats in a single row labeled from 0 to n - 1. When a student enters the room; they must sit in the seat that maximizes the distance to the closest person. If there are multiple such seats; they sit in the seat with the lowest number. If no one is in the room; then the student sits at seat number 0. Design a class that simulates the mentioned exam room. Implement the ExamRoom class: ExamRoom(int n) Initializes the object of the exam room with the number of the seats n. int seat() Returns the label of the seat at which the next student will set. void leave(int p) Indicates that the student sitting at seat p will leave the room. It is guaranteed that there will be a student sitting at seat p. Example 1: Input [""ExamRoom""; ""seat""; ""seat""; ""seat""; ""seat""; ""leave""; ""seat""] [[10]; []; []; []; []; [4]; []] Output [null; 0; 9; 4; 2; null; 5] Explanation ExamRoom examRoom = new ExamRoom(10); examRoom.seat(); // return 0; no one is in the room; then the student sits at seat number 0. examRoom.seat(); // return 9; the student sits at the last seat number 9. examRoom.seat(); // return 4; the student sits at the last seat number 4. examRoom.seat(); // return 2; the student sits at the last seat number 2. examRoom.leave(4); examRoom.seat(); // return 5; the student sits at the last seat number 5. Constraints: 1 <= n <= 109 It is guaranteed that there is a student sitting at seat p. At most 104 calls will be made to seat and leave."
Apple,901,Online Stock Span,Med,"Array, Two Pointers, Greedy, Sorting",You are given two integer arrays nums1 and nums2 both of the same length. The advantage of nums1 with respect to nums2 is the number of indices i for which nums1[i] > nums2[i]. Return any permutation of nums1 that maximizes its advantage with respect to nums2. Example 1: Input: nums1 = [2;7;11;15]; nums2 = [1;10;4;11] Output: [2;11;7;15] Example 2: Input: nums1 = [12;24;8;32]; nums2 = [13;25;32;11] Output: [24;32;8;12] Constraints: 1 <= nums1.length <= 105 nums2.length == nums1.length 0 <= nums1[i]; nums2[i] <= 109
Apple,921,Minimum Add to Make Parentheses Valid,Med,"Array, Matrix, Simulation",You start at the cell (rStart; cStart) of an rows x cols grid facing east. The northwest corner is at the first row and column in the grid; and the southeast corner is at the last row and column. You will walk in a clockwise spiral shape to visit every position in this grid. Whenever you move outside the grid's boundary; we continue our walk outside the grid (but may return to the grid boundary later.). Eventually; we reach all rows * cols spaces of the grid. Return an array of coordinates representing the positions of the grid in the order you visited them. Example 1: Input: rows = 1; cols = 4; rStart = 0; cStart = 0 Output: [[0;0];[0;1];[0;2];[0;3]] Example 2: Input: rows = 5; cols = 6; rStart = 1; cStart = 4 Output: [[1;4];[1;5];[2;5];[2;4];[2;3];[1;3];[0;3];[0;4];[0;5];[3;5];[3;4];[3;3];[3;2];[2;2];[1;2];[0;2];[4;5];[4;4];[4;3];[4;2];[4;1];[3;1];[2;1];[1;1];[0;1];[4;0];[3;0];[2;0];[1;0];[0;0]] Constraints: 1 <= rows; cols <= 100 0 <= rStart < rows 0 <= cStart < cols
Apple,929,Unique Email Addresses,Easy,"Array, Hash Table, String, Sorting","You are given an array of strings of the same length words. In one move; you can swap any two even indexed characters or any two odd indexed characters of a string words[i]. Two strings words[i] and words[j] are special-equivalent if after any number of moves; words[i] == words[j]. For example; words[i] = ""zzxy"" and words[j] = ""xyzz"" are special-equivalent because we may make the moves ""zzxy"" -> ""xzzy"" -> ""xyzz"". A group of special-equivalent strings from words is a non-empty subset of words such that: Every pair of strings in the group are special equivalent; and The group is the largest size possible (i.e.; there is not a string words[i] not in the group such that words[i] is special-equivalent to every string in the group). Return the number of groups of special-equivalent strings from words. Example 1: Input: words = [""abcd"";""cdab"";""cbad"";""xyzz"";""zzxy"";""zzyx""] Output: 3 Explanation: One group is [""abcd""; ""cdab""; ""cbad""]; since they are all pairwise special equivalent; and none of the other strings is all pairwise special equivalent to these. The other two groups are [""xyzz""; ""zzxy""] and [""zzyx""]. Note that in particular; ""zzxy"" is not special equivalent to ""zzyx"". Example 2: Input: words = [""abc"";""acb"";""bac"";""bca"";""cab"";""cba""] Output: 3 Constraints: 1 <= words.length <= 1000 1 <= words[i].length <= 20 words[i] consist of lowercase English letters. All the strings are of the same length."
Apple,933,Number of Recent Calls,Easy,"Stack, Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree; rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree; and every node has no left child and only one right child. Example 1: Input: root = [5;3;6;2;4;null;8;1;null;null;null;7;9] Output: [1;null;2;null;3;null;4;null;5;null;6;null;7;null;8;null;9] Example 2: Input: root = [5;1;7] Output: [1;null;5;null;7] Constraints: The number of nodes in the given tree will be in the range [1; 100]. 0 <= Node.val <= 1000
Apple,934,Shortest Bridge,Med,"Array, Dynamic Programming, Bit Manipulation",Given an integer array arr; return the number of distinct bitwise ORs of all the non-empty subarrays of arr. The bitwise OR of a subarray is the bitwise OR of each integer in the subarray. The bitwise OR of a subarray of one integer is that integer. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: arr = [0] Output: 1 Explanation: There is only one possible result: 0. Example 2: Input: arr = [1;1;2] Output: 3 Explanation: The possible subarrays are [1]; [1]; [2]; [1; 1]; [1; 2]; [1; 1; 2]. These yield the results 1; 1; 2; 1; 3; 3. There are 3 unique values; so the answer is 3. Example 3: Input: arr = [1;2;4] Output: 6 Explanation: The possible results are 1; 2; 3; 4; 6; and 7. Constraints: 1 <= arr.length <= 5 * 104 0 <= arr[i] <= 109
Apple,947,Most Stones Removed with Same Row or Column,Med,"Array, Hash Table, Binary Search, Design","You are given two integer arrays persons and times. In an election; the ith vote was cast for persons[i] at time times[i]. For each query at a time t; find the person that was leading the election at time t. Votes cast at time t will count towards our query. In the case of a tie; the most recent vote (among tied candidates) wins. Implement the TopVotedCandidate class: TopVotedCandidate(int[] persons; int[] times) Initializes the object with the persons and times arrays. int q(int t) Returns the number of the person that was leading the election at time t according to the mentioned rules. Example 1: Input [""TopVotedCandidate""; ""q""; ""q""; ""q""; ""q""; ""q""; ""q""] [[[0; 1; 1; 0; 0; 1; 0]; [0; 5; 10; 15; 20; 25; 30]]; [3]; [12]; [25]; [15]; [24]; [8]] Output [null; 0; 1; 1; 0; 0; 1] Explanation TopVotedCandidate topVotedCandidate = new TopVotedCandidate([0; 1; 1; 0; 0; 1; 0]; [0; 5; 10; 15; 20; 25; 30]); topVotedCandidate.q(3); // return 0; At time 3; the votes are [0]; and 0 is leading. topVotedCandidate.q(12); // return 1; At time 12; the votes are [0;1;1]; and 1 is leading. topVotedCandidate.q(25); // return 1; At time 25; the votes are [0;1;1;0;0;1]; and 1 is leading (as ties go to the most recent vote.) topVotedCandidate.q(15); // return 0 topVotedCandidate.q(24); // return 0 topVotedCandidate.q(8); // return 1 Constraints: 1 <= persons.length <= 5000 times.length == persons.length 0 <= persons[i] < persons.length 0 <= times[i] <= 109 times is sorted in a strictly increasing order. times[0] <= t <= 109 At most 104 calls will be made to q."
Apple,958,Check Completeness of a Binary Tree,Med,"Array, Two Pointers, Sorting",Given an array of integers nums; half of the integers in nums are odd; and the other half are even. Sort the array so that whenever nums[i] is odd; i is odd; and whenever nums[i] is even; i is even. Return any answer array that satisfies this condition. Example 1: Input: nums = [4;2;5;7] Output: [4;5;2;7] Explanation: [4;7;2;5]; [2;5;4;7]; [2;7;4;5] would also have been accepted. Example 2: Input: nums = [2;3] Output: [2;3] Constraints: 2 <= nums.length <= 2 * 104 nums.length is even. Half of the integers in nums are even. 0 <= nums[i] <= 1000 Follow Up: Could you solve it in-place?
Apple,997,Find the Town Judge,Easy,,
Apple,1002,Find Common Characters,Easy,"Array, Stack, Monotonic Stack",A ramp in an integer array nums is a pair (i; j) for which i < j and nums[i] <= nums[j]. The width of such a ramp is j - i. Given an integer array nums; return the maximum width of a ramp in nums. If there is no ramp in nums; return 0. Example 1: Input: nums = [6;0;8;2;1;5] Output: 4 Explanation: The maximum width ramp is achieved at (i; j) = (1; 5): nums[1] = 0 and nums[5] = 5. Example 2: Input: nums = [9;8;1;0;1;9;4;0;4;1] Output: 7 Explanation: The maximum width ramp is achieved at (i; j) = (2; 9): nums[2] = 1 and nums[9] = 1. Constraints: 2 <= nums.length <= 5 * 104 0 <= nums[i] <= 5 * 104
Apple,1010,Pairs of Songs With Total Durations Divisible by 60,Med,"Hash Table, Math, Enumeration",Given three integers x; y; and bound; return a list of all the powerful integers that have a value less than or equal to bound. An integer is powerful if it can be represented as xi + yj for some integers i >= 0 and j >= 0. You may return the answer in any order. In your answer; each value should occur at most once. Example 1: Input: x = 2; y = 3; bound = 10 Output: [2;3;4;5;7;9;10] Explanation: 2 = 20 + 30 3 = 21 + 30 4 = 20 + 31 5 = 21 + 31 7 = 22 + 31 9 = 23 + 30 10 = 20 + 32 Example 2: Input: x = 3; y = 5; bound = 15 Output: [2;4;6;8;10;14] Constraints: 1 <= x; y <= 100 0 <= bound <= 106
Apple,1026,Maximum Difference Between Node and Ancestor,Med,"String, Greedy","Given two integers a and b; return any string s such that: s has length a + b and contains exactly a 'a' letters; and exactly b 'b' letters; The substring 'aaa' does not occur in s; and The substring 'bbb' does not occur in s. Example 1: Input: a = 1; b = 2 Output: ""abb"" Explanation: ""abb""; ""bab"" and ""bba"" are all correct answers. Example 2: Input: a = 4; b = 1 Output: ""aabaa"" Constraints: 0 <= a; b <= 100 It is guaranteed such an s exists for the given a and b."
Apple,1045,Customers Who Bought All Products,Med,"String, Stack","Given a string s; determine if it is valid. A string s is valid if; starting with an empty string t = """"; you can transform t into s after performing the following operation any number of times: Insert string ""abc"" into any position in t. More formally; t becomes tleft + ""abc"" + tright; where t == tleft + tright. Note that tleft and tright may be empty. Return true if s is a valid string; otherwise; return false. Example 1: Input: s = ""aabcbc"" Output: true Explanation: """" -> ""abc"" -> ""aabcbc"" Thus; ""aabcbc"" is valid. Example 2: Input: s = ""abcabcababcc"" Output: true Explanation: """" -> ""abc"" -> ""abcabc"" -> ""abcabcabc"" -> ""abcabcababcc"" Thus; ""abcabcababcc"" is valid. Example 3: Input: s = ""abccba"" Output: false Explanation: It is impossible to get ""abccba"" using the operation. Constraints: 1 <= s.length <= 2 * 104 s consists of letters 'a'; 'b'; and 'c'"
Apple,1094,Car Pooling,Med,"Array, Math, Geometry, Sorting, Matrix",You are given four integers row; cols; rCenter; and cCenter. There is a rows x cols matrix and you are on the cell with the coordinates (rCenter; cCenter). Return the coordinates of all cells in the matrix; sorted by their distance from (rCenter; cCenter) from the smallest distance to the largest distance. You may return the answer in any order that satisfies this condition. The distance between two cells (r1; c1) and (r2; c2) is |r1 - r2| + |c1 - c2|. Example 1: Input: rows = 1; cols = 2; rCenter = 0; cCenter = 0 Output: [[0;0];[0;1]] Explanation: The distances from (0; 0) to other cells are: [0;1] Example 2: Input: rows = 2; cols = 2; rCenter = 0; cCenter = 1 Output: [[0;1];[0;0];[1;1];[1;0]] Explanation: The distances from (0; 1) to other cells are: [0;1;1;2] The answer [[0;1];[1;1];[0;0];[1;0]] would also be accepted as correct. Example 3: Input: rows = 2; cols = 3; rCenter = 1; cCenter = 2 Output: [[1;2];[0;2];[1;1];[0;1];[1;0];[0;0]] Explanation: The distances from (1; 2) to other cells are: [0;1;1;2;2;3] There are other answers that would also be accepted as correct; such as [[1;2];[1;1];[0;2];[1;0];[0;1];[0;0]]. Constraints: 1 <= rows; cols <= 100 0 <= rCenter < rows 0 <= cCenter < cols
Apple,1283,Find the Smallest Divisor Given a Threshold,Med,String,"Given a date string in the form Day Month Year; where: Day is in the set {""1st""; ""2nd""; ""3rd""; ""4th""; ...; ""30th""; ""31st""}. Month is in the set {""Jan""; ""Feb""; ""Mar""; ""Apr""; ""May""; ""Jun""; ""Jul""; ""Aug""; ""Sep""; ""Oct""; ""Nov""; ""Dec""}. Year is in the range [1900; 2100]. Convert the date string to the format YYYY-MM-DD; where: YYYY denotes the 4 digit year. MM denotes the 2 digit month. DD denotes the 2 digit day. Example 1: Input: date = ""20th Oct 2052"" Output: ""2052-10-20"" Example 2: Input: date = ""6th Jun 1933"" Output: ""1933-06-06"" Example 3: Input: date = ""26th May 1960"" Output: ""1960-05-26"" Constraints: The given dates are guaranteed to be valid; so no error handling is necessary."
Apple,1293,Shortest Path in a Grid with Obstacles Elimination,Hard,Array,Given an integer array arr; return true if there are three consecutive odd numbers in the array. Otherwise; return false. Example 1: Input: arr = [2;6;4;1] Output: false Explanation: There are no three consecutive odds. Example 2: Input: arr = [1;2;34;3;4;5;7;23;12] Output: true Explanation: [5;7;23] are three consecutive odds. Constraints: 1 <= arr.length <= 1000 1 <= arr[i] <= 1000
Apple,2305,Fair Distribution of Cookies,Med,"Array, Math, Greedy, Sorting",You are given an integer array nums and an integer k. Append k unique positive integers that do not appear in nums to nums such that the resulting total sum is minimum. Return the sum of the k integers appended to nums. Example 1: Input: nums = [1;4;25;10;25]; k = 2 Output: 5 Explanation: The two unique positive integers that do not appear in nums which we append are 2 and 3. The resulting sum of nums is 1 + 4 + 25 + 10 + 25 + 2 + 3 = 70; which is the minimum. The sum of the two integers appended is 2 + 3 = 5; so we return 5. Example 2: Input: nums = [5;6]; k = 6 Output: 25 Explanation: The six unique positive integers that do not appear in nums which we append are 1; 2; 3; 4; 7; and 8. The resulting sum of nums is 5 + 6 + 1 + 2 + 3 + 4 + 7 + 8 = 36; which is the minimum. The sum of the six integers appended is 1 + 2 + 3 + 4 + 7 + 8 = 25; so we return 25. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 109 1 <= k <= 108
Apple,1321,Restaurant Growth,Med,"String, Binary Search, Sliding Window, Prefix Sum","You are given two strings s and t of the same length and an integer maxCost. You want to change s to t. Changing the ith character of s to ith character of t costs |s[i] - t[i]| (i.e.; the absolute difference between the ASCII values of the characters). Return the maximum length of a substring of s that can be changed to be the same as the corresponding substring of t with a cost less than or equal to maxCost. If there is no substring from s that can be changed to its corresponding substring from t; return 0. Example 1: Input: s = ""abcd""; t = ""bcdf""; maxCost = 3 Output: 3 Explanation: ""abc"" of s can change to ""bcd"". That costs 3; so the maximum length is 3. Example 2: Input: s = ""abcd""; t = ""cdef""; maxCost = 3 Output: 1 Explanation: Each character in s costs 2 to change to character in t; so the maximum length is 1. Example 3: Input: s = ""abcd""; t = ""acde""; maxCost = 0 Output: 1 Explanation: You cannot make any change; so the maximum length is 1. Constraints: 1 <= s.length <= 105 t.length == s.length 0 <= maxCost <= 106 s and t consist of only lowercase English letters."
Apple,1353,Maximum Number of Events That Can Be Attended,Med,"Array, Hash Table, String, Sorting","You are given a 0-indexed string array words; where words[i] consists of lowercase English letters. In one operation; select any index i such that 0 < i < words.length and words[i - 1] and words[i] are anagrams; and delete words[i] from words. Keep performing this operation as long as you can select an index that satisfies the conditions. Return words after performing all operations. It can be shown that selecting the indices for each operation in any arbitrary order will lead to the same result. An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase using all the original letters exactly once. For example; ""dacb"" is an anagram of ""abdc"". Example 1: Input: words = [""abba"";""baba"";""bbaa"";""cd"";""cd""] Output: [""abba"";""cd""] Explanation: One of the ways we can obtain the resultant array is by using the following operations: - Since words[2] = ""bbaa"" and words[1] = ""baba"" are anagrams; we choose index 2 and delete words[2]. Now words = [""abba"";""baba"";""cd"";""cd""]. - Since words[1] = ""baba"" and words[0] = ""abba"" are anagrams; we choose index 1 and delete words[1]. Now words = [""abba"";""cd"";""cd""]. - Since words[2] = ""cd"" and words[1] = ""cd"" are anagrams; we choose index 2 and delete words[2]. Now words = [""abba"";""cd""]. We can no longer perform any operations; so [""abba"";""cd""] is the final answer. Example 2: Input: words = [""a"";""b"";""c"";""d"";""e""] Output: [""a"";""b"";""c"";""d"";""e""] Explanation: No two adjacent strings in words are anagrams of each other; so no operations are performed. Constraints: 1 <= words.length <= 100 1 <= words[i].length <= 10 words[i] consists of lowercase English letters."
Apple,1388,Pizza With 3n Slices,Hard,"Array, Dynamic Programming, Greedy, Sorting",Given an integer array nums; return the maximum possible sum of elements of the array such that it is divisible by three. Example 1: Input: nums = [3;6;5;1;8] Output: 18 Explanation: Pick numbers 3; 6; 1 and 8 their sum is 18 (maximum sum divisible by 3). Example 2: Input: nums = [4] Output: 0 Explanation: Since 4 is not divisible by 3; do not pick any number. Example 3: Input: nums = [1;2;3;4;4] Output: 12 Explanation: Pick numbers 1; 3; 4 and 4 their sum is 12 (maximum sum divisible by 3). Constraints: 1 <= nums.length <= 4 * 104 1 <= nums[i] <= 104
Apple,1389,Create Target Array in the Given Order,Easy,"Array, Breadth-First Search, Heap (Priority Queue), Matrix","A storekeeper is a game in which the player pushes boxes around in a warehouse trying to get them to target locations. The game is represented by an m x n grid of characters grid where each element is a wall; floor; or box. Your task is to move the box 'B' to the target position 'T' under the following rules: The character 'S' represents the player. The player can move up; down; left; right in grid if it is a floor (empty cell). The character '.' represents the floor which means a free cell to walk. The character '#' represents the wall which means an obstacle (impossible to walk there). There is only one box 'B' and one target cell 'T' in the grid. The box can be moved to an adjacent free cell by standing next to the box and then moving in the direction of the box. This is a push. The player cannot walk through the box. Return the minimum number of pushes to move the box to the target. If there is no way to reach the target; return -1. Example 1: Input: grid = [[""#"";""#"";""#"";""#"";""#"";""#""]; [""#"";""T"";""#"";""#"";""#"";""#""]; [""#"";""."";""."";""B"";""."";""#""]; [""#"";""."";""#"";""#"";""."";""#""]; [""#"";""."";""."";""."";""S"";""#""]; [""#"";""#"";""#"";""#"";""#"";""#""]] Output: 3 Explanation: We return only the number of times the box is pushed. Example 2: Input: grid = [[""#"";""#"";""#"";""#"";""#"";""#""]; [""#"";""T"";""#"";""#"";""#"";""#""]; [""#"";""."";""."";""B"";""."";""#""]; [""#"";""#"";""#"";""#"";""."";""#""]; [""#"";""."";""."";""."";""S"";""#""]; [""#"";""#"";""#"";""#"";""#"";""#""]] Output: -1 Example 3: Input: grid = [[""#"";""#"";""#"";""#"";""#"";""#""]; [""#"";""T"";""."";""."";""#"";""#""]; [""#"";""."";""#"";""B"";""."";""#""]; [""#"";""."";""."";""."";""."";""#""]; [""#"";""."";""."";""."";""S"";""#""]; [""#"";""#"";""#"";""#"";""#"";""#""]] Output: 5 Explanation: push the box down; left; left; up and up. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 20 grid contains only characters '.'; '#'; 'S'; 'T'; or 'B'. There is only one character 'S'; 'B'; and 'T' in the grid."
Apple,1424,Diagonal Traverse II,Med,"Array, Breadth-First Search, Graph",You have n boxes labeled from 0 to n - 1. You are given four arrays: status; candies; keys; and containedBoxes where: status[i] is 1 if the ith box is open and 0 if the ith box is closed; candies[i] is the number of candies in the ith box; keys[i] is a list of the labels of the boxes you can open after opening the ith box. containedBoxes[i] is a list of the boxes you found inside the ith box. You are given an integer array initialBoxes that contains the labels of the boxes you initially have. You can take all the candies in any open box and you can use the keys in it to open new boxes and you also can use the boxes you find in it. Return the maximum number of candies you can get following the rules above. Example 1: Input: status = [1;0;1;0]; candies = [7;5;4;100]; keys = [[];[];[1];[]]; containedBoxes = [[1;2];[3];[];[]]; initialBoxes = [0] Output: 16 Explanation: You will be initially given box 0. You will find 7 candies in it and boxes 1 and 2. Box 1 is closed and you do not have a key for it so you will open box 2. You will find 4 candies and a key to box 1 in box 2. In box 1; you will find 5 candies and box 3 but you will not find a key to box 3 so box 3 will remain closed. Total number of candies collected = 7 + 4 + 5 = 16 candy. Example 2: Input: status = [1;0;0;0;0;0]; candies = [1;1;1;1;1;1]; keys = [[1;2;3;4;5];[];[];[];[];[]]; containedBoxes = [[1;2;3;4;5];[];[];[];[];[]]; initialBoxes = [0] Output: 6 Explanation: You have initially box 0. Opening it you can find boxes 1;2;3;4 and 5 and their keys. The total number of candies will be 6. Constraints: n == status.length == candies.length == keys.length == containedBoxes.length 1 <= n <= 1000 status[i] is either 0 or 1. 1 <= candies[i] <= 1000 0 <= keys[i].length <= n 0 <= keys[i][j] < n All values of keys[i] are unique. 0 <= containedBoxes[i].length <= n 0 <= containedBoxes[i][j] < n All values of containedBoxes[i] are unique. Each box is contained in one box at most. 0 <= initialBoxes.length <= n 0 <= initialBoxes[i] < n
Apple,1456,Maximum Number of Vowels in a Substring of Given Length,Med,"Dynamic Programming, Graph, Shortest Path",There are n cities numbered from 0 to n-1. Given the array edges where edges[i] = [fromi; toi; weighti] represents a bidirectional and weighted edge between cities fromi and toi; and given the integer distanceThreshold. Return the city with the smallest number of cities that are reachable through some path and whose distance is at most distanceThreshold; If there are multiple such cities; return the city with the greatest number. Notice that the distance of a path connecting cities i and j is equal to the sum of the edges' weights along that path. Example 1: Input: n = 4; edges = [[0;1;3];[1;2;1];[1;3;4];[2;3;1]]; distanceThreshold = 4 Output: 3 Explanation: The figure above describes the graph. The neighboring cities at a distanceThreshold = 4 for each city are: City 0 -> [City 1; City 2] City 1 -> [City 0; City 2; City 3] City 2 -> [City 0; City 1; City 3] City 3 -> [City 1; City 2] Cities 0 and 3 have 2 neighboring cities at a distanceThreshold = 4; but we have to return city 3 since it has the greatest number. Example 2: Input: n = 5; edges = [[0;1;2];[0;4;8];[1;2;3];[1;4;2];[2;3;1];[3;4;1]]; distanceThreshold = 2 Output: 0 Explanation: The figure above describes the graph. The neighboring cities at a distanceThreshold = 2 for each city are: City 0 -> [City 1] City 1 -> [City 0; City 4] City 2 -> [City 3; City 4] City 3 -> [City 2; City 4] City 4 -> [City 1; City 2; City 3] The city 0 has 1 neighboring city at a distanceThreshold = 2. Constraints: 2 <= n <= 100 1 <= edges.length <= n * (n - 1) / 2 edges[i].length == 3 0 <= fromi < toi < n 1 <= weighti; distanceThreshold <= 10^4 All pairs (fromi; toi) are distinct.
Apple,1472,Design Browser History,Med,"Hash Table, String, Counting","You are given a string s. Reorder the string using the following algorithm: Remove the smallest character from s and append it to the result. Remove the smallest character from s that is greater than the last appended character; and append it to the result. Repeat step 2 until no more characters can be removed. Remove the largest character from s and append it to the result. Remove the largest character from s that is smaller than the last appended character; and append it to the result. Repeat step 5 until no more characters can be removed. Repeat steps 1 through 6 until all characters from s have been removed. If the smallest or largest character appears more than once; you may choose any occurrence to append to the result. Return the resulting string after reordering s using this algorithm. Example 1: Input: s = ""aaaabbbbcccc"" Output: ""abccbaabccba"" Explanation: After steps 1; 2 and 3 of the first iteration; result = ""abc"" After steps 4; 5 and 6 of the first iteration; result = ""abccba"" First iteration is done. Now s = ""aabbcc"" and we go back to step 1 After steps 1; 2 and 3 of the second iteration; result = ""abccbaabc"" After steps 4; 5 and 6 of the second iteration; result = ""abccbaabccba"" Example 2: Input: s = ""rat"" Output: ""art"" Explanation: The word ""rat"" becomes ""art"" after re-ordering it with the mentioned algorithm. Constraints: 1 <= s.length <= 500 s consists of only lowercase English letters."
Apple,1492,The kth Factor of n,Med,"Tree, Depth-First Search, Breadth-First Search",A company has n employees with a unique ID for each employee from 0 to n - 1. The head of the company is the one with headID. Each employee has one direct manager given in the manager array where manager[i] is the direct manager of the i-th employee; manager[headID] = -1. Also; it is guaranteed that the subordination relationships have a tree structure. The head of the company wants to inform all the company employees of an urgent piece of news. He will inform his direct subordinates; and they will inform their subordinates; and so on until all employees know about the urgent news. The i-th employee needs informTime[i] minutes to inform all of his direct subordinates (i.e.; After informTime[i] minutes; all his direct subordinates can start spreading the news). Return the number of minutes needed to inform all the employees about the urgent news. Example 1: Input: n = 1; headID = 0; manager = [-1]; informTime = [0] Output: 0 Explanation: The head of the company is the only employee in the company. Example 2: Input: n = 6; headID = 2; manager = [2;2;-1;2;2;2]; informTime = [0;0;1;0;0;0] Output: 1 Explanation: The head of the company with id = 2 is the direct manager of all the employees in the company and needs 1 minute to inform them all. The tree structure of the employees in the company is shown. Constraints: 1 <= n <= 105 0 <= headID < n manager.length == n 0 <= manager[i] < n manager[headID] == -1 informTime.length == n 0 <= informTime[i] <= 1000 informTime[i] == 0 if employee i has no subordinates. It is guaranteed that all the employees can be informed.
Apple,1502,Can Make Arithmetic Progression From Sequence,Easy,"Hash Table, String, Greedy, Counting","Given a string s and an integer k; return true if you can use all the characters in s to construct k palindrome strings or false otherwise. Example 1: Input: s = ""annabelle""; k = 2 Output: true Explanation: You can construct two palindromes using all characters in s. Some possible constructions ""anna"" + ""elble""; ""anbna"" + ""elle""; ""anellena"" + ""b"" Example 2: Input: s = ""leetcode""; k = 3 Output: false Explanation: It is impossible to construct 3 palindromes using all the characters of s. Example 3: Input: s = ""true""; k = 4 Output: true Explanation: The only possible solution is to put each character in a separate string. Constraints: 1 <= s.length <= 105 s consists of lowercase English letters. 1 <= k <= 105"
Apple,1523,Count Odd Numbers in an Interval Range,Easy,Database,Table: Stocks +---------------+---------+ | Column Name | Type | +---------------+---------+ | stock_name | varchar | | operation | enum | | operation_day | int | | price | int | +---------------+---------+ (stock_name; operation_day) is the primary key (combination of columns with unique values) for this table. The operation column is an ENUM (category) of type ('Sell'; 'Buy') Each row of this table indicates that the stock which has stock_name had an operation on the day operation_day with the price. It is guaranteed that each 'Sell' operation for a stock has a corresponding 'Buy' operation in a previous day. It is also guaranteed that each 'Buy' operation for a stock has a corresponding 'Sell' operation in an upcoming day. Write a solution to report the Capital gain/loss for each stock. The Capital gain/loss of a stock is the total gain or loss after buying and selling the stock one or many times. Return the result table in any order. The result format is in the following example. Example 1: Input: Stocks table: +---------------+-----------+---------------+--------+ | stock_name | operation | operation_day | price | +---------------+-----------+---------------+--------+ | Leetcode | Buy | 1 | 1000 | | Corona Masks | Buy | 2 | 10 | | Leetcode | Sell | 5 | 9000 | | Handbags | Buy | 17 | 30000 | | Corona Masks | Sell | 3 | 1010 | | Corona Masks | Buy | 4 | 1000 | | Corona Masks | Sell | 5 | 500 | | Corona Masks | Buy | 6 | 1000 | | Handbags | Sell | 29 | 7000 | | Corona Masks | Sell | 10 | 10000 | +---------------+-----------+---------------+--------+ Output: +---------------+-------------------+ | stock_name | capital_gain_loss | +---------------+-------------------+ | Corona Masks | 9500 | | Leetcode | 8000 | | Handbags | -23000 | +---------------+-------------------+ Explanation: Leetcode stock was bought at day 1 for 1000$ and was sold at day 5 for 9000$. Capital gain = 9000 - 1000 = 8000$. Handbags stock was bought at day 17 for 30000$ and was sold at day 29 for 7000$. Capital loss = 7000 - 30000 = -23000$. Corona Masks stock was bought at day 1 for 10$ and was sold at day 3 for 1010$. It was bought again at day 4 for 1000$ and was sold at day 5 for 500$. At last; it was bought at day 6 for 1000$ and was sold at day 10 for 10000$. Capital gain/loss is the sum of capital gains/losses for each ('Buy' --> 'Sell') operation = (1010 - 10) + (500 - 1000) + (10000 - 1000) = 1000 - 500 + 9000 = 9500$.
Apple,1539,Kth Missing Positive Number,Easy,"Array, Sorting, Heap (Priority Queue)",Given a 2D integer array nums; return all elements of nums in diagonal order as shown in the below images. Example 1: Input: nums = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;4;2;7;5;3;8;6;9] Example 2: Input: nums = [[1;2;3;4;5];[6;7];[8];[9;10;11];[12;13;14;15;16]] Output: [1;6;2;8;7;3;9;4;12;10;5;13;11;14;15;16] Constraints: 1 <= nums.length <= 105 1 <= nums[i].length <= 105 1 <= sum(nums[i].length) <= 105 1 <= nums[i][j] <= 105
Apple,1544,Make The String Great,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree","Given a binary tree root; a node X in the tree is named good if in the path from root to X there are no nodes with a value greater than X. Return the number of good nodes in the binary tree. Example 1: Input: root = [3;1;4;3;null;1;5] Output: 4 Explanation: Nodes in blue are good. Root Node (3) is always a good node. Node 4 -> (3;4) is the maximum value in the path starting from the root. Node 5 -> (3;4;5) is the maximum value in the path Node 3 -> (3;1;3) is the maximum value in the path. Example 2: Input: root = [3;3;null;4;2] Output: 3 Explanation: Node 2 -> (3; 3; 2) is not good; because ""3"" is higher than it. Example 3: Input: root = [1] Output: 1 Explanation: Root is considered as good. Constraints: The number of nodes in the binary tree is in the range [1; 10^5]. Each node's value is between [-10^4; 10^4]."
Apple,1552,Magnetic Force Between Two Balls,Med,"Array, Stack, Simulation","You are given an integer array target and an integer n. You have an empty stack with the two following operations: ""Push"": pushes an integer to the top of the stack. ""Pop"": removes the integer on the top of the stack. You also have a stream of the integers in the range [1; n]. Use the two stack operations to make the numbers in the stack (from the bottom to the top) equal to target. You should follow the following rules: If the stream of the integers is not empty; pick the next integer from the stream and push it to the top of the stack. If the stack is not empty; pop the integer at the top of the stack. If; at any moment; the elements in the stack (from the bottom to the top) are equal to target; do not read new integers from the stream and do not do more operations on the stack. Return the stack operations needed to build target following the mentioned rules. If there are multiple valid answers; return any of them. Example 1: Input: target = [1;3]; n = 3 Output: [""Push"";""Push"";""Pop"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Pop the integer on the top of the stack. s = [1]. Read 3 from the stream and push it to the stack. s = [1;3]. Example 2: Input: target = [1;2;3]; n = 3 Output: [""Push"";""Push"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Read 3 from the stream and push it to the stack. s = [1;2;3]. Example 3: Input: target = [1;2]; n = 4 Output: [""Push"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Since the stack (from the bottom to the top) is equal to target; we stop the stack operations. The answers that read integer 3 from the stream are not accepted. Constraints: 1 <= target.length <= 100 1 <= n <= 100 1 <= target[i] <= n target is strictly increasing."
Apple,1603,Design Parking System,Easy,"Array, Prefix Sum",Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]). Return the running sum of nums. Example 1: Input: nums = [1;2;3;4] Output: [1;3;6;10] Explanation: Running sum is obtained as follows: [1; 1+2; 1+2+3; 1+2+3+4]. Example 2: Input: nums = [1;1;1;1;1] Output: [1;2;3;4;5] Explanation: Running sum is obtained as follows: [1; 1+1; 1+1+1; 1+1+1+1; 1+1+1+1+1]. Example 3: Input: nums = [3;1;2;10;1] Output: [3;4;6;16;17] Constraints: 1 <= nums.length <= 1000 -10^6 <= nums[i] <= 10^6
Apple,1570,Dot Product of Two Sparse Vectors,Med,"Array, Stack, Monotonic Stack",You are given an integer array prices where prices[i] is the price of the ith item in a shop. There is a special discount for items in the shop. If you buy the ith item; then you will receive a discount equivalent to prices[j] where j is the minimum index such that j > i and prices[j] <= prices[i]. Otherwise; you will not receive any discount at all. Return an integer array answer where answer[i] is the final price you will pay for the ith item of the shop; considering the special discount. Example 1: Input: prices = [8;4;6;2;3] Output: [4;2;4;2;3] Explanation: For item 0 with price[0]=8 you will receive a discount equivalent to prices[1]=4; therefore; the final price you will pay is 8 - 4 = 4. For item 1 with price[1]=4 you will receive a discount equivalent to prices[3]=2; therefore; the final price you will pay is 4 - 2 = 2. For item 2 with price[2]=6 you will receive a discount equivalent to prices[3]=2; therefore; the final price you will pay is 6 - 2 = 4. For items 3 and 4 you will not receive any discount at all. Example 2: Input: prices = [1;2;3;4;5] Output: [1;2;3;4;5] Explanation: In this case; for all items; you will not receive any discount at all. Example 3: Input: prices = [10;1;1;6] Output: [9;0;1;6] Constraints: 1 <= prices.length <= 500 1 <= prices[i] <= 1000
Apple,1637,Widest Vertical Area Between Two Points Containing No Points,Easy,"String, Dynamic Programming","Run-length encoding is a string compression method that works by replacing consecutive identical characters (repeated 2 or more times) with the concatenation of the character and the number marking the count of the characters (length of the run). For example; to compress the string ""aabccc"" we replace ""aa"" by ""a2"" and replace ""ccc"" by ""c3"". Thus the compressed string becomes ""a2bc3"". Notice that in this problem; we are not adding '1' after single characters. Given a string s and an integer k. You need to delete at most k characters from s such that the run-length encoded version of s has minimum length. Find the minimum length of the run-length encoded version of s after deleting at most k characters. Example 1: Input: s = ""aaabcccd""; k = 2 Output: 4 Explanation: Compressing s without deleting anything will give us ""a3bc3d"" of length 6. Deleting any of the characters 'a' or 'c' would at most decrease the length of the compressed string to 5; for instance delete 2 'a' then we will have s = ""abcccd"" which compressed is abc3d. Therefore; the optimal way is to delete 'b' and 'd'; then the compressed version of s will be ""a3c3"" of length 4. Example 2: Input: s = ""aabbaa""; k = 2 Output: 2 Explanation: If we delete both 'b' characters; the resulting compressed string would be ""a4"" of length 2. Example 3: Input: s = ""aaaaaaaaaaa""; k = 0 Output: 3 Explanation: Since k is zero; we cannot delete anything. The compressed string is ""a11"" of length 3. Constraints: 1 <= s.length <= 100 0 <= k <= s.length s contains only lowercase English letters."
Apple,1624,Largest Substring Between Two Equal Characters,Easy,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree",
Apple,1658,Minimum Operations to Reduce X to Zero,Med,"Array, Greedy, Matrix",Given an n x n binary grid; in one step you can choose two adjacent rows of the grid and swap them. A grid is said to be valid if all the cells above the main diagonal are zeros. Return the minimum number of steps needed to make the grid valid; or -1 if the grid cannot be valid. The main diagonal of a grid is the diagonal that starts at cell (1; 1) and ends at cell (n; n). Example 1: Input: grid = [[0;0;1];[1;1;0];[1;0;0]] Output: 3 Example 2: Input: grid = [[0;1;1;0];[0;1;1;0];[0;1;1;0];[0;1;1;0]] Output: -1 Explanation: All rows are similar; swaps have no effect on the grid. Example 3: Input: grid = [[1;0;0];[1;1;0];[1;1;1]] Output: 0 Constraints: n == grid.length == grid[i].length 1 <= n <= 200 grid[i][j] is either 0 or 1
Apple,1662,Check If Two String Arrays are Equivalent,Easy,"Array, Greedy, Bit Manipulation",You are given an integer array nums. You have an integer array arr of the same length with all values set to 0 initially. You also have the following modify function: You want to use the modify function to convert arr to nums using the minimum number of calls. Return the minimum number of function calls to make nums from arr. The test cases are generated so that the answer fits in a 32-bit signed integer. Example 1: Input: nums = [1;5] Output: 5 Explanation: Increment by 1 (second element): [0; 0] to get [0; 1] (1 operation). Double all the elements: [0; 1] -> [0; 2] -> [0; 4] (2 operations). Increment by 1 (both elements) [0; 4] -> [1; 4] -> [1; 5] (2 operations). Total of operations: 1 + 2 + 2 = 5. Example 2: Input: nums = [2;2] Output: 3 Explanation: Increment by 1 (both elements) [0; 0] -> [0; 1] -> [1; 1] (2 operations). Double all the elements: [1; 1] -> [2; 2] (1 operation). Total of operations: 2 + 1 = 3. Example 3: Input: nums = [4;2;5] Output: 6 Explanation: (initial)[0;0;0] -> [1;0;0] -> [1;0;1] -> [2;0;2] -> [2;1;2] -> [4;2;4] -> [4;2;5](nums). Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109
Apple,1679,Max Number of K-Sum Pairs,Med,"Array, Two Pointers, Binary Search, Stack, Monotonic Stack",Given an integer array arr; remove a subarray (can be empty) from arr such that the remaining elements in arr are non-decreasing. Return the length of the shortest subarray to remove. A subarray is a contiguous subsequence of the array. Example 1: Input: arr = [1;2;3;10;4;2;3;5] Output: 3 Explanation: The shortest subarray we can remove is [10;4;2] of length 3. The remaining elements after that will be [1;2;3;3;5] which are sorted. Another correct solution is to remove the subarray [3;10;4]. Example 2: Input: arr = [5;4;3;2;1] Output: 4 Explanation: Since the array is strictly decreasing; we can only keep a single element. Therefore we need to remove a subarray of length 4; either [5;4;3;2] or [4;3;2;1]. Example 3: Input: arr = [1;2;3] Output: 0 Explanation: The array is already non-decreasing. We do not need to remove any elements. Constraints: 1 <= arr.length <= 105 0 <= arr[i] <= 109
Apple,1701,Average Waiting Time,Med,"Union Find, Graph",Alice and Bob have an undirected graph of n nodes and three types of edges: Type 1: Can be traversed by Alice only. Type 2: Can be traversed by Bob only. Type 3: Can be traversed by both Alice and Bob. Given an array edges where edges[i] = [typei; ui; vi] represents a bidirectional edge of type typei between nodes ui and vi; find the maximum number of edges you can remove so that after removing the edges; the graph can still be fully traversed by both Alice and Bob. The graph is fully traversed by Alice and Bob if starting from any node; they can reach all other nodes. Return the maximum number of edges you can remove; or return -1 if Alice and Bob cannot fully traverse the graph. Example 1: Input: n = 4; edges = [[3;1;2];[3;2;3];[1;1;3];[1;2;4];[1;1;2];[2;3;4]] Output: 2 Explanation: If we remove the 2 edges [1;1;2] and [1;1;3]. The graph will still be fully traversable by Alice and Bob. Removing any additional edge will not make it so. So the maximum number of edges we can remove is 2. Example 2: Input: n = 4; edges = [[3;1;2];[3;2;3];[1;1;4];[2;1;4]] Output: 0 Explanation: Notice that removing any edge will not make the graph fully traversable by Alice and Bob. Example 3: Input: n = 4; edges = [[3;2;3];[1;1;2];[2;3;4]] Output: -1 Explanation: In the current graph; Alice cannot reach node 4 from the other nodes. Likewise; Bob cannot reach 1. Therefore it's impossible to make the graph fully traversable. Constraints: 1 <= n <= 105 1 <= edges.length <= min(105; 3 * n * (n - 1) / 2) edges[i].length == 3 1 <= typei <= 3 1 <= ui < vi <= n All tuples (typei; ui; vi) are distinct.
Apple,1704,Determine if String Halves Are Alike,Easy,"Array, Matrix",Given an m x n binary matrix mat; return the number of special positions in mat. A position (i; j) is called special if mat[i][j] == 1 and all other elements in row i and column j are 0 (rows and columns are 0-indexed). Example 1: Input: mat = [[1;0;0];[0;0;1];[1;0;0]] Output: 1 Explanation: (1; 2) is a special position because mat[1][2] == 1 and all other elements in row 1 and column 2 are 0. Example 2: Input: mat = [[1;0;0];[0;1;0];[0;0;1]] Output: 3 Explanation: (0; 0); (1; 1) and (2; 2) are special positions. Constraints: m == mat.length n == mat[i].length 1 <= m; n <= 100 mat[i][j] is either 0 or 1.
Apple,1710,Maximum Units on a Truck,Easy,"Array, Greedy, Heap (Priority Queue), Ordered Set",You have k servers numbered from 0 to k-1 that are being used to handle multiple requests simultaneously. Each server has infinite computational capacity but cannot handle more than one request at a time. The requests are assigned to servers according to a specific algorithm: The ith (0-indexed) request arrives. If all servers are busy; the request is dropped (not handled at all). If the (i % k)th server is available; assign the request to that server. Otherwise; assign the request to the next available server (wrapping around the list of servers and starting from 0 if necessary). For example; if the ith server is busy; try to assign the request to the (i+1)th server; then the (i+2)th server; and so on. You are given a strictly increasing array arrival of positive integers; where arrival[i] represents the arrival time of the ith request; and another array load; where load[i] represents the load of the ith request (the time it takes to complete). Your goal is to find the busiest server(s). A server is considered busiest if it handled the most number of requests successfully among all the servers. Return a list containing the IDs (0-indexed) of the busiest server(s). You may return the IDs in any order. Example 1: Input: k = 3; arrival = [1;2;3;4;5]; load = [5;2;3;3;3] Output: [1] Explanation: All of the servers start out available. The first 3 requests are handled by the first 3 servers in order. Request 3 comes in. Server 0 is busy; so it's assigned to the next available server; which is 1. Request 4 comes in. It cannot be handled since all servers are busy; so it is dropped. Servers 0 and 2 handled one request each; while server 1 handled two requests. Hence server 1 is the busiest server. Example 2: Input: k = 3; arrival = [1;2;3;4]; load = [1;2;1;2] Output: [0] Explanation: The first 3 requests are handled by first 3 servers. Request 3 comes in. It is handled by server 0 since the server is available. Server 0 handled two requests; while servers 1 and 2 handled one request each. Hence server 0 is the busiest server. Example 3: Input: k = 3; arrival = [1;2;3]; load = [10;12;11] Output: [0;1;2] Explanation: Each server handles a single request; so they are all considered the busiest. Constraints: 1 <= k <= 105 1 <= arrival.length; load.length <= 105 arrival.length == load.length 1 <= arrival[i]; load[i] <= 109 arrival is strictly increasing.
Apple,1750,Minimum Length of String After Deleting Similar Ends,Med,"Hash Table, Tree, Depth-First Search, Binary Tree, Counting",
Apple,1752,Check if Array Is Sorted and Rotated,Easy,"Array, Hash Table, Sorting",A sequence of numbers is called arithmetic if it consists of at least two elements; and the difference between every two consecutive elements is the same. More formally; a sequence s is arithmetic if and only if s[i+1] - s[i] == s[1] - s[0] for all valid i. For example; these are arithmetic sequences: 1; 3; 5; 7; 9 7; 7; 7; 7 3; -1; -5; -9 The following sequence is not arithmetic: 1; 1; 2; 5; 7 You are given an array of n integers; nums; and two arrays of m integers each; l and r; representing the m range queries; where the ith query is the range [l[i]; r[i]]. All the arrays are 0-indexed. Return a list of boolean elements answer; where answer[i] is true if the subarray nums[l[i]]; nums[l[i]+1]; ... ; nums[r[i]] can be rearranged to form an arithmetic sequence; and false otherwise. Example 1: Input: nums = [4;6;5;9;3;7]; l = [0;0;2]; r = [2;3;5] Output: [true;false;true] Explanation: In the 0th query; the subarray is [4;6;5]. This can be rearranged as [6;5;4]; which is an arithmetic sequence. In the 1st query; the subarray is [4;6;5;9]. This cannot be rearranged as an arithmetic sequence. In the 2nd query; the subarray is [5;9;3;7]. This can be rearranged as [3;5;7;9]; which is an arithmetic sequence. Example 2: Input: nums = [-12;-9;-3;-12;-6;15;20;-25;-20;-15;-10]; l = [0;1;6;4;8;7]; r = [4;4;9;7;9;10] Output: [false;true;false;false;true;true] Constraints: n == nums.length m == l.length m == r.length 2 <= n <= 500 1 <= m <= 500 0 <= l[i] < r[i] < n -105 <= nums[i] <= 105
Apple,1903,Largest Odd Number in String,Easy,"Array, Hash Table, Stack, Design, Binary Indexed Tree, Ordered Set",
Apple,1970,Last Day Where You Can Still Cross,Hard,"String, Sorting","A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each word consists of lowercase and uppercase English letters. A sentence can be shuffled by appending the 1-indexed word position to each word then rearranging the words in the sentence. For example; the sentence ""This is a sentence"" can be shuffled as ""sentence4 a3 is2 This1"" or ""is2 sentence4 This1 a3"". Given a shuffled sentence s containing no more than 9 words; reconstruct and return the original sentence. Example 1: Input: s = ""is2 sentence4 This1 a3"" Output: ""This is a sentence"" Explanation: Sort the words in s to their original positions ""This1 is2 a3 sentence4""; then remove the numbers. Example 2: Input: s = ""Myself2 Me1 I4 and3"" Output: ""Me Myself and I"" Explanation: Sort the words in s to their original positions ""Me1 Myself2 and3 I4""; then remove the numbers. Constraints: 2 <= s.length <= 200 s consists of lowercase and uppercase English letters; spaces; and digits from 1 to 9. The number of words in s is between 1 and 9. The words in s are separated by a single space. s contains no leading or trailing spaces."
Apple,2004,The Number of Seniors and Juniors to Join the Company,Hard,Database,
Apple,2095,Delete the Middle Node of a Linked List,Med,"Two Pointers, String, Stack, Greedy","You are given a 0-indexed string s of even length n. The string consists of exactly n / 2 opening brackets '[' and n / 2 closing brackets ']'. A string is called balanced if and only if: It is the empty string; or It can be written as AB; where both A and B are balanced strings; or It can be written as [C]; where C is a balanced string. You may swap the brackets at any two indices any number of times. Return the minimum number of swaps to make s balanced. Example 1: Input: s = ""][]["" Output: 1 Explanation: You can make the string balanced by swapping index 0 with index 3. The resulting string is ""[[]]"". Example 2: Input: s = ""]]][[["" Output: 2 Explanation: You can do the following to make the string balanced: - Swap index 0 with index 4. s = ""[]][]["". - Swap index 1 with index 5. s = ""[[][]]"". The resulting string is ""[[][]]"". Example 3: Input: s = ""[]"" Output: 0 Explanation: The string is already balanced. Constraints: n == s.length 2 <= n <= 106 n is even. s[i] is either '[' or ']'. The number of opening brackets '[' equals n / 2; and the number of closing brackets ']' equals n / 2."
Apple,2114,Maximum Number of Words Found in Sentences,Easy,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",There are n tasks assigned to you. The task times are represented as an integer array tasks of length n; where the ith task takes tasks[i] hours to finish. A work session is when you work for at most sessionTime consecutive hours and then take a break. You should finish the given tasks in a way that satisfies the following conditions: If you start a task in a work session; you must complete it in the same work session. You can start a new task immediately after finishing the previous one. You may complete the tasks in any order. Given tasks and sessionTime; return the minimum number of work sessions needed to finish all the tasks following the conditions above. The tests are generated such that sessionTime is greater than or equal to the maximum element in tasks[i]. Example 1: Input: tasks = [1;2;3]; sessionTime = 3 Output: 2 Explanation: You can finish the tasks in two work sessions. - First work session: finish the first and the second tasks in 1 + 2 = 3 hours. - Second work session: finish the third task in 3 hours. Example 2: Input: tasks = [3;1;3;1;1]; sessionTime = 8 Output: 2 Explanation: You can finish the tasks in two work sessions. - First work session: finish all the tasks except the last one in 3 + 1 + 3 + 1 = 8 hours. - Second work session: finish the last task in 1 hour. Example 3: Input: tasks = [1;2;3;4;5]; sessionTime = 15 Output: 1 Explanation: You can finish all the tasks in one work session. Constraints: n == tasks.length 1 <= n <= 14 1 <= tasks[i] <= 10 max(tasks[i]) <= sessionTime <= 15
Apple,2130,Maximum Twin Sum of a Linked List,Med,"String, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask","Given a string s; find two disjoint palindromic subsequences of s such that the product of their lengths is maximized. The two subsequences are disjoint if they do not both pick a character at the same index. Return the maximum possible product of the lengths of the two palindromic subsequences. A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters. A string is palindromic if it reads the same forward and backward. Example 1: Input: s = ""leetcodecom"" Output: 9 Explanation: An optimal solution is to choose ""ete"" for the 1st subsequence and ""cdc"" for the 2nd subsequence. The product of their lengths is: 3 * 3 = 9. Example 2: Input: s = ""bb"" Output: 1 Explanation: An optimal solution is to choose ""b"" (the first character) for the 1st subsequence and ""b"" (the second character) for the 2nd subsequence. The product of their lengths is: 1 * 1 = 1. Example 3: Input: s = ""accbcaxxcxx"" Output: 25 Explanation: An optimal solution is to choose ""accca"" for the 1st subsequence and ""xxcxx"" for the 2nd subsequence. The product of their lengths is: 5 * 5 = 25. Constraints: 2 <= s.length <= 12 s consists of lowercase English letters only."
Apple,2161,Partition Array According to Given Pivot,Med,"Hash Table, Design, Heap (Priority Queue), Data Stream, Ordered Set","You are given a stream of records about a particular stock. Each record contains a timestamp and the corresponding price of the stock at that timestamp. Unfortunately due to the volatile nature of the stock market; the records do not come in order. Even worse; some records may be incorrect. Another record with the same timestamp may appear later in the stream correcting the price of the previous wrong record. Design an algorithm that: Updates the price of the stock at a particular timestamp; correcting the price from any previous records at the timestamp. Finds the latest price of the stock based on the current records. The latest price is the price at the latest timestamp recorded. Finds the maximum price the stock has been based on the current records. Finds the minimum price the stock has been based on the current records. Implement the StockPrice class: StockPrice() Initializes the object with no price records. void update(int timestamp; int price) Updates the price of the stock at the given timestamp. int current() Returns the latest price of the stock. int maximum() Returns the maximum price of the stock. int minimum() Returns the minimum price of the stock. Example 1: Input [""StockPrice""; ""update""; ""update""; ""current""; ""maximum""; ""update""; ""maximum""; ""update""; ""minimum""] [[]; [1; 10]; [2; 5]; []; []; [1; 3]; []; [4; 2]; []] Output [null; null; null; 5; 10; null; 5; null; 2] Explanation StockPrice stockPrice = new StockPrice(); stockPrice.update(1; 10); // Timestamps are [1] with corresponding prices [10]. stockPrice.update(2; 5); // Timestamps are [1;2] with corresponding prices [10;5]. stockPrice.current(); // return 5; the latest timestamp is 2 with the price being 5. stockPrice.maximum(); // return 10; the maximum price is 10 at timestamp 1. stockPrice.update(1; 3); // The previous timestamp 1 had the wrong price; so it is updated to 3. // Timestamps are [1;2] with corresponding prices [3;5]. stockPrice.maximum(); // return 5; the maximum price is 5 after the correction. stockPrice.update(4; 2); // Timestamps are [1;2;4] with corresponding prices [3;5;2]. stockPrice.minimum(); // return 2; the minimum price is 2 at timestamp 4. Constraints: 1 <= timestamp; price <= 109 At most 105 calls will be made in total to update; current; maximum; and minimum. current; maximum; and minimum will be called only after update has been called at least once."
Apple,2150,Find All Lonely Numbers in the Array,Med,"Array, Binary Search",Given two sorted 0-indexed integer arrays nums1 and nums2 as well as an integer k; return the kth (1-based) smallest product of nums1[i] * nums2[j] where 0 <= i < nums1.length and 0 <= j < nums2.length. Example 1: Input: nums1 = [2;5]; nums2 = [3;4]; k = 2 Output: 8 Explanation: The 2 smallest products are: - nums1[0] * nums2[0] = 2 * 3 = 6 - nums1[0] * nums2[1] = 2 * 4 = 8 The 2nd smallest product is 8. Example 2: Input: nums1 = [-4;-2;0;3]; nums2 = [2;4]; k = 6 Output: 0 Explanation: The 6 smallest products are: - nums1[0] * nums2[1] = (-4) * 4 = -16 - nums1[0] * nums2[0] = (-4) * 2 = -8 - nums1[1] * nums2[1] = (-2) * 4 = -8 - nums1[1] * nums2[0] = (-2) * 2 = -4 - nums1[2] * nums2[0] = 0 * 2 = 0 - nums1[2] * nums2[1] = 0 * 4 = 0 The 6th smallest product is 0. Example 3: Input: nums1 = [-2;-1;0;1;2]; nums2 = [-3;-1;2;4;5]; k = 3 Output: -6 Explanation: The 3 smallest products are: - nums1[0] * nums2[4] = (-2) * 5 = -10 - nums1[0] * nums2[3] = (-2) * 4 = -8 - nums1[4] * nums2[0] = 2 * (-3) = -6 The 3rd smallest product is -6. Constraints: 1 <= nums1.length; nums2.length <= 5 * 104 -105 <= nums1[i]; nums2[j] <= 105 1 <= k <= nums1.length * nums2.length nums1 and nums2 are sorted.
Apple,2351,First Letter to Appear Twice,Easy,"Math, Enumeration",You are given an integer total indicating the amount of money you have. You are also given two integers cost1 and cost2 indicating the price of a pen and pencil respectively. You can spend part or all of your money to buy multiple quantities (or none) of each kind of writing utensil. Return the number of distinct ways you can buy some number of pens and pencils. Example 1: Input: total = 20; cost1 = 10; cost2 = 5 Output: 9 Explanation: The price of a pen is 10 and the price of a pencil is 5. - If you buy 0 pens; you can buy 0; 1; 2; 3; or 4 pencils. - If you buy 1 pen; you can buy 0; 1; or 2 pencils. - If you buy 2 pens; you cannot buy any pencils. The total number of ways to buy pens and pencils is 5 + 3 + 1 = 9. Example 2: Input: total = 5; cost1 = 10; cost2 = 10 Output: 1 Explanation: The price of both pens and pencils are 10; which cost more than total; so you cannot buy any writing utensils. Therefore; there is only 1 way: buy 0 pens and 0 pencils. Constraints: 1 <= total; cost1; cost2 <= 106
Apple,2389,Longest Subsequence With Limited Sum,Easy,"Linked List, String, Stack, Design, Simulation, Doubly-Linked List","Design a text editor with a cursor that can do the following: Add text to where the cursor is. Delete text from where the cursor is (simulating the backspace key). Move the cursor either left or right. When deleting text; only characters to the left of the cursor will be deleted. The cursor will also remain within the actual text and cannot be moved beyond it. More formally; we have that 0 <= cursor.position <= currentText.length always holds. Implement the TextEditor class: TextEditor() Initializes the object with empty text. void addText(string text) Appends text to where the cursor is. The cursor ends to the right of text. int deleteText(int k) Deletes k characters to the left of the cursor. Returns the number of characters actually deleted. string cursorLeft(int k) Moves the cursor to the left k times. Returns the last min(10; len) characters to the left of the cursor; where len is the number of characters to the left of the cursor. string cursorRight(int k) Moves the cursor to the right k times. Returns the last min(10; len) characters to the left of the cursor; where len is the number of characters to the left of the cursor. Example 1: Input [""TextEditor""; ""addText""; ""deleteText""; ""addText""; ""cursorRight""; ""cursorLeft""; ""deleteText""; ""cursorLeft""; ""cursorRight""] [[]; [""leetcode""]; [4]; [""practice""]; [3]; [8]; [10]; [2]; [6]] Output [null; null; 4; null; ""etpractice""; ""leet""; 4; """"; ""practi""] Explanation TextEditor textEditor = new TextEditor(); // The current text is ""|"". (The '|' character represents the cursor) textEditor.addText(""leetcode""); // The current text is ""leetcode|"". textEditor.deleteText(4); // return 4 // The current text is ""leet|"". // 4 characters were deleted. textEditor.addText(""practice""); // The current text is ""leetpractice|"". textEditor.cursorRight(3); // return ""etpractice"" // The current text is ""leetpractice|"". // The cursor cannot be moved beyond the actual text and thus did not move. // ""etpractice"" is the last 10 characters to the left of the cursor. textEditor.cursorLeft(8); // return ""leet"" // The current text is ""leet|practice"". // ""leet"" is the last min(10; 4) = 4 characters to the left of the cursor. textEditor.deleteText(10); // return 4 // The current text is ""|practice"". // Only 4 characters were deleted. textEditor.cursorLeft(2); // return """" // The current text is ""|practice"". // The cursor cannot be moved beyond the actual text and thus did not move. // """" is the last min(10; 0) = 0 characters to the left of the cursor. textEditor.cursorRight(6); // return ""practi"" // The current text is ""practi|ce"". // ""practi"" is the last min(10; 6) = 6 characters to the left of the cursor. Constraints: 1 <= text.length; k <= 40 text consists of lowercase English letters. At most 2 * 104 calls in total will be made to addText; deleteText; cursorLeft and cursorRight. Follow-up: Could you find a solution with time complexity of O(k) per call?"
Apple,2444,Count Subarrays With Fixed Bounds,Hard,"Hash Table, String, Dynamic Programming","You are given a string s consisting of lowercase letters and an integer k. We call a string t ideal if the following conditions are satisfied: t is a subsequence of the string s. The absolute difference in the alphabet order of every two adjacent letters in t is less than or equal to k. Return the length of the longest ideal string. A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters. Note that the alphabet order is not cyclic. For example; the absolute difference in the alphabet order of 'a' and 'z' is 25; not 1. Example 1: Input: s = ""acfgbd""; k = 2 Output: 4 Explanation: The longest ideal string is ""acbd"". The length of this string is 4; so 4 is returned. Note that ""acfgbd"" is not ideal because 'c' and 'f' have a difference of 3 in alphabet order. Example 2: Input: s = ""abcd""; k = 3 Output: 4 Explanation: The longest ideal string is ""abcd"". The length of this string is 4; so 4 is returned. Constraints: 1 <= s.length <= 105 0 <= k <= 25 s consists of lowercase English letters."
Apple,2448,Minimum Cost to Make Array Equal,Hard,"Array, Hash Table, Math, Counting",You are given a 0-indexed integer array nums. A pair of indices (i; j) is a bad pair if i < j and j - i != nums[j] - nums[i]. Return the total number of bad pairs in nums. Example 1: Input: nums = [4;1;3;3] Output: 5 Explanation: The pair (0; 1) is a bad pair since 1 - 0 != 1 - 4. The pair (0; 2) is a bad pair since 2 - 0 != 3 - 4; 2 != -1. The pair (0; 3) is a bad pair since 3 - 0 != 3 - 4; 3 != -1. The pair (1; 2) is a bad pair since 2 - 1 != 3 - 1; 1 != 2. The pair (2; 3) is a bad pair since 3 - 2 != 3 - 3; 1 != 0. There are a total of 5 bad pairs; so we return 5. Example 2: Input: nums = [1;2;3;4;5] Output: 0 Explanation: There are no bad pairs. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 109
Apple,2589,Minimum Time to Complete All Tasks,Hard,"Array, String","The value of an alphanumeric string can be defined as: The numeric representation of the string in base 10; if it comprises of digits only. The length of the string; otherwise. Given an array strs of alphanumeric strings; return the maximum value of any string in strs. Example 1: Input: strs = [""alic3"";""bob"";""3"";""4"";""00000""] Output: 5 Explanation: - ""alic3"" consists of both letters and digits; so its value is its length; i.e. 5. - ""bob"" consists only of letters; so its value is also its length; i.e. 3. - ""3"" consists only of digits; so its value is its numeric equivalent; i.e. 3. - ""4"" also consists only of digits; so its value is 4. - ""00000"" consists only of digits; so its value is 0. Hence; the maximum value is 5; of ""alic3"". Example 2: Input: strs = [""1"";""01"";""001"";""0001""] Output: 1 Explanation: Each string in the array has value 1. Hence; we return 1. Constraints: 1 <= strs.length <= 100 1 <= strs[i].length <= 9 strs[i] consists of only lowercase English letters and digits."
Apple,2551,Put Marbles in Bags,Hard,"Array, Two Pointers, Simulation",You are given a 0-indexed array nums of size n consisting of non-negative integers. You need to apply n - 1 operations to this array where; in the ith operation (0-indexed); you will apply the following on the ith element of nums: If nums[i] == nums[i + 1]; then multiply nums[i] by 2 and set nums[i + 1] to 0. Otherwise; you skip this operation. After performing all the operations; shift all the 0's to the end of the array. For example; the array [1;0;2;0;0;1] after shifting all its 0's to the end; is [1;2;1;0;0;0]. Return the resulting array. Note that the operations are applied sequentially; not all at once. Example 1: Input: nums = [1;2;2;1;1;0] Output: [1;4;2;0;0;0] Explanation: We do the following operations: - i = 0: nums[0] and nums[1] are not equal; so we skip this operation. - i = 1: nums[1] and nums[2] are equal; we multiply nums[1] by 2 and change nums[2] to 0. The array becomes [1;4;0;1;1;0]. - i = 2: nums[2] and nums[3] are not equal; so we skip this operation. - i = 3: nums[3] and nums[4] are equal; we multiply nums[3] by 2 and change nums[4] to 0. The array becomes [1;4;0;2;0;0]. - i = 4: nums[4] and nums[5] are equal; we multiply nums[4] by 2 and change nums[5] to 0. The array becomes [1;4;0;2;0;0]. After that; we shift the 0's to the end; which gives the array [1;4;2;0;0;0]. Example 2: Input: nums = [0;1] Output: [1;0] Explanation: No operation can be applied; we just shift the 0 to the end. Constraints: 2 <= nums.length <= 2000 0 <= nums[i] <= 1000
Apple,2574,Left and Right Sum Differences,Easy,"Array, Hash Table, Prefix Sum",You are given an array nums of size n consisting of distinct integers from 1 to n and a positive integer k. Return the number of non-empty subarrays in nums that have a median equal to k. Note: The median of an array is the middle element after sorting the array in ascending order. If the array is of even length; the median is the left middle element. For example; the median of [2;3;1;4] is 2; and the median of [8;4;3;5;1] is 4. A subarray is a contiguous part of an array. Example 1: Input: nums = [3;2;1;4;5]; k = 4 Output: 3 Explanation: The subarrays that have a median equal to 4 are: [4]; [4;5] and [1;4;5]. Example 2: Input: nums = [2;3;1]; k = 3 Output: 1 Explanation: [3] is the only subarray that has a median equal to 3. Constraints: n == nums.length 1 <= n <= 105 1 <= nums[i]; k <= n The integers in nums are distinct.
Apple,2679,Sum in a Matrix,Med,"Array, Hash Table, Math, Simulation",You are given a positive integer n; that is initially placed on a board. Every day; for 109 days; you perform the following procedure: For each number x present on the board; find all numbers 1 <= i <= n such that x % i == 1. Then; place those numbers on the board. Return the number of distinct integers present on the board after 109 days have elapsed. Note: Once a number is placed on the board; it will remain on it until the end. % stands for the modulo operation. For example; 14 % 3 is 2. Example 1: Input: n = 5 Output: 4 Explanation: Initially; 5 is present on the board. The next day; 2 and 4 will be added since 5 % 2 == 1 and 5 % 4 == 1. After that day; 3 will be added to the board because 4 % 3 == 1. At the end of a billion days; the distinct numbers on the board will be 2; 3; 4; and 5. Example 2: Input: n = 3 Output: 2 Explanation: Since 3 % 2 == 1; 2 will be added to the board. After a billion days; the only two distinct numbers on the board are 2 and 3. Constraints: 1 <= n <= 100
Apple,2621,Sleep,Easy,"Array, Math, Bit Manipulation",You are given a 0-indexed integer array nums. The effective value of three indices i; j; and k is defined as ((nums[i] | nums[j]) & nums[k]). The xor-beauty of the array is the XORing of the effective values of all the possible triplets of indices (i; j; k) where 0 <= i; j; k < n. Return the xor-beauty of nums. Note that: val1 | val2 is bitwise OR of val1 and val2. val1 & val2 is bitwise AND of val1 and val2. Example 1: Input: nums = [1;4] Output: 5 Explanation: The triplets and their corresponding effective values are listed below: - (0;0;0) with effective value ((1 | 1) & 1) = 1 - (0;0;1) with effective value ((1 | 1) & 4) = 0 - (0;1;0) with effective value ((1 | 4) & 1) = 1 - (0;1;1) with effective value ((1 | 4) & 4) = 4 - (1;0;0) with effective value ((4 | 1) & 1) = 1 - (1;0;1) with effective value ((4 | 1) & 4) = 4 - (1;1;0) with effective value ((4 | 4) & 1) = 0 - (1;1;1) with effective value ((4 | 4) & 4) = 4 Xor-beauty of array will be bitwise XOR of all beauties = 1 ^ 0 ^ 1 ^ 4 ^ 1 ^ 4 ^ 0 ^ 4 = 5. Example 2: Input: nums = [15;45;20;2;34;35;5;44;32;30] Output: 34 Explanation: The xor-beauty of the given array is 34. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 109
Apple,2619,Array Prototype Last,Easy,Math,"Given four integers length; width; height; and mass; representing the dimensions and mass of a box; respectively; return a string representing the category of the box. The box is ""Bulky"" if: Any of the dimensions of the box is greater or equal to 104. Or; the volume of the box is greater or equal to 109. If the mass of the box is greater or equal to 100; it is ""Heavy"". If the box is both ""Bulky"" and ""Heavy""; then its category is ""Both"". If the box is neither ""Bulky"" nor ""Heavy""; then its category is ""Neither"". If the box is ""Bulky"" but not ""Heavy""; then its category is ""Bulky"". If the box is ""Heavy"" but not ""Bulky""; then its category is ""Heavy"". Note that the volume of the box is the product of its length; width and height. Example 1: Input: length = 1000; width = 35; height = 700; mass = 300 Output: ""Heavy"" Explanation: None of the dimensions of the box is greater or equal to 104. Its volume = 24500000 <= 109. So it cannot be categorized as ""Bulky"". However mass >= 100; so the box is ""Heavy"". Since the box is not ""Bulky"" but ""Heavy""; we return ""Heavy"". Example 2: Input: length = 200; width = 50; height = 800; mass = 50 Output: ""Neither"" Explanation: None of the dimensions of the box is greater or equal to 104. Its volume = 8 * 106 <= 109. So it cannot be categorized as ""Bulky"". Its mass is also less than 100; so it cannot be categorized as ""Heavy"" either. Since its neither of the two above categories; we return ""Neither"". Constraints: 1 <= length; width; height <= 105 1 <= mass <= 103"
Apple,2635,Apply Transform Over Each Element in Array,Easy,"Math, Number Theory",There exists an infinitely large grid. You are currently at point (1; 1); and you need to reach the point (targetX; targetY) using a finite number of steps. In one step; you can move from point (x; y) to any one of the following points: (x; y - x) (x - y; y) (2 * x; y) (x; 2 * y) Given two integers targetX and targetY representing the X-coordinate and Y-coordinate of your final position; return true if you can reach the point from (1; 1) using some number of steps; and false otherwise. Example 1: Input: targetX = 6; targetY = 9 Output: false Explanation: It is impossible to reach (6;9) from (1;1) using any sequence of moves; so false is returned. Example 2: Input: targetX = 4; targetY = 7 Output: true Explanation: You can follow the path (1;1) -> (1;2) -> (1;4) -> (1;8) -> (1;7) -> (2;7) -> (4;7). Constraints: 1 <= targetX; targetY <= 109
Apple,2625,Flatten Deeply Nested Array,Med,"Array, Matrix, Prefix Sum",You are given a positive integer n; indicating that we initially have an n x n 0-indexed integer matrix mat filled with zeroes. You are also given a 2D integer array query. For each query[i] = [row1i; col1i; row2i; col2i]; you should do the following operation: Add 1 to every element in the submatrix with the top left corner (row1i; col1i) and the bottom right corner (row2i; col2i). That is; add 1 to mat[x][y] for all row1i <= x <= row2i and col1i <= y <= col2i. Return the matrix mat after performing every query. Example 1: Input: n = 3; queries = [[1;1;2;2];[0;0;1;1]] Output: [[1;1;0];[1;2;1];[0;1;1]] Explanation: The diagram above shows the initial matrix; the matrix after the first query; and the matrix after the second query. - In the first query; we add 1 to every element in the submatrix with the top left corner (1; 1) and bottom right corner (2; 2). - In the second query; we add 1 to every element in the submatrix with the top left corner (0; 0) and bottom right corner (1; 1). Example 2: Input: n = 2; queries = [[0;0;1;1]] Output: [[1;1];[1;1]] Explanation: The diagram above shows the initial matrix and the matrix after the first query. - In the first query we add 1 to every element in the matrix. Constraints: 1 <= n <= 500 1 <= queries.length <= 104 0 <= row1i <= row2i < n 0 <= col1i <= col2i < n
Apple,2704,To Be Or Not To Be,Easy,"Math, Greedy",You are given an integer num. You know that Bob will sneakily remap one of the 10 possible digits (0 to 9) to another digit. Return the difference between the maximum and minimum values Bob can make by remapping exactly one digit in num. Notes: When Bob remaps a digit d1 to another digit d2; Bob replaces all occurrences of d1 in num with d2. Bob can remap a digit to itself; in which case num does not change. Bob can remap different digits for obtaining minimum and maximum values respectively. The resulting number after remapping can contain leading zeroes. Example 1: Input: num = 11891 Output: 99009 Explanation: To achieve the maximum value; Bob can remap the digit 1 to the digit 9 to yield 99899. To achieve the minimum value; Bob can remap the digit 1 to the digit 0; yielding 890. The difference between these two numbers is 99009. Example 2: Input: num = 90 Output: 99 Explanation: The maximum value that can be returned by the function is 99 (if 0 is replaced by 9) and the minimum value that can be returned by the function is 0 (if 9 is replaced by 0). Thus; we return 99. Constraints: 1 <= num <= 108
Apple,2827,Number of Beautiful Integers in the Range,Hard,"Array, Math, Union Find, Number Theory",You are given a 0-indexed integer array nums; and you are allowed to traverse between its indices. You can traverse between index i and index j; i != j; if and only if gcd(nums[i]; nums[j]) > 1; where gcd is the greatest common divisor. Your task is to determine if for every pair of indices i and j in nums; where i < j; there exists a sequence of traversals that can take us from i to j. Return true if it is possible to traverse between all such pairs of indices; or false otherwise. Example 1: Input: nums = [2;3;6] Output: true Explanation: In this example; there are 3 possible pairs of indices: (0; 1); (0; 2); and (1; 2). To go from index 0 to index 1; we can use the sequence of traversals 0 -> 2 -> 1; where we move from index 0 to index 2 because gcd(nums[0]; nums[2]) = gcd(2; 6) = 2 > 1; and then move from index 2 to index 1 because gcd(nums[2]; nums[1]) = gcd(6; 3) = 3 > 1. To go from index 0 to index 2; we can just go directly because gcd(nums[0]; nums[2]) = gcd(2; 6) = 2 > 1. Likewise; to go from index 1 to index 2; we can just go directly because gcd(nums[1]; nums[2]) = gcd(3; 6) = 3 > 1. Example 2: Input: nums = [3;9;5] Output: false Explanation: No sequence of traversals can take us from index 0 to index 2 in this example. So; we return false. Example 3: Input: nums = [4;3;12;8] Output: true Explanation: There are 6 possible pairs of indices to traverse between: (0; 1); (0; 2); (0; 3); (1; 2); (1; 3); and (2; 3). A valid sequence of traversals exists for each pair; so we return true. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105
Apple,2958,Length of Longest Subarray With at Most K Frequency,Med,,
Apple,3019,Number of Changing Keys,Easy,"String, Counting","You are given a string moves of length n consisting only of characters 'L'; 'R'; and '_'. The string represents your movement on a number line starting from the origin 0. In the ith move; you can choose one of the following directions: move to the left if moves[i] = 'L' or moves[i] = '_' move to the right if moves[i] = 'R' or moves[i] = '_' Return the distance from the origin of the furthest point you can get to after n moves. Example 1: Input: moves = ""L_RL__R"" Output: 3 Explanation: The furthest point we can reach from the origin 0 is point -3 through the following sequence of moves ""LLRLLLR"". Example 2: Input: moves = ""_R__LL_"" Output: 5 Explanation: The furthest point we can reach from the origin 0 is point -5 through the following sequence of moves ""LRLLLLL"". Example 3: Input: moves = ""_______"" Output: 7 Explanation: The furthest point we can reach from the origin 0 is point 7 through the following sequence of moves ""RRRRRRR"". Constraints: 1 <= moves.length == n <= 50 moves consists only of characters 'L'; 'R' and '_'."
Apple,47,Permutations II,Med,"Array, Backtracking",Given a collection of numbers; nums; that might contain duplicates; return all possible unique permutations in any order. Example 1: Input: nums = [1;1;2] Output: [[1;1;2]; [1;2;1]; [2;1;1]] Example 2: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Constraints: 1 <= nums.length <= 8 -10 <= nums[i] <= 10
Apple,60,Permutation Sequence,Hard,"Math, Recursion","The set [1; 2; 3; ...; n] contains a total of n! unique permutations. By listing and labeling all of the permutations in order; we get the following sequence for n = 3: ""123"" ""132"" ""213"" ""231"" ""312"" ""321"" Given n and k; return the kth permutation sequence. Example 1: Input: n = 3; k = 3 Output: ""213"" Example 2: Input: n = 4; k = 9 Output: ""2314"" Example 3: Input: n = 3; k = 1 Output: ""123"" Constraints: 1 <= n <= 9 1 <= k <= n!"
Apple,63,Unique Paths II,Med,"Array, Dynamic Programming, Matrix",You are given an m x n integer array grid. There is a robot initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. An obstacle and space are marked as 1 or 0 respectively in grid. A path that the robot takes cannot include any square that is an obstacle. Return the number of possible unique paths that the robot can take to reach the bottom-right corner. The testcases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: obstacleGrid = [[0;0;0];[0;1;0];[0;0;0]] Output: 2 Explanation: There is one obstacle in the middle of the 3x3 grid above. There are two ways to reach the bottom-right corner: 1. Right -> Right -> Down -> Down 2. Down -> Down -> Right -> Right Example 2: Input: obstacleGrid = [[0;1];[0;0]] Output: 1 Constraints: m == obstacleGrid.length n == obstacleGrid[i].length 1 <= m; n <= 100 obstacleGrid[i][j] is 0 or 1.
Apple,87,Scramble String,Hard,"String, Dynamic Programming","We can scramble a string s to get a string t using the following algorithm: If the length of the string is 1; stop. If the length of the string is > 1; do the following: Split the string into two non-empty substrings at a random index; i.e.; if the string is s; divide it to x and y where s = x + y. Randomly decide to swap the two substrings or to keep them in the same order. i.e.; after this step; s may become s = x + y or s = y + x. Apply step 1 recursively on each of the two substrings x and y. Given two strings s1 and s2 of the same length; return true if s2 is a scrambled string of s1; otherwise; return false. Example 1: Input: s1 = ""great""; s2 = ""rgeat"" Output: true Explanation: One possible scenario applied on s1 is: ""great"" --> ""gr/eat"" // divide at random index. ""gr/eat"" --> ""gr/eat"" // random decision is not to swap the two substrings and keep them in order. ""gr/eat"" --> ""g/r / e/at"" // apply the same algorithm recursively on both substrings. divide at random index each of them. ""g/r / e/at"" --> ""r/g / e/at"" // random decision was to swap the first substring and to keep the second substring in the same order. ""r/g / e/at"" --> ""r/g / e/ a/t"" // again apply the algorithm recursively; divide ""at"" to ""a/t"". ""r/g / e/ a/t"" --> ""r/g / e/ a/t"" // random decision is to keep both substrings in the same order. The algorithm stops now; and the result string is ""rgeat"" which is s2. As one possible scenario led s1 to be scrambled to s2; we return true. Example 2: Input: s1 = ""abcde""; s2 = ""caebd"" Output: false Example 3: Input: s1 = ""a""; s2 = ""a"" Output: true Constraints: s1.length == s2.length 1 <= s1.length <= 30 s1 and s2 consist of lowercase English letters."
Apple,89,Gray Code,Med,"Math, Backtracking, Bit Manipulation",An n-bit gray code sequence is a sequence of 2n integers where: Every integer is in the inclusive range [0; 2n - 1]; The first integer is 0; An integer appears no more than once in the sequence; The binary representation of every pair of adjacent integers differs by exactly one bit; and The binary representation of the first and last integers differs by exactly one bit. Given an integer n; return any valid n-bit gray code sequence. Example 1: Input: n = 2 Output: [0;1;3;2] Explanation: The binary representation of [0;1;3;2] is [00;01;11;10]. - 00 and 01 differ by one bit - 01 and 11 differ by one bit - 11 and 10 differ by one bit - 10 and 00 differ by one bit [0;2;3;1] is also a valid gray code sequence; whose binary representation is [00;10;11;01]. - 00 and 10 differ by one bit - 10 and 11 differ by one bit - 11 and 01 differ by one bit - 01 and 00 differ by one bit Example 2: Input: n = 1 Output: [0;1] Constraints: 1 <= n <= 16
Apple,106,Construct Binary Tree from Inorder and Postorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays inorder and postorder where inorder is the inorder traversal of a binary tree and postorder is the postorder traversal of the same tree; construct and return the binary tree. Example 1: Input: inorder = [9;3;15;20;7]; postorder = [9;15;7;20;3] Output: [3;9;20;null;null;15;7] Example 2: Input: inorder = [-1]; postorder = [-1] Output: [-1] Constraints: 1 <= inorder.length <= 3000 postorder.length == inorder.length -3000 <= inorder[i]; postorder[i] <= 3000 inorder and postorder consist of unique values. Each value of postorder also appears in inorder. inorder is guaranteed to be the inorder traversal of the tree. postorder is guaranteed to be the postorder traversal of the tree.
Apple,109,Convert Sorted List to Binary Search Tree,Med,"Linked List, Divide and Conquer, Tree, Binary Search Tree, Binary Tree",Given the head of a singly linked list where elements are sorted in ascending order; convert it to a height-balanced binary search tree. Example 1: Input: head = [-10;-3;0;5;9] Output: [0;-3;9;-10;null;5] Explanation: One possible answer is [0;-3;9;-10;null;5]; which represents the shown height balanced BST. Example 2: Input: head = [] Output: [] Constraints: The number of nodes in head is in the range [0; 2 * 104]. -105 <= Node.val <= 105
Apple,114,Flatten Binary Tree to Linked List,Med,"Linked List, Stack, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; flatten the tree into a ""linked list"": The ""linked list"" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. The ""linked list"" should be in the same order as a pre-order traversal of the binary tree. Example 1: Input: root = [1;2;5;3;4;null;6] Output: [1;null;2;null;3;null;4;null;5;null;6] Example 2: Input: root = [] Output: [] Example 3: Input: root = [0] Output: [0] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100 Follow up: Can you flatten the tree in-place (with O(1) extra space)?"
Apple,115,Distinct Subsequences,Hard,"String, Dynamic Programming","Given two strings s and t; return the number of distinct subsequences of s which equals t. The test cases are generated so that the answer fits on a 32-bit signed integer. Example 1: Input: s = ""rabbbit""; t = ""rabbit"" Output: 3 Explanation: As shown below; there are 3 ways you can generate ""rabbit"" from s. rabbbit rabbbit rabbbit Example 2: Input: s = ""babgbag""; t = ""bag"" Output: 5 Explanation: As shown below; there are 5 ways you can generate ""bag"" from s. babgbag babgbag babgbag babgbag babgbag Constraints: 1 <= s.length; t.length <= 1000 s and t consist of English letters."
Apple,123,Best Time to Buy and Sell Stock III,Hard,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete at most two transactions. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: prices = [3;3;5;0;0;3;1;4] Output: 6 Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Then buy on day 7 (price = 1) and sell on day 8 (price = 4); profit = 4-1 = 3. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Note that you cannot buy on day 1; buy on day 2 and sell them later; as you are engaging multiple transactions at the same time. You must sell before buying again. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transaction is done; i.e. max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 105
Apple,132,Palindrome Partitioning II,Hard,"String, Dynamic Programming","Given a string s; partition s such that every substring of the partition is a palindrome. Return the minimum cuts needed for a palindrome partitioning of s. Example 1: Input: s = ""aab"" Output: 1 Explanation: The palindrome partitioning [""aa"";""b""] could be produced using 1 cut. Example 2: Input: s = ""a"" Output: 0 Example 3: Input: s = ""ab"" Output: 1 Constraints: 1 <= s.length <= 2000 s consists of lowercase English letters only."
Apple,133,Clone Graph,Med,"Hash Table, Depth-First Search, Breadth-First Search, Graph",Given a reference of a node in a connected undirected graph. Return a deep copy (clone) of the graph. Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors. class Node { public int val; public List<Node> neighbors; } Test case format: For simplicity; each node's value is the same as the node's index (1-indexed). For example; the first node with val == 1; the second node with val == 2; and so on. The graph is represented in the test case using an adjacency list. An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph. The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph. Example 1: Input: adjList = [[2;4];[1;3];[2;4];[1;3]] Output: [[2;4];[1;3];[2;4];[1;3]] Explanation: There are 4 nodes in the graph. 1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). 3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4). 4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). Example 2: Input: adjList = [[]] Output: [[]] Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors. Example 3: Input: adjList = [] Output: [] Explanation: This an empty graph; it does not have any nodes. Constraints: The number of nodes in the graph is in the range [0; 100]. 1 <= Node.val <= 100 Node.val is unique for each node. There are no repeated edges and no self-loops in the graph. The Graph is connected and all nodes can be visited starting from the given node.
Apple,140,Word Break II,Hard,"Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization","Given a string s and a dictionary of strings wordDict; add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""catsanddog""; wordDict = [""cat"";""cats"";""and"";""sand"";""dog""] Output: [""cats and dog"";""cat sand dog""] Example 2: Input: s = ""pineapplepenapple""; wordDict = [""apple"";""pen"";""applepen"";""pine"";""pineapple""] Output: [""pine apple pen apple"";""pineapple pen apple"";""pine applepen apple""] Explanation: Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: [] Constraints: 1 <= s.length <= 20 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 10 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique. Input is generated in a way that the length of the answer doesn't exceed 105."
Apple,145,Binary Tree Postorder Traversal,Easy,"Stack, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the postorder traversal of its nodes' values. Example 1: Input: root = [1;null;2;3] Output: [3;2;1] Explanation: Example 2: Input: root = [1;2;3;4;5;null;8;null;null;6;7;9] Output: [4;6;7;5;2;9;8;3;1] Explanation: Example 3: Input: root = [] Output: [] Example 4: Input: root = [1] Output: [1] Constraints: The number of the nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100 Follow up: Recursive solution is trivial; could you do it iteratively?
Apple,171,Excel Sheet Column Number,Easy,"Math, String","Given a string columnTitle that represents the column title as appears in an Excel sheet; return its corresponding column number. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: Input: columnTitle = ""A"" Output: 1 Example 2: Input: columnTitle = ""AB"" Output: 28 Example 3: Input: columnTitle = ""ZY"" Output: 701 Constraints: 1 <= columnTitle.length <= 7 columnTitle consists only of uppercase English letters. columnTitle is in the range [""A""; ""FXSHRXW""]."
Apple,172,Factorial Trailing Zeroes,Med,Math,Given an integer n; return the number of trailing zeroes in n!. Note that n! = n * (n - 1) * (n - 2) * ... * 3 * 2 * 1. Example 1: Input: n = 3 Output: 0 Explanation: 3! = 6; no trailing zero. Example 2: Input: n = 5 Output: 1 Explanation: 5! = 120; one trailing zero. Example 3: Input: n = 0 Output: 0 Constraints: 0 <= n <= 104 Follow up: Could you write a solution that works in logarithmic time complexity?
Apple,173,Binary Search Tree Iterator,Med,"Stack, Tree, Design, Binary Search Tree, Binary Tree, Iterator","Implement the BSTIterator class that represents an iterator over the in-order traversal of a binary search tree (BST): BSTIterator(TreeNode root) Initializes an object of the BSTIterator class. The root of the BST is given as part of the constructor. The pointer should be initialized to a non-existent number smaller than any element in the BST. boolean hasNext() Returns true if there exists a number in the traversal to the right of the pointer; otherwise returns false. int next() Moves the pointer to the right; then returns the number at the pointer. Notice that by initializing the pointer to a non-existent smallest number; the first call to next() will return the smallest element in the BST. You may assume that next() calls will always be valid. That is; there will be at least a next number in the in-order traversal when next() is called. Example 1: Input [""BSTIterator""; ""next""; ""next""; ""hasNext""; ""next""; ""hasNext""; ""next""; ""hasNext""; ""next""; ""hasNext""] [[[7; 3; 15; null; null; 9; 20]]; []; []; []; []; []; []; []; []; []] Output [null; 3; 7; true; 9; true; 15; true; 20; false] Explanation BSTIterator bSTIterator = new BSTIterator([7; 3; 15; null; null; 9; 20]); bSTIterator.next(); // return 3 bSTIterator.next(); // return 7 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 9 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 15 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 20 bSTIterator.hasNext(); // return False Constraints: The number of nodes in the tree is in the range [1; 105]. 0 <= Node.val <= 106 At most 105 calls will be made to hasNext; and next. Follow up: Could you implement next() and hasNext() to run in average O(1) time and use O(h) memory; where h is the height of the tree?"
Apple,181,Employees Earning More Than Their Managers,Easy,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | salary | int | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID of an employee; their name; salary; and the ID of their manager. Write a solution to find the employees who earn more than their managers. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +----+-------+--------+-----------+ | id | name | salary | managerId | +----+-------+--------+-----------+ | 1 | Joe | 70000 | 3 | | 2 | Henry | 80000 | 4 | | 3 | Sam | 60000 | Null | | 4 | Max | 90000 | Null | +----+-------+--------+-----------+ Output: +----------+ | Employee | +----------+ | Joe | +----------+ Explanation: Joe is the only employee who earns more than his manager.
Apple,183,Customers Who Never Order,Easy,Database,Table: Customers +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID and name of a customer. Table: Orders +-------------+------+ | Column Name | Type | +-------------+------+ | id | int | | customerId | int | +-------------+------+ id is the primary key (column with unique values) for this table. customerId is a foreign key (reference columns) of the ID from the Customers table. Each row of this table indicates the ID of an order and the ID of the customer who ordered it. Write a solution to find all customers who never order anything. Return the result table in any order. The result format is in the following example. Example 1: Input: Customers table: +----+-------+ | id | name | +----+-------+ | 1 | Joe | | 2 | Henry | | 3 | Sam | | 4 | Max | +----+-------+ Orders table: +----+------------+ | id | customerId | +----+------------+ | 1 | 3 | | 2 | 1 | +----+------------+ Output: +-----------+ | Customers | +-----------+ | Henry | | Max | +-----------+
Apple,187,Repeated DNA Sequences,Med,"Hash Table, String, Bit Manipulation, Sliding Window, Rolling Hash, Hash Function","The DNA sequence is composed of a series of nucleotides abbreviated as 'A'; 'C'; 'G'; and 'T'. For example; ""ACGAATTCCG"" is a DNA sequence. When studying DNA; it is useful to identify repeated sequences within the DNA. Given a string s that represents a DNA sequence; return all the 10-letter-long sequences (substrings) that occur more than once in a DNA molecule. You may return the answer in any order. Example 1: Input: s = ""AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"" Output: [""AAAAACCCCC"";""CCCCCAAAAA""] Example 2: Input: s = ""AAAAAAAAAAAAA"" Output: [""AAAAAAAAAA""] Constraints: 1 <= s.length <= 105 s[i] is either 'A'; 'C'; 'G'; or 'T'."
Apple,193,Valid Phone Numbers,Easy,Shell,Given a text file file.txt that contains a list of phone numbers (one per line); write a one-liner bash script to print all valid phone numbers. You may assume that a valid phone number must appear in one of the following two formats: (xxx) xxx-xxxx or xxx-xxx-xxxx. (x means a digit) You may also assume each line in the text file must not contain leading or trailing white spaces. Example: Assume that file.txt has the following content: 987-123-4567 123 456 7890 (123) 456-7890 Your script should output the following valid phone numbers: 987-123-4567 (123) 456-7890
Apple,209,Minimum Size Subarray Sum,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of positive integers nums and a positive integer target; return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray; return 0 instead. Example 1: Input: target = 7; nums = [2;3;1;2;4;3] Output: 2 Explanation: The subarray [4;3] has the minimal length under the problem constraint. Example 2: Input: target = 4; nums = [1;4;4] Output: 1 Example 3: Input: target = 11; nums = [1;1;1;1;1;1;1;1] Output: 0 Constraints: 1 <= target <= 109 1 <= nums.length <= 105 1 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution of which the time complexity is O(n log(n)).
Apple,228,Summary Ranges,Easy,Array,"You are given a sorted unique integer array nums. A range [a;b] is the set of all integers from a to b (inclusive). Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is; each element of nums is covered by exactly one of the ranges; and there is no integer x such that x is in one of the ranges but not in nums. Each range [a;b] in the list should be output as: ""a->b"" if a != b ""a"" if a == b Example 1: Input: nums = [0;1;2;4;5;7] Output: [""0->2"";""4->5"";""7""] Explanation: The ranges are: [0;2] --> ""0->2"" [4;5] --> ""4->5"" [7;7] --> ""7"" Example 2: Input: nums = [0;2;3;4;6;8;9] Output: [""0"";""2->4"";""6"";""8->9""] Explanation: The ranges are: [0;0] --> ""0"" [2;4] --> ""2->4"" [6;6] --> ""6"" [8;9] --> ""8->9"" Constraints: 0 <= nums.length <= 20 -231 <= nums[i] <= 231 - 1 All the values of nums are unique. nums is sorted in ascending order."
Apple,241,Different Ways to Add Parentheses,Med,"Math, String, Dynamic Programming, Recursion, Memoization","Given a string expression of numbers and operators; return all possible results from computing all the different possible ways to group numbers and operators. You may return the answer in any order. The test cases are generated such that the output values fit in a 32-bit integer and the number of different results does not exceed 104. Example 1: Input: expression = ""2-1-1"" Output: [0;2] Explanation: ((2-1)-1) = 0 (2-(1-1)) = 2 Example 2: Input: expression = ""2*3-4*5"" Output: [-34;-14;-10;-10;10] Explanation: (2*(3-(4*5))) = -34 ((2*3)-(4*5)) = -14 ((2*(3-4))*5) = -10 (2*((3-4)*5)) = -10 (((2*3)-4)*5) = 10 Constraints: 1 <= expression.length <= 20 expression consists of digits and the operator '+'; '-'; and '*'. All the integer values in the input expression are in the range [0; 99]. The integer values in the input expression do not have a leading '-' or '+' denoting the sign."
Apple,258,Add Digits,Easy,"Math, Simulation, Number Theory",Given an integer num; repeatedly add all its digits until the result has only one digit; and return it. Example 1: Input: num = 38 Output: 2 Explanation: The process is 38 --> 3 + 8 --> 11 11 --> 1 + 1 --> 2 Since 2 has only one digit; return it. Example 2: Input: num = 0 Output: 0 Constraints: 0 <= num <= 231 - 1 Follow up: Could you do it without any loop/recursion in O(1) runtime?
Apple,264,Ugly Number II,Med,"Hash Table, Math, Dynamic Programming, Heap (Priority Queue)",An ugly number is a positive integer whose prime factors are limited to 2; 3; and 5. Given an integer n; return the nth ugly number. Example 1: Input: n = 10 Output: 12 Explanation: [1; 2; 3; 4; 5; 6; 8; 9; 10; 12] is the sequence of the first 10 ugly numbers. Example 2: Input: n = 1 Output: 1 Explanation: 1 has no prime factors; therefore all of its prime factors are limited to 2; 3; and 5. Constraints: 1 <= n <= 1690
Apple,266,Palindrome Permutation,Easy,"Hash Table, String, Bit Manipulation",
Apple,277,Find the Celebrity,Med,"Two Pointers, Graph, Interactive",
Apple,291,Word Pattern II,Med,"Hash Table, String, Backtracking",
Apple,292,Nim Game,Easy,"Math, Brainteaser, Game Theory",You are playing the following Nim Game with your friend: Initially; there is a heap of stones on the table. You and your friend will alternate taking turns; and you go first. On each turn; the person whose turn it is will remove 1 to 3 stones from the heap. The one who removes the last stone is the winner. Given n; the number of stones in the heap; return true if you can win the game assuming both you and your friend play optimally; otherwise return false. Example 1: Input: n = 4 Output: false Explanation: These are the possible outcomes: 1. You remove 1 stone. Your friend removes 3 stones; including the last stone. Your friend wins. 2. You remove 2 stones. Your friend removes 2 stones; including the last stone. Your friend wins. 3. You remove 3 stones. Your friend removes the last stone. Your friend wins. In all outcomes; your friend wins. Example 2: Input: n = 1 Output: true Example 3: Input: n = 2 Output: true Constraints: 1 <= n <= 231 - 1
Apple,301,Remove Invalid Parentheses,Hard,"String, Backtracking, Breadth-First Search","Given a string s that contains parentheses and letters; remove the minimum number of invalid parentheses to make the input string valid. Return a list of unique strings that are valid with the minimum number of removals. You may return the answer in any order. Example 1: Input: s = ""()())()"" Output: [""(())()"";""()()()""] Example 2: Input: s = ""(a)())()"" Output: [""(a())()"";""(a)()()""] Example 3: Input: s = "")("" Output: [""""] Constraints: 1 <= s.length <= 25 s consists of lowercase English letters and parentheses '(' and ')'. There will be at most 20 parentheses in s."
Apple,303,Range Sum Query - Immutable,Easy,"Array, Design, Prefix Sum","Given an integer array nums; handle multiple queries of the following type: Calculate the sum of the elements of nums between indices left and right inclusive where left <= right. Implement the NumArray class: NumArray(int[] nums) Initializes the object with the integer array nums. int sumRange(int left; int right) Returns the sum of the elements of nums between indices left and right inclusive (i.e. nums[left] + nums[left + 1] + ... + nums[right]). Example 1: Input [""NumArray""; ""sumRange""; ""sumRange""; ""sumRange""] [[[-2; 0; 3; -5; 2; -1]]; [0; 2]; [2; 5]; [0; 5]] Output [null; 1; -1; -3] Explanation NumArray numArray = new NumArray([-2; 0; 3; -5; 2; -1]); numArray.sumRange(0; 2); // return (-2) + 0 + 3 = 1 numArray.sumRange(2; 5); // return 3 + (-5) + 2 + (-1) = -1 numArray.sumRange(0; 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3 Constraints: 1 <= nums.length <= 104 -105 <= nums[i] <= 105 0 <= left <= right < nums.length At most 104 calls will be made to sumRange."
Apple,309,Best Time to Buy and Sell Stock with Cooldown,Med,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete as many transactions as you like (i.e.; buy one and sell one share of the stock multiple times) with the following restrictions: After you sell your stock; you cannot buy stock on the next day (i.e.; cooldown one day). Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: prices = [1;2;3;0;2] Output: 3 Explanation: transactions = [buy; sell; cooldown; buy; sell] Example 2: Input: prices = [1] Output: 0 Constraints: 1 <= prices.length <= 5000 0 <= prices[i] <= 1000
Apple,313,Super Ugly Number,Med,"Array, Math, Dynamic Programming",A super ugly number is a positive integer whose prime factors are in the array primes. Given an integer n and an array of integers primes; return the nth super ugly number. The nth super ugly number is guaranteed to fit in a 32-bit signed integer. Example 1: Input: n = 12; primes = [2;7;13;19] Output: 32 Explanation: [1;2;4;7;8;13;14;16;19;26;28;32] is the sequence of the first 12 super ugly numbers given primes = [2;7;13;19]. Example 2: Input: n = 1; primes = [2;3;5] Output: 1 Explanation: 1 has no prime factors; therefore all of its prime factors are in the array primes = [2;3;5]. Constraints: 1 <= n <= 105 1 <= primes.length <= 100 2 <= primes[i] <= 1000 primes[i] is guaranteed to be a prime number. All the values of primes are unique and sorted in ascending order.
Apple,317,Shortest Distance from All Buildings,Hard,"Array, Breadth-First Search, Matrix",
Apple,332,Reconstruct Itinerary,Hard,"Depth-First Search, Graph, Eulerian Circuit","You are given a list of airline tickets where tickets[i] = [fromi; toi] represent the departure and the arrival airports of one flight. Reconstruct the itinerary in order and return it. All of the tickets belong to a man who departs from ""JFK""; thus; the itinerary must begin with ""JFK"". If there are multiple valid itineraries; you should return the itinerary that has the smallest lexical order when read as a single string. For example; the itinerary [""JFK""; ""LGA""] has a smaller lexical order than [""JFK""; ""LGB""]. You may assume all tickets form at least one valid itinerary. You must use all the tickets once and only once. Example 1: Input: tickets = [[""MUC"";""LHR""];[""JFK"";""MUC""];[""SFO"";""SJC""];[""LHR"";""SFO""]] Output: [""JFK"";""MUC"";""LHR"";""SFO"";""SJC""] Example 2: Input: tickets = [[""JFK"";""SFO""];[""JFK"";""ATL""];[""SFO"";""ATL""];[""ATL"";""JFK""];[""ATL"";""SFO""]] Output: [""JFK"";""ATL"";""JFK"";""SFO"";""ATL"";""SFO""] Explanation: Another possible reconstruction is [""JFK"";""SFO"";""ATL"";""JFK"";""ATL"";""SFO""] but it is larger in lexical order. Constraints: 1 <= tickets.length <= 300 tickets[i].length == 2 fromi.length == 3 toi.length == 3 fromi and toi consist of uppercase English letters. fromi != toi"
Apple,338,Counting Bits,Easy,"Dynamic Programming, Bit Manipulation",Given an integer n; return an array ans of length n + 1 such that for each i (0 <= i <= n); ans[i] is the number of 1's in the binary representation of i. Example 1: Input: n = 2 Output: [0;1;1] Explanation: 0 --> 0 1 --> 1 2 --> 10 Example 2: Input: n = 5 Output: [0;1;1;2;1;2] Explanation: 0 --> 0 1 --> 1 2 --> 10 3 --> 11 4 --> 100 5 --> 101 Constraints: 0 <= n <= 105 Follow up: It is very easy to come up with a solution with a runtime of O(n log n). Can you do it in linear time O(n) and possibly in a single pass? Can you do it without using any built-in function (i.e.; like __builtin_popcount in C++)?
Apple,352,Data Stream as Disjoint Intervals,Hard,"Binary Search, Design, Ordered Set","Given a data stream input of non-negative integers a1; a2; ...; an; summarize the numbers seen so far as a list of disjoint intervals. Implement the SummaryRanges class: SummaryRanges() Initializes the object with an empty stream. void addNum(int value) Adds the integer value to the stream. int[][] getIntervals() Returns a summary of the integers in the stream currently as a list of disjoint intervals [starti; endi]. The answer should be sorted by starti. Example 1: Input [""SummaryRanges""; ""addNum""; ""getIntervals""; ""addNum""; ""getIntervals""; ""addNum""; ""getIntervals""; ""addNum""; ""getIntervals""; ""addNum""; ""getIntervals""] [[]; [1]; []; [3]; []; [7]; []; [2]; []; [6]; []] Output [null; null; [[1; 1]]; null; [[1; 1]; [3; 3]]; null; [[1; 1]; [3; 3]; [7; 7]]; null; [[1; 3]; [7; 7]]; null; [[1; 3]; [6; 7]]] Explanation SummaryRanges summaryRanges = new SummaryRanges(); summaryRanges.addNum(1); // arr = [1] summaryRanges.getIntervals(); // return [[1; 1]] summaryRanges.addNum(3); // arr = [1; 3] summaryRanges.getIntervals(); // return [[1; 1]; [3; 3]] summaryRanges.addNum(7); // arr = [1; 3; 7] summaryRanges.getIntervals(); // return [[1; 1]; [3; 3]; [7; 7]] summaryRanges.addNum(2); // arr = [1; 2; 3; 7] summaryRanges.getIntervals(); // return [[1; 3]; [7; 7]] summaryRanges.addNum(6); // arr = [1; 2; 3; 6; 7] summaryRanges.getIntervals(); // return [[1; 3]; [6; 7]] Constraints: 0 <= value <= 104 At most 3 * 104 calls will be made to addNum and getIntervals. At most 102 calls will be made to getIntervals. Follow up: What if there are lots of merges and the number of disjoint intervals is small compared to the size of the data stream?"
Apple,372,Super Pow,Med,"Math, Divide and Conquer",Your task is to calculate ab mod 1337 where a is a positive integer and b is an extremely large positive integer given in the form of an array. Example 1: Input: a = 2; b = [3] Output: 8 Example 2: Input: a = 2; b = [1;0] Output: 1024 Example 3: Input: a = 1; b = [4;3;3;8;5;2] Output: 1 Constraints: 1 <= a <= 231 - 1 1 <= b.length <= 2000 0 <= b[i] <= 9 b does not contain leading zeros.
Apple,377,Combination Sum IV,Med,"Array, Dynamic Programming",Given an array of distinct integers nums and a target integer target; return the number of possible combinations that add up to target. The test cases are generated so that the answer can fit in a 32-bit integer. Example 1: Input: nums = [1;2;3]; target = 4 Output: 7 Explanation: The possible combination ways are: (1; 1; 1; 1) (1; 1; 2) (1; 2; 1) (1; 3) (2; 1; 1) (2; 2) (3; 1) Note that different sequences are counted as different combinations. Example 2: Input: nums = [9]; target = 3 Output: 0 Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 1000 All the elements of nums are unique. 1 <= target <= 1000 Follow up: What if negative numbers are allowed in the given array? How does it change the problem? What limitation we need to add to the question to allow negative numbers?
Apple,378,Kth Smallest Element in a Sorted Matrix,Med,"Array, Binary Search, Sorting, Heap (Priority Queue), Matrix",Given an n x n matrix where each of the rows and columns is sorted in ascending order; return the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order; not the kth distinct element. You must find a solution with a memory complexity better than O(n2). Example 1: Input: matrix = [[1;5;9];[10;11;13];[12;13;15]]; k = 8 Output: 13 Explanation: The elements in the matrix are [1;5;9;10;11;12;13;13;15]; and the 8th smallest number is 13 Example 2: Input: matrix = [[-5]]; k = 1 Output: -5 Constraints: n == matrix.length == matrix[i].length 1 <= n <= 300 -109 <= matrix[i][j] <= 109 All the rows and columns of matrix are guaranteed to be sorted in non-decreasing order. 1 <= k <= n2 Follow up: Could you solve the problem with a constant memory (i.e.; O(1) memory complexity)? Could you solve the problem in O(n) time complexity? The solution may be too advanced for an interview but you may find reading this paper fun.
Apple,386,Lexicographical Numbers,Med,"Depth-First Search, Trie",Given an integer n; return all the numbers in the range [1; n] sorted in lexicographical order. You must write an algorithm that runs in O(n) time and uses O(1) extra space. Example 1: Input: n = 13 Output: [1;10;11;12;13;2;3;4;5;6;7;8;9] Example 2: Input: n = 2 Output: [1;2] Constraints: 1 <= n <= 5 * 104
Apple,388,Longest Absolute File Path,Med,"String, Stack, Depth-First Search","Suppose we have a file system that stores both files and directories. An example of one system is represented in the following picture: Here; we have dir as the only directory in the root. dir contains two subdirectories; subdir1 and subdir2. subdir1 contains a file file1.ext and subdirectory subsubdir1. subdir2 contains a subdirectory subsubdir2; which contains a file file2.ext. In text form; it looks like this (with ⟶ representing the tab character): dir ⟶ subdir1 ⟶ ⟶ file1.ext ⟶ ⟶ subsubdir1 ⟶ subdir2 ⟶ ⟶ subsubdir2 ⟶ ⟶ ⟶ file2.ext If we were to write this representation in code; it will look like this: ""dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext"". Note that the '\n' and '\t' are the new-line and tab characters. Every file and directory has a unique absolute path in the file system; which is the order of directories that must be opened to reach the file/directory itself; all concatenated by '/'s. Using the above example; the absolute path to file2.ext is ""dir/subdir2/subsubdir2/file2.ext"". Each directory name consists of letters; digits; and/or spaces. Each file name is of the form name.extension; where name and extension consist of letters; digits; and/or spaces. Given a string input representing the file system in the explained format; return the length of the longest absolute path to a file in the abstracted file system. If there is no file in the system; return 0. Note that the testcases are generated such that the file system is valid and no file or directory name has length 0. Example 1: Input: input = ""dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext"" Output: 20 Explanation: We have only one file; and the absolute path is ""dir/subdir2/file.ext"" of length 20. Example 2: Input: input = ""dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext"" Output: 32 Explanation: We have two files: ""dir/subdir1/file1.ext"" of length 21 ""dir/subdir2/subsubdir2/file2.ext"" of length 32. We return 32 since it is the longest absolute path to a file. Example 3: Input: input = ""a"" Output: 0 Explanation: We do not have any files; just a single directory named ""a"". Constraints: 1 <= input.length <= 104 input may contain lowercase or uppercase English letters; a new line character '\n'; a tab character '\t'; a dot '.'; a space ' '; and digits. All file and directory names have positive length."
Apple,409,Longest Palindrome,Easy,"Hash Table, String, Greedy","Given a string s which consists of lowercase or uppercase letters; return the length of the longest palindrome that can be built with those letters. Letters are case sensitive; for example; ""Aa"" is not considered a palindrome. Example 1: Input: s = ""abccccdd"" Output: 7 Explanation: One longest palindrome that can be built is ""dccaccd""; whose length is 7. Example 2: Input: s = ""a"" Output: 1 Explanation: The longest palindrome that can be built is ""a""; whose length is 1. Constraints: 1 <= s.length <= 2000 s consists of lowercase and/or uppercase English letters only."
Apple,422,Valid Word Square,Easy,"Array, Matrix",
Apple,433,Minimum Genetic Mutation,Med,"Hash Table, String, Breadth-First Search","A gene string can be represented by an 8-character long string; with choices from 'A'; 'C'; 'G'; and 'T'. Suppose we need to investigate a mutation from a gene string startGene to a gene string endGene where one mutation is defined as one single character changed in the gene string. For example; ""AACCGGTT"" --> ""AACCGGTA"" is one mutation. There is also a gene bank bank that records all the valid gene mutations. A gene must be in bank to make it a valid gene string. Given the two gene strings startGene and endGene and the gene bank bank; return the minimum number of mutations needed to mutate from startGene to endGene. If there is no such a mutation; return -1. Note that the starting point is assumed to be valid; so it might not be included in the bank. Example 1: Input: startGene = ""AACCGGTT""; endGene = ""AACCGGTA""; bank = [""AACCGGTA""] Output: 1 Example 2: Input: startGene = ""AACCGGTT""; endGene = ""AAACGGTA""; bank = [""AACCGGTA"";""AACCGCTA"";""AAACGGTA""] Output: 2 Constraints: 0 <= bank.length <= 10 startGene.length == endGene.length == bank[i].length == 8 startGene; endGene; and bank[i] consist of only the characters ['A'; 'C'; 'G'; 'T']."
Apple,500,Keyboard Row,Easy,"Array, Hash Table, String","Given an array of strings words; return the words that can be typed using letters of the alphabet on only one row of American keyboard like the image below. Note that the strings are case-insensitive; both lowercased and uppercased of the same letter are treated as if they are at the same row. In the American keyboard: the first row consists of the characters ""qwertyuiop""; the second row consists of the characters ""asdfghjkl""; and the third row consists of the characters ""zxcvbnm"". Example 1: Input: words = [""Hello"";""Alaska"";""Dad"";""Peace""] Output: [""Alaska"";""Dad""] Explanation: Both ""a"" and ""A"" are in the 2nd row of the American keyboard due to case insensitivity. Example 2: Input: words = [""omk""] Output: [] Example 3: Input: words = [""adsdf"";""sfd""] Output: [""adsdf"";""sfd""] Constraints: 1 <= words.length <= 20 1 <= words[i].length <= 100 words[i] consists of English letters (both lowercase and uppercase)."
Apple,502,IPO,Hard,"Array, Greedy, Sorting, Heap (Priority Queue)",Suppose LeetCode will start its IPO soon. In order to sell a good price of its shares to Venture Capital; LeetCode would like to work on some projects to increase its capital before the IPO. Since it has limited resources; it can only finish at most k distinct projects before the IPO. Help LeetCode design the best way to maximize its total capital after finishing at most k distinct projects. You are given n projects where the ith project has a pure profit profits[i] and a minimum capital of capital[i] is needed to start it. Initially; you have w capital. When you finish a project; you will obtain its pure profit and the profit will be added to your total capital. Pick a list of at most k distinct projects from given projects to maximize your final capital; and return the final maximized capital. The answer is guaranteed to fit in a 32-bit signed integer. Example 1: Input: k = 2; w = 0; profits = [1;2;3]; capital = [0;1;1] Output: 4 Explanation: Since your initial capital is 0; you can only start the project indexed 0. After finishing it you will obtain profit 1 and your capital becomes 1. With capital 1; you can either start the project indexed 1 or the project indexed 2. Since you can choose at most 2 projects; you need to finish the project indexed 2 to get the maximum capital. Therefore; output the final maximized capital; which is 0 + 1 + 3 = 4. Example 2: Input: k = 3; w = 0; profits = [1;2;3]; capital = [0;1;2] Output: 6 Constraints: 1 <= k <= 105 0 <= w <= 109 n == profits.length n == capital.length 1 <= n <= 105 0 <= profits[i] <= 104 0 <= capital[i] <= 109
Apple,507,Perfect Number,Easy,Math,A perfect number is a positive integer that is equal to the sum of its positive divisors; excluding the number itself. A divisor of an integer x is an integer that can divide x evenly. Given an integer n; return true if n is a perfect number; otherwise return false. Example 1: Input: num = 28 Output: true Explanation: 28 = 1 + 2 + 4 + 7 + 14 1; 2; 4; 7; and 14 are all divisors of 28. Example 2: Input: num = 7 Output: false Constraints: 1 <= num <= 108
Apple,513,Find Bottom Left Tree Value,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the leftmost value in the last row of the tree. Example 1: Input: root = [2;1;3] Output: 1 Example 2: Input: root = [1;2;3;4;null;5;6;null;null;7] Output: 7 Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Apple,514,Freedom Trail,Hard,"String, Dynamic Programming, Depth-First Search, Breadth-First Search","In the video game Fallout 4; the quest ""Road to Freedom"" requires players to reach a metal dial called the ""Freedom Trail Ring"" and use the dial to spell a specific keyword to open the door. Given a string ring that represents the code engraved on the outer ring and another string key that represents the keyword that needs to be spelled; return the minimum number of steps to spell all the characters in the keyword. Initially; the first character of the ring is aligned at the ""12:00"" direction. You should spell all the characters in key one by one by rotating ring clockwise or anticlockwise to make each character of the string key aligned at the ""12:00"" direction and then by pressing the center button. At the stage of rotating the ring to spell the key character key[i]: You can rotate the ring clockwise or anticlockwise by one place; which counts as one step. The final purpose of the rotation is to align one of ring's characters at the ""12:00"" direction; where this character must equal key[i]. If the character key[i] has been aligned at the ""12:00"" direction; press the center button to spell; which also counts as one step. After the pressing; you could begin to spell the next character in the key (next stage). Otherwise; you have finished all the spelling. Example 1: Input: ring = ""godding""; key = ""gd"" Output: 4 Explanation: For the first key character 'g'; since it is already in place; we just need 1 step to spell this character. For the second key character 'd'; we need to rotate the ring ""godding"" anticlockwise by two steps to make it become ""ddinggo"". Also; we need 1 more step for spelling. So the final output is 4. Example 2: Input: ring = ""godding""; key = ""godding"" Output: 13 Constraints: 1 <= ring.length; key.length <= 100 ring and key consist of only lower case English letters. It is guaranteed that key could always be spelled by rotating ring."
Apple,515,Find Largest Value in Each Tree Row,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return an array of the largest value in each row of the tree (0-indexed). Example 1: Input: root = [1;3;2;5;3;null;9] Output: [1;3;9] Example 2: Input: root = [1;2;3] Output: [1;3] Constraints: The number of nodes in the tree will be in the range [0; 104]. -231 <= Node.val <= 231 - 1
Apple,516,Longest Palindromic Subsequence,Med,"String, Dynamic Programming","Given a string s; find the longest palindromic subsequence's length in s. A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements. Example 1: Input: s = ""bbbab"" Output: 4 Explanation: One possible longest palindromic subsequence is ""bbbb"". Example 2: Input: s = ""cbbd"" Output: 2 Explanation: One possible longest palindromic subsequence is ""bb"". Constraints: 1 <= s.length <= 1000 s consists only of lowercase English letters."
Apple,526,Beautiful Arrangement,Med,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",Suppose you have n integers labeled 1 through n. A permutation of those n integers perm (1-indexed) is considered a beautiful arrangement if for every i (1 <= i <= n); either of the following is true: perm[i] is divisible by i. i is divisible by perm[i]. Given an integer n; return the number of the beautiful arrangements that you can construct. Example 1: Input: n = 2 Output: 2 Explanation: The first beautiful arrangement is [1;2]: - perm[1] = 1 is divisible by i = 1 - perm[2] = 2 is divisible by i = 2 The second beautiful arrangement is [2;1]: - perm[1] = 2 is divisible by i = 1 - i = 2 is divisible by perm[2] = 1 Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 15
Apple,529,Minesweeper,Med,"Array, Depth-First Search, Breadth-First Search, Matrix","Let's play the minesweeper game (Wikipedia; online game)! You are given an m x n char matrix board representing the game board where: 'M' represents an unrevealed mine; 'E' represents an unrevealed empty square; 'B' represents a revealed blank square that has no adjacent mines (i.e.; above; below; left; right; and all 4 diagonals); digit ('1' to '8') represents how many mines are adjacent to this revealed square; and 'X' represents a revealed mine. You are also given an integer array click where click = [clickr; clickc] represents the next click position among all the unrevealed squares ('M' or 'E'). Return the board after revealing this position according to the following rules: If a mine 'M' is revealed; then the game is over. You should change it to 'X'. If an empty square 'E' with no adjacent mines is revealed; then change it to a revealed blank 'B' and all of its adjacent unrevealed squares should be revealed recursively. If an empty square 'E' with at least one adjacent mine is revealed; then change it to a digit ('1' to '8') representing the number of adjacent mines. Return the board when no more squares will be revealed. Example 1: Input: board = [[""E"";""E"";""E"";""E"";""E""];[""E"";""E"";""M"";""E"";""E""];[""E"";""E"";""E"";""E"";""E""];[""E"";""E"";""E"";""E"";""E""]]; click = [3;0] Output: [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""M"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]] Example 2: Input: board = [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""M"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]]; click = [1;2] Output: [[""B"";""1"";""E"";""1"";""B""];[""B"";""1"";""X"";""1"";""B""];[""B"";""1"";""1"";""1"";""B""];[""B"";""B"";""B"";""B"";""B""]] Constraints: m == board.length n == board[i].length 1 <= m; n <= 50 board[i][j] is either 'M'; 'E'; 'B'; or a digit from '1' to '8'. click.length == 2 0 <= clickr < m 0 <= clickc < n board[clickr][clickc] is either 'M' or 'E'."
Apple,541,Reverse String II,Easy,"Two Pointers, String","Given a string s and an integer k; reverse the first k characters for every 2k characters counting from the start of the string. If there are fewer than k characters left; reverse all of them. If there are less than 2k but greater than or equal to k characters; then reverse the first k characters and leave the other as original. Example 1: Input: s = ""abcdefg""; k = 2 Output: ""bacdfeg"" Example 2: Input: s = ""abcd""; k = 2 Output: ""bacd"" Constraints: 1 <= s.length <= 104 s consists of only lowercase English letters. 1 <= k <= 104"
Apple,547,Number of Provinces,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",There are n cities. Some of them are connected; while some are not. If city a is connected directly with city b; and city b is connected directly with city c; then city a is connected indirectly with city c. A province is a group of directly or indirectly connected cities and no other cities outside of the group. You are given an n x n matrix isConnected where isConnected[i][j] = 1 if the ith city and the jth city are directly connected; and isConnected[i][j] = 0 otherwise. Return the total number of provinces. Example 1: Input: isConnected = [[1;1;0];[1;1;0];[0;0;1]] Output: 2 Example 2: Input: isConnected = [[1;0;0];[0;1;0];[0;0;1]] Output: 3 Constraints: 1 <= n <= 200 n == isConnected.length n == isConnected[i].length isConnected[i][j] is 1 or 0. isConnected[i][i] == 1 isConnected[i][j] == isConnected[j][i]
Apple,564,Find the Closest Palindrome,Hard,"Math, String","Given a string n representing an integer; return the closest integer (not including itself); which is a palindrome. If there is a tie; return the smaller one. The closest is defined as the absolute difference minimized between two integers. Example 1: Input: n = ""123"" Output: ""121"" Example 2: Input: n = ""1"" Output: ""0"" Explanation: 0 and 2 are the closest palindromes but we return the smallest which is 0. Constraints: 1 <= n.length <= 18 n consists of only digits. n does not have leading zeros. n is representing an integer in the range [1; 1018 - 1]."
Apple,571,Find Median Given Frequency of Numbers,Hard,Database,
Apple,576,Out of Boundary Paths,Med,Dynamic Programming,There is an m x n grid with a ball. The ball is initially at the position [startRow; startColumn]. You are allowed to move the ball to one of the four adjacent cells in the grid (possibly out of the grid crossing the grid boundary). You can apply at most maxMove moves to the ball. Given the five integers m; n; maxMove; startRow; startColumn; return the number of paths to move the ball out of the grid boundary. Since the answer can be very large; return it modulo 109 + 7. Example 1: Input: m = 2; n = 2; maxMove = 2; startRow = 0; startColumn = 0 Output: 6 Example 2: Input: m = 1; n = 3; maxMove = 3; startRow = 0; startColumn = 1 Output: 12 Constraints: 1 <= m; n <= 50 0 <= maxMove <= 50 0 <= startRow < m 0 <= startColumn < n
Apple,586,Customer Placing the Largest Number of Orders,Easy,Database,Table: Orders +-----------------+----------+ | Column Name | Type | +-----------------+----------+ | order_number | int | | customer_number | int | +-----------------+----------+ order_number is the primary key (column with unique values) for this table. This table contains information about the order ID and the customer ID. Write a solution to find the customer_number for the customer who has placed the largest number of orders. The test cases are generated so that exactly one customer will have placed more orders than any other customer. The result format is in the following example. Example 1: Input: Orders table: +--------------+-----------------+ | order_number | customer_number | +--------------+-----------------+ | 1 | 1 | | 2 | 2 | | 3 | 3 | | 4 | 3 | +--------------+-----------------+ Output: +-----------------+ | customer_number | +-----------------+ | 3 | +-----------------+ Explanation: The customer with number 3 has two orders; which is greater than either customer 1 or 2 because each of them only has one order. So the result is customer_number 3. Follow up: What if more than one customer has the largest number of orders; can you find all the customer_number in this case?
Apple,594,Longest Harmonious Subsequence,Easy,"Array, Hash Table, Sliding Window, Sorting, Counting",We define a harmonious array as an array where the difference between its maximum value and its minimum value is exactly 1. Given an integer array nums; return the length of its longest harmonious subsequence among all its possible subsequences. Example 1: Input: nums = [1;3;2;2;5;2;3;7] Output: 5 Explanation: The longest harmonious subsequence is [3;2;2;2;3]. Example 2: Input: nums = [1;2;3;4] Output: 2 Explanation: The longest harmonious subsequences are [1;2]; [2;3]; and [3;4]; all of which have a length of 2. Example 3: Input: nums = [1;1;1;1] Output: 0 Explanation: No harmonic subsequence exists. Constraints: 1 <= nums.length <= 2 * 104 -109 <= nums[i] <= 109
Apple,606,Construct String from Binary Tree,Med,"String, Tree, Depth-First Search, Binary Tree","Given the root node of a binary tree; your task is to create a string representation of the tree following a specific set of formatting rules. The representation should be based on a preorder traversal of the binary tree and must adhere to the following guidelines: Node Representation: Each node in the tree should be represented by its integer value. Parentheses for Children: If a node has at least one child (either left or right); its children should be represented inside parentheses. Specifically: If a node has a left child; the value of the left child should be enclosed in parentheses immediately following the node's value. If a node has a right child; the value of the right child should also be enclosed in parentheses. The parentheses for the right child should follow those of the left child. Omitting Empty Parentheses: Any empty parentheses pairs (i.e.; ()) should be omitted from the final string representation of the tree; with one specific exception: when a node has a right child but no left child. In such cases; you must include an empty pair of parentheses to indicate the absence of the left child. This ensures that the one-to-one mapping between the string representation and the original binary tree structure is maintained. In summary; empty parentheses pairs should be omitted when a node has only a left child or no children. However; when a node has a right child but no left child; an empty pair of parentheses must precede the representation of the right child to reflect the tree's structure accurately. Example 1: Input: root = [1;2;3;4] Output: ""1(2(4))(3)"" Explanation: Originally; it needs to be ""1(2(4)())(3()())""; but you need to omit all the empty parenthesis pairs. And it will be ""1(2(4))(3)"". Example 2: Input: root = [1;2;3;null;4] Output: ""1(2()(4))(3)"" Explanation: Almost the same as the first example; except the () after 2 is necessary to indicate the absence of a left child for 2 and the presence of a right child. Constraints: The number of nodes in the tree is in the range [1; 104]. -1000 <= Node.val <= 1000"
Apple,619,Biggest Single Number,Easy,Database,Table: MyNumbers +-------------+------+ | Column Name | Type | +-------------+------+ | num | int | +-------------+------+ This table may contain duplicates (In other words; there is no primary key for this table in SQL). Each row of this table contains an integer. A single number is a number that appeared only once in the MyNumbers table. Find the largest single number. If there is no single number; report null. The result format is in the following example. Example 1: Input: MyNumbers table: +-----+ | num | +-----+ | 8 | | 8 | | 3 | | 3 | | 1 | | 4 | | 5 | | 6 | +-----+ Output: +-----+ | num | +-----+ | 6 | +-----+ Explanation: The single numbers are 1; 4; 5; and 6. Since 6 is the largest single number; we return it. Example 2: Input: MyNumbers table: +-----+ | num | +-----+ | 8 | | 8 | | 7 | | 7 | | 3 | | 3 | | 3 | +-----+ Output: +------+ | num | +------+ | null | +------+ Explanation: There are no single numbers in the input table so we return null.
Apple,627,Swap Salary,Easy,Database,Table: Salary +-------------+----------+ | Column Name | Type | +-------------+----------+ | id | int | | name | varchar | | sex | ENUM | | salary | int | +-------------+----------+ id is the primary key (column with unique values) for this table. The sex column is ENUM (category) value of type ('m'; 'f'). The table contains information about an employee. Write a solution to swap all 'f' and 'm' values (i.e.; change all 'f' values to 'm' and vice versa) with a single update statement and no intermediate temporary tables. Note that you must write a single update statement; do not write any select statement for this problem. The result format is in the following example. Example 1: Input: Salary table: +----+------+-----+--------+ | id | name | sex | salary | +----+------+-----+--------+ | 1 | A | m | 2500 | | 2 | B | f | 1500 | | 3 | C | m | 5500 | | 4 | D | f | 500 | +----+------+-----+--------+ Output: +----+------+-----+--------+ | id | name | sex | salary | +----+------+-----+--------+ | 1 | A | f | 2500 | | 2 | B | m | 1500 | | 3 | C | f | 5500 | | 4 | D | m | 500 | +----+------+-----+--------+ Explanation: (1; A) and (3; C) were changed from 'm' to 'f'. (2; B) and (4; D) were changed from 'f' to 'm'.
Apple,632,Smallest Range Covering Elements from K Lists,Hard,"Array, Hash Table, Greedy, Sliding Window, Sorting, Heap (Priority Queue)",You have k lists of sorted integers in non-decreasing order. Find the smallest range that includes at least one number from each of the k lists. We define the range [a; b] is smaller than range [c; d] if b - a < d - c or a < c if b - a == d - c. Example 1: Input: nums = [[4;10;15;24;26];[0;9;12;20];[5;18;22;30]] Output: [20;24] Explanation: List 1: [4; 10; 15; 24;26]; 24 is in range [20;24]. List 2: [0; 9; 12; 20]; 20 is in range [20;24]. List 3: [5; 18; 22; 30]; 22 is in range [20;24]. Example 2: Input: nums = [[1;2;3];[1;2;3];[1;2;3]] Output: [1;1] Constraints: nums.length == k 1 <= k <= 3500 1 <= nums[i].length <= 50 -105 <= nums[i][j] <= 105 nums[i] is sorted in non-decreasing order.
Apple,633,Sum of Square Numbers,Med,"Math, Two Pointers, Binary Search",Given a non-negative integer c; decide whether there're two integers a and b such that a2 + b2 = c. Example 1: Input: c = 5 Output: true Explanation: 1 * 1 + 2 * 2 = 5 Example 2: Input: c = 3 Output: false Constraints: 0 <= c <= 231 - 1
Apple,637,Average of Levels in Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the average value of the nodes on each level in the form of an array. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: root = [3;9;20;null;null;15;7] Output: [3.00000;14.50000;11.00000] Explanation: The average value of nodes on level 0 is 3; on level 1 is 14.5; and on level 2 is 11. Hence return [3; 14.5; 11]. Example 2: Input: root = [3;9;20;15;7] Output: [3.00000;14.50000;11.00000] Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Apple,670,Maximum Swap,Med,"Math, Greedy",You are given an integer num. You can swap two digits at most once to get the maximum valued number. Return the maximum valued number you can get. Example 1: Input: num = 2736 Output: 7236 Explanation: Swap the number 2 and the number 7. Example 2: Input: num = 9973 Output: 9973 Explanation: No swap. Constraints: 0 <= num <= 108
Apple,674,Longest Continuous Increasing Subsequence,Easy,Array,Given an unsorted array of integers nums; return the length of the longest continuous increasing subsequence (i.e. subarray). The subsequence must be strictly increasing. A continuous increasing subsequence is defined by two indices l and r (l < r) such that it is [nums[l]; nums[l + 1]; ...; nums[r - 1]; nums[r]] and for each l <= i < r; nums[i] < nums[i + 1]. Example 1: Input: nums = [1;3;5;4;7] Output: 3 Explanation: The longest continuous increasing subsequence is [1;3;5] with length 3. Even though [1;3;5;7] is an increasing subsequence; it is not continuous as elements 5 and 7 are separated by element 4. Example 2: Input: nums = [2;2;2;2;2] Output: 1 Explanation: The longest continuous increasing subsequence is [2] with length 1. Note that it must be strictly increasing. Constraints: 1 <= nums.length <= 104 -109 <= nums[i] <= 109
Apple,679,24 Game,Hard,"Array, Math, Backtracking","You are given an integer array cards of length 4. You have four cards; each containing a number in the range [1; 9]. You should arrange the numbers on these cards in a mathematical expression using the operators ['+'; '-'; '*'; '/'] and the parentheses '(' and ')' to get the value 24. You are restricted with the following rules: The division operator '/' represents real division; not integer division. For example; 4 / (1 - 2 / 3) = 4 / (1 / 3) = 12. Every operation done is between two numbers. In particular; we cannot use '-' as a unary operator. For example; if cards = [1; 1; 1; 1]; the expression ""-1 - 1 - 1 - 1"" is not allowed. You cannot concatenate numbers together For example; if cards = [1; 2; 1; 2]; the expression ""12 + 12"" is not valid. Return true if you can get such expression that evaluates to 24; and false otherwise. Example 1: Input: cards = [4;1;8;7] Output: true Explanation: (8-4) * (7-1) = 24 Example 2: Input: cards = [1;2;1;2] Output: false Constraints: cards.length == 4 1 <= cards[i] <= 9"
Apple,684,Redundant Connection,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",In this problem; a tree is an undirected graph that is connected and has no cycles. You are given a graph that started as a tree with n nodes labeled from 1 to n; with one additional edge added. The added edge has two different vertices chosen from 1 to n; and was not an edge that already existed. The graph is represented as an array edges of length n where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the graph. Return an edge that can be removed so that the resulting graph is a tree of n nodes. If there are multiple answers; return the answer that occurs last in the input. Example 1: Input: edges = [[1;2];[1;3];[2;3]] Output: [2;3] Example 2: Input: edges = [[1;2];[2;3];[3;4];[1;4];[1;5]] Output: [1;4] Constraints: n == edges.length 3 <= n <= 1000 edges[i].length == 2 1 <= ai < bi <= edges.length ai != bi There are no repeated edges. The given graph is connected.
Apple,718,Maximum Length of Repeated Subarray,Med,"Array, Binary Search, Dynamic Programming, Sliding Window, Rolling Hash, Hash Function",Given two integer arrays nums1 and nums2; return the maximum length of a subarray that appears in both arrays. Example 1: Input: nums1 = [1;2;3;2;1]; nums2 = [3;2;1;4;7] Output: 3 Explanation: The repeated subarray with maximum length is [3;2;1]. Example 2: Input: nums1 = [0;0;0;0;0]; nums2 = [0;0;0;0;0] Output: 5 Explanation: The repeated subarray with maximum length is [0;0;0;0;0]. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 100
Apple,722,Remove Comments,Med,"Array, String","Given a C++ program; remove comments from it. The program source is an array of strings source where source[i] is the ith line of the source code. This represents the result of splitting the original source code string by the newline character '\n'. In C++; there are two types of comments; line comments; and block comments. The string ""//"" denotes a line comment; which represents that it and the rest of the characters to the right of it in the same line should be ignored. The string ""/*"" denotes a block comment; which represents that all characters until the next (non-overlapping) occurrence of ""*/"" should be ignored. (Here; occurrences happen in reading order: line by line from left to right.) To be clear; the string ""/*/"" does not yet end the block comment; as the ending would be overlapping the beginning. The first effective comment takes precedence over others. For example; if the string ""//"" occurs in a block comment; it is ignored. Similarly; if the string ""/*"" occurs in a line or block comment; it is also ignored. If a certain line of code is empty after removing comments; you must not output that line: each string in the answer list will be non-empty. There will be no control characters; single quote; or double quote characters. For example; source = ""string s = ""/* Not a comment. */"";"" will not be a test case. Also; nothing else such as defines or macros will interfere with the comments. It is guaranteed that every open block comment will eventually be closed; so ""/*"" outside of a line or block comment always starts a new comment. Finally; implicit newline characters can be deleted by block comments. Please see the examples below for details. After removing the comments from the source code; return the source code in the same format. Example 1: Input: source = [""/*Test program */""; ""int main()""; ""{ ""; "" // variable declaration ""; ""int a; b; c;""; ""/* This is a test""; "" multiline ""; "" comment for ""; "" testing */""; ""a = b + c;""; ""}""] Output: [""int main()"";""{ "";"" "";""int a; b; c;"";""a = b + c;"";""}""] Explanation: The line by line code is visualized as below: /*Test program */ int main() { // variable declaration int a; b; c; /* This is a test multiline comment for testing */ a = b + c; } The string /* denotes a block comment; including line 1 and lines 6-9. The string // denotes line 4 as comments. The line by line output code is visualized as below: int main() { int a; b; c; a = b + c; } Example 2: Input: source = [""a/*comment""; ""line""; ""more_comment*/b""] Output: [""ab""] Explanation: The original source string is ""a/*comment\nline\nmore_comment*/b""; where we have bolded the newline characters. After deletion; the implicit newline characters are deleted; leaving the string ""ab""; which when delimited by newline characters becomes [""ab""]. Constraints: 1 <= source.length <= 100 0 <= source[i].length <= 80 source[i] consists of printable ASCII characters. Every open block comment is eventually closed. There are no single-quote or double-quote in the input."
Apple,729,My Calendar I,Med,"Array, Binary Search, Design, Segment Tree, Ordered Set","You are implementing a program to use as your calendar. We can add a new event if adding the event will not cause a double booking. A double booking happens when two events have some non-empty intersection (i.e.; some moment is common to both events.). The event can be represented as a pair of integers startTime and endTime that represents a booking on the half-open interval [startTime; endTime); the range of real numbers x such that startTime <= x < endTime. Implement the MyCalendar class: MyCalendar() Initializes the calendar object. boolean book(int startTime; int endTime) Returns true if the event can be added to the calendar successfully without causing a double booking. Otherwise; return false and do not add the event to the calendar. Example 1: Input [""MyCalendar""; ""book""; ""book""; ""book""] [[]; [10; 20]; [15; 25]; [20; 30]] Output [null; true; false; true] Explanation MyCalendar myCalendar = new MyCalendar(); myCalendar.book(10; 20); // return True myCalendar.book(15; 25); // return False; It can not be booked because time 15 is already booked by another event. myCalendar.book(20; 30); // return True; The event can be booked; as the first event takes every time less than 20; but not including 20. Constraints: 0 <= start < end <= 109 At most 1000 calls will be made to book."
Apple,709,To Lower Case,Easy,,
Apple,743,Network Delay Time,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",
Apple,744,Find Smallest Letter Greater Than Target,Easy,"Depth-First Search, Breadth-First Search, Graph, Heap (Priority Queue), Shortest Path",You are given a network of n nodes; labeled from 1 to n. You are also given times; a list of travel times as directed edges times[i] = (ui; vi; wi); where ui is the source node; vi is the target node; and wi is the time it takes for a signal to travel from source to target. We will send a signal from a given node k. Return the minimum time it takes for all the n nodes to receive the signal. If it is impossible for all the n nodes to receive the signal; return -1. Example 1: Input: times = [[2;1;1];[2;3;1];[3;4;1]]; n = 4; k = 2 Output: 2 Example 2: Input: times = [[1;2;1]]; n = 2; k = 1 Output: 1 Example 3: Input: times = [[1;2;1]]; n = 2; k = 2 Output: -1 Constraints: 1 <= k <= n <= 100 1 <= times.length <= 6000 times[i].length == 3 1 <= ui; vi <= n ui != vi 0 <= wi <= 100 All the pairs (ui; vi) are unique. (i.e.; no multiple edges.)
Apple,746,Min Cost Climbing Stairs,Easy,"Array, Hash Table, String, Design, Trie","Design a special dictionary that searches the words in it by a prefix and a suffix. Implement the WordFilter class: WordFilter(string[] words) Initializes the object with the words in the dictionary. f(string pref; string suff) Returns the index of the word in the dictionary; which has the prefix pref and the suffix suff. If there is more than one valid index; return the largest of them. If there is no such word in the dictionary; return -1. Example 1: Input [""WordFilter""; ""f""] [[[""apple""]]; [""a""; ""e""]] Output [null; 0] Explanation WordFilter wordFilter = new WordFilter([""apple""]); wordFilter.f(""a""; ""e""); // return 0; because the word at index 0 has prefix = ""a"" and suffix = ""e"". Constraints: 1 <= words.length <= 104 1 <= words[i].length <= 7 1 <= pref.length; suff.length <= 7 words[i]; pref and suff consist of lowercase English letters only. At most 104 calls will be made to the function f."
Apple,426,Convert Binary Search Tree to Sorted Doubly Linked List,Med,,
Apple,784,Letter Case Permutation,Med,"Tree, Binary Search Tree, Binary Tree",You are given the root node of a binary search tree (BST) and a value to insert into the tree. Return the root node of the BST after the insertion. It is guaranteed that the new value does not exist in the original BST. Notice that there may exist multiple valid ways for the insertion; as long as the tree remains a BST after insertion. You can return any of them. Example 1: Input: root = [4;2;7;1;3]; val = 5 Output: [4;2;7;1;3;5] Explanation: Another accepted tree is: Example 2: Input: root = [40;20;60;10;30;50;70]; val = 25 Output: [40;20;60;10;30;50;70;null;null;25] Example 3: Input: root = [4;2;7;1;3;null;null;null;null;null;null]; val = 5 Output: [4;2;7;1;3;5] Constraints: The number of nodes in the tree will be in the range [0; 104]. -108 <= Node.val <= 108 All the values Node.val are unique. -108 <= val <= 108 It's guaranteed that val does not exist in the original BST.
Apple,792,Number of Matching Subsequences,Med,"Array, Binary Search",Given an array of integers nums which is sorted in ascending order; and an integer target; write a function to search target in nums. If target exists; then return its index. Otherwise; return -1. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [-1;0;3;5;9;12]; target = 9 Output: 4 Explanation: 9 exists in nums and its index is 4 Example 2: Input: nums = [-1;0;3;5;9;12]; target = 2 Output: -1 Explanation: 2 does not exist in nums so return -1 Constraints: 1 <= nums.length <= 104 -104 < nums[i]; target < 104 All the integers in nums are unique. nums is sorted in ascending order.
Apple,797,All Paths From Source to Target,Med,"Array, Hash Table, Math, Greedy","There is a forest with an unknown number of rabbits. We asked n rabbits ""How many rabbits have the same color as you?"" and collected the answers in an integer array answers where answers[i] is the answer of the ith rabbit. Given the array answers; return the minimum number of rabbits that could be in the forest. Example 1: Input: answers = [1;1;2] Output: 5 Explanation: The two rabbits that answered ""1"" could both be the same color; say red. The rabbit that answered ""2"" can't be red or the answers would be inconsistent. Say the rabbit that answered ""2"" was blue. Then there should be 2 other blue rabbits in the forest that didn't answer into the array. The smallest possible number of rabbits in the forest is therefore 5: 3 that answered plus 2 that didn't. Example 2: Input: answers = [10;10;10] Output: 11 Constraints: 1 <= answers.length <= 1000 0 <= answers[i] < 1000"
Apple,819,Most Common Word,Easy,"Array, Dynamic Programming",You are given two integer arrays of the same length nums1 and nums2. In one operation; you are allowed to swap nums1[i] with nums2[i]. For example; if nums1 = [1;2;3;8]; and nums2 = [5;6;7;4]; you can swap the element at i = 3 to obtain nums1 = [1;2;3;4] and nums2 = [5;6;7;8]. Return the minimum number of needed operations to make nums1 and nums2 strictly increasing. The test cases are generated so that the given input always makes it possible. An array arr is strictly increasing if and only if arr[0] < arr[1] < arr[2] < ... < arr[arr.length - 1]. Example 1: Input: nums1 = [1;3;5;4]; nums2 = [1;2;3;7] Output: 1 Explanation: Swap nums1[3] and nums2[3]. Then the sequences are: nums1 = [1; 3; 5; 7] and nums2 = [1; 2; 3; 4] which are both strictly increasing. Example 2: Input: nums1 = [0;3;5;8;9]; nums2 = [2;1;4;6;9] Output: 1 Constraints: 2 <= nums1.length <= 105 nums2.length == nums1.length 0 <= nums1[i]; nums2[i] <= 2 * 105
Apple,827,Making A Large Island,Hard,"Array, Two Pointers, String","Sometimes people repeat letters to represent extra feeling. For example: ""hello"" -> ""heeellooo"" ""hi"" -> ""hiiii"" In these strings like ""heeellooo""; we have groups of adjacent letters that are all the same: ""h""; ""eee""; ""ll""; ""ooo"". You are given a string s and an array of query strings words. A query word is stretchy if it can be made to be equal to s by any number of applications of the following extension operation: choose a group consisting of characters c; and add some number of characters c to the group so that the size of the group is three or more. For example; starting with ""hello""; we could do an extension on the group ""o"" to get ""hellooo""; but we cannot get ""helloo"" since the group ""oo"" has a size less than three. Also; we could do another extension like ""ll"" -> ""lllll"" to get ""helllllooo"". If s = ""helllllooo""; then the query word ""hello"" would be stretchy because of these two extension operations: query = ""hello"" -> ""hellooo"" -> ""helllllooo"" = s. Return the number of query strings that are stretchy. Example 1: Input: s = ""heeellooo""; words = [""hello""; ""hi""; ""helo""] Output: 1 Explanation: We can extend ""e"" and ""o"" in the word ""hello"" to get ""heeellooo"". We can't extend ""helo"" to get ""heeellooo"" because the group ""ll"" is not size 3 or more. Example 2: Input: s = ""zzzzzyyyyy""; words = [""zzyy"";""zy"";""zyy""] Output: 3 Constraints: 1 <= s.length; words.length <= 100 1 <= words[i].length <= 100 s and words[i] consist of lowercase letters."
Apple,829,Consecutive Numbers Sum,Hard,"Array, Hash Table, String, Counting","A website domain ""discuss.leetcode.com"" consists of various subdomains. At the top level; we have ""com""; at the next level; we have ""leetcode.com"" and at the lowest level; ""discuss.leetcode.com"". When we visit a domain like ""discuss.leetcode.com""; we will also visit the parent domains ""leetcode.com"" and ""com"" implicitly. A count-paired domain is a domain that has one of the two formats ""rep d1.d2.d3"" or ""rep d1.d2"" where rep is the number of visits to the domain and d1.d2.d3 is the domain itself. For example; ""9001 discuss.leetcode.com"" is a count-paired domain that indicates that discuss.leetcode.com was visited 9001 times. Given an array of count-paired domains cpdomains; return an array of the count-paired domains of each subdomain in the input. You may return the answer in any order. Example 1: Input: cpdomains = [""9001 discuss.leetcode.com""] Output: [""9001 leetcode.com"";""9001 discuss.leetcode.com"";""9001 com""] Explanation: We only have one website domain: ""discuss.leetcode.com"". As discussed above; the subdomain ""leetcode.com"" and ""com"" will also be visited. So they will all be visited 9001 times. Example 2: Input: cpdomains = [""900 google.mail.com""; ""50 yahoo.com""; ""1 intel.mail.com""; ""5 wiki.org""] Output: [""901 mail.com"";""50 yahoo.com"";""900 google.mail.com"";""5 wiki.org"";""5 org"";""1 intel.mail.com"";""951 com""] Explanation: We will visit ""google.mail.com"" 900 times; ""yahoo.com"" 50 times; ""intel.mail.com"" once and ""wiki.org"" 5 times. For the subdomains; we will visit ""mail.com"" 900 + 1 = 901 times; ""com"" 900 + 50 + 1 = 951 times; and ""org"" 5 times. Constraints: 1 <= cpdomain.length <= 100 1 <= cpdomain[i].length <= 100 cpdomain[i] follows either the ""repi d1i.d2i.d3i"" format or the ""repi d1i.d2i"" format. repi is an integer in the range [1; 104]. d1i; d2i; and d3i consist of lowercase English letters."
Apple,841,Keys and Rooms,Med,"Array, Two Pointers, String","Given a string s and a character c that occurs in s; return an array of integers answer where answer.length == s.length and answer[i] is the distance from index i to the closest occurrence of character c in s. The distance between two indices i and j is abs(i - j); where abs is the absolute value function. Example 1: Input: s = ""loveleetcode""; c = ""e"" Output: [3;2;1;0;1;0;0;1;2;2;1;0] Explanation: The character 'e' appears at indices 3; 5; 6; and 11 (0-indexed). The closest occurrence of 'e' for index 0 is at index 3; so the distance is abs(0 - 3) = 3. The closest occurrence of 'e' for index 1 is at index 3; so the distance is abs(1 - 3) = 2. For index 4; there is a tie between the 'e' at index 3 and the 'e' at index 5; but the distance is still the same: abs(4 - 3) == abs(4 - 5) = 1. The closest occurrence of 'e' for index 8 is at index 6; so the distance is abs(8 - 6) = 2. Example 2: Input: s = ""aaab""; c = ""b"" Output: [3;2;1;0] Constraints: 1 <= s.length <= 104 s[i] and c are lowercase English letters. It is guaranteed that c occurs at least once in s."
Apple,846,Hand of Straights,Med,,
Apple,847,Shortest Path Visiting All Nodes,Hard,,
Apple,849,Maximize Distance to Closest Person,Med,,
Apple,856,Score of Parentheses,Med,"Math, Enumeration",Given an integer n; return the number of ways you can write n as the sum of consecutive positive integers. Example 1: Input: n = 5 Output: 2 Explanation: 5 = 2 + 3 Example 2: Input: n = 9 Output: 3 Explanation: 9 = 4 + 5 = 2 + 3 + 4 Example 3: Input: n = 15 Output: 4 Explanation: 15 = 8 + 7 = 4 + 5 + 6 = 1 + 2 + 3 + 4 + 5 Constraints: 1 <= n <= 109
Apple,862,Shortest Subarray with Sum at Least K,Hard,"Array, Hash Table, String, Sorting","You are given a 0-indexed string s that you must perform k replacement operations on. The replacement operations are given as three 0-indexed parallel arrays; indices; sources; and targets; all of length k. To complete the ith replacement operation: Check if the substring sources[i] occurs at index indices[i] in the original string s. If it does not occur; do nothing. Otherwise if it does occur; replace that substring with targets[i]. For example; if s = ""abcd""; indices[i] = 0; sources[i] = ""ab""; and targets[i] = ""eee""; then the result of this replacement will be ""eeecd"". All replacement operations must occur simultaneously; meaning the replacement operations should not affect the indexing of each other. The testcases will be generated such that the replacements will not overlap. For example; a testcase with s = ""abc""; indices = [0; 1]; and sources = [""ab"";""bc""] will not be generated because the ""ab"" and ""bc"" replacements overlap. Return the resulting string after performing all replacement operations on s. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""abcd""; indices = [0; 2]; sources = [""a""; ""cd""]; targets = [""eee""; ""ffff""] Output: ""eeebffff"" Explanation: ""a"" occurs at index 0 in s; so we replace it with ""eee"". ""cd"" occurs at index 2 in s; so we replace it with ""ffff"". Example 2: Input: s = ""abcd""; indices = [0; 2]; sources = [""ab"";""ec""]; targets = [""eee"";""ffff""] Output: ""eeecd"" Explanation: ""ab"" occurs at index 0 in s; so we replace it with ""eee"". ""ec"" does not occur at index 2 in s; so we do nothing. Constraints: 1 <= s.length <= 1000 k == indices.length == sources.length == targets.length 1 <= k <= 100 0 <= indexes[i] < s.length 1 <= sources[i].length; targets[i].length <= 50 s consists of only lowercase English letters. sources[i] and targets[i] consist of only lowercase English letters."
Apple,872,Leaf-Similar Trees,Easy,"String, Backtracking","You are given a string of digits num; such as ""123456579"". We can split it into a Fibonacci-like sequence [123; 456; 579]. Formally; a Fibonacci-like sequence is a list f of non-negative integers such that: 0 <= f[i] < 231; (that is; each integer fits in a 32-bit signed integer type); f.length >= 3; and f[i] + f[i + 1] == f[i + 2] for all 0 <= i < f.length - 2. Note that when splitting the string into pieces; each piece must not have extra leading zeroes; except if the piece is the number 0 itself. Return any Fibonacci-like sequence split from num; or return [] if it cannot be done. Example 1: Input: num = ""1101111"" Output: [11;0;11;11] Explanation: The output [110; 1; 111] would also be accepted. Example 2: Input: num = ""112358130"" Output: [] Explanation: The task is impossible. Example 3: Input: num = ""0123"" Output: [] Explanation: Leading zeroes are not allowed; so ""01""; ""2""; ""3"" is not valid. Constraints: 1 <= num.length <= 200 num contains only digits."
Apple,878,Nth Magical Number,Hard,"Array, String, Prefix Sum","You are given a string s of lowercase English letters and an integer array shifts of the same length. Call the shift() of a letter; the next letter in the alphabet; (wrapping around so that 'z' becomes 'a'). For example; shift('a') = 'b'; shift('t') = 'u'; and shift('z') = 'a'. Now for each shifts[i] = x; we want to shift the first i + 1 letters of s; x times. Return the final string after all such shifts to s are applied. Example 1: Input: s = ""abc""; shifts = [3;5;9] Output: ""rpl"" Explanation: We start with ""abc"". After shifting the first 1 letters of s by 3; we have ""dbc"". After shifting the first 2 letters of s by 5; we have ""igc"". After shifting the first 3 letters of s by 9; we have ""rpl""; the answer. Example 2: Input: s = ""aaa""; shifts = [1;2;3] Output: ""gfd"" Constraints: 1 <= s.length <= 105 s consists of lowercase English letters. shifts.length == s.length 0 <= shifts[i] <= 109"
Apple,880,Decoded String at Index,Med,"Array, Segment Tree, Line Sweep, Ordered Set",You are given a 2D array of axis-aligned rectangles. Each rectangle[i] = [xi1; yi1; xi2; yi2] denotes the ith rectangle where (xi1; yi1) are the coordinates of the bottom-left corner; and (xi2; yi2) are the coordinates of the top-right corner. Calculate the total area covered by all rectangles in the plane. Any area covered by two or more rectangles should only be counted once. Return the total area. Since the answer may be too large; return it modulo 109 + 7. Example 1: Input: rectangles = [[0;0;2;2];[1;0;2;3];[1;0;3;1]] Output: 6 Explanation: A total area of 6 is covered by all three rectangles; as illustrated in the picture. From (1;1) to (2;2); the green and red rectangles overlap. From (1;0) to (2;3); all three rectangles overlap. Example 2: Input: rectangles = [[0;0;1000000000;1000000000]] Output: 49 Explanation: The answer is 1018 modulo (109 + 7); which is 49. Constraints: 1 <= rectangles.length <= 200 rectanges[i].length == 4 0 <= xi1; yi1; xi2; yi2 <= 109 xi1 <= xi2 yi1 <= yi2
Apple,888,Fair Candy Swap,Easy,"Math, Geometry, Number Theory",There is a special square room with mirrors on each of the four walls. Except for the southwest corner; there are receptors on each of the remaining corners; numbered 0; 1; and 2. The square room has walls of length p and a laser ray from the southwest corner first meets the east wall at a distance q from the 0th receptor. Given the two integers p and q; return the number of the receptor that the ray meets first. The test cases are guaranteed so that the ray will meet a receptor eventually. Example 1: Input: p = 2; q = 1 Output: 2 Explanation: The ray meets receptor 2 the first time it gets reflected back to the left wall. Example 2: Input: p = 3; q = 1 Output: 1 Constraints: 1 <= q <= p <= 1000
Apple,917,Reverse Only Letters,Easy,"Array, Two Pointers, Greedy, Sorting",You are given an array people where people[i] is the weight of the ith person; and an infinite number of boats where each boat can carry a maximum weight of limit. Each boat carries at most two people at the same time; provided the sum of the weight of those people is at most limit. Return the minimum number of boats to carry every given person. Example 1: Input: people = [1;2]; limit = 3 Output: 1 Explanation: 1 boat (1; 2) Example 2: Input: people = [3;2;2;1]; limit = 3 Output: 3 Explanation: 3 boats (1; 2); (2) and (3) Example 3: Input: people = [3;5;3;4]; limit = 5 Output: 4 Explanation: 4 boats (3); (3); (4); (5) Constraints: 1 <= people.length <= 5 * 104 1 <= people[i] <= limit <= 3 * 104
Apple,918,Maximum Sum Circular Subarray,Med,"Graph, Heap (Priority Queue), Shortest Path","You are given an undirected graph (the ""original graph"") with n nodes labeled from 0 to n - 1. You decide to subdivide each edge in the graph into a chain of nodes; with the number of new nodes varying between each edge. The graph is given as a 2D array of edges where edges[i] = [ui; vi; cnti] indicates that there is an edge between nodes ui and vi in the original graph; and cnti is the total number of new nodes that you will subdivide the edge into. Note that cnti == 0 means you will not subdivide the edge. To subdivide the edge [ui; vi]; replace it with (cnti + 1) new edges and cnti new nodes. The new nodes are x1; x2; ...; xcnti; and the new edges are [ui; x1]; [x1; x2]; [x2; x3]; ...; [xcnti-1; xcnti]; [xcnti; vi]. In this new graph; you want to know how many nodes are reachable from the node 0; where a node is reachable if the distance is maxMoves or less. Given the original graph and maxMoves; return the number of nodes that are reachable from node 0 in the new graph. Example 1: Input: edges = [[0;1;10];[0;2;1];[1;2;2]]; maxMoves = 6; n = 3 Output: 13 Explanation: The edge subdivisions are shown in the image above. The nodes that are reachable are highlighted in yellow. Example 2: Input: edges = [[0;1;4];[1;2;6];[0;2;8];[1;3;1]]; maxMoves = 10; n = 4 Output: 23 Example 3: Input: edges = [[1;2;4];[1;4;5];[1;3;1];[2;3;4];[3;4;5]]; maxMoves = 17; n = 5 Output: 1 Explanation: Node 0 is disconnected from the rest of the graph; so only node 0 is reachable. Constraints: 0 <= edges.length <= min(n * (n - 1) / 2; 104) edges[i].length == 3 0 <= ui < vi < n There are no multiple edges in the graph. 0 <= cnti <= 104 0 <= maxMoves <= 109 1 <= n <= 3000"
Apple,923,3Sum With Multiplicity,Med,"Math, Binary Search, Dynamic Programming",You are given k identical eggs and you have access to a building with n floors labeled from 1 to n. You know that there exists a floor f where 0 <= f <= n such that any egg dropped at a floor higher than f will break; and any egg dropped at or below floor f will not break. Each move; you may take an unbroken egg and drop it from any floor x (where 1 <= x <= n). If the egg breaks; you can no longer use it. However; if the egg does not break; you may reuse it in future moves. Return the minimum number of moves that you need to determine with certainty what the value of f is. Example 1: Input: k = 1; n = 2 Output: 2 Explanation: Drop the egg from floor 1. If it breaks; we know that f = 0. Otherwise; drop the egg from floor 2. If it breaks; we know that f = 1. If it does not break; then we know f = 2. Hence; we need at minimum 2 moves to determine with certainty what the value of f is. Example 2: Input: k = 2; n = 6 Output: 3 Example 3: Input: k = 3; n = 14 Output: 4 Constraints: 1 <= k <= 100 1 <= n <= 104
Apple,945,Minimum Increment to Make Array Unique,Med,"Array, Breadth-First Search, Matrix",You are given an n x n integer matrix board where the cells are labeled from 1 to n2 in a Boustrophedon style starting from the bottom left of the board (i.e. board[n - 1][0]) and alternating direction each row. You start on square 1 of the board. In each move; starting from square curr; do the following: Choose a destination square next with a label in the range [curr + 1; min(curr + 6; n2)]. This choice simulates the result of a standard 6-sided die roll: i.e.; there are always at most 6 destinations; regardless of the size of the board. If next has a snake or ladder; you must move to the destination of that snake or ladder. Otherwise; you move to next. The game ends when you reach the square n2. A board square on row r and column c has a snake or ladder if board[r][c] != -1. The destination of that snake or ladder is board[r][c]. Squares 1 and n2 are not the starting points of any snake or ladder. Note that you only take a snake or ladder at most once per dice roll. If the destination to a snake or ladder is the start of another snake or ladder; you do not follow the subsequent snake or ladder. For example; suppose the board is [[-1;4];[-1;3]]; and on the first move; your destination square is 2. You follow the ladder to square 3; but do not follow the subsequent ladder to 4. Return the least number of dice rolls required to reach the square n2. If it is not possible to reach the square; return -1. Example 1: Input: board = [[-1;-1;-1;-1;-1;-1];[-1;-1;-1;-1;-1;-1];[-1;-1;-1;-1;-1;-1];[-1;35;-1;-1;13;-1];[-1;-1;-1;-1;-1;-1];[-1;15;-1;-1;-1;-1]] Output: 4 Explanation: In the beginning; you start at square 1 (at row 5; column 0). You decide to move to square 2 and must take the ladder to square 15. You then decide to move to square 17 and must take the snake to square 13. You then decide to move to square 14 and must take the ladder to square 35. You then decide to move to square 36; ending the game. This is the lowest possible number of moves to reach the last square; so return 4. Example 2: Input: board = [[-1;-1];[-1;3]] Output: 1 Constraints: n == board.length == board[i].length 2 <= n <= 20 board[i][j] is either -1 or in the range [1; n2]. The squares labeled 1 and n2 are not the starting points of any snake or ladder.
Apple,950,Reveal Cards In Increasing Order,Med,"Array, Hash Table, Math, Counting, Number Theory",You are given an integer array deck where deck[i] represents the number written on the ith card. Partition the cards into one or more groups such that: Each group has exactly x cards where x > 1; and All the cards in one group have the same integer written on them. Return true if such partition is possible; or false otherwise. Example 1: Input: deck = [1;2;3;4;4;3;2;1] Output: true Explanation: Possible partition [1;1];[2;2];[3;3];[4;4]. Example 2: Input: deck = [1;1;1;2;2;2;3;3] Output: false Explanation: No possible partition. Constraints: 1 <= deck.length <= 104 0 <= deck[i] < 104
Apple,953,Verifying an Alien Dictionary,Easy,"Two Pointers, String","Given a string s; reverse the string according to the following rules: All the characters that are not English letters remain in the same position. All the English letters (lowercase or uppercase) should be reversed. Return s after reversing it. Example 1: Input: s = ""ab-cd"" Output: ""dc-ba"" Example 2: Input: s = ""a-bC-dEf-ghIj"" Output: ""j-Ih-gfE-dCba"" Example 3: Input: s = ""Test1ng-Leet=code-Q!"" Output: ""Qedo1ct-eeLg=ntse-T!"" Constraints: 1 <= s.length <= 100 s consists of characters with ASCII values in the range [33; 122]. s does not contain '\""' or '\\'."
Apple,968,Binary Tree Cameras,Hard,"Array, Math, Divide and Conquer",An array nums of length n is beautiful if: nums is a permutation of the integers in the range [1; n]. For every 0 <= i < j < n; there is no index k with i < k < j where 2 * nums[k] == nums[i] + nums[j]. Given the integer n; return any beautiful array nums of length n. There will be at least one valid answer for the given n. Example 1: Input: n = 4 Output: [2;1;4;3] Example 2: Input: n = 5 Output: [3;1;2;5;4] Constraints: 1 <= n <= 1000
Apple,969,Pancake Sorting,Med,"Design, Queue, Data Stream","You have a RecentCounter class which counts the number of recent requests within a certain time frame. Implement the RecentCounter class: RecentCounter() Initializes the counter with zero recent requests. int ping(int t) Adds a new request at time t; where t represents some time in milliseconds; and returns the number of requests that has happened in the past 3000 milliseconds (including the new request). Specifically; return the number of requests that have happened in the inclusive range [t - 3000; t]. It is guaranteed that every call to ping uses a strictly larger value of t than the previous call. Example 1: Input [""RecentCounter""; ""ping""; ""ping""; ""ping""; ""ping""] [[]; [1]; [100]; [3001]; [3002]] Output [null; 1; 2; 3; 3] Explanation RecentCounter recentCounter = new RecentCounter(); recentCounter.ping(1); // requests = [1]; range is [-2999;1]; return 1 recentCounter.ping(100); // requests = [1; 100]; range is [-2900;100]; return 2 recentCounter.ping(3001); // requests = [1; 100; 3001]; range is [1;3001]; return 3 recentCounter.ping(3002); // requests = [1; 100; 3001; 3002]; range is [2;3002]; return 3 Constraints: 1 <= t <= 109 Each test case will call ping with strictly increasing values of t. At most 104 calls will be made to ping."
Apple,976,Largest Perimeter Triangle,Easy,"Array, Hash Table, Math, Geometry, Sorting",You are given an array of points in the X-Y plane points where points[i] = [xi; yi]. Return the minimum area of a rectangle formed from these points; with sides parallel to the X and Y axes. If there is not any such rectangle; return 0. Example 1: Input: points = [[1;1];[1;3];[3;1];[3;3];[2;2]] Output: 4 Example 2: Input: points = [[1;1];[1;3];[3;1];[3;3];[4;1];[4;3]] Output: 2 Constraints: 1 <= points.length <= 500 points[i].length == 2 0 <= xi; yi <= 4 * 104 All the given points are unique.
Apple,979,Distribute Coins in Binary Tree,Med,"Array, Two Pointers, String, Greedy","A permutation perm of n + 1 integers of all the integers in the range [0; n] can be represented as a string s of length n where: s[i] == 'I' if perm[i] < perm[i + 1]; and s[i] == 'D' if perm[i] > perm[i + 1]. Given a string s; reconstruct the permutation perm and return it. If there are multiple valid permutations perm; return any of them. Example 1: Input: s = ""IDID"" Output: [0;4;1;3;2] Example 2: Input: s = ""III"" Output: [0;1;2;3] Example 3: Input: s = ""DDI"" Output: [3;2;0;1] Constraints: 1 <= s.length <= 105 s[i] is either 'I' or 'D'."
Apple,982,Triples with Bitwise AND Equal To Zero,Hard,"Array, Greedy, Sorting, Counting",You are given an integer array nums. In one move; you can pick an index i where 0 <= i < nums.length and increment nums[i] by 1. Return the minimum number of moves to make every value in nums unique. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: nums = [1;2;2] Output: 1 Explanation: After 1 move; the array could be [1; 2; 3]. Example 2: Input: nums = [3;2;1;2;1;7] Output: 6 Explanation: After 6 moves; the array could be [3; 4; 1; 2; 5; 7]. It can be shown that it is impossible for the array to have all unique values with 5 or less moves. Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 105
Apple,983,Minimum Cost For Tickets,Med,"Array, Stack, Simulation",Given two integer arrays pushed and popped each with distinct values; return true if this could have been the result of a sequence of push and pop operations on an initially empty stack; or false otherwise. Example 1: Input: pushed = [1;2;3;4;5]; popped = [4;5;3;2;1] Output: true Explanation: We might do the following sequence: push(1); push(2); push(3); push(4); pop() -> 4; push(5); pop() -> 5; pop() -> 3; pop() -> 2; pop() -> 1 Example 2: Input: pushed = [1;2;3;4;5]; popped = [4;3;5;1;2] Output: false Explanation: 1 cannot be popped before 2. Constraints: 1 <= pushed.length <= 1000 0 <= pushed[i] <= 1000 All the elements of pushed are unique. popped.length == pushed.length popped is a permutation of pushed.
Apple,986,Interval List Intersections,Med,"Array, String, Enumeration","Given an array arr of 4 digits; find the latest 24-hour time that can be made using each digit exactly once. 24-hour times are formatted as ""HH:MM""; where HH is between 00 and 23; and MM is between 00 and 59. The earliest 24-hour time is 00:00; and the latest is 23:59. Return the latest 24-hour time in ""HH:MM"" format. If no valid time can be made; return an empty string. Example 1: Input: arr = [1;2;3;4] Output: ""23:41"" Explanation: The valid 24-hour times are ""12:34""; ""12:43""; ""13:24""; ""13:42""; ""14:23""; ""14:32""; ""21:34""; ""21:43""; ""23:14""; and ""23:41"". Of these times; ""23:41"" is the latest. Example 2: Input: arr = [5;5;5;5] Output: """" Explanation: There are no valid 24-hour times as ""55:55"" is not valid. Constraints: arr.length == 4 0 <= arr[i] <= 9"
Apple,992,Subarrays with K Different Integers,Hard,"Array, String, Greedy","You are given an array of n strings strs; all of the same length. We may choose any deletion indices; and we delete all the characters in those indices for each string. For example; if we have strs = [""abcdef"";""uvwxyz""] and deletion indices {0; 2; 3}; then the final array after deletions is [""bef""; ""vyz""]. Suppose we chose a set of deletion indices answer such that after deletions; the final array has its elements in lexicographic order (i.e.; strs[0] <= strs[1] <= strs[2] <= ... <= strs[n - 1]). Return the minimum possible value of answer.length. Example 1: Input: strs = [""ca"";""bb"";""ac""] Output: 1 Explanation: After deleting the first column; strs = [""a""; ""b""; ""c""]. Now strs is in lexicographic order (ie. strs[0] <= strs[1] <= strs[2]). We require at least 1 deletion since initially strs was not in lexicographic order; so the answer is 1. Example 2: Input: strs = [""xc"";""yb"";""za""] Output: 0 Explanation: strs is already in lexicographic order; so we do not need to delete anything. Note that the rows of strs are not necessarily in lexicographic order: i.e.; it is NOT necessarily true that (strs[0][0] <= strs[0][1] <= ...) Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: We have to delete every column. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Apple,1008,Construct Binary Search Tree from Preorder Traversal,Med,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree. We install cameras on the tree nodes where each camera at a node can monitor its parent; itself; and its immediate children. Return the minimum number of cameras needed to monitor all nodes of the tree. Example 1: Input: root = [0;0;null;0;0] Output: 1 Explanation: One camera is enough to monitor all nodes if placed as shown. Example 2: Input: root = [0;0;null;0;null;0;null;null;0] Output: 2 Explanation: At least two cameras are needed to monitor all nodes of the tree. The above image shows one of the valid configurations of camera placement. Constraints: The number of nodes in the tree is in the range [1; 1000]. Node.val == 0
Apple,1021,Remove Outermost Parentheses,Easy,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes where each node in the tree has node.val coins. There are n coins in total throughout the whole tree. In one move; we may choose two adjacent nodes and move one coin from one node to another. A move may be from parent to child; or from child to parent. Return the minimum number of moves required to make every node have exactly one coin. Example 1: Input: root = [3;0;0] Output: 2 Explanation: From the root of the tree; we move one coin to its left child; and one coin to its right child. Example 2: Input: root = [0;3;0] Output: 3 Explanation: From the left child of the root; we move two coins to the root [taking two moves]. Then; we move one coin from the root of the tree to the right child. Constraints: The number of nodes in the tree is n. 1 <= n <= 100 0 <= Node.val <= n The sum of all Node.val is n.
Apple,1023,Camelcase Matching,Med,"Hash Table, String, Binary Search, Design","Design a time-based key-value data structure that can store multiple values for the same key at different time stamps and retrieve the key's value at a certain timestamp. Implement the TimeMap class: TimeMap() Initializes the object of the data structure. void set(String key; String value; int timestamp) Stores the key key with the value value at the given time timestamp. String get(String key; int timestamp) Returns a value such that set was called previously; with timestamp_prev <= timestamp. If there are multiple such values; it returns the value associated with the largest timestamp_prev. If there are no values; it returns """". Example 1: Input [""TimeMap""; ""set""; ""get""; ""get""; ""set""; ""get""; ""get""] [[]; [""foo""; ""bar""; 1]; [""foo""; 1]; [""foo""; 3]; [""foo""; ""bar2""; 4]; [""foo""; 4]; [""foo""; 5]] Output [null; null; ""bar""; ""bar""; null; ""bar2""; ""bar2""] Explanation TimeMap timeMap = new TimeMap(); timeMap.set(""foo""; ""bar""; 1); // store the key ""foo"" and value ""bar"" along with timestamp = 1. timeMap.get(""foo""; 1); // return ""bar"" timeMap.get(""foo""; 3); // return ""bar""; since there is no value corresponding to foo at timestamp 3 and timestamp 2; then the only value is at timestamp 1 is ""bar"". timeMap.set(""foo""; ""bar2""; 4); // store the key ""foo"" and value ""bar2"" along with timestamp = 4. timeMap.get(""foo""; 4); // return ""bar2"" timeMap.get(""foo""; 5); // return ""bar2"" Constraints: 1 <= key.length; value.length <= 100 key and value consist of lowercase English letters and digits. 1 <= timestamp <= 107 All the timestamps timestamp of set are strictly increasing. At most 2 * 105 calls will be made to set and get."
Apple,1025,Divisor Game,Easy,"Array, Dynamic Programming",You have planned some train traveling one year in advance. The days of the year in which you will travel are given as an integer array days. Each day is an integer from 1 to 365. Train tickets are sold in three different ways: a 1-day pass is sold for costs[0] dollars; a 7-day pass is sold for costs[1] dollars; and a 30-day pass is sold for costs[2] dollars. The passes allow that many days of consecutive travel. For example; if we get a 7-day pass on day 2; then we can travel for 7 days: 2; 3; 4; 5; 6; 7; and 8. Return the minimum number of dollars you need to travel every day in the given list of days. Example 1: Input: days = [1;4;6;7;8;20]; costs = [2;7;15] Output: 11 Explanation: For example; here is one way to buy passes that lets you travel your travel plan: On day 1; you bought a 1-day pass for costs[0] = $2; which covered day 1. On day 3; you bought a 7-day pass for costs[1] = $7; which covered days 3; 4; ...; 9. On day 20; you bought a 1-day pass for costs[0] = $2; which covered day 20. In total; you spent $11 and covered all the days of your travel. Example 2: Input: days = [1;2;3;4;5;6;7;8;9;10;30;31]; costs = [2;7;15] Output: 17 Explanation: For example; here is one way to buy passes that lets you travel your travel plan: On day 1; you bought a 30-day pass for costs[2] = $15 which covered days 1; 2; ...; 30. On day 31; you bought a 1-day pass for costs[0] = $2 which covered day 31. In total; you spent $17 and covered all the days of your travel. Constraints: 1 <= days.length <= 365 1 <= days[i] <= 365 days is in strictly increasing order. costs.length == 3 1 <= costs[i] <= 1000
Apple,1027,Longest Arithmetic Subsequence,Med,"Array, Simulation",You are given an integer array nums and an array queries where queries[i] = [vali; indexi]. For each query i; first; apply nums[indexi] = nums[indexi] + vali; then print the sum of the even values of nums. Return an integer array answer where answer[i] is the answer to the ith query. Example 1: Input: nums = [1;2;3;4]; queries = [[1;0];[-3;1];[-4;0];[2;3]] Output: [8;6;2;4] Explanation: At the beginning; the array is [1;2;3;4]. After adding 1 to nums[0]; the array is [2;2;3;4]; and the sum of even values is 2 + 2 + 4 = 8. After adding -3 to nums[1]; the array is [2;-1;3;4]; and the sum of even values is 2 + 4 = 6. After adding -4 to nums[0]; the array is [-2;-1;3;4]; and the sum of even values is -2 + 4 = 2. After adding 2 to nums[3]; the array is [-2;-1;3;6]; and the sum of even values is -2 + 6 = 4. Example 2: Input: nums = [1]; queries = [[4;0]] Output: [0] Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 1 <= queries.length <= 104 -104 <= vali <= 104 0 <= indexi < nums.length
Apple,1035,Uncrossed Lines,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree with unique values and the values of two different nodes of the tree x and y; return true if the nodes corresponding to the values x and y in the tree are cousins; or false otherwise. Two nodes of a binary tree are cousins if they have the same depth with different parents. Note that in a binary tree; the root node is at the depth 0; and children of each depth k node are at the depth k + 1. Example 1: Input: root = [1;2;3;4]; x = 4; y = 3 Output: false Example 2: Input: root = [1;2;3;null;4;null;5]; x = 5; y = 4 Output: true Example 3: Input: root = [1;2;3;null;4]; x = 2; y = 3 Output: false Constraints: The number of nodes in the tree is in the range [2; 100]. 1 <= Node.val <= 100 Each node has a unique value. x != y x and y are exist in the tree.
Apple,1039,Minimum Score Triangulation of Polygon,Med,"Array, Hash Table, Graph",In a town; there are n people labeled from 1 to n. There is a rumor that one of these people is secretly the town judge. If the town judge exists; then: The town judge trusts nobody. Everybody (except for the town judge) trusts the town judge. There is exactly one person that satisfies properties 1 and 2. You are given an array trust where trust[i] = [ai; bi] representing that the person labeled ai trusts the person labeled bi. If a trust relationship does not exist in trust array; then such a trust relationship does not exist. Return the label of the town judge if the town judge exists and can be identified; or return -1 otherwise. Example 1: Input: n = 2; trust = [[1;2]] Output: 2 Example 2: Input: n = 3; trust = [[1;3];[2;3]] Output: 3 Example 3: Input: n = 3; trust = [[1;3];[2;3];[3;1]] Output: -1 Constraints: 1 <= n <= 1000 0 <= trust.length <= 104 trust[i].length == 2 All the pairs of trust are unique. ai != bi 1 <= ai; bi <= n
Apple,1161,Maximum Level Sum of a Binary Tree,Med,Database,Table: Project +-------------+---------+ | Column Name | Type | +-------------+---------+ | project_id | int | | employee_id | int | +-------------+---------+ (project_id; employee_id) is the primary key of this table. employee_id is a foreign key to Employee table. Each row of this table indicates that the employee with employee_id is working on the project with project_id. Table: Employee +------------------+---------+ | Column Name | Type | +------------------+---------+ | employee_id | int | | name | varchar | | experience_years | int | +------------------+---------+ employee_id is the primary key of this table. It's guaranteed that experience_years is not NULL. Each row of this table contains information about one employee. Write an SQL query that reports the average experience years of all the employees for each project; rounded to 2 digits. Return the result table in any order. The query result format is in the following example. Example 1: Input: Project table: +-------------+-------------+ | project_id | employee_id | +-------------+-------------+ | 1 | 1 | | 1 | 2 | | 1 | 3 | | 2 | 1 | | 2 | 4 | +-------------+-------------+ Employee table: +-------------+--------+------------------+ | employee_id | name | experience_years | +-------------+--------+------------------+ | 1 | Khaled | 3 | | 2 | Ali | 2 | | 3 | John | 1 | | 4 | Doe | 2 | +-------------+--------+------------------+ Output: +-------------+---------------+ | project_id | average_years | +-------------+---------------+ | 1 | 2.00 | | 2 | 2.50 | +-------------+---------------+ Explanation: The average experience years for the first project is (3 + 2 + 1) / 3 = 2.00 and for the second project is (3 + 2) / 2 = 2.50
Apple,1052,Grumpy Bookstore Owner,Med,"Array, Greedy, Sorting",
Apple,1054,Distant Barcodes,Med,Bit Manipulation,"The complement of an integer is the integer you get when you flip all the 0's to 1's and all the 1's to 0's in its binary representation. For example; The integer 5 is ""101"" in binary and its complement is ""010"" which is the integer 2. Given an integer n; return its complement. Example 1: Input: n = 5 Output: 2 Explanation: 5 is ""101"" in binary; with complement ""010"" in binary; which is 2 in base-10. Example 2: Input: n = 7 Output: 0 Explanation: 7 is ""111"" in binary; with complement ""000"" in binary; which is 0 in base-10. Example 3: Input: n = 10 Output: 5 Explanation: 10 is ""1010"" in binary; with complement ""0101"" in binary; which is 5 in base-10. Constraints: 0 <= n < 109 Note: This question is the same as 476: https://leetcode.com/problems/number-complement/"
Apple,1075,Project Employees I,Easy,"Array, String, Trie, Sorting",
Apple,1092,Shortest Common Supersequence,Hard,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; find the maximum value v for which there exist different nodes a and b where v = |a.val - b.val| and a is an ancestor of b. A node a is an ancestor of b if either: any child of a is equal to b or any child of a is an ancestor of b. Example 1: Input: root = [8;3;10;1;6;null;14;null;null;4;7;13] Output: 7 Explanation: We have various ancestor-node differences; some of which are given below : |8 - 3| = 5 |3 - 7| = 4 |8 - 1| = 7 |10 - 13| = 3 Among all possible differences; the maximum value of 7 is obtained by |8 - 1| = 7. Example 2: Input: root = [1;null;2;null;0;3] Output: 3 Constraints: The number of nodes in the tree is in the range [2; 5000]. 0 <= Node.val <= 105
Apple,1245,Tree Diameter,Med,Database,Table: Activity +---------------+---------+ | Column Name | Type | +---------------+---------+ | user_id | int | | session_id | int | | activity_date | date | | activity_type | enum | +---------------+---------+ This table may have duplicate rows. The activity_type column is an ENUM (category) of type ('open_session'; 'end_session'; 'scroll_down'; 'send_message'). The table shows the user activities for a social media website. Note that each session belongs to exactly one user. Write a solution to find the daily active user count for a period of 30 days ending 2019-07-27 inclusively. A user was active on someday if they made at least one activity on that day. Return the result table in any order. The result format is in the following example. Example 1: Input: Activity table: +---------+------------+---------------+---------------+ | user_id | session_id | activity_date | activity_type | +---------+------------+---------------+---------------+ | 1 | 1 | 2019-07-20 | open_session | | 1 | 1 | 2019-07-20 | scroll_down | | 1 | 1 | 2019-07-20 | end_session | | 2 | 4 | 2019-07-20 | open_session | | 2 | 4 | 2019-07-21 | send_message | | 2 | 4 | 2019-07-21 | end_session | | 3 | 2 | 2019-07-21 | open_session | | 3 | 2 | 2019-07-21 | send_message | | 3 | 2 | 2019-07-21 | end_session | | 4 | 3 | 2019-06-25 | open_session | | 4 | 3 | 2019-06-25 | end_session | +---------+------------+---------------+---------------+ Output: +------------+--------------+ | day | active_users | +------------+--------------+ | 2019-07-20 | 2 | | 2019-07-21 | 2 | +------------+--------------+ Explanation: Note that we do not care about days with zero active users.
Apple,1258,Synonymous Sentences,Med,Database,Table: Views +---------------+---------+ | Column Name | Type | +---------------+---------+ | article_id | int | | author_id | int | | viewer_id | int | | view_date | date | +---------------+---------+ There is no primary key (column with unique values) for this table; the table may have duplicate rows. Each row of this table indicates that some viewer viewed an article (written by some author) on some date. Note that equal author_id and viewer_id indicate the same person. Write a solution to find all the authors that viewed at least one of their own articles. Return the result table sorted by id in ascending order. The result format is in the following example. Example 1: Input: Views table: +------------+-----------+-----------+------------+ | article_id | author_id | viewer_id | view_date | +------------+-----------+-----------+------------+ | 1 | 3 | 5 | 2019-08-01 | | 1 | 3 | 6 | 2019-08-02 | | 2 | 7 | 7 | 2019-08-01 | | 2 | 7 | 6 | 2019-08-02 | | 4 | 7 | 1 | 2019-07-22 | | 3 | 4 | 4 | 2019-07-21 | | 3 | 4 | 4 | 2019-07-21 | +------------+-----------+-----------+------------+ Output: +------+ | id | +------+ | 4 | | 7 | +------+
Apple,1106,Parsing A Boolean Expression,Hard,"Array, Hash Table, Depth-First Search, Breadth-First Search",There is a 1 million by 1 million grid on an XY-plane; and the coordinates of each grid square are (x; y). We start at the source = [sx; sy] square and want to reach the target = [tx; ty] square. There is also an array of blocked squares; where each blocked[i] = [xi; yi] represents a blocked square with coordinates (xi; yi). Each move; we can walk one square north; east; south; or west if the square is not in the array of blocked squares. We are also not allowed to walk outside of the grid. Return true if and only if it is possible to reach the target square from the source square through a sequence of valid moves. Example 1: Input: blocked = [[0;1];[1;0]]; source = [0;0]; target = [0;2] Output: false Explanation: The target square is inaccessible starting from the source square because we cannot move. We cannot move north or east because those squares are blocked. We cannot move south or west because we cannot go outside of the grid. Example 2: Input: blocked = []; source = [0;0]; target = [999999;999999] Output: true Explanation: Because there are no blocked cells; it is possible to reach the target square. Constraints: 0 <= blocked.length <= 200 blocked[i].length == 2 0 <= xi; yi < 106 source.length == target.length == 2 0 <= sx; sy; tx; ty < 106 source != target It is guaranteed that source and target are not blocked.
Apple,1108,Defanging an IP Address,Easy,"Array, Hash Table, Sorting",
Apple,1110,Delete Nodes And Return Forest,Med,,
Apple,1124,Longest Well-Performing Interval,Med,"Hash Table, String",
Apple,1289,Minimum Falling Path Sum II,Hard,Math,"Given a date; return the corresponding day of the week for that date. The input is given as three integers representing the day; month and year respectively. Return the answer as one of the following values {""Sunday""; ""Monday""; ""Tuesday""; ""Wednesday""; ""Thursday""; ""Friday""; ""Saturday""}. Example 1: Input: day = 31; month = 8; year = 2019 Output: ""Saturday"" Example 2: Input: day = 18; month = 7; year = 1999 Output: ""Sunday"" Example 3: Input: day = 15; month = 8; year = 1993 Output: ""Sunday"" Constraints: The given dates are valid dates between the years 1971 and 2100."
Apple,1128,Number of Equivalent Domino Pairs,Easy,"String, Stack","You are given a string s consisting of lowercase English letters. A duplicate removal consists of choosing two adjacent and equal letters and removing them. We repeatedly make duplicate removals on s until we no longer can. Return the final string after all such duplicate removals have been made. It can be proven that the answer is unique. Example 1: Input: s = ""abbaca"" Output: ""ca"" Explanation: For example; in ""abbaca"" we could remove ""bb"" since the letters are adjacent and equal; and this is the only possible move. The result of this move is that the string is ""aaca""; of which only ""aa"" is possible; so the final string is ""ca"". Example 2: Input: s = ""azxxzy"" Output: ""ay"" Constraints: 1 <= s.length <= 105 s consists of lowercase English letters."
Apple,1155,Number of Dice Rolls With Target Sum,Med,Database,Table: Sales +-------------+-------+ | Column Name | Type | +-------------+-------+ | sale_id | int | | product_id | int | | year | int | | quantity | int | | price | int | +-------------+-------+ (sale_id; year) is the primary key (combination of columns with unique values) of this table. product_id is a foreign key (reference column) to Product table. Each row of this table shows a sale on the product product_id in a certain year. Note that the price is per unit. Table: Product +--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | +--------------+---------+ product_id is the primary key (column with unique values) of this table. Each row of this table indicates the product name of each product. Write a solution to select the product id; year; quantity; and price for the first year of every product sold. Return the resulting table in any order. The result format is in the following example. Example 1: Input: Sales table: +---------+------------+------+----------+-------+ | sale_id | product_id | year | quantity | price | +---------+------------+------+----------+-------+ | 1 | 100 | 2008 | 10 | 5000 | | 2 | 100 | 2009 | 12 | 5000 | | 7 | 200 | 2011 | 15 | 9000 | +---------+------------+------+----------+-------+ Product table: +------------+--------------+ | product_id | product_name | +------------+--------------+ | 100 | Nokia | | 200 | Apple | | 300 | Samsung | +------------+--------------+ Output: +------------+------------+----------+-------+ | product_id | first_year | quantity | price | +------------+------------+----------+-------+ | 100 | 2008 | 10 | 5000 | | 200 | 2011 | 15 | 9000 | +------------+------------+----------+-------+
Apple,1171,Remove Zero Sum Consecutive Nodes from Linked List,Med,"Array, Breadth-First Search, Matrix",Given an n x n binary matrix grid; return the length of the shortest clear path in the matrix. If there is no clear path; return -1. A clear path in a binary matrix is a path from the top-left cell (i.e.; (0; 0)) to the bottom-right cell (i.e.; (n - 1; n - 1)) such that: All the visited cells of the path are 0. All the adjacent cells of the path are 8-directionally connected (i.e.; they are different and they share an edge or a corner). The length of a clear path is the number of visited cells of this path. Example 1: Input: grid = [[0;1];[1;0]] Output: 2 Example 2: Input: grid = [[0;0;0];[1;1;0];[1;1;0]] Output: 4 Example 3: Input: grid = [[1;0;0];[1;1;0];[1;1;0]] Output: -1 Constraints: n == grid.length n == grid[i].length 1 <= n <= 100 grid[i][j] is 0 or 1
Apple,1425,Constrained Subsequence Sum,Hard,Database,
Apple,1189,Maximum Number of Balloons,Easy,"Math, String, Bit Manipulation",
Apple,1193,Monthly Transactions I,Med,Database,
Apple,1217,Minimum Cost to Move Chips to The Same Position,Easy,"Array, Hash Table, Sorting, Counting Sort",Given two arrays arr1 and arr2; the elements of arr2 are distinct; and all elements in arr2 are also in arr1. Sort the elements of arr1 such that the relative ordering of items in arr1 are the same as in arr2. Elements that do not appear in arr2 should be placed at the end of arr1 in ascending order. Example 1: Input: arr1 = [2;3;1;3;2;4;6;7;9;2;19]; arr2 = [2;1;4;3;9;6] Output: [2;2;2;1;4;3;3;9;6;7;19] Example 2: Input: arr1 = [28;6;22;8;44;17]; arr2 = [22;28;8;6] Output: [22;28;8;6;17;44] Constraints: 1 <= arr1.length; arr2.length <= 1000 0 <= arr1[i]; arr2[i] <= 1000 All the elements of arr2 are distinct. Each arr2[i] is in arr1.
Apple,1220,Count Vowels Permutation,Hard,"Array, Dynamic Programming, Bit Manipulation, Bitmask","In a project; you have a list of required skills req_skills; and a list of people. The ith person people[i] contains a list of skills that the person has. Consider a sufficient team: a set of people such that for every required skill in req_skills; there is at least one person in the team who has that skill. We can represent these teams by the index of each person. For example; team = [0; 1; 3] represents the people with skills people[0]; people[1]; and people[3]. Return any sufficient team of the smallest possible size; represented by the index of each person. You may return the answer in any order. It is guaranteed an answer exists. Example 1: Input: req_skills = [""java"";""nodejs"";""reactjs""]; people = [[""java""];[""nodejs""];[""nodejs"";""reactjs""]] Output: [0;2] Example 2: Input: req_skills = [""algorithms"";""math"";""java"";""reactjs"";""csharp"";""aws""]; people = [[""algorithms"";""math"";""java""];[""algorithms"";""math"";""reactjs""];[""java"";""csharp"";""aws""];[""reactjs"";""csharp""];[""csharp"";""math""];[""aws"";""java""]] Output: [1;2] Constraints: 1 <= req_skills.length <= 16 1 <= req_skills[i].length <= 16 req_skills[i] consists of lowercase English letters. All the strings of req_skills are unique. 1 <= people.length <= 60 0 <= people[i].length <= 16 1 <= people[i][j].length <= 16 people[i][j] consists of lowercase English letters. All the strings of people[i] are unique. Every skill in people[i] is a skill in req_skills. It is guaranteed a sufficient team exists."
Apple,1226,The Dining Philosophers,Med,Database,
Apple,1239,Maximum Length of a Concatenated String with Unique Characters,Med,"Array, Dynamic Programming, Matrix",Given a 2D grid of 0s and 1s; return the number of elements in the largest square subgrid that has all 1s on its border; or 0 if such a subgrid doesn't exist in the grid. Example 1: Input: grid = [[1;1;1];[1;0;1];[1;1;1]] Output: 9 Example 2: Input: grid = [[1;1;0;0]] Output: 1 Constraints: 1 <= grid.length <= 100 1 <= grid[0].length <= 100 grid[i][j] is 0 or 1
Apple,1242,Web Crawler Multithreaded,Med,"Array, Matrix, Prefix Sum",Given a m x n matrix mat and an integer k; return a matrix answer where each answer[i][j] is the sum of all elements mat[r][c] for: i - k <= r <= i + k; j - k <= c <= j + k; and (r; c) is a valid position in the matrix. Example 1: Input: mat = [[1;2;3];[4;5;6];[7;8;9]]; k = 1 Output: [[12;21;16];[27;45;33];[24;39;28]] Example 2: Input: mat = [[1;2;3];[4;5;6];[7;8;9]]; k = 2 Output: [[45;45;45];[45;45;45];[45;45;45]] Constraints: m == mat.length n == mat[i].length 1 <= m; n; k <= 100 1 <= mat[i][j] <= 100
Apple,1250,Check If It Is a Good Array,Hard,"String, Dynamic Programming","Given two strings text1 and text2; return the length of their longest common subsequence. If there is no common subsequence; return 0. A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters. For example; ""ace"" is a subsequence of ""abcde"". A common subsequence of two strings is a subsequence that is common to both strings. Example 1: Input: text1 = ""abcde""; text2 = ""ace"" Output: 3 Explanation: The longest common subsequence is ""ace"" and its length is 3. Example 2: Input: text1 = ""abc""; text2 = ""abc"" Output: 3 Explanation: The longest common subsequence is ""abc"" and its length is 3. Example 3: Input: text1 = ""abc""; text2 = ""def"" Output: 0 Explanation: There is no such common subsequence; so the result is 0. Constraints: 1 <= text1.length; text2.length <= 1000 text1 and text2 consist of only lowercase English characters."
Apple,1309,Decrypt String from Alphabet to Integer Mapping,Easy,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are n items each belonging to zero or one of m groups where group[i] is the group that the i-th item belongs to and it's equal to -1 if the i-th item belongs to no group. The items and the groups are zero indexed. A group can have no item belonging to it. Return a sorted list of the items such that: The items that belong to the same group are next to each other in the sorted list. There are some relations between these items where beforeItems[i] is a list containing all the items that should come before the i-th item in the sorted array (to the left of the i-th item). Return any solution if there is more than one solution and return an empty list if there is no solution. Example 1: Input: n = 8; m = 2; group = [-1;-1;1;0;0;1;0;-1]; beforeItems = [[];[6];[5];[6];[3;6];[];[];[]] Output: [6;3;4;1;5;2;0;7] Example 2: Input: n = 8; m = 2; group = [-1;-1;1;0;0;1;0;-1]; beforeItems = [[];[6];[5];[6];[3];[];[4];[]] Output: [] Explanation: This is the same as example 1 except that 4 needs to be before 6 in the sorted list. Constraints: 1 <= m <= n <= 3 * 104 group.length == beforeItems.length == n -1 <= group[i] <= m - 1 0 <= beforeItems[i].length <= n - 1 0 <= beforeItems[i][j] <= n - 1 i != beforeItems[i][j] beforeItems[i] does not contain duplicates elements.
Apple,1342,Number of Steps to Reduce a Number to Zero,Easy,"Array, Matrix, Simulation",On a 0-indexed 8 x 8 chessboard; there can be multiple black queens and one white king. You are given a 2D integer array queens where queens[i] = [xQueeni; yQueeni] represents the position of the ith black queen on the chessboard. You are also given an integer array king of length 2 where king = [xKing; yKing] represents the position of the white king. Return the coordinates of the black queens that can directly attack the king. You may return the answer in any order. Example 1: Input: queens = [[0;1];[1;0];[4;0];[0;4];[3;3];[2;4]]; king = [0;0] Output: [[0;1];[1;0];[3;3]] Explanation: The diagram above shows the three queens that can directly attack the king and the three queens that cannot attack the king (i.e.; marked with red dashes). Example 2: Input: queens = [[0;0];[1;1];[2;2];[3;4];[3;5];[4;4];[4;5]]; king = [3;3] Output: [[2;2];[3;4];[4;4]] Explanation: The diagram above shows the three queens that can directly attack the king and the three queens that cannot attack the king (i.e.; marked with red dashes). Constraints: 1 <= queens.length < 64 queens[i].length == king.length == 2 0 <= xQueeni; yQueeni; xKing; yKing < 8 All the given positions are unique.
Apple,1335,Minimum Difficulty of a Job Schedule,Hard,"Array, Binary Search",You are given a 0-indexed integer array candies. Each element in the array denotes a pile of candies of size candies[i]. You can divide each pile into any number of sub piles; but you cannot merge two piles together. You are also given an integer k. You should allocate piles of candies to k children such that each child gets the same number of candies. Each child can take at most one pile of candies and some piles of candies may go unused. Return the maximum number of candies each child can get. Example 1: Input: candies = [5;8;6]; k = 3 Output: 5 Explanation: We can divide candies[1] into 2 piles of size 5 and 3; and candies[2] into 2 piles of size 5 and 1. We now have five piles of candies of sizes 5; 5; 3; 5; and 1. We can allocate the 3 piles of size 5 to 3 children. It can be proven that each child cannot receive more than 5 candies. Example 2: Input: candies = [2;5]; k = 11 Output: 0 Explanation: There are 11 children but only 7 candies in total; so it is impossible to ensure each child receives at least one candy. Thus; each child gets no candy and the answer is 0. Constraints: 1 <= candies.length <= 105 1 <= candies[i] <= 107 1 <= k <= 1012
Apple,1359,Count All Valid Pickup and Delivery Options,Hard,"Math, Backtracking, Bit Manipulation",Given 2 integers n and start. Your task is return any permutation p of (0;1;2.....;2^n -1) such that : p[0] = start p[i] and p[i+1] differ by only one bit in their binary representation. p[0] and p[2^n -1] must also differ by only one bit in their binary representation. Example 1: Input: n = 2; start = 3 Output: [3;2;0;1] Explanation: The binary representation of the permutation is (11;10;00;01). All the adjacent element differ by one bit. Another valid permutation is [3;1;0;2] Example 2: Input: n = 3; start = 2 Output: [2;6;7;5;4;0;1;3] Explanation: The binary representation of the permutation is (010;110;111;101;100;000;001;011). Constraints: 1 <= n <= 16 0 <= start < 2 ^ n
Apple,1337,The K Weakest Rows in a Matrix,Easy,"Linked List, Design","Design a Skiplist without using any built-in libraries. A skiplist is a data structure that takes O(log(n)) time to add; erase and search. Comparing with treap and red-black tree which has the same function and performance; the code length of Skiplist can be comparatively short and the idea behind Skiplists is just simple linked lists. For example; we have a Skiplist containing [30;40;50;60;70;90] and we want to add 80 and 45 into it. The Skiplist works this way: Artyom Kalinin [CC BY-SA 3.0]; via Wikimedia Commons You can see there are many layers in the Skiplist. Each layer is a sorted linked list. With the help of the top layers; add; erase and search can be faster than O(n). It can be proven that the average time complexity for each operation is O(log(n)) and space complexity is O(n). See more about Skiplist: https://en.wikipedia.org/wiki/Skip_list Implement the Skiplist class: Skiplist() Initializes the object of the skiplist. bool search(int target) Returns true if the integer target exists in the Skiplist or false otherwise. void add(int num) Inserts the value num into the SkipList. bool erase(int num) Removes the value num from the Skiplist and returns true. If num does not exist in the Skiplist; do nothing and return false. If there exist multiple num values; removing any one of them is fine. Note that duplicates may exist in the Skiplist; your code needs to handle this situation. Example 1: Input [""Skiplist""; ""add""; ""add""; ""add""; ""search""; ""add""; ""search""; ""erase""; ""erase""; ""search""] [[]; [1]; [2]; [3]; [0]; [4]; [1]; [0]; [1]; [1]] Output [null; null; null; null; false; null; true; false; true; false] Explanation Skiplist skiplist = new Skiplist(); skiplist.add(1); skiplist.add(2); skiplist.add(3); skiplist.search(0); // return False skiplist.add(4); skiplist.search(1); // return True skiplist.erase(0); // return False; 0 is not in skiplist. skiplist.erase(1); // return True skiplist.search(1); // return False; 1 has already been erased. Constraints: 0 <= num; target <= 2 * 104 At most 5 * 104 calls will be made to search; add; and erase."
Apple,1339,Maximum Product of Splitted Binary Tree,Med,Database,
Apple,1347,Minimum Number of Steps to Make Two Strings Anagram,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
Apple,1372,Longest ZigZag Path in a Binary Tree,Med,"Array, Math, Number Theory",Given an array nums of positive integers. Your task is to select some subset of nums; multiply each element by an integer and add all these numbers. The array is said to be good if you can obtain a sum of 1 from the array by any possible subset and multiplicand. Return True if the array is good otherwise return False. Example 1: Input: nums = [12;5;7;23] Output: true Explanation: Pick numbers 5 and 7. 5*3 + 7*(-2) = 1 Example 2: Input: nums = [29;6;10] Output: true Explanation: Pick numbers 29; 6 and 10. 29*1 + 6*(-3) + 10*(-1) = 1 Example 3: Input: nums = [3;6] Output: false Constraints: 1 <= nums.length <= 10^5 1 <= nums[i] <= 10^9
Apple,1373,Maximum Sum BST in Binary Tree,Hard,,
Apple,1351,Count Negative Numbers in a Sorted Matrix,Easy,"String, Sliding Window","You are given a string s of length n containing only four kinds of characters: 'Q'; 'W'; 'E'; and 'R'. A string is said to be balanced if each of its characters appears n / 4 times where n is the length of the string. Return the minimum length of the substring that can be replaced with any other string of the same length to make s balanced. If s is already balanced; return 0. Example 1: Input: s = ""QWER"" Output: 0 Explanation: s is already balanced. Example 2: Input: s = ""QQWE"" Output: 1 Explanation: We need to replace a 'Q' to 'R'; so that ""RQWE"" (or ""QRWE"") is balanced. Example 3: Input: s = ""QQQW"" Output: 2 Explanation: We can replace the first ""QQ"" to ""ER"". Constraints: n == s.length 4 <= n <= 105 n is a multiple of 4. s contains only 'Q'; 'W'; 'E'; and 'R'."
Apple,1365,How Many Numbers Are Smaller Than the Current Number,Easy,,
Apple,1406,Stone Game III,Hard,Math,Given an integer number n; return the difference between the product of its digits and the sum of its digits. Example 1: Input: n = 234 Output: 15 Explanation: Product of digits = 2 * 3 * 4 = 24 Sum of digits = 2 + 3 + 4 = 9 Result = 24 - 9 = 15 Example 2: Input: n = 4421 Output: 21 Explanation: Product of digits = 4 * 4 * 2 * 1 = 32 Sum of digits = 4 + 4 + 2 + 1 = 11 Result = 32 - 11 = 21 Constraints: 1 <= n <= 10^5
Apple,1393,Capital Gain/Loss,Med,"Array, Dynamic Programming, Prefix Sum",There are n piles of coins on a table. Each pile consists of a positive number of coins of assorted denominations. In one move; you can choose any coin on top of any pile; remove it; and add it to your wallet. Given a list piles; where piles[i] is a list of integers denoting the composition of the ith pile from top to bottom; and a positive integer k; return the maximum total value of coins you can have in your wallet if you choose exactly k coins optimally. Example 1: Input: piles = [[1;100;3];[7;8;9]]; k = 2 Output: 101 Explanation: The above diagram shows the different ways we can choose k coins. The maximum total we can obtain is 101. Example 2: Input: piles = [[100];[100];[100];[100];[100];[100];[1;1;1;1;1;1;700]]; k = 7 Output: 706 Explanation: The maximum total can be obtained if we choose all coins from the last pile. Constraints: n == piles.length 1 <= n <= 1000 1 <= piles[i][j] <= 105 1 <= k <= sum(piles[i].length) <= 2000
Apple,1436,Destination City,Easy,"Array, Hash Table, Breadth-First Search, Graph, Sorting","There are n people; each person has a unique id between 0 and n-1. Given the arrays watchedVideos and friends; where watchedVideos[i] and friends[i] contain the list of watched videos and the list of friends respectively for the person with id = i. Level 1 of videos are all watched videos by your friends; level 2 of videos are all watched videos by the friends of your friends and so on. In general; the level k of videos are all watched videos by people with the shortest path exactly equal to k with you. Given your id and the level of videos; return the list of videos ordered by their frequencies (increasing). For videos with the same frequency order them alphabetically from least to greatest. Example 1: Input: watchedVideos = [[""A"";""B""];[""C""];[""B"";""C""];[""D""]]; friends = [[1;2];[0;3];[0;3];[1;2]]; id = 0; level = 1 Output: [""B"";""C""] Explanation: You have id = 0 (green color in the figure) and your friends are (yellow color in the figure): Person with id = 1 -> watchedVideos = [""C""] Person with id = 2 -> watchedVideos = [""B"";""C""] The frequencies of watchedVideos by your friends are: B -> 1 C -> 2 Example 2: Input: watchedVideos = [[""A"";""B""];[""C""];[""B"";""C""];[""D""]]; friends = [[1;2];[0;3];[0;3];[1;2]]; id = 0; level = 2 Output: [""D""] Explanation: You have id = 0 (green color in the figure) and the only friend of your friends is the person with id = 3 (yellow color in the figure). Constraints: n == watchedVideos.length == friends.length 2 <= n <= 100 1 <= watchedVideos[i].length <= 100 1 <= watchedVideos[i][j].length <= 8 0 <= friends[i].length < n 0 <= friends[i][j] < n 0 <= id < n 1 <= level < n if friends[i] contains j; then friends[j] contains i"
Apple,1443,Minimum Time to Collect All Apples in a Tree,Med,"String, Dynamic Programming","You have a keyboard layout as shown above in the X-Y plane; where each English uppercase letter is located at some coordinate. For example; the letter 'A' is located at coordinate (0; 0); the letter 'B' is located at coordinate (0; 1); the letter 'P' is located at coordinate (2; 3) and the letter 'Z' is located at coordinate (4; 1). Given the string word; return the minimum total distance to type such string using only two fingers. The distance between coordinates (x1; y1) and (x2; y2) is |x1 - x2| + |y1 - y2|. Note that the initial positions of your two fingers are considered free so do not count towards your total distance; also your two fingers do not have to start at the first letter or the first two letters. Example 1: Input: word = ""CAKE"" Output: 3 Explanation: Using two fingers; one optimal way to type ""CAKE"" is: Finger 1 on letter 'C' -> cost = 0 Finger 1 on letter 'A' -> cost = Distance from letter 'C' to letter 'A' = 2 Finger 2 on letter 'K' -> cost = 0 Finger 2 on letter 'E' -> cost = Distance from letter 'K' to letter 'E' = 1 Total distance = 3 Example 2: Input: word = ""HAPPY"" Output: 6 Explanation: Using two fingers; one optimal way to type ""HAPPY"" is: Finger 1 on letter 'H' -> cost = 0 Finger 1 on letter 'A' -> cost = Distance from letter 'H' to letter 'A' = 2 Finger 2 on letter 'P' -> cost = 0 Finger 2 on letter 'P' -> cost = Distance from letter 'P' to letter 'P' = 0 Finger 1 on letter 'Y' -> cost = Distance from letter 'A' to letter 'Y' = 4 Total distance = 6 Constraints: 2 <= word.length <= 300 word consists of uppercase English letters."
Apple,1478,Allocate Mailboxes,Hard,"Array, Greedy, Sorting, Heap (Priority Queue)",You are given an array of events where events[i] = [startDayi; endDayi]. Every event i starts at startDayi and ends at endDayi. You can attend an event i at any day d where startTimei <= d <= endTimei. You can only attend one event at any time d. Return the maximum number of events you can attend. Example 1: Input: events = [[1;2];[2;3];[3;4]] Output: 3 Explanation: You can attend all the three events. One way to attend them all is as shown. Attend the first event on day 1. Attend the second event on day 2. Attend the third event on day 3. Example 2: Input: events= [[1;2];[2;3];[3;4];[1;2]] Output: 4 Constraints: 1 <= events.length <= 105 events[i].length == 2 1 <= startDayi <= endDayi <= 105
Apple,1481,Least Number of Unique Integers after K Removals,Med,Database,
Apple,1498,Number of Subsequences That Satisfy the Given Sum Condition,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given two binary trees original and cloned and given a reference to a node target in the original tree. The cloned tree is a copy of the original tree. Return a reference to the same node in the cloned tree. Note that you are not allowed to change any of the two trees or the target node and the answer must be a reference to a node in the cloned tree. Example 1: Input: tree = [7;4;3;null;null;6;19]; target = 3 Output: 3 Explanation: In all examples the original and cloned trees are shown. The target node is a green node from the original tree. The answer is the yellow node from the cloned tree. Example 2: Input: tree = [7]; target = 7 Output: 7 Example 3: Input: tree = [8;null;6;null;5;null;4;null;3;null;2;null;1]; target = 4 Output: 4 Constraints: The number of nodes in the tree is in the range [1; 104]. The values of the nodes of the tree are unique. target node is a node from the original tree and is not null. Follow up: Could you solve the problem if repeated values on the tree are allowed?
Apple,1528,Shuffle String,Easy,Array,There are n kids with candies. You are given an integer array candies; where each candies[i] represents the number of candies the ith kid has; and an integer extraCandies; denoting the number of extra candies that you have. Return a boolean array result of length n; where result[i] is true if; after giving the ith kid all the extraCandies; they will have the greatest number of candies among all the kids; or false otherwise. Note that multiple kids can have the greatest number of candies. Example 1: Input: candies = [2;3;5;1;3]; extraCandies = 3 Output: [true;true;true;false;true] Explanation: If you give all extraCandies to: - Kid 1; they will have 2 + 3 = 5 candies; which is the greatest among the kids. - Kid 2; they will have 3 + 3 = 6 candies; which is the greatest among the kids. - Kid 3; they will have 5 + 3 = 8 candies; which is the greatest among the kids. - Kid 4; they will have 1 + 3 = 4 candies; which is not the greatest among the kids. - Kid 5; they will have 3 + 3 = 6 candies; which is the greatest among the kids. Example 2: Input: candies = [4;2;1;1;2]; extraCandies = 1 Output: [true;false;false;false;false] Explanation: There is only 1 extra candy. Kid 1 will always have the greatest number of candies; even if a different kid is given the extra candy. Example 3: Input: candies = [12;1;12]; extraCandies = 10 Output: [true;false;true] Constraints: n == candies.length 2 <= n <= 100 1 <= candies[i] <= 100 1 <= extraCandies <= 50
Apple,1534,Count Good Triplets,Easy,"String, Counting","You are given the string croakOfFrogs; which represents a combination of the string ""croak"" from different frogs; that is; multiple frogs can croak at the same time; so multiple ""croak"" are mixed. Return the minimum number of different frogs to finish all the croaks in the given string. A valid ""croak"" means a frog is printing five letters 'c'; 'r'; 'o'; 'a'; and 'k' sequentially. The frogs have to print all five letters to finish a croak. If the given string is not a combination of a valid ""croak"" return -1. Example 1: Input: croakOfFrogs = ""croakcroak"" Output: 1 Explanation: One frog yelling ""croak"" twice. Example 2: Input: croakOfFrogs = ""crcoakroak"" Output: 2 Explanation: The minimum number of frogs is two. The first frog could yell ""crcoakroak"". The second frog could yell later ""crcoakroak"". Example 3: Input: croakOfFrogs = ""croakcrook"" Output: -1 Explanation: The given string is an invalid combination of ""croak"" from different frogs. Constraints: 1 <= croakOfFrogs.length <= 105 croakOfFrogs is either 'c'; 'r'; 'o'; 'a'; or 'k'."
Apple,1561,Maximum Number of Coins You Can Get,Med,"String, Sorting","Given a sentence text (A sentence is a string of space-separated words) in the following format: First letter is in upper case. Each word in text are separated by a single space. Your task is to rearrange the words in text such that all words are rearranged in an increasing order of their lengths. If two words have the same length; arrange them in their original order. Return the new text following the format shown above. Example 1: Input: text = ""Leetcode is cool"" Output: ""Is cool leetcode"" Explanation: There are 3 words; ""Leetcode"" of length 8; ""is"" of length 2 and ""cool"" of length 4. Output is ordered by length and the new first word starts with capital letter. Example 2: Input: text = ""Keep calm and code on"" Output: ""On and keep calm code"" Explanation: Output is ordered as follows: ""On"" 2 letters. ""and"" 3 letters. ""keep"" 4 letters in case of tie order by position in original text. ""calm"" 4 letters. ""code"" 4 letters. Example 3: Input: text = ""To be or not to be"" Output: ""To be or to be not"" Constraints: text begins with a capital letter and then contains lowercase letters and single space between words. 1 <= text.length <= 10^5"
Apple,1614,Maximum Nesting Depth of the Parentheses,Easy,,
Apple,1636,Sort Array by Increasing Frequency,Easy,"Math, String","Given a binary string s; return the number of substrings with all characters 1's. Since the answer may be too large; return it modulo 109 + 7. Example 1: Input: s = ""0110111"" Output: 9 Explanation: There are 9 substring in total with only 1's characters. ""1"" -> 5 times. ""11"" -> 3 times. ""111"" -> 1 time. Example 2: Input: s = ""101"" Output: 2 Explanation: Substring ""1"" is shown 2 times in s. Example 3: Input: s = ""111111"" Output: 21 Explanation: Each substring contains only 1's characters. Constraints: 1 <= s.length <= 105 s[i] is either '0' or '1'."
Apple,1639,Number of Ways to Form a Target String Given a Dictionary,Hard,Database,
Apple,1626,Best Team With No Conflicts,Med,"Array, Sorting",A sequence of numbers is called an arithmetic progression if the difference between any two consecutive elements is the same. Given an array of numbers arr; return true if the array can be rearranged to form an arithmetic progression. Otherwise; return false. Example 1: Input: arr = [3;5;1] Output: true Explanation: We can reorder the elements as [1;3;5] or [5;3;1] with differences 2 and -2 respectively; between each consecutive elements. Example 2: Input: arr = [1;2;4] Output: false Explanation: There is no way to reorder the elements to obtain an arithmetic progression. Constraints: 2 <= arr.length <= 1000 -106 <= arr[i] <= 106
Apple,1631,Path With Minimum Effort,Med,"Array, Math, Dynamic Programming, Prefix Sum",Given an array of integers arr; return the number of subarrays with an odd sum. Since the answer can be very large; return it modulo 109 + 7. Example 1: Input: arr = [1;3;5] Output: 4 Explanation: All subarrays are [[1];[1;3];[1;3;5];[3];[3;5];[5]] All sub-arrays sum are [1;4;9;3;8;5]. Odd sums are [1;9;3;5] so the answer is 4. Example 2: Input: arr = [2;4;6] Output: 0 Explanation: All subarrays are [[2];[2;4];[2;4;6];[4];[4;6];[6]] All sub-arrays sum are [2;6;12;4;10;6]. All sub-arrays have even sum and the answer is 0. Example 3: Input: arr = [1;2;3;4;5;6;7] Output: 16 Constraints: 1 <= arr.length <= 105 1 <= arr[i] <= 100
Apple,1641,Count Sorted Vowel Strings,Med,Database,
Apple,1650,Lowest Common Ancestor of a Binary Tree III,Med,"Hash Table, Bit Manipulation, Tree, Depth-First Search",
Apple,1700,Number of Students Unable to Eat Lunch,Easy,"Array, String, Dynamic Programming, Greedy","Alice has n balloons arranged on a rope. You are given a 0-indexed string colors where colors[i] is the color of the ith balloon. Alice wants the rope to be colorful. She does not want two consecutive balloons to be of the same color; so she asks Bob for help. Bob can remove some balloons from the rope to make it colorful. You are given a 0-indexed integer array neededTime where neededTime[i] is the time (in seconds) that Bob needs to remove the ith balloon from the rope. Return the minimum time Bob needs to make the rope colorful. Example 1: Input: colors = ""abaac""; neededTime = [1;2;3;4;5] Output: 3 Explanation: In the above image; 'a' is blue; 'b' is red; and 'c' is green. Bob can remove the blue balloon at index 2. This takes 3 seconds. There are no longer two consecutive balloons of the same color. Total time = 3. Example 2: Input: colors = ""abc""; neededTime = [1;2;3] Output: 0 Explanation: The rope is already colorful. Bob does not need to remove any balloons from the rope. Example 3: Input: colors = ""aabaa""; neededTime = [1;2;3;4;1] Output: 2 Explanation: Bob will remove the balloons at indices 0 and 4. Each balloons takes 1 second to remove. There are no longer two consecutive balloons of the same color. Total time = 1 + 1 = 2. Constraints: n == colors.length == neededTime.length 1 <= n <= 105 1 <= neededTime[i] <= 104 colors contains only lowercase English letters."
Apple,1689,Partitioning Into Minimum Number Of Deci-Binary Numbers,Med,"Array, Enumeration",Given an array of positive integers arr; find a pattern of length m that is repeated k or more times. A pattern is a subarray (consecutive sub-sequence) that consists of one or more values; repeated multiple times consecutively without overlapping. A pattern is defined by its length and the number of repetitions. Return true if there exists a pattern of length m that is repeated k or more times; otherwise return false. Example 1: Input: arr = [1;2;4;4;4;4]; m = 1; k = 3 Output: true Explanation: The pattern (4) of length 1 is repeated 4 consecutive times. Notice that pattern can be repeated k or more times but not less. Example 2: Input: arr = [1;2;1;2;1;1;1;3]; m = 2; k = 2 Output: true Explanation: The pattern (1;2) of length 2 is repeated 2 consecutive times. Another valid pattern (2;1) is also repeated 2 times. Example 3: Input: arr = [1;2;1;2;1;3]; m = 2; k = 3 Output: false Explanation: The pattern (1;2) is of length 2 but is repeated only 2 times. There is no pattern of length 2 that is repeated 3 or more times. Constraints: 2 <= arr.length <= 100 1 <= arr[i] <= 100 1 <= m <= 100 2 <= k <= 100
Apple,1697,Checking Existence of Edge Length Limited Paths,Hard,"Hash Table, String, Rolling Hash, Hash Function",
Apple,1748,Sum of Unique Elements,Easy,"Array, Dynamic Programming, Sorting",You are the manager of a basketball team. For the upcoming tournament; you want to choose the team with the highest overall score. The score of the team is the sum of scores of all the players in the team. However; the basketball team is not allowed to have conflicts. A conflict exists if a younger player has a strictly higher score than an older player. A conflict does not occur between players of the same age. Given two lists; scores and ages; where each scores[i] and ages[i] represents the score and age of the ith player; respectively; return the highest overall score of all possible basketball teams. Example 1: Input: scores = [1;3;5;10;15]; ages = [1;2;3;4;5] Output: 34 Explanation: You can choose all the players. Example 2: Input: scores = [4;5;6;5]; ages = [2;1;2;1] Output: 16 Explanation: It is best to choose the last 3 players. Notice that you are allowed to choose multiple people of the same age. Example 3: Input: scores = [1;2;3;5]; ages = [8;9;10;1] Output: 6 Explanation: It is best to choose the first 3 players. Constraints: 1 <= scores.length; ages.length <= 1000 scores.length == ages.length 1 <= scores[i] <= 106 1 <= ages[i] <= 1000
Apple,1751,Maximum Number of Events That Can Be Attended II,Hard,"Array, String","A newly designed keypad was tested; where a tester pressed a sequence of n keys; one at a time. You are given a string keysPressed of length n; where keysPressed[i] was the ith key pressed in the testing sequence; and a sorted list releaseTimes; where releaseTimes[i] was the time the ith key was released. Both arrays are 0-indexed. The 0th key was pressed at the time 0; and every subsequent key was pressed at the exact time the previous key was released. The tester wants to know the key of the keypress that had the longest duration. The ith keypress had a duration of releaseTimes[i] - releaseTimes[i - 1]; and the 0th keypress had a duration of releaseTimes[0]. Note that the same key could have been pressed multiple times during the test; and these multiple presses of the same key may not have had the same duration. Return the key of the keypress that had the longest duration. If there are multiple such keypresses; return the lexicographically largest key of the keypresses. Example 1: Input: releaseTimes = [9;29;49;50]; keysPressed = ""cbcd"" Output: ""c"" Explanation: The keypresses were as follows: Keypress for 'c' had a duration of 9 (pressed at time 0 and released at time 9). Keypress for 'b' had a duration of 29 - 9 = 20 (pressed at time 9 right after the release of the previous character and released at time 29). Keypress for 'c' had a duration of 49 - 29 = 20 (pressed at time 29 right after the release of the previous character and released at time 49). Keypress for 'd' had a duration of 50 - 49 = 1 (pressed at time 49 right after the release of the previous character and released at time 50). The longest of these was the keypress for 'b' and the second keypress for 'c'; both with duration 20. 'c' is lexicographically larger than 'b'; so the answer is 'c'. Example 2: Input: releaseTimes = [12;23;36;46;62]; keysPressed = ""spuda"" Output: ""a"" Explanation: The keypresses were as follows: Keypress for 's' had a duration of 12. Keypress for 'p' had a duration of 23 - 12 = 11. Keypress for 'u' had a duration of 36 - 23 = 13. Keypress for 'd' had a duration of 46 - 36 = 10. Keypress for 'a' had a duration of 62 - 46 = 16. The longest of these was the keypress for 'a' with duration 16. Constraints: releaseTimes.length == n keysPressed.length == n 2 <= n <= 1000 1 <= releaseTimes[i] <= 109 releaseTimes[i] < releaseTimes[i+1] keysPressed contains only lowercase English letters."
Apple,1822,Sign of the Product of an Array,Easy,"String, Dynamic Programming",
Apple,1824,Minimum Sideway Jumps,Med,"Array, Greedy, Heap (Priority Queue)",There is a special kind of apple tree that grows apples every day for n days. On the ith day; the tree grows apples[i] apples that will rot after days[i] days; that is on day i + days[i] the apples will be rotten and cannot be eaten. On some days; the apple tree does not grow any apples; which are denoted by apples[i] == 0 and days[i] == 0. You decided to eat at most one apple a day (to keep the doctors away). Note that you can keep eating after the first n days. Given two integer arrays days and apples of length n; return the maximum number of apples you can eat. Example 1: Input: apples = [1;2;3;5;2]; days = [3;2;1;4;2] Output: 7 Explanation: You can eat 7 apples: - On the first day; you eat an apple that grew on the first day. - On the second day; you eat an apple that grew on the second day. - On the third day; you eat an apple that grew on the second day. After this day; the apples that grew on the third day rot. - On the fourth to the seventh days; you eat apples that grew on the fourth day. Example 2: Input: apples = [3;0;0;0;0;2]; days = [3;0;0;0;0;2] Output: 5 Explanation: You can eat 5 apples: - On the first to the third day you eat apples that grew on the first day. - Do nothing on the fouth and fifth days. - On the sixth and seventh days you eat apples that grew on the sixth day. Constraints: n == apples.length == days.length 1 <= n <= 2 * 104 0 <= apples[i]; days[i] <= 2 * 104 days[i] = 0 if and only if apples[i] = 0.
Apple,1846,Maximum Element After Decreasing and Rearranging,Med,,
Apple,1834,Single-Threaded CPU,Med,"Array, Hash Table, Greedy",On a social network consisting of m users and some friendships between users; two users can communicate with each other if they know a common language. You are given an integer n; an array languages; and an array friendships where: There are n languages numbered 1 through n; languages[i] is the set of languages the i​​​​​​th​​​​ user knows; and friendships[i] = [u​​​​​​i​​​; v​​​​​​i] denotes a friendship between the users u​​​​​​​​​​​i​​​​​ and vi. You can choose one language and teach it to some users so that all friends can communicate with each other. Return the minimum number of users you need to teach. Note that friendships are not transitive; meaning if x is a friend of y and y is a friend of z; this doesn't guarantee that x is a friend of z. Example 1: Input: n = 2; languages = [[1];[2];[1;2]]; friendships = [[1;2];[1;3];[2;3]] Output: 1 Explanation: You can either teach user 1 the second language or user 2 the first language. Example 2: Input: n = 3; languages = [[2];[1;3];[1;2];[3]]; friendships = [[1;4];[1;2];[3;4];[2;3]] Output: 2 Explanation: Teach the third language to users 1 and 3; yielding two users to teach. Constraints: 2 <= n <= 500 languages.length == m 1 <= m <= 500 1 <= languages[i].length <= n 1 <= languages[i][j] <= n 1 <= u​​​​​​i < v​​​​​​i <= languages.length 1 <= friendships.length <= 500 All tuples (u​​​​​i; v​​​​​​i) are unique languages[i] contains only unique values
Apple,1863,Sum of All Subset XOR Totals,Easy,,
Apple,1926,Nearest Exit from Entrance in Maze,Med,Database,
Apple,1915,Number of Wonderful Substrings,Med,"Hash Table, String, Counting","You are given two strings s1 and s2 of equal length. A string swap is an operation where you choose two indices in a string (not necessarily different) and swap the characters at these indices. Return true if it is possible to make both strings equal by performing at most one string swap on exactly one of the strings. Otherwise; return false. Example 1: Input: s1 = ""bank""; s2 = ""kanb"" Output: true Explanation: For example; swap the first character with the last character of s2 to make ""bank"". Example 2: Input: s1 = ""attack""; s2 = ""defend"" Output: false Explanation: It is impossible to make them equal with one string swap. Example 3: Input: s1 = ""kelb""; s2 = ""kelb"" Output: true Explanation: The two strings are already equal; so no string swap operation is required. Constraints: 1 <= s1.length; s2.length <= 100 s1.length == s2.length s1 and s2 consist of only lowercase English letters."
Apple,1901,Find a Peak Element II,Med,"Array, Hash Table, Greedy, Counting",You are given two arrays of integers nums1 and nums2; possibly of different lengths. The values in the arrays are between 1 and 6; inclusive. In one operation; you can change any integer's value in any of the arrays to any value between 1 and 6; inclusive. Return the minimum number of operations required to make the sum of values in nums1 equal to the sum of values in nums2. Return -1​​​​​ if it is not possible to make the sum of the two arrays equal. Example 1: Input: nums1 = [1;2;3;4;5;6]; nums2 = [1;1;2;2;2;2] Output: 3 Explanation: You can make the sums of nums1 and nums2 equal with 3 operations. All indices are 0-indexed. - Change nums2[0] to 6. nums1 = [1;2;3;4;5;6]; nums2 = [6;1;2;2;2;2]. - Change nums1[5] to 1. nums1 = [1;2;3;4;5;1]; nums2 = [6;1;2;2;2;2]. - Change nums1[2] to 2. nums1 = [1;2;2;4;5;1]; nums2 = [6;1;2;2;2;2]. Example 2: Input: nums1 = [1;1;1;1;1;1;1]; nums2 = [6] Output: -1 Explanation: There is no way to decrease the sum of nums1 or to increase the sum of nums2 to make them equal. Example 3: Input: nums1 = [6;6]; nums2 = [1] Output: 3 Explanation: You can make the sums of nums1 and nums2 equal with 3 operations. All indices are 0-indexed. - Change nums1[0] to 2. nums1 = [2;6]; nums2 = [1]. - Change nums1[1] to 2. nums1 = [2;2]; nums2 = [1]. - Change nums2[0] to 4. nums1 = [2;2]; nums2 = [4]. Constraints: 1 <= nums1.length; nums2.length <= 105 1 <= nums1[i]; nums2[i] <= 6
Apple,1929,Concatenation of Array,Easy,"Binary Search, Greedy",You are given three positive integers: n; index; and maxSum. You want to construct an array nums (0-indexed) that satisfies the following conditions: nums.length == n nums[i] is a positive integer where 0 <= i < n. abs(nums[i] - nums[i+1]) <= 1 where 0 <= i < n-1. The sum of all the elements of nums does not exceed maxSum. nums[index] is maximized. Return nums[index] of the constructed array. Note that abs(x) equals x if x >= 0; and -x otherwise. Example 1: Input: n = 4; index = 2; maxSum = 6 Output: 2 Explanation: nums = [1;2;2;1] is one array that satisfies all the conditions. There are no arrays that satisfy all the conditions and have nums[2] == 3; so 2 is the maximum nums[2]. Example 2: Input: n = 6; index = 1; maxSum = 10 Output: 3 Constraints: 1 <= n <= maxSum <= 109 0 <= index < n
Apple,1930,Unique Length-3 Palindromic Subsequences,Med,"Array, Greedy, Sorting",You are given an integer array coins of length n which represents the n coins that you own. The value of the ith coin is coins[i]. You can make some value x if you can choose some of your n coins such that their values sum up to x. Return the maximum number of consecutive integer values that you can make with your coins starting from and including 0. Note that you may have multiple coins of the same value. Example 1: Input: coins = [1;3] Output: 2 Explanation: You can make the following values: - 0: take [] - 1: take [1] You can make 2 consecutive integer values starting from 0. Example 2: Input: coins = [1;1;1;4] Output: 8 Explanation: You can make the following values: - 0: take [] - 1: take [1] - 2: take [1;1] - 3: take [1;1;1] - 4: take [4] - 5: take [4;1] - 6: take [4;1;1] - 7: take [4;1;1;1] You can make 8 consecutive integer values starting from 0. Example 3: Input: coins = [1;4;10;3;1] Output: 20 Constraints: coins.length == n 1 <= n <= 4 * 104 1 <= coins[i] <= 4 * 104
Apple,1963,Minimum Number of Swaps to Make the String Balanced,Med,"Array, Math, Bit Manipulation",The XOR sum of a list is the bitwise XOR of all its elements. If the list only contains one element; then its XOR sum will be equal to this element. For example; the XOR sum of [1;2;3;4] is equal to 1 XOR 2 XOR 3 XOR 4 = 4; and the XOR sum of [3] is equal to 3. You are given two 0-indexed arrays arr1 and arr2 that consist only of non-negative integers. Consider the list containing the result of arr1[i] AND arr2[j] (bitwise AND) for every (i; j) pair where 0 <= i < arr1.length and 0 <= j < arr2.length. Return the XOR sum of the aforementioned list. Example 1: Input: arr1 = [1;2;3]; arr2 = [6;5] Output: 0 Explanation: The list = [1 AND 6; 1 AND 5; 2 AND 6; 2 AND 5; 3 AND 6; 3 AND 5] = [0;1;2;0;2;1]. The XOR sum = 0 XOR 1 XOR 2 XOR 0 XOR 2 XOR 1 = 0. Example 2: Input: arr1 = [12]; arr2 = [4] Output: 4 Explanation: The list = [12 AND 4] = [4]. The XOR sum = 4. Constraints: 1 <= arr1.length; arr2.length <= 105 0 <= arr1[i]; arr2[j] <= 109
Apple,1978,Employees Whose Manager Left the Company,Easy,"Two Pointers, String, Greedy","You are given a string num; representing a large integer; and an integer k. We call some integer wonderful if it is a permutation of the digits in num and is greater in value than num. There can be many wonderful integers. However; we only care about the smallest-valued ones. For example; when num = ""5489355142"": The 1st smallest wonderful integer is ""5489355214"". The 2nd smallest wonderful integer is ""5489355241"". The 3rd smallest wonderful integer is ""5489355412"". The 4th smallest wonderful integer is ""5489355421"". Return the minimum number of adjacent digit swaps that needs to be applied to num to reach the kth smallest wonderful integer. The tests are generated in such a way that kth smallest wonderful integer exists. Example 1: Input: num = ""5489355142""; k = 4 Output: 2 Explanation: The 4th smallest wonderful number is ""5489355421"". To get this number: - Swap index 7 with index 8: ""5489355142"" -> ""5489355412"" - Swap index 8 with index 9: ""5489355412"" -> ""5489355421"" Example 2: Input: num = ""11112""; k = 4 Output: 4 Explanation: The 4th smallest wonderful number is ""21111"". To get this number: - Swap index 3 with index 4: ""11112"" -> ""11121"" - Swap index 2 with index 3: ""11121"" -> ""11211"" - Swap index 1 with index 2: ""11211"" -> ""12111"" - Swap index 0 with index 1: ""12111"" -> ""21111"" Example 3: Input: num = ""00123""; k = 1 Output: 1 Explanation: The 1st smallest wonderful number is ""00132"". To get this number: - Swap index 3 with index 4: ""00123"" -> ""00132"" Constraints: 2 <= num.length <= 1000 1 <= k <= 1000 num only consists of digits."
Apple,2002,Maximum Product of the Length of Two Palindromic Subsequences,Med,"Array, Math, Dynamic Programming, Prefix Sum, Game Theory",Alice and Bob take turns playing a game; with Alice starting first. There are n stones arranged in a row. On each player's turn; while the number of stones is more than one; they will do the following: Choose an integer x > 1; and remove the leftmost x stones from the row. Add the sum of the removed stones' values to the player's score. Place a new stone; whose value is equal to that sum; on the left side of the row. The game stops when only one stone is left in the row. The score difference between Alice and Bob is (Alice's score - Bob's score). Alice's goal is to maximize the score difference; and Bob's goal is the minimize the score difference. Given an integer array stones of length n where stones[i] represents the value of the ith stone from the left; return the score difference between Alice and Bob if they both play optimally. Example 1: Input: stones = [-1;2;-3;4;-5] Output: 5 Explanation: - Alice removes the first 4 stones; adds (-1) + 2 + (-3) + 4 = 2 to her score; and places a stone of value 2 on the left. stones = [2;-5]. - Bob removes the first 2 stones; adds 2 + (-5) = -3 to his score; and places a stone of value -3 on the left. stones = [-3]. The difference between their scores is 2 - (-3) = 5. Example 2: Input: stones = [7;-6;5;10;5;-2;-6] Output: 13 Explanation: - Alice removes all stones; adds 7 + (-6) + 5 + 10 + 5 + (-2) + (-6) = 13 to her score; and places a stone of value 13 on the left. stones = [13]. The difference between their scores is 13 - 0 = 13. Example 3: Input: stones = [-10;-12] Output: -22 Explanation: - Alice can only make one move; which is to remove both stones. She adds (-10) + (-12) = -22 to her score and places a stone of value -22 on the left. stones = [-22]. The difference between their scores is (-22) - 0 = -22. Constraints: n == stones.length 2 <= n <= 105 -104 <= stones[i] <= 104
Apple,2022,Convert 1D Array Into 2D Array,Easy,"Array, Dynamic Programming",The alternating sum of a 0-indexed array is defined as the sum of the elements at even indices minus the sum of the elements at odd indices. For example; the alternating sum of [4;2;5;3] is (4 + 5) - (2 + 3) = 4. Given an array nums; return the maximum alternating sum of any subsequence of nums (after reindexing the elements of the subsequence). A subsequence of an array is a new array generated from the original array by deleting some elements (possibly none) without changing the remaining elements' relative order. For example; [2;7;4] is a subsequence of [4;2;3;7;2;1;4] (the underlined elements); while [2;4;2] is not. Example 1: Input: nums = [4;2;5;3] Output: 7 Explanation: It is optimal to choose the subsequence [4;2;5] with alternating sum (4 + 5) - 2 = 7. Example 2: Input: nums = [5;6;7;8] Output: 8 Explanation: It is optimal to choose the subsequence [8] with alternating sum 8. Example 3: Input: nums = [6;2;1;2;4;5] Output: 10 Explanation: It is optimal to choose the subsequence [6;1;5] with alternating sum (6 + 5) - 1 = 10. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105
Apple,2024,Maximize the Confusion of an Exam,Med,Database,Table: Employees +-------------+---------+ | Column Name | Type | +-------------+---------+ | employee_id | int | | name | varchar | | salary | int | +-------------+---------+ employee_id is the primary key (column with unique values) for this table. Each row of this table indicates the employee ID; employee name; and salary. Write a solution to calculate the bonus of each employee. The bonus of an employee is 100% of their salary if the ID of the employee is an odd number and the employee's name does not start with the character 'M'. The bonus of an employee is 0 otherwise. Return the result table ordered by employee_id. The result format is in the following example. Example 1: Input: Employees table: +-------------+---------+--------+ | employee_id | name | salary | +-------------+---------+--------+ | 2 | Meir | 3000 | | 3 | Michael | 3800 | | 7 | Addilyn | 7400 | | 8 | Juan | 6100 | | 9 | Kannon | 7700 | +-------------+---------+--------+ Output: +-------------+-------+ | employee_id | bonus | +-------------+-------+ | 2 | 0 | | 3 | 0 | | 7 | 7400 | | 8 | 0 | | 9 | 7700 | +-------------+-------+ Explanation: The employees with IDs 2 and 8 get 0 bonus because they have an even employee_id. The employee with ID 3 gets 0 bonus because their name starts with 'M'. The rest of the employees get a 100% bonus.
Apple,2038,Remove Colored Pieces if Both Neighbors are the Same Color,Med,"Array, Breadth-First Search, Matrix","You are given an m x n matrix maze (0-indexed) with empty cells (represented as '.') and walls (represented as '+'). You are also given the entrance of the maze; where entrance = [entrancerow; entrancecol] denotes the row and column of the cell you are initially standing at. In one step; you can move one cell up; down; left; or right. You cannot step into a cell with a wall; and you cannot step outside the maze. Your goal is to find the nearest exit from the entrance. An exit is defined as an empty cell that is at the border of the maze. The entrance does not count as an exit. Return the number of steps in the shortest path from the entrance to the nearest exit; or -1 if no such path exists. Example 1: Input: maze = [[""+"";""+"";""."";""+""];[""."";""."";""."";""+""];[""+"";""+"";""+"";"".""]]; entrance = [1;2] Output: 1 Explanation: There are 3 exits in this maze at [1;0]; [0;2]; and [2;3]. Initially; you are at the entrance cell [1;2]. - You can reach [1;0] by moving 2 steps left. - You can reach [0;2] by moving 1 step up. It is impossible to reach [2;3] from the entrance. Thus; the nearest exit is [0;2]; which is 1 step away. Example 2: Input: maze = [[""+"";""+"";""+""];[""."";""."";"".""];[""+"";""+"";""+""]]; entrance = [1;0] Output: 2 Explanation: There is 1 exit in this maze at [1;2]. [1;0] does not count as an exit since it is the entrance cell. Initially; you are at the entrance cell [1;0]. - You can reach [1;2] by moving 2 steps right. Thus; the nearest exit is [1;2]; which is 2 steps away. Example 3: Input: maze = [[""."";""+""]]; entrance = [0;0] Output: -1 Explanation: There are no exits in this maze. Constraints: maze.length == m maze[i].length == n 1 <= m; n <= 100 maze[i][j] is either '.' or '+'. entrance.length == 2 0 <= entrancerow < m 0 <= entrancecol < n entrance will always be an empty cell."
Apple,2101,Detonate the Maximum Bombs,Med,"Array, Binary Search, Depth-First Search, Breadth-First Search, Union Find, Matrix",There is a 1-based binary matrix where 0 represents land and 1 represents water. You are given integers row and col representing the number of rows and columns in the matrix; respectively. Initially on day 0; the entire matrix is land. However; each day a new cell becomes flooded with water. You are given a 1-based 2D array cells; where cells[i] = [ri; ci] represents that on the ith day; the cell on the rith row and cith column (1-based coordinates) will be covered with water (i.e.; changed to 1). You want to find the last day that it is possible to walk from the top to the bottom by only walking on land cells. You can start from any cell in the top row and end at any cell in the bottom row. You can only travel in the four cardinal directions (left; right; up; and down). Return the last day where it is possible to walk from the top to the bottom by only walking on land cells. Example 1: Input: row = 2; col = 2; cells = [[1;1];[2;1];[1;2];[2;2]] Output: 2 Explanation: The above image depicts how the matrix changes each day starting from day 0. The last day where it is possible to cross from top to bottom is on day 2. Example 2: Input: row = 2; col = 2; cells = [[1;1];[1;2];[2;1];[2;2]] Output: 1 Explanation: The above image depicts how the matrix changes each day starting from day 0. The last day where it is possible to cross from top to bottom is on day 1. Example 3: Input: row = 3; col = 3; cells = [[1;2];[2;1];[3;3];[2;2];[1;1];[1;3];[2;3];[3;2];[3;1]] Output: 3 Explanation: The above image depicts how the matrix changes each day starting from day 0. The last day where it is possible to cross from top to bottom is on day 3. Constraints: 2 <= row; col <= 2 * 104 4 <= row * col <= 2 * 104 cells.length == row * col 1 <= ri <= row 1 <= ci <= col All the values of cells are unique.
Apple,2103,Rings and Rods,Easy,"Array, Depth-First Search, Breadth-First Search, Matrix",You are given a 0-indexed m x n binary matrix land where a 0 represents a hectare of forested land and a 1 represents a hectare of farmland. To keep the land organized; there are designated rectangular areas of hectares that consist entirely of farmland. These rectangular areas are called groups. No two groups are adjacent; meaning farmland in one group is not four-directionally adjacent to another farmland in a different group. land can be represented by a coordinate system where the top left corner of land is (0; 0) and the bottom right corner of land is (m-1; n-1). Find the coordinates of the top left and bottom right corner of each group of farmland. A group of farmland with a top left corner at (r1; c1) and a bottom right corner at (r2; c2) is represented by the 4-length array [r1; c1; r2; c2]. Return a 2D array containing the 4-length arrays described above for each group of farmland in land. If there are no groups of farmland; return an empty array. You may return the answer in any order. Example 1: Input: land = [[1;0;0];[0;1;1];[0;1;1]] Output: [[0;0;0;0];[1;1;2;2]] Explanation: The first group has a top left corner at land[0][0] and a bottom right corner at land[0][0]. The second group has a top left corner at land[1][1] and a bottom right corner at land[2][2]. Example 2: Input: land = [[1;1];[1;1]] Output: [[0;0;1;1]] Explanation: The first group has a top left corner at land[0][0] and a bottom right corner at land[1][1]. Example 3: Input: land = [[0]] Output: [] Explanation: There are no groups of farmland. Constraints: m == land.length n == land[i].length 1 <= m; n <= 300 land consists of only 0's and 1's. Groups of farmland are rectangular in shape.
Apple,2104,Sum of Subarray Ranges,Med,"Array, Hash Table, Tree, Depth-First Search, Breadth-First Search, Design","You are given a tree with n nodes numbered from 0 to n - 1 in the form of a parent array parent where parent[i] is the parent of the ith node. The root of the tree is node 0; so parent[0] = -1 since it has no parent. You want to design a data structure that allows users to lock; unlock; and upgrade nodes in the tree. The data structure should support the following functions: Lock: Locks the given node for the given user and prevents other users from locking the same node. You may only lock a node using this function if the node is unlocked. Unlock: Unlocks the given node for the given user. You may only unlock a node using this function if it is currently locked by the same user. Upgrade: Locks the given node for the given user and unlocks all of its descendants regardless of who locked it. You may only upgrade a node if all 3 conditions are true: The node is unlocked; It has at least one locked descendant (by any user); and It does not have any locked ancestors. Implement the LockingTree class: LockingTree(int[] parent) initializes the data structure with the parent array. lock(int num; int user) returns true if it is possible for the user with id user to lock the node num; or false otherwise. If it is possible; the node num will become locked by the user with id user. unlock(int num; int user) returns true if it is possible for the user with id user to unlock the node num; or false otherwise. If it is possible; the node num will become unlocked. upgrade(int num; int user) returns true if it is possible for the user with id user to upgrade the node num; or false otherwise. If it is possible; the node num will be upgraded. Example 1: Input [""LockingTree""; ""lock""; ""unlock""; ""unlock""; ""lock""; ""upgrade""; ""lock""] [[[-1; 0; 0; 1; 1; 2; 2]]; [2; 2]; [2; 3]; [2; 2]; [4; 5]; [0; 1]; [0; 1]] Output [null; true; false; true; true; true; false] Explanation LockingTree lockingTree = new LockingTree([-1; 0; 0; 1; 1; 2; 2]); lockingTree.lock(2; 2); // return true because node 2 is unlocked. // Node 2 will now be locked by user 2. lockingTree.unlock(2; 3); // return false because user 3 cannot unlock a node locked by user 2. lockingTree.unlock(2; 2); // return true because node 2 was previously locked by user 2. // Node 2 will now be unlocked. lockingTree.lock(4; 5); // return true because node 4 is unlocked. // Node 4 will now be locked by user 5. lockingTree.upgrade(0; 1); // return true because node 0 is unlocked and has at least one locked descendant (node 4). // Node 0 will now be locked by user 1 and node 4 will now be unlocked. lockingTree.lock(0; 1); // return false because node 0 is already locked. Constraints: n == parent.length 2 <= n <= 2000 0 <= parent[i] <= n - 1 for i != 0 parent[0] == -1 0 <= num <= n - 1 1 <= user <= 104 parent represents a valid tree. At most 2000 calls in total will be made to lock; unlock; and upgrade."
Apple,2131,Longest Palindrome by Concatenating Two Letter Words,Med,"Dynamic Programming, Tree, Depth-First Search, Union Find",There is a family tree rooted at 0 consisting of n nodes numbered 0 to n - 1. You are given a 0-indexed integer array parents; where parents[i] is the parent for node i. Since node 0 is the root; parents[0] == -1. There are 105 genetic values; each represented by an integer in the inclusive range [1; 105]. You are given a 0-indexed integer array nums; where nums[i] is a distinct genetic value for node i. Return an array ans of length n where ans[i] is the smallest genetic value that is missing from the subtree rooted at node i. The subtree rooted at a node x contains node x and all of its descendant nodes. Example 1: Input: parents = [-1;0;0;2]; nums = [1;2;3;4] Output: [5;1;1;1] Explanation: The answer for each subtree is calculated as follows: - 0: The subtree contains nodes [0;1;2;3] with values [1;2;3;4]. 5 is the smallest missing value. - 1: The subtree contains only node 1 with value 2. 1 is the smallest missing value. - 2: The subtree contains nodes [2;3] with values [3;4]. 1 is the smallest missing value. - 3: The subtree contains only node 3 with value 4. 1 is the smallest missing value. Example 2: Input: parents = [-1;0;1;0;3;3]; nums = [5;4;6;2;1;3] Output: [7;1;1;4;2;1] Explanation: The answer for each subtree is calculated as follows: - 0: The subtree contains nodes [0;1;2;3;4;5] with values [5;4;6;2;1;3]. 7 is the smallest missing value. - 1: The subtree contains nodes [1;2] with values [4;6]. 1 is the smallest missing value. - 2: The subtree contains only node 2 with value 6. 1 is the smallest missing value. - 3: The subtree contains nodes [3;4;5] with values [2;1;3]. 4 is the smallest missing value. - 4: The subtree contains only node 4 with value 1. 2 is the smallest missing value. - 5: The subtree contains only node 5 with value 3. 1 is the smallest missing value. Example 3: Input: parents = [-1;2;3;0;2;4;1]; nums = [2;3;4;5;6;7;8] Output: [1;1;1;1;1;1;1] Explanation: The value 1 is missing from all the subtrees. Constraints: n == parents.length == nums.length 2 <= n <= 105 0 <= parents[i] <= n - 1 for i != 0 parents[0] == -1 parents represents a valid tree. 1 <= nums[i] <= 105 Each nums[i] is distinct.
Apple,2147,Number of Ways to Divide a Long Corridor,Hard,"Array, Math, String, Dynamic Programming, Stack, Memoization","You are given a string s that contains digits 0-9; addition symbols '+'; and multiplication symbols '*' only; representing a valid math expression of single digit numbers (e.g.; 3+5*2). This expression was given to n elementary school students. The students were instructed to get the answer of the expression by following this order of operations: Compute multiplication; reading from left to right; Then; Compute addition; reading from left to right. You are given an integer array answers of length n; which are the submitted answers of the students in no particular order. You are asked to grade the answers; by following these rules: If an answer equals the correct answer of the expression; this student will be rewarded 5 points; Otherwise; if the answer could be interpreted as if the student applied the operators in the wrong order but had correct arithmetic; this student will be rewarded 2 points; Otherwise; this student will be rewarded 0 points. Return the sum of the points of the students. Example 1: Input: s = ""7+3*1*2""; answers = [20;13;42] Output: 7 Explanation: As illustrated above; the correct answer of the expression is 13; therefore one student is rewarded 5 points: [20;13;42] A student might have applied the operators in this wrong order: ((7+3)*1)*2 = 20. Therefore one student is rewarded 2 points: [20;13;42] The points for the students are: [2;5;0]. The sum of the points is 2+5+0=7. Example 2: Input: s = ""3+5*2""; answers = [13;0;10;13;13;16;16] Output: 19 Explanation: The correct answer of the expression is 13; therefore three students are rewarded 5 points each: [13;0;10;13;13;16;16] A student might have applied the operators in this wrong order: ((3+5)*2 = 16. Therefore two students are rewarded 2 points: [13;0;10;13;13;16;16] The points for the students are: [5;0;0;5;5;2;2]. The sum of the points is 5+0+0+5+5+2+2=19. Example 3: Input: s = ""6+0*1""; answers = [12;9;6;4;8;6] Output: 10 Explanation: The correct answer of the expression is 6. If a student had incorrectly done (6+0)*1; the answer would also be 6. By the rules of grading; the students will still be rewarded 5 points (as they got the correct answer); not 2 points. The points for the students are: [0;0;5;0;0;5]. The sum of the points is 10. Constraints: 3 <= s.length <= 31 s represents a valid expression that contains only digits 0-9; '+'; and '*' only. All the integer operands in the expression are in the inclusive range [0; 9]. 1 <= The count of all operators ('+' and '*') in the math expression <= 15 Test data are generated such that the correct answer of the expression is in the range of [0; 1000]. n == answers.length 1 <= n <= 104 0 <= answers[i] <= 1000"
Apple,2160,Minimum Sum of Four Digit Number After Splitting Digits,Easy,"Array, Math, Sorting, Matrix",You are given a 2D integer grid of size m x n and an integer x. In one operation; you can add x to or subtract x from any element in the grid. A uni-value grid is a grid where all the elements of it are equal. Return the minimum number of operations to make the grid uni-value. If it is not possible; return -1. Example 1: Input: grid = [[2;4];[6;8]]; x = 2 Output: 4 Explanation: We can make every element equal to 4 by doing the following: - Add x to 2 once. - Subtract x from 6 once. - Subtract x from 8 twice. A total of 4 operations were used. Example 2: Input: grid = [[1;5];[2;3]]; x = 1 Output: 5 Explanation: We can make every element equal to 3. Example 3: Input: grid = [[1;2];[3;4]]; x = 2 Output: -1 Explanation: It is impossible to make every element equal. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 105 1 <= m * n <= 105 1 <= x; grid[i][j] <= 104
Apple,2165,Smallest Value of the Rearranged Number,Med,"Array, String, Binary Search, Prefix Sum","There is a long table with a line of plates and candles arranged on top of it. You are given a 0-indexed string s consisting of characters '*' and '|' only; where a '*' represents a plate and a '|' represents a candle. You are also given a 0-indexed 2D integer array queries where queries[i] = [lefti; righti] denotes the substring s[lefti...righti] (inclusive). For each query; you need to find the number of plates between candles that are in the substring. A plate is considered between candles if there is at least one candle to its left and at least one candle to its right in the substring. For example; s = ""||**||**|*""; and a query [3; 8] denotes the substring ""*||**|"". The number of plates between candles in this substring is 2; as each of the two plates has at least one candle in the substring to its left and right. Return an integer array answer where answer[i] is the answer to the ith query. Example 1: Input: s = ""**|**|***|""; queries = [[2;5];[5;9]] Output: [2;3] Explanation: - queries[0] has two plates between candles. - queries[1] has three plates between candles. Example 2: Input: s = ""***|**|*****|**||**|*""; queries = [[1;17];[4;5];[14;17];[5;11];[15;16]] Output: [9;0;0;0;0] Explanation: - queries[0] has nine plates between candles. - The other queries have zero plates between candles. Constraints: 3 <= s.length <= 105 s consists of '*' and '|' characters. 1 <= queries.length <= 105 queries[i].length == 2 0 <= lefti <= righti < s.length"
Apple,2281,Sum of Total Strength of Wizards,Hard,Database,
Apple,2331,Evaluate Boolean Binary Tree,Easy,"Array, Hash Table, Sorting, Counting",Given a 2D integer array nums where nums[i] is a non-empty array of distinct positive integers; return the list of integers that are present in each array of nums sorted in ascending order. Example 1: Input: nums = [[3;1;2;4;5];[1;2;3;4];[3;4;5;6]] Output: [3;4] Explanation: The only integers present in each of nums[0] = [3;1;2;4;5]; nums[1] = [1;2;3;4]; and nums[2] = [3;4;5;6] are 3 and 4; so we return [3;4]. Example 2: Input: nums = [[1;2;3];[4;5;6]] Output: [] Explanation: There does not exist any integer present both in nums[0] and nums[1]; so we return an empty list []. Constraints: 1 <= nums.length <= 1000 1 <= sum(nums[i].length) <= 1000 1 <= nums[i][j] <= 1000 All the values of nums[i] are unique.
Apple,2375,Construct Smallest Number From DI String,Med,"Array, Breadth-First Search, Graph, Heap (Priority Queue), Matrix, Shortest Path",You are given a 0-indexed 2D integer array grid of size m x n. Each cell has one of two values: 0 represents an empty cell; 1 represents an obstacle that may be removed. You can move up; down; left; or right from and to an empty cell. Return the minimum number of obstacles to remove so you can move from the upper left corner (0; 0) to the lower right corner (m - 1; n - 1). Example 1: Input: grid = [[0;1;1];[1;1;0];[1;1;0]] Output: 2 Explanation: We can remove the obstacles at (0; 1) and (0; 2) to create a path from (0; 0) to (2; 2). It can be shown that we need to remove at least 2 obstacles; so we return 2. Note that there may be other ways to remove 2 obstacles to create a path. Example 2: Input: grid = [[0;1;0;0;0];[0;1;0;1;0];[0;0;0;1;0]] Output: 0 Explanation: We can move from (0; 0) to (2; 4) without removing any obstacles; so we return 0. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 105 2 <= m * n <= 105 grid[i][j] is either 0 or 1. grid[0][0] == grid[m - 1][n - 1] == 0
Apple,2385,Amount of Time for Binary Tree to Be Infected,Med,"Array, Prefix Sum",
Apple,2392,Build a Matrix With Conditions,Hard,"Array, Two Pointers, Binary Search, Sorting",You are given two positive integer arrays spells and potions; of length n and m respectively; where spells[i] represents the strength of the ith spell and potions[j] represents the strength of the jth potion. You are also given an integer success. A spell and potion pair is considered successful if the product of their strengths is at least success. Return an integer array pairs of length n where pairs[i] is the number of potions that will form a successful pair with the ith spell. Example 1: Input: spells = [5;1;3]; potions = [1;2;3;4;5]; success = 7 Output: [4;0;3] Explanation: - 0th spell: 5 * [1;2;3;4;5] = [5;10;15;20;25]. 4 pairs are successful. - 1st spell: 1 * [1;2;3;4;5] = [1;2;3;4;5]. 0 pairs are successful. - 2nd spell: 3 * [1;2;3;4;5] = [3;6;9;12;15]. 3 pairs are successful. Thus; [4;0;3] is returned. Example 2: Input: spells = [3;1;2]; potions = [8;5;8]; success = 16 Output: [2;0;2] Explanation: - 0th spell: 3 * [8;5;8] = [24;15;24]. 2 pairs are successful. - 1st spell: 1 * [8;5;8] = [8;5;8]. 0 pairs are successful. - 2nd spell: 2 * [8;5;8] = [16;10;16]. 2 pairs are successful. Thus; [2;0;2] is returned. Constraints: n == spells.length m == potions.length 1 <= n; m <= 105 1 <= spells[i]; potions[i] <= 105 1 <= success <= 1010
Apple,2418,Sort the People,Easy,"Array, Binary Search, Greedy, Sorting, Heap (Priority Queue)",You are given two positive 0-indexed integer arrays nums1 and nums2; both of length n. The sum of squared difference of arrays nums1 and nums2 is defined as the sum of (nums1[i] - nums2[i])2 for each 0 <= i < n. You are also given two positive integers k1 and k2. You can modify any of the elements of nums1 by +1 or -1 at most k1 times. Similarly; you can modify any of the elements of nums2 by +1 or -1 at most k2 times. Return the minimum sum of squared difference after modifying array nums1 at most k1 times and modifying array nums2 at most k2 times. Note: You are allowed to modify the array elements to become negative integers. Example 1: Input: nums1 = [1;2;3;4]; nums2 = [2;10;20;19]; k1 = 0; k2 = 0 Output: 579 Explanation: The elements in nums1 and nums2 cannot be modified because k1 = 0 and k2 = 0. The sum of square difference will be: (1 - 2)2 + (2 - 10)2 + (3 - 20)2 + (4 - 19)2 = 579. Example 2: Input: nums1 = [1;4;10;12]; nums2 = [5;8;6;9]; k1 = 1; k2 = 1 Output: 43 Explanation: One way to obtain the minimum sum of square difference is: - Increase nums1[0] once. - Increase nums2[2] once. The minimum of the sum of square difference will be: (2 - 5)2 + (4 - 8)2 + (10 - 7)2 + (12 - 9)2 = 43. Note that; there are other ways to obtain the minimum of the sum of square difference; but there is no way to obtain a sum smaller than 43. Constraints: n == nums1.length == nums2.length 1 <= n <= 105 0 <= nums1[i]; nums2[i] <= 105 0 <= k1; k2 <= 109
Apple,2433,Find The Original Array of Prefix Xor,Med,"Array, Hash Table, Counting","You are given an integer array ranks and a character array suits. You have 5 cards where the ith card has a rank of ranks[i] and a suit of suits[i]. The following are the types of poker hands you can make from best to worst: ""Flush"": Five cards of the same suit. ""Three of a Kind"": Three cards of the same rank. ""Pair"": Two cards of the same rank. ""High Card"": Any single card. Return a string representing the best type of poker hand you can make with the given cards. Note that the return values are case-sensitive. Example 1: Input: ranks = [13;2;3;1;9]; suits = [""a"";""a"";""a"";""a"";""a""] Output: ""Flush"" Explanation: The hand with all the cards consists of 5 cards with the same suit; so we have a ""Flush"". Example 2: Input: ranks = [4;4;2;4;4]; suits = [""d"";""a"";""a"";""b"";""c""] Output: ""Three of a Kind"" Explanation: The hand with the first; second; and fourth card consists of 3 cards with the same rank; so we have a ""Three of a Kind"". Note that we could also make a ""Pair"" hand but ""Three of a Kind"" is a better hand. Also note that other cards could be used to make the ""Three of a Kind"" hand. Example 3: Input: ranks = [10;10;2;12;9]; suits = [""a"";""b"";""c"";""a"";""d""] Output: ""Pair"" Explanation: The hand with the first and second card consists of 2 cards with the same rank; so we have a ""Pair"". Note that we cannot make a ""Flush"" or a ""Three of a Kind"". Constraints: ranks.length == suits.length == 5 1 <= ranks[i] <= 13 'a' <= suits[i] <= 'd' No two cards have the same rank and suit."
Apple,2407,Longest Increasing Subsequence II,Hard,,
Apple,2477,Minimum Fuel Cost to Report to the Capital,Med,"Math, Dynamic Programming, Combinatorics",You are given two positive integers startPos and endPos. Initially; you are standing at position startPos on an infinite number line. With one step; you can move either one position to the left; or one position to the right. Given a positive integer k; return the number of different ways to reach the position endPos starting from startPos; such that you perform exactly k steps. Since the answer may be very large; return it modulo 109 + 7. Two ways are considered different if the order of the steps made is not exactly the same. Note that the number line includes negative integers. Example 1: Input: startPos = 1; endPos = 2; k = 3 Output: 3 Explanation: We can reach position 2 from 1 in exactly 3 steps in three ways: - 1 -> 2 -> 3 -> 2. - 1 -> 2 -> 1 -> 2. - 1 -> 0 -> 1 -> 2. It can be proven that no other way is possible; so we return 3. Example 2: Input: startPos = 2; endPos = 5; k = 10 Output: 0 Explanation: It is impossible to reach position 5 from position 2 in exactly 10 steps. Constraints: 1 <= startPos; endPos; k <= 1000
Apple,2487,Remove Nodes From Linked List,Med,"Hash Table, String, Greedy","Given a string s; partition the string into one or more substrings such that the characters in each substring are unique. That is; no letter appears in a single substring more than once. Return the minimum number of substrings in such a partition. Note that each character should belong to exactly one substring in a partition. Example 1: Input: s = ""abacaba"" Output: 4 Explanation: Two possible partitions are (""a"";""ba"";""cab"";""a"") and (""ab"";""a"";""ca"";""ba""). It can be shown that 4 is the minimum number of substrings needed. Example 2: Input: s = ""ssssss"" Output: 6 Explanation: The only valid partition is (""s"";""s"";""s"";""s"";""s"";""s""). Constraints: 1 <= s.length <= 105 s consists of only English lowercase letters."
Apple,2493,Divide Nodes Into the Maximum Number of Groups,Hard,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a perfect binary tree; reverse the node values at each odd level of the tree. For example; suppose the node values at level 3 are [2;1;3;4;7;11;29;18]; then it should become [18;29;11;7;4;3;1;2]. Return the root of the reversed tree. A binary tree is perfect if all parent nodes have two children and all leaves are on the same level. The level of a node is the number of edges along the path between it and the root node. Example 1: Input: root = [2;3;5;8;13;21;34] Output: [2;5;3;8;13;21;34] Explanation: The tree has only one odd level. The nodes at level 1 are 3; 5 respectively; which are reversed and become 5; 3. Example 2: Input: root = [7;13;11] Output: [7;11;13] Explanation: The nodes at level 1 are 13; 11; which are reversed and become 11; 13. Example 3: Input: root = [0;1;2;0;0;0;0;1;1;1;1;2;2;2;2] Output: [0;2;1;0;0;0;0;2;2;2;2;1;1;1;1] Explanation: The odd levels have non-zero values. The nodes at level 1 were 1; 2; and are 2; 1 after the reversal. The nodes at level 3 were 1; 1; 1; 1; 2; 2; 2; 2; and are 2; 2; 2; 2; 1; 1; 1; 1 after the reversal. Constraints: The number of nodes in the tree is in the range [1; 214]. 0 <= Node.val <= 105 root is a perfect binary tree.
Apple,2506,Count Pairs Of Similar Strings,Easy,"Array, Union Find, Graph, Topological Sort, Sorting, Matrix",
Apple,2482,Difference Between Ones and Zeros in Row and Column,Med,"Array, Backtracking, Bit Manipulation, Matrix, Enumeration",You are given an m x n binary matrix matrix and an integer numSelect. Your goal is to select exactly numSelect distinct columns from matrix such that you cover as many rows as possible. A row is considered covered if all the 1's in that row are also part of a column that you have selected. If a row does not have any 1s; it is also considered covered. More formally; let us consider selected = {c1; c2; ....; cnumSelect} as the set of columns selected by you. A row i is covered by selected if: For each cell where matrix[i][j] == 1; the column j is in selected. Or; no cell in row i has a value of 1. Return the maximum number of rows that can be covered by a set of numSelect columns. Example 1: Input: matrix = [[0;0;0];[1;0;1];[0;1;1];[0;0;1]]; numSelect = 2 Output: 3 Explanation: One possible way to cover 3 rows is shown in the diagram above. We choose s = {0; 2}. - Row 0 is covered because it has no occurrences of 1. - Row 1 is covered because the columns with value 1; i.e. 0 and 2 are present in s. - Row 2 is not covered because matrix[2][1] == 1 but 1 is not present in s. - Row 3 is covered because matrix[2][2] == 1 and 2 is present in s. Thus; we can cover three rows. Note that s = {1; 2} will also cover 3 rows; but it can be shown that no more than three rows can be covered. Example 2: Input: matrix = [[1];[0]]; numSelect = 1 Output: 2 Explanation: Selecting the only column will result in both rows being covered since the entire matrix is selected. Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 12 matrix[i][j] is either 0 or 1. 1 <= numSelect <= n
Apple,2513,Minimize the Maximum of Two Arrays,Med,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",You are given two 0-indexed integer arrays nums1 and nums2; each of size n; and an integer diff. Find the number of pairs (i; j) such that: 0 <= i < j <= n - 1 and nums1[i] - nums1[j] <= nums2[i] - nums2[j] + diff. Return the number of pairs that satisfy the conditions. Example 1: Input: nums1 = [3;2;5]; nums2 = [2;2;1]; diff = 1 Output: 3 Explanation: There are 3 pairs that satisfy the conditions: 1. i = 0; j = 1: 3 - 2 <= 2 - 2 + 1. Since i < j and 1 <= 1; this pair satisfies the conditions. 2. i = 0; j = 2: 3 - 5 <= 2 - 1 + 1. Since i < j and -2 <= 2; this pair satisfies the conditions. 3. i = 1; j = 2: 2 - 5 <= 2 - 1 + 1. Since i < j and -3 <= 2; this pair satisfies the conditions. Therefore; we return 3. Example 2: Input: nums1 = [3;-1]; nums2 = [-2;2]; diff = -1 Output: 0 Explanation: Since there does not exist any pair that satisfies the conditions; we return 0. Constraints: n == nums1.length == nums2.length 2 <= n <= 105 -104 <= nums1[i]; nums2[i] <= 104 -104 <= diff <= 104
Apple,2540,Minimum Common Value,Easy,"Array, Math",
Apple,2549,Count Distinct Numbers on Board,Easy,"Array, Binary Search, Stack, Sorting, Heap (Priority Queue), Monotonic Stack",You are given a 0-indexed array of non-negative integers nums. For each integer in nums; you must find its respective second greater integer. The second greater integer of nums[i] is nums[j] such that: j > i nums[j] > nums[i] There exists exactly one index k such that nums[k] > nums[i] and i < k < j. If there is no such nums[j]; the second greater integer is considered to be -1. For example; in the array [1; 2; 4; 3]; the second greater integer of 1 is 4; 2 is 3; and that of 3 and 4 is -1. Return an integer array answer; where answer[i] is the second greater integer of nums[i]. Example 1: Input: nums = [2;4;0;9;6] Output: [9;6;6;-1;-1] Explanation: 0th index: 4 is the first integer greater than 2; and 9 is the second integer greater than 2; to the right of 2. 1st index: 9 is the first; and 6 is the second integer greater than 4; to the right of 4. 2nd index: 9 is the first; and 6 is the second integer greater than 0; to the right of 0. 3rd index: There is no integer greater than 9 to its right; so the second greater integer is considered to be -1. 4th index: There is no integer greater than 6 to its right; so the second greater integer is considered to be -1. Thus; we return [9;6;6;-1;-1]. Example 2: Input: nums = [3;3] Output: [-1;-1] Explanation: We return [-1;-1] since neither integer has any integer greater than it. Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109
Apple,2565,Subsequence With the Minimum Score,Hard,"Array, Two Pointers, Greedy",
Apple,2602,Minimum Operations to Make All Array Elements Equal,Med,"Array, Two Pointers",You are given a 0-indexed integer array forts of length n representing the positions of several forts. forts[i] can be -1; 0; or 1 where: -1 represents there is no fort at the ith position. 0 indicates there is an enemy fort at the ith position. 1 indicates the fort at the ith the position is under your command. Now you have decided to move your army from one of your forts at position i to an empty position j such that: 0 <= i; j <= n - 1 The army travels over enemy forts only. Formally; for all k where min(i;j) < k < max(i;j); forts[k] == 0. While moving the army; all the enemy forts that come in the way are captured. Return the maximum number of enemy forts that can be captured. In case it is impossible to move your army; or you do not have any fort under your command; return 0. Example 1: Input: forts = [1;0;0;-1;0;0;0;0;1] Output: 4 Explanation: - Moving the army from position 0 to position 3 captures 2 enemy forts; at 1 and 2. - Moving the army from position 8 to position 3 captures 4 enemy forts. Since 4 is the maximum number of enemy forts that can be captured; we return 4. Example 2: Input: forts = [0;0;1;-1] Output: 0 Explanation: Since no enemy fort can be captured; 0 is returned. Constraints: 1 <= forts.length <= 1000 -1 <= forts[i] <= 1
Apple,2616,Minimize the Maximum Difference of Pairs,Med,"Array, Greedy, Heap (Priority Queue)",You are given a 0-indexed integer array nums and an integer k. You have a starting score of 0. In one operation: choose an index i such that 0 <= i < nums.length; increase your score by nums[i]; and replace nums[i] with ceil(nums[i] / 3). Return the maximum possible score you can attain after applying exactly k operations. The ceiling function ceil(val) is the least integer greater than or equal to val. Example 1: Input: nums = [10;10;10;10;10]; k = 5 Output: 50 Explanation: Apply the operation to each array element exactly once. The final score is 10 + 10 + 10 + 10 + 10 = 50. Example 2: Input: nums = [1;10;3;3;3]; k = 3 Output: 17 Explanation: You can do the following operations: Operation 1: Select i = 1; so nums becomes [1;4;3;3;3]. Your score increases by 10. Operation 2: Select i = 1; so nums becomes [1;2;3;3;3]. Your score increases by 4. Operation 3: Select i = 2; so nums becomes [1;2;1;3;3]. Your score increases by 3. The final score is 10 + 4 + 3 = 17. Constraints: 1 <= nums.length; k <= 105 1 <= nums[i] <= 109
Apple,2610,Convert an Array Into a 2D Array With Conditions,Med,"Math, Number Theory",Given two positive integers left and right; find the two integers num1 and num2 such that: left <= num1 < num2 <= right . num1 and num2 are both prime numbers. num2 - num1 is the minimum amongst all other pairs satisfying the above conditions. Return the positive integer array ans = [num1; num2]. If there are multiple pairs satisfying these conditions; return the one with the minimum num1 value or [-1; -1] if such numbers do not exist. A number greater than 1 is called prime if it is only divisible by 1 and itself. Example 1: Input: left = 10; right = 19 Output: [11;13] Explanation: The prime numbers between 10 and 19 are 11; 13; 17; and 19. The closest gap between any pair is 2; which can be achieved by [11;13] or [17;19]. Since 11 is smaller than 17; we return the first pair. Example 2: Input: left = 4; right = 6 Output: [-1;-1] Explanation: There exists only one prime number in the given range; so the conditions cannot be satisfied. Constraints: 1 <= left <= right <= 106
Apple,2623,Memoize,Med,"Tree, Depth-First Search, Graph, Trie",
Apple,2627,Debounce,Med,"Array, Dynamic Programming, Tree, Depth-First Search",There exists an undirected and initially unrooted tree with n nodes indexed from 0 to n - 1. You are given the integer n and a 2D integer array edges of length n - 1; where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Each node has an associated price. You are given an integer array price; where price[i] is the price of the ith node. The price sum of a given path is the sum of the prices of all nodes lying on that path. The tree can be rooted at any node root of your choice. The incurred cost after choosing root is the difference between the maximum and minimum price sum amongst all paths starting at root. Return the maximum possible cost amongst all possible root choices. Example 1: Input: n = 6; edges = [[0;1];[1;2];[1;3];[3;4];[3;5]]; price = [9;8;7;6;10;5] Output: 24 Explanation: The diagram above denotes the tree after rooting it at node 2. The first part (colored in red) shows the path with the maximum price sum. The second part (colored in blue) shows the path with the minimum price sum. - The first path contains nodes [2;1;3;4]: the prices are [7;8;6;10]; and the sum of the prices is 31. - The second path contains the node [2] with the price [7]. The difference between the maximum and minimum price sum is 24. It can be proved that 24 is the maximum cost. Example 2: Input: n = 3; edges = [[0;1];[1;2]]; price = [1;1;1] Output: 2 Explanation: The diagram above denotes the tree after rooting it at node 0. The first part (colored in red) shows the path with the maximum price sum. The second part (colored in blue) shows the path with the minimum price sum. - The first path contains nodes [0;1;2]: the prices are [1;1;1]; and the sum of the prices is 3. - The second path contains node [0] with a price [1]. The difference between the maximum and minimum price sum is 2. It can be proved that 2 is the maximum cost. Constraints: 1 <= n <= 105 edges.length == n - 1 0 <= ai; bi <= n - 1 edges represents a valid tree. price.length == n 1 <= price[i] <= 105
Apple,2634,Filter Elements from Array,Easy,"Array, Hash Table, Two Pointers, Binary Search",Given two integer arrays nums1 and nums2; sorted in non-decreasing order; return the minimum integer common to both arrays. If there is no common integer amongst nums1 and nums2; return -1. Note that an integer is said to be common to nums1 and nums2 if both arrays have at least one occurrence of that integer. Example 1: Input: nums1 = [1;2;3]; nums2 = [2;4] Output: 2 Explanation: The smallest element common to both arrays is 2; so we return 2. Example 2: Input: nums1 = [1;2;3;6]; nums2 = [2;3;4;5] Output: 2 Explanation: There are two common elements in the array 2 and 3 out of which 2 is the smallest; so 2 is returned. Constraints: 1 <= nums1.length; nums2.length <= 105 1 <= nums1[i]; nums2[j] <= 109 Both nums1 and nums2 are sorted in non-decreasing order.
Apple,2618,Check if Object Instance of Class,Med,"Array, Binary Search, Greedy, Queue, Sliding Window, Prefix Sum",You are given a 0-indexed integer array stations of length n; where stations[i] represents the number of power stations in the ith city. Each power station can provide power to every city in a fixed range. In other words; if the range is denoted by r; then a power station at city i can provide power to all cities j such that |i - j| <= r and 0 <= i; j <= n - 1. Note that |x| denotes absolute value. For example; |7 - 5| = 2 and |3 - 10| = 7. The power of a city is the total number of power stations it is being provided power from. The government has sanctioned building k more power stations; each of which can be built in any city; and have the same range as the pre-existing ones. Given the two integers r and k; return the maximum possible minimum power of a city; if the additional power stations are built optimally. Note that you can build the k power stations in multiple cities. Example 1: Input: stations = [1;2;4;5;0]; r = 1; k = 2 Output: 5 Explanation: One of the optimal ways is to install both the power stations at city 1. So stations will become [1;4;4;5;0]. - City 0 is provided by 1 + 4 = 5 power stations. - City 1 is provided by 1 + 4 + 4 = 9 power stations. - City 2 is provided by 4 + 4 + 5 = 13 power stations. - City 3 is provided by 5 + 4 = 9 power stations. - City 4 is provided by 5 + 0 = 5 power stations. So the minimum power of a city is 5. Since it is not possible to obtain a larger power; we return 5. Example 2: Input: stations = [4;4;4;4]; r = 0; k = 3 Output: 4 Explanation: It can be proved that we cannot make the minimum power of a city greater than 4. Constraints: n == stations.length 1 <= n <= 105 0 <= stations[i] <= 105 0 <= r <= n - 1 0 <= k <= 109
Apple,2626,Array Reduce Transformation,Easy,"Array, Hash Table, Sliding Window",Given an integer array nums and an integer k; return the number of good subarrays of nums. A subarray arr is good if it there are at least k pairs of indices (i; j) such that i < j and arr[i] == arr[j]. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1;1;1]; k = 10 Output: 1 Explanation: The only good subarray is the array nums itself. Example 2: Input: nums = [3;1;4;3;2;2;4]; k = 2 Output: 4 Explanation: There are 4 different good subarrays: - [3;1;4;3;2;2] that has 2 pairs. - [3;1;4;3;2;2;4] that has 3 pairs. - [1;4;3;2;2;4] that has 2 pairs. - [4;3;2;2;4] that has 2 pairs. Constraints: 1 <= nums.length <= 105 1 <= nums[i]; k <= 109
Apple,2666,Allow One Function Call,Easy,"Array, Two Pointers, Binary Search, Sorting",
Apple,2739,Total Distance Traveled,Easy,"Array, Dynamic Programming, Tree, Depth-First Search, Graph",There exists an undirected and unrooted tree with n nodes indexed from 0 to n - 1. You are given the integer n and a 2D integer array edges of length n - 1; where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Each node has an associated price. You are given an integer array price; where price[i] is the price of the ith node. The price sum of a given path is the sum of the prices of all nodes lying on that path. Additionally; you are given a 2D integer array trips; where trips[i] = [starti; endi] indicates that you start the ith trip from the node starti and travel to the node endi by any path you like. Before performing your first trip; you can choose some non-adjacent nodes and halve the prices. Return the minimum total price sum to perform all the given trips. Example 1: Input: n = 4; edges = [[0;1];[1;2];[1;3]]; price = [2;2;10;6]; trips = [[0;3];[2;1];[2;3]] Output: 23 Explanation: The diagram above denotes the tree after rooting it at node 2. The first part shows the initial tree and the second part shows the tree after choosing nodes 0; 2; and 3; and making their price half. For the 1st trip; we choose path [0;1;3]. The price sum of that path is 1 + 2 + 3 = 6. For the 2nd trip; we choose path [2;1]. The price sum of that path is 2 + 5 = 7. For the 3rd trip; we choose path [2;1;3]. The price sum of that path is 5 + 2 + 3 = 10. The total price sum of all trips is 6 + 7 + 10 = 23. It can be proven; that 23 is the minimum answer that we can achieve. Example 2: Input: n = 2; edges = [[0;1]]; price = [2;2]; trips = [[0;0]] Output: 1 Explanation: The diagram above denotes the tree after rooting it at node 0. The first part shows the initial tree and the second part shows the tree after choosing node 0; and making its price half. For the 1st trip; we choose path [0]. The price sum of that path is 1. The total price sum of all trips is 1. It can be proven; that 1 is the minimum answer that we can achieve. Constraints: 1 <= n <= 50 edges.length == n - 1 0 <= ai; bi <= n - 1 edges represents a valid tree. price.length == n price[i] is an even integer. 1 <= price[i] <= 1000 1 <= trips.length <= 100 0 <= starti; endi <= n - 1
Apple,2722,Join Two Arrays by ID,Med,"Array, Math, Matrix, Number Theory",You are given a 0-indexed two-dimensional integer array nums. Return the largest prime number that lies on at least one of the diagonals of nums. In case; no prime is present on any of the diagonals; return 0. Note that: An integer is prime if it is greater than 1 and has no positive integer divisors other than 1 and itself. An integer val is on one of the diagonals of nums if there exists an integer i for which nums[i][i] = val or an i for which nums[i][nums.length - i - 1] = val. In the above diagram; one diagonal is [1;5;9] and another diagonal is [3;5;7]. Example 1: Input: nums = [[1;2;3];[5;6;7];[9;10;11]] Output: 11 Explanation: The numbers 1; 3; 6; 9; and 11 are the only numbers present on at least one of the diagonals. Since 11 is the largest prime; we return 11. Example 2: Input: nums = [[1;2;3];[5;17;7];[9;11;10]] Output: 17 Explanation: The numbers 1; 3; 9; 10; and 17 are all present on at least one of the diagonals. 17 is the largest prime; so we return 17. Constraints: 1 <= nums.length <= 300 nums.length == numsi.length 1 <= nums[i][j] <= 4*106
Apple,2750,Ways to Split Array Into Good Subarrays,Med,,
Apple,2808,Minimum Seconds to Equalize a Circular Array,Med,"Array, Dynamic Programming",You are given two 0-indexed integer arrays; cost and time; of size n representing the costs and the time taken to paint n different walls respectively. There are two painters available: A paid painter that paints the ith wall in time[i] units of time and takes cost[i] units of money. A free painter that paints any wall in 1 unit of time at a cost of 0. But the free painter can only be used if the paid painter is already occupied. Return the minimum amount of money required to paint the n walls. Example 1: Input: cost = [1;2;3;2]; time = [1;2;3;2] Output: 3 Explanation: The walls at index 0 and 1 will be painted by the paid painter; and it will take 3 units of time; meanwhile; the free painter will paint the walls at index 2 and 3; free of cost in 2 units of time. Thus; the total cost is 1 + 2 = 3. Example 2: Input: cost = [2;3;4;2]; time = [1;1;1;1] Output: 4 Explanation: The walls at index 0 and 3 will be painted by the paid painter; and it will take 2 units of time; meanwhile; the free painter will paint the walls at index 1 and 2; free of cost in 2 units of time. Thus; the total cost is 2 + 2 = 4. Constraints: 1 <= cost.length <= 500 cost.length == time.length 1 <= cost[i] <= 106 1 <= time[i] <= 500
Apple,2843,Count Symmetric Integers,Easy,"Tree, Depth-First Search, Binary Tree",
Apple,2850,Minimum Moves to Spread Stones Over Grid,Med,"Math, Dynamic Programming, Greedy, Brainteaser","You are given three integers x; y; and z. You have x strings equal to ""AA""; y strings equal to ""BB""; and z strings equal to ""AB"". You want to choose some (possibly all or none) of these strings and concatenate them in some order to form a new string. This new string must not contain ""AAA"" or ""BBB"" as a substring. Return the maximum possible length of the new string. A substring is a contiguous non-empty sequence of characters within a string. Example 1: Input: x = 2; y = 5; z = 1 Output: 12 Explanation: We can concactenate the strings ""BB""; ""AA""; ""BB""; ""AA""; ""BB""; and ""AB"" in that order. Then; our new string is ""BBAABBAABBAB"". That string has length 12; and we can show that it is impossible to construct a string of longer length. Example 2: Input: x = 3; y = 2; z = 2 Output: 14 Explanation: We can concactenate the strings ""AB""; ""AB""; ""AA""; ""BB""; ""AA""; ""BB""; and ""AA"" in that order. Then; our new string is ""ABABAABBAABBAA"". That string has length 14; and we can show that it is impossible to construct a string of longer length. Constraints: 1 <= x; y; z <= 50"
Apple,2971,Find Polygon With the Largest Perimeter,Med,,
Apple,3091,Apply Operations to Make Sum of Array Greater Than or Equal to k,Med,"Array, Hash Table, Dynamic Programming, Sliding Window",You are given a 0-indexed array nums of non-negative integers; and two integers l and r. Return the count of sub-multisets within nums where the sum of elements in each subset falls within the inclusive range of [l; r]. Since the answer may be large; return it modulo 109 + 7. A sub-multiset is an unordered collection of elements of the array in which a given value x can occur 0; 1; ...; occ[x] times; where occ[x] is the number of occurrences of x in the array. Note that: Two sub-multisets are the same if sorting both sub-multisets results in identical multisets. The sum of an empty multiset is 0. Example 1: Input: nums = [1;2;2;3]; l = 6; r = 6 Output: 1 Explanation: The only subset of nums that has a sum of 6 is {1; 2; 3}. Example 2: Input: nums = [2;1;4;2;7]; l = 1; r = 5 Output: 7 Explanation: The subsets of nums that have a sum within the range [1; 5] are {1}; {2}; {4}; {2; 2}; {1; 2}; {1; 4}; and {1; 2; 2}. Example 3: Input: nums = [1;2;1;3;5;2]; l = 3; r = 5 Output: 9 Explanation: The subsets of nums that have a sum within the range [3; 5] are {3}; {5}; {1; 2}; {1; 3}; {2; 2}; {2; 3}; {1; 1; 2}; {1; 1; 3}; and {1; 2; 2}. Constraints: 1 <= nums.length <= 2 * 104 0 <= nums[i] <= 2 * 104 Sum of nums does not exceed 2 * 104. 0 <= l <= r <= 2 * 104
Microsoft,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Microsoft,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Microsoft,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Microsoft,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Microsoft,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Microsoft,1768,Merge Strings Alternately,Easy,"Array, Math, Stack, Tree, Design, Binary Tree",
Microsoft,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Microsoft,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Microsoft,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Microsoft,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Microsoft,1757,Recyclable and Low Fat Products,Easy,"Array, Dynamic Programming, Breadth-First Search",A certain bug's home is on the x-axis at position x. Help them get there from position 0. The bug jumps according to the following rules: It can jump exactly a positions forward (to the right). It can jump exactly b positions backward (to the left). It cannot jump backward twice in a row. It cannot jump to any forbidden positions. The bug may jump forward beyond its home; but it cannot jump to positions numbered with negative integers. Given an array of integers forbidden; where forbidden[i] means that the bug cannot jump to the position forbidden[i]; and integers a; b; and x; return the minimum number of jumps needed for the bug to reach its home. If there is no possible sequence of jumps that lands the bug on position x; return -1. Example 1: Input: forbidden = [14;4;18;1;15]; a = 3; b = 15; x = 9 Output: 3 Explanation: 3 jumps forward (0 -> 3 -> 6 -> 9) will get the bug home. Example 2: Input: forbidden = [8;3;16;6;12;20]; a = 15; b = 13; x = 11 Output: -1 Example 3: Input: forbidden = [1;6;2;14;5;17;4]; a = 16; b = 9; x = 7 Output: 2 Explanation: One jump forward (0 -> 16) then one jump backward (16 -> 7) will get the bug home. Constraints: 1 <= forbidden.length <= 1000 1 <= a; b; forbidden[i] <= 2000 0 <= x <= 2000 All the elements in forbidden are distinct. Position x is not forbidden.
Microsoft,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Microsoft,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Microsoft,2667,Create Hello World Function,Easy,"Array, Hash Table, Math, Stack, Sliding Window",
Microsoft,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Microsoft,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Microsoft,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Microsoft,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
Microsoft,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Microsoft,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Microsoft,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Microsoft,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Microsoft,13,Roman to Integer,Easy,"Hash Table, Math, String","Roman numerals are represented by seven different symbols: I; V; X; L; C; D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example; 2 is written as II in Roman numeral; just two ones added together. 12 is written as XII; which is simply X + II. The number 27 is written as XXVII; which is XX + V + II. Roman numerals are usually written largest to smallest from left to right. However; the numeral for four is not IIII. Instead; the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine; which is written as IX. There are six instances where subtraction is used: I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral; convert it to an integer. Example 1: Input: s = ""III"" Output: 3 Explanation: III = 3. Example 2: Input: s = ""LVIII"" Output: 58 Explanation: L = 50; V= 5; III = 3. Example 3: Input: s = ""MCMXCIV"" Output: 1994 Explanation: M = 1000; CM = 900; XC = 90 and IV = 4. Constraints: 1 <= s.length <= 15 s contains only the characters ('I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M'). It is guaranteed that s is a valid roman numeral in the range [1; 3999]."
Microsoft,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Microsoft,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Microsoft,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Microsoft,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Microsoft,1466,Reorder Routes to Make All Paths Lead to the City Zero,Med,"Array, Dynamic Programming, Sorting",Given an array of integers arr and an integer d. In one step you can jump from index i to index: i + x where: i + x < arr.length and 0 < x <= d. i - x where: i - x >= 0 and 0 < x <= d. In addition; you can only jump from index i to index j if arr[i] > arr[j] and arr[i] > arr[k] for all indices k between i and j (More formally min(i; j) < k < max(i; j)). You can choose any index of the array and start jumping. Return the maximum number of indices you can visit. Notice that you can not jump outside of the array at any time. Example 1: Input: arr = [6;4;14;6;8;13;9;7;10;6;12]; d = 2 Output: 4 Explanation: You can start at index 10. You can jump 10 --> 8 --> 6 --> 7 as shown. Note that if you start at index 6 you can only jump to index 7. You cannot jump to index 5 because 13 > 9. You cannot jump to index 4 because index 5 is between index 4 and 6 and 13 > 9. Similarly You cannot jump from index 3 to index 2 or index 1. Example 2: Input: arr = [3;3;3;3;3]; d = 3 Output: 1 Explanation: You can start at any index. You always cannot jump to any index. Example 3: Input: arr = [7;6;5;4;3;2;1]; d = 1 Output: 7 Explanation: Start at index 0. You can visit all the indicies. Constraints: 1 <= arr.length <= 1000 1 <= arr[i] <= 105 1 <= d <= arr.length
Microsoft,26,Remove Duplicates from Sorted Array,Easy,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums. Consider the number of unique elements of nums to be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;2] Output: 2; nums = [1;2;_] Explanation: Your function should return k = 2; with the first two elements of nums being 1 and 2 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;2;2;3;3;4] Output: 5; nums = [0;1;2;3;4;_;_;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums being 0; 1; 2; 3; and 4 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -100 <= nums[i] <= 100 nums is sorted in non-decreasing order.
Microsoft,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Microsoft,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Microsoft,273,Integer to English Words,Hard,"Math, String, Recursion","Convert a non-negative integer num to its English words representation. Example 1: Input: num = 123 Output: ""One Hundred Twenty Three"" Example 2: Input: num = 12345 Output: ""Twelve Thousand Three Hundred Forty Five"" Example 3: Input: num = 1234567 Output: ""One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"" Constraints: 0 <= num <= 231 - 1"
Microsoft,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Microsoft,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Microsoft,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Microsoft,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Microsoft,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Microsoft,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
Microsoft,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Microsoft,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Microsoft,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Microsoft,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Microsoft,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Microsoft,128,Longest Consecutive Sequence,Med,"Array, Hash Table, Union Find",Given an unsorted array of integers nums; return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time. Example 1: Input: nums = [100;4;200;1;3;2] Output: 4 Explanation: The longest consecutive elements sequence is [1; 2; 3; 4]. Therefore its length is 4. Example 2: Input: nums = [0;3;7;2;5;8;4;6;0;1] Output: 9 Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109
Microsoft,189,Rotate Array,Med,"Array, Math, Two Pointers",Given an integer array nums; rotate the array to the right by k steps; where k is non-negative. Example 1: Input: nums = [1;2;3;4;5;6;7]; k = 3 Output: [5;6;7;1;2;3;4] Explanation: rotate 1 steps to the right: [7;1;2;3;4;5;6] rotate 2 steps to the right: [6;7;1;2;3;4;5] rotate 3 steps to the right: [5;6;7;1;2;3;4] Example 2: Input: nums = [-1;-100;3;99]; k = 2 Output: [3;99;-1;-100] Explanation: rotate 1 steps to the right: [99;-1;-100;3] rotate 2 steps to the right: [3;99;-1;-100] Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 0 <= k <= 105 Follow up: Try to come up with as many solutions as you can. There are at least three different ways to solve this problem. Could you do it in-place with O(1) extra space?
Microsoft,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Microsoft,2246,Longest Path With Different Adjacent Characters,Hard,"Depth-First Search, Graph, Topological Sort",A company is organizing a meeting and has a list of n employees; waiting to be invited. They have arranged for a large circular table; capable of seating any number of employees. The employees are numbered from 0 to n - 1. Each employee has a favorite person and they will attend the meeting only if they can sit next to their favorite person at the table. The favorite person of an employee is not themself. Given a 0-indexed integer array favorite; where favorite[i] denotes the favorite person of the ith employee; return the maximum number of employees that can be invited to the meeting. Example 1: Input: favorite = [2;2;1;2] Output: 3 Explanation: The above figure shows how the company can invite employees 0; 1; and 2; and seat them at the round table. All employees cannot be invited because employee 2 cannot sit beside employees 0; 1; and 3; simultaneously. Note that the company can also invite employees 1; 2; and 3; and give them their desired seats. The maximum number of employees that can be invited to the meeting is 3. Example 2: Input: favorite = [1;2;0] Output: 3 Explanation: Each employee is the favorite person of at least one other employee; and the only way the company can invite them is if they invite every employee. The seating arrangement will be the same as that in the figure given in example 1: - Employee 0 will sit between employees 2 and 1. - Employee 1 will sit between employees 0 and 2. - Employee 2 will sit between employees 1 and 0. The maximum number of employees that can be invited to the meeting is 3. Example 3: Input: favorite = [3;0;1;4;1] Output: 4 Explanation: The above figure shows how the company will invite employees 0; 1; 3; and 4; and seat them at the round table. Employee 2 cannot be invited because the two spots next to their favorite employee 1 are taken. So the company leaves them out of the meeting. The maximum number of employees that can be invited to the meeting is 4. Constraints: n == favorite.length 2 <= n <= 105 0 <= favorite[i] <= n - 1 favorite[i] != i
Microsoft,7,Reverse Integer,Med,Math,Given a signed 32-bit integer x; return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231; 231 - 1]; then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: Input: x = 123 Output: 321 Example 2: Input: x = -123 Output: -321 Example 3: Input: x = 120 Output: 21 Constraints: -231 <= x <= 231 - 1
Microsoft,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Microsoft,236,Lowest Common Ancestor of a Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",Given a binary tree; find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3. Example 2: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [1;2]; p = 1; q = 2 Output: 1 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the tree.
Microsoft,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Microsoft,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Microsoft,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Microsoft,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Microsoft,125,Valid Palindrome,Easy,"Two Pointers, String","A phrase is a palindrome if; after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters; it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s; return true if it is a palindrome; or false otherwise. Example 1: Input: s = ""A man; a plan; a canal: Panama"" Output: true Explanation: ""amanaplanacanalpanama"" is a palindrome. Example 2: Input: s = ""race a car"" Output: false Explanation: ""raceacar"" is not a palindrome. Example 3: Input: s = "" "" Output: true Explanation: s is an empty string """" after removing non-alphanumeric characters. Since an empty string reads the same forward and backward; it is a palindrome. Constraints: 1 <= s.length <= 2 * 105 s consists only of printable ASCII characters."
Microsoft,217,Contains Duplicate,Easy,"Array, Hash Table, Sorting",Given an integer array nums; return true if any value appears at least twice in the array; and return false if every element is distinct. Example 1: Input: nums = [1;2;3;1] Output: true Explanation: The element 1 occurs at the indices 0 and 3. Example 2: Input: nums = [1;2;3;4] Output: false Explanation: All elements are distinct. Example 3: Input: nums = [1;1;1;3;3;4;3;2;4;2] Output: true Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109
Microsoft,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Microsoft,567,Permutation in String,Med,"Hash Table, Two Pointers, String, Sliding Window","Given two strings s1 and s2; return true if s2 contains a permutation of s1; or false otherwise. In other words; return true if one of s1's permutations is the substring of s2. Example 1: Input: s1 = ""ab""; s2 = ""eidbaooo"" Output: true Explanation: s2 contains one permutation of s1 (""ba""). Example 2: Input: s1 = ""ab""; s2 = ""eidboaoo"" Output: false Constraints: 1 <= s1.length; s2.length <= 104 s1 and s2 consist of lowercase English letters."
Microsoft,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
Microsoft,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Microsoft,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
Microsoft,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Microsoft,64,Minimum Path Sum,Med,"Array, Dynamic Programming, Matrix",Given a m x n grid filled with non-negative numbers; find a path from top left to bottom right; which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1;3;1];[1;5;1];[4;2;1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. Example 2: Input: grid = [[1;2;3];[4;5;6]] Output: 12 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 200 0 <= grid[i][j] <= 200
Microsoft,73,Set Matrix Zeroes,Med,"Array, Hash Table, Matrix",Given an m x n integer matrix matrix; if an element is 0; set its entire row and column to 0's. You must do it in place. Example 1: Input: matrix = [[1;1;1];[1;0;1];[1;1;1]] Output: [[1;0;1];[0;0;0];[1;0;1]] Example 2: Input: matrix = [[0;1;2;0];[3;4;5;2];[1;3;1;5]] Output: [[0;0;0;0];[0;4;5;0];[0;3;1;0]] Constraints: m == matrix.length n == matrix[0].length 1 <= m; n <= 200 -231 <= matrix[i][j] <= 231 - 1 Follow up: A straightforward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space; but still not the best solution. Could you devise a constant space solution?
Microsoft,93,Restore IP Addresses,Med,"String, Backtracking","A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. For example; ""0.1.2.201"" and ""192.168.1.1"" are valid IP addresses; but ""0.011.255.245""; ""192.168.1.312"" and ""192.168@1.1"" are invalid IP addresses. Given a string s containing only digits; return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order. Example 1: Input: s = ""25525511135"" Output: [""255.255.11.135"";""255.255.111.35""] Example 2: Input: s = ""0000"" Output: [""0.0.0.0""] Example 3: Input: s = ""101023"" Output: [""1.0.10.23"";""1.0.102.3"";""10.1.0.23"";""10.10.2.3"";""101.0.2.3""] Constraints: 1 <= s.length <= 20 s consists of digits only."
Microsoft,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Microsoft,102,Binary Tree Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the level order traversal of its nodes' values. (i.e.; from left to right; level by level). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[9;20];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -1000 <= Node.val <= 1000
Microsoft,135,Candy,Hard,"Array, Greedy",There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings. You are giving candies to these children subjected to the following requirements: Each child must have at least one candy. Children with a higher rating get more candies than their neighbors. Return the minimum number of candies you need to have to distribute the candies to the children. Example 1: Input: ratings = [1;0;2] Output: 5 Explanation: You can allocate to the first; second and third child with 2; 1; 2 candies respectively. Example 2: Input: ratings = [1;2;2] Output: 4 Explanation: You can allocate to the first; second and third child with 1; 2; 1 candies respectively. The third child gets 1 candy because it satisfies the above two conditions. Constraints: n == ratings.length 1 <= n <= 2 * 104 0 <= ratings[i] <= 2 * 104
Microsoft,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Microsoft,213,House Robber II,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile; adjacent houses have a security system connected; and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [2;3;2] Output: 3 Explanation: You cannot rob house 1 (money = 2) and then rob house 3 (money = 2); because they are adjacent houses. Example 2: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 3: Input: nums = [1;2;3] Output: 3 Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 1000
Microsoft,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Microsoft,875,Koko Eating Bananas,Med,"Array, Two Pointers, Dynamic Programming, Enumeration",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr; return the length of the longest subarray; which is a mountain. Return 0 if there is no mountain subarray. Example 1: Input: arr = [2;1;4;7;3;2;5] Output: 5 Explanation: The largest mountain is [1;4;7;3;2] which has length 5. Example 2: Input: arr = [2;2;2] Output: 0 Explanation: There is no mountain. Constraints: 1 <= arr.length <= 104 0 <= arr[i] <= 104 Follow up: Can you solve it using only one pass? Can you solve it in O(1) space?
Microsoft,2998,Minimum Number of Operations to Make X and Y Equal,Med,"Math, Enumeration",You are given two positive integers low and high. An integer x consisting of 2 * n digits is symmetric if the sum of the first n digits of x is equal to the sum of the last n digits of x. Numbers with an odd number of digits are never symmetric. Return the number of symmetric integers in the range [low; high]. Example 1: Input: low = 1; high = 100 Output: 9 Explanation: There are 9 symmetric integers between 1 and 100: 11; 22; 33; 44; 55; 66; 77; 88; and 99. Example 2: Input: low = 1200; high = 1230 Output: 4 Explanation: There are 4 symmetric integers between 1200 and 1230: 1203; 1212; 1221; and 1230. Constraints: 1 <= low <= high <= 104
Microsoft,24,Swap Nodes in Pairs,Med,"Linked List, Recursion",Given a linked list; swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e.; only nodes themselves may be changed.) Example 1: Input: head = [1;2;3;4] Output: [2;1;4;3] Explanation: Example 2: Input: head = [] Output: [] Example 3: Input: head = [1] Output: [1] Example 4: Input: head = [1;2;3] Output: [2;1;3] Constraints: The number of nodes in the list is in the range [0; 100]. 0 <= Node.val <= 100
Microsoft,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Microsoft,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Microsoft,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
Microsoft,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Microsoft,103,Binary Tree Zigzag Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the zigzag level order traversal of its nodes' values. (i.e.; from left to right; then right to left for the next level and alternate between). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[20;9];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100
Microsoft,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Microsoft,165,Compare Version Numbers,Med,"Two Pointers, String","Given two version strings; version1 and version2; compare them. A version string consists of revisions separated by dots '.'. The value of the revision is its integer conversion ignoring leading zeros. To compare version strings; compare their revision values in left-to-right order. If one of the version strings has fewer revisions; treat the missing revision values as 0. Return the following: If version1 < version2; return -1. If version1 > version2; return 1. Otherwise; return 0. Example 1: Input: version1 = ""1.2""; version2 = ""1.10"" Output: -1 Explanation: version1's second revision is ""2"" and version2's second revision is ""10"": 2 < 10; so version1 < version2. Example 2: Input: version1 = ""1.01""; version2 = ""1.001"" Output: 0 Explanation: Ignoring leading zeroes; both ""01"" and ""001"" represent the same integer ""1"". Example 3: Input: version1 = ""1.0""; version2 = ""1.0.0.0"" Output: 0 Explanation: version1 has less revisions; which means every missing revision are treated as ""0"". Constraints: 1 <= version1.length; version2.length <= 500 version1 and version2 only contain digits and '.'. version1 and version2 are valid version numbers. All the given revisions in version1 and version2 can be stored in a 32-bit integer."
Microsoft,268,Missing Number,Easy,"Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting",Given an array nums containing n distinct numbers in the range [0; n]; return the only number in the range that is missing from the array. Example 1: Input: nums = [3;0;1] Output: 2 Explanation: n = 3 since there are 3 numbers; so all numbers are in the range [0;3]. 2 is the missing number in the range since it does not appear in nums. Example 2: Input: nums = [0;1] Output: 2 Explanation: n = 2 since there are 2 numbers; so all numbers are in the range [0;2]. 2 is the missing number in the range since it does not appear in nums. Example 3: Input: nums = [9;6;4;2;3;5;7;0;1] Output: 8 Explanation: n = 9 since there are 9 numbers; so all numbers are in the range [0;9]. 8 is the missing number in the range since it does not appear in nums. Constraints: n == nums.length 1 <= n <= 104 0 <= nums[i] <= n All the numbers of nums are unique. Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?
Microsoft,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Microsoft,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
Microsoft,912,Sort an Array,Med,"Array, Math, Binary Search, Prefix Sum, Randomized","You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index. You need to implement the function pickIndex(); which randomly picks an index in the range [0; w.length - 1] (inclusive) and returns it. The probability of picking an index i is w[i] / sum(w). For example; if w = [1; 3]; the probability of picking index 0 is 1 / (1 + 3) = 0.25 (i.e.; 25%); and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e.; 75%). Example 1: Input [""Solution"";""pickIndex""] [[[1]];[]] Output [null;0] Explanation Solution solution = new Solution([1]); solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w. Example 2: Input [""Solution"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex""] [[[1;3]];[];[];[];[];[]] Output [null;1;1;1;1;0] Explanation Solution solution = new Solution([1; 3]); solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4. solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4. Since this is a randomization problem; multiple answers are allowed. All of the following outputs can be considered correct: [null;1;1;1;1;0] [null;1;1;1;1;1] [null;1;1;1;0;0] [null;1;1;1;0;1] [null;1;0;1;0;0] ...... and so on. Constraints: 1 <= w.length <= 104 1 <= w[i] <= 105 pickIndex will be called at most 104 times."
Microsoft,949,Largest Time for Given Digits,Med,"Math, Dynamic Programming, Graph, Topological Sort, Memoization, Game Theory",A game on an undirected graph is played by two players; Mouse and Cat; who alternate turns. The graph is given as follows: graph[a] is a list of all nodes b such that ab is an edge of the graph. The mouse starts at node 1 and goes first; the cat starts at node 2 and goes second; and there is a hole at node 0. During each player's turn; they must travel along one edge of the graph that meets where they are. For example; if the Mouse is at node 1; it must travel to any node in graph[1]. Additionally; it is not allowed for the Cat to travel to the Hole (node 0). Then; the game can end in three ways: If ever the Cat occupies the same node as the Mouse; the Cat wins. If ever the Mouse reaches the Hole; the Mouse wins. If ever a position is repeated (i.e.; the players are in the same position as a previous turn; and it is the same player's turn to move); the game is a draw. Given a graph; and assuming both players play optimally; return 1 if the mouse wins the game; 2 if the cat wins the game; or 0 if the game is a draw. Example 1: Input: graph = [[2;5];[3];[0;4;5];[1;4;5];[2;3];[0;2;3]] Output: 0 Example 2: Input: graph = [[1;3];[0];[3];[0;2]] Output: 1 Constraints: 3 <= graph.length <= 50 1 <= graph[i].length < graph.length 0 <= graph[i][j] < graph.length graph[i][j] != i graph[i] is unique. The mouse and the cat can always move.
Microsoft,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Microsoft,3139,Minimum Cost to Equalize Array,Hard,"Array, Dynamic Programming, Binary Indexed Tree, Segment Tree",You are given a 0-indexed integer array nums. The distinct count of a subarray of nums is defined as: Let nums[i..j] be a subarray of nums consisting of all the indices from i to j such that 0 <= i <= j < nums.length. Then the number of distinct values in nums[i..j] is called the distinct count of nums[i..j]. Return the sum of the squares of distinct counts of all subarrays of nums. Since the answer may be very large; return it modulo 109 + 7. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;2;1] Output: 15 Explanation: Six possible subarrays are: [1]: 1 distinct value [2]: 1 distinct value [1]: 1 distinct value [1;2]: 2 distinct values [2;1]: 2 distinct values [1;2;1]: 2 distinct values The sum of the squares of the distinct counts in all subarrays is equal to 12 + 12 + 12 + 22 + 22 + 22 = 15. Example 2: Input: nums = [2;2] Output: 3 Explanation: Three possible subarrays are: [2]: 1 distinct value [2]: 1 distinct value [2;2]: 1 distinct value The sum of the squares of the distinct counts in all subarrays is equal to 12 + 12 + 12 = 3. Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105
Microsoft,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Microsoft,27,Remove Element,Easy,"Array, Two Pointers",Given an integer array nums and an integer val; remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val. Consider the number of elements in nums which are not equal to val be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the elements which are not equal to val. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int val = ...; // Value to remove int[] expectedNums = [...]; // The expected answer with correct length. // It is sorted with no values equaling val. int k = removeElement(nums; val); // Calls your implementation assert k == expectedNums.length; sort(nums; 0; k); // Sort the first k elements of nums for (int i = 0; i < actualLength; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [3;2;2;3]; val = 3 Output: 2; nums = [2;2;_;_] Explanation: Your function should return k = 2; with the first two elements of nums being 2. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;1;2;2;3;0;4;2]; val = 2 Output: 5; nums = [0;1;4;0;3;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums containing 0; 0; 1; 3; and 4. Note that the five elements can be returned in any order. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 0 <= nums.length <= 100 0 <= nums[i] <= 50 0 <= val <= 100
Microsoft,28,Find the Index of the First Occurrence in a String,Easy,"Two Pointers, String, String Matching","Given two strings needle and haystack; return the index of the first occurrence of needle in haystack; or -1 if needle is not part of haystack. Example 1: Input: haystack = ""sadbutsad""; needle = ""sad"" Output: 0 Explanation: ""sad"" occurs at index 0 and 6. The first occurrence is at index 0; so we return 0. Example 2: Input: haystack = ""leetcode""; needle = ""leeto"" Output: -1 Explanation: ""leeto"" did not occur in ""leetcode""; so we return -1. Constraints: 1 <= haystack.length; needle.length <= 104 haystack and needle consist of only lowercase English characters."
Microsoft,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
Microsoft,71,Simplify Path,Med,"String, Stack","You are given an absolute path for a Unix-style file system; which always begins with a slash '/'. Your task is to transform this absolute path into its simplified canonical path. The rules of a Unix-style file system are as follows: A single period '.' represents the current directory. A double period '..' represents the previous/parent directory. Multiple consecutive slashes such as '//' and '///' are treated as a single slash '/'. Any sequence of periods that does not match the rules above should be treated as a valid directory or file name. For example; '...' and '....' are valid directory or file names. The simplified canonical path should follow these rules: The path must start with a single slash '/'. Directories within the path must be separated by exactly one slash '/'. The path must not end with a slash '/'; unless it is the root directory. The path must not have any single or double periods ('.' and '..') used to denote current or parent directories. Return the simplified canonical path. Example 1: Input: path = ""/home/"" Output: ""/home"" Explanation: The trailing slash should be removed. Example 2: Input: path = ""/home//foo/"" Output: ""/home/foo"" Explanation: Multiple consecutive slashes are replaced by a single one. Example 3: Input: path = ""/home/user/Documents/../Pictures"" Output: ""/home/user/Pictures"" Explanation: A double period "".."" refers to the directory up a level (the parent directory). Example 4: Input: path = ""/../"" Output: ""/"" Explanation: Going one level up from the root directory is not possible. Example 5: Input: path = ""/.../a/../b/c/../d/./"" Output: ""/.../b/d"" Explanation: ""..."" is a valid name for a directory in this problem. Constraints: 1 <= path.length <= 3000 path consists of English letters; digits; period '.'; slash '/' or '_'. path is a valid absolute Unix path."
Microsoft,85,Maximal Rectangle,Hard,"Array, Dynamic Programming, Stack, Matrix, Monotonic Stack","Given a rows x cols binary matrix filled with 0's and 1's; find the largest rectangle containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 6 Explanation: The maximal rectangle is shown in the above picture. Example 2: Input: matrix = [[""0""]] Output: 0 Example 3: Input: matrix = [[""1""]] Output: 1 Constraints: rows == matrix.length cols == matrix[i].length 1 <= row; cols <= 200 matrix[i][j] is '0' or '1'."
Microsoft,105,Construct Binary Tree from Preorder and Inorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree; construct and return the binary tree. Example 1: Input: preorder = [3;9;20;15;7]; inorder = [9;3;15;20;7] Output: [3;9;20;null;null;15;7] Example 2: Input: preorder = [-1]; inorder = [-1] Output: [-1] Constraints: 1 <= preorder.length <= 3000 inorder.length == preorder.length -3000 <= preorder[i]; inorder[i] <= 3000 preorder and inorder consist of unique values. Each value of inorder also appears in preorder. preorder is guaranteed to be the preorder traversal of the tree. inorder is guaranteed to be the inorder traversal of the tree.
Microsoft,114,Flatten Binary Tree to Linked List,Med,"Linked List, Stack, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; flatten the tree into a ""linked list"": The ""linked list"" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. The ""linked list"" should be in the same order as a pre-order traversal of the binary tree. Example 1: Input: root = [1;2;5;3;4;null;6] Output: [1;null;2;null;3;null;4;null;5;null;6] Example 2: Input: root = [] Output: [] Example 3: Input: root = [0] Output: [0] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100 Follow up: Can you flatten the tree in-place (with O(1) extra space)?"
Microsoft,116,Populating Next Right Pointers in Each Node,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given a perfect binary tree where all leaves are on the same level; and every parent has two children. The binary tree has the following definition: struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;6;7] Output: [1;#;2;3;#;4;5;6;7;#] Explanation: Given the above perfect binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 212 - 1]. -1000 <= Node.val <= 1000 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Microsoft,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Microsoft,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Microsoft,141,Linked List Cycle,Easy,"Hash Table, Linked List, Two Pointers",Given head; the head of a linked list; determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise; return false. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 1st node (0-indexed). Example 2: Input: head = [1;2]; pos = 0 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 0th node. Example 3: Input: head = [1]; pos = -1 Output: false Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Oracle,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Oracle,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
Oracle,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Oracle,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Oracle,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Oracle,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Oracle,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Oracle,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Oracle,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Oracle,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Oracle,1611,Minimum One Bit Operations to Make Integers Zero,Hard,"Array, Hash Table, String","Given an array of strings names of size n. You will create n folders in your file system such that; at the ith minute; you will create a folder with the name names[i]. Since two files cannot have the same name; if you enter a folder name that was previously used; the system will have a suffix addition to its name in the form of (k); where; k is the smallest positive integer such that the obtained name remains unique. Return an array of strings of length n where ans[i] is the actual name the system will assign to the ith folder when you create it. Example 1: Input: names = [""pes"";""fifa"";""gta"";""pes(2019)""] Output: [""pes"";""fifa"";""gta"";""pes(2019)""] Explanation: Let's see how the file system creates folder names: ""pes"" --> not assigned before; remains ""pes"" ""fifa"" --> not assigned before; remains ""fifa"" ""gta"" --> not assigned before; remains ""gta"" ""pes(2019)"" --> not assigned before; remains ""pes(2019)"" Example 2: Input: names = [""gta"";""gta(1)"";""gta"";""avalon""] Output: [""gta"";""gta(1)"";""gta(2)"";""avalon""] Explanation: Let's see how the file system creates folder names: ""gta"" --> not assigned before; remains ""gta"" ""gta(1)"" --> not assigned before; remains ""gta(1)"" ""gta"" --> the name is reserved; system adds (k); since ""gta(1)"" is also reserved; systems put k = 2. it becomes ""gta(2)"" ""avalon"" --> not assigned before; remains ""avalon"" Example 3: Input: names = [""onepiece"";""onepiece(1)"";""onepiece(2)"";""onepiece(3)"";""onepiece""] Output: [""onepiece"";""onepiece(1)"";""onepiece(2)"";""onepiece(3)"";""onepiece(4)""] Explanation: When the last folder is created; the smallest positive valid k is 4; and it becomes ""onepiece(4)"". Constraints: 1 <= names.length <= 5 * 104 1 <= names[i].length <= 20 names[i] consists of lowercase English letters; digits; and/or round brackets."
Oracle,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Oracle,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Oracle,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Oracle,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Oracle,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Oracle,316,Remove Duplicate Letters,Med,"String, Stack, Greedy, Monotonic Stack","Given a string s; remove duplicate letters so that every letter appears once and only once. You must make sure your result is the smallest in lexicographical order among all possible results. Example 1: Input: s = ""bcabc"" Output: ""abc"" Example 2: Input: s = ""cbacdcbc"" Output: ""acdb"" Constraints: 1 <= s.length <= 104 s consists of lowercase English letters. Note: This question is the same as 1081: https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/"
Oracle,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Oracle,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
Oracle,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Oracle,128,Longest Consecutive Sequence,Med,"Array, Hash Table, Union Find",Given an unsorted array of integers nums; return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time. Example 1: Input: nums = [100;4;200;1;3;2] Output: 4 Explanation: The longest consecutive elements sequence is [1; 2; 3; 4]. Therefore its length is 4. Example 2: Input: nums = [0;3;7;2;5;8;4;6;0;1] Output: 9 Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109
Oracle,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Oracle,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Oracle,1010,Pairs of Songs With Total Durations Divisible by 60,Med,"Hash Table, Math, Enumeration",Given three integers x; y; and bound; return a list of all the powerful integers that have a value less than or equal to bound. An integer is powerful if it can be represented as xi + yj for some integers i >= 0 and j >= 0. You may return the answer in any order. In your answer; each value should occur at most once. Example 1: Input: x = 2; y = 3; bound = 10 Output: [2;3;4;5;7;9;10] Explanation: 2 = 20 + 30 3 = 21 + 30 4 = 20 + 31 5 = 21 + 31 7 = 22 + 31 9 = 23 + 30 10 = 20 + 32 Example 2: Input: x = 3; y = 5; bound = 15 Output: [2;4;6;8;10;14] Constraints: 1 <= x; y <= 100 0 <= bound <= 106
Oracle,2192,All Ancestors of a Node in a Directed Acyclic Graph,Med,"Array, Greedy",There is an m x n grid; where (0; 0) is the top-left cell and (m - 1; n - 1) is the bottom-right cell. You are given an integer array startPos where startPos = [startrow; startcol] indicates that initially; a robot is at the cell (startrow; startcol). You are also given an integer array homePos where homePos = [homerow; homecol] indicates that its home is at the cell (homerow; homecol). The robot needs to go to its home. It can move one cell in four directions: left; right; up; or down; and it can not move outside the boundary. Every move incurs some cost. You are further given two 0-indexed integer arrays: rowCosts of length m and colCosts of length n. If the robot moves up or down into a cell whose row is r; then this move costs rowCosts[r]. If the robot moves left or right into a cell whose column is c; then this move costs colCosts[c]. Return the minimum total cost for this robot to return home. Example 1: Input: startPos = [1; 0]; homePos = [2; 3]; rowCosts = [5; 4; 3]; colCosts = [8; 2; 6; 7] Output: 18 Explanation: One optimal path is that: Starting from (1; 0) -> It goes down to (2; 0). This move costs rowCosts[2] = 3. -> It goes right to (2; 1). This move costs colCosts[1] = 2. -> It goes right to (2; 2). This move costs colCosts[2] = 6. -> It goes right to (2; 3). This move costs colCosts[3] = 7. The total cost is 3 + 2 + 6 + 7 = 18 Example 2: Input: startPos = [0; 0]; homePos = [0; 0]; rowCosts = [5]; colCosts = [26] Output: 0 Explanation: The robot is already at its home. Since no moves occur; the total cost is 0. Constraints: m == rowCosts.length n == colCosts.length 1 <= m; n <= 105 0 <= rowCosts[r]; colCosts[c] <= 104 startPos.length == 2 homePos.length == 2 0 <= startrow; homerow < m 0 <= startcol; homecol < n
Oracle,1380,Lucky Numbers in a Matrix,Easy,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",Given a 2D grid consists of 0s (land) and 1s (water). An island is a maximal 4-directionally connected group of 0s and a closed island is an island totally (all left; top; right; bottom) surrounded by 1s. Return the number of closed islands. Example 1: Input: grid = [[1;1;1;1;1;1;1;0];[1;0;0;0;0;1;1;0];[1;0;1;0;1;1;1;0];[1;0;0;0;0;1;0;1];[1;1;1;1;1;1;1;0]] Output: 2 Explanation: Islands in gray are closed because they are completely surrounded by water (group of 1s). Example 2: Input: grid = [[0;0;1;0;0];[0;1;0;1;0];[0;1;1;1;0]] Output: 1 Example 3: Input: grid = [[1;1;1;1;1;1;1]; [1;0;0;0;0;0;1]; [1;0;1;1;1;0;1]; [1;0;1;0;1;0;1]; [1;0;1;1;1;0;1]; [1;0;0;0;0;0;1]; [1;1;1;1;1;1;1]] Output: 2 Constraints: 1 <= grid.length; grid[0].length <= 100 0 <= grid[i][j] <=1
Oracle,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Oracle,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Oracle,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Oracle,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Oracle,199,Binary Tree Right Side View,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; imagine yourself standing on the right side of it; return the values of the nodes you can see ordered from top to bottom. Example 1: Input: root = [1;2;3;null;5;null;4] Output: [1;3;4] Example 2: Input: root = [1;null;3] Output: [1;3] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Oracle,1410,HTML Entity Parser,Med,Concurrency,
Oracle,2466,Count Ways To Build Good Strings,Med,"Array, Union Find, Prefix Sum, Ordered Set",You are given two 0-indexed integer arrays nums and removeQueries; both of length n. For the ith query; the element in nums at the index removeQueries[i] is removed; splitting nums into different segments. A segment is a contiguous sequence of positive integers in nums. A segment sum is the sum of every element in a segment. Return an integer array answer; of length n; where answer[i] is the maximum segment sum after applying the ith removal. Note: The same index will not be removed more than once. Example 1: Input: nums = [1;2;5;6;1]; removeQueries = [0;3;2;4;1] Output: [14;7;2;2;0] Explanation: Using 0 to indicate a removed element; the answer is as follows: Query 1: Remove the 0th element; nums becomes [0;2;5;6;1] and the maximum segment sum is 14 for segment [2;5;6;1]. Query 2: Remove the 3rd element; nums becomes [0;2;5;0;1] and the maximum segment sum is 7 for segment [2;5]. Query 3: Remove the 2nd element; nums becomes [0;2;0;0;1] and the maximum segment sum is 2 for segment [2]. Query 4: Remove the 4th element; nums becomes [0;2;0;0;0] and the maximum segment sum is 2 for segment [2]. Query 5: Remove the 1st element; nums becomes [0;0;0;0;0] and the maximum segment sum is 0; since there are no segments. Finally; we return [14;7;2;2;0]. Example 2: Input: nums = [3;2;11;1]; removeQueries = [3;2;1;0] Output: [16;5;3;0] Explanation: Using 0 to indicate a removed element; the answer is as follows: Query 1: Remove the 3rd element; nums becomes [3;2;11;0] and the maximum segment sum is 16 for segment [3;2;11]. Query 2: Remove the 2nd element; nums becomes [3;2;0;0] and the maximum segment sum is 5 for segment [3;2]. Query 3: Remove the 1st element; nums becomes [3;0;0;0] and the maximum segment sum is 3 for segment [3]. Query 4: Remove the 0th element; nums becomes [0;0;0;0] and the maximum segment sum is 0; since there are no segments. Finally; we return [16;5;3;0]. Constraints: n == nums.length == removeQueries.length 1 <= n <= 105 1 <= nums[i] <= 109 0 <= removeQueries[i] < n All the values of removeQueries are unique.
Oracle,2506,Count Pairs Of Similar Strings,Easy,"Array, Union Find, Graph, Topological Sort, Sorting, Matrix",
Oracle,2580,Count Ways to Group Overlapping Ranges,Med,String,"A sentence is a list of words that are separated by a single space with no leading or trailing spaces. For example; ""Hello World""; ""HELLO""; ""hello world hello world"" are all sentences. Words consist of only uppercase and lowercase English letters. Uppercase and lowercase English letters are considered different. A sentence is circular if: The last character of a word is equal to the first character of the next word. The last character of the last word is equal to the first character of the first word. For example; ""leetcode exercises sound delightful""; ""eetcode""; ""leetcode eats soul"" are all circular sentences. However; ""Leetcode is cool""; ""happy Leetcode""; ""Leetcode"" and ""I like Leetcode"" are not circular sentences. Given a string sentence; return true if it is circular. Otherwise; return false. Example 1: Input: sentence = ""leetcode exercises sound delightful"" Output: true Explanation: The words in sentence are [""leetcode""; ""exercises""; ""sound""; ""delightful""]. - leetcode's last character is equal to exercises's first character. - exercises's last character is equal to sound's first character. - sound's last character is equal to delightful's first character. - delightful's last character is equal to leetcode's first character. The sentence is circular. Example 2: Input: sentence = ""eetcode"" Output: true Explanation: The words in sentence are [""eetcode""]. - eetcode's last character is equal to eetcode's first character. The sentence is circular. Example 3: Input: sentence = ""Leetcode is cool"" Output: false Explanation: The words in sentence are [""Leetcode""; ""is""; ""cool""]. - Leetcode's last character is not equal to is's first character. The sentence is not circular. Constraints: 1 <= sentence.length <= 500 sentence consist of only lowercase and uppercase English letters and spaces. The words in sentence are separated by a single space. There are no leading or trailing spaces."
Oracle,2549,Count Distinct Numbers on Board,Easy,"Array, Binary Search, Stack, Sorting, Heap (Priority Queue), Monotonic Stack",You are given a 0-indexed array of non-negative integers nums. For each integer in nums; you must find its respective second greater integer. The second greater integer of nums[i] is nums[j] such that: j > i nums[j] > nums[i] There exists exactly one index k such that nums[k] > nums[i] and i < k < j. If there is no such nums[j]; the second greater integer is considered to be -1. For example; in the array [1; 2; 4; 3]; the second greater integer of 1 is 4; 2 is 3; and that of 3 and 4 is -1. Return an integer array answer; where answer[i] is the second greater integer of nums[i]. Example 1: Input: nums = [2;4;0;9;6] Output: [9;6;6;-1;-1] Explanation: 0th index: 4 is the first integer greater than 2; and 9 is the second integer greater than 2; to the right of 2. 1st index: 9 is the first; and 6 is the second integer greater than 4; to the right of 4. 2nd index: 9 is the first; and 6 is the second integer greater than 0; to the right of 0. 3rd index: There is no integer greater than 9 to its right; so the second greater integer is considered to be -1. 4th index: There is no integer greater than 6 to its right; so the second greater integer is considered to be -1. Thus; we return [9;6;6;-1;-1]. Example 2: Input: nums = [3;3] Output: [-1;-1] Explanation: We return [-1;-1] since neither integer has any integer greater than it. Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109
Oracle,2836,Maximize Value of Function in a Ball Passing Game,Hard,"Array, Sorting",Given an integer array nums containing distinct positive integers; find and return any number from the array that is neither the minimum nor the maximum value in the array; or -1 if there is no such number. Return the selected integer. Example 1: Input: nums = [3;2;1;4] Output: 2 Explanation: In this example; the minimum value is 1 and the maximum value is 4. Therefore; either 2 or 3 can be valid answers. Example 2: Input: nums = [1;2] Output: -1 Explanation: Since there is no number in nums that is neither the maximum nor the minimum; we cannot select a number that satisfies the given condition. Therefore; there is no answer. Example 3: Input: nums = [2;1;3] Output: 2 Explanation: Since 2 is neither the maximum nor the minimum value in nums; it is the only valid answer. Constraints: 1 <= nums.length <= 100 1 <= nums[i] <= 100 All values in nums are distinct
Oracle,3012,Minimize Length of Array Using Operations,Med,,
Oracle,3015,Count the Number of Houses at a Certain Distance I,Med,,
Oracle,3017,Count the Number of Houses at a Certain Distance II,Hard,"Math, Dynamic Programming",You are given positive integers low; high; and k. A number is beautiful if it meets both of the following conditions: The count of even digits in the number is equal to the count of odd digits. The number is divisible by k. Return the number of beautiful integers in the range [low; high]. Example 1: Input: low = 10; high = 20; k = 3 Output: 2 Explanation: There are 2 beautiful integers in the given range: [12;18]. - 12 is beautiful because it contains 1 odd digit and 1 even digit; and is divisible by k = 3. - 18 is beautiful because it contains 1 odd digit and 1 even digit; and is divisible by k = 3. Additionally we can see that: - 16 is not beautiful because it is not divisible by k = 3. - 15 is not beautiful because it does not contain equal counts even and odd digits. It can be shown that there are only 2 beautiful integers in the given range. Example 2: Input: low = 1; high = 10; k = 1 Output: 1 Explanation: There is 1 beautiful integer in the given range: [10]. - 10 is beautiful because it contains 1 odd digit and 1 even digit; and is divisible by k = 1. It can be shown that there is only 1 beautiful integer in the given range. Example 3: Input: low = 5; high = 5; k = 2 Output: 0 Explanation: There are 0 beautiful integers in the given range. - 5 is not beautiful because it is not divisible by k = 2 and it does not contain equal even and odd digits. Constraints: 0 < low <= high <= 109 0 < k <= 20
Oracle,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Oracle,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
Oracle,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Oracle,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Oracle,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Oracle,240,Search a 2D Matrix II,Med,"Array, Binary Search, Divide and Conquer, Matrix",Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. Example 1: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 5 Output: true Example 2: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 20 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= n; m <= 300 -109 <= matrix[i][j] <= 109 All the integers in each row are sorted in ascending order. All the integers in each column are sorted in ascending order. -109 <= target <= 109
Oracle,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Oracle,359,Logger Rate Limiter,Easy,"Hash Table, Design, Data Stream",
Oracle,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
Oracle,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Oracle,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Oracle,96,Unique Binary Search Trees,Med,"Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree",Given an integer n; return the number of structurally unique BST's (binary search trees) which has exactly n nodes of unique values from 1 to n. Example 1: Input: n = 3 Output: 5 Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 19
Oracle,134,Gas Station,Med,"Array, Greedy",There are n gas stations along a circular route; where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations. Given two integer arrays gas and cost; return the starting gas station's index if you can travel around the circuit once in the clockwise direction; otherwise return -1. If there exists a solution; it is guaranteed to be unique. Example 1: Input: gas = [1;2;3;4;5]; cost = [3;4;5;1;2] Output: 3 Explanation: Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 4. Your tank = 4 - 1 + 5 = 8 Travel to station 0. Your tank = 8 - 2 + 1 = 7 Travel to station 1. Your tank = 7 - 3 + 2 = 6 Travel to station 2. Your tank = 6 - 4 + 3 = 5 Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. Therefore; return 3 as the starting index. Example 2: Input: gas = [2;3;4]; cost = [3;4;3] Output: -1 Explanation: You can't start at station 0 or 1; as there is not enough gas to travel to the next station. Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 0. Your tank = 4 - 3 + 2 = 3 Travel to station 1. Your tank = 3 - 3 + 3 = 3 You cannot travel back to station 2; as it requires 4 unit of gas but you only have 3. Therefore; you can't travel around the circuit once no matter where you start. Constraints: n == gas.length == cost.length 1 <= n <= 105 0 <= gas[i]; cost[i] <= 104
Oracle,141,Linked List Cycle,Easy,"Hash Table, Linked List, Two Pointers",Given head; the head of a linked list; determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise; return false. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 1st node (0-indexed). Example 2: Input: head = [1;2]; pos = 0 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 0th node. Example 3: Input: head = [1]; pos = -1 Output: false Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Oracle,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Oracle,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Oracle,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Oracle,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
Oracle,450,Delete Node in a BST,Med,"Tree, Binary Search Tree, Binary Tree",Given a root node reference of a BST and a key; delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST. Basically; the deletion can be divided into two stages: Search for a node to remove. If the node is found; delete the node. Example 1: Input: root = [5;3;6;2;4;null;7]; key = 3 Output: [5;4;6;2;null;null;7] Explanation: Given key to delete is 3. So we find the node with value 3 and delete it. One valid answer is [5;4;6;2;null;null;7]; shown in the above BST. Please notice that another valid answer is [5;2;6;null;4;null;7] and it's also accepted. Example 2: Input: root = [5;3;6;2;4;null;7]; key = 0 Output: [5;3;6;2;4;null;7] Explanation: The tree does not contain a node with value = 0. Example 3: Input: root = []; key = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -105 <= Node.val <= 105 Each node has a unique value. root is a valid binary search tree. -105 <= key <= 105 Follow up: Could you solve it with time complexity O(height of tree)?
Oracle,525,Contiguous Array,Med,"Array, Hash Table, Prefix Sum",Given a binary array nums; return the maximum length of a contiguous subarray with an equal number of 0 and 1. Example 1: Input: nums = [0;1] Output: 2 Explanation: [0; 1] is the longest contiguous subarray with an equal number of 0 and 1. Example 2: Input: nums = [0;1;0] Output: 2 Explanation: [0; 1] (or [1; 0]) is a longest contiguous subarray with equal number of 0 and 1. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Oracle,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Oracle,692,Top K Frequent Words,Med,"Hash Table, String, Trie, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given an array of strings words and an integer k; return the k most frequent strings. Return the answer sorted by the frequency from highest to lowest. Sort the words with the same frequency by their lexicographical order. Example 1: Input: words = [""i"";""love"";""leetcode"";""i"";""love"";""coding""]; k = 2 Output: [""i"";""love""] Explanation: ""i"" and ""love"" are the two most frequent words. Note that ""i"" comes before ""love"" due to a lower alphabetical order. Example 2: Input: words = [""the"";""day"";""is"";""sunny"";""the"";""the"";""the"";""sunny"";""is"";""is""]; k = 4 Output: [""the"";""is"";""sunny"";""day""] Explanation: ""the""; ""is""; ""sunny"" and ""day"" are the four most frequent words; with the number of occurrence being 4; 3; 2 and 1 respectively. Constraints: 1 <= words.length <= 500 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. k is in the range [1; The number of unique words[i]] Follow-up: Could you solve it in O(n log(k)) time and O(n) extra space?"
Oracle,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
Oracle,13,Roman to Integer,Easy,"Hash Table, Math, String","Roman numerals are represented by seven different symbols: I; V; X; L; C; D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example; 2 is written as II in Roman numeral; just two ones added together. 12 is written as XII; which is simply X + II. The number 27 is written as XXVII; which is XX + V + II. Roman numerals are usually written largest to smallest from left to right. However; the numeral for four is not IIII. Instead; the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine; which is written as IX. There are six instances where subtraction is used: I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral; convert it to an integer. Example 1: Input: s = ""III"" Output: 3 Explanation: III = 3. Example 2: Input: s = ""LVIII"" Output: 58 Explanation: L = 50; V= 5; III = 3. Example 3: Input: s = ""MCMXCIV"" Output: 1994 Explanation: M = 1000; CM = 900; XC = 90 and IV = 4. Constraints: 1 <= s.length <= 15 s contains only the characters ('I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M'). It is guaranteed that s is a valid roman numeral in the range [1; 3999]."
Oracle,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Oracle,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Oracle,73,Set Matrix Zeroes,Med,"Array, Hash Table, Matrix",Given an m x n integer matrix matrix; if an element is 0; set its entire row and column to 0's. You must do it in place. Example 1: Input: matrix = [[1;1;1];[1;0;1];[1;1;1]] Output: [[1;0;1];[0;0;0];[1;0;1]] Example 2: Input: matrix = [[0;1;2;0];[3;4;5;2];[1;3;1;5]] Output: [[0;0;0;0];[0;4;5;0];[0;3;1;0]] Constraints: m == matrix.length n == matrix[0].length 1 <= m; n <= 200 -231 <= matrix[i][j] <= 231 - 1 Follow up: A straightforward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space; but still not the best solution. Could you devise a constant space solution?
Oracle,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Oracle,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Oracle,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Oracle,103,Binary Tree Zigzag Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the zigzag level order traversal of its nodes' values. (i.e.; from left to right; then right to left for the next level and alternate between). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[20;9];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100
Oracle,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Oracle,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Oracle,236,Lowest Common Ancestor of a Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",Given a binary tree; find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3. Example 2: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [1;2]; p = 1; q = 2 Output: 1 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the tree.
Oracle,273,Integer to English Words,Hard,"Math, String, Recursion","Convert a non-negative integer num to its English words representation. Example 1: Input: num = 123 Output: ""One Hundred Twenty Three"" Example 2: Input: num = 12345 Output: ""Twelve Thousand Three Hundred Forty Five"" Example 3: Input: num = 1234567 Output: ""One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"" Constraints: 0 <= num <= 231 - 1"
Oracle,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Oracle,697,Degree of an Array,Easy,"Array, Hash Table",Given a non-empty array of non-negative integers nums; the degree of this array is defined as the maximum frequency of any one of its elements. Your task is to find the smallest possible length of a (contiguous) subarray of nums; that has the same degree as nums. Example 1: Input: nums = [1;2;2;3;1] Output: 2 Explanation: The input array has a degree of 2 because both elements 1 and 2 appear twice. Of the subarrays that have the same degree: [1; 2; 2; 3; 1]; [1; 2; 2; 3]; [2; 2; 3; 1]; [1; 2; 2]; [2; 2; 3]; [2; 2] The shortest length is 2. So return 2. Example 2: Input: nums = [1;2;2;3;1;4;2] Output: 6 Explanation: The degree is 3 because the element 2 is repeated 3 times. So [2;2;3;1;4;2] is the shortest subarray; therefore returning 6. Constraints: nums.length will be between 1 and 50;000. nums[i] will be an integer between 0 and 49;999.
Oracle,2439,Minimize Maximum of Array,Med,"Depth-First Search, Graph, Topological Sort",You are given a directed graph of n nodes numbered from 0 to n - 1; where each node has at most one outgoing edge. The graph is represented with a given 0-indexed array edges of size n; indicating that there is a directed edge from node i to node edges[i]. If there is no outgoing edge from node i; then edges[i] == -1. Return the length of the longest cycle in the graph. If no cycle exists; return -1. A cycle is a path that starts and ends at the same node. Example 1: Input: edges = [3;3;4;2;3] Output: 3 Explanation: The longest cycle in the graph is the cycle: 2 -> 4 -> 3 -> 2. The length of this cycle is 3; so 3 is returned. Example 2: Input: edges = [2;-1;3;1] Output: -1 Explanation: There are no cycles in this graph. Constraints: n == edges.length 2 <= n <= 105 -1 <= edges[i] < n edges[i] != i
Oracle,6,Zigzag Conversion,Med,String,"The string ""PAYPALISHIRING"" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: ""PAHNAPLSIIGYIR"" Write the code that will take a string and make this conversion given a number of rows: string convert(string s; int numRows); Example 1: Input: s = ""PAYPALISHIRING""; numRows = 3 Output: ""PAHNAPLSIIGYIR"" Example 2: Input: s = ""PAYPALISHIRING""; numRows = 4 Output: ""PINALSIGYAHRPI"" Explanation: P I N A L S I G Y A H R P I Example 3: Input: s = ""A""; numRows = 1 Output: ""A"" Constraints: 1 <= s.length <= 1000 s consists of English letters (lower-case and upper-case); ';' and '.'. 1 <= numRows <= 1000"
Oracle,12,Integer to Roman,Med,"Hash Table, Math, String","Seven different symbols represent Roman numerals with the following values: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules: If the value does not start with 4 or 9; select the symbol of the maximal value that can be subtracted from the input; append that symbol to the result; subtract its value; and convert the remainder to a Roman numeral. If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol; for example; 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV); 9 (IX); 40 (XL); 90 (XC); 400 (CD) and 900 (CM). Only powers of 10 (I; X; C; M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V); 50 (L); or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form. Given an integer; convert it to a Roman numeral. Example 1: Input: num = 3749 Output: ""MMMDCCXLIX"" Explanation: 3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M) 700 = DCC as 500 (D) + 100 (C) + 100 (C) 40 = XL as 10 (X) less of 50 (L) 9 = IX as 1 (I) less of 10 (X) Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places Example 2: Input: num = 58 Output: ""LVIII"" Explanation: 50 = L 8 = VIII Example 3: Input: num = 1994 Output: ""MCMXCIV"" Explanation: 1000 = M 900 = CM 90 = XC 4 = IV Constraints: 1 <= num <= 3999"
Oracle,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Oracle,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Oracle,102,Binary Tree Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the level order traversal of its nodes' values. (i.e.; from left to right; level by level). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[9;20];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -1000 <= Node.val <= 1000
Oracle,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Oracle,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Oracle,412,Fizz Buzz,Easy,"Math, String, Simulation","Given an integer n; return a string array answer (1-indexed) where: answer[i] == ""FizzBuzz"" if i is divisible by 3 and 5. answer[i] == ""Fizz"" if i is divisible by 3. answer[i] == ""Buzz"" if i is divisible by 5. answer[i] == i (as a string) if none of the above conditions are true. Example 1: Input: n = 3 Output: [""1"";""2"";""Fizz""] Example 2: Input: n = 5 Output: [""1"";""2"";""Fizz"";""4"";""Buzz""] Example 3: Input: n = 15 Output: [""1"";""2"";""Fizz"";""4"";""Buzz"";""Fizz"";""7"";""8"";""Fizz"";""Buzz"";""11"";""Fizz"";""13"";""14"";""FizzBuzz""] Constraints: 1 <= n <= 104"
Oracle,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Oracle,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
Oracle,1200,Minimum Absolute Difference,Easy,Array,
Oracle,1797,Design Authentication Manager,Med,String,"You own a Goal Parser that can interpret a string command. The command consists of an alphabet of ""G""; ""()"" and/or ""(al)"" in some order. The Goal Parser will interpret ""G"" as the string ""G""; ""()"" as the string ""o""; and ""(al)"" as the string ""al"". The interpreted strings are then concatenated in the original order. Given the string command; return the Goal Parser's interpretation of command. Example 1: Input: command = ""G()(al)"" Output: ""Goal"" Explanation: The Goal Parser interprets the command as follows: G -> G () -> o (al) -> al The final concatenated result is ""Goal"". Example 2: Input: command = ""G()()()()(al)"" Output: ""Gooooal"" Example 3: Input: command = ""(al)G(al)()()G"" Output: ""alGalooG"" Constraints: 1 <= command.length <= 100 command consists of ""G""; ""()""; and/or ""(al)"" in some order."
Oracle,2561,Rearranging Fruits,Hard,"Array, Hash Table, Two Pointers, Sorting",You are given a 0-indexed integer array nums of even length. As long as nums is not empty; you must repetitively: Find the minimum number in nums and remove it. Find the maximum number in nums and remove it. Calculate the average of the two removed numbers. The average of two numbers a and b is (a + b) / 2. For example; the average of 2 and 3 is (2 + 3) / 2 = 2.5. Return the number of distinct averages calculated using the above process. Note that when there is a tie for a minimum or maximum number; any can be removed. Example 1: Input: nums = [4;1;4;0;3;5] Output: 2 Explanation: 1. Remove 0 and 5; and the average is (0 + 5) / 2 = 2.5. Now; nums = [4;1;4;3]. 2. Remove 1 and 4. The average is (1 + 4) / 2 = 2.5; and nums = [4;3]. 3. Remove 3 and 4; and the average is (3 + 4) / 2 = 3.5. Since there are 2 distinct numbers among 2.5; 2.5; and 3.5; we return 2. Example 2: Input: nums = [1;100] Output: 1 Explanation: There is only one average to be calculated after removing 1 and 100; so we return 1. Constraints: 2 <= nums.length <= 100 nums.length is even. 0 <= nums[i] <= 100
Oracle,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Oracle,32,Longest Valid Parentheses,Hard,"String, Dynamic Programming, Stack","Given a string containing just the characters '(' and ')'; return the length of the longest valid (well-formed) parentheses substring. Example 1: Input: s = ""(()"" Output: 2 Explanation: The longest valid parentheses substring is ""()"". Example 2: Input: s = "")()())"" Output: 4 Explanation: The longest valid parentheses substring is ""()()"". Example 3: Input: s = """" Output: 0 Constraints: 0 <= s.length <= 3 * 104 s[i] is '('; or ')'."
Oracle,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
Oracle,93,Restore IP Addresses,Med,"String, Backtracking","A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. For example; ""0.1.2.201"" and ""192.168.1.1"" are valid IP addresses; but ""0.011.255.245""; ""192.168.1.312"" and ""192.168@1.1"" are invalid IP addresses. Given a string s containing only digits; return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order. Example 1: Input: s = ""25525511135"" Output: [""255.255.11.135"";""255.255.111.35""] Example 2: Input: s = ""0000"" Output: [""0.0.0.0""] Example 3: Input: s = ""101023"" Output: [""1.0.10.23"";""1.0.102.3"";""10.1.0.23"";""10.10.2.3"";""101.0.2.3""] Constraints: 1 <= s.length <= 20 s consists of digits only."
Oracle,116,Populating Next Right Pointers in Each Node,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given a perfect binary tree where all leaves are on the same level; and every parent has two children. The binary tree has the following definition: struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;6;7] Output: [1;#;2;3;#;4;5;6;7;#] Explanation: Given the above perfect binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 212 - 1]. -1000 <= Node.val <= 1000 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Oracle,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Oracle,205,Isomorphic Strings,Easy,"Hash Table, String","Given two strings s and t; determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character; but a character may map to itself. Example 1: Input: s = ""egg""; t = ""add"" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = ""foo""; t = ""bar"" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = ""paper""; t = ""title"" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character."
Oracle,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Oracle,237,Delete Node in a Linked List,Med,Linked List,There is a singly-linked list head and we want to delete a node node in it. You are given the node to be deleted node. You will not be given access to the first node of head. All the values of the linked list are unique; and it is guaranteed that the given node node is not the last node in the linked list. Delete the given node. Note that by deleting the node; we do not mean removing it from memory. We mean: The value of the given node should not exist in the linked list. The number of nodes in the linked list should decrease by one. All the values before node should be in the same order. All the values after node should be in the same order. Custom testing: For the input; you should provide the entire linked list head and the node to be given node. node should not be the last node of the list and should be an actual node in the list. We will build the linked list and pass the node to your function. The output will be the entire list after calling your function. Example 1: Input: head = [4;5;1;9]; node = 5 Output: [4;1;9] Explanation: You are given the second node with value 5; the linked list should become 4 -> 1 -> 9 after calling your function. Example 2: Input: head = [4;5;1;9]; node = 1 Output: [4;5;9] Explanation: You are given the third node with value 1; the linked list should become 4 -> 5 -> 9 after calling your function. Constraints: The number of the nodes in the given list is in the range [2; 1000]. -1000 <= Node.val <= 1000 The value of each node in the list is unique. The node to be deleted is in the list and is not a tail node.
Oracle,252,Meeting Rooms,Easy,"Array, Sorting",
Oracle,463,Island Perimeter,Easy,"Array, Depth-First Search, Breadth-First Search, Matrix","You are given row x col grid representing a map where grid[i][j] = 1 represents land and grid[i][j] = 0 represents water. Grid cells are connected horizontally/vertically (not diagonally). The grid is completely surrounded by water; and there is exactly one island (i.e.; one or more connected land cells). The island doesn't have ""lakes""; meaning the water inside isn't connected to the water around the island. One cell is a square with side length 1. The grid is rectangular; width and height don't exceed 100. Determine the perimeter of the island. Example 1: Input: grid = [[0;1;0;0];[1;1;1;0];[0;1;0;0];[1;1;0;0]] Output: 16 Explanation: The perimeter is the 16 yellow stripes in the image above. Example 2: Input: grid = [[1]] Output: 4 Example 3: Input: grid = [[1;0]] Output: 4 Constraints: row == grid.length col == grid[i].length 1 <= row; col <= 100 grid[i][j] is 0 or 1. There is exactly one island in grid."
Oracle,844,Backspace String Compare,Easy,,
Oracle,992,Subarrays with K Different Integers,Hard,"Array, String, Greedy","You are given an array of n strings strs; all of the same length. We may choose any deletion indices; and we delete all the characters in those indices for each string. For example; if we have strs = [""abcdef"";""uvwxyz""] and deletion indices {0; 2; 3}; then the final array after deletions is [""bef""; ""vyz""]. Suppose we chose a set of deletion indices answer such that after deletions; the final array has its elements in lexicographic order (i.e.; strs[0] <= strs[1] <= strs[2] <= ... <= strs[n - 1]). Return the minimum possible value of answer.length. Example 1: Input: strs = [""ca"";""bb"";""ac""] Output: 1 Explanation: After deleting the first column; strs = [""a""; ""b""; ""c""]. Now strs is in lexicographic order (ie. strs[0] <= strs[1] <= strs[2]). We require at least 1 deletion since initially strs was not in lexicographic order; so the answer is 1. Example 2: Input: strs = [""xc"";""yb"";""za""] Output: 0 Explanation: strs is already in lexicographic order; so we do not need to delete anything. Note that the rows of strs are not necessarily in lexicographic order: i.e.; it is NOT necessarily true that (strs[0][0] <= strs[0][1] <= ...) Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: We have to delete every column. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Oracle,1143,Longest Common Subsequence,Med,"Array, Hash Table, Binary Search, Matrix, Counting",
Oracle,1751,Maximum Number of Events That Can Be Attended II,Hard,"Array, String","A newly designed keypad was tested; where a tester pressed a sequence of n keys; one at a time. You are given a string keysPressed of length n; where keysPressed[i] was the ith key pressed in the testing sequence; and a sorted list releaseTimes; where releaseTimes[i] was the time the ith key was released. Both arrays are 0-indexed. The 0th key was pressed at the time 0; and every subsequent key was pressed at the exact time the previous key was released. The tester wants to know the key of the keypress that had the longest duration. The ith keypress had a duration of releaseTimes[i] - releaseTimes[i - 1]; and the 0th keypress had a duration of releaseTimes[0]. Note that the same key could have been pressed multiple times during the test; and these multiple presses of the same key may not have had the same duration. Return the key of the keypress that had the longest duration. If there are multiple such keypresses; return the lexicographically largest key of the keypresses. Example 1: Input: releaseTimes = [9;29;49;50]; keysPressed = ""cbcd"" Output: ""c"" Explanation: The keypresses were as follows: Keypress for 'c' had a duration of 9 (pressed at time 0 and released at time 9). Keypress for 'b' had a duration of 29 - 9 = 20 (pressed at time 9 right after the release of the previous character and released at time 29). Keypress for 'c' had a duration of 49 - 29 = 20 (pressed at time 29 right after the release of the previous character and released at time 49). Keypress for 'd' had a duration of 50 - 49 = 1 (pressed at time 49 right after the release of the previous character and released at time 50). The longest of these was the keypress for 'b' and the second keypress for 'c'; both with duration 20. 'c' is lexicographically larger than 'b'; so the answer is 'c'. Example 2: Input: releaseTimes = [12;23;36;46;62]; keysPressed = ""spuda"" Output: ""a"" Explanation: The keypresses were as follows: Keypress for 's' had a duration of 12. Keypress for 'p' had a duration of 23 - 12 = 11. Keypress for 'u' had a duration of 36 - 23 = 13. Keypress for 'd' had a duration of 46 - 36 = 10. Keypress for 'a' had a duration of 62 - 46 = 16. The longest of these was the keypress for 'a' with duration 16. Constraints: releaseTimes.length == n keysPressed.length == n 2 <= n <= 1000 1 <= releaseTimes[i] <= 109 releaseTimes[i] < releaseTimes[i+1] keysPressed contains only lowercase English letters."
Oracle,2472,Maximum Number of Non-overlapping Palindrome Substrings,Hard,"Array, Graph, Topological Sort, Matrix",You are given a positive integer k. You are also given: a 2D integer array rowConditions of size n where rowConditions[i] = [abovei; belowi]; and a 2D integer array colConditions of size m where colConditions[i] = [lefti; righti]. The two arrays contain integers from 1 to k. You have to build a k x k matrix that contains each of the numbers from 1 to k exactly once. The remaining cells should have the value 0. The matrix should also satisfy the following conditions: The number abovei should appear in a row that is strictly above the row at which the number belowi appears for all i from 0 to n - 1. The number lefti should appear in a column that is strictly left of the column at which the number righti appears for all i from 0 to m - 1. Return any matrix that satisfies the conditions. If no answer exists; return an empty matrix. Example 1: Input: k = 3; rowConditions = [[1;2];[3;2]]; colConditions = [[2;1];[3;2]] Output: [[3;0;0];[0;0;1];[0;2;0]] Explanation: The diagram above shows a valid example of a matrix that satisfies all the conditions. The row conditions are the following: - Number 1 is in row 1; and number 2 is in row 2; so 1 is above 2 in the matrix. - Number 3 is in row 0; and number 2 is in row 2; so 3 is above 2 in the matrix. The column conditions are the following: - Number 2 is in column 1; and number 1 is in column 2; so 2 is left of 1 in the matrix. - Number 3 is in column 0; and number 2 is in column 1; so 3 is left of 2 in the matrix. Note that there may be multiple correct answers. Example 2: Input: k = 3; rowConditions = [[1;2];[2;3];[3;1];[2;3]]; colConditions = [[2;1]] Output: [] Explanation: From the first two conditions; 3 has to be below 1 but the third conditions needs 3 to be above 1 to be satisfied. No matrix can satisfy all the conditions; so we return the empty matrix. Constraints: 2 <= k <= 400 1 <= rowConditions.length; colConditions.length <= 104 rowConditions[i].length == colConditions[i].length == 2 1 <= abovei; belowi; lefti; righti <= k abovei != belowi lefti != righti
Oracle,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Oracle,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Oracle,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Oracle,62,Unique Paths,Med,"Math, Dynamic Programming, Combinatorics",There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n; return the number of possible unique paths that the robot can take to reach the bottom-right corner. The test cases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: m = 3; n = 7 Output: 28 Example 2: Input: m = 3; n = 2 Output: 3 Explanation: From the top-left corner; there are a total of 3 ways to reach the bottom-right corner: 1. Right -> Down -> Down 2. Down -> Down -> Right 3. Down -> Right -> Down Constraints: 1 <= m; n <= 100
Oracle,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Oracle,149,Max Points on a Line,Hard,"Array, Hash Table, Math, Geometry",Given an array of points where points[i] = [xi; yi] represents a point on the X-Y plane; return the maximum number of points that lie on the same straight line. Example 1: Input: points = [[1;1];[2;2];[3;3]] Output: 3 Example 2: Input: points = [[1;1];[3;2];[5;3];[4;1];[2;3];[1;4]] Output: 4 Constraints: 1 <= points.length <= 300 points[i].length == 2 -104 <= xi; yi <= 104 All the points are unique.
Oracle,168,Excel Sheet Column Title,Easy,"Math, String","Given an integer columnNumber; return its corresponding column title as it appears in an Excel sheet. For example: A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ... Example 1: Input: columnNumber = 1 Output: ""A"" Example 2: Input: columnNumber = 28 Output: ""AB"" Example 3: Input: columnNumber = 701 Output: ""ZY"" Constraints: 1 <= columnNumber <= 231 - 1"
Oracle,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Oracle,189,Rotate Array,Med,"Array, Math, Two Pointers",Given an integer array nums; rotate the array to the right by k steps; where k is non-negative. Example 1: Input: nums = [1;2;3;4;5;6;7]; k = 3 Output: [5;6;7;1;2;3;4] Explanation: rotate 1 steps to the right: [7;1;2;3;4;5;6] rotate 2 steps to the right: [6;7;1;2;3;4;5] rotate 3 steps to the right: [5;6;7;1;2;3;4] Example 2: Input: nums = [-1;-100;3;99]; k = 2 Output: [3;99;-1;-100] Explanation: rotate 1 steps to the right: [99;-1;-100;3] rotate 2 steps to the right: [3;99;-1;-100] Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 0 <= k <= 105 Follow up: Try to come up with as many solutions as you can. There are at least three different ways to solve this problem. Could you do it in-place with O(1) extra space?
Oracle,209,Minimum Size Subarray Sum,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of positive integers nums and a positive integer target; return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray; return 0 instead. Example 1: Input: target = 7; nums = [2;3;1;2;4;3] Output: 2 Explanation: The subarray [4;3] has the minimal length under the problem constraint. Example 2: Input: target = 4; nums = [1;4;4] Output: 1 Example 3: Input: target = 11; nums = [1;1;1;1;1;1;1;1] Output: 0 Constraints: 1 <= target <= 109 1 <= nums.length <= 105 1 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution of which the time complexity is O(n log(n)).
Oracle,230,Kth Smallest Element in a BST,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary search tree; and an integer k; return the kth smallest value (1-indexed) of all the values of the nodes in the tree. Example 1: Input: root = [3;1;4;null;2]; k = 1 Output: 1 Example 2: Input: root = [5;3;6;2;4;null;null;1]; k = 3 Output: 3 Constraints: The number of nodes in the tree is n. 1 <= k <= n <= 104 0 <= Node.val <= 104 Follow up: If the BST is modified often (i.e.; we can do insert and delete operations) and you need to find the kth smallest frequently; how would you optimize?
Oracle,242,Valid Anagram,Easy,"Hash Table, String, Sorting","Given two strings s and t; return true if t is an anagram of s; and false otherwise. Example 1: Input: s = ""anagram""; t = ""nagaram"" Output: true Example 2: Input: s = ""rat""; t = ""car"" Output: false Constraints: 1 <= s.length; t.length <= 5 * 104 s and t consist of lowercase English letters. Follow up: What if the inputs contain Unicode characters? How would you adapt your solution to such a case?"
Oracle,270,Closest Binary Search Tree Value,Easy,"Binary Search, Tree, Depth-First Search, Binary Search Tree, Binary Tree",
Oracle,287,Find the Duplicate Number,Med,"Array, Two Pointers, Binary Search, Bit Manipulation",Given an array of integers nums containing n + 1 integers where each integer is in the range [1; n] inclusive. There is only one repeated number in nums; return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Example 1: Input: nums = [1;3;4;2;2] Output: 2 Example 2: Input: nums = [3;1;3;4;2] Output: 3 Example 3: Input: nums = [3;3;3;3;3] Output: 3 Constraints: 1 <= n <= 105 nums.length == n + 1 1 <= nums[i] <= n All the integers in nums appear only once except for precisely one integer which appears two or more times. Follow up: How can we prove that at least one duplicate number must exist in nums? Can you solve the problem in linear runtime complexity?
Oracle,378,Kth Smallest Element in a Sorted Matrix,Med,"Array, Binary Search, Sorting, Heap (Priority Queue), Matrix",Given an n x n matrix where each of the rows and columns is sorted in ascending order; return the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order; not the kth distinct element. You must find a solution with a memory complexity better than O(n2). Example 1: Input: matrix = [[1;5;9];[10;11;13];[12;13;15]]; k = 8 Output: 13 Explanation: The elements in the matrix are [1;5;9;10;11;12;13;13;15]; and the 8th smallest number is 13 Example 2: Input: matrix = [[-5]]; k = 1 Output: -5 Constraints: n == matrix.length == matrix[i].length 1 <= n <= 300 -109 <= matrix[i][j] <= 109 All the rows and columns of matrix are guaranteed to be sorted in non-decreasing order. 1 <= k <= n2 Follow up: Could you solve the problem with a constant memory (i.e.; O(1) memory complexity)? Could you solve the problem in O(n) time complexity? The solution may be too advanced for an interview but you may find reading this paper fun.
Oracle,468,Validate IP Address,Med,String,"Given a string queryIP; return ""IPv4"" if IP is a valid IPv4 address; ""IPv6"" if IP is a valid IPv6 address or ""Neither"" if IP is not a correct IP of any type. A valid IPv4 address is an IP in the form ""x1.x2.x3.x4"" where 0 <= xi <= 255 and xi cannot contain leading zeros. For example; ""192.168.1.1"" and ""192.168.1.0"" are valid IPv4 addresses while ""192.168.01.1""; ""192.168.1.00""; and ""192.168@1.1"" are invalid IPv4 addresses. A valid IPv6 address is an IP in the form ""x1:x2:x3:x4:x5:x6:x7:x8"" where: 1 <= xi.length <= 4 xi is a hexadecimal string which may contain digits; lowercase English letter ('a' to 'f') and upper-case English letters ('A' to 'F'). Leading zeros are allowed in xi. For example; ""2001:0db8:85a3:0000:0000:8a2e:0370:7334"" and ""2001:db8:85a3:0:0:8A2E:0370:7334"" are valid IPv6 addresses; while ""2001:0db8:85a3::8A2E:037j:7334"" and ""02001:0db8:85a3:0000:0000:8a2e:0370:7334"" are invalid IPv6 addresses. Example 1: Input: queryIP = ""172.16.254.1"" Output: ""IPv4"" Explanation: This is a valid IPv4 address; return ""IPv4"". Example 2: Input: queryIP = ""2001:0db8:85a3:0:0:8A2E:0370:7334"" Output: ""IPv6"" Explanation: This is a valid IPv6 address; return ""IPv6"". Example 3: Input: queryIP = ""256.256.256.256"" Output: ""Neither"" Explanation: This is neither a IPv4 address nor a IPv6 address. Constraints: queryIP consists only of English letters; digits and the characters '.' and ':'."
Oracle,540,Single Element in a Sorted Array,Med,"Array, Binary Search",You are given a sorted array consisting of only integers where every element appears exactly twice; except for one element which appears exactly once. Return the single element that appears only once. Your solution must run in O(log n) time and O(1) space. Example 1: Input: nums = [1;1;2;3;3;4;4;8;8] Output: 2 Example 2: Input: nums = [3;3;7;7;10;11;11] Output: 10 Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 105
Oracle,582,Kill Process,Med,"Array, Hash Table, Tree, Depth-First Search, Breadth-First Search",
Oracle,588,Design In-Memory File System,Hard,"Hash Table, String, Design, Trie, Sorting",
Oracle,696,Count Binary Substrings,Easy,"Two Pointers, String","Given a binary string s; return the number of non-empty substrings that have the same number of 0's and 1's; and all the 0's and all the 1's in these substrings are grouped consecutively. Substrings that occur multiple times are counted the number of times they occur. Example 1: Input: s = ""00110011"" Output: 6 Explanation: There are 6 substrings that have equal number of consecutive 1's and 0's: ""0011""; ""01""; ""1100""; ""10""; ""0011""; and ""01"". Notice that some of these substrings repeat and are counted the number of times they occur. Also; ""00110011"" is not a valid substring because all the 0's (and 1's) are not grouped together. Example 2: Input: s = ""10101"" Output: 4 Explanation: There are 4 substrings: ""10""; ""01""; ""10""; ""01"" that have equal number of consecutive 1's and 0's. Constraints: 1 <= s.length <= 105 s[i] is either '0' or '1'."
Oracle,787,Cheapest Flights Within K Stops,Med,"Array, Breadth-First Search, Matrix",On an 2 x 3 board; there are five tiles labeled from 1 to 5; and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of the board is solved if and only if the board is [[1;2;3];[4;5;0]]. Given the puzzle board board; return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved; return -1. Example 1: Input: board = [[1;2;3];[4;0;5]] Output: 1 Explanation: Swap the 0 and the 5 in one move. Example 2: Input: board = [[1;2;3];[5;4;0]] Output: -1 Explanation: No number of moves will make the board solved. Example 3: Input: board = [[4;1;2];[5;0;3]] Output: 5 Explanation: 5 is the smallest number of moves that solves the board. An example path: After move 0: [[4;1;2];[5;0;3]] After move 1: [[4;1;2];[0;5;3]] After move 2: [[0;1;2];[4;5;3]] After move 3: [[1;0;2];[4;5;3]] After move 4: [[1;2;0];[4;5;3]] After move 5: [[1;2;3];[4;5;0]] Constraints: board.length == 2 board[i].length == 3 0 <= board[i][j] <= 5 Each value board[i][j] is unique.
Oracle,706,Design HashMap,Easy,,
Oracle,622,Design Circular Queue,Med,,
Oracle,973,K Closest Points to Origin,Med,"String, Stack, Greedy, Queue","You are given two strings stamp and target. Initially; there is a string s of length target.length with all s[i] == '?'. In one turn; you can place stamp over s and replace every letter in the s with the corresponding letter from stamp. For example; if stamp = ""abc"" and target = ""abcba""; then s is ""?????"" initially. In one turn you can: place stamp at index 0 of s to obtain ""abc??""; place stamp at index 1 of s to obtain ""?abc?""; or place stamp at index 2 of s to obtain ""??abc"". Note that stamp must be fully contained in the boundaries of s in order to stamp (i.e.; you cannot place stamp at index 3 of s). We want to convert s to target using at most 10 * target.length turns. Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns; return an empty array. Example 1: Input: stamp = ""abc""; target = ""ababc"" Output: [0;2] Explanation: Initially s = ""?????"". - Place stamp at index 0 to get ""abc??"". - Place stamp at index 2 to get ""ababc"". [1;0;2] would also be accepted as an answer; as well as some other answers. Example 2: Input: stamp = ""abca""; target = ""aabcaca"" Output: [3;0;1] Explanation: Initially s = ""???????"". - Place stamp at index 3 to get ""???abca"". - Place stamp at index 0 to get ""abcabca"". - Place stamp at index 1 to get ""aabcaca"". Constraints: 1 <= stamp.length <= target.length <= 1000 stamp and target consist of lowercase English letters."
Oracle,981,Time Based Key-Value Store,Med,"Array, String","You are given an array of n strings strs; all of the same length. The strings can be arranged such that there is one on each line; making a grid. For example; strs = [""abc""; ""bce""; ""cae""] can be arranged as follows: abc bce cae You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed); columns 0 ('a'; 'b'; 'c') and 2 ('c'; 'e'; 'e') are sorted; while column 1 ('b'; 'c'; 'a') is not; so you would delete column 1. Return the number of columns that you will delete. Example 1: Input: strs = [""cba"";""daf"";""ghi""] Output: 1 Explanation: The grid looks as follows: cba daf ghi Columns 0 and 2 are sorted; but column 1 is not; so you only need to delete 1 column. Example 2: Input: strs = [""a"";""b""] Output: 0 Explanation: The grid looks as follows: a b Column 0 is the only column and is sorted; so you will not delete any columns. Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: The grid looks as follows: zyx wvu tsr All 3 columns are not sorted; so you will delete all 3. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 1000 strs[i] consists of lowercase English letters."
Oracle,987,Vertical Order Traversal of a Binary Tree,Hard,"Array, Queue, Sorting, Simulation",You are given an integer array deck. There is a deck of cards where every card has a unique integer. The integer on the ith card is deck[i]. You can order the deck in any order you want. Initially; all the cards start face down (unrevealed) in one deck. You will do the following steps repeatedly until all cards are revealed: Take the top card of the deck; reveal it; and take it out of the deck. If there are still cards in the deck then put the next top card of the deck at the bottom of the deck. If there are still unrevealed cards; go back to step 1. Otherwise; stop. Return an ordering of the deck that would reveal the cards in increasing order. Note that the first entry in the answer is considered to be the top of the deck. Example 1: Input: deck = [17;13;11;2;3;5;7] Output: [2;13;3;11;5;17;7] Explanation: We get the deck in the order [17;13;11;2;3;5;7] (this order does not matter); and reorder it. After reordering; the deck starts as [2;13;3;11;5;17;7]; where 2 is the top of the deck. We reveal 2; and move 13 to the bottom. The deck is now [3;11;5;17;7;13]. We reveal 3; and move 11 to the bottom. The deck is now [5;17;7;13;11]. We reveal 5; and move 17 to the bottom. The deck is now [7;13;11;17]. We reveal 7; and move 13 to the bottom. The deck is now [11;17;13]. We reveal 11; and move 17 to the bottom. The deck is now [13;17]. We reveal 13; and move 17 to the bottom. The deck is now [17]. We reveal 17. Since all the cards revealed are in increasing order; the answer is correct. Example 2: Input: deck = [1;1000] Output: [1;1000] Constraints: 1 <= deck.length <= 1000 1 <= deck[i] <= 106 All the values of deck are unique.
Oracle,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Oracle,1081,Smallest Subsequence of Distinct Characters,Med,"Array, Dynamic Programming, Greedy",You are given a series of video clips from a sporting event that lasted time seconds. These video clips can be overlapping with each other and have varying lengths. Each video clip is described by an array clips where clips[i] = [starti; endi] indicates that the ith clip started at starti and ended at endi. We can cut these clips into segments freely. For example; a clip [0; 7] can be cut into segments [0; 1] + [1; 3] + [3; 7]. Return the minimum number of clips needed so that we can cut the clips into segments that cover the entire sporting event [0; time]. If the task is impossible; return -1. Example 1: Input: clips = [[0;2];[4;6];[8;10];[1;9];[1;5];[5;9]]; time = 10 Output: 3 Explanation: We take the clips [0;2]; [8;10]; [1;9]; a total of 3 clips. Then; we can reconstruct the sporting event as follows: We cut [1;9] into segments [1;2] + [2;8] + [8;9]. Now we have segments [0;2] + [2;8] + [8;10] which cover the sporting event [0; 10]. Example 2: Input: clips = [[0;1];[1;2]]; time = 5 Output: -1 Explanation: We cannot cover [0;5] with only [0;1] and [1;2]. Example 3: Input: clips = [[0;1];[6;8];[0;2];[5;6];[0;4];[0;3];[6;7];[1;3];[4;7];[1;4];[2;5];[2;6];[3;4];[4;5];[5;7];[6;9]]; time = 9 Output: 3 Explanation: We can take clips [0;4]; [4;7]; and [6;9]. Constraints: 1 <= clips.length <= 100 0 <= starti <= endi <= 100 1 <= time <= 100
Oracle,1328,Break a Palindrome,Med,Database,
Oracle,1209,Remove All Adjacent Duplicates in String II,Med,Concurrency,
Oracle,1235,Maximum Profit in Job Scheduling,Hard,,
Oracle,1268,Search Suggestions System,Med,Database,Table: Users +----------------+---------+ | Column Name | Type | +----------------+---------+ | user_id | int | | join_date | date | | favorite_brand | varchar | +----------------+---------+ user_id is the primary key (column with unique values) of this table. This table has the info of the users of an online shopping website where users can sell and buy items. Table: Orders +---------------+---------+ | Column Name | Type | +---------------+---------+ | order_id | int | | order_date | date | | item_id | int | | buyer_id | int | | seller_id | int | +---------------+---------+ order_id is the primary key (column with unique values) of this table. item_id is a foreign key (reference column) to the Items table. buyer_id and seller_id are foreign keys to the Users table. Table: Items +---------------+---------+ | Column Name | Type | +---------------+---------+ | item_id | int | | item_brand | varchar | +---------------+---------+ item_id is the primary key (column with unique values) of this table. Write a solution to find for each user; the join date and the number of orders they made as a buyer in 2019. Return the result table in any order. The result format is in the following example. Example 1: Input: Users table: +---------+------------+----------------+ | user_id | join_date | favorite_brand | +---------+------------+----------------+ | 1 | 2018-01-01 | Lenovo | | 2 | 2018-02-09 | Samsung | | 3 | 2018-01-19 | LG | | 4 | 2018-05-21 | HP | +---------+------------+----------------+ Orders table: +----------+------------+---------+----------+-----------+ | order_id | order_date | item_id | buyer_id | seller_id | +----------+------------+---------+----------+-----------+ | 1 | 2019-08-01 | 4 | 1 | 2 | | 2 | 2018-08-02 | 2 | 1 | 3 | | 3 | 2019-08-03 | 3 | 2 | 3 | | 4 | 2018-08-04 | 1 | 4 | 2 | | 5 | 2018-08-04 | 1 | 3 | 4 | | 6 | 2019-08-05 | 2 | 2 | 4 | +----------+------------+---------+----------+-----------+ Items table: +---------+------------+ | item_id | item_brand | +---------+------------+ | 1 | Samsung | | 2 | Lenovo | | 3 | LG | | 4 | HP | +---------+------------+ Output: +-----------+------------+----------------+ | buyer_id | join_date | orders_in_2019 | +-----------+------------+----------------+ | 1 | 2018-01-01 | 1 | | 2 | 2018-02-09 | 2 | | 3 | 2018-01-19 | 0 | | 4 | 2018-05-21 | 0 | +-----------+------------+----------------+
Oracle,1636,Sort Array by Increasing Frequency,Easy,"Math, String","Given a binary string s; return the number of substrings with all characters 1's. Since the answer may be too large; return it modulo 109 + 7. Example 1: Input: s = ""0110111"" Output: 9 Explanation: There are 9 substring in total with only 1's characters. ""1"" -> 5 times. ""11"" -> 3 times. ""111"" -> 1 time. Example 2: Input: s = ""101"" Output: 2 Explanation: Substring ""1"" is shown 2 times in s. Example 3: Input: s = ""111111"" Output: 21 Explanation: Each substring contains only 1's characters. Constraints: 1 <= s.length <= 105 s[i] is either '0' or '1'."
Oracle,1839,Longest Substring Of All Vowels in Order,Med,"Array, Bit Manipulation",There is a hidden integer array arr that consists of n non-negative integers. It was encoded into another integer array encoded of length n - 1; such that encoded[i] = arr[i] XOR arr[i + 1]. For example; if arr = [1;0;2;1]; then encoded = [1;2;3]. You are given the encoded array. You are also given an integer first; that is the first element of arr; i.e. arr[0]. Return the original array arr. It can be proved that the answer exists and is unique. Example 1: Input: encoded = [1;2;3]; first = 1 Output: [1;0;2;1] Explanation: If arr = [1;0;2;1]; then first = 1 and encoded = [1 XOR 0; 0 XOR 2; 2 XOR 1] = [1;2;3] Example 2: Input: encoded = [6;2;7;3]; first = 4 Output: [4;2;0;7;4] Constraints: 2 <= n <= 104 encoded.length == n - 1 0 <= encoded[i] <= 105 0 <= first <= 105
Oracle,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
Oracle,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Oracle,26,Remove Duplicates from Sorted Array,Easy,"Array, Two Pointers",Given an integer array nums sorted in non-decreasing order; remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in nums. Consider the number of unique elements of nums to be k; to get accepted; you need to do the following things: Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums. Return k. Custom Judge: The judge will test your solution with the following code: int[] nums = [...]; // Input array int[] expectedNums = [...]; // The expected answer with correct length int k = removeDuplicates(nums); // Calls your implementation assert k == expectedNums.length; for (int i = 0; i < k; i++) { assert nums[i] == expectedNums[i]; } If all assertions pass; then your solution will be accepted. Example 1: Input: nums = [1;1;2] Output: 2; nums = [1;2;_] Explanation: Your function should return k = 2; with the first two elements of nums being 1 and 2 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Example 2: Input: nums = [0;0;1;1;1;2;2;3;3;4] Output: 5; nums = [0;1;2;3;4;_;_;_;_;_] Explanation: Your function should return k = 5; with the first five elements of nums being 0; 1; 2; 3; and 4 respectively. It does not matter what you leave beyond the returned k (hence they are underscores). Constraints: 1 <= nums.length <= 3 * 104 -100 <= nums[i] <= 100 nums is sorted in non-decreasing order.
Oracle,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
Oracle,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Oracle,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
Oracle,57,Insert Interval,Med,Array,You are given an array of non-overlapping intervals intervals where intervals[i] = [starti; endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start; end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary). Return intervals after the insertion. Note that you don't need to modify intervals in-place. You can make a new array and return it. Example 1: Input: intervals = [[1;3];[6;9]]; newInterval = [2;5] Output: [[1;5];[6;9]] Example 2: Input: intervals = [[1;2];[3;5];[6;7];[8;10];[12;16]]; newInterval = [4;8] Output: [[1;2];[3;10];[12;16]] Explanation: Because the new interval [4;8] overlaps with [3;5];[6;7];[8;10]. Constraints: 0 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 105 intervals is sorted by starti in ascending order. newInterval.length == 2 0 <= start <= end <= 105
Oracle,61,Rotate List,Med,"Linked List, Two Pointers",Given the head of a linked list; rotate the list to the right by k places. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [4;5;1;2;3] Example 2: Input: head = [0;1;2]; k = 4 Output: [2;0;1] Constraints: The number of nodes in the list is in the range [0; 500]. -100 <= Node.val <= 100 0 <= k <= 2 * 109
Oracle,68,Text Justification,Hard,"Array, String, Simulation","Given an array of strings words and a width maxWidth; format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is; pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words; the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text; it should be left-justified; and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = [""This""; ""is""; ""an""; ""example""; ""of""; ""text""; ""justification.""]; maxWidth = 16 Output: [ ""This is an""; ""example of text""; ""justification. "" ] Example 2: Input: words = [""What"";""must"";""be"";""acknowledgment"";""shall"";""be""]; maxWidth = 16 Output: [ ""What must be""; ""acknowledgment ""; ""shall be "" ] Explanation: Note that the last line is ""shall be "" instead of ""shall be""; because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = [""Science"";""is"";""what"";""we"";""understand"";""well"";""enough"";""to"";""explain"";""to"";""a"";""computer."";""Art"";""is"";""everything"";""else"";""we"";""do""]; maxWidth = 20 Output: [ ""Science is what we""; ""understand well""; ""enough to explain to""; ""a computer. Art is""; ""everything else we""; ""do "" ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth"
Oracle,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Oracle,83,Remove Duplicates from Sorted List,Easy,Linked List,Given the head of a sorted linked list; delete all duplicates such that each element appears only once. Return the linked list sorted as well. Example 1: Input: head = [1;1;2] Output: [1;2] Example 2: Input: head = [1;1;2;3;3] Output: [1;2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Oracle,99,Recover Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",You are given the root of a binary search tree (BST); where the values of exactly two nodes of the tree were swapped by mistake. Recover the tree without changing its structure. Example 1: Input: root = [1;3;null;null;2] Output: [3;1;null;null;2] Explanation: 3 cannot be a left child of 1 because 3 > 1. Swapping 1 and 3 makes the BST valid. Example 2: Input: root = [3;1;4;null;null;2] Output: [2;1;4;null;null;3] Explanation: 2 cannot be in the right subtree of 3 because 2 < 3. Swapping 2 and 3 makes the BST valid. Constraints: The number of nodes in the tree is in the range [2; 1000]. -231 <= Node.val <= 231 - 1 Follow up: A solution using O(n) space is pretty straight-forward. Could you devise a constant O(1) space solution?
Oracle,140,Word Break II,Hard,"Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization","Given a string s and a dictionary of strings wordDict; add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""catsanddog""; wordDict = [""cat"";""cats"";""and"";""sand"";""dog""] Output: [""cats and dog"";""cat sand dog""] Example 2: Input: s = ""pineapplepenapple""; wordDict = [""apple"";""pen"";""applepen"";""pine"";""pineapple""] Output: [""pine apple pen apple"";""pineapple pen apple"";""pine applepen apple""] Explanation: Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: [] Constraints: 1 <= s.length <= 20 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 10 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique. Input is generated in a way that the length of the answer doesn't exceed 105."
Oracle,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
Oracle,167,Two Sum II - Input Array Is Sorted,Med,"Array, Two Pointers, Binary Search",Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order; find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 1 <= index1 < index2 <= numbers.length. Return the indices of the two numbers; index1 and index2; added by one as an integer array [index1; index2] of length 2. The tests are generated such that there is exactly one solution. You may not use the same element twice. Your solution must use only constant extra space. Example 1: Input: numbers = [2;7;11;15]; target = 9 Output: [1;2] Explanation: The sum of 2 and 7 is 9. Therefore; index1 = 1; index2 = 2. We return [1; 2]. Example 2: Input: numbers = [2;3;4]; target = 6 Output: [1;3] Explanation: The sum of 2 and 4 is 6. Therefore index1 = 1; index2 = 3. We return [1; 3]. Example 3: Input: numbers = [-1;0]; target = -1 Output: [1;2] Explanation: The sum of -1 and 0 is -1. Therefore index1 = 1; index2 = 2. We return [1; 2]. Constraints: 2 <= numbers.length <= 3 * 104 -1000 <= numbers[i] <= 1000 numbers is sorted in non-decreasing order. -1000 <= target <= 1000 The tests are generated such that there is exactly one solution.
Oracle,179,Largest Number,Med,"Array, String, Greedy, Sorting","Given a list of non-negative integers nums; arrange them such that they form the largest number and return it. Since the result may be very large; so you need to return a string instead of an integer. Example 1: Input: nums = [10;2] Output: ""210"" Example 2: Input: nums = [3;30;34;5;9] Output: ""9534330"" Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 109"
Oracle,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Oracle,217,Contains Duplicate,Easy,"Array, Hash Table, Sorting",Given an integer array nums; return true if any value appears at least twice in the array; and return false if every element is distinct. Example 1: Input: nums = [1;2;3;1] Output: true Explanation: The element 1 occurs at the indices 0 and 3. Example 2: Input: nums = [1;2;3;4] Output: false Explanation: All elements are distinct. Example 3: Input: nums = [1;1;1;3;3;4;3;2;4;2] Output: true Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109
Oracle,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Oracle,225,Implement Stack using Queues,Easy,"Stack, Design, Queue","Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push; top; pop; and empty). Implement the MyStack class: void push(int x) Pushes element x to the top of the stack. int pop() Removes the element on the top of the stack and returns it. int top() Returns the element on the top of the stack. boolean empty() Returns true if the stack is empty; false otherwise. Notes: You must use only standard operations of a queue; which means that only push to back; peek/pop from front; size and is empty operations are valid. Depending on your language; the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations. Example 1: Input [""MyStack""; ""push""; ""push""; ""top""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 2; 2; false] Explanation MyStack myStack = new MyStack(); myStack.push(1); myStack.push(2); myStack.top(); // return 2 myStack.pop(); // return 2 myStack.empty(); // return False Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; top; and empty. All the calls to pop and top are valid. Follow-up: Can you implement the stack using only one queue?"
Oracle,232,Implement Queue using Stacks,Easy,"Stack, Design, Queue","Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push; peek; pop; and empty). Implement the MyQueue class: void push(int x) Pushes element x to the back of the queue. int pop() Removes the element from the front of the queue and returns it. int peek() Returns the element at the front of the queue. boolean empty() Returns true if the queue is empty; false otherwise. Notes: You must use only standard operations of a stack; which means only push to top; peek/pop from top; size; and is empty operations are valid. Depending on your language; the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack's standard operations. Example 1: Input [""MyQueue""; ""push""; ""push""; ""peek""; ""pop""; ""empty""] [[]; [1]; [2]; []; []; []] Output [null; null; null; 1; 1; false] Explanation MyQueue myQueue = new MyQueue(); myQueue.push(1); // queue is: [1] myQueue.push(2); // queue is: [1; 2] (leftmost is front of the queue) myQueue.peek(); // return 1 myQueue.pop(); // return 1; queue is [2] myQueue.empty(); // return false Constraints: 1 <= x <= 9 At most 100 calls will be made to push; pop; peek; and empty. All the calls to pop and peek are valid. Follow-up: Can you implement the queue such that each operation is amortized O(1) time complexity? In other words; performing n operations will take overall O(n) time even if one of those operations may take longer."
Oracle,234,Palindrome Linked List,Easy,"Linked List, Two Pointers, Stack, Recursion",Given the head of a singly linked list; return true if it is a palindrome or false otherwise. Example 1: Input: head = [1;2;2;1] Output: true Example 2: Input: head = [1;2] Output: false Constraints: The number of nodes in the list is in the range [1; 105]. 0 <= Node.val <= 9 Follow up: Could you do it in O(n) time and O(1) space?
Oracle,291,Word Pattern II,Med,"Hash Table, String, Backtracking",
Oracle,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
Oracle,409,Longest Palindrome,Easy,"Hash Table, String, Greedy","Given a string s which consists of lowercase or uppercase letters; return the length of the longest palindrome that can be built with those letters. Letters are case sensitive; for example; ""Aa"" is not considered a palindrome. Example 1: Input: s = ""abccccdd"" Output: 7 Explanation: One longest palindrome that can be built is ""dccaccd""; whose length is 7. Example 2: Input: s = ""a"" Output: 1 Explanation: The longest palindrome that can be built is ""a""; whose length is 1. Constraints: 1 <= s.length <= 2000 s consists of lowercase and/or uppercase English letters only."
Oracle,424,Longest Repeating Character Replacement,Med,"Hash Table, String, Sliding Window","You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times. Return the length of the longest substring containing the same letter you can get after performing the above operations. Example 1: Input: s = ""ABAB""; k = 2 Output: 4 Explanation: Replace the two 'A's with two 'B's or vice versa. Example 2: Input: s = ""AABABBA""; k = 1 Output: 4 Explanation: Replace the one 'A' in the middle with 'B' and form ""AABBBBA"". The substring ""BBBB"" has the longest repeating letters; which is 4. There may exists other ways to achieve this answer too. Constraints: 1 <= s.length <= 105 s consists of only uppercase English letters. 0 <= k <= s.length"
Oracle,543,Diameter of Binary Tree,Easy,"Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them. Example 1: Input: root = [1;2;3;4;5] Output: 3 Explanation: 3 is the length of the path [4;2;1;3] or [5;2;1;3]. Example 2: Input: root = [1;2] Output: 1 Constraints: The number of nodes in the tree is in the range [1; 104]. -100 <= Node.val <= 100
Oracle,564,Find the Closest Palindrome,Hard,"Math, String","Given a string n representing an integer; return the closest integer (not including itself); which is a palindrome. If there is a tie; return the smaller one. The closest is defined as the absolute difference minimized between two integers. Example 1: Input: n = ""123"" Output: ""121"" Example 2: Input: n = ""1"" Output: ""0"" Explanation: 0 and 2 are the closest palindromes but we return the smallest which is 0. Constraints: 1 <= n.length <= 18 n consists of only digits. n does not have leading zeros. n is representing an integer in the range [1; 1018 - 1]."
Oracle,621,Task Scheduler,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting","You are given an array of CPU tasks; each labeled with a letter from A to Z; and a number n. Each CPU interval can be idle or allow the completion of one task. Tasks can be completed in any order; but there's a constraint: there has to be a gap of at least n intervals between two tasks with the same label. Return the minimum number of CPU intervals required to complete all tasks. Example 1: Input: tasks = [""A"";""A"";""A"";""B"";""B"";""B""]; n = 2 Output: 8 Explanation: A possible sequence is: A -> B -> idle -> A -> B -> idle -> A -> B. After completing task A; you must wait two intervals before doing A again. The same applies to task B. In the 3rd interval; neither A nor B can be done; so you idle. By the 4th interval; you can do A again as 2 intervals have passed. Example 2: Input: tasks = [""A"";""C"";""A"";""B"";""D"";""B""]; n = 1 Output: 6 Explanation: A possible sequence is: A -> B -> C -> D -> A -> B. With a cooling interval of 1; you can repeat a task after just one other task. Example 3: Input: tasks = [""A"";""A"";""A""; ""B"";""B"";""B""]; n = 3 Output: 10 Explanation: A possible sequence is: A -> B -> idle -> idle -> A -> B -> idle -> idle -> A -> B. There are only two types of tasks; A and B; which need to be separated by 3 intervals. This leads to idling twice between repetitions of these tasks. Constraints: 1 <= tasks.length <= 104 tasks[i] is an uppercase English letter. 0 <= n <= 100"
Oracle,694,Number of Distinct Islands,Med,"Hash Table, Depth-First Search, Breadth-First Search, Union Find, Hash Function",
Oracle,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
Oracle,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
Oracle,1166,Design File System,Med,"Array, Math, Dynamic Programming, Probability and Statistics",
Oracle,1046,Last Stone Weight,Easy,"Array, Binary Search, Sliding Window, Prefix Sum",Given a binary array nums and an integer k; return the maximum number of consecutive 1's in the array if you can flip at most k 0's. Example 1: Input: nums = [1;1;1;0;0;0;1;1;1;1;0]; k = 2 Output: 6 Explanation: [1;1;1;0;0;1;1;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Example 2: Input: nums = [0;0;1;1;0;0;1;1;1;0;1;1;0;0;0;1;1;1;1]; k = 3 Output: 10 Explanation: [0;0;1;1;1;1;1;1;1;1;1;1;0;0;0;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1. 0 <= k <= nums.length
Oracle,1047,Remove All Adjacent Duplicates In String,Easy,"Array, Greedy, Sorting",Given an integer array nums and an integer k; modify the array in the following way: choose an index i and replace nums[i] with -nums[i]. You should apply this process exactly k times. You may choose the same index i multiple times. Return the largest possible sum of the array after modifying it in this way. Example 1: Input: nums = [4;2;3]; k = 1 Output: 5 Explanation: Choose index 1 and nums becomes [4;-2;3]. Example 2: Input: nums = [3;-1;0;2]; k = 3 Output: 6 Explanation: Choose indices (1; 2; 2) and nums becomes [3;1;0;2]. Example 3: Input: nums = [2;-3;-1;5;-4]; k = 2 Output: 13 Explanation: Choose indices (1; 4) and nums becomes [2;3;-1;5;4]. Constraints: 1 <= nums.length <= 104 -100 <= nums[i] <= 100 1 <= k <= 104
Oracle,1091,Shortest Path in Binary Matrix,Med,"Tree, Depth-First Search, Binary Tree",
Oracle,1507,Reformat Date,Easy,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n grid. Each cell of grid represents a street. The street of grid[i][j] can be: 1 which means a street connecting the left cell and the right cell. 2 which means a street connecting the upper cell and the lower cell. 3 which means a street connecting the left cell and the lower cell. 4 which means a street connecting the right cell and the lower cell. 5 which means a street connecting the left cell and the upper cell. 6 which means a street connecting the right cell and the upper cell. You will initially start at the street of the upper-left cell (0; 0). A valid path in the grid is a path that starts from the upper left cell (0; 0) and ends at the bottom-right cell (m - 1; n - 1). The path should only follow the streets. Notice that you are not allowed to change any street. Return true if there is a valid path in the grid or false otherwise. Example 1: Input: grid = [[2;4;3];[6;5;2]] Output: true Explanation: As shown you can start at cell (0; 0) and visit all the cells of the grid to reach (m - 1; n - 1). Example 2: Input: grid = [[1;2;1];[1;2;1]] Output: false Explanation: As shown you the street at cell (0; 0) is not connected with any street of any other cell and you will get stuck at cell (0; 0) Example 3: Input: grid = [[1;1;2]] Output: false Explanation: You will get stuck at cell (0; 1) and you cannot reach cell (0; 2). Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 1 <= grid[i][j] <= 6
Oracle,1347,Minimum Number of Steps to Make Two Strings Anagram,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
Oracle,1353,Maximum Number of Events That Can Be Attended,Med,"Array, Hash Table, String, Sorting","You are given a 0-indexed string array words; where words[i] consists of lowercase English letters. In one operation; select any index i such that 0 < i < words.length and words[i - 1] and words[i] are anagrams; and delete words[i] from words. Keep performing this operation as long as you can select an index that satisfies the conditions. Return words after performing all operations. It can be shown that selecting the indices for each operation in any arbitrary order will lead to the same result. An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase using all the original letters exactly once. For example; ""dacb"" is an anagram of ""abdc"". Example 1: Input: words = [""abba"";""baba"";""bbaa"";""cd"";""cd""] Output: [""abba"";""cd""] Explanation: One of the ways we can obtain the resultant array is by using the following operations: - Since words[2] = ""bbaa"" and words[1] = ""baba"" are anagrams; we choose index 2 and delete words[2]. Now words = [""abba"";""baba"";""cd"";""cd""]. - Since words[1] = ""baba"" and words[0] = ""abba"" are anagrams; we choose index 1 and delete words[1]. Now words = [""abba"";""cd"";""cd""]. - Since words[2] = ""cd"" and words[1] = ""cd"" are anagrams; we choose index 2 and delete words[2]. Now words = [""abba"";""cd""]. We can no longer perform any operations; so [""abba"";""cd""] is the final answer. Example 2: Input: words = [""a"";""b"";""c"";""d"";""e""] Output: [""a"";""b"";""c"";""d"";""e""] Explanation: No two adjacent strings in words are anagrams of each other; so no operations are performed. Constraints: 1 <= words.length <= 100 1 <= words[i].length <= 10 words[i] consists of lowercase English letters."
Oracle,1834,Single-Threaded CPU,Med,"Array, Hash Table, Greedy",On a social network consisting of m users and some friendships between users; two users can communicate with each other if they know a common language. You are given an integer n; an array languages; and an array friendships where: There are n languages numbered 1 through n; languages[i] is the set of languages the i​​​​​​th​​​​ user knows; and friendships[i] = [u​​​​​​i​​​; v​​​​​​i] denotes a friendship between the users u​​​​​​​​​​​i​​​​​ and vi. You can choose one language and teach it to some users so that all friends can communicate with each other. Return the minimum number of users you need to teach. Note that friendships are not transitive; meaning if x is a friend of y and y is a friend of z; this doesn't guarantee that x is a friend of z. Example 1: Input: n = 2; languages = [[1];[2];[1;2]]; friendships = [[1;2];[1;3];[2;3]] Output: 1 Explanation: You can either teach user 1 the second language or user 2 the first language. Example 2: Input: n = 3; languages = [[2];[1;3];[1;2];[3]]; friendships = [[1;4];[1;2];[3;4];[2;3]] Output: 2 Explanation: Teach the third language to users 1 and 3; yielding two users to teach. Constraints: 2 <= n <= 500 languages.length == m 1 <= m <= 500 1 <= languages[i].length <= n 1 <= languages[i][j] <= n 1 <= u​​​​​​i < v​​​​​​i <= languages.length 1 <= friendships.length <= 500 All tuples (u​​​​​i; v​​​​​​i) are unique languages[i] contains only unique values
Oracle,2006,Count Number of Pairs With Absolute Difference K,Easy,"Array, Binary Search, Simulation, Prefix Sum",There are n students in a class numbered from 0 to n - 1. The teacher will give each student a problem starting with the student number 0; then the student number 1; and so on until the teacher reaches the student number n - 1. After that; the teacher will restart the process; starting with the student number 0 again. You are given a 0-indexed integer array chalk and an integer k. There are initially k pieces of chalk. When the student number i is given a problem to solve; they will use chalk[i] pieces of chalk to solve that problem. However; if the current number of chalk pieces is strictly less than chalk[i]; then the student number i will be asked to replace the chalk. Return the index of the student that will replace the chalk pieces. Example 1: Input: chalk = [5;1;5]; k = 22 Output: 0 Explanation: The students go in turns as follows: - Student number 0 uses 5 chalk; so k = 17. - Student number 1 uses 1 chalk; so k = 16. - Student number 2 uses 5 chalk; so k = 11. - Student number 0 uses 5 chalk; so k = 6. - Student number 1 uses 1 chalk; so k = 5. - Student number 2 uses 5 chalk; so k = 0. Student number 0 does not have enough chalk; so they will have to replace it. Example 2: Input: chalk = [3;4;1;2]; k = 25 Output: 1 Explanation: The students go in turns as follows: - Student number 0 uses 3 chalk so k = 22. - Student number 1 uses 4 chalk so k = 18. - Student number 2 uses 1 chalk so k = 17. - Student number 3 uses 2 chalk so k = 15. - Student number 0 uses 3 chalk so k = 12. - Student number 1 uses 4 chalk so k = 8. - Student number 2 uses 1 chalk so k = 7. - Student number 3 uses 2 chalk so k = 5. - Student number 0 uses 3 chalk so k = 2. Student number 1 does not have enough chalk; so they will have to replace it. Constraints: chalk.length == n 1 <= n <= 105 1 <= chalk[i] <= 105 1 <= k <= 109
Oracle,2099,Find Subsequence of Length K With the Largest Sum,Easy,"Array, String","Given an array of strings patterns and a string word; return the number of strings in patterns that exist as a substring in word. A substring is a contiguous sequence of characters within a string. Example 1: Input: patterns = [""a"";""abc"";""bc"";""d""]; word = ""abc"" Output: 3 Explanation: - ""a"" appears as a substring in ""abc"". - ""abc"" appears as a substring in ""abc"". - ""bc"" appears as a substring in ""abc"". - ""d"" does not appear as a substring in ""abc"". 3 of the strings in patterns appear as a substring in word. Example 2: Input: patterns = [""a"";""b"";""c""]; word = ""aaaaabbbbb"" Output: 2 Explanation: - ""a"" appears as a substring in ""aaaaabbbbb"". - ""b"" appears as a substring in ""aaaaabbbbb"". - ""c"" does not appear as a substring in ""aaaaabbbbb"". 2 of the strings in patterns appear as a substring in word. Example 3: Input: patterns = [""a"";""a"";""a""]; word = ""ab"" Output: 3 Explanation: Each of the patterns appears as a substring in word ""ab"". Constraints: 1 <= patterns.length <= 100 1 <= patterns[i].length <= 100 1 <= word.length <= 100 patterns[i] and word consist of lowercase English letters."
Oracle,2151,Maximum Good People Based on Statements,Hard,"Array, Breadth-First Search, Graph",There is a network of n servers; labeled from 0 to n - 1. You are given a 2D integer array edges; where edges[i] = [ui; vi] indicates there is a message channel between servers ui and vi; and they can pass any number of messages to each other directly in one second. You are also given a 0-indexed integer array patience of length n. All servers are connected; i.e.; a message can be passed from one server to any other server(s) directly or indirectly through the message channels. The server labeled 0 is the master server. The rest are data servers. Each data server needs to send its message to the master server for processing and wait for a reply. Messages move between servers optimally; so every message takes the least amount of time to arrive at the master server. The master server will process all newly arrived messages instantly and send a reply to the originating server via the reversed path the message had gone through. At the beginning of second 0; each data server sends its message to be processed. Starting from second 1; at the beginning of every second; each data server will check if it has received a reply to the message it sent (including any newly arrived replies) from the master server: If it has not; it will resend the message periodically. The data server i will resend the message every patience[i] second(s); i.e.; the data server i will resend the message if patience[i] second(s) have elapsed since the last time the message was sent from this server. Otherwise; no more resending will occur from this server. The network becomes idle when there are no messages passing between servers or arriving at servers. Return the earliest second starting from which the network becomes idle. Example 1: Input: edges = [[0;1];[1;2]]; patience = [0;2;1] Output: 8 Explanation: At (the beginning of) second 0; - Data server 1 sends its message (denoted 1A) to the master server. - Data server 2 sends its message (denoted 2A) to the master server. At second 1; - Message 1A arrives at the master server. Master server processes message 1A instantly and sends a reply 1A back. - Server 1 has not received any reply. 1 second (1 < patience[1] = 2) elapsed since this server has sent the message; therefore it does not resend the message. - Server 2 has not received any reply. 1 second (1 == patience[2] = 1) elapsed since this server has sent the message; therefore it resends the message (denoted 2B). At second 2; - The reply 1A arrives at server 1. No more resending will occur from server 1. - Message 2A arrives at the master server. Master server processes message 2A instantly and sends a reply 2A back. - Server 2 resends the message (denoted 2C). ... At second 4; - The reply 2A arrives at server 2. No more resending will occur from server 2. ... At second 7; reply 2D arrives at server 2. Starting from the beginning of the second 8; there are no messages passing between servers or arriving at servers. This is the time when the network becomes idle. Example 2: Input: edges = [[0;1];[0;2];[1;2]]; patience = [0;10;10] Output: 3 Explanation: Data servers 1 and 2 receive a reply back at the beginning of second 2. From the beginning of the second 3; the network becomes idle. Constraints: n == patience.length 2 <= n <= 105 patience[0] == 0 1 <= patience[i] <= 105 for 1 <= i < n 1 <= edges.length <= min(105; n * (n - 1) / 2) edges[i].length == 2 0 <= ui; vi < n ui != vi There are no duplicate edges. Each server can directly or indirectly reach another server.
Oracle,2251,Number of Flowers in Full Bloom,Hard,"Math, String, Dynamic Programming","Along a long library corridor; there is a line of seats and decorative plants. You are given a 0-indexed string corridor of length n consisting of letters 'S' and 'P' where each 'S' represents a seat and each 'P' represents a plant. One room divider has already been installed to the left of index 0; and another to the right of index n - 1. Additional room dividers can be installed. For each position between indices i - 1 and i (1 <= i <= n - 1); at most one divider can be installed. Divide the corridor into non-overlapping sections; where each section has exactly two seats with any number of plants. There may be multiple ways to perform the division. Two ways are different if there is a position with a room divider installed in the first way but not in the second way. Return the number of ways to divide the corridor. Since the answer may be very large; return it modulo 109 + 7. If there is no way; return 0. Example 1: Input: corridor = ""SSPPSPS"" Output: 3 Explanation: There are 3 different ways to divide the corridor. The black bars in the above image indicate the two room dividers already installed. Note that in each of the ways; each section has exactly two seats. Example 2: Input: corridor = ""PPSPSP"" Output: 1 Explanation: There is only 1 way to divide the corridor; by not installing any additional dividers. Installing any would create some section that does not have exactly two seats. Example 3: Input: corridor = ""S"" Output: 0 Explanation: There is no way to divide the corridor because there will always be a section that does not have exactly two seats. Constraints: n == corridor.length 1 <= n <= 105 corridor[i] is either 'S' or 'P'."
Oracle,2296,Design a Text Editor,Hard,Database,
Oracle,2444,Count Subarrays With Fixed Bounds,Hard,"Hash Table, String, Dynamic Programming","You are given a string s consisting of lowercase letters and an integer k. We call a string t ideal if the following conditions are satisfied: t is a subsequence of the string s. The absolute difference in the alphabet order of every two adjacent letters in t is less than or equal to k. Return the length of the longest ideal string. A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters. Note that the alphabet order is not cyclic. For example; the absolute difference in the alphabet order of 'a' and 'z' is 25; not 1. Example 1: Input: s = ""acfgbd""; k = 2 Output: 4 Explanation: The longest ideal string is ""acbd"". The length of this string is 4; so 4 is returned. Note that ""acfgbd"" is not ideal because 'c' and 'f' have a difference of 3 in alphabet order. Example 2: Input: s = ""abcd""; k = 3 Output: 4 Explanation: The longest ideal string is ""abcd"". The length of this string is 4; so 4 is returned. Constraints: 1 <= s.length <= 105 0 <= k <= 25 s consists of lowercase English letters."
Oracle,2539,Count the Number of Good Subsequences,Med,"Array, Greedy, Sorting",You are given two positive integer arrays nums and target; of the same length. In one operation; you can choose any two distinct indices i and j where 0 <= i; j < nums.length and: set nums[i] = nums[i] + 2 and set nums[j] = nums[j] - 2. Two arrays are considered to be similar if the frequency of each element is the same. Return the minimum number of operations required to make nums similar to target. The test cases are generated such that nums can always be similar to target. Example 1: Input: nums = [8;12;6]; target = [2;14;10] Output: 2 Explanation: It is possible to make nums similar to target in two operations: - Choose i = 0 and j = 2; nums = [10;12;4]. - Choose i = 1 and j = 2; nums = [10;14;2]. It can be shown that 2 is the minimum number of operations needed. Example 2: Input: nums = [1;2;5]; target = [4;1;3] Output: 1 Explanation: We can make nums similar to target in one operation: - Choose i = 1 and j = 2; nums = [1;4;3]. Example 3: Input: nums = [1;1;1;1;1]; target = [1;1;1;1;1] Output: 0 Explanation: The array nums is already similiar to target. Constraints: n == nums.length == target.length 1 <= n <= 105 1 <= nums[i]; target[i] <= 106 It is possible to make nums similar to target.
Oracle,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Oracle,18,4Sum,Med,"Array, Two Pointers, Sorting",Given an array nums of n integers; return an array of all the unique quadruplets [nums[a]; nums[b]; nums[c]; nums[d]] such that: 0 <= a; b; c; d < n a; b; c; and d are distinct. nums[a] + nums[b] + nums[c] + nums[d] == target You may return the answer in any order. Example 1: Input: nums = [1;0;-1;0;-2;2]; target = 0 Output: [[-2;-1;1;2];[-2;0;0;2];[-1;0;0;1]] Example 2: Input: nums = [2;2;2;2;2]; target = 8 Output: [[2;2;2;2]] Constraints: 1 <= nums.length <= 200 -109 <= nums[i] <= 109 -109 <= target <= 109
Oracle,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Oracle,29,Divide Two Integers,Med,"Math, Bit Manipulation",Given two integers dividend and divisor; divide two integers without using multiplication; division; and mod operator. The integer division should truncate toward zero; which means losing its fractional part. For example; 8.345 would be truncated to 8; and -2.7335 would be truncated to -2. Return the quotient after dividing dividend by divisor. Note: Assume we are dealing with an environment that could only store integers within the 32-bit signed integer range: [−231; 231 − 1]. For this problem; if the quotient is strictly greater than 231 - 1; then return 231 - 1; and if the quotient is strictly less than -231; then return -231. Example 1: Input: dividend = 10; divisor = 3 Output: 3 Explanation: 10/3 = 3.33333.. which is truncated to 3. Example 2: Input: dividend = 7; divisor = -3 Output: -2 Explanation: 7/-3 = -2.33333.. which is truncated to -2. Constraints: -231 <= dividend; divisor <= 231 - 1 divisor != 0
Oracle,69,Sqrt(x),Easy,"Math, Binary Search",Given a non-negative integer x; return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. For example; do not use pow(x; 0.5) in c++ or x ** 0.5 in python. Example 1: Input: x = 4 Output: 2 Explanation: The square root of 4 is 2; so we return 2. Example 2: Input: x = 8 Output: 2 Explanation: The square root of 8 is 2.82842...; and since we round it down to the nearest integer; 2 is returned. Constraints: 0 <= x <= 231 - 1
Oracle,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Oracle,81,Search in Rotated Sorted Array II,Med,"Array, Binary Search",There is an integer array nums sorted in non-decreasing order (not necessarily with distinct values). Before being passed to your function; nums is rotated at an unknown pivot index k (0 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;4;4;5;6;6;7] might be rotated at pivot index 5 and become [4;5;6;6;7;0;1;2;4;4]. Given the array nums after the rotation and an integer target; return true if target is in nums; or false if it is not in nums. You must decrease the overall operation steps as much as possible. Example 1: Input: nums = [2;5;6;0;0;1;2]; target = 0 Output: true Example 2: Input: nums = [2;5;6;0;0;1;2]; target = 3 Output: false Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 nums is guaranteed to be rotated at some pivot. -104 <= target <= 104 Follow up: This problem is similar to Search in Rotated Sorted Array; but nums may contain duplicates. Would this affect the runtime complexity? How and why?
Oracle,82,Remove Duplicates from Sorted List II,Med,"Linked List, Two Pointers",Given the head of a sorted linked list; delete all nodes that have duplicate numbers; leaving only distinct numbers from the original list. Return the linked list sorted as well. Example 1: Input: head = [1;2;3;3;4;4;5] Output: [1;2;5] Example 2: Input: head = [1;1;1;2;3] Output: [2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Oracle,85,Maximal Rectangle,Hard,"Array, Dynamic Programming, Stack, Matrix, Monotonic Stack","Given a rows x cols binary matrix filled with 0's and 1's; find the largest rectangle containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 6 Explanation: The maximal rectangle is shown in the above picture. Example 2: Input: matrix = [[""0""]] Output: 0 Example 3: Input: matrix = [[""1""]] Output: 1 Constraints: rows == matrix.length cols == matrix[i].length 1 <= row; cols <= 200 matrix[i][j] is '0' or '1'."
Oracle,92,Reverse Linked List II,Med,Linked List,Given the head of a singly linked list and two integers left and right where left <= right; reverse the nodes of the list from position left to position right; and return the reversed list. Example 1: Input: head = [1;2;3;4;5]; left = 2; right = 4 Output: [1;4;3;2;5] Example 2: Input: head = [5]; left = 1; right = 1 Output: [5] Constraints: The number of nodes in the list is n. 1 <= n <= 500 -500 <= Node.val <= 500 1 <= left <= right <= n Follow up: Could you do it in one pass?
Oracle,104,Maximum Depth of Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; return its maximum depth. A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. Example 1: Input: root = [3;9;20;null;null;15;7] Output: 3 Example 2: Input: root = [1;null;2] Output: 2 Constraints: The number of nodes in the tree is in the range [0; 104]. -100 <= Node.val <= 100
Oracle,113,Path Sum II,Med,"Backtracking, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree and an integer targetSum; return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path should be returned as a list of the node values; not node references. A root-to-leaf path is a path starting from the root and ending at any leaf node. A leaf is a node with no children. Example 1: Input: root = [5;4;8;11;null;13;4;7;2;null;null;5;1]; targetSum = 22 Output: [[5;4;11;2];[5;8;4;5]] Explanation: There are two paths whose sum equals targetSum: 5 + 4 + 11 + 2 = 22 5 + 8 + 4 + 5 = 22 Example 2: Input: root = [1;2;3]; targetSum = 5 Output: [] Example 3: Input: root = [1;2]; targetSum = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 5000]. -1000 <= Node.val <= 1000 -1000 <= targetSum <= 1000
Oracle,114,Flatten Binary Tree to Linked List,Med,"Linked List, Stack, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; flatten the tree into a ""linked list"": The ""linked list"" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. The ""linked list"" should be in the same order as a pre-order traversal of the binary tree. Example 1: Input: root = [1;2;5;3;4;null;6] Output: [1;null;2;null;3;null;4;null;5;null;6] Example 2: Input: root = [] Output: [] Example 3: Input: root = [0] Output: [0] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100 Follow up: Can you flatten the tree in-place (with O(1) extra space)?"
Oracle,115,Distinct Subsequences,Hard,"String, Dynamic Programming","Given two strings s and t; return the number of distinct subsequences of s which equals t. The test cases are generated so that the answer fits on a 32-bit signed integer. Example 1: Input: s = ""rabbbit""; t = ""rabbit"" Output: 3 Explanation: As shown below; there are 3 ways you can generate ""rabbit"" from s. rabbbit rabbbit rabbbit Example 2: Input: s = ""babgbag""; t = ""bag"" Output: 5 Explanation: As shown below; there are 5 ways you can generate ""bag"" from s. babgbag babgbag babgbag babgbag babgbag Constraints: 1 <= s.length; t.length <= 1000 s and t consist of English letters."
Oracle,118,Pascal's Triangle,Easy,"Array, Dynamic Programming",Given an integer numRows; return the first numRows of Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: numRows = 5 Output: [[1];[1;1];[1;2;1];[1;3;3;1];[1;4;6;4;1]] Example 2: Input: numRows = 1 Output: [[1]] Constraints: 1 <= numRows <= 30
Oracle,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Oracle,135,Candy,Hard,"Array, Greedy",There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings. You are giving candies to these children subjected to the following requirements: Each child must have at least one candy. Children with a higher rating get more candies than their neighbors. Return the minimum number of candies you need to have to distribute the candies to the children. Example 1: Input: ratings = [1;0;2] Output: 5 Explanation: You can allocate to the first; second and third child with 2; 1; 2 candies respectively. Example 2: Input: ratings = [1;2;2] Output: 4 Explanation: You can allocate to the first; second and third child with 1; 2; 1 candies respectively. The third child gets 1 candy because it satisfies the above two conditions. Constraints: n == ratings.length 1 <= n <= 2 * 104 0 <= ratings[i] <= 2 * 104
Oracle,148,Sort List,Med,"Linked List, Two Pointers, Divide and Conquer, Sorting, Merge Sort",Given the head of a linked list; return the list after sorting it in ascending order. Example 1: Input: head = [4;2;1;3] Output: [1;2;3;4] Example 2: Input: head = [-1;5;3;4;0] Output: [-1;0;3;4;5] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is in the range [0; 5 * 104]. -105 <= Node.val <= 105 Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?
Oracle,150,Evaluate Reverse Polish Notation,Med,"Array, Math, Stack","You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression. Return an integer that represents the value of the expression. Note that: The valid operators are '+'; '-'; '*'; and '/'. Each operand may be an integer or another expression. The division between two integers always truncates toward zero. There will not be any division by zero. The input represents a valid arithmetic expression in a reverse polish notation. The answer and all the intermediate calculations can be represented in a 32-bit integer. Example 1: Input: tokens = [""2"";""1"";""+"";""3"";""*""] Output: 9 Explanation: ((2 + 1) * 3) = 9 Example 2: Input: tokens = [""4"";""13"";""5"";""/"";""+""] Output: 6 Explanation: (4 + (13 / 5)) = 6 Example 3: Input: tokens = [""10"";""6"";""9"";""3"";""+"";""-11"";""*"";""/"";""*"";""17"";""+"";""5"";""+""] Output: 22 Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 = ((10 * (6 / (12 * -11))) + 17) + 5 = ((10 * (6 / -132)) + 17) + 5 = ((10 * 0) + 17) + 5 = (0 + 17) + 5 = 17 + 5 = 22 Constraints: 1 <= tokens.length <= 104 tokens[i] is either an operator: ""+""; ""-""; ""*""; or ""/""; or an integer in the range [-200; 200]."
Oracle,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Oracle,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Oracle,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
Oracle,159,Longest Substring with At Most Two Distinct Characters,Med,"Hash Table, String, Sliding Window",
Oracle,160,Intersection of Two Linked Lists,Easy,"Hash Table, Linked List, Two Pointers",Given the heads of two singly linked-lists headA and headB; return the node at which the two lists intersect. If the two linked lists have no intersection at all; return null. For example; the following two linked lists begin to intersect at node c1: The test cases are generated such that there are no cycles anywhere in the entire linked structure. Note that the linked lists must retain their original structure after the function returns. Custom Judge: The inputs to the judge are given as follows (your program is not given these inputs): intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node. listA - The first linked list. listB - The second linked list. skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node. skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node. The judge will then create the linked structure based on these inputs and pass the two heads; headA and headB to your program. If you correctly return the intersected node; then your solution will be accepted. Example 1: Input: intersectVal = 8; listA = [4;1;8;4;5]; listB = [5;6;1;8;4;5]; skipA = 2; skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [4;1;8;4;5]. From the head of B; it reads as [5;6;1;8;4;5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words; they point to two different locations in memory; while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory. Example 2: Input: intersectVal = 2; listA = [1;9;1;2;4]; listB = [3;2;4]; skipA = 3; skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [1;9;1;2;4]. From the head of B; it reads as [3;2;4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B. Example 3: Input: intersectVal = 0; listA = [2;6;4]; listB = [1;5]; skipA = 3; skipB = 2 Output: No intersection Explanation: From the head of A; it reads as [2;6;4]. From the head of B; it reads as [1;5]. Since the two lists do not intersect; intersectVal must be 0; while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect; so return null. Constraints: The number of nodes of listA is in the m. The number of nodes of listB is in the n. 1 <= m; n <= 3 * 104 1 <= Node.val <= 105 0 <= skipA <= m 0 <= skipB <= n intersectVal is 0 if listA and listB do not intersect. intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect. Follow up: Could you write a solution that runs in O(m + n) time and use only O(1) memory?
Oracle,165,Compare Version Numbers,Med,"Two Pointers, String","Given two version strings; version1 and version2; compare them. A version string consists of revisions separated by dots '.'. The value of the revision is its integer conversion ignoring leading zeros. To compare version strings; compare their revision values in left-to-right order. If one of the version strings has fewer revisions; treat the missing revision values as 0. Return the following: If version1 < version2; return -1. If version1 > version2; return 1. Otherwise; return 0. Example 1: Input: version1 = ""1.2""; version2 = ""1.10"" Output: -1 Explanation: version1's second revision is ""2"" and version2's second revision is ""10"": 2 < 10; so version1 < version2. Example 2: Input: version1 = ""1.01""; version2 = ""1.001"" Output: 0 Explanation: Ignoring leading zeroes; both ""01"" and ""001"" represent the same integer ""1"". Example 3: Input: version1 = ""1.0""; version2 = ""1.0.0.0"" Output: 0 Explanation: version1 has less revisions; which means every missing revision are treated as ""0"". Constraints: 1 <= version1.length; version2.length <= 500 version1 and version2 only contain digits and '.'. version1 and version2 are valid version numbers. All the given revisions in version1 and version2 can be stored in a 32-bit integer."
Oracle,181,Employees Earning More Than Their Managers,Easy,Database,Table: Employee +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | name | varchar | | salary | int | | managerId | int | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table indicates the ID of an employee; their name; salary; and the ID of their manager. Write a solution to find the employees who earn more than their managers. Return the result table in any order. The result format is in the following example. Example 1: Input: Employee table: +----+-------+--------+-----------+ | id | name | salary | managerId | +----+-------+--------+-----------+ | 1 | Joe | 70000 | 3 | | 2 | Henry | 80000 | 4 | | 3 | Sam | 60000 | Null | | 4 | Max | 90000 | Null | +----+-------+--------+-----------+ Output: +----------+ | Employee | +----------+ | Joe | +----------+ Explanation: Joe is the only employee who earns more than his manager.
Oracle,192,Word Frequency,Med,Shell,Write a bash script to calculate the frequency of each word in a text file words.txt. For simplicity sake; you may assume: words.txt contains only lowercase characters and space ' ' characters. Each word must consist of lowercase characters only. Words are separated by one or more whitespace characters. Example: Assume that words.txt has the following content: the day is sunny the the the sunny is is Your script should output the following; sorted by descending frequency: the 4 is 3 sunny 2 day 1 Note: Don't worry about handling ties; it is guaranteed that each word's frequency count is unique. Could you write it in one-line using Unix pipes?
Oracle,196,Delete Duplicate Emails,Easy,Database,Table: Person +-------------+---------+ | Column Name | Type | +-------------+---------+ | id | int | | email | varchar | +-------------+---------+ id is the primary key (column with unique values) for this table. Each row of this table contains an email. The emails will not contain uppercase letters. Write a solution to delete all duplicate emails; keeping only one unique email with the smallest id. For SQL users; please note that you are supposed to write a DELETE statement and not a SELECT one. For Pandas users; please note that you are supposed to modify Person in place. After running your script; the answer shown is the Person table. The driver will first compile and run your piece of code and then show the Person table. The final order of the Person table does not matter. The result format is in the following example. Example 1: Input: Person table: +----+------------------+ | id | email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | | 3 | john@example.com | +----+------------------+ Output: +----+------------------+ | id | email | +----+------------------+ | 1 | john@example.com | | 2 | bob@example.com | +----+------------------+ Explanation: john@example.com is repeated two times. We keep the row with the smallest Id = 1.
Oracle,226,Invert Binary Tree,Easy,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; invert the tree; and return its root. Example 1: Input: root = [4;2;7;1;3;6;9] Output: [4;7;2;9;6;3;1] Example 2: Input: root = [2;1;3] Output: [2;3;1] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Oracle,227,Basic Calculator II,Med,"Math, String, Stack","Given a string s which represents an expression; evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""3+2*2"" Output: 7 Example 2: Input: s = "" 3/2 "" Output: 1 Example 3: Input: s = "" 3+5 / 2 "" Output: 5 Constraints: 1 <= s.length <= 3 * 105 s consists of integers and operators ('+'; '-'; '*'; '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0; 231 - 1]. The answer is guaranteed to fit in a 32-bit integer."
Oracle,235,Lowest Common Ancestor of a Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given a binary search tree (BST); find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [2;1]; p = 2; q = 1 Output: 2 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.
Oracle,269,Alien Dictionary,Hard,"Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort",
Oracle,271,Encode and Decode Strings,Med,"Array, String, Design",
Oracle,289,Game of Life,Med,"Array, Matrix, Simulation","According to Wikipedia's article: ""The Game of Life; also known simply as Life; is a cellular automaton devised by the British mathematician John Horton Conway in 1970."" The board is made up of an m x n grid of cells; where each cell has an initial state: live (represented by a 1) or dead (represented by a 0). Each cell interacts with its eight neighbors (horizontal; vertical; diagonal) using the following four rules (taken from the above Wikipedia article): Any live cell with fewer than two live neighbors dies as if caused by under-population. Any live cell with two or three live neighbors lives on to the next generation. Any live cell with more than three live neighbors dies; as if by over-population. Any dead cell with exactly three live neighbors becomes a live cell; as if by reproduction. The next state of the board is determined by applying the above rules simultaneously to every cell in the current state of the m x n grid board. In this process; births and deaths occur simultaneously. Given the current state of the board; update the board to reflect its next state. Note that you do not need to return anything. Example 1: Input: board = [[0;1;0];[0;0;1];[1;1;1];[0;0;0]] Output: [[0;0;0];[1;0;1];[0;1;1];[0;1;0]] Example 2: Input: board = [[1;1];[1;0]] Output: [[1;1];[1;1]] Constraints: m == board.length n == board[i].length 1 <= m; n <= 25 board[i][j] is 0 or 1. Follow up: Could you solve it in-place? Remember that the board needs to be updated simultaneously: You cannot update some cells first and then use their updated values to update other cells. In this question; we represent the board using a 2D array. In principle; the board is infinite; which would cause problems when the active area encroaches upon the border of the array (i.e.; live cells reach the border). How would you address these problems?"
Oracle,328,Odd Even Linked List,Med,Linked List,Given the head of a singly linked list; group all the nodes with odd indices together followed by the nodes with even indices; and return the reordered list. The first node is considered odd; and the second node is even; and so on. Note that the relative order inside both the even and odd groups should remain as it was in the input. You must solve the problem in O(1) extra space complexity and O(n) time complexity. Example 1: Input: head = [1;2;3;4;5] Output: [1;3;5;2;4] Example 2: Input: head = [2;1;3;5;6;4;7] Output: [2;3;6;7;1;5;4] Constraints: The number of nodes in the linked list is in the range [0; 104]. -106 <= Node.val <= 106
Oracle,345,Reverse Vowels of a String,Easy,"Two Pointers, String","Given a string s; reverse only all the vowels in the string and return it. The vowels are 'a'; 'e'; 'i'; 'o'; and 'u'; and they can appear in both lower and upper cases; more than once. Example 1: Input: s = ""IceCreAm"" Output: ""AceCreIm"" Explanation: The vowels in s are ['I'; 'e'; 'e'; 'A']. On reversing the vowels; s becomes ""AceCreIm"". Example 2: Input: s = ""leetcode"" Output: ""leotcede"" Constraints: 1 <= s.length <= 3 * 105 s consist of printable ASCII characters."
Oracle,365,Water and Jug Problem,Med,"Math, Depth-First Search, Breadth-First Search",You are given two jugs with capacities x liters and y liters. You have an infinite water supply. Return whether the total amount of water in both jugs may reach target using the following operations: Fill either jug completely with water. Completely empty either jug. Pour water from one jug into another until the receiving jug is full; or the transferring jug is empty. Example 1: Input: x = 3; y = 5; target = 4 Output: true Explanation: Follow these steps to reach a total of 4 liters: Fill the 5-liter jug (0; 5). Pour from the 5-liter jug into the 3-liter jug; leaving 2 liters (3; 2). Empty the 3-liter jug (0; 2). Transfer the 2 liters from the 5-liter jug to the 3-liter jug (2; 0). Fill the 5-liter jug again (2; 5). Pour from the 5-liter jug into the 3-liter jug until the 3-liter jug is full. This leaves 4 liters in the 5-liter jug (3; 4). Empty the 3-liter jug. Now; you have exactly 4 liters in the 5-liter jug (0; 4). Reference: The Die Hard example. Example 2: Input: x = 2; y = 6; target = 5 Output: false Example 3: Input: x = 1; y = 2; target = 3 Output: true Explanation: Fill both jugs. The total amount of water in both jugs is equal to 3 now. Constraints: 1 <= x; y; target <= 103
Oracle,373,Find K Pairs with Smallest Sums,Med,"Array, Heap (Priority Queue)",You are given two integer arrays nums1 and nums2 sorted in non-decreasing order and an integer k. Define a pair (u; v) which consists of one element from the first array and one element from the second array. Return the k pairs (u1; v1); (u2; v2); ...; (uk; vk) with the smallest sums. Example 1: Input: nums1 = [1;7;11]; nums2 = [2;4;6]; k = 3 Output: [[1;2];[1;4];[1;6]] Explanation: The first 3 pairs are returned from the sequence: [1;2];[1;4];[1;6];[7;2];[7;4];[11;2];[7;6];[11;4];[11;6] Example 2: Input: nums1 = [1;1;2]; nums2 = [1;2;3]; k = 2 Output: [[1;1];[1;1]] Explanation: The first 2 pairs are returned from the sequence: [1;1];[1;1];[1;2];[2;1];[1;2];[2;2];[1;3];[1;3];[2;3] Constraints: 1 <= nums1.length; nums2.length <= 105 -109 <= nums1[i]; nums2[i] <= 109 nums1 and nums2 both are sorted in non-decreasing order. 1 <= k <= 104 k <= nums1.length * nums2.length
Oracle,377,Combination Sum IV,Med,"Array, Dynamic Programming",Given an array of distinct integers nums and a target integer target; return the number of possible combinations that add up to target. The test cases are generated so that the answer can fit in a 32-bit integer. Example 1: Input: nums = [1;2;3]; target = 4 Output: 7 Explanation: The possible combination ways are: (1; 1; 1; 1) (1; 1; 2) (1; 2; 1) (1; 3) (2; 1; 1) (2; 2) (3; 1) Note that different sequences are counted as different combinations. Example 2: Input: nums = [9]; target = 3 Output: 0 Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 1000 All the elements of nums are unique. 1 <= target <= 1000 Follow up: What if negative numbers are allowed in the given array? How does it change the problem? What limitation we need to add to the question to allow negative numbers?
Oracle,415,Add Strings,Easy,"Math, String, Simulation","Given two non-negative integers; num1 and num2 represented as string; return the sum of num1 and num2 as a string. You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly. Example 1: Input: num1 = ""11""; num2 = ""123"" Output: ""134"" Example 2: Input: num1 = ""456""; num2 = ""77"" Output: ""533"" Example 3: Input: num1 = ""0""; num2 = ""0"" Output: ""0"" Constraints: 1 <= num1.length; num2.length <= 104 num1 and num2 consist of only digits. num1 and num2 don't have any leading zeros except for the zero itself."
Oracle,416,Partition Equal Subset Sum,Med,"Array, Dynamic Programming",Given an integer array nums; return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise. Example 1: Input: nums = [1;5;11;5] Output: true Explanation: The array can be partitioned as [1; 5; 5] and [11]. Example 2: Input: nums = [1;2;3;5] Output: false Explanation: The array cannot be partitioned into equal sum subsets. Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 100
Oracle,435,Non-overlapping Intervals,Med,"Array, Dynamic Programming, Greedy, Sorting",Given an array of intervals intervals where intervals[i] = [starti; endi]; return the minimum number of intervals you need to remove to make the rest of the intervals non-overlapping. Note that intervals which only touch at a point are non-overlapping. For example; [1; 2] and [2; 3] are non-overlapping. Example 1: Input: intervals = [[1;2];[2;3];[3;4];[1;3]] Output: 1 Explanation: [1;3] can be removed and the rest of the intervals are non-overlapping. Example 2: Input: intervals = [[1;2];[1;2];[1;2]] Output: 2 Explanation: You need to remove two [1;2] to make the rest of the intervals non-overlapping. Example 3: Input: intervals = [[1;2];[2;3]] Output: 0 Explanation: You don't need to remove any of the intervals since they're already non-overlapping. Constraints: 1 <= intervals.length <= 105 intervals[i].length == 2 -5 * 104 <= starti < endi <= 5 * 104
Oracle,451,Sort Characters By Frequency,Med,"Hash Table, String, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given a string s; sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers; return any of them. Example 1: Input: s = ""tree"" Output: ""eert"" Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore ""eetr"" is also a valid answer. Example 2: Input: s = ""cccaaa"" Output: ""aaaccc"" Explanation: Both 'c' and 'a' appear three times; so both ""cccaaa"" and ""aaaccc"" are valid answers. Note that ""cacaca"" is incorrect; as the same characters must be together. Example 3: Input: s = ""Aabb"" Output: ""bbAa"" Explanation: ""bbaA"" is also a valid answer; but ""Aabb"" is incorrect. Note that 'A' and 'a' are treated as two different characters. Constraints: 1 <= s.length <= 5 * 105 s consists of uppercase and lowercase English letters and digits."
Oracle,485,Max Consecutive Ones,Easy,Array,Given a binary array nums; return the maximum number of consecutive 1's in the array. Example 1: Input: nums = [1;1;0;1;1;1] Output: 3 Explanation: The first two digits or the last three digits are consecutive 1s. The maximum number of consecutive 1s is 3. Example 2: Input: nums = [1;0;1;1;0;1] Output: 2 Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1.
Oracle,496,Next Greater Element I,Easy,"Array, Hash Table, Stack, Monotonic Stack",The next greater element of some element x in an array is the first greater element that is to the right of x in the same array. You are given two distinct 0-indexed integer arrays nums1 and nums2; where nums1 is a subset of nums2. For each 0 <= i < nums1.length; find the index j such that nums1[i] == nums2[j] and determine the next greater element of nums2[j] in nums2. If there is no next greater element; then the answer for this query is -1. Return an array ans of length nums1.length such that ans[i] is the next greater element as described above. Example 1: Input: nums1 = [4;1;2]; nums2 = [1;3;4;2] Output: [-1;3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 4 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. - 1 is underlined in nums2 = [1;3;4;2]. The next greater element is 3. - 2 is underlined in nums2 = [1;3;4;2]. There is no next greater element; so the answer is -1. Example 2: Input: nums1 = [2;4]; nums2 = [1;2;3;4] Output: [3;-1] Explanation: The next greater element for each value of nums1 is as follows: - 2 is underlined in nums2 = [1;2;3;4]. The next greater element is 3. - 4 is underlined in nums2 = [1;2;3;4]. There is no next greater element; so the answer is -1. Constraints: 1 <= nums1.length <= nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 104 All integers in nums1 and nums2 are unique. All the integers of nums1 also appear in nums2. Follow up: Could you find an O(nums1.length + nums2.length) solution?
Oracle,505,The Maze II,Med,"Array, Depth-First Search, Breadth-First Search, Graph, Heap (Priority Queue), Matrix, Shortest Path",
Oracle,1721,Swapping Nodes in a Linked List,Med,"Array, Simulation",You are the operator of a Centennial Wheel that has four gondolas; and each gondola has room for up to four people. You have the ability to rotate the gondolas counterclockwise; which costs you runningCost dollars. You are given an array customers of length n where customers[i] is the number of new customers arriving just before the ith rotation (0-indexed). This means you must rotate the wheel i times before the customers[i] customers arrive. You cannot make customers wait if there is room in the gondola. Each customer pays boardingCost dollars when they board on the gondola closest to the ground and will exit once that gondola reaches the ground again. You can stop the wheel at any time; including before serving all customers. If you decide to stop serving customers; all subsequent rotations are free in order to get all the customers down safely. Note that if there are currently more than four customers waiting at the wheel; only four will board the gondola; and the rest will wait for the next rotation. Return the minimum number of rotations you need to perform to maximize your profit. If there is no scenario where the profit is positive; return -1. Example 1: Input: customers = [8;3]; boardingCost = 5; runningCost = 6 Output: 3 Explanation: The numbers written on the gondolas are the number of people currently there. 1. 8 customers arrive; 4 board and 4 wait for the next gondola; the wheel rotates. Current profit is 4 * $5 - 1 * $6 = $14. 2. 3 customers arrive; the 4 waiting board the wheel and the other 3 wait; the wheel rotates. Current profit is 8 * $5 - 2 * $6 = $28. 3. The final 3 customers board the gondola; the wheel rotates. Current profit is 11 * $5 - 3 * $6 = $37. The highest profit was $37 after rotating the wheel 3 times. Example 2: Input: customers = [10;9;6]; boardingCost = 6; runningCost = 4 Output: 7 Explanation: 1. 10 customers arrive; 4 board and 6 wait for the next gondola; the wheel rotates. Current profit is 4 * $6 - 1 * $4 = $20. 2. 9 customers arrive; 4 board and 11 wait (2 originally waiting; 9 newly waiting); the wheel rotates. Current profit is 8 * $6 - 2 * $4 = $40. 3. The final 6 customers arrive; 4 board and 13 wait; the wheel rotates. Current profit is 12 * $6 - 3 * $4 = $60. 4. 4 board and 9 wait; the wheel rotates. Current profit is 16 * $6 - 4 * $4 = $80. 5. 4 board and 5 wait; the wheel rotates. Current profit is 20 * $6 - 5 * $4 = $100. 6. 4 board and 1 waits; the wheel rotates. Current profit is 24 * $6 - 6 * $4 = $120. 7. 1 boards; the wheel rotates. Current profit is 25 * $6 - 7 * $4 = $122. The highest profit was $122 after rotating the wheel 7 times. Example 3: Input: customers = [3;4;0;5;1]; boardingCost = 1; runningCost = 92 Output: -1 Explanation: 1. 3 customers arrive; 3 board and 0 wait; the wheel rotates. Current profit is 3 * $1 - 1 * $92 = -$89. 2. 4 customers arrive; 4 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 2 * $92 = -$177. 3. 0 customers arrive; 0 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 3 * $92 = -$269. 4. 5 customers arrive; 4 board and 1 waits; the wheel rotates. Current profit is 11 * $1 - 4 * $92 = -$357. 5. 1 customer arrives; 2 board and 0 wait; the wheel rotates. Current profit is 13 * $1 - 5 * $92 = -$447. The profit was never positive; so return -1. Constraints: n == customers.length 1 <= n <= 105 0 <= customers[i] <= 50 1 <= boardingCost; runningCost <= 100
Oracle,545,Boundary of Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",
Oracle,567,Permutation in String,Med,"Hash Table, Two Pointers, String, Sliding Window","Given two strings s1 and s2; return true if s2 contains a permutation of s1; or false otherwise. In other words; return true if one of s1's permutations is the substring of s2. Example 1: Input: s1 = ""ab""; s2 = ""eidbaooo"" Output: true Explanation: s2 contains one permutation of s1 (""ba""). Example 2: Input: s1 = ""ab""; s2 = ""eidboaoo"" Output: false Constraints: 1 <= s1.length; s2.length <= 104 s1 and s2 consist of lowercase English letters."
Oracle,652,Find Duplicate Subtrees,Med,"Hash Table, Tree, Depth-First Search, Binary Tree",Given the root of a binary tree; return all duplicate subtrees. For each kind of duplicate subtrees; you only need to return the root node of any one of them. Two trees are duplicate if they have the same structure with the same node values. Example 1: Input: root = [1;2;3;4;null;2;4;null;null;4] Output: [[2;4];[4]] Example 2: Input: root = [2;1;1] Output: [[1]] Example 3: Input: root = [2;2;2;3;null;3;null] Output: [[2;3];[3]] Constraints: The number of the nodes in the tree will be in the range [1; 5000] -200 <= Node.val <= 200
Oracle,695,Max Area of Island,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island. Return the maximum area of an island in grid. If there is no island; return 0. Example 1: Input: grid = [[0;0;1;0;0;0;0;1;0;0;0;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;1;1;0;1;0;0;0;0;0;0;0;0];[0;1;0;0;1;1;0;0;1;0;1;0;0];[0;1;0;0;1;1;0;0;1;1;1;0;0];[0;0;0;0;0;0;0;0;0;0;1;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;0;0;0;0;0;0;1;1;0;0;0;0]] Output: 6 Explanation: The answer is not 11; because the island must be connected 4-directionally. Example 2: Input: grid = [[0;0;0;0;0;0;0;0]] Output: 0 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 50 grid[i][j] is either 0 or 1.
Oracle,713,Subarray Product Less Than K,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of integers nums and an integer k; return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k. Example 1: Input: nums = [10;5;2;6]; k = 100 Output: 8 Explanation: The 8 subarrays that have product less than 100 are: [10]; [5]; [2]; [6]; [10; 5]; [5; 2]; [2; 6]; [5; 2; 6] Note that [10; 5; 2] is not included as the product of 100 is not strictly less than k. Example 2: Input: nums = [1;2;3]; k = 0 Output: 0 Constraints: 1 <= nums.length <= 3 * 104 1 <= nums[i] <= 1000 0 <= k <= 106
Oracle,716,Max Stack,Hard,"Linked List, Stack, Design, Doubly-Linked List, Ordered Set",
Oracle,704,Binary Search,Easy,,
Oracle,814,Binary Tree Pruning,Med,"Array, Prefix Sum",You are given an array nums. You can rotate it by a non-negative integer k so that the array becomes [nums[k]; nums[k + 1]; ... nums[nums.length - 1]; nums[0]; nums[1]; ...; nums[k-1]]. Afterward; any entries that are less than or equal to their index are worth one point. For example; if we have nums = [2;4;1;3;0]; and we rotate by k = 2; it becomes [1;3;0;2;4]. This is worth 3 points because 1 > 0 [no points]; 3 > 1 [no points]; 0 <= 2 [one point]; 2 <= 3 [one point]; 4 <= 4 [one point]. Return the rotation index k that corresponds to the highest score we can achieve if we rotated nums by it. If there are multiple answers; return the smallest such index k. Example 1: Input: nums = [2;3;1;4;0] Output: 3 Explanation: Scores for each k are listed below: k = 0; nums = [2;3;1;4;0]; score 2 k = 1; nums = [3;1;4;0;2]; score 3 k = 2; nums = [1;4;0;2;3]; score 3 k = 3; nums = [4;0;2;3;1]; score 4 k = 4; nums = [0;2;3;1;4]; score 3 So we should choose k = 3; which has the highest score. Example 2: Input: nums = [1;3;0;2;4] Output: 0 Explanation: nums will always have 3 points no matter how it shifts. So we will choose the smallest k; which is 0. Constraints: 1 <= nums.length <= 105 0 <= nums[i] < nums.length
Oracle,834,Sum of Distances in Tree,Hard,"String, Backtracking, Enumeration","We had some 2-dimensional coordinates; like ""(1; 3)"" or ""(2; 0.5)"". Then; we removed all commas; decimal points; and spaces and ended up with the string s. For example; ""(1; 3)"" becomes s = ""(13)"" and ""(2; 0.5)"" becomes s = ""(205)"". Return a list of strings representing all possibilities for what our original coordinates could have been. Our original representation never had extraneous zeroes; so we never started with numbers like ""00""; ""0.0""; ""0.00""; ""1.0""; ""001""; ""00.01""; or any other number that can be represented with fewer digits. Also; a decimal point within a number never occurs without at least one digit occurring before it; so we never started with numbers like "".1"". The final answer list can be returned in any order. All coordinates in the final answer have exactly one space between them (occurring after the comma.) Example 1: Input: s = ""(123)"" Output: [""(1; 2.3)"";""(1; 23)"";""(1.2; 3)"";""(12; 3)""] Example 2: Input: s = ""(0123)"" Output: [""(0; 1.23)"";""(0; 12.3)"";""(0; 123)"";""(0.1; 2.3)"";""(0.1; 23)"";""(0.12; 3)""] Explanation: 0.0; 00; 0001 or 00.01 are not allowed. Example 3: Input: s = ""(00011)"" Output: [""(0; 0.011)"";""(0.001; 1)""] Constraints: 4 <= s.length <= 12 s[0] == '(' and s[s.length - 1] == ')'. The rest of s are digits."
Oracle,836,Rectangle Overlap,Easy,Dynamic Programming,"Your car starts at position 0 and speed +1 on an infinite number line. Your car can go into negative positions. Your car drives automatically according to a sequence of instructions 'A' (accelerate) and 'R' (reverse): When you get an instruction 'A'; your car does the following: position += speed speed *= 2 When you get an instruction 'R'; your car does the following: If your speed is positive then speed = -1 otherwise speed = 1 Your position stays the same. For example; after commands ""AAR""; your car goes to positions 0 --> 1 --> 3 --> 3; and your speed goes to 1 --> 2 --> 4 --> -1. Given a target position target; return the length of the shortest sequence of instructions to get there. Example 1: Input: target = 3 Output: 2 Explanation: The shortest instruction sequence is ""AA"". Your position goes from 0 --> 1 --> 3. Example 2: Input: target = 6 Output: 5 Explanation: The shortest instruction sequence is ""AAARA"". Your position goes from 0 --> 1 --> 3 --> 7 --> 7 --> 6. Constraints: 1 <= target <= 104"
Oracle,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
Oracle,890,Find and Replace Pattern,Med,"Array, Greedy",At a lemonade stand; each lemonade costs $5. Customers are standing in a queue to buy from you and order one at a time (in the order specified by bills). Each customer will only buy one lemonade and pay with either a $5; $10; or $20 bill. You must provide the correct change to each customer so that the net transaction is that the customer pays $5. Note that you do not have any change in hand at first. Given an integer array bills where bills[i] is the bill the ith customer pays; return true if you can provide every customer with the correct change; or false otherwise. Example 1: Input: bills = [5;5;5;10;20] Output: true Explanation: From the first 3 customers; we collect three $5 bills in order. From the fourth customer; we collect a $10 bill and give back a $5. From the fifth customer; we give a $10 bill and a $5 bill. Since all customers got correct change; we output true. Example 2: Input: bills = [5;5;10;10;20] Output: false Explanation: From the first two customers in order; we collect two $5 bills. For the next two customers in order; we collect a $10 bill and give back a $5 bill. For the last customer; we can not give the change of $15 back because we only have two $10 bills. Since not every customer received the correct change; the answer is false. Constraints: 1 <= bills.length <= 105 bills[i] is either 5; 10; or 20.
Oracle,909,Snakes and Ladders,Med,"Array, Math, Dynamic Programming, Game Theory",Alice and Bob play a game with piles of stones. There are an even number of piles arranged in a row; and each pile has a positive integer number of stones piles[i]. The objective of the game is to end with the most stones. The total number of stones across all the piles is odd; so there are no ties. Alice and Bob take turns; with Alice starting first. Each turn; a player takes the entire pile of stones either from the beginning or from the end of the row. This continues until there are no more piles left; at which point the person with the most stones wins. Assuming Alice and Bob play optimally; return true if Alice wins the game; or false if Bob wins. Example 1: Input: piles = [5;3;4;5] Output: true Explanation: Alice starts first; and can only take the first 5 or the last 5. Say she takes the first 5; so that the row becomes [3; 4; 5]. If Bob takes 3; then the board is [4; 5]; and Alice takes 5 to win with 10 points. If Bob takes the last 5; then the board is [3; 4]; and Alice takes 4 to win with 9 points. This demonstrated that taking the first 5 was a winning move for Alice; so we return true. Example 2: Input: piles = [3;7;2;3] Output: true Constraints: 2 <= piles.length <= 500 piles.length is even. 1 <= piles[i] <= 500 sum(piles[i]) is odd.
Oracle,912,Sort an Array,Med,"Array, Math, Binary Search, Prefix Sum, Randomized","You are given a 0-indexed array of positive integers w where w[i] describes the weight of the ith index. You need to implement the function pickIndex(); which randomly picks an index in the range [0; w.length - 1] (inclusive) and returns it. The probability of picking an index i is w[i] / sum(w). For example; if w = [1; 3]; the probability of picking index 0 is 1 / (1 + 3) = 0.25 (i.e.; 25%); and the probability of picking index 1 is 3 / (1 + 3) = 0.75 (i.e.; 75%). Example 1: Input [""Solution"";""pickIndex""] [[[1]];[]] Output [null;0] Explanation Solution solution = new Solution([1]); solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w. Example 2: Input [""Solution"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex"";""pickIndex""] [[[1;3]];[];[];[];[];[]] Output [null;1;1;1;1;0] Explanation Solution solution = new Solution([1; 3]); solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4. solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 1 solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4. Since this is a randomization problem; multiple answers are allowed. All of the following outputs can be considered correct: [null;1;1;1;1;0] [null;1;1;1;1;1] [null;1;1;1;0;0] [null;1;1;1;0;1] [null;1;0;1;0;0] ...... and so on. Constraints: 1 <= w.length <= 104 1 <= w[i] <= 105 pickIndex will be called at most 104 times."
Oracle,939,Minimum Area Rectangle,Med,"String, Dynamic Programming, Prefix Sum","You are given a string s of length n where s[i] is either: 'D' means decreasing; or 'I' means increasing. A permutation perm of n + 1 integers of all the integers in the range [0; n] is called a valid permutation if for all valid i: If s[i] == 'D'; then perm[i] > perm[i + 1]; and If s[i] == 'I'; then perm[i] < perm[i + 1]. Return the number of valid permutations perm. Since the answer may be large; return it modulo 109 + 7. Example 1: Input: s = ""DID"" Output: 5 Explanation: The 5 valid permutations of (0; 1; 2; 3) are: (1; 0; 3; 2) (2; 0; 3; 1) (2; 1; 3; 0) (3; 0; 2; 1) (3; 1; 2; 0) Example 2: Input: s = ""D"" Output: 1 Constraints: n == s.length 1 <= n <= 200 s[i] is either 'I' or 'D'."
Oracle,968,Binary Tree Cameras,Hard,"Array, Math, Divide and Conquer",An array nums of length n is beautiful if: nums is a permutation of the integers in the range [1; n]. For every 0 <= i < j < n; there is no index k with i < k < j where 2 * nums[k] == nums[i] + nums[j]. Given the integer n; return any beautiful array nums of length n. There will be at least one valid answer for the given n. Example 1: Input: n = 4 Output: [2;1;4;3] Example 2: Input: n = 5 Output: [3;1;2;5;4] Constraints: 1 <= n <= 1000
Oracle,969,Pancake Sorting,Med,"Design, Queue, Data Stream","You have a RecentCounter class which counts the number of recent requests within a certain time frame. Implement the RecentCounter class: RecentCounter() Initializes the counter with zero recent requests. int ping(int t) Adds a new request at time t; where t represents some time in milliseconds; and returns the number of requests that has happened in the past 3000 milliseconds (including the new request). Specifically; return the number of requests that have happened in the inclusive range [t - 3000; t]. It is guaranteed that every call to ping uses a strictly larger value of t than the previous call. Example 1: Input [""RecentCounter""; ""ping""; ""ping""; ""ping""; ""ping""] [[]; [1]; [100]; [3001]; [3002]] Output [null; 1; 2; 3; 3] Explanation RecentCounter recentCounter = new RecentCounter(); recentCounter.ping(1); // requests = [1]; range is [-2999;1]; return 1 recentCounter.ping(100); // requests = [1; 100]; range is [-2900;100]; return 2 recentCounter.ping(3001); // requests = [1; 100; 3001]; range is [1;3001]; return 3 recentCounter.ping(3002); // requests = [1; 100; 3001; 3002]; range is [2;3002]; return 3 Constraints: 1 <= t <= 109 Each test case will call ping with strictly increasing values of t. At most 104 calls will be made to ping."
Oracle,977,Squares of a Sorted Array,Easy,"String, Dynamic Programming","Given a string s; return the number of distinct non-empty subsequences of s. Since the answer may be very large; return it modulo 109 + 7. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not. Example 1: Input: s = ""abc"" Output: 7 Explanation: The 7 distinct subsequences are ""a""; ""b""; ""c""; ""ab""; ""ac""; ""bc""; and ""abc"". Example 2: Input: s = ""aba"" Output: 6 Explanation: The 6 distinct subsequences are ""a""; ""b""; ""ab""; ""aa""; ""ba""; and ""aba"". Example 3: Input: s = ""aaa"" Output: 3 Explanation: The 3 distinct subsequences are ""a""; ""aa"" and ""aaa"". Constraints: 1 <= s.length <= 2000 s consists of lowercase English letters."
Oracle,1002,Find Common Characters,Easy,"Array, Stack, Monotonic Stack",A ramp in an integer array nums is a pair (i; j) for which i < j and nums[i] <= nums[j]. The width of such a ramp is j - i. Given an integer array nums; return the maximum width of a ramp in nums. If there is no ramp in nums; return 0. Example 1: Input: nums = [6;0;8;2;1;5] Output: 4 Explanation: The maximum width ramp is achieved at (i; j) = (1; 5): nums[1] = 0 and nums[5] = 5. Example 2: Input: nums = [9;8;1;0;1;9;4;0;4;1] Output: 7 Explanation: The maximum width ramp is achieved at (i; j) = (2; 9): nums[2] = 1 and nums[9] = 1. Constraints: 2 <= nums.length <= 5 * 104 0 <= nums[i] <= 5 * 104
Oracle,1026,Maximum Difference Between Node and Ancestor,Med,"String, Greedy","Given two integers a and b; return any string s such that: s has length a + b and contains exactly a 'a' letters; and exactly b 'b' letters; The substring 'aaa' does not occur in s; and The substring 'bbb' does not occur in s. Example 1: Input: a = 1; b = 2 Output: ""abb"" Explanation: ""abb""; ""bab"" and ""bba"" are all correct answers. Example 2: Input: a = 4; b = 1 Output: ""aabaa"" Constraints: 0 <= a; b <= 100 It is guaranteed such an s exists for the given a and b."
Oracle,1287,Element Appearing More Than 25% In Sorted Array,Easy,Array,A bus has n stops numbered from 0 to n - 1 that form a circle. We know the distance between all pairs of neighboring stops where distance[i] is the distance between the stops number i and (i + 1) % n. The bus goes along both directions i.e. clockwise and counterclockwise. Return the shortest distance between the given start and destination stops. Example 1: Input: distance = [1;2;3;4]; start = 0; destination = 1 Output: 1 Explanation: Distance between 0 and 1 is 1 or 9; minimum is 1. Example 2: Input: distance = [1;2;3;4]; start = 0; destination = 2 Output: 3 Explanation: Distance between 0 and 2 is 3 or 7; minimum is 3. Example 3: Input: distance = [1;2;3;4]; start = 0; destination = 3 Output: 4 Explanation: Distance between 0 and 3 is 6 or 4; minimum is 4. Constraints: 1 <= n <= 10^4 distance.length == n 0 <= start; destination < n 0 <= distance[i] <= 10^4
Oracle,2303,Calculate Amount Paid in Taxes,Easy,"Hash Table, String, Rolling Hash, Counting, Hash Function",
Oracle,1251,Average Selling Price,Easy,"Two Pointers, String, Dynamic Programming, Greedy, Rolling Hash, Hash Function","You are given a string text. You should split it to k substrings (subtext1; subtext2; ...; subtextk) such that: subtexti is a non-empty string. The concatenation of all the substrings is equal to text (i.e.; subtext1 + subtext2 + ... + subtextk == text). subtexti == subtextk - i + 1 for all valid values of i (i.e.; 1 <= i <= k). Return the largest possible value of k. Example 1: Input: text = ""ghiabcdefhelloadamhelloabcdefghi"" Output: 7 Explanation: We can split the string on ""(ghi)(abcdef)(hello)(adam)(hello)(abcdef)(ghi)"". Example 2: Input: text = ""merchant"" Output: 1 Explanation: We can split the string on ""(merchant)"". Example 3: Input: text = ""antaprezatepzapreanta"" Output: 11 Explanation: We can split the string on ""(a)(nt)(a)(pre)(za)(tep)(za)(pre)(a)(nt)(a)"". Constraints: 1 <= text.length <= 1000 text consists only of lowercase English characters."
Oracle,2263,Make Array Non-decreasing or Non-increasing,Hard,"Array, Binary Search, Greedy, Sorting",You have n computers. You are given the integer n and a 0-indexed integer array batteries where the ith battery can run a computer for batteries[i] minutes. You are interested in running all n computers simultaneously using the given batteries. Initially; you can insert at most one battery into each computer. After that and at any integer time moment; you can remove a battery from a computer and insert another battery any number of times. The inserted battery can be a totally new battery or a battery from another computer. You may assume that the removing and inserting processes take no time. Note that the batteries cannot be recharged. Return the maximum number of minutes you can run all the n computers simultaneously. Example 1: Input: n = 2; batteries = [3;3;3] Output: 4 Explanation: Initially; insert battery 0 into the first computer and battery 1 into the second computer. After two minutes; remove battery 1 from the second computer and insert battery 2 instead. Note that battery 1 can still run for one minute. At the end of the third minute; battery 0 is drained; and you need to remove it from the first computer and insert battery 1 instead. By the end of the fourth minute; battery 1 is also drained; and the first computer is no longer running. We can run the two computers simultaneously for at most 4 minutes; so we return 4. Example 2: Input: n = 2; batteries = [1;1;1;1] Output: 2 Explanation: Initially; insert battery 0 into the first computer and battery 2 into the second computer. After one minute; battery 0 and battery 2 are drained so you need to remove them and insert battery 1 into the first computer and battery 3 into the second computer. After another minute; battery 1 and battery 3 are also drained so the first and second computers are no longer running. We can run the two computers simultaneously for at most 2 minutes; so we return 2. Constraints: 1 <= n <= batteries.length <= 105 1 <= batteries[i] <= 109
Oracle,1537,Get the Maximum Score,Hard,"String, Prefix Sum","Given a string s of zeros and ones; return the maximum score after splitting the string into two non-empty substrings (i.e. left substring and right substring). The score after splitting a string is the number of zeros in the left substring plus the number of ones in the right substring. Example 1: Input: s = ""011101"" Output: 5 Explanation: All possible ways of splitting s into two non-empty substrings are: left = ""0"" and right = ""11101""; score = 1 + 4 = 5 left = ""01"" and right = ""1101""; score = 1 + 3 = 4 left = ""011"" and right = ""101""; score = 1 + 2 = 3 left = ""0111"" and right = ""01""; score = 1 + 1 = 2 left = ""01110"" and right = ""1""; score = 2 + 1 = 3 Example 2: Input: s = ""00111"" Output: 5 Explanation: When left = ""00"" and right = ""111""; we get the maximum score = 2 + 3 = 5 Example 3: Input: s = ""1111"" Output: 3 Constraints: 2 <= s.length <= 500 The string s consists of characters '0' and '1' only."
Oracle,1547,Minimum Cost to Cut a Stick,Hard,"Array, Hash Table, String","You are given the array paths; where paths[i] = [cityAi; cityBi] means there exists a direct path going from cityAi to cityBi. Return the destination city; that is; the city without any path outgoing to another city. It is guaranteed that the graph of paths forms a line without any loop; therefore; there will be exactly one destination city. Example 1: Input: paths = [[""London"";""New York""];[""New York"";""Lima""];[""Lima"";""Sao Paulo""]] Output: ""Sao Paulo"" Explanation: Starting at ""London"" city you will reach ""Sao Paulo"" city which is the destination city. Your trip consist of: ""London"" -> ""New York"" -> ""Lima"" -> ""Sao Paulo"". Example 2: Input: paths = [[""B"";""C""];[""D"";""B""];[""C"";""A""]] Output: ""A"" Explanation: All possible trips are: ""D"" -> ""B"" -> ""C"" -> ""A"". ""B"" -> ""C"" -> ""A"". ""C"" -> ""A"". ""A"". Clearly the destination city is ""A"". Example 3: Input: paths = [[""A"";""Z""]] Output: ""Z"" Constraints: 1 <= paths.length <= 100 paths[i].length == 2 1 <= cityAi.length; cityBi.length <= 10 cityAi != cityBi All strings consist of lowercase and uppercase English letters and the space character."
Oracle,1712,Ways to Split Array Into Three Subarrays,Med,Database,
Oracle,1802,Maximum Value at a Given Index in a Bounded Array,Med,"Array, Stack, Queue, Simulation",The school cafeteria offers circular and square sandwiches at lunch break; referred to by numbers 0 and 1 respectively. All students stand in a queue. Each student either prefers square or circular sandwiches. The number of sandwiches in the cafeteria is equal to the number of students. The sandwiches are placed in a stack. At each step: If the student at the front of the queue prefers the sandwich on the top of the stack; they will take it and leave the queue. Otherwise; they will leave it and go to the queue's end. This continues until none of the queue students want to take the top sandwich and are thus unable to eat. You are given two integer arrays students and sandwiches where sandwiches[i] is the type of the i​​​​​​th sandwich in the stack (i = 0 is the top of the stack) and students[j] is the preference of the j​​​​​​th student in the initial queue (j = 0 is the front of the queue). Return the number of students that are unable to eat. Example 1: Input: students = [1;1;0;0]; sandwiches = [0;1;0;1] Output: 0 Explanation: - Front student leaves the top sandwich and returns to the end of the line making students = [1;0;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;0;1;1]. - Front student takes the top sandwich and leaves the line making students = [0;1;1] and sandwiches = [1;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [1;1;0]. - Front student takes the top sandwich and leaves the line making students = [1;0] and sandwiches = [0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;1]. - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = [1]. - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = []. Hence all students are able to eat. Example 2: Input: students = [1;1;1;0;0;1]; sandwiches = [1;0;0;0;1;1] Output: 3 Constraints: 1 <= students.length; sandwiches.length <= 100 students.length == sandwiches.length sandwiches[i] is 0 or 1. students[i] is 0 or 1.
Oracle,1823,Find the Winner of the Circular Game,Med,"String, Counting","You are given a string s of even length. Split this string into two halves of equal lengths; and let a be the first half and b be the second half. Two strings are alike if they have the same number of vowels ('a'; 'e'; 'i'; 'o'; 'u'; 'A'; 'E'; 'I'; 'O'; 'U'). Notice that s contains uppercase and lowercase letters. Return true if a and b are alike. Otherwise; return false. Example 1: Input: s = ""book"" Output: true Explanation: a = ""bo"" and b = ""ok"". a has 1 vowel and b has 1 vowel. Therefore; they are alike. Example 2: Input: s = ""textbook"" Output: false Explanation: a = ""text"" and b = ""book"". a has 1 vowel whereas b has 2. Therefore; they are not alike. Notice that the vowel o is counted twice. Constraints: 2 <= s.length <= 1000 s.length is even. s consists of uppercase and lowercase letters."
Oracle,1987,Number of Unique Good Subsequences,Hard,"Hash Table, String, Sliding Window, Counting","A string is good if there are no repeated characters. Given a string s​​​​​; return the number of good substrings of length three in s​​​​​​. Note that if there are multiple occurrences of the same substring; every occurrence should be counted. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""xyzzaz"" Output: 1 Explanation: There are 4 substrings of size 3: ""xyz""; ""yzz""; ""zza""; and ""zaz"". The only good substring of length 3 is ""xyz"". Example 2: Input: s = ""aababcabc"" Output: 4 Explanation: There are 7 substrings of size 3: ""aab""; ""aba""; ""bab""; ""abc""; ""bca""; ""cab""; and ""abc"". The good substrings are ""abc""; ""bca""; ""cab""; and ""abc"". Constraints: 1 <= s.length <= 100 s​​​​​​ consists of lowercase English letters."
Oracle,2062,Count Vowel Substrings of a String,Easy,"Array, Math, Dynamic Programming, Bit Manipulation, Brainteaser, Game Theory",
Oracle,2291,Maximum Profit From Trading Stocks,Med,"Array, Dynamic Programming, Bit Manipulation, Bitmask",You are given an integer array nums of length n and an integer numSlots such that 2 * numSlots >= n. There are numSlots slots numbered from 1 to numSlots. You have to place all n integers into the slots such that each slot contains at most two numbers. The AND sum of a given placement is the sum of the bitwise AND of every number with its respective slot number. For example; the AND sum of placing the numbers [1; 3] into slot 1 and [4; 6] into slot 2 is equal to (1 AND 1) + (3 AND 1) + (4 AND 2) + (6 AND 2) = 1 + 1 + 0 + 2 = 4. Return the maximum possible AND sum of nums given numSlots slots. Example 1: Input: nums = [1;2;3;4;5;6]; numSlots = 3 Output: 9 Explanation: One possible placement is [1; 4] into slot 1; [2; 6] into slot 2; and [3; 5] into slot 3. This gives the maximum AND sum of (1 AND 1) + (4 AND 1) + (2 AND 2) + (6 AND 2) + (3 AND 3) + (5 AND 3) = 1 + 0 + 2 + 2 + 3 + 1 = 9. Example 2: Input: nums = [1;3;10;4;7;1]; numSlots = 9 Output: 24 Explanation: One possible placement is [1; 1] into slot 1; [3] into slot 3; [4] into slot 4; [7] into slot 7; and [10] into slot 9. This gives the maximum AND sum of (1 AND 1) + (1 AND 1) + (3 AND 3) + (4 AND 4) + (7 AND 7) + (10 AND 9) = 1 + 1 + 3 + 4 + 7 + 8 = 24. Note that slots 2; 5; 6; and 8 are empty which is permitted. Constraints: n == nums.length 1 <= numSlots <= 9 1 <= n <= 2 * numSlots 1 <= nums[i] <= 15
Oracle,2422,Merge Operations to Turn Array Into a Palindrome,Med,"Array, String, Divide and Conquer, Sorting, Heap (Priority Queue), Radix Sort, Quickselect","You are given a 0-indexed array of strings nums; where each string is of equal length and consists of only digits. You are also given a 0-indexed 2D integer array queries where queries[i] = [ki; trimi]. For each queries[i]; you need to: Trim each number in nums to its rightmost trimi digits. Determine the index of the kith smallest trimmed number in nums. If two trimmed numbers are equal; the number with the lower index is considered to be smaller. Reset each number in nums to its original length. Return an array answer of the same length as queries; where answer[i] is the answer to the ith query. Note: To trim to the rightmost x digits means to keep removing the leftmost digit; until only x digits remain. Strings in nums may contain leading zeros. Example 1: Input: nums = [""102"";""473"";""251"";""814""]; queries = [[1;1];[2;3];[4;2];[1;2]] Output: [2;2;1;0] Explanation: 1. After trimming to the last digit; nums = [""2"";""3"";""1"";""4""]. The smallest number is 1 at index 2. 2. Trimmed to the last 3 digits; nums is unchanged. The 2nd smallest number is 251 at index 2. 3. Trimmed to the last 2 digits; nums = [""02"";""73"";""51"";""14""]. The 4th smallest number is 73. 4. Trimmed to the last 2 digits; the smallest number is 2 at index 0. Note that the trimmed number ""02"" is evaluated as 2. Example 2: Input: nums = [""24"";""37"";""96"";""04""]; queries = [[2;1];[2;2]] Output: [3;0] Explanation: 1. Trimmed to the last digit; nums = [""4"";""7"";""6"";""4""]. The 2nd smallest number is 4 at index 3. There are two occurrences of 4; but the one at index 0 is considered smaller than the one at index 3. 2. Trimmed to the last 2 digits; nums is unchanged. The 2nd smallest number is 24. Constraints: 1 <= nums.length <= 100 1 <= nums[i].length <= 100 nums[i] consists of only digits. All nums[i].length are equal. 1 <= queries.length <= 100 queries[i].length == 2 1 <= ki <= nums.length 1 <= trimi <= nums[i].length Follow up: Could you use the Radix Sort Algorithm to solve this problem? What will be the complexity of that solution?"
Oracle,2484,Count Palindromic Subsequences,Hard,Database,
Oracle,2747,Count Zero Request Servers,Med,,Given an integer array arr and a mapping function fn; return a new array with a transformation applied to each element. The returned array should be created such that returnedArray[i] = fn(arr[i]; i). Please solve it without the built-in Array.map method. Example 1: Input: arr = [1;2;3]; fn = function plusone(n) { return n + 1; } Output: [2;3;4] Explanation: const newArray = map(arr; plusone); // [2;3;4] The function increases each value in the array by one. Example 2: Input: arr = [1;2;3]; fn = function plusI(n; i) { return n + i; } Output: [1;3;5] Explanation: The function increases each value by the index it resides in. Example 3: Input: arr = [10;20;30]; fn = function constant() { return 42; } Output: [42;42;42] Explanation: The function always returns 42. Constraints: 0 <= arr.length <= 1000 -109 <= arr[i] <= 109 fn returns a number
TikTok,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
TikTok,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
TikTok,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
TikTok,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
TikTok,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
TikTok,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
TikTok,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
TikTok,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
TikTok,2334,Subarray With Elements Greater Than Varying Threshold,Hard,"Array, Hash Table, Binary Search, Sorting, Prefix Sum, Ordered Set",You are given a 0-indexed 2D integer array flowers; where flowers[i] = [starti; endi] means the ith flower will be in full bloom from starti to endi (inclusive). You are also given a 0-indexed integer array people of size n; where people[i] is the time that the ith person will arrive to see the flowers. Return an integer array answer of size n; where answer[i] is the number of flowers that are in full bloom when the ith person arrives. Example 1: Input: flowers = [[1;6];[3;7];[9;12];[4;13]]; people = [2;3;7;11] Output: [1;2;2;2] Explanation: The figure above shows the times when the flowers are in full bloom and when the people arrive. For each person; we return the number of flowers in full bloom during their arrival. Example 2: Input: flowers = [[1;10];[3;3]]; people = [3;3;2] Output: [2;2;1] Explanation: The figure above shows the times when the flowers are in full bloom and when the people arrive. For each person; we return the number of flowers in full bloom during their arrival. Constraints: 1 <= flowers.length <= 5 * 104 flowers[i].length == 2 1 <= starti <= endi <= 109 1 <= people.length <= 5 * 104 1 <= people[i] <= 109
TikTok,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
TikTok,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
TikTok,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
TikTok,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
TikTok,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
TikTok,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
TikTok,815,Bus Routes,Hard,Dynamic Programming,We stack glasses in a pyramid; where the first row has 1 glass; the second row has 2 glasses; and so on until the 100th row. Each glass holds one cup of champagne. Then; some champagne is poured into the first glass at the top. When the topmost glass is full; any excess liquid poured will fall equally to the glass immediately to the left and right of it. When those glasses become full; any excess champagne will fall equally to the left and right of those glasses; and so on. (A glass at the bottom row has its excess champagne fall on the floor.) For example; after one cup of champagne is poured; the top most glass is full. After two cups of champagne are poured; the two glasses on the second row are half full. After three cups of champagne are poured; those two cups become full - there are 3 full glasses total now. After four cups of champagne are poured; the third row has the middle glass half full; and the two outside glasses are a quarter full; as pictured below. Now after pouring some non-negative integer cups of champagne; return how full the jth glass in the ith row is (both i and j are 0-indexed.) Example 1: Input: poured = 1; query_row = 1; query_glass = 1 Output: 0.00000 Explanation: We poured 1 cup of champange to the top glass of the tower (which is indexed as (0; 0)). There will be no excess liquid so all the glasses under the top glass will remain empty. Example 2: Input: poured = 2; query_row = 1; query_glass = 1 Output: 0.50000 Explanation: We poured 2 cups of champange to the top glass of the tower (which is indexed as (0; 0)). There is one cup of excess liquid. The glass indexed as (1; 0) and the glass indexed as (1; 1) will share the excess liquid equally; and each will get half cup of champange. Example 3: Input: poured = 100000009; query_row = 33; query_glass = 17 Output: 1.00000 Constraints: 0 <= poured <= 109 0 <= query_glass <= query_row < 100
TikTok,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
TikTok,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
TikTok,588,Design In-Memory File System,Hard,"Hash Table, String, Design, Trie, Sorting",
TikTok,694,Number of Distinct Islands,Med,"Hash Table, Depth-First Search, Breadth-First Search, Union Find, Hash Function",
TikTok,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
TikTok,395,Longest Substring with At Least K Repeating Characters,Med,"Hash Table, String, Divide and Conquer, Sliding Window","Given a string s and an integer k; return the length of the longest substring of s such that the frequency of each character in this substring is greater than or equal to k. if no such substring exists; return 0. Example 1: Input: s = ""aaabb""; k = 3 Output: 3 Explanation: The longest substring is ""aaa""; as 'a' is repeated 3 times. Example 2: Input: s = ""ababbc""; k = 2 Output: 5 Explanation: The longest substring is ""ababb""; as 'a' is repeated 2 times and 'b' is repeated 3 times. Constraints: 1 <= s.length <= 104 s consists of only lowercase English letters. 1 <= k <= 105"
TikTok,772,Basic Calculator III,Hard,"Array, Divide and Conquer, Tree, Matrix",Given a n * n matrix grid of 0's and 1's only. We want to represent grid with a Quad-Tree. Return the root of the Quad-Tree representing grid. A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides; each node has two attributes: val: True if the node represents a grid of 1's or False if the node represents a grid of 0's. Notice that you can assign the val to True or False when isLeaf is False; and both are accepted in the answer. isLeaf: True if the node is a leaf node on the tree or False if the node has four children. class Node { public boolean val; public boolean isLeaf; public Node topLeft; public Node topRight; public Node bottomLeft; public Node bottomRight; } We can construct a Quad-Tree from a two-dimensional area using the following steps: If the current grid has the same value (i.e all 1's or all 0's) set isLeaf True and set val to the value of the grid and set the four children to Null and stop. If the current grid has different values; set isLeaf to False and set val to any value and divide the current grid into four sub-grids as shown in the photo. Recurse for each of the children with the proper sub-grid. If you want to know more about the Quad-Tree; you can refer to the wiki. Quad-Tree format: You don't need to read this section for solving the problem. This is only if you want to understand the output format here. The output represents the serialized format of a Quad-Tree using level order traversal; where null signifies a path terminator where no node exists below. It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list [isLeaf; val]. If the value of isLeaf or val is True we represent it as 1 in the list [isLeaf; val] and if the value of isLeaf or val is False we represent it as 0. Example 1: Input: grid = [[0;1];[1;0]] Output: [[0;1];[1;0];[1;1];[1;1];[1;0]] Explanation: The explanation of this example is shown below: Notice that 0 represents False and 1 represents True in the photo representing the Quad-Tree. Example 2: Input: grid = [[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;1;1;1;1];[1;1;1;1;1;1;1;1];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0]] Output: [[0;1];[1;1];[0;1];[1;1];[1;0];null;null;null;null;[1;0];[1;0];[1;1];[1;1]] Explanation: All values in the grid are not the same. We divide the grid into four sub-grids. The topLeft; bottomLeft and bottomRight each has the same value. The topRight have different values so we divide it into 4 sub-grids where each has the same value. Explanation is shown in the photo below: Constraints: n == grid.length == grid[i].length n == 2x where 0 <= x <= 6
TikTok,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
TikTok,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
TikTok,1293,Shortest Path in a Grid with Obstacles Elimination,Hard,Array,Given an integer array arr; return true if there are three consecutive odd numbers in the array. Otherwise; return false. Example 1: Input: arr = [2;6;4;1] Output: false Explanation: There are no three consecutive odds. Example 2: Input: arr = [1;2;34;3;4;5;7;23;12] Output: true Explanation: [5;7;23] are three consecutive odds. Constraints: 1 <= arr.length <= 1000 1 <= arr[i] <= 1000
TikTok,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
TikTok,93,Restore IP Addresses,Med,"String, Backtracking","A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. For example; ""0.1.2.201"" and ""192.168.1.1"" are valid IP addresses; but ""0.011.255.245""; ""192.168.1.312"" and ""192.168@1.1"" are invalid IP addresses. Given a string s containing only digits; return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order. Example 1: Input: s = ""25525511135"" Output: [""255.255.11.135"";""255.255.111.35""] Example 2: Input: s = ""0000"" Output: [""0.0.0.0""] Example 3: Input: s = ""101023"" Output: [""1.0.10.23"";""1.0.102.3"";""10.1.0.23"";""10.10.2.3"";""101.0.2.3""] Constraints: 1 <= s.length <= 20 s consists of digits only."
TikTok,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
TikTok,856,Score of Parentheses,Med,"Math, Enumeration",Given an integer n; return the number of ways you can write n as the sum of consecutive positive integers. Example 1: Input: n = 5 Output: 2 Explanation: 5 = 2 + 3 Example 2: Input: n = 9 Output: 3 Explanation: 9 = 4 + 5 = 2 + 3 + 4 Example 3: Input: n = 15 Output: 4 Explanation: 15 = 8 + 7 = 4 + 5 + 6 = 1 + 2 + 3 + 4 + 5 Constraints: 1 <= n <= 109
TikTok,1249,Minimum Remove to Make Valid Parentheses,Med,"Array, Hash Table, Binary Search, Design","Implement a SnapshotArray that supports the following interface: SnapshotArray(int length) initializes an array-like data structure with the given length. Initially; each element equals 0. void set(index; val) sets the element at the given index to be equal to val. int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1. int get(index; snap_id) returns the value at the given index; at the time we took the snapshot with the given snap_id Example 1: Input: [""SnapshotArray"";""set"";""snap"";""set"";""get""] [[3];[0;5];[];[0;6];[0;0]] Output: [null;null;0;null;5] Explanation: SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3 snapshotArr.set(0;5); // Set array[0] = 5 snapshotArr.snap(); // Take a snapshot; return snap_id = 0 snapshotArr.set(0;6); snapshotArr.get(0;0); // Get the value of array[0] with snap_id = 0; return 5 Constraints: 1 <= length <= 5 * 104 0 <= index < length 0 <= val <= 109 0 <= snap_id < (the total number of times we call snap()) At most 5 * 104 calls will be made to set; snap; and get."
TikTok,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
TikTok,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
TikTok,424,Longest Repeating Character Replacement,Med,"Hash Table, String, Sliding Window","You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times. Return the length of the longest substring containing the same letter you can get after performing the above operations. Example 1: Input: s = ""ABAB""; k = 2 Output: 4 Explanation: Replace the two 'A's with two 'B's or vice versa. Example 2: Input: s = ""AABABBA""; k = 1 Output: 4 Explanation: Replace the one 'A' in the middle with 'B' and form ""AABBBBA"". The substring ""BBBB"" has the longest repeating letters; which is 4. There may exists other ways to achieve this answer too. Constraints: 1 <= s.length <= 105 s consists of only uppercase English letters. 0 <= k <= s.length"
TikTok,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
TikTok,1151,Minimum Swaps to Group All 1's Together,Med,"Math, Backtracking, Breadth-First Search",
TikTok,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
TikTok,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
TikTok,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
TikTok,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
TikTok,403,Frog Jump,Hard,"Array, Dynamic Programming",A frog is crossing a river. The river is divided into some number of units; and at each unit; there may or may not exist a stone. The frog can jump on a stone; but it must not jump into the water. Given a list of stones positions (in units) in sorted ascending order; determine if the frog can cross the river by landing on the last stone. Initially; the frog is on the first stone and assumes the first jump must be 1 unit. If the frog's last jump was k units; its next jump must be either k - 1; k; or k + 1 units. The frog can only jump in the forward direction. Example 1: Input: stones = [0;1;3;5;6;8;12;17] Output: true Explanation: The frog can jump to the last stone by jumping 1 unit to the 2nd stone; then 2 units to the 3rd stone; then 2 units to the 4th stone; then 3 units to the 6th stone; 4 units to the 7th stone; and 5 units to the 8th stone. Example 2: Input: stones = [0;1;2;3;4;8;9;11] Output: false Explanation: There is no way to jump to the last stone as the gap between the 5th and 6th stone is too large. Constraints: 2 <= stones.length <= 2000 0 <= stones[i] <= 231 - 1 stones[0] == 0 stones is sorted in a strictly increasing order.
TikTok,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
TikTok,69,Sqrt(x),Easy,"Math, Binary Search",Given a non-negative integer x; return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. For example; do not use pow(x; 0.5) in c++ or x ** 0.5 in python. Example 1: Input: x = 4 Output: 2 Explanation: The square root of 4 is 2; so we return 2. Example 2: Input: x = 8 Output: 2 Explanation: The square root of 8 is 2.82842...; and since we round it down to the nearest integer; 2 is returned. Constraints: 0 <= x <= 231 - 1
TikTok,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
TikTok,140,Word Break II,Hard,"Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization","Given a string s and a dictionary of strings wordDict; add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""catsanddog""; wordDict = [""cat"";""cats"";""and"";""sand"";""dog""] Output: [""cats and dog"";""cat sand dog""] Example 2: Input: s = ""pineapplepenapple""; wordDict = [""apple"";""pen"";""applepen"";""pine"";""pineapple""] Output: [""pine apple pen apple"";""pineapple pen apple"";""pine applepen apple""] Explanation: Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: [] Constraints: 1 <= s.length <= 20 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 10 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique. Input is generated in a way that the length of the answer doesn't exceed 105."
TikTok,227,Basic Calculator II,Med,"Math, String, Stack","Given a string s which represents an expression; evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""3+2*2"" Output: 7 Example 2: Input: s = "" 3/2 "" Output: 1 Example 3: Input: s = "" 3+5 / 2 "" Output: 5 Constraints: 1 <= s.length <= 3 * 105 s consists of integers and operators ('+'; '-'; '*'; '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0; 231 - 1]. The answer is guaranteed to fit in a 32-bit integer."
TikTok,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
TikTok,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
TikTok,621,Task Scheduler,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting","You are given an array of CPU tasks; each labeled with a letter from A to Z; and a number n. Each CPU interval can be idle or allow the completion of one task. Tasks can be completed in any order; but there's a constraint: there has to be a gap of at least n intervals between two tasks with the same label. Return the minimum number of CPU intervals required to complete all tasks. Example 1: Input: tasks = [""A"";""A"";""A"";""B"";""B"";""B""]; n = 2 Output: 8 Explanation: A possible sequence is: A -> B -> idle -> A -> B -> idle -> A -> B. After completing task A; you must wait two intervals before doing A again. The same applies to task B. In the 3rd interval; neither A nor B can be done; so you idle. By the 4th interval; you can do A again as 2 intervals have passed. Example 2: Input: tasks = [""A"";""C"";""A"";""B"";""D"";""B""]; n = 1 Output: 6 Explanation: A possible sequence is: A -> B -> C -> D -> A -> B. With a cooling interval of 1; you can repeat a task after just one other task. Example 3: Input: tasks = [""A"";""A"";""A""; ""B"";""B"";""B""]; n = 3 Output: 10 Explanation: A possible sequence is: A -> B -> idle -> idle -> A -> B -> idle -> idle -> A -> B. There are only two types of tasks; A and B; which need to be separated by 3 intervals. This leads to idling twice between repetitions of these tasks. Constraints: 1 <= tasks.length <= 104 tasks[i] is an uppercase English letter. 0 <= n <= 100"
TikTok,695,Max Area of Island,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island. Return the maximum area of an island in grid. If there is no island; return 0. Example 1: Input: grid = [[0;0;1;0;0;0;0;1;0;0;0;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;1;1;0;1;0;0;0;0;0;0;0;0];[0;1;0;0;1;1;0;0;1;0;1;0;0];[0;1;0;0;1;1;0;0;1;1;1;0;0];[0;0;0;0;0;0;0;0;0;0;1;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;0;0;0;0;0;0;1;1;0;0;0;0]] Output: 6 Explanation: The answer is not 11; because the island must be connected 4-directionally. Example 2: Input: grid = [[0;0;0;0;0;0;0;0]] Output: 0 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 50 grid[i][j] is either 0 or 1.
TikTok,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
TikTok,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
TikTok,1802,Maximum Value at a Given Index in a Bounded Array,Med,"Array, Stack, Queue, Simulation",The school cafeteria offers circular and square sandwiches at lunch break; referred to by numbers 0 and 1 respectively. All students stand in a queue. Each student either prefers square or circular sandwiches. The number of sandwiches in the cafeteria is equal to the number of students. The sandwiches are placed in a stack. At each step: If the student at the front of the queue prefers the sandwich on the top of the stack; they will take it and leave the queue. Otherwise; they will leave it and go to the queue's end. This continues until none of the queue students want to take the top sandwich and are thus unable to eat. You are given two integer arrays students and sandwiches where sandwiches[i] is the type of the i​​​​​​th sandwich in the stack (i = 0 is the top of the stack) and students[j] is the preference of the j​​​​​​th student in the initial queue (j = 0 is the front of the queue). Return the number of students that are unable to eat. Example 1: Input: students = [1;1;0;0]; sandwiches = [0;1;0;1] Output: 0 Explanation: - Front student leaves the top sandwich and returns to the end of the line making students = [1;0;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;0;1;1]. - Front student takes the top sandwich and leaves the line making students = [0;1;1] and sandwiches = [1;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [1;1;0]. - Front student takes the top sandwich and leaves the line making students = [1;0] and sandwiches = [0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;1]. - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = [1]. - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = []. Hence all students are able to eat. Example 2: Input: students = [1;1;1;0;0;1]; sandwiches = [1;0;0;0;1;1] Output: 3 Constraints: 1 <= students.length; sandwiches.length <= 100 students.length == sandwiches.length sandwiches[i] is 0 or 1. students[i] is 0 or 1.
TikTok,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
TikTok,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
TikTok,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
TikTok,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
TikTok,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
TikTok,666,Path Sum IV,Med,"Array, Hash Table, Tree, Depth-First Search, Binary Tree",
TikTok,1209,Remove All Adjacent Duplicates in String II,Med,Concurrency,
TikTok,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
TikTok,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
TikTok,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
TikTok,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
TikTok,378,Kth Smallest Element in a Sorted Matrix,Med,"Array, Binary Search, Sorting, Heap (Priority Queue), Matrix",Given an n x n matrix where each of the rows and columns is sorted in ascending order; return the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order; not the kth distinct element. You must find a solution with a memory complexity better than O(n2). Example 1: Input: matrix = [[1;5;9];[10;11;13];[12;13;15]]; k = 8 Output: 13 Explanation: The elements in the matrix are [1;5;9;10;11;12;13;13;15]; and the 8th smallest number is 13 Example 2: Input: matrix = [[-5]]; k = 1 Output: -5 Constraints: n == matrix.length == matrix[i].length 1 <= n <= 300 -109 <= matrix[i][j] <= 109 All the rows and columns of matrix are guaranteed to be sorted in non-decreasing order. 1 <= k <= n2 Follow up: Could you solve the problem with a constant memory (i.e.; O(1) memory complexity)? Could you solve the problem in O(n) time complexity? The solution may be too advanced for an interview but you may find reading this paper fun.
TikTok,787,Cheapest Flights Within K Stops,Med,"Array, Breadth-First Search, Matrix",On an 2 x 3 board; there are five tiles labeled from 1 to 5; and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of the board is solved if and only if the board is [[1;2;3];[4;5;0]]. Given the puzzle board board; return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved; return -1. Example 1: Input: board = [[1;2;3];[4;0;5]] Output: 1 Explanation: Swap the 0 and the 5 in one move. Example 2: Input: board = [[1;2;3];[5;4;0]] Output: -1 Explanation: No number of moves will make the board solved. Example 3: Input: board = [[4;1;2];[5;0;3]] Output: 5 Explanation: 5 is the smallest number of moves that solves the board. An example path: After move 0: [[4;1;2];[5;0;3]] After move 1: [[4;1;2];[0;5;3]] After move 2: [[0;1;2];[4;5;3]] After move 3: [[1;0;2];[4;5;3]] After move 4: [[1;2;0];[4;5;3]] After move 5: [[1;2;3];[4;5;0]] Constraints: board.length == 2 board[i].length == 3 0 <= board[i][j] <= 5 Each value board[i][j] is unique.
TikTok,1530,Number of Good Leaf Nodes Pairs,Med,"String, Greedy, Sorting","Given two strings: s1 and s2 with the same size; check if some permutation of string s1 can break some permutation of string s2 or vice-versa. In other words s2 can break s1 or vice-versa. A string x can break string y (both of size n) if x[i] >= y[i] (in alphabetical order) for all i between 0 and n-1. Example 1: Input: s1 = ""abc""; s2 = ""xya"" Output: true Explanation: ""ayx"" is a permutation of s2=""xya"" which can break to string ""abc"" which is a permutation of s1=""abc"". Example 2: Input: s1 = ""abe""; s2 = ""acd"" Output: false Explanation: All permutations for s1=""abe"" are: ""abe""; ""aeb""; ""bae""; ""bea""; ""eab"" and ""eba"" and all permutation for s2=""acd"" are: ""acd""; ""adc""; ""cad""; ""cda""; ""dac"" and ""dca"". However; there is not any permutation from s1 which can break some permutation from s2 and vice-versa. Example 3: Input: s1 = ""leetcodee""; s2 = ""interview"" Output: true Constraints: s1.length == n s2.length == n 1 <= n <= 10^5 All strings consist of lowercase English letters."
TikTok,2523,Closest Prime Numbers in Range,Med,Database,
TikTok,2640,Find the Score of All Prefixes of an Array,Med,"Array, Hash Table, Binary Search, Greedy, Sorting",You are given an integer array banned and two integers n and maxSum. You are choosing some number of integers following the below rules: The chosen integers have to be in the range [1; n]. Each integer can be chosen at most once. The chosen integers should not be in the array banned. The sum of the chosen integers should not exceed maxSum. Return the maximum number of integers you can choose following the mentioned rules. Example 1: Input: banned = [1;6;5]; n = 5; maxSum = 6 Output: 2 Explanation: You can choose the integers 2 and 4. 2 and 4 are from the range [1; 5]; both did not appear in banned; and their sum is 6; which did not exceed maxSum. Example 2: Input: banned = [1;2;3;4;5;6;7]; n = 8; maxSum = 1 Output: 0 Explanation: You cannot choose any integer while following the mentioned conditions. Example 3: Input: banned = [11]; n = 7; maxSum = 50 Output: 7 Explanation: You can choose the integers 1; 2; 3; 4; 5; 6; and 7. They are from the range [1; 7]; all did not appear in banned; and their sum is 28; which did not exceed maxSum. Constraints: 1 <= banned.length <= 104 1 <= banned[i]; n <= 104 1 <= maxSum <= 109
TikTok,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
TikTok,68,Text Justification,Hard,"Array, String, Simulation","Given an array of strings words and a width maxWidth; format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is; pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words; the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text; it should be left-justified; and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = [""This""; ""is""; ""an""; ""example""; ""of""; ""text""; ""justification.""]; maxWidth = 16 Output: [ ""This is an""; ""example of text""; ""justification. "" ] Example 2: Input: words = [""What"";""must"";""be"";""acknowledgment"";""shall"";""be""]; maxWidth = 16 Output: [ ""What must be""; ""acknowledgment ""; ""shall be "" ] Explanation: Note that the last line is ""shall be "" instead of ""shall be""; because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = [""Science"";""is"";""what"";""we"";""understand"";""well"";""enough"";""to"";""explain"";""to"";""a"";""computer."";""Art"";""is"";""everything"";""else"";""we"";""do""]; maxWidth = 20 Output: [ ""Science is what we""; ""understand well""; ""enough to explain to""; ""a computer. Art is""; ""everything else we""; ""do "" ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth"
TikTok,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
TikTok,105,Construct Binary Tree from Preorder and Inorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree; construct and return the binary tree. Example 1: Input: preorder = [3;9;20;15;7]; inorder = [9;3;15;20;7] Output: [3;9;20;null;null;15;7] Example 2: Input: preorder = [-1]; inorder = [-1] Output: [-1] Constraints: 1 <= preorder.length <= 3000 inorder.length == preorder.length -3000 <= preorder[i]; inorder[i] <= 3000 preorder and inorder consist of unique values. Each value of inorder also appears in preorder. preorder is guaranteed to be the preorder traversal of the tree. inorder is guaranteed to be the inorder traversal of the tree.
TikTok,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
TikTok,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
TikTok,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
TikTok,886,Possible Bipartition,Med,"String, Stack","Given a balanced parentheses string s; return the score of the string. The score of a balanced parentheses string is based on the following rule: ""()"" has score 1. AB has score A + B; where A and B are balanced parentheses strings. (A) has score 2 * A; where A is a balanced parentheses string. Example 1: Input: s = ""()"" Output: 1 Example 2: Input: s = ""(())"" Output: 2 Example 3: Input: s = ""()()"" Output: 2 Constraints: 2 <= s.length <= 50 s consists of only '(' and ')'. s is a balanced parentheses string."
TikTok,1010,Pairs of Songs With Total Durations Divisible by 60,Med,"Hash Table, Math, Enumeration",Given three integers x; y; and bound; return a list of all the powerful integers that have a value less than or equal to bound. An integer is powerful if it can be represented as xi + yj for some integers i >= 0 and j >= 0. You may return the answer in any order. In your answer; each value should occur at most once. Example 1: Input: x = 2; y = 3; bound = 10 Output: [2;3;4;5;7;9;10] Explanation: 2 = 20 + 30 3 = 21 + 30 4 = 20 + 31 5 = 21 + 31 7 = 22 + 31 9 = 23 + 30 10 = 20 + 32 Example 2: Input: x = 3; y = 5; bound = 15 Output: [2;4;6;8;10;14] Constraints: 1 <= x; y <= 100 0 <= bound <= 106
TikTok,1860,Incremental Memory Leak,Med,"Array, Divide and Conquer, Bit Manipulation, Sorting, Heap (Priority Queue), Matrix, Prefix Sum, Quickselect",You are given a 2D matrix of size m x n; consisting of non-negative integers. You are also given an integer k. The value of coordinate (a; b) of the matrix is the XOR of all matrix[i][j] where 0 <= i <= a < m and 0 <= j <= b < n (0-indexed). Find the kth largest value (1-indexed) of all the coordinates of matrix. Example 1: Input: matrix = [[5;2];[1;6]]; k = 1 Output: 7 Explanation: The value of coordinate (0;1) is 5 XOR 2 = 7; which is the largest value. Example 2: Input: matrix = [[5;2];[1;6]]; k = 2 Output: 5 Explanation: The value of coordinate (0;0) is 5 = 5; which is the 2nd largest value. Example 3: Input: matrix = [[5;2];[1;6]]; k = 3 Output: 4 Explanation: The value of coordinate (1;0) is 5 XOR 1 = 4; which is the 3rd largest value. Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 1000 0 <= matrix[i][j] <= 106 1 <= k <= m * n
TikTok,2145,Count the Hidden Sequences,Med,"Array, Matrix, Prefix Sum",You are given a 0-indexed 2D array grid of size 2 x n; where grid[r][c] represents the number of points at position (r; c) on the matrix. Two robots are playing a game on this matrix. Both robots initially start at (0; 0) and want to reach (1; n-1). Each robot may only move to the right ((r; c) to (r; c + 1)) or down ((r; c) to (r + 1; c)). At the start of the game; the first robot moves from (0; 0) to (1; n-1); collecting all the points from the cells on its path. For all cells (r; c) traversed on the path; grid[r][c] is set to 0. Then; the second robot moves from (0; 0) to (1; n-1); collecting the points on its path. Note that their paths may intersect with one another. The first robot wants to minimize the number of points collected by the second robot. In contrast; the second robot wants to maximize the number of points it collects. If both robots play optimally; return the number of points collected by the second robot. Example 1: Input: grid = [[2;5;4];[1;5;1]] Output: 4 Explanation: The optimal path taken by the first robot is shown in red; and the optimal path taken by the second robot is shown in blue. The cells visited by the first robot are set to 0. The second robot will collect 0 + 0 + 4 + 0 = 4 points. Example 2: Input: grid = [[3;3;1];[8;5;2]] Output: 4 Explanation: The optimal path taken by the first robot is shown in red; and the optimal path taken by the second robot is shown in blue. The cells visited by the first robot are set to 0. The second robot will collect 0 + 3 + 1 + 0 = 4 points. Example 3: Input: grid = [[1;3;1;15];[1;3;3;1]] Output: 7 Explanation: The optimal path taken by the first robot is shown in red; and the optimal path taken by the second robot is shown in blue. The cells visited by the first robot are set to 0. The second robot will collect 0 + 1 + 3 + 3 + 0 = 7 points. Constraints: grid.length == 2 n == grid[r].length 1 <= n <= 5 * 104 1 <= grid[r][c] <= 105
TikTok,2414,Length of the Longest Alphabetical Continuous Substring,Med,"Two Pointers, String","You are given two strings start and target; both of length n. Each string consists only of the characters 'L'; 'R'; and '_' where: The characters 'L' and 'R' represent pieces; where a piece 'L' can move to the left only if there is a blank space directly to its left; and a piece 'R' can move to the right only if there is a blank space directly to its right. The character '_' represents a blank space that can be occupied by any of the 'L' or 'R' pieces. Return true if it is possible to obtain the string target by moving the pieces of the string start any number of times. Otherwise; return false. Example 1: Input: start = ""_L__R__R_""; target = ""L______RR"" Output: true Explanation: We can obtain the string target from start by doing the following moves: - Move the first piece one step to the left; start becomes equal to ""L___R__R_"". - Move the last piece one step to the right; start becomes equal to ""L___R___R"". - Move the second piece three steps to the right; start becomes equal to ""L______RR"". Since it is possible to get the string target from start; we return true. Example 2: Input: start = ""R_L_""; target = ""__LR"" Output: false Explanation: The 'R' piece in the string start can move one step to the right to obtain ""_RL_"". After that; no pieces can move anymore; so it is impossible to obtain the string target from start. Example 3: Input: start = ""_R""; target = ""R_"" Output: false Explanation: The piece in the string start can move only to the right; so it is impossible to obtain the string target from start. Constraints: n == start.length == target.length 1 <= n <= 105 start and target consist of the characters 'L'; 'R'; and '_'."
TikTok,2456,Most Popular Video Creator,Med,"String, Backtracking, Stack, Greedy","You are given a 0-indexed string pattern of length n consisting of the characters 'I' meaning increasing and 'D' meaning decreasing. A 0-indexed string num of length n + 1 is created using the following conditions: num consists of the digits '1' to '9'; where each digit is used at most once. If pattern[i] == 'I'; then num[i] < num[i + 1]. If pattern[i] == 'D'; then num[i] > num[i + 1]. Return the lexicographically smallest possible string num that meets the conditions. Example 1: Input: pattern = ""IIIDIDDD"" Output: ""123549876"" Explanation: At indices 0; 1; 2; and 4 we must have that num[i] < num[i+1]. At indices 3; 5; 6; and 7 we must have that num[i] > num[i+1]. Some possible values of num are ""245639871""; ""135749862""; and ""123849765"". It can be proven that ""123549876"" is the smallest possible num that meets the conditions. Note that ""123414321"" is not possible because the digit '1' is used more than once. Example 2: Input: pattern = ""DDD"" Output: ""4321"" Explanation: Some possible values of num are ""9876""; ""7321""; and ""8742"". It can be proven that ""4321"" is the smallest possible num that meets the conditions. Constraints: 1 <= pattern.length <= 8 pattern consists of only the letters 'I' and 'D'."
TikTok,2799,Count Complete Subarrays in an Array,Med,,
TikTok,3086,Minimum Moves to Pick K Ones,Hard,,
TikTok,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
TikTok,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
TikTok,51,N-Queens,Hard,"Array, Backtracking","The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n; return all distinct solutions to the n-queens puzzle. You may return the answer in any order. Each solution contains a distinct board configuration of the n-queens' placement; where 'Q' and '.' both indicate a queen and an empty space; respectively. Example 1: Input: n = 4 Output: [["".Q.."";""...Q"";""Q..."";""..Q.""];[""..Q."";""Q..."";""...Q"";"".Q..""]] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above Example 2: Input: n = 1 Output: [[""Q""]] Constraints: 1 <= n <= 9"
TikTok,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
TikTok,78,Subsets,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums of unique elements; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;3] Output: [[];[1];[2];[1;2];[3];[1;3];[2;3];[1;2;3]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10 All the numbers of nums are unique.
TikTok,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
TikTok,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
TikTok,199,Binary Tree Right Side View,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; imagine yourself standing on the right side of it; return the values of the nodes you can see ordered from top to bottom. Example 1: Input: root = [1;2;3;null;5;null;4] Output: [1;3;4] Example 2: Input: root = [1;null;3] Output: [1;3] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
TikTok,209,Minimum Size Subarray Sum,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of positive integers nums and a positive integer target; return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray; return 0 instead. Example 1: Input: target = 7; nums = [2;3;1;2;4;3] Output: 2 Explanation: The subarray [4;3] has the minimal length under the problem constraint. Example 2: Input: target = 4; nums = [1;4;4] Output: 1 Example 3: Input: target = 11; nums = [1;1;1;1;1;1;1;1] Output: 0 Constraints: 1 <= target <= 109 1 <= nums.length <= 105 1 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution of which the time complexity is O(n log(n)).
TikTok,259,3Sum Smaller,Med,"Array, Two Pointers, Binary Search, Sorting",
TikTok,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
TikTok,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
TikTok,301,Remove Invalid Parentheses,Hard,"String, Backtracking, Breadth-First Search","Given a string s that contains parentheses and letters; remove the minimum number of invalid parentheses to make the input string valid. Return a list of unique strings that are valid with the minimum number of removals. You may return the answer in any order. Example 1: Input: s = ""()())()"" Output: [""(())()"";""()()()""] Example 2: Input: s = ""(a)())()"" Output: [""(a())()"";""(a)()()""] Example 3: Input: s = "")("" Output: [""""] Constraints: 1 <= s.length <= 25 s consists of lowercase English letters and parentheses '(' and ')'. There will be at most 20 parentheses in s."
TikTok,358,Rearrange String k Distance Apart,Hard,"Hash Table, String, Greedy, Sorting, Heap (Priority Queue), Counting",
TikTok,465,Optimal Account Balancing,Hard,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",
TikTok,799,Champagne Tower,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Search Tree, Binary Tree",Given the root of a Binary Search Tree (BST); return the minimum difference between the values of any two different nodes in the tree. Example 1: Input: root = [4;2;6;1;3] Output: 1 Example 2: Input: root = [1;0;48;null;null;12;49] Output: 1 Constraints: The number of nodes in the tree is in the range [2; 100]. 0 <= Node.val <= 105 Note: This question is the same as 530: https://leetcode.com/problems/minimum-absolute-difference-in-bst/
Walmart Labs,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Walmart Labs,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Walmart Labs,716,Max Stack,Hard,"Linked List, Stack, Design, Doubly-Linked List, Ordered Set",
Walmart Labs,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Walmart Labs,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Walmart Labs,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Walmart Labs,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Walmart Labs,876,Middle of the Linked List,Easy,"Array, Hash Table, Greedy, Sorting",Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize; and consists of groupSize consecutive cards. Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize; return true if she can rearrange the cards; or false otherwise. Example 1: Input: hand = [1;2;3;6;2;3;4;7;8]; groupSize = 3 Output: true Explanation: Alice's hand can be rearranged as [1;2;3];[2;3;4];[6;7;8] Example 2: Input: hand = [1;2;3;4;5]; groupSize = 4 Output: false Explanation: Alice's hand can not be rearranged into groups of 4. Constraints: 1 <= hand.length <= 104 0 <= hand[i] <= 109 1 <= groupSize <= hand.length Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/
Walmart Labs,1238,Circular Permutation in Binary Representation,Med,"Hash Table, String","On an alphabet board; we start at position (0; 0); corresponding to character board[0][0]. Here; board = [""abcde""; ""fghij""; ""klmno""; ""pqrst""; ""uvwxy""; ""z""]; as shown in the diagram below. We may make the following moves: 'U' moves our position up one row; if the position exists on the board; 'D' moves our position down one row; if the position exists on the board; 'L' moves our position left one column; if the position exists on the board; 'R' moves our position right one column; if the position exists on the board; '!' adds the character board[r][c] at our current position (r; c) to the answer. (Here; the only positions that exist on the board are positions with letters on them.) Return a sequence of moves that makes our answer equal to target in the minimum number of moves. You may return any path that does so. Example 1: Input: target = ""leet"" Output: ""DDR!UURRR!!DDD!"" Example 2: Input: target = ""code"" Output: ""RR!DDRR!UUL!R!"" Constraints: 1 <= target.length <= 100 target consists only of English lowercase letters."
Walmart Labs,1486,XOR Operation in an Array,Easy,"Array, Two Pointers, Binary Search, Sorting",Given two integer arrays arr1 and arr2; and the integer d; return the distance value between the two arrays. The distance value is defined as the number of elements arr1[i] such that there is not any element arr2[j] where |arr1[i]-arr2[j]| <= d. Example 1: Input: arr1 = [4;5;8]; arr2 = [10;9;1;8]; d = 2 Output: 2 Explanation: For arr1[0]=4 we have: |4-10|=6 > d=2 |4-9|=5 > d=2 |4-1|=3 > d=2 |4-8|=4 > d=2 For arr1[1]=5 we have: |5-10|=5 > d=2 |5-9|=4 > d=2 |5-1|=4 > d=2 |5-8|=3 > d=2 For arr1[2]=8 we have: |8-10|=2 <= d=2 |8-9|=1 <= d=2 |8-1|=7 > d=2 |8-8|=0 <= d=2 Example 2: Input: arr1 = [1;4;2;3]; arr2 = [-4;-3;6;10;20;30]; d = 3 Output: 2 Example 3: Input: arr1 = [2;1;100;3]; arr2 = [-5;-2;10;-3;7]; d = 6 Output: 1 Constraints: 1 <= arr1.length; arr2.length <= 500 -1000 <= arr1[i]; arr2[j] <= 1000 0 <= d <= 100
Walmart Labs,1977,Number of Ways to Separate Numbers,Hard,"Array, Binary Search, Line Sweep, Sorting, Heap (Priority Queue)",You are given a 2D integer array intervals; where intervals[i] = [lefti; righti] describes the ith interval starting at lefti and ending at righti (inclusive). The size of an interval is defined as the number of integers it contains; or more formally righti - lefti + 1. You are also given an integer array queries. The answer to the jth query is the size of the smallest interval i such that lefti <= queries[j] <= righti. If no such interval exists; the answer is -1. Return an array containing the answers to the queries. Example 1: Input: intervals = [[1;4];[2;4];[3;6];[4;4]]; queries = [2;3;4;5] Output: [3;3;1;4] Explanation: The queries are processed as follows: - Query = 2: The interval [2;4] is the smallest interval containing 2. The answer is 4 - 2 + 1 = 3. - Query = 3: The interval [2;4] is the smallest interval containing 3. The answer is 4 - 2 + 1 = 3. - Query = 4: The interval [4;4] is the smallest interval containing 4. The answer is 4 - 4 + 1 = 1. - Query = 5: The interval [3;6] is the smallest interval containing 5. The answer is 6 - 3 + 1 = 4. Example 2: Input: intervals = [[2;3];[2;5];[1;8];[20;25]]; queries = [2;19;5;22] Output: [2;-1;4;6] Explanation: The queries are processed as follows: - Query = 2: The interval [2;3] is the smallest interval containing 2. The answer is 3 - 2 + 1 = 2. - Query = 19: None of the intervals contain 19. The answer is -1. - Query = 5: The interval [2;5] is the smallest interval containing 5. The answer is 5 - 2 + 1 = 4. - Query = 22: The interval [20;25] is the smallest interval containing 22. The answer is 25 - 20 + 1 = 6. Constraints: 1 <= intervals.length <= 105 1 <= queries.length <= 105 intervals[i].length == 2 1 <= lefti <= righti <= 107 1 <= queries[j] <= 107
Walmart Labs,2071,Maximum Number of Tasks You Can Assign,Hard,"Array, Hash Table, Counting",
Walmart Labs,2072,The Winner University,Easy,"Array, Stack, Monotonic Stack",
Walmart Labs,2179,Count Good Triplets in an Array,Hard,"Array, Binary Search, Sorting",You are given a 2D integer array items where items[i] = [pricei; beautyi] denotes the price and beauty of an item respectively. You are also given a 0-indexed integer array queries. For each queries[j]; you want to determine the maximum beauty of an item whose price is less than or equal to queries[j]. If no such item exists; then the answer to this query is 0. Return an array answer of the same length as queries where answer[j] is the answer to the jth query. Example 1: Input: items = [[1;2];[3;2];[2;4];[5;6];[3;5]]; queries = [1;2;3;4;5;6] Output: [2;4;5;5;6;6] Explanation: - For queries[0]=1; [1;2] is the only item which has price <= 1. Hence; the answer for this query is 2. - For queries[1]=2; the items which can be considered are [1;2] and [2;4]. The maximum beauty among them is 4. - For queries[2]=3 and queries[3]=4; the items which can be considered are [1;2]; [3;2]; [2;4]; and [3;5]. The maximum beauty among them is 5. - For queries[4]=5 and queries[5]=6; all items can be considered. Hence; the answer for them is the maximum beauty of all items; i.e.; 6. Example 2: Input: items = [[1;2];[1;2];[1;3];[1;4]]; queries = [1] Output: [4] Explanation: The price of every item is equal to 1; so we choose the item with the maximum beauty 4. Note that multiple items can have the same price and/or beauty. Example 3: Input: items = [[10;1000]]; queries = [5] Output: [0] Explanation: No item has a price less than or equal to 5; so no item can be chosen. Hence; the answer to the query is 0. Constraints: 1 <= items.length; queries.length <= 105 items[i].length == 2 1 <= pricei; beautyi; queries[j] <= 109
Walmart Labs,2406,Divide Intervals Into Minimum Number of Groups,Med,"Hash Table, String","You are given the strings key and message; which represent a cipher key and a secret message; respectively. The steps to decode message are as follows: Use the first appearance of all 26 lowercase English letters in key as the order of the substitution table. Align the substitution table with the regular English alphabet. Each letter in message is then substituted using the table. Spaces ' ' are transformed to themselves. For example; given key = ""happy boy"" (actual key would have at least one instance of each letter in the alphabet); we have the partial substitution table of ('h' -> 'a'; 'a' -> 'b'; 'p' -> 'c'; 'y' -> 'd'; 'b' -> 'e'; 'o' -> 'f'). Return the decoded message. Example 1: Input: key = ""the quick brown fox jumps over the lazy dog""; message = ""vkbs bs t suepuv"" Output: ""this is a secret"" Explanation: The diagram above shows the substitution table. It is obtained by taking the first appearance of each letter in ""the quick brown fox jumps over the lazy dog"". Example 2: Input: key = ""eljuxhpwnyrdgtqkviszcfmabo""; message = ""zwx hnfx lqantp mnoeius ycgk vcnjrdb"" Output: ""the five boxing wizards jump quickly"" Explanation: The diagram above shows the substitution table. It is obtained by taking the first appearance of each letter in ""eljuxhpwnyrdgtqkviszcfmabo"". Constraints: 26 <= key.length <= 2000 key consists of lowercase English letters and ' '. key contains every letter in the English alphabet ('a' to 'z') at least once. 1 <= message.length <= 2000 message consists of lowercase English letters and ' '."
Walmart Labs,2449,Minimum Number of Operations to Make Arrays Similar,Hard,"Array, Binary Search, Queue, Sliding Window, Heap (Priority Queue), Prefix Sum, Monotonic Queue",You have n robots. You are given two 0-indexed integer arrays; chargeTimes and runningCosts; both of length n. The ith robot costs chargeTimes[i] units to charge and costs runningCosts[i] units to run. You are also given an integer budget. The total cost of running k chosen robots is equal to max(chargeTimes) + k * sum(runningCosts); where max(chargeTimes) is the largest charge cost among the k robots and sum(runningCosts) is the sum of running costs among the k robots. Return the maximum number of consecutive robots you can run such that the total cost does not exceed budget. Example 1: Input: chargeTimes = [3;6;1;3;4]; runningCosts = [2;1;3;4;5]; budget = 25 Output: 3 Explanation: It is possible to run all individual and consecutive pairs of robots within budget. To obtain answer 3; consider the first 3 robots. The total cost will be max(3;6;1) + 3 * sum(2;1;3) = 6 + 3 * 6 = 24 which is less than 25. It can be shown that it is not possible to run more than 3 consecutive robots within budget; so we return 3. Example 2: Input: chargeTimes = [11;12;19]; runningCosts = [10;8;7]; budget = 19 Output: 0 Explanation: No robot can be run that does not exceed the budget; so we return 0. Constraints: chargeTimes.length == runningCosts.length == n 1 <= n <= 5 * 104 1 <= chargeTimes[i]; runningCosts[i] <= 105 1 <= budget <= 1015
Walmart Labs,2541,Minimum Operations to Make Array Equal II,Med,"Math, Enumeration",Given a non-negative integer num; return true if num can be expressed as the sum of any non-negative integer and its reverse; or false otherwise. Example 1: Input: num = 443 Output: true Explanation: 172 + 271 = 443 so we return true. Example 2: Input: num = 63 Output: false Explanation: 63 cannot be expressed as the sum of a non-negative integer and its reverse so we return false. Example 3: Input: num = 181 Output: true Explanation: 140 + 041 = 181 so we return true. Note that when a number is reversed; there may be leading zeros. Constraints: 0 <= num <= 105
Walmart Labs,3005,Count Elements With Maximum Frequency,Easy,,
Walmart Labs,3090,Maximum Length Substring With Two Occurrences,Easy,,
Walmart Labs,3179,Find the N-th Value After K Seconds,Med,"Array, Dynamic Programming, Bit Manipulation, Tree, Depth-First Search",There exists an undirected tree rooted at node 0 with n nodes labeled from 0 to n - 1. You are given a 2D integer array edges of length n - 1; where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. You are also given a 0-indexed array coins of size n where coins[i] indicates the number of coins in the vertex i; and an integer k. Starting from the root; you have to collect all the coins such that the coins at a node can only be collected if the coins of its ancestors have been already collected. Coins at nodei can be collected in one of the following ways: Collect all the coins; but you will get coins[i] - k points. If coins[i] - k is negative then you will lose abs(coins[i] - k) points. Collect all the coins; but you will get floor(coins[i] / 2) points. If this way is used; then for all the nodej present in the subtree of nodei; coins[j] will get reduced to floor(coins[j] / 2). Return the maximum points you can get after collecting the coins from all the tree nodes. Example 1: Input: edges = [[0;1];[1;2];[2;3]]; coins = [10;10;3;3]; k = 5 Output: 11 Explanation: Collect all the coins from node 0 using the first way. Total points = 10 - 5 = 5. Collect all the coins from node 1 using the first way. Total points = 5 + (10 - 5) = 10. Collect all the coins from node 2 using the second way so coins left at node 3 will be floor(3 / 2) = 1. Total points = 10 + floor(3 / 2) = 11. Collect all the coins from node 3 using the second way. Total points = 11 + floor(1 / 2) = 11. It can be shown that the maximum points we can get after collecting coins from all the nodes is 11. Example 2: Input: edges = [[0;1];[0;2]]; coins = [8;4;4]; k = 0 Output: 16 Explanation: Coins will be collected from all the nodes using the first way. Therefore; total points = (8 - 0) + (4 - 0) + (4 - 0) = 16. Constraints: n == coins.length 2 <= n <= 105 0 <= coins[i] <= 104 edges.length == n - 1 0 <= edges[i][0]; edges[i][1] < n 0 <= k <= 104
Walmart Labs,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Walmart Labs,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Walmart Labs,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Walmart Labs,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Walmart Labs,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Walmart Labs,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Walmart Labs,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Walmart Labs,863,All Nodes Distance K in Binary Tree,Med,"Dynamic Programming, Tree, Depth-First Search, Graph",There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Return an array answer of length n where answer[i] is the sum of the distances between the ith node in the tree and all other nodes. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;3];[2;4];[2;5]] Output: [8;12;6;10;10;10] Explanation: The tree is shown above. We can see that dist(0;1) + dist(0;2) + dist(0;3) + dist(0;4) + dist(0;5) equals 1 + 1 + 2 + 2 + 2 = 8. Hence; answer[0] = 8; and so on. Example 2: Input: n = 1; edges = [] Output: [0] Example 3: Input: n = 2; edges = [[1;0]] Output: [1;1] Constraints: 1 <= n <= 3 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n ai != bi The given input represents a valid tree.
Walmart Labs,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Walmart Labs,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Walmart Labs,67,Add Binary,Easy,"Math, String, Bit Manipulation, Simulation","Given two binary strings a and b; return their sum as a binary string. Example 1: Input: a = ""11""; b = ""1"" Output: ""100"" Example 2: Input: a = ""1010""; b = ""1011"" Output: ""10101"" Constraints: 1 <= a.length; b.length <= 104 a and b consist only of '0' or '1' characters. Each string does not contain leading zeros except for the zero itself."
Walmart Labs,103,Binary Tree Zigzag Level Order Traversal,Med,"Tree, Breadth-First Search, Binary Tree",Given the root of a binary tree; return the zigzag level order traversal of its nodes' values. (i.e.; from left to right; then right to left for the next level and alternate between). Example 1: Input: root = [3;9;20;null;null;15;7] Output: [[3];[20;9];[15;7]] Example 2: Input: root = [1] Output: [[1]] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100
Walmart Labs,189,Rotate Array,Med,"Array, Math, Two Pointers",Given an integer array nums; rotate the array to the right by k steps; where k is non-negative. Example 1: Input: nums = [1;2;3;4;5;6;7]; k = 3 Output: [5;6;7;1;2;3;4] Explanation: rotate 1 steps to the right: [7;1;2;3;4;5;6] rotate 2 steps to the right: [6;7;1;2;3;4;5] rotate 3 steps to the right: [5;6;7;1;2;3;4] Example 2: Input: nums = [-1;-100;3;99]; k = 2 Output: [3;99;-1;-100] Explanation: rotate 1 steps to the right: [99;-1;-100;3] rotate 2 steps to the right: [3;99;-1;-100] Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 0 <= k <= 105 Follow up: Try to come up with as many solutions as you can. There are at least three different ways to solve this problem. Could you do it in-place with O(1) extra space?
Walmart Labs,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Walmart Labs,697,Degree of an Array,Easy,"Array, Hash Table",Given a non-empty array of non-negative integers nums; the degree of this array is defined as the maximum frequency of any one of its elements. Your task is to find the smallest possible length of a (contiguous) subarray of nums; that has the same degree as nums. Example 1: Input: nums = [1;2;2;3;1] Output: 2 Explanation: The input array has a degree of 2 because both elements 1 and 2 appear twice. Of the subarrays that have the same degree: [1; 2; 2; 3; 1]; [1; 2; 2; 3]; [2; 2; 3; 1]; [1; 2; 2]; [2; 2; 3]; [2; 2] The shortest length is 2. So return 2. Example 2: Input: nums = [1;2;2;3;1;4;2] Output: 6 Explanation: The degree is 3 because the element 2 is repeated 3 times. So [2;2;3;1;4;2] is the shortest subarray; therefore returning 6. Constraints: nums.length will be between 1 and 50;000. nums[i] will be an integer between 0 and 49;999.
Walmart Labs,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
Walmart Labs,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Walmart Labs,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Walmart Labs,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
Walmart Labs,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Walmart Labs,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
Walmart Labs,977,Squares of a Sorted Array,Easy,"String, Dynamic Programming","Given a string s; return the number of distinct non-empty subsequences of s. Since the answer may be very large; return it modulo 109 + 7. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not. Example 1: Input: s = ""abc"" Output: 7 Explanation: The 7 distinct subsequences are ""a""; ""b""; ""c""; ""ab""; ""ac""; ""bc""; and ""abc"". Example 2: Input: s = ""aba"" Output: 6 Explanation: The 6 distinct subsequences are ""a""; ""b""; ""ab""; ""aa""; ""ba""; and ""aba"". Example 3: Input: s = ""aaa"" Output: 3 Explanation: The 3 distinct subsequences are ""a""; ""aa"" and ""aaa"". Constraints: 1 <= s.length <= 2000 s consists of lowercase English letters."
Walmart Labs,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Walmart Labs,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Walmart Labs,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Walmart Labs,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Walmart Labs,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Walmart Labs,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Walmart Labs,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Walmart Labs,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Walmart Labs,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Walmart Labs,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Walmart Labs,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Walmart Labs,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Walmart Labs,199,Binary Tree Right Side View,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; imagine yourself standing on the right side of it; return the values of the nodes you can see ordered from top to bottom. Example 1: Input: root = [1;2;3;null;5;null;4] Output: [1;3;4] Example 2: Input: root = [1;null;3] Output: [1;3] Example 3: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 100]. -100 <= Node.val <= 100
Walmart Labs,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Walmart Labs,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
Walmart Labs,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
Walmart Labs,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
Walmart Labs,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Walmart Labs,841,Keys and Rooms,Med,"Array, Two Pointers, String","Given a string s and a character c that occurs in s; return an array of integers answer where answer.length == s.length and answer[i] is the distance from index i to the closest occurrence of character c in s. The distance between two indices i and j is abs(i - j); where abs is the absolute value function. Example 1: Input: s = ""loveleetcode""; c = ""e"" Output: [3;2;1;0;1;0;0;1;2;2;1;0] Explanation: The character 'e' appears at indices 3; 5; 6; and 11 (0-indexed). The closest occurrence of 'e' for index 0 is at index 3; so the distance is abs(0 - 3) = 3. The closest occurrence of 'e' for index 1 is at index 3; so the distance is abs(1 - 3) = 2. For index 4; there is a tie between the 'e' at index 3 and the 'e' at index 5; but the distance is still the same: abs(4 - 3) == abs(4 - 5) = 1. The closest occurrence of 'e' for index 8 is at index 6; so the distance is abs(8 - 6) = 2. Example 2: Input: s = ""aaab""; c = ""b"" Output: [3;2;1;0] Constraints: 1 <= s.length <= 104 s[i] and c are lowercase English letters. It is guaranteed that c occurs at least once in s."
Walmart Labs,921,Minimum Add to Make Parentheses Valid,Med,"Array, Matrix, Simulation",You start at the cell (rStart; cStart) of an rows x cols grid facing east. The northwest corner is at the first row and column in the grid; and the southeast corner is at the last row and column. You will walk in a clockwise spiral shape to visit every position in this grid. Whenever you move outside the grid's boundary; we continue our walk outside the grid (but may return to the grid boundary later.). Eventually; we reach all rows * cols spaces of the grid. Return an array of coordinates representing the positions of the grid in the order you visited them. Example 1: Input: rows = 1; cols = 4; rStart = 0; cStart = 0 Output: [[0;0];[0;1];[0;2];[0;3]] Example 2: Input: rows = 5; cols = 6; rStart = 1; cStart = 4 Output: [[1;4];[1;5];[2;5];[2;4];[2;3];[1;3];[0;3];[0;4];[0;5];[3;5];[3;4];[3;3];[3;2];[2;2];[1;2];[0;2];[4;5];[4;4];[4;3];[4;2];[4;1];[3;1];[2;1];[1;1];[0;1];[4;0];[3;0];[2;0];[1;0];[0;0]] Constraints: 1 <= rows; cols <= 100 0 <= rStart < rows 0 <= cStart < cols
Walmart Labs,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Walmart Labs,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Walmart Labs,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Walmart Labs,44,Wildcard Matching,Hard,"String, Dynamic Programming, Greedy, Recursion","Given an input string (s) and a pattern (p); implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""*"" Output: true Explanation: '*' matches any sequence. Example 3: Input: s = ""cb""; p = ""?a"" Output: false Explanation: '?' matches 'c'; but the second letter is 'a'; which does not match 'b'. Constraints: 0 <= s.length; p.length <= 2000 s contains only lowercase English letters. p contains only lowercase English letters; '?' or '*'."
Walmart Labs,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
Walmart Labs,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Walmart Labs,84,Largest Rectangle in Histogram,Hard,"Array, Stack, Monotonic Stack",Given an array of integers heights representing the histogram's bar height where the width of each bar is 1; return the area of the largest rectangle in the histogram. Example 1: Input: heights = [2;1;5;6;2;3] Output: 10 Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area; which has an area = 10 units. Example 2: Input: heights = [2;4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104
Walmart Labs,90,Subsets II,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums that may contain duplicates; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;2] Output: [[];[1];[1;2];[1;2;2];[2];[2;2]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10
Walmart Labs,97,Interleaving String,Med,"String, Dynamic Programming","Given strings s1; s2; and s3; find whether s3 is formed by an interleaving of s1 and s2. An interleaving of two strings s and t is a configuration where s and t are divided into n and m substrings respectively; such that: s = s1 + s2 + ... + sn t = t1 + t2 + ... + tm |n - m| <= 1 The interleaving is s1 + t1 + s2 + t2 + s3 + t3 + ... or t1 + s1 + t2 + s2 + t3 + s3 + ... Note: a + b is the concatenation of strings a and b. Example 1: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbcbcac"" Output: true Explanation: One way to obtain s3 is: Split s1 into s1 = ""aa"" + ""bc"" + ""c""; and s2 into s2 = ""dbbc"" + ""a"". Interleaving the two splits; we get ""aa"" + ""dbbc"" + ""bc"" + ""a"" + ""c"" = ""aadbbcbcac"". Since s3 can be obtained by interleaving s1 and s2; we return true. Example 2: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbbaccc"" Output: false Explanation: Notice how it is impossible to interleave s2 with any other string to obtain s3. Example 3: Input: s1 = """"; s2 = """"; s3 = """" Output: true Constraints: 0 <= s1.length; s2.length <= 100 0 <= s3.length <= 200 s1; s2; and s3 consist of lowercase English letters. Follow up: Could you solve it using only O(s2.length) additional memory space?"
Walmart Labs,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Walmart Labs,128,Longest Consecutive Sequence,Med,"Array, Hash Table, Union Find",Given an unsorted array of integers nums; return the length of the longest consecutive elements sequence. You must write an algorithm that runs in O(n) time. Example 1: Input: nums = [100;4;200;1;3;2] Output: 4 Explanation: The longest consecutive elements sequence is [1; 2; 3; 4]. Therefore its length is 4. Example 2: Input: nums = [0;3;7;2;5;8;4;6;0;1] Output: 9 Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109
Walmart Labs,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Walmart Labs,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Walmart Labs,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Walmart Labs,341,Flatten Nested List Iterator,Med,"Stack, Tree, Depth-First Search, Design, Queue, Iterator",You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it. Implement the NestedIterator class: NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList. int next() Returns the next integer in the nested list. boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise. Your code will be tested with the following pseudocode: initialize iterator with nestedList res = [] while iterator.hasNext() append iterator.next() to the end of res return res If res matches the expected flattened list; then your code will be judged as correct. Example 1: Input: nestedList = [[1;1];2;[1;1]] Output: [1;1;2;1;1] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;1;2;1;1]. Example 2: Input: nestedList = [1;[4;[6]]] Output: [1;4;6] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;4;6]. Constraints: 1 <= nestedList.length <= 500 The values of the integers in the nested list is in the range [-106; 106].
Walmart Labs,407,Trapping Rain Water II,Hard,"Array, Breadth-First Search, Heap (Priority Queue), Matrix",Given an m x n integer matrix heightMap representing the height of each unit cell in a 2D elevation map; return the volume of water it can trap after raining. Example 1: Input: heightMap = [[1;4;3;1;3;2];[3;2;1;3;2;4];[2;3;3;2;3;1]] Output: 4 Explanation: After the rain; water is trapped between the blocks. We have two small ponds 1 and 3 units trapped. The total volume of water trapped is 4. Example 2: Input: heightMap = [[3;3;3;3;3];[3;2;2;2;3];[3;2;1;2;3];[3;2;2;2;3];[3;3;3;3;3]] Output: 10 Constraints: m == heightMap.length n == heightMap[i].length 1 <= m; n <= 200 0 <= heightMap[i][j] <= 2 * 104
Walmart Labs,416,Partition Equal Subset Sum,Med,"Array, Dynamic Programming",Given an integer array nums; return true if you can partition the array into two subsets such that the sum of the elements in both subsets is equal or false otherwise. Example 1: Input: nums = [1;5;11;5] Output: true Explanation: The array can be partitioned as [1; 5; 5] and [11]. Example 2: Input: nums = [1;2;3;5] Output: false Explanation: The array cannot be partitioned into equal sum subsets. Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 100
Walmart Labs,875,Koko Eating Bananas,Med,"Array, Two Pointers, Dynamic Programming, Enumeration",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr; return the length of the longest subarray; which is a mountain. Return 0 if there is no mountain subarray. Example 1: Input: arr = [2;1;4;7;3;2;5] Output: 5 Explanation: The largest mountain is [1;4;7;3;2] which has length 5. Example 2: Input: arr = [2;2;2] Output: 0 Explanation: There is no mountain. Constraints: 1 <= arr.length <= 104 0 <= arr[i] <= 104 Follow up: Can you solve it using only one pass? Can you solve it in O(1) space?
Walmart Labs,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Walmart Labs,1052,Grumpy Bookstore Owner,Med,"Array, Greedy, Sorting",
Walmart Labs,1143,Longest Common Subsequence,Med,"Array, Hash Table, Binary Search, Matrix, Counting",
Walmart Labs,1249,Minimum Remove to Make Valid Parentheses,Med,"Array, Hash Table, Binary Search, Design","Implement a SnapshotArray that supports the following interface: SnapshotArray(int length) initializes an array-like data structure with the given length. Initially; each element equals 0. void set(index; val) sets the element at the given index to be equal to val. int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1. int get(index; snap_id) returns the value at the given index; at the time we took the snapshot with the given snap_id Example 1: Input: [""SnapshotArray"";""set"";""snap"";""set"";""get""] [[3];[0;5];[];[0;6];[0;0]] Output: [null;null;0;null;5] Explanation: SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3 snapshotArr.set(0;5); // Set array[0] = 5 snapshotArr.snap(); // Take a snapshot; return snap_id = 0 snapshotArr.set(0;6); snapshotArr.get(0;0); // Get the value of array[0] with snap_id = 0; return 5 Constraints: 1 <= length <= 5 * 104 0 <= index < length 0 <= val <= 109 0 <= snap_id < (the total number of times we call snap()) At most 5 * 104 calls will be made to set; snap; and get."
Walmart Labs,1636,Sort Array by Increasing Frequency,Easy,"Math, String","Given a binary string s; return the number of substrings with all characters 1's. Since the answer may be too large; return it modulo 109 + 7. Example 1: Input: s = ""0110111"" Output: 9 Explanation: There are 9 substring in total with only 1's characters. ""1"" -> 5 times. ""11"" -> 3 times. ""111"" -> 1 time. Example 2: Input: s = ""101"" Output: 2 Explanation: Substring ""1"" is shown 2 times in s. Example 3: Input: s = ""111111"" Output: 21 Explanation: Each substring contains only 1's characters. Constraints: 1 <= s.length <= 105 s[i] is either '0' or '1'."
Walmart Labs,2291,Maximum Profit From Trading Stocks,Med,"Array, Dynamic Programming, Bit Manipulation, Bitmask",You are given an integer array nums of length n and an integer numSlots such that 2 * numSlots >= n. There are numSlots slots numbered from 1 to numSlots. You have to place all n integers into the slots such that each slot contains at most two numbers. The AND sum of a given placement is the sum of the bitwise AND of every number with its respective slot number. For example; the AND sum of placing the numbers [1; 3] into slot 1 and [4; 6] into slot 2 is equal to (1 AND 1) + (3 AND 1) + (4 AND 2) + (6 AND 2) = 1 + 1 + 0 + 2 = 4. Return the maximum possible AND sum of nums given numSlots slots. Example 1: Input: nums = [1;2;3;4;5;6]; numSlots = 3 Output: 9 Explanation: One possible placement is [1; 4] into slot 1; [2; 6] into slot 2; and [3; 5] into slot 3. This gives the maximum AND sum of (1 AND 1) + (4 AND 1) + (2 AND 2) + (6 AND 2) + (3 AND 3) + (5 AND 3) = 1 + 0 + 2 + 2 + 3 + 1 = 9. Example 2: Input: nums = [1;3;10;4;7;1]; numSlots = 9 Output: 24 Explanation: One possible placement is [1; 1] into slot 1; [3] into slot 3; [4] into slot 4; [7] into slot 7; and [10] into slot 9. This gives the maximum AND sum of (1 AND 1) + (1 AND 1) + (3 AND 3) + (4 AND 4) + (7 AND 7) + (10 AND 9) = 1 + 1 + 3 + 4 + 7 + 8 = 24. Note that slots 2; 5; 6; and 8 are empty which is permitted. Constraints: n == nums.length 1 <= numSlots <= 9 1 <= n <= 2 * numSlots 1 <= nums[i] <= 15
Walmart Labs,2625,Flatten Deeply Nested Array,Med,"Array, Matrix, Prefix Sum",You are given a positive integer n; indicating that we initially have an n x n 0-indexed integer matrix mat filled with zeroes. You are also given a 2D integer array query. For each query[i] = [row1i; col1i; row2i; col2i]; you should do the following operation: Add 1 to every element in the submatrix with the top left corner (row1i; col1i) and the bottom right corner (row2i; col2i). That is; add 1 to mat[x][y] for all row1i <= x <= row2i and col1i <= y <= col2i. Return the matrix mat after performing every query. Example 1: Input: n = 3; queries = [[1;1;2;2];[0;0;1;1]] Output: [[1;1;0];[1;2;1];[0;1;1]] Explanation: The diagram above shows the initial matrix; the matrix after the first query; and the matrix after the second query. - In the first query; we add 1 to every element in the submatrix with the top left corner (1; 1) and bottom right corner (2; 2). - In the second query; we add 1 to every element in the submatrix with the top left corner (0; 0) and bottom right corner (1; 1). Example 2: Input: n = 2; queries = [[0;0;1;1]] Output: [[1;1];[1;1]] Explanation: The diagram above shows the initial matrix and the matrix after the first query. - In the first query we add 1 to every element in the matrix. Constraints: 1 <= n <= 500 1 <= queries.length <= 104 0 <= row1i <= row2i < n 0 <= col1i <= col2i < n
Walmart Labs,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Walmart Labs,6,Zigzag Conversion,Med,String,"The string ""PAYPALISHIRING"" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: ""PAHNAPLSIIGYIR"" Write the code that will take a string and make this conversion given a number of rows: string convert(string s; int numRows); Example 1: Input: s = ""PAYPALISHIRING""; numRows = 3 Output: ""PAHNAPLSIIGYIR"" Example 2: Input: s = ""PAYPALISHIRING""; numRows = 4 Output: ""PINALSIGYAHRPI"" Explanation: P I N A L S I G Y A H R P I Example 3: Input: s = ""A""; numRows = 1 Output: ""A"" Constraints: 1 <= s.length <= 1000 s consists of English letters (lower-case and upper-case); ';' and '.'. 1 <= numRows <= 1000"
Walmart Labs,7,Reverse Integer,Med,Math,Given a signed 32-bit integer x; return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231; 231 - 1]; then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: Input: x = 123 Output: 321 Example 2: Input: x = -123 Output: -321 Example 3: Input: x = 120 Output: 21 Constraints: -231 <= x <= 231 - 1
Walmart Labs,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
Walmart Labs,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Walmart Labs,32,Longest Valid Parentheses,Hard,"String, Dynamic Programming, Stack","Given a string containing just the characters '(' and ')'; return the length of the longest valid (well-formed) parentheses substring. Example 1: Input: s = ""(()"" Output: 2 Explanation: The longest valid parentheses substring is ""()"". Example 2: Input: s = "")()())"" Output: 4 Explanation: The longest valid parentheses substring is ""()()"". Example 3: Input: s = """" Output: 0 Constraints: 0 <= s.length <= 3 * 104 s[i] is '('; or ')'."
Walmart Labs,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
Walmart Labs,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Walmart Labs,57,Insert Interval,Med,Array,You are given an array of non-overlapping intervals intervals where intervals[i] = [starti; endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start; end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary). Return intervals after the insertion. Note that you don't need to modify intervals in-place. You can make a new array and return it. Example 1: Input: intervals = [[1;3];[6;9]]; newInterval = [2;5] Output: [[1;5];[6;9]] Example 2: Input: intervals = [[1;2];[3;5];[6;7];[8;10];[12;16]]; newInterval = [4;8] Output: [[1;2];[3;10];[12;16]] Explanation: Because the new interval [4;8] overlaps with [3;5];[6;7];[8;10]. Constraints: 0 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 105 intervals is sorted by starti in ascending order. newInterval.length == 2 0 <= start <= end <= 105
Walmart Labs,68,Text Justification,Hard,"Array, String, Simulation","Given an array of strings words and a width maxWidth; format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is; pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words; the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text; it should be left-justified; and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = [""This""; ""is""; ""an""; ""example""; ""of""; ""text""; ""justification.""]; maxWidth = 16 Output: [ ""This is an""; ""example of text""; ""justification. "" ] Example 2: Input: words = [""What"";""must"";""be"";""acknowledgment"";""shall"";""be""]; maxWidth = 16 Output: [ ""What must be""; ""acknowledgment ""; ""shall be "" ] Explanation: Note that the last line is ""shall be "" instead of ""shall be""; because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = [""Science"";""is"";""what"";""we"";""understand"";""well"";""enough"";""to"";""explain"";""to"";""a"";""computer."";""Art"";""is"";""everything"";""else"";""we"";""do""]; maxWidth = 20 Output: [ ""Science is what we""; ""understand well""; ""enough to explain to""; ""a computer. Art is""; ""everything else we""; ""do "" ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth"
Walmart Labs,81,Search in Rotated Sorted Array II,Med,"Array, Binary Search",There is an integer array nums sorted in non-decreasing order (not necessarily with distinct values). Before being passed to your function; nums is rotated at an unknown pivot index k (0 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;4;4;5;6;6;7] might be rotated at pivot index 5 and become [4;5;6;6;7;0;1;2;4;4]. Given the array nums after the rotation and an integer target; return true if target is in nums; or false if it is not in nums. You must decrease the overall operation steps as much as possible. Example 1: Input: nums = [2;5;6;0;0;1;2]; target = 0 Output: true Example 2: Input: nums = [2;5;6;0;0;1;2]; target = 3 Output: false Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 nums is guaranteed to be rotated at some pivot. -104 <= target <= 104 Follow up: This problem is similar to Search in Rotated Sorted Array; but nums may contain duplicates. Would this affect the runtime complexity? How and why?
Walmart Labs,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Walmart Labs,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Nvidia,1046,Last Stone Weight,Easy,"Array, Binary Search, Sliding Window, Prefix Sum",Given a binary array nums and an integer k; return the maximum number of consecutive 1's in the array if you can flip at most k 0's. Example 1: Input: nums = [1;1;1;0;0;0;1;1;1;1;0]; k = 2 Output: 6 Explanation: [1;1;1;0;0;1;1;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Example 2: Input: nums = [0;0;1;1;0;0;1;1;1;0;1;1;0;0;0;1;1;1;1]; k = 3 Output: 10 Explanation: [0;0;1;1;1;1;1;1;1;1;1;1;0;0;0;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1. 0 <= k <= nums.length
Nvidia,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Nvidia,2571,Minimum Operations to Reduce an Integer to 0,Med,"Math, Prefix Sum",Given a positive integer n; find the pivot integer x such that: The sum of all elements between 1 and x inclusively equals the sum of all elements between x and n inclusively. Return the pivot integer x. If no such integer exists; return -1. It is guaranteed that there will be at most one pivot index for the given input. Example 1: Input: n = 8 Output: 6 Explanation: 6 is the pivot integer since: 1 + 2 + 3 + 4 + 5 + 6 = 6 + 7 + 8 = 21. Example 2: Input: n = 1 Output: 1 Explanation: 1 is the pivot integer since: 1 = 1. Example 3: Input: n = 4 Output: -1 Explanation: It can be proved that no such integer exist. Constraints: 1 <= n <= 1000
Nvidia,761,Special Binary String,Hard,"Array, Sorting, Heap (Priority Queue)",
Nvidia,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Nvidia,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Nvidia,1610,Maximum Number of Visible Points,Hard,"Math, Bit Manipulation","You are given an integer n and an integer start. Define an array nums where nums[i] = start + 2 * i (0-indexed) and n == nums.length. Return the bitwise XOR of all elements of nums. Example 1: Input: n = 5; start = 0 Output: 8 Explanation: Array nums is equal to [0; 2; 4; 6; 8] where (0 ^ 2 ^ 4 ^ 6 ^ 8) = 8. Where ""^"" corresponds to bitwise XOR operator. Example 2: Input: n = 4; start = 3 Output: 8 Explanation: Array nums is equal to [3; 5; 7; 9] where (3 ^ 5 ^ 7 ^ 9) = 8. Constraints: 1 <= n <= 1000 0 <= start <= 1000 n == nums.length"
Nvidia,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Nvidia,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Nvidia,268,Missing Number,Easy,"Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting",Given an array nums containing n distinct numbers in the range [0; n]; return the only number in the range that is missing from the array. Example 1: Input: nums = [3;0;1] Output: 2 Explanation: n = 3 since there are 3 numbers; so all numbers are in the range [0;3]. 2 is the missing number in the range since it does not appear in nums. Example 2: Input: nums = [0;1] Output: 2 Explanation: n = 2 since there are 2 numbers; so all numbers are in the range [0;2]. 2 is the missing number in the range since it does not appear in nums. Example 3: Input: nums = [9;6;4;2;3;5;7;0;1] Output: 8 Explanation: n = 9 since there are 9 numbers; so all numbers are in the range [0;9]. 8 is the missing number in the range since it does not appear in nums. Constraints: n == nums.length 1 <= n <= 104 0 <= nums[i] <= n All the numbers of nums are unique. Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?
Nvidia,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Nvidia,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Nvidia,190,Reverse Bits,Easy,"Divide and Conquer, Bit Manipulation",Reverse bits of a given 32 bits unsigned integer. Note: Note that in some languages; such as Java; there is no unsigned integer type. In this case; both input and output will be given as a signed integer type. They should not affect your implementation; as the integer's internal binary representation is the same; whether it is signed or unsigned. In Java; the compiler represents the signed integers using 2's complement notation. Therefore; in Example 2 above; the input represents the signed integer -3 and the output represents the signed integer -1073741825. Example 1: Input: n = 00000010100101000001111010011100 Output: 964176192 (00111001011110000010100101000000) Explanation: The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596; so return 964176192 which its binary representation is 00111001011110000010100101000000. Example 2: Input: n = 11111111111111111111111111111101 Output: 3221225471 (10111111111111111111111111111111) Explanation: The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293; so return 3221225471 which its binary representation is 10111111111111111111111111111111. Constraints: The input must be a binary string of length 32 Follow up: If this function is called many times; how would you optimize it?
Nvidia,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Nvidia,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Nvidia,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Nvidia,138,Copy List with Random Pointer,Med,"Hash Table, Linked List",A linked list of length n is given such that each node contains an additional random pointer; which could point to any node in the list; or null. Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes; where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list. For example; if there are two nodes X and Y in the original list; where X.random --> Y; then for the corresponding two nodes x and y in the copied list; x.random --> y. Return the head of the copied linked list. The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val; random_index] where: val: an integer representing Node.val random_index: the index of the node (range from 0 to n-1) that the random pointer points to; or null if it does not point to any node. Your code will only be given the head of the original linked list. Example 1: Input: head = [[7;null];[13;0];[11;4];[10;2];[1;0]] Output: [[7;null];[13;0];[11;4];[10;2];[1;0]] Example 2: Input: head = [[1;1];[2;1]] Output: [[1;1];[2;1]] Example 3: Input: head = [[3;null];[3;0];[3;null]] Output: [[3;null];[3;0];[3;null]] Constraints: 0 <= n <= 1000 -104 <= Node.val <= 104 Node.random is null or is pointing to some node in the linked list.
Nvidia,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Nvidia,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Nvidia,509,Fibonacci Number,Easy,"Tree, Binary Search Tree, Binary Tree",
Nvidia,1570,Dot Product of Two Sparse Vectors,Med,"Array, Stack, Monotonic Stack",You are given an integer array prices where prices[i] is the price of the ith item in a shop. There is a special discount for items in the shop. If you buy the ith item; then you will receive a discount equivalent to prices[j] where j is the minimum index such that j > i and prices[j] <= prices[i]. Otherwise; you will not receive any discount at all. Return an integer array answer where answer[i] is the final price you will pay for the ith item of the shop; considering the special discount. Example 1: Input: prices = [8;4;6;2;3] Output: [4;2;4;2;3] Explanation: For item 0 with price[0]=8 you will receive a discount equivalent to prices[1]=4; therefore; the final price you will pay is 8 - 4 = 4. For item 1 with price[1]=4 you will receive a discount equivalent to prices[3]=2; therefore; the final price you will pay is 4 - 2 = 2. For item 2 with price[2]=6 you will receive a discount equivalent to prices[3]=2; therefore; the final price you will pay is 6 - 2 = 4. For items 3 and 4 you will not receive any discount at all. Example 2: Input: prices = [1;2;3;4;5] Output: [1;2;3;4;5] Explanation: In this case; for all items; you will not receive any discount at all. Example 3: Input: prices = [10;1;1;6] Output: [9;0;1;6] Constraints: 1 <= prices.length <= 500 1 <= prices[i] <= 1000
Nvidia,2365,Task Scheduler II,Med,String,"Given a string s and a character letter; return the percentage of characters in s that equal letter rounded down to the nearest whole percent. Example 1: Input: s = ""foobar""; letter = ""o"" Output: 33 Explanation: The percentage of characters in s that equal the letter 'o' is 2 / 6 * 100% = 33% when rounded down; so we return 33. Example 2: Input: s = ""jjjj""; letter = ""k"" Output: 0 Explanation: The percentage of characters in s that equal the letter 'k' is 0%; so we return 0. Constraints: 1 <= s.length <= 100 s consists of lowercase English letters. letter is a lowercase English letter."
Nvidia,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Nvidia,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Nvidia,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Nvidia,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Nvidia,7,Reverse Integer,Med,Math,Given a signed 32-bit integer x; return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231; 231 - 1]; then return 0. Assume the environment does not allow you to store 64-bit integers (signed or unsigned). Example 1: Input: x = 123 Output: 321 Example 2: Input: x = -123 Output: -321 Example 3: Input: x = 120 Output: 21 Constraints: -231 <= x <= 231 - 1
Nvidia,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Nvidia,92,Reverse Linked List II,Med,Linked List,Given the head of a singly linked list and two integers left and right where left <= right; reverse the nodes of the list from position left to position right; and return the reversed list. Example 1: Input: head = [1;2;3;4;5]; left = 2; right = 4 Output: [1;4;3;2;5] Example 2: Input: head = [5]; left = 1; right = 1 Output: [5] Constraints: The number of nodes in the list is n. 1 <= n <= 500 -500 <= Node.val <= 500 1 <= left <= right <= n Follow up: Could you do it in one pass?
Nvidia,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Nvidia,160,Intersection of Two Linked Lists,Easy,"Hash Table, Linked List, Two Pointers",Given the heads of two singly linked-lists headA and headB; return the node at which the two lists intersect. If the two linked lists have no intersection at all; return null. For example; the following two linked lists begin to intersect at node c1: The test cases are generated such that there are no cycles anywhere in the entire linked structure. Note that the linked lists must retain their original structure after the function returns. Custom Judge: The inputs to the judge are given as follows (your program is not given these inputs): intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node. listA - The first linked list. listB - The second linked list. skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node. skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node. The judge will then create the linked structure based on these inputs and pass the two heads; headA and headB to your program. If you correctly return the intersected node; then your solution will be accepted. Example 1: Input: intersectVal = 8; listA = [4;1;8;4;5]; listB = [5;6;1;8;4;5]; skipA = 2; skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [4;1;8;4;5]. From the head of B; it reads as [5;6;1;8;4;5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words; they point to two different locations in memory; while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory. Example 2: Input: intersectVal = 2; listA = [1;9;1;2;4]; listB = [3;2;4]; skipA = 3; skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [1;9;1;2;4]. From the head of B; it reads as [3;2;4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B. Example 3: Input: intersectVal = 0; listA = [2;6;4]; listB = [1;5]; skipA = 3; skipB = 2 Output: No intersection Explanation: From the head of A; it reads as [2;6;4]. From the head of B; it reads as [1;5]. Since the two lists do not intersect; intersectVal must be 0; while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect; so return null. Constraints: The number of nodes of listA is in the m. The number of nodes of listB is in the n. 1 <= m; n <= 3 * 104 1 <= Node.val <= 105 0 <= skipA <= m 0 <= skipB <= n intersectVal is 0 if listA and listB do not intersect. intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect. Follow up: Could you write a solution that runs in O(m + n) time and use only O(1) memory?
Nvidia,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Nvidia,274,H-Index,Med,"Array, Sorting, Counting Sort",Given an array of integers citations where citations[i] is the number of citations a researcher received for their ith paper; return the researcher's h-index. According to the definition of h-index on Wikipedia: The h-index is defined as the maximum value of h such that the given researcher has published at least h papers that have each been cited at least h times. Example 1: Input: citations = [3;0;6;1;5] Output: 3 Explanation: [3;0;6;1;5] means the researcher has 5 papers in total and each of them had received 3; 0; 6; 1; 5 citations respectively. Since the researcher has 3 papers with at least 3 citations each and the remaining two with no more than 3 citations each; their h-index is 3. Example 2: Input: citations = [1;3;1] Output: 1 Constraints: n == citations.length 1 <= n <= 5000 0 <= citations[i] <= 1000
Nvidia,287,Find the Duplicate Number,Med,"Array, Two Pointers, Binary Search, Bit Manipulation",Given an array of integers nums containing n + 1 integers where each integer is in the range [1; n] inclusive. There is only one repeated number in nums; return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Example 1: Input: nums = [1;3;4;2;2] Output: 2 Example 2: Input: nums = [3;1;3;4;2] Output: 3 Example 3: Input: nums = [3;3;3;3;3] Output: 3 Constraints: 1 <= n <= 105 nums.length == n + 1 1 <= nums[i] <= n All the integers in nums appear only once except for precisely one integer which appears two or more times. Follow up: How can we prove that at least one duplicate number must exist in nums? Can you solve the problem in linear runtime complexity?
Nvidia,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Nvidia,540,Single Element in a Sorted Array,Med,"Array, Binary Search",You are given a sorted array consisting of only integers where every element appears exactly twice; except for one element which appears exactly once. Return the single element that appears only once. Your solution must run in O(log n) time and O(1) space. Example 1: Input: nums = [1;1;2;3;3;4;4;8;8] Output: 2 Example 2: Input: nums = [3;3;7;7;10;11;11] Output: 10 Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 105
Nvidia,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
Nvidia,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
Nvidia,136,Single Number,Easy,"Array, Bit Manipulation",Given a non-empty array of integers nums; every element appears twice except for one. Find that single one. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;1] Output: 1 Example 2: Input: nums = [4;1;2;1;2] Output: 4 Example 3: Input: nums = [1] Output: 1 Constraints: 1 <= nums.length <= 3 * 104 -3 * 104 <= nums[i] <= 3 * 104 Each element in the array appears twice except for one element which appears only once.
Nvidia,149,Max Points on a Line,Hard,"Array, Hash Table, Math, Geometry",Given an array of points where points[i] = [xi; yi] represents a point on the X-Y plane; return the maximum number of points that lie on the same straight line. Example 1: Input: points = [[1;1];[2;2];[3;3]] Output: 3 Example 2: Input: points = [[1;1];[3;2];[5;3];[4;1];[2;3];[1;4]] Output: 4 Constraints: 1 <= points.length <= 300 points[i].length == 2 -104 <= xi; yi <= 104 All the points are unique.
Nvidia,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Nvidia,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Nvidia,188,Best Time to Buy and Sell Stock IV,Hard,"Array, Dynamic Programming",You are given an integer array prices where prices[i] is the price of a given stock on the ith day; and an integer k. Find the maximum profit you can achieve. You may complete at most k transactions: i.e. you may buy at most k times and sell at most k times. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: k = 2; prices = [2;4;1] Output: 2 Explanation: Buy on day 1 (price = 2) and sell on day 2 (price = 4); profit = 4-2 = 2. Example 2: Input: k = 2; prices = [3;2;6;5;0;3] Output: 7 Explanation: Buy on day 2 (price = 2) and sell on day 3 (price = 6); profit = 6-2 = 4. Then buy on day 5 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Constraints: 1 <= k <= 100 1 <= prices.length <= 1000 0 <= prices[i] <= 1000
Nvidia,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Nvidia,208,Implement Trie (Prefix Tree),Med,"Hash Table, String, Design, Trie","A trie (pronounced as ""try"") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure; such as autocomplete and spellchecker. Implement the Trie class: Trie() Initializes the trie object. void insert(String word) Inserts the string word into the trie. boolean search(String word) Returns true if the string word is in the trie (i.e.; was inserted before); and false otherwise. boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix; and false otherwise. Example 1: Input [""Trie""; ""insert""; ""search""; ""search""; ""startsWith""; ""insert""; ""search""] [[]; [""apple""]; [""apple""]; [""app""]; [""app""]; [""app""]; [""app""]] Output [null; null; true; false; true; null; true] Explanation Trie trie = new Trie(); trie.insert(""apple""); trie.search(""apple""); // return True trie.search(""app""); // return False trie.startsWith(""app""); // return True trie.insert(""app""); trie.search(""app""); // return True Constraints: 1 <= word.length; prefix.length <= 2000 word and prefix consist only of lowercase English letters. At most 3 * 104 calls in total will be made to insert; search; and startsWith."
Nvidia,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Nvidia,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
Nvidia,338,Counting Bits,Easy,"Dynamic Programming, Bit Manipulation",Given an integer n; return an array ans of length n + 1 such that for each i (0 <= i <= n); ans[i] is the number of 1's in the binary representation of i. Example 1: Input: n = 2 Output: [0;1;1] Explanation: 0 --> 0 1 --> 1 2 --> 10 Example 2: Input: n = 5 Output: [0;1;1;2;1;2] Explanation: 0 --> 0 1 --> 1 2 --> 10 3 --> 11 4 --> 100 5 --> 101 Constraints: 0 <= n <= 105 Follow up: It is very easy to come up with a solution with a runtime of O(n log n). Can you do it in linear time O(n) and possibly in a single pass? Can you do it without using any built-in function (i.e.; like __builtin_popcount in C++)?
Nvidia,349,Intersection of Two Arrays,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must be unique and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [9;4] Explanation: [4;9] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000
Nvidia,384,Shuffle an Array,Med,"Array, Math, Design, Randomized","Given an integer array nums; design an algorithm to randomly shuffle the array. All permutations of the array should be equally likely as a result of the shuffling. Implement the Solution class: Solution(int[] nums) Initializes the object with the integer array nums. int[] reset() Resets the array to its original configuration and returns it. int[] shuffle() Returns a random shuffling of the array. Example 1: Input [""Solution""; ""shuffle""; ""reset""; ""shuffle""] [[[1; 2; 3]]; []; []; []] Output [null; [3; 1; 2]; [1; 2; 3]; [1; 3; 2]] Explanation Solution solution = new Solution([1; 2; 3]); solution.shuffle(); // Shuffle the array [1;2;3] and return its result. // Any permutation of [1;2;3] must be equally likely to be returned. // Example: return [3; 1; 2] solution.reset(); // Resets the array back to its original configuration [1;2;3]. Return [1; 2; 3] solution.shuffle(); // Returns the random shuffling of array [1;2;3]. Example: return [1; 3; 2] Constraints: 1 <= nums.length <= 50 -106 <= nums[i] <= 106 All the elements of nums are unique. At most 104 calls in total will be made to reset and shuffle."
Nvidia,392,Is Subsequence,Easy,"Two Pointers, String, Dynamic Programming","Given two strings s and t; return true if s is a subsequence of t; or false otherwise. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not). Example 1: Input: s = ""abc""; t = ""ahbgdc"" Output: true Example 2: Input: s = ""axc""; t = ""ahbgdc"" Output: false Constraints: 0 <= s.length <= 100 0 <= t.length <= 104 s and t consist only of lowercase English letters. Follow up: Suppose there are lots of incoming s; say s1; s2; ...; sk where k >= 109; and you want to check one by one to see if t has its subsequence. In this scenario; how would you change your code?"
Nvidia,724,Find Pivot Index,Easy,"Array, Prefix Sum",Given an array of integers nums; calculate the pivot index of this array. The pivot index is the index where the sum of all the numbers strictly to the left of the index is equal to the sum of all the numbers strictly to the index's right. If the index is on the left edge of the array; then the left sum is 0 because there are no elements to the left. This also applies to the right edge of the array. Return the leftmost pivot index. If no such index exists; return -1. Example 1: Input: nums = [1;7;3;6;5;6] Output: 3 Explanation: The pivot index is 3. Left sum = nums[0] + nums[1] + nums[2] = 1 + 7 + 3 = 11 Right sum = nums[4] + nums[5] = 5 + 6 = 11 Example 2: Input: nums = [1;2;3] Output: -1 Explanation: There is no index that satisfies the conditions in the problem statement. Example 3: Input: nums = [2;1;-1] Output: 0 Explanation: The pivot index is 0. Left sum = 0 (no elements to the left of index 0) Right sum = nums[1] + nums[2] = 1 + -1 = 0 Constraints: 1 <= nums.length <= 104 -1000 <= nums[i] <= 1000 Note: This question is the same as 1991: https://leetcode.com/problems/find-the-middle-index-in-array/
Nvidia,426,Convert Binary Search Tree to Sorted Doubly Linked List,Med,,
Nvidia,773,Sliding Puzzle,Hard,"Divide and Conquer, Tree",A Binary Matrix is a matrix in which all the elements are either 0 or 1. Given quadTree1 and quadTree2. quadTree1 represents a n * n binary matrix and quadTree2 represents another n * n binary matrix. Return a Quad-Tree representing the n * n binary matrix which is the result of logical bitwise OR of the two binary matrixes represented by quadTree1 and quadTree2. Notice that you can assign the value of a node to True or False when isLeaf is False; and both are accepted in the answer. A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides; each node has two attributes: val: True if the node represents a grid of 1's or False if the node represents a grid of 0's. isLeaf: True if the node is leaf node on the tree or False if the node has the four children. class Node { public boolean val; public boolean isLeaf; public Node topLeft; public Node topRight; public Node bottomLeft; public Node bottomRight; } We can construct a Quad-Tree from a two-dimensional area using the following steps: If the current grid has the same value (i.e all 1's or all 0's) set isLeaf True and set val to the value of the grid and set the four children to Null and stop. If the current grid has different values; set isLeaf to False and set val to any value and divide the current grid into four sub-grids as shown in the photo. Recurse for each of the children with the proper sub-grid. If you want to know more about the Quad-Tree; you can refer to the wiki. Quad-Tree format: The input/output represents the serialized format of a Quad-Tree using level order traversal; where null signifies a path terminator where no node exists below. It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list [isLeaf; val]. If the value of isLeaf or val is True we represent it as 1 in the list [isLeaf; val] and if the value of isLeaf or val is False we represent it as 0. Example 1: Input: quadTree1 = [[0;1];[1;1];[1;1];[1;0];[1;0]] ; quadTree2 = [[0;1];[1;1];[0;1];[1;1];[1;0];null;null;null;null;[1;0];[1;0];[1;1];[1;1]] Output: [[0;0];[1;1];[1;1];[1;1];[1;0]] Explanation: quadTree1 and quadTree2 are shown above. You can see the binary matrix which is represented by each Quad-Tree. If we apply logical bitwise OR on the two binary matrices we get the binary matrix below which is represented by the result Quad-Tree. Notice that the binary matrices shown are only for illustration; you don't have to construct the binary matrix to get the result tree. Example 2: Input: quadTree1 = [[1;0]]; quadTree2 = [[1;0]] Output: [[1;0]] Explanation: Each tree represents a binary matrix of size 1*1. Each matrix contains only zero. The resulting matrix is of size 1*1 with also zero. Constraints: quadTree1 and quadTree2 are both valid Quad-Trees each representing a n * n grid. n == 2x where 0 <= x <= 9.
Nvidia,706,Design HashMap,Easy,,
Nvidia,841,Keys and Rooms,Med,"Array, Two Pointers, String","Given a string s and a character c that occurs in s; return an array of integers answer where answer.length == s.length and answer[i] is the distance from index i to the closest occurrence of character c in s. The distance between two indices i and j is abs(i - j); where abs is the absolute value function. Example 1: Input: s = ""loveleetcode""; c = ""e"" Output: [3;2;1;0;1;0;0;1;2;2;1;0] Explanation: The character 'e' appears at indices 3; 5; 6; and 11 (0-indexed). The closest occurrence of 'e' for index 0 is at index 3; so the distance is abs(0 - 3) = 3. The closest occurrence of 'e' for index 1 is at index 3; so the distance is abs(1 - 3) = 2. For index 4; there is a tie between the 'e' at index 3 and the 'e' at index 5; but the distance is still the same: abs(4 - 3) == abs(4 - 5) = 1. The closest occurrence of 'e' for index 8 is at index 6; so the distance is abs(8 - 6) = 2. Example 2: Input: s = ""aaab""; c = ""b"" Output: [3;2;1;0] Constraints: 1 <= s.length <= 104 s[i] and c are lowercase English letters. It is guaranteed that c occurs at least once in s."
Nvidia,894,All Possible Full Binary Trees,Med,"Array, Hash Table, Math, Binary Search, Sorting, Randomized","You are given an integer n and an array of unique integers blacklist. Design an algorithm to pick a random integer in the range [0; n - 1] that is not in blacklist. Any integer that is in the mentioned range and not in blacklist should be equally likely to be returned. Optimize your algorithm such that it minimizes the number of calls to the built-in random function of your language. Implement the Solution class: Solution(int n; int[] blacklist) Initializes the object with the integer n and the blacklisted integers blacklist. int pick() Returns a random integer in the range [0; n - 1] and not in blacklist. Example 1: Input [""Solution""; ""pick""; ""pick""; ""pick""; ""pick""; ""pick""; ""pick""; ""pick""] [[7; [2; 3; 5]]; []; []; []; []; []; []; []] Output [null; 0; 4; 1; 6; 1; 0; 4] Explanation Solution solution = new Solution(7; [2; 3; 5]); solution.pick(); // return 0; any integer from [0;1;4;6] should be ok. Note that for every call of pick; // 0; 1; 4; and 6 must be equally likely to be returned (i.e.; with probability 1/4). solution.pick(); // return 4 solution.pick(); // return 1 solution.pick(); // return 6 solution.pick(); // return 1 solution.pick(); // return 0 solution.pick(); // return 4 Constraints: 1 <= n <= 109 0 <= blacklist.length <= min(105; n - 1) 0 <= blacklist[i] < n All the values of blacklist are unique. At most 2 * 104 calls will be made to pick."
Nvidia,921,Minimum Add to Make Parentheses Valid,Med,"Array, Matrix, Simulation",You start at the cell (rStart; cStart) of an rows x cols grid facing east. The northwest corner is at the first row and column in the grid; and the southeast corner is at the last row and column. You will walk in a clockwise spiral shape to visit every position in this grid. Whenever you move outside the grid's boundary; we continue our walk outside the grid (but may return to the grid boundary later.). Eventually; we reach all rows * cols spaces of the grid. Return an array of coordinates representing the positions of the grid in the order you visited them. Example 1: Input: rows = 1; cols = 4; rStart = 0; cStart = 0 Output: [[0;0];[0;1];[0;2];[0;3]] Example 2: Input: rows = 5; cols = 6; rStart = 1; cStart = 4 Output: [[1;4];[1;5];[2;5];[2;4];[2;3];[1;3];[0;3];[0;4];[0;5];[3;5];[3;4];[3;3];[3;2];[2;2];[1;2];[0;2];[4;5];[4;4];[4;3];[4;2];[4;1];[3;1];[2;1];[1;1];[0;1];[4;0];[3;0];[2;0];[1;0];[0;0]] Constraints: 1 <= rows; cols <= 100 0 <= rStart < rows 0 <= cStart < cols
Nvidia,1197,Minimum Knight Moves,Med,"String, Stack, Recursion","A boolean expression is an expression that evaluates to either true or false. It can be in one of the following shapes: 't' that evaluates to true. 'f' that evaluates to false. '!(subExpr)' that evaluates to the logical NOT of the inner expression subExpr. '&(subExpr1; subExpr2; ...; subExprn)' that evaluates to the logical AND of the inner expressions subExpr1; subExpr2; ...; subExprn where n >= 1. '|(subExpr1; subExpr2; ...; subExprn)' that evaluates to the logical OR of the inner expressions subExpr1; subExpr2; ...; subExprn where n >= 1. Given a string expression that represents a boolean expression; return the evaluation of that expression. It is guaranteed that the given expression is valid and follows the given rules. Example 1: Input: expression = ""&(|(f))"" Output: false Explanation: First; evaluate |(f) --> f. The expression is now ""&(f)"". Then; evaluate &(f) --> f. The expression is now ""f"". Finally; return false. Example 2: Input: expression = ""|(f;f;f;t)"" Output: true Explanation: The evaluation of (false OR false OR false OR true) is true. Example 3: Input: expression = ""!(&(f;t))"" Output: true Explanation: First; evaluate &(f;t) --> (false AND true) --> false --> f. The expression is now ""!(f)"". Then; evaluate !(f) --> NOT false --> true. We return true. Constraints: 1 <= expression.length <= 2 * 104 expression[i] is one following characters: '('; ')'; '&'; '|'; '!'; 't'; 'f'; and ';'."
Nvidia,1146,Snapshot Array,Med,"Math, String","For two strings s and t; we say ""t divides s"" if and only if s = t + t + t + ... + t + t (i.e.; t is concatenated with itself one or more times). Given two strings str1 and str2; return the largest string x such that x divides both str1 and str2. Example 1: Input: str1 = ""ABCABC""; str2 = ""ABC"" Output: ""ABC"" Example 2: Input: str1 = ""ABABAB""; str2 = ""ABAB"" Output: ""AB"" Example 3: Input: str1 = ""LEET""; str2 = ""CODE"" Output: """" Constraints: 1 <= str1.length; str2.length <= 1000 str1 and str2 consist of English uppercase letters."
Nvidia,1328,Break a Palindrome,Med,Database,
Nvidia,2433,Find The Original Array of Prefix Xor,Med,"Array, Hash Table, Counting","You are given an integer array ranks and a character array suits. You have 5 cards where the ith card has a rank of ranks[i] and a suit of suits[i]. The following are the types of poker hands you can make from best to worst: ""Flush"": Five cards of the same suit. ""Three of a Kind"": Three cards of the same rank. ""Pair"": Two cards of the same rank. ""High Card"": Any single card. Return a string representing the best type of poker hand you can make with the given cards. Note that the return values are case-sensitive. Example 1: Input: ranks = [13;2;3;1;9]; suits = [""a"";""a"";""a"";""a"";""a""] Output: ""Flush"" Explanation: The hand with all the cards consists of 5 cards with the same suit; so we have a ""Flush"". Example 2: Input: ranks = [4;4;2;4;4]; suits = [""d"";""a"";""a"";""b"";""c""] Output: ""Three of a Kind"" Explanation: The hand with the first; second; and fourth card consists of 3 cards with the same rank; so we have a ""Three of a Kind"". Note that we could also make a ""Pair"" hand but ""Three of a Kind"" is a better hand. Also note that other cards could be used to make the ""Three of a Kind"" hand. Example 3: Input: ranks = [10;10;2;12;9]; suits = [""a"";""b"";""c"";""a"";""d""] Output: ""Pair"" Explanation: The hand with the first and second card consists of 2 cards with the same rank; so we have a ""Pair"". Note that we cannot make a ""Flush"" or a ""Three of a Kind"". Constraints: ranks.length == suits.length == 5 1 <= ranks[i] <= 13 'a' <= suits[i] <= 'd' No two cards have the same rank and suit."
Nvidia,2461,Maximum Sum of Distinct Subarrays With Length K,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given the root of a binary tree with unique values; and an integer start. At minute 0; an infection starts from the node with value start. Each minute; a node becomes infected if: The node is currently uninfected. The node is adjacent to an infected node. Return the number of minutes needed for the entire tree to be infected. Example 1: Input: root = [1;5;3;null;4;10;6;9;2]; start = 3 Output: 4 Explanation: The following nodes are infected during: - Minute 0: Node 3 - Minute 1: Nodes 1; 10 and 6 - Minute 2: Node 5 - Minute 3: Node 4 - Minute 4: Nodes 9 and 2 It takes 4 minutes for the whole tree to be infected so we return 4. Example 2: Input: root = [1]; start = 1 Output: 0 Explanation: At minute 0; the only node in the tree is infected so we return 0. Constraints: The number of nodes in the tree is in the range [1; 105]. 1 <= Node.val <= 105 Each node has a unique value. A node with a value of start exists in the tree.
Nvidia,8,String to Integer (atoi),Med,String,"Implement the myAtoi(string s) function; which converts a string to a 32-bit signed integer. The algorithm for myAtoi(string s) is as follows: Whitespace: Ignore any leading whitespace ("" ""). Signedness: Determine the sign by checking if the next character is '-' or '+'; assuming positivity if neither present. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read; then the result is 0. Rounding: If the integer is out of the 32-bit signed integer range [-231; 231 - 1]; then round the integer to remain in the range. Specifically; integers less than -231 should be rounded to -231; and integers greater than 231 - 1 should be rounded to 231 - 1. Return the integer as the final result. Example 1: Input: s = ""42"" Output: 42 Explanation: The underlined characters are what is read in and the caret is the current reader position. Step 1: ""42"" (no characters read because there is no leading whitespace) ^ Step 2: ""42"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""42"" (""42"" is read in) ^ Example 2: Input: s = "" -042"" Output: -42 Explanation: Step 1: "" -042"" (leading whitespace is read and ignored) ^ Step 2: "" -042"" ('-' is read; so the result should be negative) ^ Step 3: "" -042"" (""042"" is read in; leading zeros ignored in the result) ^ Example 3: Input: s = ""1337c0d3"" Output: 1337 Explanation: Step 1: ""1337c0d3"" (no characters read because there is no leading whitespace) ^ Step 2: ""1337c0d3"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""1337c0d3"" (""1337"" is read in; reading stops because the next character is a non-digit) ^ Example 4: Input: s = ""0-1"" Output: 0 Explanation: Step 1: ""0-1"" (no characters read because there is no leading whitespace) ^ Step 2: ""0-1"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""0-1"" (""0"" is read in; reading stops because the next character is a non-digit) ^ Example 5: Input: s = ""words and 987"" Output: 0 Explanation: Reading stops at the first non-digit character 'w'. Constraints: 0 <= s.length <= 200 s consists of English letters (lower-case and upper-case); digits (0-9); ' '; '+'; '-'; and '.'."
Nvidia,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Nvidia,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Nvidia,22,Generate Parentheses,Med,"String, Dynamic Programming, Backtracking","Given n pairs of parentheses; write a function to generate all combinations of well-formed parentheses. Example 1: Input: n = 3 Output: [""((()))"";""(()())"";""(())()"";""()(())"";""()()()""] Example 2: Input: n = 1 Output: [""()""] Constraints: 1 <= n <= 8"
Nvidia,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
Nvidia,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Nvidia,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Nvidia,57,Insert Interval,Med,Array,You are given an array of non-overlapping intervals intervals where intervals[i] = [starti; endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start; end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary). Return intervals after the insertion. Note that you don't need to modify intervals in-place. You can make a new array and return it. Example 1: Input: intervals = [[1;3];[6;9]]; newInterval = [2;5] Output: [[1;5];[6;9]] Example 2: Input: intervals = [[1;2];[3;5];[6;7];[8;10];[12;16]]; newInterval = [4;8] Output: [[1;2];[3;10];[12;16]] Explanation: Because the new interval [4;8] overlaps with [3;5];[6;7];[8;10]. Constraints: 0 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 105 intervals is sorted by starti in ascending order. newInterval.length == 2 0 <= start <= end <= 105
Nvidia,73,Set Matrix Zeroes,Med,"Array, Hash Table, Matrix",Given an m x n integer matrix matrix; if an element is 0; set its entire row and column to 0's. You must do it in place. Example 1: Input: matrix = [[1;1;1];[1;0;1];[1;1;1]] Output: [[1;0;1];[0;0;0];[1;0;1]] Example 2: Input: matrix = [[0;1;2;0];[3;4;5;2];[1;3;1;5]] Output: [[0;0;0;0];[0;4;5;0];[0;3;1;0]] Constraints: m == matrix.length n == matrix[0].length 1 <= m; n <= 200 -231 <= matrix[i][j] <= 231 - 1 Follow up: A straightforward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space; but still not the best solution. Could you devise a constant space solution?
Nvidia,83,Remove Duplicates from Sorted List,Easy,Linked List,Given the head of a sorted linked list; delete all duplicates such that each element appears only once. Return the linked list sorted as well. Example 1: Input: head = [1;1;2] Output: [1;2] Example 2: Input: head = [1;1;2;3;3] Output: [1;2;3] Constraints: The number of nodes in the list is in the range [0; 300]. -100 <= Node.val <= 100 The list is guaranteed to be sorted in ascending order.
Nvidia,142,Linked List Cycle II,Med,"Hash Table, Linked List, Two Pointers",Given the head of a linked list; return the node where the cycle begins. If there is no cycle; return null. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to (0-indexed). It is -1 if there is no cycle. Note that pos is not passed as a parameter. Do not modify the linked list. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: tail connects to node index 1 Explanation: There is a cycle in the linked list; where tail connects to the second node. Example 2: Input: head = [1;2]; pos = 0 Output: tail connects to node index 0 Explanation: There is a cycle in the linked list; where tail connects to the first node. Example 3: Input: head = [1]; pos = -1 Output: no cycle Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Nvidia,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Nvidia,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Nvidia,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
Nvidia,191,Number of 1 Bits,Easy,"Divide and Conquer, Bit Manipulation",Given a positive integer n; write a function that returns the number of set bits in its binary representation (also known as the Hamming weight). Example 1: Input: n = 11 Output: 3 Explanation: The input binary string 1011 has a total of three set bits. Example 2: Input: n = 128 Output: 1 Explanation: The input binary string 10000000 has a total of one set bit. Example 3: Input: n = 2147483645 Output: 30 Explanation: The input binary string 1111111111111111111111111111101 has a total of thirty set bits. Constraints: 1 <= n <= 231 - 1 Follow up: If this function is called many times; how would you optimize it?
Nvidia,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Nvidia,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Nvidia,209,Minimum Size Subarray Sum,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of positive integers nums and a positive integer target; return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray; return 0 instead. Example 1: Input: target = 7; nums = [2;3;1;2;4;3] Output: 2 Explanation: The subarray [4;3] has the minimal length under the problem constraint. Example 2: Input: target = 4; nums = [1;4;4] Output: 1 Example 3: Input: target = 11; nums = [1;1;1;1;1;1;1;1] Output: 0 Constraints: 1 <= target <= 109 1 <= nums.length <= 105 1 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution of which the time complexity is O(n log(n)).
Nvidia,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Nvidia,223,Rectangle Area,Med,"Math, Geometry",Given the coordinates of two rectilinear rectangles in a 2D plane; return the total area covered by the two rectangles. The first rectangle is defined by its bottom-left corner (ax1; ay1) and its top-right corner (ax2; ay2). The second rectangle is defined by its bottom-left corner (bx1; by1) and its top-right corner (bx2; by2). Example 1: Input: ax1 = -3; ay1 = 0; ax2 = 3; ay2 = 4; bx1 = 0; by1 = -1; bx2 = 9; by2 = 2 Output: 45 Example 2: Input: ax1 = -2; ay1 = -2; ax2 = 2; ay2 = 2; bx1 = -2; by1 = -2; bx2 = 2; by2 = 2 Output: 16 Constraints: -104 <= ax1 <= ax2 <= 104 -104 <= ay1 <= ay2 <= 104 -104 <= bx1 <= bx2 <= 104 -104 <= by1 <= by2 <= 104
Nvidia,237,Delete Node in a Linked List,Med,Linked List,There is a singly-linked list head and we want to delete a node node in it. You are given the node to be deleted node. You will not be given access to the first node of head. All the values of the linked list are unique; and it is guaranteed that the given node node is not the last node in the linked list. Delete the given node. Note that by deleting the node; we do not mean removing it from memory. We mean: The value of the given node should not exist in the linked list. The number of nodes in the linked list should decrease by one. All the values before node should be in the same order. All the values after node should be in the same order. Custom testing: For the input; you should provide the entire linked list head and the node to be given node. node should not be the last node of the list and should be an actual node in the list. We will build the linked list and pass the node to your function. The output will be the entire list after calling your function. Example 1: Input: head = [4;5;1;9]; node = 5 Output: [4;1;9] Explanation: You are given the second node with value 5; the linked list should become 4 -> 1 -> 9 after calling your function. Example 2: Input: head = [4;5;1;9]; node = 1 Output: [4;5;9] Explanation: You are given the third node with value 1; the linked list should become 4 -> 5 -> 9 after calling your function. Constraints: The number of the nodes in the given list is in the range [2; 1000]. -1000 <= Node.val <= 1000 The value of each node in the list is unique. The node to be deleted is in the list and is not a tail node.
Nvidia,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Nvidia,255,Verify Preorder Sequence in Binary Search Tree,Med,"Array, Stack, Tree, Binary Search Tree, Recursion, Monotonic Stack, Binary Tree",
Nvidia,304,Range Sum Query 2D - Immutable,Med,"Array, Design, Matrix, Prefix Sum","Given a 2D matrix matrix; handle multiple queries of the following type: Calculate the sum of the elements of matrix inside the rectangle defined by its upper left corner (row1; col1) and lower right corner (row2; col2). Implement the NumMatrix class: NumMatrix(int[][] matrix) Initializes the object with the integer matrix matrix. int sumRegion(int row1; int col1; int row2; int col2) Returns the sum of the elements of matrix inside the rectangle defined by its upper left corner (row1; col1) and lower right corner (row2; col2). You must design an algorithm where sumRegion works on O(1) time complexity. Example 1: Input [""NumMatrix""; ""sumRegion""; ""sumRegion""; ""sumRegion""] [[[[3; 0; 1; 4; 2]; [5; 6; 3; 2; 1]; [1; 2; 0; 1; 5]; [4; 1; 0; 1; 7]; [1; 0; 3; 0; 5]]]; [2; 1; 4; 3]; [1; 1; 2; 2]; [1; 2; 2; 4]] Output [null; 8; 11; 12] Explanation NumMatrix numMatrix = new NumMatrix([[3; 0; 1; 4; 2]; [5; 6; 3; 2; 1]; [1; 2; 0; 1; 5]; [4; 1; 0; 1; 7]; [1; 0; 3; 0; 5]]); numMatrix.sumRegion(2; 1; 4; 3); // return 8 (i.e sum of the red rectangle) numMatrix.sumRegion(1; 1; 2; 2); // return 11 (i.e sum of the green rectangle) numMatrix.sumRegion(1; 2; 2; 4); // return 12 (i.e sum of the blue rectangle) Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 -104 <= matrix[i][j] <= 104 0 <= row1 <= row2 < m 0 <= col1 <= col2 < n At most 104 calls will be made to sumRegion."
Nvidia,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Nvidia,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
Nvidia,344,Reverse String,Easy,"Two Pointers, String","Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory. Example 1: Input: s = [""h"";""e"";""l"";""l"";""o""] Output: [""o"";""l"";""l"";""e"";""h""] Example 2: Input: s = [""H"";""a"";""n"";""n"";""a"";""h""] Output: [""h"";""a"";""n"";""n"";""a"";""H""] Constraints: 1 <= s.length <= 105 s[i] is a printable ascii character."
Nvidia,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Nvidia,382,Linked List Random Node,Med,"Linked List, Math, Reservoir Sampling, Randomized","Given a singly linked list; return a random node's value from the linked list. Each node must have the same probability of being chosen. Implement the Solution class: Solution(ListNode head) Initializes the object with the head of the singly-linked list head. int getRandom() Chooses a node randomly from the list and returns its value. All the nodes of the list should be equally likely to be chosen. Example 1: Input [""Solution""; ""getRandom""; ""getRandom""; ""getRandom""; ""getRandom""; ""getRandom""] [[[1; 2; 3]]; []; []; []; []; []] Output [null; 1; 3; 2; 2; 3] Explanation Solution solution = new Solution([1; 2; 3]); solution.getRandom(); // return 1 solution.getRandom(); // return 3 solution.getRandom(); // return 2 solution.getRandom(); // return 2 solution.getRandom(); // return 3 // getRandom() should return either 1; 2; or 3 randomly. Each element should have equal probability of returning. Constraints: The number of nodes in the linked list will be in the range [1; 104]. -104 <= Node.val <= 104 At most 104 calls will be made to getRandom. Follow up: What if the linked list is extremely large and its length is unknown to you? Could you solve this efficiently without using extra space?"
Nvidia,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
Nvidia,412,Fizz Buzz,Easy,"Math, String, Simulation","Given an integer n; return a string array answer (1-indexed) where: answer[i] == ""FizzBuzz"" if i is divisible by 3 and 5. answer[i] == ""Fizz"" if i is divisible by 3. answer[i] == ""Buzz"" if i is divisible by 5. answer[i] == i (as a string) if none of the above conditions are true. Example 1: Input: n = 3 Output: [""1"";""2"";""Fizz""] Example 2: Input: n = 5 Output: [""1"";""2"";""Fizz"";""4"";""Buzz""] Example 3: Input: n = 15 Output: [""1"";""2"";""Fizz"";""4"";""Buzz"";""Fizz"";""7"";""8"";""Fizz"";""Buzz"";""11"";""Fizz"";""13"";""14"";""FizzBuzz""] Constraints: 1 <= n <= 104"
Nvidia,451,Sort Characters By Frequency,Med,"Hash Table, String, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given a string s; sort it in decreasing order based on the frequency of the characters. The frequency of a character is the number of times it appears in the string. Return the sorted string. If there are multiple answers; return any of them. Example 1: Input: s = ""tree"" Output: ""eert"" Explanation: 'e' appears twice while 'r' and 't' both appear once. So 'e' must appear before both 'r' and 't'. Therefore ""eetr"" is also a valid answer. Example 2: Input: s = ""cccaaa"" Output: ""aaaccc"" Explanation: Both 'c' and 'a' appear three times; so both ""cccaaa"" and ""aaaccc"" are valid answers. Note that ""cacaca"" is incorrect; as the same characters must be together. Example 3: Input: s = ""Aabb"" Output: ""bbAa"" Explanation: ""bbaA"" is also a valid answer; but ""Aabb"" is incorrect. Note that 'A' and 'a' are treated as two different characters. Constraints: 1 <= s.length <= 5 * 105 s consists of uppercase and lowercase English letters and digits."
Nvidia,468,Validate IP Address,Med,String,"Given a string queryIP; return ""IPv4"" if IP is a valid IPv4 address; ""IPv6"" if IP is a valid IPv6 address or ""Neither"" if IP is not a correct IP of any type. A valid IPv4 address is an IP in the form ""x1.x2.x3.x4"" where 0 <= xi <= 255 and xi cannot contain leading zeros. For example; ""192.168.1.1"" and ""192.168.1.0"" are valid IPv4 addresses while ""192.168.01.1""; ""192.168.1.00""; and ""192.168@1.1"" are invalid IPv4 addresses. A valid IPv6 address is an IP in the form ""x1:x2:x3:x4:x5:x6:x7:x8"" where: 1 <= xi.length <= 4 xi is a hexadecimal string which may contain digits; lowercase English letter ('a' to 'f') and upper-case English letters ('A' to 'F'). Leading zeros are allowed in xi. For example; ""2001:0db8:85a3:0000:0000:8a2e:0370:7334"" and ""2001:db8:85a3:0:0:8A2E:0370:7334"" are valid IPv6 addresses; while ""2001:0db8:85a3::8A2E:037j:7334"" and ""02001:0db8:85a3:0000:0000:8a2e:0370:7334"" are invalid IPv6 addresses. Example 1: Input: queryIP = ""172.16.254.1"" Output: ""IPv4"" Explanation: This is a valid IPv4 address; return ""IPv4"". Example 2: Input: queryIP = ""2001:0db8:85a3:0:0:8A2E:0370:7334"" Output: ""IPv6"" Explanation: This is a valid IPv6 address; return ""IPv6"". Example 3: Input: queryIP = ""256.256.256.256"" Output: ""Neither"" Explanation: This is neither a IPv4 address nor a IPv6 address. Constraints: queryIP consists only of English letters; digits and the characters '.' and ':'."
Nvidia,526,Beautiful Arrangement,Med,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",Suppose you have n integers labeled 1 through n. A permutation of those n integers perm (1-indexed) is considered a beautiful arrangement if for every i (1 <= i <= n); either of the following is true: perm[i] is divisible by i. i is divisible by perm[i]. Given an integer n; return the number of the beautiful arrangements that you can construct. Example 1: Input: n = 2 Output: 2 Explanation: The first beautiful arrangement is [1;2]: - perm[1] = 1 is divisible by i = 1 - perm[2] = 2 is divisible by i = 2 The second beautiful arrangement is [2;1]: - perm[1] = 2 is divisible by i = 1 - i = 2 is divisible by perm[2] = 1 Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 15
Nvidia,1721,Swapping Nodes in a Linked List,Med,"Array, Simulation",You are the operator of a Centennial Wheel that has four gondolas; and each gondola has room for up to four people. You have the ability to rotate the gondolas counterclockwise; which costs you runningCost dollars. You are given an array customers of length n where customers[i] is the number of new customers arriving just before the ith rotation (0-indexed). This means you must rotate the wheel i times before the customers[i] customers arrive. You cannot make customers wait if there is room in the gondola. Each customer pays boardingCost dollars when they board on the gondola closest to the ground and will exit once that gondola reaches the ground again. You can stop the wheel at any time; including before serving all customers. If you decide to stop serving customers; all subsequent rotations are free in order to get all the customers down safely. Note that if there are currently more than four customers waiting at the wheel; only four will board the gondola; and the rest will wait for the next rotation. Return the minimum number of rotations you need to perform to maximize your profit. If there is no scenario where the profit is positive; return -1. Example 1: Input: customers = [8;3]; boardingCost = 5; runningCost = 6 Output: 3 Explanation: The numbers written on the gondolas are the number of people currently there. 1. 8 customers arrive; 4 board and 4 wait for the next gondola; the wheel rotates. Current profit is 4 * $5 - 1 * $6 = $14. 2. 3 customers arrive; the 4 waiting board the wheel and the other 3 wait; the wheel rotates. Current profit is 8 * $5 - 2 * $6 = $28. 3. The final 3 customers board the gondola; the wheel rotates. Current profit is 11 * $5 - 3 * $6 = $37. The highest profit was $37 after rotating the wheel 3 times. Example 2: Input: customers = [10;9;6]; boardingCost = 6; runningCost = 4 Output: 7 Explanation: 1. 10 customers arrive; 4 board and 6 wait for the next gondola; the wheel rotates. Current profit is 4 * $6 - 1 * $4 = $20. 2. 9 customers arrive; 4 board and 11 wait (2 originally waiting; 9 newly waiting); the wheel rotates. Current profit is 8 * $6 - 2 * $4 = $40. 3. The final 6 customers arrive; 4 board and 13 wait; the wheel rotates. Current profit is 12 * $6 - 3 * $4 = $60. 4. 4 board and 9 wait; the wheel rotates. Current profit is 16 * $6 - 4 * $4 = $80. 5. 4 board and 5 wait; the wheel rotates. Current profit is 20 * $6 - 5 * $4 = $100. 6. 4 board and 1 waits; the wheel rotates. Current profit is 24 * $6 - 6 * $4 = $120. 7. 1 boards; the wheel rotates. Current profit is 25 * $6 - 7 * $4 = $122. The highest profit was $122 after rotating the wheel 7 times. Example 3: Input: customers = [3;4;0;5;1]; boardingCost = 1; runningCost = 92 Output: -1 Explanation: 1. 3 customers arrive; 3 board and 0 wait; the wheel rotates. Current profit is 3 * $1 - 1 * $92 = -$89. 2. 4 customers arrive; 4 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 2 * $92 = -$177. 3. 0 customers arrive; 0 board and 0 wait; the wheel rotates. Current profit is 7 * $1 - 3 * $92 = -$269. 4. 5 customers arrive; 4 board and 1 waits; the wheel rotates. Current profit is 11 * $1 - 4 * $92 = -$357. 5. 1 customer arrives; 2 board and 0 wait; the wheel rotates. Current profit is 13 * $1 - 5 * $92 = -$447. The profit was never positive; so return -1. Constraints: n == customers.length 1 <= n <= 105 0 <= customers[i] <= 50 1 <= boardingCost; runningCost <= 100
Nvidia,621,Task Scheduler,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting","You are given an array of CPU tasks; each labeled with a letter from A to Z; and a number n. Each CPU interval can be idle or allow the completion of one task. Tasks can be completed in any order; but there's a constraint: there has to be a gap of at least n intervals between two tasks with the same label. Return the minimum number of CPU intervals required to complete all tasks. Example 1: Input: tasks = [""A"";""A"";""A"";""B"";""B"";""B""]; n = 2 Output: 8 Explanation: A possible sequence is: A -> B -> idle -> A -> B -> idle -> A -> B. After completing task A; you must wait two intervals before doing A again. The same applies to task B. In the 3rd interval; neither A nor B can be done; so you idle. By the 4th interval; you can do A again as 2 intervals have passed. Example 2: Input: tasks = [""A"";""C"";""A"";""B"";""D"";""B""]; n = 1 Output: 6 Explanation: A possible sequence is: A -> B -> C -> D -> A -> B. With a cooling interval of 1; you can repeat a task after just one other task. Example 3: Input: tasks = [""A"";""A"";""A""; ""B"";""B"";""B""]; n = 3 Output: 10 Explanation: A possible sequence is: A -> B -> idle -> idle -> A -> B -> idle -> idle -> A -> B. There are only two types of tasks; A and B; which need to be separated by 3 intervals. This leads to idling twice between repetitions of these tasks. Constraints: 1 <= tasks.length <= 104 tasks[i] is an uppercase English letter. 0 <= n <= 100"
Nvidia,713,Subarray Product Less Than K,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of integers nums and an integer k; return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k. Example 1: Input: nums = [10;5;2;6]; k = 100 Output: 8 Explanation: The 8 subarrays that have product less than 100 are: [10]; [5]; [2]; [6]; [10; 5]; [5; 2]; [2; 6]; [5; 2; 6] Note that [10; 5; 2] is not included as the product of 100 is not strictly less than k. Example 2: Input: nums = [1;2;3]; k = 0 Output: 0 Constraints: 1 <= nums.length <= 3 * 104 1 <= nums[i] <= 1000 0 <= k <= 106
PayPal,6,Zigzag Conversion,Med,String,"The string ""PAYPALISHIRING"" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility) P A H N A P L S I I G Y I R And then read line by line: ""PAHNAPLSIIGYIR"" Write the code that will take a string and make this conversion given a number of rows: string convert(string s; int numRows); Example 1: Input: s = ""PAYPALISHIRING""; numRows = 3 Output: ""PAHNAPLSIIGYIR"" Example 2: Input: s = ""PAYPALISHIRING""; numRows = 4 Output: ""PINALSIGYAHRPI"" Explanation: P I N A L S I G Y A H R P I Example 3: Input: s = ""A""; numRows = 1 Output: ""A"" Constraints: 1 <= s.length <= 1000 s consists of English letters (lower-case and upper-case); ';' and '.'. 1 <= numRows <= 1000"
PayPal,1010,Pairs of Songs With Total Durations Divisible by 60,Med,"Hash Table, Math, Enumeration",Given three integers x; y; and bound; return a list of all the powerful integers that have a value less than or equal to bound. An integer is powerful if it can be represented as xi + yj for some integers i >= 0 and j >= 0. You may return the answer in any order. In your answer; each value should occur at most once. Example 1: Input: x = 2; y = 3; bound = 10 Output: [2;3;4;5;7;9;10] Explanation: 2 = 20 + 30 3 = 21 + 30 4 = 20 + 31 5 = 21 + 31 7 = 22 + 31 9 = 23 + 30 10 = 20 + 32 Example 2: Input: x = 3; y = 5; bound = 15 Output: [2;4;6;8;10;14] Constraints: 1 <= x; y <= 100 0 <= bound <= 106
PayPal,2586,Count the Number of Vowel Strings in Range,Easy,"Array, Hash Table, Binary Search, Dynamic Programming, Sorting",You are given an integer array nums. A subsequence of nums is called a square streak if: The length of the subsequence is at least 2; and after sorting the subsequence; each element (except the first element) is the square of the previous number. Return the length of the longest square streak in nums; or return -1 if there is no square streak. A subsequence is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements. Example 1: Input: nums = [4;3;6;16;8;2] Output: 3 Explanation: Choose the subsequence [4;16;2]. After sorting it; it becomes [2;4;16]. - 4 = 2 * 2. - 16 = 4 * 4. Therefore; [4;16;2] is a square streak. It can be shown that every subsequence of length 4 is not a square streak. Example 2: Input: nums = [2;3;5;6;7] Output: -1 Explanation: There is no square streak in nums so return -1. Constraints: 2 <= nums.length <= 105 2 <= nums[i] <= 105
PayPal,2559,Count Vowel Strings in Ranges,Med,"Two Pointers, String, Dynamic Programming, Greedy","You are given a string s and a positive integer k. Select a set of non-overlapping substrings from the string s that satisfy the following conditions: The length of each substring is at least k. Each substring is a palindrome. Return the maximum number of substrings in an optimal selection. A substring is a contiguous sequence of characters within a string. Example 1: Input: s = ""abaccdbbd""; k = 3 Output: 2 Explanation: We can select the substrings underlined in s = ""abaccdbbd"". Both ""aba"" and ""dbbd"" are palindromes and have a length of at least k = 3. It can be shown that we cannot find a selection with more than two valid substrings. Example 2: Input: s = ""adbcda""; k = 2 Output: 0 Explanation: There is no palindrome substring of length at least 2 in the string. Constraints: 1 <= k <= s.length <= 2000 s consists of lowercase English letters."
PayPal,2056,Number of Valid Move Combinations On Chessboard,Hard,"Array, Dynamic Programming, Stack, Graph, Monotonic Stack, Shortest Path",
PayPal,2183,Count Array Pairs Divisible by K,Hard,"Array, Breadth-First Search",You are given a 0-indexed integer array nums containing distinct numbers; an integer start; and an integer goal. There is an integer x that is initially set to start; and you want to perform operations on x such that it is converted to goal. You can perform the following operation repeatedly on the number x: If 0 <= x <= 1000; then for any index i in the array (0 <= i < nums.length); you can set x to any of the following: x + nums[i] x - nums[i] x ^ nums[i] (bitwise-XOR) Note that you can use each nums[i] any number of times in any order. Operations that set x to be out of the range 0 <= x <= 1000 are valid; but no more operations can be done afterward. Return the minimum number of operations needed to convert x = start into goal; and -1 if it is not possible. Example 1: Input: nums = [2;4;12]; start = 2; goal = 12 Output: 2 Explanation: We can go from 2 → 14 → 12 with the following 2 operations. - 2 + 12 = 14 - 14 - 2 = 12 Example 2: Input: nums = [3;5;7]; start = 0; goal = -4 Output: 2 Explanation: We can go from 0 → 3 → -4 with the following 2 operations. - 0 + 3 = 3 - 3 - 7 = -4 Note that the last operation sets x out of the range 0 <= x <= 1000; which is valid. Example 3: Input: nums = [2;8;16]; start = 0; goal = 1 Output: -1 Explanation: There is no way to convert 0 into 1. Constraints: 1 <= nums.length <= 1000 -109 <= nums[i]; goal <= 109 0 <= start <= 1000 start != goal All the integers in nums are distinct.
PayPal,2380,Time Needed to Rearrange a Binary String,Med,"Binary Search, Design, Binary Indexed Tree, Segment Tree","A concert hall has n rows numbered from 0 to n - 1; each with m seats; numbered from 0 to m - 1. You need to design a ticketing system that can allocate seats in the following cases: If a group of k spectators can sit together in a row. If every member of a group of k spectators can get a seat. They may or may not sit together. Note that the spectators are very picky. Hence: They will book seats only if each member of their group can get a seat with row number less than or equal to maxRow. maxRow can vary from group to group. In case there are multiple rows to choose from; the row with the smallest number is chosen. If there are multiple seats to choose in the same row; the seat with the smallest number is chosen. Implement the BookMyShow class: BookMyShow(int n; int m) Initializes the object with n as number of rows and m as number of seats per row. int[] gather(int k; int maxRow) Returns an array of length 2 denoting the row and seat number (respectively) of the first seat being allocated to the k members of the group; who must sit together. In other words; it returns the smallest possible r and c such that all [c; c + k - 1] seats are valid and empty in row r; and r <= maxRow. Returns [] in case it is not possible to allocate seats to the group. boolean scatter(int k; int maxRow) Returns true if all k members of the group can be allocated seats in rows 0 to maxRow; who may or may not sit together. If the seats can be allocated; it allocates k seats to the group with the smallest row numbers; and the smallest possible seat numbers in each row. Otherwise; returns false. Example 1: Input [""BookMyShow""; ""gather""; ""gather""; ""scatter""; ""scatter""] [[2; 5]; [4; 0]; [2; 0]; [5; 1]; [5; 1]] Output [null; [0; 0]; []; true; false] Explanation BookMyShow bms = new BookMyShow(2; 5); // There are 2 rows with 5 seats each bms.gather(4; 0); // return [0; 0] // The group books seats [0; 3] of row 0. bms.gather(2; 0); // return [] // There is only 1 seat left in row 0; // so it is not possible to book 2 consecutive seats. bms.scatter(5; 1); // return True // The group books seat 4 of row 0 and seats [0; 3] of row 1. bms.scatter(5; 1); // return False // There is only one seat left in the hall. Constraints: 1 <= n <= 5 * 104 1 <= m; k <= 109 0 <= maxRow <= n - 1 At most 5 * 104 calls in total will be made to gather and scatter."
PayPal,1229,Meeting Scheduler,Med,"Breadth-First Search, Graph",You are given an integer n; the number of nodes in a directed graph where the nodes are labeled from 0 to n - 1. Each edge is red or blue in this graph; and there could be self-edges and parallel edges. You are given two arrays redEdges and blueEdges where: redEdges[i] = [ai; bi] indicates that there is a directed red edge from node ai to node bi in the graph; and blueEdges[j] = [uj; vj] indicates that there is a directed blue edge from node uj to node vj in the graph. Return an array answer of length n; where each answer[x] is the length of the shortest path from node 0 to node x such that the edge colors alternate along the path; or -1 if such a path does not exist. Example 1: Input: n = 3; redEdges = [[0;1];[1;2]]; blueEdges = [] Output: [0;1;-1] Example 2: Input: n = 3; redEdges = [[0;1]]; blueEdges = [[2;1]] Output: [0;1;-1] Constraints: 1 <= n <= 100 0 <= redEdges.length; blueEdges.length <= 400 redEdges[i].length == blueEdges[j].length == 2 0 <= ai; bi; uj; vj < n
PayPal,1473,Paint House III,Hard,"Hash Table, String, Bit Manipulation, Prefix Sum","Given the string s; return the size of the longest substring containing each vowel an even number of times. That is; 'a'; 'e'; 'i'; 'o'; and 'u' must appear an even number of times. Example 1: Input: s = ""eleetminicoworoep"" Output: 13 Explanation: The longest substring is ""leetminicowor"" which contains two each of the vowels: e; i and o and zero of the vowels: a and u. Example 2: Input: s = ""leetcodeisgreat"" Output: 5 Explanation: The longest substring is ""leetc"" which contains two e's. Example 3: Input: s = ""bcbcbc"" Output: 6 Explanation: In this case; the given string ""bcbcbc"" is the longest because all vowels: a; e; i; o and u appear zero times. Constraints: 1 <= s.length <= 5 x 10^5 s contains only lowercase English letters."
PayPal,1589,Maximum Sum Obtained of Any Permutation,Med,,
PayPal,1969,Minimum Non-Zero Product of the Array Elements,Med,"Array, Depth-First Search, Graph, Matrix",
PayPal,1999,Smallest Greater Multiple Made of Two Digits,Med,String,"Given a binary string s; return true if the longest contiguous segment of 1's is strictly longer than the longest contiguous segment of 0's in s; or return false otherwise. For example; in s = ""110100010"" the longest continuous segment of 1s has length 2; and the longest continuous segment of 0s has length 3. Note that if there are no 0's; then the longest continuous segment of 0's is considered to have a length 0. The same applies if there is no 1's. Example 1: Input: s = ""1101"" Output: true Explanation: The longest contiguous segment of 1s has length 2: ""1101"" The longest contiguous segment of 0s has length 1: ""1101"" The segment of 1s is longer; so return true. Example 2: Input: s = ""111000"" Output: false Explanation: The longest contiguous segment of 1s has length 3: ""111000"" The longest contiguous segment of 0s has length 3: ""111000"" The segment of 1s is not longer; so return false. Example 3: Input: s = ""110100010"" Output: false Explanation: The longest contiguous segment of 1s has length 2: ""110100010"" The longest contiguous segment of 0s has length 3: ""110100010"" The segment of 1s is not longer; so return false. Constraints: 1 <= s.length <= 100 s[i] is either '0' or '1'."
PayPal,2366,Minimum Replacements to Sort the Array,Hard,"Array, Greedy, Sorting",You have n bags numbered from 0 to n - 1. You are given two 0-indexed integer arrays capacity and rocks. The ith bag can hold a maximum of capacity[i] rocks and currently contains rocks[i] rocks. You are also given an integer additionalRocks; the number of additional rocks you can place in any of the bags. Return the maximum number of bags that could have full capacity after placing the additional rocks in some bags. Example 1: Input: capacity = [2;3;4;5]; rocks = [1;2;4;4]; additionalRocks = 2 Output: 3 Explanation: Place 1 rock in bag 0 and 1 rock in bag 1. The number of rocks in each bag are now [2;3;4;4]. Bags 0; 1; and 2 have full capacity. There are 3 bags at full capacity; so we return 3. It can be shown that it is not possible to have more than 3 bags at full capacity. Note that there may be other ways of placing the rocks that result in an answer of 3. Example 2: Input: capacity = [10;2;2]; rocks = [2;2;0]; additionalRocks = 100 Output: 3 Explanation: Place 8 rocks in bag 0 and 2 rocks in bag 2. The number of rocks in each bag are now [10;2;2]. Bags 0; 1; and 2 have full capacity. There are 3 bags at full capacity; so we return 3. It can be shown that it is not possible to have more than 3 bags at full capacity. Note that we did not use all of the additional rocks. Constraints: n == capacity.length == rocks.length 1 <= n <= 5 * 104 1 <= capacity[i] <= 109 0 <= rocks[i] <= capacity[i] 1 <= additionalRocks <= 109
PayPal,2554,Maximum Number of Integers to Choose From a Range I,Med,"Array, Dynamic Programming, Sorting",There are some robots and factories on the X-axis. You are given an integer array robot where robot[i] is the position of the ith robot. You are also given a 2D integer array factory where factory[j] = [positionj; limitj] indicates that positionj is the position of the jth factory and that the jth factory can repair at most limitj robots. The positions of each robot are unique. The positions of each factory are also unique. Note that a robot can be in the same position as a factory initially. All the robots are initially broken; they keep moving in one direction. The direction could be the negative or the positive direction of the X-axis. When a robot reaches a factory that did not reach its limit; the factory repairs the robot; and it stops moving. At any moment; you can set the initial direction of moving for some robot. Your target is to minimize the total distance traveled by all the robots. Return the minimum total distance traveled by all the robots. The test cases are generated such that all the robots can be repaired. Note that All robots move at the same speed. If two robots move in the same direction; they will never collide. If two robots move in opposite directions and they meet at some point; they do not collide. They cross each other. If a robot passes by a factory that reached its limits; it crosses it as if it does not exist. If the robot moved from a position x to a position y; the distance it moved is |y - x|. Example 1: Input: robot = [0;4;6]; factory = [[2;2];[6;2]] Output: 4 Explanation: As shown in the figure: - The first robot at position 0 moves in the positive direction. It will be repaired at the first factory. - The second robot at position 4 moves in the negative direction. It will be repaired at the first factory. - The third robot at position 6 will be repaired at the second factory. It does not need to move. The limit of the first factory is 2; and it fixed 2 robots. The limit of the second factory is 2; and it fixed 1 robot. The total distance is |2 - 0| + |2 - 4| + |6 - 6| = 4. It can be shown that we cannot achieve a better total distance than 4. Example 2: Input: robot = [1;-1]; factory = [[-2;1];[2;1]] Output: 2 Explanation: As shown in the figure: - The first robot at position 1 moves in the positive direction. It will be repaired at the second factory. - The second robot at position -1 moves in the negative direction. It will be repaired at the first factory. The limit of the first factory is 1; and it fixed 1 robot. The limit of the second factory is 1; and it fixed 1 robot. The total distance is |2 - 1| + |(-2) - (-1)| = 2. It can be shown that we cannot achieve a better total distance than 2. Constraints: 1 <= robot.length; factory.length <= 100 factory[j].length == 2 -109 <= robot[i]; positionj <= 109 0 <= limitj <= robot.length The input will be generated such that it is always possible to repair every robot.
PayPal,2524,Maximum Frequency Score of a Subarray,Hard,"Array, Hash Table, Two Pointers, Sorting",Given an integer array nums that does not contain any zeros; find the largest positive integer k such that -k also exists in the array. Return the positive integer k. If there is no such integer; return -1. Example 1: Input: nums = [-1;2;-3;3] Output: 3 Explanation: 3 is the only valid k we can find in the array. Example 2: Input: nums = [-1;10;6;7;-7;1] Output: 7 Explanation: Both 1 and 7 have their corresponding negative values in the array. 7 has a larger value. Example 3: Input: nums = [-10;8;6;7;-2;-3] Output: -1 Explanation: There is no a single valid k; we return -1. Constraints: 1 <= nums.length <= 1000 -1000 <= nums[i] <= 1000 nums[i] != 0
PayPal,2557,Maximum Number of Integers to Choose From a Range II,Med,"Array, Math, Number Theory",Given an integer array nums and an integer k; return the number of subarrays of nums where the least common multiple of the subarray's elements is k. A subarray is a contiguous non-empty sequence of elements within an array. The least common multiple of an array is the smallest positive integer that is divisible by all the array elements. Example 1: Input: nums = [3;6;2;7;1]; k = 6 Output: 4 Explanation: The subarrays of nums where 6 is the least common multiple of all the subarray's elements are: - [3;6;2;7;1] - [3;6;2;7;1] - [3;6;2;7;1] - [3;6;2;7;1] Example 2: Input: nums = [3]; k = 2 Output: 0 Explanation: There are no subarrays of nums where 2 is the least common multiple of all the subarray's elements. Constraints: 1 <= nums.length <= 1000 1 <= nums[i]; k <= 1000
PayPal,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
PayPal,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
PayPal,88,Merge Sorted Array,Easy,"Array, Two Pointers, Sorting",You are given two integer arrays nums1 and nums2; sorted in non-decreasing order; and two integers m and n; representing the number of elements in nums1 and nums2 respectively. Merge nums1 and nums2 into a single array sorted in non-decreasing order. The final sorted array should not be returned by the function; but instead be stored inside the array nums1. To accommodate this; nums1 has a length of m + n; where the first m elements denote the elements that should be merged; and the last n elements are set to 0 and should be ignored. nums2 has a length of n. Example 1: Input: nums1 = [1;2;3;0;0;0]; m = 3; nums2 = [2;5;6]; n = 3 Output: [1;2;2;3;5;6] Explanation: The arrays we are merging are [1;2;3] and [2;5;6]. The result of the merge is [1;2;2;3;5;6] with the underlined elements coming from nums1. Example 2: Input: nums1 = [1]; m = 1; nums2 = []; n = 0 Output: [1] Explanation: The arrays we are merging are [1] and []. The result of the merge is [1]. Example 3: Input: nums1 = [0]; m = 0; nums2 = [1]; n = 1 Output: [1] Explanation: The arrays we are merging are [] and [1]. The result of the merge is [1]. Note that because m = 0; there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1. Constraints: nums1.length == m + n nums2.length == n 0 <= m; n <= 200 1 <= m + n <= 200 -109 <= nums1[i]; nums2[j] <= 109 Follow up: Can you come up with an algorithm that runs in O(m + n) time?
PayPal,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
PayPal,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
PayPal,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
PayPal,1200,Minimum Absolute Difference,Easy,Array,
PayPal,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
PayPal,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
PayPal,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
PayPal,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
PayPal,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
PayPal,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
PayPal,1283,Find the Smallest Divisor Given a Threshold,Med,String,"Given a date string in the form Day Month Year; where: Day is in the set {""1st""; ""2nd""; ""3rd""; ""4th""; ...; ""30th""; ""31st""}. Month is in the set {""Jan""; ""Feb""; ""Mar""; ""Apr""; ""May""; ""Jun""; ""Jul""; ""Aug""; ""Sep""; ""Oct""; ""Nov""; ""Dec""}. Year is in the range [1900; 2100]. Convert the date string to the format YYYY-MM-DD; where: YYYY denotes the 4 digit year. MM denotes the 2 digit month. DD denotes the 2 digit day. Example 1: Input: date = ""20th Oct 2052"" Output: ""2052-10-20"" Example 2: Input: date = ""6th Jun 1933"" Output: ""1933-06-06"" Example 3: Input: date = ""26th May 1960"" Output: ""1960-05-26"" Constraints: The given dates are guaranteed to be valid; so no error handling is necessary."
PayPal,34,Find First and Last Position of Element in Sorted Array,Med,"Array, Binary Search",Given an array of integers nums sorted in non-decreasing order; find the starting and ending position of a given target value. If target is not found in the array; return [-1; -1]. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [5;7;7;8;8;10]; target = 8 Output: [3;4] Example 2: Input: nums = [5;7;7;8;8;10]; target = 6 Output: [-1;-1] Example 3: Input: nums = []; target = 0 Output: [-1;-1] Constraints: 0 <= nums.length <= 105 -109 <= nums[i] <= 109 nums is a non-decreasing array. -109 <= target <= 109
PayPal,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
PayPal,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
PayPal,2062,Count Vowel Substrings of a String,Easy,"Array, Math, Dynamic Programming, Bit Manipulation, Brainteaser, Game Theory",
PayPal,2402,Meeting Rooms III,Hard,"Array, Math, Bit Manipulation",You are given a 0-indexed integer array nums. In one operation; select any non-negative integer x and an index i; then update nums[i] to be equal to nums[i] AND (nums[i] XOR x). Note that AND is the bitwise AND operation and XOR is the bitwise XOR operation. Return the maximum possible bitwise XOR of all elements of nums after applying the operation any number of times. Example 1: Input: nums = [3;2;4;6] Output: 7 Explanation: Apply the operation with x = 4 and i = 3; num[3] = 6 AND (6 XOR 4) = 6 AND 2 = 2. Now; nums = [3; 2; 4; 2] and the bitwise XOR of all the elements = 3 XOR 2 XOR 4 XOR 2 = 7. It can be shown that 7 is the maximum possible bitwise XOR. Note that other operations may be used to achieve a bitwise XOR of 7. Example 2: Input: nums = [1;2;3;9;2] Output: 11 Explanation: Apply the operation zero times. The bitwise XOR of all the elements = 1 XOR 2 XOR 3 XOR 9 XOR 2 = 11. It can be shown that 11 is the maximum possible bitwise XOR. Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 108
PayPal,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
PayPal,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
PayPal,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
PayPal,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
PayPal,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
PayPal,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
PayPal,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
PayPal,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
PayPal,212,Word Search II,Hard,"Array, String, Backtracking, Trie, Matrix","Given an m x n board of characters and a list of strings words; return all words on the board. Each word must be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example 1: Input: board = [[""o"";""a"";""a"";""n""];[""e"";""t"";""a"";""e""];[""i"";""h"";""k"";""r""];[""i"";""f"";""l"";""v""]]; words = [""oath"";""pea"";""eat"";""rain""] Output: [""eat"";""oath""] Example 2: Input: board = [[""a"";""b""];[""c"";""d""]]; words = [""abcb""] Output: [] Constraints: m == board.length n == board[i].length 1 <= m; n <= 12 board[i][j] is a lowercase English letter. 1 <= words.length <= 3 * 104 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. All the strings of words are unique."
PayPal,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
PayPal,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
PayPal,713,Subarray Product Less Than K,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of integers nums and an integer k; return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k. Example 1: Input: nums = [10;5;2;6]; k = 100 Output: 8 Explanation: The 8 subarrays that have product less than 100 are: [10]; [5]; [2]; [6]; [10; 5]; [5; 2]; [2; 6]; [5; 2; 6] Note that [10; 5; 2] is not included as the product of 100 is not strictly less than k. Example 2: Input: nums = [1;2;3]; k = 0 Output: 0 Constraints: 1 <= nums.length <= 3 * 104 1 <= nums[i] <= 1000 0 <= k <= 106
PayPal,895,Maximum Frequency Stack,Hard,"Array, Bit Manipulation, Breadth-First Search, Matrix","You are given an m x n grid grid where: '.' is an empty cell. '#' is a wall. '@' is the starting point. Lowercase letters represent keys. Uppercase letters represent locks. You start at the starting point and one move consists of walking one space in one of the four cardinal directions. You cannot walk outside the grid; or walk into a wall. If you walk over a key; you can pick it up and you cannot walk over a lock unless you have its corresponding key. For some 1 <= k <= 6; there is exactly one lowercase and one uppercase letter of the first k letters of the English alphabet in the grid. This means that there is exactly one key for each lock; and one lock for each key; and also that the letters used to represent the keys and locks were chosen in the same order as the English alphabet. Return the lowest number of moves to acquire all keys. If it is impossible; return -1. Example 1: Input: grid = [""@.a.."";""###.#"";""b.A.B""] Output: 8 Explanation: Note that the goal is to obtain all the keys not to open all the locks. Example 2: Input: grid = [""@..aA"";""..B#."";""....b""] Output: 6 Example 3: Input: grid = [""@Aa""] Output: -1 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 30 grid[i][j] is either an English letter; '.'; '#'; or '@'. There is exactly one '@' in the grid. The number of keys in the grid is in the range [1; 6]. Each key in the grid is unique. Each key in the grid has a matching lock."
PayPal,1328,Break a Palindrome,Med,Database,
PayPal,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
PayPal,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
PayPal,9,Palindrome Number,Easy,Math,Given an integer x; return true if x is a palindrome; and false otherwise. Example 1: Input: x = 121 Output: true Explanation: 121 reads as 121 from left to right and from right to left. Example 2: Input: x = -121 Output: false Explanation: From left to right; it reads -121. From right to left; it becomes 121-. Therefore it is not a palindrome. Example 3: Input: x = 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Constraints: -231 <= x <= 231 - 1 Follow up: Could you solve it without converting the integer to a string?
PayPal,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
PayPal,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
PayPal,19,Remove Nth Node From End of List,Med,"Linked List, Two Pointers",Given the head of a linked list; remove the nth node from the end of the list and return its head. Example 1: Input: head = [1;2;3;4;5]; n = 2 Output: [1;2;3;5] Example 2: Input: head = [1]; n = 1 Output: [] Example 3: Input: head = [1;2]; n = 1 Output: [1] Constraints: The number of nodes in the list is sz. 1 <= sz <= 30 0 <= Node.val <= 100 1 <= n <= sz Follow up: Could you do this in one pass?
PayPal,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
PayPal,38,Count and Say,Med,String,"The count-and-say sequence is a sequence of digit strings defined by the recursive formula: countAndSay(1) = ""1"" countAndSay(n) is the run-length encoding of countAndSay(n - 1). Run-length encoding (RLE) is a string compression method that works by replacing consecutive identical characters (repeated 2 or more times) with the concatenation of the character and the number marking the count of the characters (length of the run). For example; to compress the string ""3322251"" we replace ""33"" with ""23""; replace ""222"" with ""32""; replace ""5"" with ""15"" and replace ""1"" with ""11"". Thus the compressed string becomes ""23321511"". Given a positive integer n; return the nth element of the count-and-say sequence. Example 1: Input: n = 4 Output: ""1211"" Explanation: countAndSay(1) = ""1"" countAndSay(2) = RLE of ""1"" = ""11"" countAndSay(3) = RLE of ""11"" = ""21"" countAndSay(4) = RLE of ""21"" = ""1211"" Example 2: Input: n = 1 Output: ""1"" Explanation: This is the base case. Constraints: 1 <= n <= 30 Follow up: Could you solve it iteratively?"
PayPal,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
PayPal,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
PayPal,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
PayPal,68,Text Justification,Hard,"Array, String, Simulation","Given an array of strings words and a width maxWidth; format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is; pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words; the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text; it should be left-justified; and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = [""This""; ""is""; ""an""; ""example""; ""of""; ""text""; ""justification.""]; maxWidth = 16 Output: [ ""This is an""; ""example of text""; ""justification. "" ] Example 2: Input: words = [""What"";""must"";""be"";""acknowledgment"";""shall"";""be""]; maxWidth = 16 Output: [ ""What must be""; ""acknowledgment ""; ""shall be "" ] Explanation: Note that the last line is ""shall be "" instead of ""shall be""; because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = [""Science"";""is"";""what"";""we"";""understand"";""well"";""enough"";""to"";""explain"";""to"";""a"";""computer."";""Art"";""is"";""everything"";""else"";""we"";""do""]; maxWidth = 20 Output: [ ""Science is what we""; ""understand well""; ""enough to explain to""; ""a computer. Art is""; ""everything else we""; ""do "" ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth"
PayPal,84,Largest Rectangle in Histogram,Hard,"Array, Stack, Monotonic Stack",Given an array of integers heights representing the histogram's bar height where the width of each bar is 1; return the area of the largest rectangle in the histogram. Example 1: Input: heights = [2;1;5;6;2;3] Output: 10 Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area; which has an area = 10 units. Example 2: Input: heights = [2;4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104
PayPal,125,Valid Palindrome,Easy,"Two Pointers, String","A phrase is a palindrome if; after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters; it reads the same forward and backward. Alphanumeric characters include letters and numbers. Given a string s; return true if it is a palindrome; or false otherwise. Example 1: Input: s = ""A man; a plan; a canal: Panama"" Output: true Explanation: ""amanaplanacanalpanama"" is a palindrome. Example 2: Input: s = ""race a car"" Output: false Explanation: ""raceacar"" is not a palindrome. Example 3: Input: s = "" "" Output: true Explanation: s is an empty string """" after removing non-alphanumeric characters. Since an empty string reads the same forward and backward; it is a palindrome. Constraints: 1 <= s.length <= 2 * 105 s consists only of printable ASCII characters."
PayPal,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
PayPal,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
PayPal,236,Lowest Common Ancestor of a Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",Given a binary tree; find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3. Example 2: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [1;2]; p = 1; q = 2 Output: 1 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the tree.
PayPal,237,Delete Node in a Linked List,Med,Linked List,There is a singly-linked list head and we want to delete a node node in it. You are given the node to be deleted node. You will not be given access to the first node of head. All the values of the linked list are unique; and it is guaranteed that the given node node is not the last node in the linked list. Delete the given node. Note that by deleting the node; we do not mean removing it from memory. We mean: The value of the given node should not exist in the linked list. The number of nodes in the linked list should decrease by one. All the values before node should be in the same order. All the values after node should be in the same order. Custom testing: For the input; you should provide the entire linked list head and the node to be given node. node should not be the last node of the list and should be an actual node in the list. We will build the linked list and pass the node to your function. The output will be the entire list after calling your function. Example 1: Input: head = [4;5;1;9]; node = 5 Output: [4;1;9] Explanation: You are given the second node with value 5; the linked list should become 4 -> 1 -> 9 after calling your function. Example 2: Input: head = [4;5;1;9]; node = 1 Output: [4;5;9] Explanation: You are given the third node with value 1; the linked list should become 4 -> 5 -> 9 after calling your function. Constraints: The number of the nodes in the given list is in the range [2; 1000]. -1000 <= Node.val <= 1000 The value of each node in the list is unique. The node to be deleted is in the list and is not a tail node.
PayPal,242,Valid Anagram,Easy,"Hash Table, String, Sorting","Given two strings s and t; return true if t is an anagram of s; and false otherwise. Example 1: Input: s = ""anagram""; t = ""nagaram"" Output: true Example 2: Input: s = ""rat""; t = ""car"" Output: false Constraints: 1 <= s.length; t.length <= 5 * 104 s and t consist of lowercase English letters. Follow up: What if the inputs contain Unicode characters? How would you adapt your solution to such a case?"
PayPal,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
PayPal,344,Reverse String,Easy,"Two Pointers, String","Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory. Example 1: Input: s = [""h"";""e"";""l"";""l"";""o""] Output: [""o"";""l"";""l"";""e"";""h""] Example 2: Input: s = [""H"";""a"";""n"";""n"";""a"";""h""] Output: [""h"";""a"";""n"";""n"";""a"";""H""] Constraints: 1 <= s.length <= 105 s[i] is a printable ascii character."
PayPal,349,Intersection of Two Arrays,Easy,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given two integer arrays nums1 and nums2; return an array of their intersection. Each element in the result must be unique and you may return the result in any order. Example 1: Input: nums1 = [1;2;2;1]; nums2 = [2;2] Output: [2] Example 2: Input: nums1 = [4;9;5]; nums2 = [9;4;9;8;4] Output: [9;4] Explanation: [4;9] is also accepted. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 1000
PayPal,355,Design Twitter,Med,"Hash Table, Linked List, Design, Heap (Priority Queue)","Design a simplified version of Twitter where users can post tweets; follow/unfollow another user; and is able to see the 10 most recent tweets in the user's news feed. Implement the Twitter class: Twitter() Initializes your twitter object. void postTweet(int userId; int tweetId) Composes a new tweet with ID tweetId by the user userId. Each call to this function will be made with a unique tweetId. List<Integer> getNewsFeed(int userId) Retrieves the 10 most recent tweet IDs in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user themself. Tweets must be ordered from most recent to least recent. void follow(int followerId; int followeeId) The user with ID followerId started following the user with ID followeeId. void unfollow(int followerId; int followeeId) The user with ID followerId started unfollowing the user with ID followeeId. Example 1: Input [""Twitter""; ""postTweet""; ""getNewsFeed""; ""follow""; ""postTweet""; ""getNewsFeed""; ""unfollow""; ""getNewsFeed""] [[]; [1; 5]; [1]; [1; 2]; [2; 6]; [1]; [1; 2]; [1]] Output [null; null; [5]; null; null; [6; 5]; null; [5]] Explanation Twitter twitter = new Twitter(); twitter.postTweet(1; 5); // User 1 posts a new tweet (id = 5). twitter.getNewsFeed(1); // User 1's news feed should return a list with 1 tweet id -> [5]. return [5] twitter.follow(1; 2); // User 1 follows user 2. twitter.postTweet(2; 6); // User 2 posts a new tweet (id = 6). twitter.getNewsFeed(1); // User 1's news feed should return a list with 2 tweet ids -> [6; 5]. Tweet id 6 should precede tweet id 5 because it is posted after tweet id 5. twitter.unfollow(1; 2); // User 1 unfollows user 2. twitter.getNewsFeed(1); // User 1's news feed should return a list with 1 tweet id -> [5]; since user 1 is no longer following user 2. Constraints: 1 <= userId; followerId; followeeId <= 500 0 <= tweetId <= 104 All the tweets have unique IDs. At most 3 * 104 calls will be made to postTweet; getNewsFeed; follow; and unfollow."
PayPal,438,Find All Anagrams in a String,Med,"Hash Table, String, Sliding Window","Given two strings s and p; return an array of all the start indices of p's anagrams in s. You may return the answer in any order. Example 1: Input: s = ""cbaebabacd""; p = ""abc"" Output: [0;6] Explanation: The substring with start index = 0 is ""cba""; which is an anagram of ""abc"". The substring with start index = 6 is ""bac""; which is an anagram of ""abc"". Example 2: Input: s = ""abab""; p = ""ab"" Output: [0;1;2] Explanation: The substring with start index = 0 is ""ab""; which is an anagram of ""ab"". The substring with start index = 1 is ""ba""; which is an anagram of ""ab"". The substring with start index = 2 is ""ab""; which is an anagram of ""ab"". Constraints: 1 <= s.length; p.length <= 3 * 104 s and p consist of lowercase English letters."
PayPal,557,Reverse Words in a String III,Easy,"Two Pointers, String","Given a string s; reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order. Example 1: Input: s = ""Let's take LeetCode contest"" Output: ""s'teL ekat edoCteeL tsetnoc"" Example 2: Input: s = ""Mr Ding"" Output: ""rM gniD"" Constraints: 1 <= s.length <= 5 * 104 s contains printable ASCII characters. s does not contain any leading or trailing spaces. There is at least one word in s. All the words in s are separated by a single space."
PayPal,658,Find K Closest Elements,Med,"Array, Two Pointers, Binary Search, Sliding Window, Sorting, Heap (Priority Queue)",Given a sorted integer array arr; two integers k and x; return the k closest integers to x in the array. The result should also be sorted in ascending order. An integer a is closer to x than an integer b if: |a - x| < |b - x|; or |a - x| == |b - x| and a < b Example 1: Input: arr = [1;2;3;4;5]; k = 4; x = 3 Output: [1;2;3;4] Example 2: Input: arr = [1;1;2;3;4;5]; k = 4; x = -1 Output: [1;1;2;3] Constraints: 1 <= k <= arr.length 1 <= arr.length <= 104 arr is sorted in ascending order. -104 <= arr[i]; x <= 104
PayPal,851,Loud and Rich,Med,String,"You are given a string sentence that consist of words separated by spaces. Each word consists of lowercase and uppercase letters only. We would like to convert the sentence to ""Goat Latin"" (a made-up language similar to Pig Latin.) The rules of Goat Latin are as follows: If a word begins with a vowel ('a'; 'e'; 'i'; 'o'; or 'u'); append ""ma"" to the end of the word. For example; the word ""apple"" becomes ""applema"". If a word begins with a consonant (i.e.; not a vowel); remove the first letter and append it to the end; then add ""ma"". For example; the word ""goat"" becomes ""oatgma"". Add one letter 'a' to the end of each word per its word index in the sentence; starting with 1. For example; the first word gets ""a"" added to the end; the second word gets ""aa"" added to the end; and so on. Return the final sentence representing the conversion from sentence to Goat Latin. Example 1: Input: sentence = ""I speak Goat Latin"" Output: ""Imaa peaksmaaa oatGmaaaa atinLmaaaaa"" Example 2: Input: sentence = ""The quick brown fox jumped over the lazy dog"" Output: ""heTmaa uickqmaaa rownbmaaaa oxfmaaaaa umpedjmaaaaaa overmaaaaaaa hetmaaaaaaaa azylmaaaaaaaaa ogdmaaaaaaaaaa"" Constraints: 1 <= sentence.length <= 150 sentence consists of English letters and spaces. sentence has no leading or trailing spaces. All the words in sentence are separated by a single space."
PayPal,863,All Nodes Distance K in Binary Tree,Med,"Dynamic Programming, Tree, Depth-First Search, Graph",There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Return an array answer of length n where answer[i] is the sum of the distances between the ith node in the tree and all other nodes. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;3];[2;4];[2;5]] Output: [8;12;6;10;10;10] Explanation: The tree is shown above. We can see that dist(0;1) + dist(0;2) + dist(0;3) + dist(0;4) + dist(0;5) equals 1 + 1 + 2 + 2 + 2 = 8. Hence; answer[0] = 8; and so on. Example 2: Input: n = 1; edges = [] Output: [0] Example 3: Input: n = 2; edges = [[1;0]] Output: [1;1] Constraints: 1 <= n <= 3 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n ai != bi The given input represents a valid tree.
PayPal,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
PayPal,945,Minimum Increment to Make Array Unique,Med,"Array, Breadth-First Search, Matrix",You are given an n x n integer matrix board where the cells are labeled from 1 to n2 in a Boustrophedon style starting from the bottom left of the board (i.e. board[n - 1][0]) and alternating direction each row. You start on square 1 of the board. In each move; starting from square curr; do the following: Choose a destination square next with a label in the range [curr + 1; min(curr + 6; n2)]. This choice simulates the result of a standard 6-sided die roll: i.e.; there are always at most 6 destinations; regardless of the size of the board. If next has a snake or ladder; you must move to the destination of that snake or ladder. Otherwise; you move to next. The game ends when you reach the square n2. A board square on row r and column c has a snake or ladder if board[r][c] != -1. The destination of that snake or ladder is board[r][c]. Squares 1 and n2 are not the starting points of any snake or ladder. Note that you only take a snake or ladder at most once per dice roll. If the destination to a snake or ladder is the start of another snake or ladder; you do not follow the subsequent snake or ladder. For example; suppose the board is [[-1;4];[-1;3]]; and on the first move; your destination square is 2. You follow the ladder to square 3; but do not follow the subsequent ladder to 4. Return the least number of dice rolls required to reach the square n2. If it is not possible to reach the square; return -1. Example 1: Input: board = [[-1;-1;-1;-1;-1;-1];[-1;-1;-1;-1;-1;-1];[-1;-1;-1;-1;-1;-1];[-1;35;-1;-1;13;-1];[-1;-1;-1;-1;-1;-1];[-1;15;-1;-1;-1;-1]] Output: 4 Explanation: In the beginning; you start at square 1 (at row 5; column 0). You decide to move to square 2 and must take the ladder to square 15. You then decide to move to square 17 and must take the snake to square 13. You then decide to move to square 14 and must take the ladder to square 35. You then decide to move to square 36; ending the game. This is the lowest possible number of moves to reach the last square; so return 4. Example 2: Input: board = [[-1;-1];[-1;3]] Output: 1 Constraints: n == board.length == board[i].length 2 <= n <= 20 board[i][j] is either -1 or in the range [1; n2]. The squares labeled 1 and n2 are not the starting points of any snake or ladder.
PayPal,974,Subarray Sums Divisible by K,Med,"Array, String, Sorting","You are given an array of logs. Each log is a space-delimited string of words; where the first word is the identifier. There are two types of logs: Letter-logs: All words (except the identifier) consist of lowercase English letters. Digit-logs: All words (except the identifier) consist of digits. Reorder these logs so that: The letter-logs come before all digit-logs. The letter-logs are sorted lexicographically by their contents. If their contents are the same; then sort them lexicographically by their identifiers. The digit-logs maintain their relative ordering. Return the final order of the logs. Example 1: Input: logs = [""dig1 8 1 5 1"";""let1 art can"";""dig2 3 6"";""let2 own kit dig"";""let3 art zero""] Output: [""let1 art can"";""let3 art zero"";""let2 own kit dig"";""dig1 8 1 5 1"";""dig2 3 6""] Explanation: The letter-log contents are all different; so their ordering is ""art can""; ""art zero""; ""own kit dig"". The digit-logs have a relative order of ""dig1 8 1 5 1""; ""dig2 3 6"". Example 2: Input: logs = [""a1 9 2 3 1"";""g1 act car"";""zo4 4 7"";""ab1 off key dog"";""a8 act zoo""] Output: [""g1 act car"";""a8 act zoo"";""ab1 off key dog"";""a1 9 2 3 1"";""zo4 4 7""] Constraints: 1 <= logs.length <= 100 3 <= logs[i].length <= 100 All the tokens of logs[i] are separated by a single space. logs[i] is guaranteed to have an identifier and at least one word after the identifier."
PayPal,1046,Last Stone Weight,Easy,"Array, Binary Search, Sliding Window, Prefix Sum",Given a binary array nums and an integer k; return the maximum number of consecutive 1's in the array if you can flip at most k 0's. Example 1: Input: nums = [1;1;1;0;0;0;1;1;1;1;0]; k = 2 Output: 6 Explanation: [1;1;1;0;0;1;1;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Example 2: Input: nums = [0;0;1;1;0;0;1;1;1;0;1;1;0;0;0;1;1;1;1]; k = 3 Output: 10 Explanation: [0;0;1;1;1;1;1;1;1;1;1;1;0;0;0;1;1;1;1] Bolded numbers were flipped from 0 to 1. The longest subarray is underlined. Constraints: 1 <= nums.length <= 105 nums[i] is either 0 or 1. 0 <= k <= nums.length
PayPal,1169,Invalid Transactions,Med,"Array, Hash Table, Greedy, Sorting, Counting",You are given n item's value and label as two integer arrays values and labels. You are also given two integers numWanted and useLimit. Your task is to find a subset of items with the maximum sum of their values such that: The number of items is at most numWanted. The number of items with the same label is at most useLimit. Return the maximum sum. Example 1: Input: values = [5;4;3;2;1]; labels = [1;1;2;2;3]; numWanted = 3; useLimit = 1 Output: 9 Explanation: The subset chosen is the first; third; and fifth items with the sum of values 5 + 3 + 1. Example 2: Input: values = [5;4;3;2;1]; labels = [1;3;3;3;2]; numWanted = 3; useLimit = 2 Output: 12 Explanation: The subset chosen is the first; second; and third items with the sum of values 5 + 4 + 3. Example 3: Input: values = [9;8;8;7;6]; labels = [0;0;0;1;1]; numWanted = 3; useLimit = 1 Output: 16 Explanation: The subset chosen is the first and fourth items with the sum of values 9 + 7. Constraints: n == values.length == labels.length 1 <= n <= 2 * 104 0 <= values[i]; labels[i] <= 2 * 104 1 <= numWanted; useLimit <= n
PayPal,1358,Number of Substrings Containing All Three Characters,Med,"Math, Two Pointers, Binary Search, Interactive",Given a callable function f(x; y) with a hidden formula and a value z; reverse engineer the formula and return all positive integer pairs x and y where f(x;y) == z. You may return the pairs in any order. While the exact formula is hidden; the function is monotonically increasing; i.e.: f(x; y) < f(x + 1; y) f(x; y) < f(x; y + 1) The function interface is defined like this: interface CustomFunction { public: // Returns some positive integer f(x; y) for two positive integers x and y based on a formula. int f(int x; int y); }; We will judge your solution as follows: The judge has a list of 9 hidden implementations of CustomFunction; along with a way to generate an answer key of all valid pairs for a specific z. The judge will receive two inputs: a function_id (to determine which implementation to test your code with); and the target z. The judge will call your findSolution and compare your results with the answer key. If your results match the answer key; your solution will be Accepted. Example 1: Input: function_id = 1; z = 5 Output: [[1;4];[2;3];[3;2];[4;1]] Explanation: The hidden formula for function_id = 1 is f(x; y) = x + y. The following positive integer values of x and y make f(x; y) equal to 5: x=1; y=4 -> f(1; 4) = 1 + 4 = 5. x=2; y=3 -> f(2; 3) = 2 + 3 = 5. x=3; y=2 -> f(3; 2) = 3 + 2 = 5. x=4; y=1 -> f(4; 1) = 4 + 1 = 5. Example 2: Input: function_id = 2; z = 5 Output: [[1;5];[5;1]] Explanation: The hidden formula for function_id = 2 is f(x; y) = x * y. The following positive integer values of x and y make f(x; y) equal to 5: x=1; y=5 -> f(1; 5) = 1 * 5 = 5. x=5; y=1 -> f(5; 1) = 5 * 1 = 5. Constraints: 1 <= function_id <= 9 1 <= z <= 100 It is guaranteed that the solutions of f(x; y) == z will be in the range 1 <= x; y <= 1000. It is also guaranteed that f(x; y) will fit in 32 bit signed integer if 1 <= x; y <= 1000.
PayPal,1671,Minimum Number of Removals to Make Mountain Array,Hard,Database,
PayPal,1802,Maximum Value at a Given Index in a Bounded Array,Med,"Array, Stack, Queue, Simulation",The school cafeteria offers circular and square sandwiches at lunch break; referred to by numbers 0 and 1 respectively. All students stand in a queue. Each student either prefers square or circular sandwiches. The number of sandwiches in the cafeteria is equal to the number of students. The sandwiches are placed in a stack. At each step: If the student at the front of the queue prefers the sandwich on the top of the stack; they will take it and leave the queue. Otherwise; they will leave it and go to the queue's end. This continues until none of the queue students want to take the top sandwich and are thus unable to eat. You are given two integer arrays students and sandwiches where sandwiches[i] is the type of the i​​​​​​th sandwich in the stack (i = 0 is the top of the stack) and students[j] is the preference of the j​​​​​​th student in the initial queue (j = 0 is the front of the queue). Return the number of students that are unable to eat. Example 1: Input: students = [1;1;0;0]; sandwiches = [0;1;0;1] Output: 0 Explanation: - Front student leaves the top sandwich and returns to the end of the line making students = [1;0;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;0;1;1]. - Front student takes the top sandwich and leaves the line making students = [0;1;1] and sandwiches = [1;0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [1;1;0]. - Front student takes the top sandwich and leaves the line making students = [1;0] and sandwiches = [0;1]. - Front student leaves the top sandwich and returns to the end of the line making students = [0;1]. - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = [1]. - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = []. Hence all students are able to eat. Example 2: Input: students = [1;1;1;0;0;1]; sandwiches = [1;0;0;0;1;1] Output: 3 Constraints: 1 <= students.length; sandwiches.length <= 100 students.length == sandwiches.length sandwiches[i] is 0 or 1. students[i] is 0 or 1.
PayPal,1823,Find the Winner of the Circular Game,Med,"String, Counting","You are given a string s of even length. Split this string into two halves of equal lengths; and let a be the first half and b be the second half. Two strings are alike if they have the same number of vowels ('a'; 'e'; 'i'; 'o'; 'u'; 'A'; 'E'; 'I'; 'O'; 'U'). Notice that s contains uppercase and lowercase letters. Return true if a and b are alike. Otherwise; return false. Example 1: Input: s = ""book"" Output: true Explanation: a = ""bo"" and b = ""ok"". a has 1 vowel and b has 1 vowel. Therefore; they are alike. Example 2: Input: s = ""textbook"" Output: false Explanation: a = ""text"" and b = ""book"". a has 1 vowel whereas b has 2. Therefore; they are not alike. Notice that the vowel o is counted twice. Constraints: 2 <= s.length <= 1000 s.length is even. s consists of uppercase and lowercase letters."
PayPal,1854,Maximum Population Year,Easy,,
PayPal,1882,Process Tasks Using Servers,Med,Database,Table: Employees +-------------+----------+ | Column Name | Type | +-------------+----------+ | employee_id | int | | name | varchar | | reports_to | int | | age | int | +-------------+----------+ employee_id is the column with unique values for this table. This table contains information about the employees and the id of the manager they report to. Some employees do not report to anyone (reports_to is null). For this problem; we will consider a manager an employee who has at least 1 other employee reporting to them. Write a solution to report the ids and the names of all managers; the number of employees who report directly to them; and the average age of the reports rounded to the nearest integer. Return the result table ordered by employee_id. The result format is in the following example. Example 1: Input: Employees table: +-------------+---------+------------+-----+ | employee_id | name | reports_to | age | +-------------+---------+------------+-----+ | 9 | Hercy | null | 43 | | 6 | Alice | 9 | 41 | | 4 | Bob | 9 | 36 | | 2 | Winston | null | 37 | +-------------+---------+------------+-----+ Output: +-------------+-------+---------------+-------------+ | employee_id | name | reports_count | average_age | +-------------+-------+---------------+-------------+ | 9 | Hercy | 2 | 39 | +-------------+-------+---------------+-------------+ Explanation: Hercy has 2 people report directly to him; Alice and Bob. Their average age is (41+36)/2 = 38.5; which is 39 after rounding it to the nearest integer. Example 2: Input: Employees table: +-------------+---------+------------+-----+ | employee_id | name | reports_to | age | |-------------|---------|------------|-----| | 1 | Michael | null | 45 | | 2 | Alice | 1 | 38 | | 3 | Bob | 1 | 42 | | 4 | Charlie | 2 | 34 | | 5 | David | 2 | 40 | | 6 | Eve | 3 | 37 | | 7 | Frank | null | 50 | | 8 | Grace | null | 48 | +-------------+---------+------------+-----+ Output: +-------------+---------+---------------+-------------+ | employee_id | name | reports_count | average_age | | ----------- | ------- | ------------- | ----------- | | 1 | Michael | 2 | 40 | | 2 | Alice | 2 | 37 | | 3 | Bob | 1 | 37 | +-------------+---------+---------------+-------------+
PayPal,1963,Minimum Number of Swaps to Make the String Balanced,Med,"Array, Math, Bit Manipulation",The XOR sum of a list is the bitwise XOR of all its elements. If the list only contains one element; then its XOR sum will be equal to this element. For example; the XOR sum of [1;2;3;4] is equal to 1 XOR 2 XOR 3 XOR 4 = 4; and the XOR sum of [3] is equal to 3. You are given two 0-indexed arrays arr1 and arr2 that consist only of non-negative integers. Consider the list containing the result of arr1[i] AND arr2[j] (bitwise AND) for every (i; j) pair where 0 <= i < arr1.length and 0 <= j < arr2.length. Return the XOR sum of the aforementioned list. Example 1: Input: arr1 = [1;2;3]; arr2 = [6;5] Output: 0 Explanation: The list = [1 AND 6; 1 AND 5; 2 AND 6; 2 AND 5; 3 AND 6; 3 AND 5] = [0;1;2;0;2;1]. The XOR sum = 0 XOR 1 XOR 2 XOR 0 XOR 2 XOR 1 = 0. Example 2: Input: arr1 = [12]; arr2 = [4] Output: 4 Explanation: The list = [12 AND 4] = [4]. The XOR sum = 4. Constraints: 1 <= arr1.length; arr2.length <= 105 0 <= arr1[i]; arr2[j] <= 109
PayPal,2134,Minimum Swaps to Group All 1's Together II,Med,"String, Binary Search, Sliding Window, Prefix Sum","A teacher is writing a test with n true/false questions; with 'T' denoting true and 'F' denoting false. He wants to confuse the students by maximizing the number of consecutive questions with the same answer (multiple trues or multiple falses in a row). You are given a string answerKey; where answerKey[i] is the original answer to the ith question. In addition; you are given an integer k; the maximum number of times you may perform the following operation: Change the answer key for any question to 'T' or 'F' (i.e.; set answerKey[i] to 'T' or 'F'). Return the maximum number of consecutive 'T's or 'F's in the answer key after performing the operation at most k times. Example 1: Input: answerKey = ""TTFF""; k = 2 Output: 4 Explanation: We can replace both the 'F's with 'T's to make answerKey = ""TTTT"". There are four consecutive 'T's. Example 2: Input: answerKey = ""TFFT""; k = 1 Output: 3 Explanation: We can replace the first 'T' with an 'F' to make answerKey = ""FFFT"". Alternatively; we can replace the second 'T' with an 'F' to make answerKey = ""TFFF"". In both cases; there are three consecutive 'F's. Example 3: Input: answerKey = ""TTFTTFTT""; k = 1 Output: 5 Explanation: We can replace the first 'F' to make answerKey = ""TTTTTFTT"" Alternatively; we can replace the second 'F' to make answerKey = ""TTFTTTTT"". In both cases; there are five consecutive 'T's. Constraints: n == answerKey.length 1 <= n <= 5 * 104 answerKey[i] is either 'T' or 'F' 1 <= k <= n"
PayPal,2385,Amount of Time for Binary Tree to Be Infected,Med,"Array, Prefix Sum",
PayPal,2491,Divide Players Into Teams of Equal Skill,Med,"Math, Number Theory",Given a positive integer n; return the smallest positive integer that is a multiple of both 2 and n. Example 1: Input: n = 5 Output: 10 Explanation: The smallest multiple of both 5 and 2 is 10. Example 2: Input: n = 6 Output: 6 Explanation: The smallest multiple of both 6 and 2 is 6. Note that a number is a multiple of itself. Constraints: 1 <= n <= 150
Snap,231,Power of Two,Easy,"Math, Bit Manipulation, Recursion",Given an integer n; return true if it is a power of two. Otherwise; return false. An integer n is a power of two; if there exists an integer x such that n == 2x. Example 1: Input: n = 1 Output: true Explanation: 20 = 1 Example 2: Input: n = 16 Output: true Explanation: 24 = 16 Example 3: Input: n = 3 Output: false Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Snap,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Snap,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Snap,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Snap,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
Snap,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
Snap,140,Word Break II,Hard,"Array, Hash Table, String, Dynamic Programming, Backtracking, Trie, Memoization","Given a string s and a dictionary of strings wordDict; add spaces in s to construct a sentence where each word is a valid dictionary word. Return all such possible sentences in any order. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""catsanddog""; wordDict = [""cat"";""cats"";""and"";""sand"";""dog""] Output: [""cats and dog"";""cat sand dog""] Example 2: Input: s = ""pineapplepenapple""; wordDict = [""apple"";""pen"";""applepen"";""pine"";""pineapple""] Output: [""pine apple pen apple"";""pineapple pen apple"";""pine applepen apple""] Explanation: Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: [] Constraints: 1 <= s.length <= 20 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 10 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique. Input is generated in a way that the length of the answer doesn't exceed 105."
Snap,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Snap,161,One Edit Distance,Med,"Two Pointers, String",
Snap,269,Alien Dictionary,Hard,"Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort",
Snap,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Snap,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Snap,40,Combination Sum II,Med,"Array, Backtracking",Given a collection of candidate numbers (candidates) and a target number (target); find all unique combinations in candidates where the candidate numbers sum to target. Each number in candidates may only be used once in the combination. Note: The solution set must not contain duplicate combinations. Example 1: Input: candidates = [10;1;2;7;6;1;5]; target = 8 Output: [ [1;1;6]; [1;2;5]; [1;7]; [2;6] ] Example 2: Input: candidates = [2;5;2;1;2]; target = 5 Output: [ [1;2;2]; [5] ] Constraints: 1 <= candidates.length <= 100 1 <= candidates[i] <= 50 1 <= target <= 30
Snap,44,Wildcard Matching,Hard,"String, Dynamic Programming, Greedy, Recursion","Given an input string (s) and a pattern (p); implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""*"" Output: true Explanation: '*' matches any sequence. Example 3: Input: s = ""cb""; p = ""?a"" Output: false Explanation: '?' matches 'c'; but the second letter is 'a'; which does not match 'b'. Constraints: 0 <= s.length; p.length <= 2000 s contains only lowercase English letters. p contains only lowercase English letters; '?' or '*'."
Snap,96,Unique Binary Search Trees,Med,"Math, Dynamic Programming, Tree, Binary Search Tree, Binary Tree",Given an integer n; return the number of structurally unique BST's (binary search trees) which has exactly n nodes of unique values from 1 to n. Example 1: Input: n = 3 Output: 5 Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 19
Snap,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Snap,206,Reverse Linked List,Easy,"Linked List, Recursion",Given the head of a singly linked list; reverse the list; and return the reversed list. Example 1: Input: head = [1;2;3;4;5] Output: [5;4;3;2;1] Example 2: Input: head = [1;2] Output: [2;1] Example 3: Input: head = [] Output: [] Constraints: The number of nodes in the list is the range [0; 5000]. -5000 <= Node.val <= 5000 Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Snap,270,Closest Binary Search Tree Value,Easy,"Binary Search, Tree, Depth-First Search, Binary Search Tree, Binary Tree",
Snap,289,Game of Life,Med,"Array, Matrix, Simulation","According to Wikipedia's article: ""The Game of Life; also known simply as Life; is a cellular automaton devised by the British mathematician John Horton Conway in 1970."" The board is made up of an m x n grid of cells; where each cell has an initial state: live (represented by a 1) or dead (represented by a 0). Each cell interacts with its eight neighbors (horizontal; vertical; diagonal) using the following four rules (taken from the above Wikipedia article): Any live cell with fewer than two live neighbors dies as if caused by under-population. Any live cell with two or three live neighbors lives on to the next generation. Any live cell with more than three live neighbors dies; as if by over-population. Any dead cell with exactly three live neighbors becomes a live cell; as if by reproduction. The next state of the board is determined by applying the above rules simultaneously to every cell in the current state of the m x n grid board. In this process; births and deaths occur simultaneously. Given the current state of the board; update the board to reflect its next state. Note that you do not need to return anything. Example 1: Input: board = [[0;1;0];[0;0;1];[1;1;1];[0;0;0]] Output: [[0;0;0];[1;0;1];[0;1;1];[0;1;0]] Example 2: Input: board = [[1;1];[1;0]] Output: [[1;1];[1;1]] Constraints: m == board.length n == board[i].length 1 <= m; n <= 25 board[i][j] is 0 or 1. Follow up: Could you solve it in-place? Remember that the board needs to be updated simultaneously: You cannot update some cells first and then use their updated values to update other cells. In this question; we represent the board using a 2D array. In principle; the board is infinite; which would cause problems when the active area encroaches upon the border of the array (i.e.; live cells reach the border). How would you address these problems?"
Snap,312,Burst Balloons,Hard,"Array, Dynamic Programming",You are given n balloons; indexed from 0 to n - 1. Each balloon is painted with a number on it represented by an array nums. You are asked to burst all the balloons. If you burst the ith balloon; you will get nums[i - 1] * nums[i] * nums[i + 1] coins. If i - 1 or i + 1 goes out of bounds of the array; then treat it as if there is a balloon with a 1 painted on it. Return the maximum coins you can collect by bursting the balloons wisely. Example 1: Input: nums = [3;1;5;8] Output: 167 Explanation: nums = [3;1;5;8] --> [3;5;8] --> [3;8] --> [8] --> [] coins = 3*1*5 + 3*5*8 + 1*3*8 + 1*8*1 = 167 Example 2: Input: nums = [1;5] Output: 10 Constraints: n == nums.length 1 <= n <= 300 0 <= nums[i] <= 100
Snap,314,Binary Tree Vertical Order Traversal,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Sorting, Binary Tree",
Snap,377,Combination Sum IV,Med,"Array, Dynamic Programming",Given an array of distinct integers nums and a target integer target; return the number of possible combinations that add up to target. The test cases are generated so that the answer can fit in a 32-bit integer. Example 1: Input: nums = [1;2;3]; target = 4 Output: 7 Explanation: The possible combination ways are: (1; 1; 1; 1) (1; 1; 2) (1; 2; 1) (1; 3) (2; 1; 1) (2; 2) (3; 1) Note that different sequences are counted as different combinations. Example 2: Input: nums = [9]; target = 3 Output: 0 Constraints: 1 <= nums.length <= 200 1 <= nums[i] <= 1000 All the elements of nums are unique. 1 <= target <= 1000 Follow up: What if negative numbers are allowed in the given array? How does it change the problem? What limitation we need to add to the question to allow negative numbers?
Snap,402,Remove K Digits,Med,"String, Stack, Greedy, Monotonic Stack","Given string num representing a non-negative integer num; and an integer k; return the smallest possible integer after removing k digits from num. Example 1: Input: num = ""1432219""; k = 3 Output: ""1219"" Explanation: Remove the three digits 4; 3; and 2 to form the new number 1219 which is the smallest. Example 2: Input: num = ""10200""; k = 1 Output: ""200"" Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes. Example 3: Input: num = ""10""; k = 2 Output: ""0"" Explanation: Remove all the digits from the number and it is left with nothing which is 0. Constraints: 1 <= k <= num.length <= 105 num consists of only digits. num does not have any leading zeros except for the zero itself."
Snap,403,Frog Jump,Hard,"Array, Dynamic Programming",A frog is crossing a river. The river is divided into some number of units; and at each unit; there may or may not exist a stone. The frog can jump on a stone; but it must not jump into the water. Given a list of stones positions (in units) in sorted ascending order; determine if the frog can cross the river by landing on the last stone. Initially; the frog is on the first stone and assumes the first jump must be 1 unit. If the frog's last jump was k units; its next jump must be either k - 1; k; or k + 1 units. The frog can only jump in the forward direction. Example 1: Input: stones = [0;1;3;5;6;8;12;17] Output: true Explanation: The frog can jump to the last stone by jumping 1 unit to the 2nd stone; then 2 units to the 3rd stone; then 2 units to the 4th stone; then 3 units to the 6th stone; 4 units to the 7th stone; and 5 units to the 8th stone. Example 2: Input: stones = [0;1;2;3;4;8;9;11] Output: false Explanation: There is no way to jump to the last stone as the gap between the 5th and 6th stone is too large. Constraints: 2 <= stones.length <= 2000 0 <= stones[i] <= 231 - 1 stones[0] == 0 stones is sorted in a strictly increasing order.
Snap,439,Ternary Expression Parser,Med,"String, Stack, Recursion",
Snap,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Snap,527,Word Abbreviation,Hard,"Array, String, Greedy, Trie, Sorting",
Snap,635,Design Log Storage System,Med,"Hash Table, String, Design, Ordered Set",
Snap,964,Least Operators to Express Number,Hard,"Array, Hash Table, Depth-First Search, Breadth-First Search, Union Find, Graph",You are given a network of n nodes represented as an n x n adjacency matrix graph; where the ith node is directly connected to the jth node if graph[i][j] == 1. Some nodes initial are initially infected by malware. Whenever two nodes are directly connected; and at least one of those two nodes is infected by malware; both nodes will be infected by malware. This spread of malware will continue until no more nodes can be infected in this manner. Suppose M(initial) is the final number of nodes infected with malware in the entire network after the spread of malware stops. We will remove exactly one node from initial; completely removing it and any connections from this node to any other node. Return the node that; if removed; would minimize M(initial). If multiple nodes could be removed to minimize M(initial); return such a node with the smallest index. Example 1: Input: graph = [[1;1;0];[1;1;0];[0;0;1]]; initial = [0;1] Output: 0 Example 2: Input: graph = [[1;1;0];[1;1;1];[0;1;1]]; initial = [0;1] Output: 1 Example 3: Input: graph = [[1;1;0;0];[1;1;1;0];[0;1;1;1];[0;0;1;1]]; initial = [0;1] Output: 1 Constraints: n == graph.length n == graph[i].length 2 <= n <= 300 graph[i][j] is 0 or 1. graph[i][j] == graph[j][i] graph[i][i] == 1 1 <= initial.length < n 0 <= initial[i] <= n - 1 All the integers in initial are unique.
Snap,1754,Largest Merge Of Two Strings,Med,,
Snap,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Snap,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Snap,787,Cheapest Flights Within K Stops,Med,"Array, Breadth-First Search, Matrix",On an 2 x 3 board; there are five tiles labeled from 1 to 5; and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of the board is solved if and only if the board is [[1;2;3];[4;5;0]]. Given the puzzle board board; return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved; return -1. Example 1: Input: board = [[1;2;3];[4;0;5]] Output: 1 Explanation: Swap the 0 and the 5 in one move. Example 2: Input: board = [[1;2;3];[5;4;0]] Output: -1 Explanation: No number of moves will make the board solved. Example 3: Input: board = [[4;1;2];[5;0;3]] Output: 5 Explanation: 5 is the smallest number of moves that solves the board. An example path: After move 0: [[4;1;2];[5;0;3]] After move 1: [[4;1;2];[0;5;3]] After move 2: [[0;1;2];[4;5;3]] After move 3: [[1;0;2];[4;5;3]] After move 4: [[1;2;0];[4;5;3]] After move 5: [[1;2;3];[4;5;0]] Constraints: board.length == 2 board[i].length == 3 0 <= board[i][j] <= 5 Each value board[i][j] is unique.
Snap,227,Basic Calculator II,Med,"Math, String, Stack","Given a string s which represents an expression; evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""3+2*2"" Output: 7 Example 2: Input: s = "" 3/2 "" Output: 1 Example 3: Input: s = "" 3+5 / 2 "" Output: 5 Constraints: 1 <= s.length <= 3 * 105 s consists of integers and operators ('+'; '-'; '*'; '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0; 231 - 1]. The answer is guaranteed to fit in a 32-bit integer."
Snap,934,Shortest Bridge,Med,"Array, Dynamic Programming, Bit Manipulation",Given an integer array arr; return the number of distinct bitwise ORs of all the non-empty subarrays of arr. The bitwise OR of a subarray is the bitwise OR of each integer in the subarray. The bitwise OR of a subarray of one integer is that integer. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: arr = [0] Output: 1 Explanation: There is only one possible result: 0. Example 2: Input: arr = [1;1;2] Output: 3 Explanation: The possible subarrays are [1]; [1]; [2]; [1; 1]; [1; 2]; [1; 1; 2]. These yield the results 1; 1; 2; 1; 3; 3. There are 3 unique values; so the answer is 3. Example 3: Input: arr = [1;2;4] Output: 6 Explanation: The possible results are 1; 2; 3; 4; 6; and 7. Constraints: 1 <= arr.length <= 5 * 104 0 <= arr[i] <= 109
Snap,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Snap,1293,Shortest Path in a Grid with Obstacles Elimination,Hard,Array,Given an integer array arr; return true if there are three consecutive odd numbers in the array. Otherwise; return false. Example 1: Input: arr = [2;6;4;1] Output: false Explanation: There are no three consecutive odds. Example 2: Input: arr = [1;2;34;3;4;5;7;23;12] Output: true Explanation: [5;7;23] are three consecutive odds. Constraints: 1 <= arr.length <= 1000 1 <= arr[i] <= 1000
Snap,1306,Jump Game III,Med,"Array, Sorting",Given an array of distinct integers arr; find all pairs of elements with the minimum absolute difference of any two elements. Return a list of pairs in ascending order(with respect to pairs); each pair [a; b] follows a; b are from arr a < b b - a equals to the minimum absolute difference of any two elements in arr Example 1: Input: arr = [4;2;1;3] Output: [[1;2];[2;3];[3;4]] Explanation: The minimum absolute difference is 1. List all pairs with difference equal to 1 in ascending order. Example 2: Input: arr = [1;3;6;10;15] Output: [[1;3]] Example 3: Input: arr = [3;8;-10;23;19;-4;-14;27] Output: [[-14;-10];[19;23];[23;27]] Constraints: 2 <= arr.length <= 105 -106 <= arr[i] <= 106
Snap,2050,Parallel Courses III,Hard,"Math, Recursion","A digit string is good if the digits (0-indexed) at even indices are even and the digits at odd indices are prime (2; 3; 5; or 7). For example; ""2582"" is good because the digits (2 and 8) at even positions are even and the digits (5 and 2) at odd positions are prime. However; ""3245"" is not good because 3 is at an even index but is not even. Given an integer n; return the total number of good digit strings of length n. Since the answer may be large; return it modulo 109 + 7. A digit string is a string consisting of digits 0 through 9 that may contain leading zeros. Example 1: Input: n = 1 Output: 5 Explanation: The good numbers of length 1 are ""0""; ""2""; ""4""; ""6""; ""8"". Example 2: Input: n = 4 Output: 400 Example 3: Input: n = 50 Output: 564908303 Constraints: 1 <= n <= 1015"
Snap,2097,Valid Arrangement of Pairs,Hard,Database,
Snap,21,Merge Two Sorted Lists,Easy,"Linked List, Recursion",You are given the heads of two sorted linked lists list1 and list2. Merge the two lists into one sorted list. The list should be made by splicing together the nodes of the first two lists. Return the head of the merged linked list. Example 1: Input: list1 = [1;2;4]; list2 = [1;3;4] Output: [1;1;2;3;4;4] Example 2: Input: list1 = []; list2 = [] Output: [] Example 3: Input: list1 = []; list2 = [0] Output: [0] Constraints: The number of nodes in both lists is in the range [0; 50]. -100 <= Node.val <= 100 Both list1 and list2 are sorted in non-decreasing order.
Snap,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Snap,305,Number of Islands II,Hard,"Array, Hash Table, Union Find",
Snap,871,Minimum Number of Refueling Stops,Hard,"Depth-First Search, Breadth-First Search, Graph",There are n rooms labeled from 0 to n - 1 and all the rooms are locked except for room 0. Your goal is to visit all the rooms. However; you cannot enter a locked room without having its key. When you visit a room; you may find a set of distinct keys in it. Each key has a number on it; denoting which room it unlocks; and you can take all of them with you to unlock the other rooms. Given an array rooms where rooms[i] is the set of keys that you can obtain if you visited room i; return true if you can visit all the rooms; or false otherwise. Example 1: Input: rooms = [[1];[2];[3];[]] Output: true Explanation: We visit room 0 and pick up key 1. We then visit room 1 and pick up key 2. We then visit room 2 and pick up key 3. We then visit room 3. Since we were able to visit every room; we return true. Example 2: Input: rooms = [[1;3];[3;0;1];[2];[0]] Output: false Explanation: We can not enter room number 2 since the only key that unlocks it is in that room. Constraints: n == rooms.length 2 <= n <= 1000 0 <= rooms[i].length <= 1000 1 <= sum(rooms[i].length) <= 3000 0 <= rooms[i][j] < n All the values of rooms[i] are unique.
Snap,2296,Design a Text Editor,Hard,Database,
Snap,2268,Minimum Number of Keypresses,Med,"Array, Math, Bit Manipulation, Matrix",
Snap,2385,Amount of Time for Binary Tree to Be Infected,Med,"Array, Prefix Sum",
Snap,2589,Minimum Time to Complete All Tasks,Hard,"Array, String","The value of an alphanumeric string can be defined as: The numeric representation of the string in base 10; if it comprises of digits only. The length of the string; otherwise. Given an array strs of alphanumeric strings; return the maximum value of any string in strs. Example 1: Input: strs = [""alic3"";""bob"";""3"";""4"";""00000""] Output: 5 Explanation: - ""alic3"" consists of both letters and digits; so its value is its length; i.e. 5. - ""bob"" consists only of letters; so its value is also its length; i.e. 3. - ""3"" consists only of digits; so its value is its numeric equivalent; i.e. 3. - ""4"" also consists only of digits; so its value is 4. - ""00000"" consists only of digits; so its value is 0. Hence; the maximum value is 5; of ""alic3"". Example 2: Input: strs = [""1"";""01"";""001"";""0001""] Output: 1 Explanation: Each string in the array has value 1. Hence; we return 1. Constraints: 1 <= strs.length <= 100 1 <= strs[i].length <= 9 strs[i] consists of only lowercase English letters and digits."
Snap,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Snap,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Snap,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
Snap,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Snap,317,Shortest Distance from All Buildings,Hard,"Array, Breadth-First Search, Matrix",
Snap,332,Reconstruct Itinerary,Hard,"Depth-First Search, Graph, Eulerian Circuit","You are given a list of airline tickets where tickets[i] = [fromi; toi] represent the departure and the arrival airports of one flight. Reconstruct the itinerary in order and return it. All of the tickets belong to a man who departs from ""JFK""; thus; the itinerary must begin with ""JFK"". If there are multiple valid itineraries; you should return the itinerary that has the smallest lexical order when read as a single string. For example; the itinerary [""JFK""; ""LGA""] has a smaller lexical order than [""JFK""; ""LGB""]. You may assume all tickets form at least one valid itinerary. You must use all the tickets once and only once. Example 1: Input: tickets = [[""MUC"";""LHR""];[""JFK"";""MUC""];[""SFO"";""SJC""];[""LHR"";""SFO""]] Output: [""JFK"";""MUC"";""LHR"";""SFO"";""SJC""] Example 2: Input: tickets = [[""JFK"";""SFO""];[""JFK"";""ATL""];[""SFO"";""ATL""];[""ATL"";""JFK""];[""ATL"";""SFO""]] Output: [""JFK"";""ATL"";""JFK"";""SFO"";""ATL"";""SFO""] Explanation: Another possible reconstruction is [""JFK"";""SFO"";""ATL"";""JFK"";""ATL"";""SFO""] but it is larger in lexical order. Constraints: 1 <= tickets.length <= 300 tickets[i].length == 2 fromi.length == 3 toi.length == 3 fromi and toi consist of uppercase English letters. fromi != toi"
Snap,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Snap,399,Evaluate Division,Med,"Array, String, Depth-First Search, Breadth-First Search, Union Find, Graph, Shortest Path","You are given an array of variable pairs equations and an array of real numbers values; where equations[i] = [Ai; Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable. You are also given some queries; where queries[j] = [Cj; Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries. If a single answer cannot be determined; return -1.0. Note: The input is always valid. You may assume that evaluating the queries will not result in division by zero and that there is no contradiction. Note: The variables that do not occur in the list of equations are undefined; so the answer cannot be determined for them. Example 1: Input: equations = [[""a"";""b""];[""b"";""c""]]; values = [2.0;3.0]; queries = [[""a"";""c""];[""b"";""a""];[""a"";""e""];[""a"";""a""];[""x"";""x""]] Output: [6.00000;0.50000;-1.00000;1.00000;-1.00000] Explanation: Given: a / b = 2.0; b / c = 3.0 queries are: a / c = ?; b / a = ?; a / e = ?; a / a = ?; x / x = ? return: [6.0; 0.5; -1.0; 1.0; -1.0 ] note: x is undefined => -1.0 Example 2: Input: equations = [[""a"";""b""];[""b"";""c""];[""bc"";""cd""]]; values = [1.5;2.5;5.0]; queries = [[""a"";""c""];[""c"";""b""];[""bc"";""cd""];[""cd"";""bc""]] Output: [3.75000;0.40000;5.00000;0.20000] Example 3: Input: equations = [[""a"";""b""]]; values = [0.5]; queries = [[""a"";""b""];[""b"";""a""];[""a"";""c""];[""x"";""y""]] Output: [0.50000;2.00000;-1.00000;-1.00000] Constraints: 1 <= equations.length <= 20 equations[i].length == 2 1 <= Ai.length; Bi.length <= 5 values.length == equations.length 0.0 < values[i] <= 20.0 1 <= queries.length <= 20 queries[i].length == 2 1 <= Cj.length; Dj.length <= 5 Ai; Bi; Cj; Dj consist of lower case English letters and digits."
Snap,632,Smallest Range Covering Elements from K Lists,Hard,"Array, Hash Table, Greedy, Sliding Window, Sorting, Heap (Priority Queue)",You have k lists of sorted integers in non-decreasing order. Find the smallest range that includes at least one number from each of the k lists. We define the range [a; b] is smaller than range [c; d] if b - a < d - c or a < c if b - a == d - c. Example 1: Input: nums = [[4;10;15;24;26];[0;9;12;20];[5;18;22;30]] Output: [20;24] Explanation: List 1: [4; 10; 15; 24;26]; 24 is in range [20;24]. List 2: [0; 9; 12; 20]; 20 is in range [20;24]. List 3: [5; 18; 22; 30]; 22 is in range [20;24]. Example 2: Input: nums = [[1;2;3];[1;2;3];[1;2;3]] Output: [1;1] Constraints: nums.length == k 1 <= k <= 3500 1 <= nums[i].length <= 50 -105 <= nums[i][j] <= 105 nums[i] is sorted in non-decreasing order.
Snap,721,Accounts Merge,Med,"Array, Hash Table, String, Depth-First Search, Breadth-First Search, Union Find, Sorting","Given a list of accounts where each element accounts[i] is a list of strings; where the first element accounts[i][0] is a name; and the rest of the elements are emails representing emails of the account. Now; we would like to merge these accounts. Two accounts definitely belong to the same person if there is some common email to both accounts. Note that even if two accounts have the same name; they may belong to different people as people could have the same name. A person can have any number of accounts initially; but all of their accounts definitely have the same name. After merging the accounts; return the accounts in the following format: the first element of each account is the name; and the rest of the elements are emails in sorted order. The accounts themselves can be returned in any order. Example 1: Input: accounts = [[""John"";""johnsmith@mail.com"";""john_newyork@mail.com""];[""John"";""johnsmith@mail.com"";""john00@mail.com""];[""Mary"";""mary@mail.com""];[""John"";""johnnybravo@mail.com""]] Output: [[""John"";""john00@mail.com"";""john_newyork@mail.com"";""johnsmith@mail.com""];[""Mary"";""mary@mail.com""];[""John"";""johnnybravo@mail.com""]] Explanation: The first and second John's are the same person as they have the common email ""johnsmith@mail.com"". The third John and Mary are different people as none of their email addresses are used by other accounts. We could return these lists in any order; for example the answer [['Mary'; 'mary@mail.com']; ['John'; 'johnnybravo@mail.com']; ['John'; 'john00@mail.com'; 'john_newyork@mail.com'; 'johnsmith@mail.com']] would still be accepted. Example 2: Input: accounts = [[""Gabe"";""Gabe0@m.co"";""Gabe3@m.co"";""Gabe1@m.co""];[""Kevin"";""Kevin3@m.co"";""Kevin5@m.co"";""Kevin0@m.co""];[""Ethan"";""Ethan5@m.co"";""Ethan4@m.co"";""Ethan0@m.co""];[""Hanzo"";""Hanzo3@m.co"";""Hanzo1@m.co"";""Hanzo0@m.co""];[""Fern"";""Fern5@m.co"";""Fern1@m.co"";""Fern0@m.co""]] Output: [[""Ethan"";""Ethan0@m.co"";""Ethan4@m.co"";""Ethan5@m.co""];[""Gabe"";""Gabe0@m.co"";""Gabe1@m.co"";""Gabe3@m.co""];[""Hanzo"";""Hanzo0@m.co"";""Hanzo1@m.co"";""Hanzo3@m.co""];[""Kevin"";""Kevin0@m.co"";""Kevin3@m.co"";""Kevin5@m.co""];[""Fern"";""Fern0@m.co"";""Fern1@m.co"";""Fern5@m.co""]] Constraints: 1 <= accounts.length <= 1000 2 <= accounts[i].length <= 10 1 <= accounts[i][j].length <= 30 accounts[i][0] consists of English letters. accounts[i][j] (for j > 0) is a valid email."
Snap,856,Score of Parentheses,Med,"Math, Enumeration",Given an integer n; return the number of ways you can write n as the sum of consecutive positive integers. Example 1: Input: n = 5 Output: 2 Explanation: 5 = 2 + 3 Example 2: Input: n = 9 Output: 3 Explanation: 9 = 4 + 5 = 2 + 3 + 4 Example 3: Input: n = 15 Output: 4 Explanation: 15 = 8 + 7 = 4 + 5 + 6 = 1 + 2 + 3 + 4 + 5 Constraints: 1 <= n <= 109
Snap,1004,Max Consecutive Ones III,Med,"Math, Dynamic Programming, Memoization","Given a single positive integer x; we will write an expression of the form x (op1) x (op2) x (op3) x ... where each operator op1; op2; etc. is either addition; subtraction; multiplication; or division (+; -; *; or /). For example; with x = 3; we might write 3 * 3 / 3 + 3 - 3 which is a value of 3. When writing such an expression; we adhere to the following conventions: The division operator (/) returns rational numbers. There are no parentheses placed anywhere. We use the usual order of operations: multiplication and division happen before addition and subtraction. It is not allowed to use the unary negation operator (-). For example; ""x - x"" is a valid expression as it only uses subtraction; but ""-x + x"" is not because it uses negation. We would like to write an expression with the least number of operators such that the expression equals the given target. Return the least number of operators used. Example 1: Input: x = 3; target = 19 Output: 5 Explanation: 3 * 3 + 3 * 3 + 3 / 3. The expression contains 5 operations. Example 2: Input: x = 5; target = 501 Output: 8 Explanation: 5 * 5 * 5 * 5 - 5 * 5 * 5 + 5 / 5. The expression contains 8 operations. Example 3: Input: x = 100; target = 100000000 Output: 3 Explanation: 100 * 100 * 100 * 100. The expression contains 3 operations. Constraints: 2 <= x <= 100 1 <= target <= 2 * 108"
Snap,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Snap,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Snap,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Snap,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Snap,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Snap,64,Minimum Path Sum,Med,"Array, Dynamic Programming, Matrix",Given a m x n grid filled with non-negative numbers; find a path from top left to bottom right; which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1;3;1];[1;5;1];[4;2;1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. Example 2: Input: grid = [[1;2;3];[4;5;6]] Output: 12 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 200 0 <= grid[i][j] <= 200
Snap,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Snap,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Snap,123,Best Time to Buy and Sell Stock III,Hard,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete at most two transactions. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: prices = [3;3;5;0;0;3;1;4] Output: 6 Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Then buy on day 7 (price = 1) and sell on day 8 (price = 4); profit = 4-1 = 3. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Note that you cannot buy on day 1; buy on day 2 and sell them later; as you are engaging multiple transactions at the same time. You must sell before buying again. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transaction is done; i.e. max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 105
Snap,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Snap,162,Find Peak Element,Med,"Array, Binary Search",A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed integer array nums; find a peak element; and return its index. If the array contains multiple peaks; return the index to any of the peaks. You may imagine that nums[-1] = nums[n] = -∞. In other words; an element is always considered to be strictly greater than a neighbor that is outside the array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [1;2;3;1] Output: 2 Explanation: 3 is a peak element and your function should return the index number 2. Example 2: Input: nums = [1;2;1;3;5;6;4] Output: 5 Explanation: Your function can return either index number 1 where the peak element is 2; or index number 5 where the peak element is 6. Constraints: 1 <= nums.length <= 1000 -231 <= nums[i] <= 231 - 1 nums[i] != nums[i + 1] for all valid i.
Snap,166,Fraction to Recurring Decimal,Med,"Hash Table, Math, String","Given two integers representing the numerator and denominator of a fraction; return the fraction in string format. If the fractional part is repeating; enclose the repeating part in parentheses. If multiple answers are possible; return any of them. It is guaranteed that the length of the answer string is less than 104 for all the given inputs. Example 1: Input: numerator = 1; denominator = 2 Output: ""0.5"" Example 2: Input: numerator = 2; denominator = 1 Output: ""2"" Example 3: Input: numerator = 4; denominator = 333 Output: ""0.(012)"" Constraints: -231 <= numerator; denominator <= 231 - 1 denominator != 0"
Snap,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Snap,240,Search a 2D Matrix II,Med,"Array, Binary Search, Divide and Conquer, Matrix",Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. Example 1: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 5 Output: true Example 2: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 20 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= n; m <= 300 -109 <= matrix[i][j] <= 109 All the integers in each row are sorted in ascending order. All the integers in each column are sorted in ascending order. -109 <= target <= 109
Snap,282,Expression Add Operators,Hard,"Math, String, Backtracking","Given a string num that contains only digits and an integer target; return all possibilities to insert the binary operators '+'; '-'; and/or '*' between the digits of num so that the resultant expression evaluates to the target value. Note that operands in the returned expressions should not contain leading zeros. Example 1: Input: num = ""123""; target = 6 Output: [""1*2*3"";""1+2+3""] Explanation: Both ""1*2*3"" and ""1+2+3"" evaluate to 6. Example 2: Input: num = ""232""; target = 8 Output: [""2*3+2"";""2+3*2""] Explanation: Both ""2*3+2"" and ""2+3*2"" evaluate to 8. Example 3: Input: num = ""3456237490""; target = 9191 Output: [] Explanation: There are no expressions that can be created from ""3456237490"" to evaluate to 9191. Constraints: 1 <= num.length <= 10 num consists of only digits. -231 <= target <= 231 - 1"
Snap,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
Snap,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Snap,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Snap,636,Exclusive Time of Functions,Med,"Array, Stack","On a single-threaded CPU; we execute a program containing n functions. Each function has a unique ID between 0 and n-1. Function calls are stored in a call stack: when a function call starts; its ID is pushed onto the stack; and when a function call ends; its ID is popped off the stack. The function whose ID is at the top of the stack is the current function being executed. Each time a function starts or ends; we write a log with the ID; whether it started or ended; and the timestamp. You are given a list logs; where logs[i] represents the ith log message formatted as a string ""{function_id}:{""start"" | ""end""}:{timestamp}"". For example; ""0:start:3"" means a function call with function ID 0 started at the beginning of timestamp 3; and ""1:end:2"" means a function call with function ID 1 ended at the end of timestamp 2. Note that a function can be called multiple times; possibly recursively. A function's exclusive time is the sum of execution times for all function calls in the program. For example; if a function is called twice; one call executing for 2 time units and another call executing for 1 time unit; the exclusive time is 2 + 1 = 3. Return the exclusive time of each function in an array; where the value at the ith index represents the exclusive time for the function with ID i. Example 1: Input: n = 2; logs = [""0:start:0"";""1:start:2"";""1:end:5"";""0:end:6""] Output: [3;4] Explanation: Function 0 starts at the beginning of time 0; then it executes 2 for units of time and reaches the end of time 1. Function 1 starts at the beginning of time 2; executes for 4 units of time; and ends at the end of time 5. Function 0 resumes execution at the beginning of time 6 and executes for 1 unit of time. So function 0 spends 2 + 1 = 3 units of total time executing; and function 1 spends 4 units of total time executing. Example 2: Input: n = 1; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""0:start:6"";""0:end:6"";""0:end:7""] Output: [8] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls itself again. Function 0 (2nd recursive call) starts at the beginning of time 6 and executes for 1 unit of time. Function 0 (initial call) resumes execution at the beginning of time 7 and executes for 1 unit of time. So function 0 spends 2 + 4 + 1 + 1 = 8 units of total time executing. Example 3: Input: n = 2; logs = [""0:start:0"";""0:start:2"";""0:end:5"";""1:start:6"";""1:end:6"";""0:end:7""] Output: [7;1] Explanation: Function 0 starts at the beginning of time 0; executes for 2 units of time; and recursively calls itself. Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time. Function 0 (initial call) resumes execution then immediately calls function 1. Function 1 starts at the beginning of time 6; executes 1 unit of time; and ends at the end of time 6. Function 0 resumes execution at the beginning of time 6 and executes for 2 units of time. So function 0 spends 2 + 4 + 1 = 7 units of total time executing; and function 1 spends 1 unit of total time executing. Constraints: 1 <= n <= 100 1 <= logs.length <= 500 0 <= function_id < n 0 <= timestamp <= 109 No two start events will happen at the same timestamp. No two end events will happen at the same timestamp. Each function has an ""end"" log for each ""start"" log."
Snap,716,Max Stack,Hard,"Linked List, Stack, Design, Doubly-Linked List, Ordered Set",
Snap,772,Basic Calculator III,Hard,"Array, Divide and Conquer, Tree, Matrix",Given a n * n matrix grid of 0's and 1's only. We want to represent grid with a Quad-Tree. Return the root of the Quad-Tree representing grid. A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides; each node has two attributes: val: True if the node represents a grid of 1's or False if the node represents a grid of 0's. Notice that you can assign the val to True or False when isLeaf is False; and both are accepted in the answer. isLeaf: True if the node is a leaf node on the tree or False if the node has four children. class Node { public boolean val; public boolean isLeaf; public Node topLeft; public Node topRight; public Node bottomLeft; public Node bottomRight; } We can construct a Quad-Tree from a two-dimensional area using the following steps: If the current grid has the same value (i.e all 1's or all 0's) set isLeaf True and set val to the value of the grid and set the four children to Null and stop. If the current grid has different values; set isLeaf to False and set val to any value and divide the current grid into four sub-grids as shown in the photo. Recurse for each of the children with the proper sub-grid. If you want to know more about the Quad-Tree; you can refer to the wiki. Quad-Tree format: You don't need to read this section for solving the problem. This is only if you want to understand the output format here. The output represents the serialized format of a Quad-Tree using level order traversal; where null signifies a path terminator where no node exists below. It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list [isLeaf; val]. If the value of isLeaf or val is True we represent it as 1 in the list [isLeaf; val] and if the value of isLeaf or val is False we represent it as 0. Example 1: Input: grid = [[0;1];[1;0]] Output: [[0;1];[1;0];[1;1];[1;1];[1;0]] Explanation: The explanation of this example is shown below: Notice that 0 represents False and 1 represents True in the photo representing the Quad-Tree. Example 2: Input: grid = [[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;1;1;1;1];[1;1;1;1;1;1;1;1];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0]] Output: [[0;1];[1;1];[0;1];[1;1];[1;0];null;null;null;null;[1;0];[1;0];[1;1];[1;1]] Explanation: All values in the grid are not the same. We divide the grid into four sub-grids. The topLeft; bottomLeft and bottomRight each has the same value. The topRight have different values so we divide it into 4 sub-grids where each has the same value. Explanation is shown in the photo below: Constraints: n == grid.length == grid[i].length n == 2x where 0 <= x <= 6
Snap,773,Sliding Puzzle,Hard,"Divide and Conquer, Tree",A Binary Matrix is a matrix in which all the elements are either 0 or 1. Given quadTree1 and quadTree2. quadTree1 represents a n * n binary matrix and quadTree2 represents another n * n binary matrix. Return a Quad-Tree representing the n * n binary matrix which is the result of logical bitwise OR of the two binary matrixes represented by quadTree1 and quadTree2. Notice that you can assign the value of a node to True or False when isLeaf is False; and both are accepted in the answer. A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides; each node has two attributes: val: True if the node represents a grid of 1's or False if the node represents a grid of 0's. isLeaf: True if the node is leaf node on the tree or False if the node has the four children. class Node { public boolean val; public boolean isLeaf; public Node topLeft; public Node topRight; public Node bottomLeft; public Node bottomRight; } We can construct a Quad-Tree from a two-dimensional area using the following steps: If the current grid has the same value (i.e all 1's or all 0's) set isLeaf True and set val to the value of the grid and set the four children to Null and stop. If the current grid has different values; set isLeaf to False and set val to any value and divide the current grid into four sub-grids as shown in the photo. Recurse for each of the children with the proper sub-grid. If you want to know more about the Quad-Tree; you can refer to the wiki. Quad-Tree format: The input/output represents the serialized format of a Quad-Tree using level order traversal; where null signifies a path terminator where no node exists below. It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list [isLeaf; val]. If the value of isLeaf or val is True we represent it as 1 in the list [isLeaf; val] and if the value of isLeaf or val is False we represent it as 0. Example 1: Input: quadTree1 = [[0;1];[1;1];[1;1];[1;0];[1;0]] ; quadTree2 = [[0;1];[1;1];[0;1];[1;1];[1;0];null;null;null;null;[1;0];[1;0];[1;1];[1;1]] Output: [[0;0];[1;1];[1;1];[1;1];[1;0]] Explanation: quadTree1 and quadTree2 are shown above. You can see the binary matrix which is represented by each Quad-Tree. If we apply logical bitwise OR on the two binary matrices we get the binary matrix below which is represented by the result Quad-Tree. Notice that the binary matrices shown are only for illustration; you don't have to construct the binary matrix to get the result tree. Example 2: Input: quadTree1 = [[1;0]]; quadTree2 = [[1;0]] Output: [[1;0]] Explanation: Each tree represents a binary matrix of size 1*1. Each matrix contains only zero. The resulting matrix is of size 1*1 with also zero. Constraints: quadTree1 and quadTree2 are both valid Quad-Trees each representing a n * n grid. n == 2x where 0 <= x <= 9.
Snap,785,Is Graph Bipartite?,Med,"Math, String, Stack, Recursion",
Snap,791,Custom Sort String,Med,"Tree, Binary Search Tree, Recursion, Binary Tree",
Snap,827,Making A Large Island,Hard,"Array, Two Pointers, String","Sometimes people repeat letters to represent extra feeling. For example: ""hello"" -> ""heeellooo"" ""hi"" -> ""hiiii"" In these strings like ""heeellooo""; we have groups of adjacent letters that are all the same: ""h""; ""eee""; ""ll""; ""ooo"". You are given a string s and an array of query strings words. A query word is stretchy if it can be made to be equal to s by any number of applications of the following extension operation: choose a group consisting of characters c; and add some number of characters c to the group so that the size of the group is three or more. For example; starting with ""hello""; we could do an extension on the group ""o"" to get ""hellooo""; but we cannot get ""helloo"" since the group ""oo"" has a size less than three. Also; we could do another extension like ""ll"" -> ""lllll"" to get ""helllllooo"". If s = ""helllllooo""; then the query word ""hello"" would be stretchy because of these two extension operations: query = ""hello"" -> ""hellooo"" -> ""helllllooo"" = s. Return the number of query strings that are stretchy. Example 1: Input: s = ""heeellooo""; words = [""hello""; ""hi""; ""helo""] Output: 1 Explanation: We can extend ""e"" and ""o"" in the word ""hello"" to get ""heeellooo"". We can't extend ""helo"" to get ""heeellooo"" because the group ""ll"" is not size 3 or more. Example 2: Input: s = ""zzzzzyyyyy""; words = [""zzyy"";""zy"";""zyy""] Output: 3 Constraints: 1 <= s.length; words.length <= 100 1 <= words[i].length <= 100 s and words[i] consist of lowercase letters."
Snap,839,Similar String Groups,Hard,"Array, Hash Table, String, Trie","A valid encoding of an array of words is any reference string s and array of indices indices such that: words.length == indices.length The reference string s ends with the '#' character. For each index indices[i]; the substring of s starting from indices[i] and up to (but not including) the next '#' character is equal to words[i]. Given an array of words; return the length of the shortest reference string s possible of any valid encoding of words. Example 1: Input: words = [""time""; ""me""; ""bell""] Output: 10 Explanation: A valid encoding would be s = ""time#bell#"" and indices = [0; 2; 5]. words[0] = ""time""; the substring of s starting from indices[0] = 0 to the next '#' is underlined in ""time#bell#"" words[1] = ""me""; the substring of s starting from indices[1] = 2 to the next '#' is underlined in ""time#bell#"" words[2] = ""bell""; the substring of s starting from indices[2] = 5 to the next '#' is underlined in ""time#bell#"" Example 2: Input: words = [""t""] Output: 2 Explanation: A valid encoding would be s = ""t#"" and indices = [0]. Constraints: 1 <= words.length <= 2000 1 <= words[i].length <= 7 words[i] consists of only lowercase letters."
Snap,849,Maximize Distance to Closest Person,Med,,
Snap,853,Car Fleet,Med,"Array, Two Pointers, Binary Search, Greedy, Sorting",You have n jobs and m workers. You are given three arrays: difficulty; profit; and worker where: difficulty[i] and profit[i] are the difficulty and the profit of the ith job; and worker[j] is the ability of jth worker (i.e.; the jth worker can only complete a job with difficulty at most worker[j]). Every worker can be assigned at most one job; but one job can be completed multiple times. For example; if three workers attempt the same job that pays $1; then the total profit will be $3. If a worker cannot complete any job; their profit is $0. Return the maximum profit we can achieve after assigning the workers to the jobs. Example 1: Input: difficulty = [2;4;6;8;10]; profit = [10;20;30;40;50]; worker = [4;5;6;7] Output: 100 Explanation: Workers are assigned jobs of difficulty [4;4;6;6] and they get a profit of [20;20;30;30] separately. Example 2: Input: difficulty = [85;47;57]; profit = [24;66;99]; worker = [40;25;25] Output: 0 Constraints: n == difficulty.length n == profit.length m == worker.length 1 <= n; m <= 104 1 <= difficulty[i]; profit[i]; worker[i] <= 105
Snap,863,All Nodes Distance K in Binary Tree,Med,"Dynamic Programming, Tree, Depth-First Search, Graph",There is an undirected connected tree with n nodes labeled from 0 to n - 1 and n - 1 edges. You are given the integer n and the array edges where edges[i] = [ai; bi] indicates that there is an edge between nodes ai and bi in the tree. Return an array answer of length n where answer[i] is the sum of the distances between the ith node in the tree and all other nodes. Example 1: Input: n = 6; edges = [[0;1];[0;2];[2;3];[2;4];[2;5]] Output: [8;12;6;10;10;10] Explanation: The tree is shown above. We can see that dist(0;1) + dist(0;2) + dist(0;3) + dist(0;4) + dist(0;5) equals 1 + 1 + 2 + 2 + 2 = 8. Hence; answer[0] = 8; and so on. Example 2: Input: n = 1; edges = [] Output: [0] Example 3: Input: n = 2; edges = [[1;0]] Output: [1;1] Constraints: 1 <= n <= 3 * 104 edges.length == n - 1 edges[i].length == 2 0 <= ai; bi < n ai != bi The given input represents a valid tree.
Snap,876,Middle of the Linked List,Easy,"Array, Hash Table, Greedy, Sorting",Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize; and consists of groupSize consecutive cards. Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize; return true if she can rearrange the cards; or false otherwise. Example 1: Input: hand = [1;2;3;6;2;3;4;7;8]; groupSize = 3 Output: true Explanation: Alice's hand can be rearranged as [1;2;3];[2;3;4];[6;7;8] Example 2: Input: hand = [1;2;3;4;5]; groupSize = 4 Output: false Explanation: Alice's hand can not be rearranged into groups of 4. Constraints: 1 <= hand.length <= 104 0 <= hand[i] <= 109 1 <= groupSize <= hand.length Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/
Snap,528,Random Pick with Weight,Med,"Linked List, Two Pointers",You are given the head of a linked list; and an integer k. Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed). Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [1;4;3;2;5] Example 2: Input: head = [7;9;6;6;7;8;3;0;9;5]; k = 5 Output: [7;9;6;6;8;7;3;0;9;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 105 0 <= Node.val <= 100
Snap,895,Maximum Frequency Stack,Hard,"Array, Bit Manipulation, Breadth-First Search, Matrix","You are given an m x n grid grid where: '.' is an empty cell. '#' is a wall. '@' is the starting point. Lowercase letters represent keys. Uppercase letters represent locks. You start at the starting point and one move consists of walking one space in one of the four cardinal directions. You cannot walk outside the grid; or walk into a wall. If you walk over a key; you can pick it up and you cannot walk over a lock unless you have its corresponding key. For some 1 <= k <= 6; there is exactly one lowercase and one uppercase letter of the first k letters of the English alphabet in the grid. This means that there is exactly one key for each lock; and one lock for each key; and also that the letters used to represent the keys and locks were chosen in the same order as the English alphabet. Return the lowest number of moves to acquire all keys. If it is impossible; return -1. Example 1: Input: grid = [""@.a.."";""###.#"";""b.A.B""] Output: 8 Explanation: Note that the goal is to obtain all the keys not to open all the locks. Example 2: Input: grid = [""@..aA"";""..B#."";""....b""] Output: 6 Example 3: Input: grid = [""@Aa""] Output: -1 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 30 grid[i][j] is either an English letter; '.'; '#'; or '@'. There is exactly one '@' in the grid. The number of keys in the grid is in the range [1; 6]. Each key in the grid is unique. Each key in the grid has a matching lock."
Snap,926,Flip String to Monotone Increasing,Med,"Array, Hash Table, String","Given a list of strings words and a string pattern; return a list of words[i] that match pattern. You may return the answer in any order. A word matches the pattern if there exists a permutation of letters p so that after replacing every letter x in the pattern with p(x); we get the desired word. Recall that a permutation of letters is a bijection from letters to letters: every letter maps to another letter; and no two letters map to the same letter. Example 1: Input: words = [""abc"";""deq"";""mee"";""aqq"";""dkd"";""ccc""]; pattern = ""abb"" Output: [""mee"";""aqq""] Explanation: ""mee"" matches the pattern because there is a permutation {a -> m; b -> e; ...}. ""ccc"" does not match the pattern because {a -> c; b -> c; ...} is not a permutation; since a and b map to the same letter. Example 2: Input: words = [""a"";""b"";""c""]; pattern = ""a"" Output: [""a"";""b"";""c""] Constraints: 1 <= pattern.length <= 20 1 <= words.length <= 50 words[i].length == pattern.length pattern and words[i] are lowercase English letters."
Snap,935,Knight Dialer,Med,"Math, String, Sorting","You are given a string s and an integer k. You can choose one of the first k letters of s and append it at the end of the string. Return the lexicographically smallest string you could have after applying the mentioned step any number of moves. Example 1: Input: s = ""cba""; k = 1 Output: ""acb"" Explanation: In the first move; we move the 1st character 'c' to the end; obtaining the string ""bac"". In the second move; we move the 1st character 'b' to the end; obtaining the final result ""acb"". Example 2: Input: s = ""baaca""; k = 3 Output: ""aaabc"" Explanation: In the first move; we move the 1st character 'b' to the end; obtaining the string ""aacab"". In the second move; we move the 3rd character 'c' to the end; obtaining the final result ""aaabc"". Constraints: 1 <= k <= s.length <= 1000 s consist of lowercase English letters."
Snap,937,Reorder Data in Log Files,Med,"Stack, Design, Monotonic Stack, Data Stream","Design an algorithm that collects daily price quotes for some stock and returns the span of that stock's price for the current day. The span of the stock's price in one day is the maximum number of consecutive days (starting from that day and going backward) for which the stock price was less than or equal to the price of that day. For example; if the prices of the stock in the last four days is [7;2;1;2] and the price of the stock today is 2; then the span of today is 4 because starting from today; the price of the stock was less than or equal 2 for 4 consecutive days. Also; if the prices of the stock in the last four days is [7;34;1;2] and the price of the stock today is 8; then the span of today is 3 because starting from today; the price of the stock was less than or equal 8 for 3 consecutive days. Implement the StockSpanner class: StockSpanner() Initializes the object of the class. int next(int price) Returns the span of the stock's price given that today's price is price. Example 1: Input [""StockSpanner""; ""next""; ""next""; ""next""; ""next""; ""next""; ""next""; ""next""] [[]; [100]; [80]; [60]; [70]; [60]; [75]; [85]] Output [null; 1; 1; 1; 2; 1; 4; 6] Explanation StockSpanner stockSpanner = new StockSpanner(); stockSpanner.next(100); // return 1 stockSpanner.next(80); // return 1 stockSpanner.next(60); // return 1 stockSpanner.next(70); // return 2 stockSpanner.next(60); // return 1 stockSpanner.next(75); // return 4; because the last 4 prices (including today's price of 75) were less than or equal to today's price. stockSpanner.next(85); // return 6 Constraints: 1 <= price <= 105 At most 104 calls will be made to next."
Snap,939,Minimum Area Rectangle,Med,"String, Dynamic Programming, Prefix Sum","You are given a string s of length n where s[i] is either: 'D' means decreasing; or 'I' means increasing. A permutation perm of n + 1 integers of all the integers in the range [0; n] is called a valid permutation if for all valid i: If s[i] == 'D'; then perm[i] > perm[i + 1]; and If s[i] == 'I'; then perm[i] < perm[i + 1]. Return the number of valid permutations perm. Since the answer may be large; return it modulo 109 + 7. Example 1: Input: s = ""DID"" Output: 5 Explanation: The 5 valid permutations of (0; 1; 2; 3) are: (1; 0; 3; 2) (2; 0; 3; 1) (2; 1; 3; 0) (3; 0; 2; 1) (3; 1; 2; 0) Example 2: Input: s = ""D"" Output: 1 Constraints: n == s.length 1 <= n <= 200 s[i] is either 'I' or 'D'."
Snap,953,Verifying an Alien Dictionary,Easy,"Two Pointers, String","Given a string s; reverse the string according to the following rules: All the characters that are not English letters remain in the same position. All the English letters (lowercase or uppercase) should be reversed. Return s after reversing it. Example 1: Input: s = ""ab-cd"" Output: ""dc-ba"" Example 2: Input: s = ""a-bC-dEf-ghIj"" Output: ""j-Ih-gfE-dCba"" Example 3: Input: s = ""Test1ng-Leet=code-Q!"" Output: ""Qedo1ct-eeLg=ntse-T!"" Constraints: 1 <= s.length <= 100 s consists of characters with ASCII values in the range [33; 122]. s does not contain '\""' or '\\'."
Snap,973,K Closest Points to Origin,Med,"String, Stack, Greedy, Queue","You are given two strings stamp and target. Initially; there is a string s of length target.length with all s[i] == '?'. In one turn; you can place stamp over s and replace every letter in the s with the corresponding letter from stamp. For example; if stamp = ""abc"" and target = ""abcba""; then s is ""?????"" initially. In one turn you can: place stamp at index 0 of s to obtain ""abc??""; place stamp at index 1 of s to obtain ""?abc?""; or place stamp at index 2 of s to obtain ""??abc"". Note that stamp must be fully contained in the boundaries of s in order to stamp (i.e.; you cannot place stamp at index 3 of s). We want to convert s to target using at most 10 * target.length turns. Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns; return an empty array. Example 1: Input: stamp = ""abc""; target = ""ababc"" Output: [0;2] Explanation: Initially s = ""?????"". - Place stamp at index 0 to get ""abc??"". - Place stamp at index 2 to get ""ababc"". [1;0;2] would also be accepted as an answer; as well as some other answers. Example 2: Input: stamp = ""abca""; target = ""aabcaca"" Output: [3;0;1] Explanation: Initially s = ""???????"". - Place stamp at index 3 to get ""???abca"". - Place stamp at index 0 to get ""abcabca"". - Place stamp at index 1 to get ""aabcaca"". Constraints: 1 <= stamp.length <= target.length <= 1000 stamp and target consist of lowercase English letters."
Snap,981,Time Based Key-Value Store,Med,"Array, String","You are given an array of n strings strs; all of the same length. The strings can be arranged such that there is one on each line; making a grid. For example; strs = [""abc""; ""bce""; ""cae""] can be arranged as follows: abc bce cae You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed); columns 0 ('a'; 'b'; 'c') and 2 ('c'; 'e'; 'e') are sorted; while column 1 ('b'; 'c'; 'a') is not; so you would delete column 1. Return the number of columns that you will delete. Example 1: Input: strs = [""cba"";""daf"";""ghi""] Output: 1 Explanation: The grid looks as follows: cba daf ghi Columns 0 and 2 are sorted; but column 1 is not; so you only need to delete 1 column. Example 2: Input: strs = [""a"";""b""] Output: 0 Explanation: The grid looks as follows: a b Column 0 is the only column and is sorted; so you will not delete any columns. Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: The grid looks as follows: zyx wvu tsr All 3 columns are not sorted; so you will delete all 3. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 1000 strs[i] consists of lowercase English letters."
Snap,983,Minimum Cost For Tickets,Med,"Array, Stack, Simulation",Given two integer arrays pushed and popped each with distinct values; return true if this could have been the result of a sequence of push and pop operations on an initially empty stack; or false otherwise. Example 1: Input: pushed = [1;2;3;4;5]; popped = [4;5;3;2;1] Output: true Explanation: We might do the following sequence: push(1); push(2); push(3); push(4); pop() -> 4; push(5); pop() -> 5; pop() -> 3; pop() -> 2; pop() -> 1 Example 2: Input: pushed = [1;2;3;4;5]; popped = [4;3;5;1;2] Output: false Explanation: 1 cannot be popped before 2. Constraints: 1 <= pushed.length <= 1000 0 <= pushed[i] <= 1000 All the elements of pushed are unique. popped.length == pushed.length popped is a permutation of pushed.
Airbnb,336,Palindrome Pairs,Hard,"Array, Hash Table, String, Trie","You are given a 0-indexed array of unique strings words. A palindrome pair is a pair of integers (i; j) such that: 0 <= i; j < words.length; i != j; and words[i] + words[j] (the concatenation of the two strings) is a palindrome. Return an array of all the palindrome pairs of words. You must write an algorithm with O(sum of words[i].length) runtime complexity. Example 1: Input: words = [""abcd"";""dcba"";""lls"";""s"";""sssll""] Output: [[0;1];[1;0];[3;2];[2;4]] Explanation: The palindromes are [""abcddcba"";""dcbaabcd"";""slls"";""llssssll""] Example 2: Input: words = [""bat"";""tab"";""cat""] Output: [[0;1];[1;0]] Explanation: The palindromes are [""battab"";""tabbat""] Example 3: Input: words = [""a"";""""] Output: [[0;1];[1;0]] Explanation: The palindromes are [""a"";""a""] Constraints: 1 <= words.length <= 5000 0 <= words[i].length <= 300 words[i] consists of lowercase English letters."
Airbnb,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Airbnb,251,Flatten 2D Vector,Med,"Array, Two Pointers, Design, Iterator",
Airbnb,269,Alien Dictionary,Hard,"Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort",
Airbnb,68,Text Justification,Hard,"Array, String, Simulation","Given an array of strings words and a width maxWidth; format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is; pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words; the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text; it should be left-justified; and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = [""This""; ""is""; ""an""; ""example""; ""of""; ""text""; ""justification.""]; maxWidth = 16 Output: [ ""This is an""; ""example of text""; ""justification. "" ] Example 2: Input: words = [""What"";""must"";""be"";""acknowledgment"";""shall"";""be""]; maxWidth = 16 Output: [ ""What must be""; ""acknowledgment ""; ""shall be "" ] Explanation: Note that the last line is ""shall be "" instead of ""shall be""; because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = [""Science"";""is"";""what"";""we"";""understand"";""well"";""enough"";""to"";""explain"";""to"";""a"";""computer."";""Art"";""is"";""everything"";""else"";""we"";""do""]; maxWidth = 20 Output: [ ""Science is what we""; ""understand well""; ""enough to explain to""; ""a computer. Art is""; ""everything else we""; ""do "" ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth"
Airbnb,755,Pour Water,Med,"Math, Binary Search",You are standing at position 0 on an infinite number line. There is a destination at position target. You can make some number of moves numMoves so that: On each move; you can either go left or right. During the ith move (starting from i == 1 to i == numMoves); you take i steps in the chosen direction. Given the integer target; return the minimum number of moves required (i.e.; the minimum numMoves) to reach the destination. Example 1: Input: target = 2 Output: 3 Explanation: On the 1st move; we step from 0 to 1 (1 step). On the 2nd move; we step from 1 to -1 (2 steps). On the 3rd move; we step from -1 to 2 (3 steps). Example 2: Input: target = 3 Output: 2 Explanation: On the 1st move; we step from 0 to 1 (1 step). On the 2nd move; we step from 1 to 3 (2 steps). Constraints: -109 <= target <= 109 target != 0
Airbnb,787,Cheapest Flights Within K Stops,Med,"Array, Breadth-First Search, Matrix",On an 2 x 3 board; there are five tiles labeled from 1 to 5; and an empty square represented by 0. A move consists of choosing 0 and a 4-directionally adjacent number and swapping it. The state of the board is solved if and only if the board is [[1;2;3];[4;5;0]]. Given the puzzle board board; return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved; return -1. Example 1: Input: board = [[1;2;3];[4;0;5]] Output: 1 Explanation: Swap the 0 and the 5 in one move. Example 2: Input: board = [[1;2;3];[5;4;0]] Output: -1 Explanation: No number of moves will make the board solved. Example 3: Input: board = [[4;1;2];[5;0;3]] Output: 5 Explanation: 5 is the smallest number of moves that solves the board. An example path: After move 0: [[4;1;2];[5;0;3]] After move 1: [[4;1;2];[0;5;3]] After move 2: [[0;1;2];[4;5;3]] After move 3: [[1;0;2];[4;5;3]] After move 4: [[1;2;0];[4;5;3]] After move 5: [[1;2;3];[4;5;0]] Constraints: board.length == 2 board[i].length == 3 0 <= board[i][j] <= 5 Each value board[i][j] is unique.
Airbnb,1257,Smallest Common Region,Med,"Array, Union Find, Graph, Topological Sort, Sorting, Matrix",Given an m x n matrix; return a new matrix answer where answer[row][col] is the rank of matrix[row][col]. The rank is an integer that represents how large an element is compared to other elements. It is calculated using the following rules: The rank is an integer starting from 1. If two elements p and q are in the same row or column; then: If p < q then rank(p) < rank(q) If p == q then rank(p) == rank(q) If p > q then rank(p) > rank(q) The rank should be as small as possible. The test cases are generated so that answer is unique under the given rules. Example 1: Input: matrix = [[1;2];[3;4]] Output: [[1;2];[2;3]] Explanation: The rank of matrix[0][0] is 1 because it is the smallest integer in its row and column. The rank of matrix[0][1] is 2 because matrix[0][1] > matrix[0][0] and matrix[0][0] is rank 1. The rank of matrix[1][0] is 2 because matrix[1][0] > matrix[0][0] and matrix[0][0] is rank 1. The rank of matrix[1][1] is 3 because matrix[1][1] > matrix[0][1]; matrix[1][1] > matrix[1][0]; and both matrix[0][1] and matrix[1][0] are rank 2. Example 2: Input: matrix = [[7;7];[7;7]] Output: [[1;1];[1;1]] Example 3: Input: matrix = [[20;-21;14];[-19;4;19];[22;-47;24];[-19;4;19]] Output: [[4;2;3];[1;3;4];[5;1;6];[1;3;4]] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 500 -109 <= matrix[row][col] <= 109
Airbnb,1235,Maximum Profit in Job Scheduling,Hard,,
Airbnb,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Airbnb,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Airbnb,773,Sliding Puzzle,Hard,"Divide and Conquer, Tree",A Binary Matrix is a matrix in which all the elements are either 0 or 1. Given quadTree1 and quadTree2. quadTree1 represents a n * n binary matrix and quadTree2 represents another n * n binary matrix. Return a Quad-Tree representing the n * n binary matrix which is the result of logical bitwise OR of the two binary matrixes represented by quadTree1 and quadTree2. Notice that you can assign the value of a node to True or False when isLeaf is False; and both are accepted in the answer. A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides; each node has two attributes: val: True if the node represents a grid of 1's or False if the node represents a grid of 0's. isLeaf: True if the node is leaf node on the tree or False if the node has the four children. class Node { public boolean val; public boolean isLeaf; public Node topLeft; public Node topRight; public Node bottomLeft; public Node bottomRight; } We can construct a Quad-Tree from a two-dimensional area using the following steps: If the current grid has the same value (i.e all 1's or all 0's) set isLeaf True and set val to the value of the grid and set the four children to Null and stop. If the current grid has different values; set isLeaf to False and set val to any value and divide the current grid into four sub-grids as shown in the photo. Recurse for each of the children with the proper sub-grid. If you want to know more about the Quad-Tree; you can refer to the wiki. Quad-Tree format: The input/output represents the serialized format of a Quad-Tree using level order traversal; where null signifies a path terminator where no node exists below. It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list [isLeaf; val]. If the value of isLeaf or val is True we represent it as 1 in the list [isLeaf; val] and if the value of isLeaf or val is False we represent it as 0. Example 1: Input: quadTree1 = [[0;1];[1;1];[1;1];[1;0];[1;0]] ; quadTree2 = [[0;1];[1;1];[0;1];[1;1];[1;0];null;null;null;null;[1;0];[1;0];[1;1];[1;1]] Output: [[0;0];[1;1];[1;1];[1;1];[1;0]] Explanation: quadTree1 and quadTree2 are shown above. You can see the binary matrix which is represented by each Quad-Tree. If we apply logical bitwise OR on the two binary matrices we get the binary matrix below which is represented by the result Quad-Tree. Notice that the binary matrices shown are only for illustration; you don't have to construct the binary matrix to get the result tree. Example 2: Input: quadTree1 = [[1;0]]; quadTree2 = [[1;0]] Output: [[1;0]] Explanation: Each tree represents a binary matrix of size 1*1. Each matrix contains only zero. The resulting matrix is of size 1*1 with also zero. Constraints: quadTree1 and quadTree2 are both valid Quad-Trees each representing a n * n grid. n == 2x where 0 <= x <= 9.
Airbnb,864,Shortest Path to Get All Keys,Hard,"Array, Matrix",You are given two images; img1 and img2; represented as binary; square matrices of size n x n. A binary matrix has only 0s and 1s as values. We translate one image however we choose by sliding all the 1 bits left; right; up; and/or down any number of units. We then place it on top of the other image. We can then calculate the overlap by counting the number of positions that have a 1 in both images. Note also that a translation does not include any kind of rotation. Any 1 bits that are translated outside of the matrix borders are erased. Return the largest possible overlap. Example 1: Input: img1 = [[1;1;0];[0;1;0];[0;1;0]]; img2 = [[0;0;0];[0;1;1];[0;0;1]] Output: 3 Explanation: We translate img1 to right by 1 unit and down by 1 unit. The number of positions that have a 1 in both images is 3 (shown in red). Example 2: Input: img1 = [[1]]; img2 = [[1]] Output: 1 Example 3: Input: img1 = [[0]]; img2 = [[0]] Output: 0 Constraints: n == img1.length == img1[i].length n == img2.length == img2[i].length 1 <= n <= 30 img1[i][j] is either 0 or 1. img2[i][j] is either 0 or 1.
Airbnb,751,IP to CIDR,Med,"Array, Math, Dynamic Programming, Matrix",
Airbnb,759,Employee Free Time,Hard,"Array, Greedy, Sorting",You are given a 2D integer array intervals where intervals[i] = [starti; endi] represents all the integers from starti to endi inclusively. A containing set is an array nums where each interval from intervals has at least two integers in nums. For example; if intervals = [[1;3]; [3;7]; [8;9]]; then [1;2;4;7;8;9] and [2;3;4;8;9] are containing sets. Return the minimum possible size of a containing set. Example 1: Input: intervals = [[1;3];[3;7];[8;9]] Output: 5 Explanation: let nums = [2; 3; 4; 8; 9]. It can be shown that there cannot be any containing array of size 4. Example 2: Input: intervals = [[1;3];[1;4];[2;5];[3;5]] Output: 3 Explanation: let nums = [2; 3; 4]. It can be shown that there cannot be any containing array of size 2. Example 3: Input: intervals = [[1;2];[2;3];[2;4];[4;5]] Output: 5 Explanation: let nums = [1; 2; 3; 4; 5]. It can be shown that there cannot be any containing array of size 4. Constraints: 1 <= intervals.length <= 3000 intervals[i].length == 2 0 <= starti < endi <= 108
Airbnb,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Airbnb,160,Intersection of Two Linked Lists,Easy,"Hash Table, Linked List, Two Pointers",Given the heads of two singly linked-lists headA and headB; return the node at which the two lists intersect. If the two linked lists have no intersection at all; return null. For example; the following two linked lists begin to intersect at node c1: The test cases are generated such that there are no cycles anywhere in the entire linked structure. Note that the linked lists must retain their original structure after the function returns. Custom Judge: The inputs to the judge are given as follows (your program is not given these inputs): intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node. listA - The first linked list. listB - The second linked list. skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node. skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node. The judge will then create the linked structure based on these inputs and pass the two heads; headA and headB to your program. If you correctly return the intersected node; then your solution will be accepted. Example 1: Input: intersectVal = 8; listA = [4;1;8;4;5]; listB = [5;6;1;8;4;5]; skipA = 2; skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [4;1;8;4;5]. From the head of B; it reads as [5;6;1;8;4;5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words; they point to two different locations in memory; while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory. Example 2: Input: intersectVal = 2; listA = [1;9;1;2;4]; listB = [3;2;4]; skipA = 3; skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [1;9;1;2;4]. From the head of B; it reads as [3;2;4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B. Example 3: Input: intersectVal = 0; listA = [2;6;4]; listB = [1;5]; skipA = 3; skipB = 2 Output: No intersection Explanation: From the head of A; it reads as [2;6;4]. From the head of B; it reads as [1;5]. Since the two lists do not intersect; intersectVal must be 0; while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect; so return null. Constraints: The number of nodes of listA is in the m. The number of nodes of listB is in the n. 1 <= m; n <= 3 * 104 1 <= Node.val <= 105 0 <= skipA <= m 0 <= skipB <= n intersectVal is 0 if listA and listB do not intersect. intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect. Follow up: Could you write a solution that runs in O(m + n) time and use only O(1) memory?
Airbnb,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Airbnb,212,Word Search II,Hard,"Array, String, Backtracking, Trie, Matrix","Given an m x n board of characters and a list of strings words; return all words on the board. Each word must be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example 1: Input: board = [[""o"";""a"";""a"";""n""];[""e"";""t"";""a"";""e""];[""i"";""h"";""k"";""r""];[""i"";""f"";""l"";""v""]]; words = [""oath"";""pea"";""eat"";""rain""] Output: [""eat"";""oath""] Example 2: Input: board = [[""a"";""b""];[""c"";""d""]]; words = [""abcb""] Output: [] Constraints: m == board.length n == board[i].length 1 <= m; n <= 12 board[i][j] is a lowercase English letter. 1 <= words.length <= 3 * 104 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. All the strings of words are unique."
Airbnb,227,Basic Calculator II,Med,"Math, String, Stack","Given a string s which represents an expression; evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""3+2*2"" Output: 7 Example 2: Input: s = "" 3/2 "" Output: 1 Example 3: Input: s = "" 3+5 / 2 "" Output: 5 Constraints: 1 <= s.length <= 3 * 105 s consists of integers and operators ('+'; '-'; '*'; '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0; 231 - 1]. The answer is guaranteed to fit in a 32-bit integer."
Airbnb,756,Pyramid Transition Matrix,Med,"Array, Simulation",
Airbnb,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Airbnb,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Airbnb,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Airbnb,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Airbnb,108,Convert Sorted Array to Binary Search Tree,Easy,"Array, Divide and Conquer, Tree, Binary Search Tree, Binary Tree",Given an integer array nums where the elements are sorted in ascending order; convert it to a height-balanced binary search tree. Example 1: Input: nums = [-10;-3;0;5;9] Output: [0;-3;9;-10;null;5] Explanation: [0;-10;5;null;-3;null;9] is also accepted: Example 2: Input: nums = [1;3] Output: [3;1] Explanation: [1;null;3] and [3;1] are both height-balanced BSTs. Constraints: 1 <= nums.length <= 104 -104 <= nums[i] <= 104 nums is sorted in a strictly increasing order.
Airbnb,136,Single Number,Easy,"Array, Bit Manipulation",Given a non-empty array of integers nums; every element appears twice except for one. Find that single one. You must implement a solution with a linear runtime complexity and use only constant extra space. Example 1: Input: nums = [2;2;1] Output: 1 Example 2: Input: nums = [4;1;2;1;2] Output: 4 Example 3: Input: nums = [1] Output: 1 Constraints: 1 <= nums.length <= 3 * 104 -3 * 104 <= nums[i] <= 3 * 104 Each element in the array appears twice except for one element which appears only once.
Airbnb,190,Reverse Bits,Easy,"Divide and Conquer, Bit Manipulation",Reverse bits of a given 32 bits unsigned integer. Note: Note that in some languages; such as Java; there is no unsigned integer type. In this case; both input and output will be given as a signed integer type. They should not affect your implementation; as the integer's internal binary representation is the same; whether it is signed or unsigned. In Java; the compiler represents the signed integers using 2's complement notation. Therefore; in Example 2 above; the input represents the signed integer -3 and the output represents the signed integer -1073741825. Example 1: Input: n = 00000010100101000001111010011100 Output: 964176192 (00111001011110000010100101000000) Explanation: The input binary string 00000010100101000001111010011100 represents the unsigned integer 43261596; so return 964176192 which its binary representation is 00111001011110000010100101000000. Example 2: Input: n = 11111111111111111111111111111101 Output: 3221225471 (10111111111111111111111111111111) Explanation: The input binary string 11111111111111111111111111111101 represents the unsigned integer 4294967293; so return 3221225471 which its binary representation is 10111111111111111111111111111111. Constraints: The input must be a binary string of length 32 Follow up: If this function is called many times; how would you optimize it?
Airbnb,202,Happy Number,Easy,"Hash Table, Math, Two Pointers",Write an algorithm to determine if a number n is happy. A happy number is a number defined by the following process: Starting with any positive integer; replace the number by the sum of the squares of its digits. Repeat the process until the number equals 1 (where it will stay); or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy. Return true if n is a happy number; and false if not. Example 1: Input: n = 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1 Example 2: Input: n = 2 Output: false Constraints: 1 <= n <= 231 - 1
Airbnb,217,Contains Duplicate,Easy,"Array, Hash Table, Sorting",Given an integer array nums; return true if any value appears at least twice in the array; and return false if every element is distinct. Example 1: Input: nums = [1;2;3;1] Output: true Explanation: The element 1 occurs at the indices 0 and 3. Example 2: Input: nums = [1;2;3;4] Output: false Explanation: All elements are distinct. Example 3: Input: nums = [1;1;1;3;3;4;3;2;4;2] Output: true Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109
Airbnb,219,Contains Duplicate II,Easy,"Array, Hash Table, Sliding Window",Given an integer array nums and an integer k; return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k. Example 1: Input: nums = [1;2;3;1]; k = 3 Output: true Example 2: Input: nums = [1;0;1;1]; k = 1 Output: true Example 3: Input: nums = [1;2;3;1;2;3]; k = 2 Output: false Constraints: 1 <= nums.length <= 105 -109 <= nums[i] <= 109 0 <= k <= 105
Airbnb,220,Contains Duplicate III,Hard,"Array, Sliding Window, Sorting, Bucket Sort, Ordered Set",You are given an integer array nums and two integers indexDiff and valueDiff. Find a pair of indices (i; j) such that: i != j; abs(i - j) <= indexDiff. abs(nums[i] - nums[j]) <= valueDiff; and Return true if such pair exists or false otherwise. Example 1: Input: nums = [1;2;3;1]; indexDiff = 3; valueDiff = 0 Output: true Explanation: We can choose (i; j) = (0; 3). We satisfy the three conditions: i != j --> 0 != 3 abs(i - j) <= indexDiff --> abs(0 - 3) <= 3 abs(nums[i] - nums[j]) <= valueDiff --> abs(1 - 1) <= 0 Example 2: Input: nums = [1;5;9;1;5;9]; indexDiff = 2; valueDiff = 3 Output: false Explanation: After trying all the possible pairs (i; j); we cannot satisfy the three conditions; so we return false. Constraints: 2 <= nums.length <= 105 -109 <= nums[i] <= 109 1 <= indexDiff <= nums.length 0 <= valueDiff <= 109
Airbnb,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Airbnb,385,Mini Parser,Med,"String, Stack, Depth-First Search","Given a string s represents the serialization of a nested list; implement a parser to deserialize it and return the deserialized NestedInteger. Each element is either an integer or a list whose elements may also be integers or other lists. Example 1: Input: s = ""324"" Output: 324 Explanation: You should return a NestedInteger object which contains a single integer 324. Example 2: Input: s = ""[123;[456;[789]]]"" Output: [123;[456;[789]]] Explanation: Return a NestedInteger object containing a nested list with 2 elements: 1. An integer containing value 123. 2. A nested list containing two elements: i. An integer containing value 456. ii. A nested list with one element: a. An integer containing value 789 Constraints: 1 <= s.length <= 5 * 104 s consists of digits; square brackets ""[]""; negative sign '-'; and commas ';'. s is the serialization of valid NestedInteger. All the values in the input are in the range [-106; 106]."
Airbnb,415,Add Strings,Easy,"Math, String, Simulation","Given two non-negative integers; num1 and num2 represented as string; return the sum of num1 and num2 as a string. You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly. Example 1: Input: num1 = ""11""; num2 = ""123"" Output: ""134"" Example 2: Input: num1 = ""456""; num2 = ""77"" Output: ""533"" Example 3: Input: num1 = ""0""; num2 = ""0"" Output: ""0"" Constraints: 1 <= num1.length; num2.length <= 104 num1 and num2 consist of only digits. num1 and num2 don't have any leading zeros except for the zero itself."
Airbnb,1058,Minimize Rounding Error to Meet Target,Med,"String, Union Find","You are given two strings of the same length s1 and s2 and a string baseStr. We say s1[i] and s2[i] are equivalent characters. For example; if s1 = ""abc"" and s2 = ""cde""; then we have 'a' == 'c'; 'b' == 'd'; and 'c' == 'e'. Equivalent characters follow the usual rules of any equivalence relation: Reflexivity: 'a' == 'a'. Symmetry: 'a' == 'b' implies 'b' == 'a'. Transitivity: 'a' == 'b' and 'b' == 'c' implies 'a' == 'c'. For example; given the equivalency information from s1 = ""abc"" and s2 = ""cde""; ""acd"" and ""aab"" are equivalent strings of baseStr = ""eed""; and ""aab"" is the lexicographically smallest equivalent string of baseStr. Return the lexicographically smallest equivalent string of baseStr by using the equivalency information from s1 and s2. Example 1: Input: s1 = ""parker""; s2 = ""morris""; baseStr = ""parser"" Output: ""makkek"" Explanation: Based on the equivalency information in s1 and s2; we can group their characters as [m;p]; [a;o]; [k;r;s]; [e;i]. The characters in each group are equivalent and sorted in lexicographical order. So the answer is ""makkek"". Example 2: Input: s1 = ""hello""; s2 = ""world""; baseStr = ""hold"" Output: ""hdld"" Explanation: Based on the equivalency information in s1 and s2; we can group their characters as [h;w]; [d;e;o]; [l;r]. So only the second letter 'o' in baseStr is changed to 'd'; the answer is ""hdld"". Example 3: Input: s1 = ""leetcode""; s2 = ""programs""; baseStr = ""sourcecode"" Output: ""aauaaaaada"" Explanation: We group the equivalent characters in s1 and s2 as [a;o;e;r;s;c]; [l;p]; [g;t] and [d;m]; thus all letters in baseStr except 'u' and 'd' are transformed to 'a'; the answer is ""aauaaaaada"". Constraints: 1 <= s1.length; s2.length; baseStr <= 1000 s1.length == s2.length s1; s2; and baseStr consist of lowercase English letters."
Airbnb,1017,Convert to Base -2,Med,"Array, Dynamic Programming, Stack, Monotonic Stack, Ordered Set",You are given an integer array arr. From some starting index; you can make a series of jumps. The (1st; 3rd; 5th; ...) jumps in the series are called odd-numbered jumps; and the (2nd; 4th; 6th; ...) jumps in the series are called even-numbered jumps. Note that the jumps are numbered; not the indices. You may jump forward from index i to index j (with i < j) in the following way: During odd-numbered jumps (i.e.; jumps 1; 3; 5; ...); you jump to the index j such that arr[i] <= arr[j] and arr[j] is the smallest possible value. If there are multiple such indices j; you can only jump to the smallest such index j. During even-numbered jumps (i.e.; jumps 2; 4; 6; ...); you jump to the index j such that arr[i] >= arr[j] and arr[j] is the largest possible value. If there are multiple such indices j; you can only jump to the smallest such index j. It may be the case that for some index i; there are no legal jumps. A starting index is good if; starting from that index; you can reach the end of the array (index arr.length - 1) by jumping some number of times (possibly 0 or more than once). Return the number of good starting indices. Example 1: Input: arr = [10;13;12;14;15] Output: 2 Explanation: From starting index i = 0; we can make our 1st jump to i = 2 (since arr[2] is the smallest among arr[1]; arr[2]; arr[3]; arr[4] that is greater or equal to arr[0]); then we cannot jump any more. From starting index i = 1 and i = 2; we can make our 1st jump to i = 3; then we cannot jump any more. From starting index i = 3; we can make our 1st jump to i = 4; so we have reached the end. From starting index i = 4; we have reached the end already. In total; there are 2 different starting indices i = 3 and i = 4; where we can reach the end with some number of jumps. Example 2: Input: arr = [2;3;1;1;4] Output: 3 Explanation: From starting index i = 0; we make jumps to i = 1; i = 2; i = 3: During our 1st jump (odd-numbered); we first jump to i = 1 because arr[1] is the smallest value in [arr[1]; arr[2]; arr[3]; arr[4]] that is greater than or equal to arr[0]. During our 2nd jump (even-numbered); we jump from i = 1 to i = 2 because arr[2] is the largest value in [arr[2]; arr[3]; arr[4]] that is less than or equal to arr[1]. arr[3] is also the largest value; but 2 is a smaller index; so we can only jump to i = 2 and not i = 3 During our 3rd jump (odd-numbered); we jump from i = 2 to i = 3 because arr[3] is the smallest value in [arr[3]; arr[4]] that is greater than or equal to arr[2]. We can't jump from i = 3 to i = 4; so the starting index i = 0 is not good. In a similar manner; we can deduce that: From starting index i = 1; we jump to i = 4; so we reach the end. From starting index i = 2; we jump to i = 3; and then we can't jump anymore. From starting index i = 3; we jump to i = 4; so we reach the end. From starting index i = 4; we are already at the end. In total; there are 3 different starting indices i = 1; i = 3; and i = 4; where we can reach the end with some number of jumps. Example 3: Input: arr = [5;1;3;4;2] Output: 3 Explanation: We can reach the end from starting indices 1; 2; and 4. Constraints: 1 <= arr.length <= 2 * 104 0 <= arr[i] < 105
Airbnb,1041,Robot Bounded In Circle,Med,"Array, Matrix, Simulation","You are given an 8 x 8 matrix representing a chessboard. There is exactly one white rook represented by 'R'; some number of white bishops 'B'; and some number of black pawns 'p'. Empty squares are represented by '.'. A rook can move any number of squares horizontally or vertically (up; down; left; right) until it reaches another piece or the edge of the board. A rook is attacking a pawn if it can move to the pawn's square in one move. Note: A rook cannot move through other pieces; such as bishops or pawns. This means a rook cannot attack a pawn if there is another piece blocking the path. Return the number of pawns the white rook is attacking. Example 1: Input: board = [[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""."";""."";""."";""R"";""."";""."";""."";""p""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""]] Output: 3 Explanation: In this example; the rook is attacking all the pawns. Example 2: Input: board = [[""."";""."";""."";""."";""."";""."";"".""];[""."";""p"";""p"";""p"";""p"";""p"";""."";"".""];[""."";""p"";""p"";""B"";""p"";""p"";""."";"".""];[""."";""p"";""B"";""R"";""B"";""p"";""."";"".""];[""."";""p"";""p"";""B"";""p"";""p"";""."";"".""];[""."";""p"";""p"";""p"";""p"";""p"";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""]] Output: 0 Explanation: The bishops are blocking the rook from attacking any of the pawns. Example 3: Input: board = [[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""p"";""p"";""."";""R"";""."";""p"";""B"";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""B"";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""]] Output: 3 Explanation: The rook is attacking the pawns at positions b5; d6; and f5. Constraints: board.length == 8 board[i].length == 8 board[i][j] is either 'R'; '.'; 'B'; or 'p' There is exactly one cell with board[i][j] == 'R'"
Airbnb,1166,Design File System,Med,"Array, Math, Dynamic Programming, Probability and Statistics",
Airbnb,2189,Number of Ways to Build House of Cards,Med,"Array, Backtracking, Graph",There is an undirected graph with n nodes numbered from 0 to n - 1 (inclusive). You are given a 0-indexed integer array values where values[i] is the value of the ith node. You are also given a 0-indexed 2D integer array edges; where each edges[j] = [uj; vj; timej] indicates that there is an undirected edge between the nodes uj and vj; and it takes timej seconds to travel between the two nodes. Finally; you are given an integer maxTime. A valid path in the graph is any path that starts at node 0; ends at node 0; and takes at most maxTime seconds to complete. You may visit the same node multiple times. The quality of a valid path is the sum of the values of the unique nodes visited in the path (each node's value is added at most once to the sum). Return the maximum quality of a valid path. Note: There are at most four edges connected to each node. Example 1: Input: values = [0;32;10;43]; edges = [[0;1;10];[1;2;15];[0;3;10]]; maxTime = 49 Output: 75 Explanation: One possible path is 0 -> 1 -> 0 -> 3 -> 0. The total time taken is 10 + 10 + 10 + 10 = 40 <= 49. The nodes visited are 0; 1; and 3; giving a maximal path quality of 0 + 32 + 43 = 75. Example 2: Input: values = [5;10;15;20]; edges = [[0;1;10];[1;2;10];[0;3;10]]; maxTime = 30 Output: 25 Explanation: One possible path is 0 -> 3 -> 0. The total time taken is 10 + 10 = 20 <= 30. The nodes visited are 0 and 3; giving a maximal path quality of 5 + 20 = 25. Example 3: Input: values = [1;2;3;4]; edges = [[0;1;10];[1;2;11];[2;3;12];[1;3;13]]; maxTime = 50 Output: 7 Explanation: One possible path is 0 -> 1 -> 3 -> 1 -> 0. The total time taken is 10 + 13 + 13 + 10 = 46 <= 50. The nodes visited are 0; 1; and 3; giving a maximal path quality of 1 + 2 + 4 = 7. Constraints: n == values.length 1 <= n <= 1000 0 <= values[i] <= 108 0 <= edges.length <= 2000 edges[j].length == 3 0 <= uj < vj <= n - 1 10 <= timej; maxTime <= 100 All the pairs [uj; vj] are unique. There are at most four edges connected to each node. The graph may not be connected.
Airbnb,1284,Minimum Number of Flips to Convert Binary Matrix to Zero Matrix,Hard,"Array, Math",Given an integer array nums; return the sum of divisors of the integers in that array that have exactly four divisors. If there is no such integer in the array; return 0. Example 1: Input: nums = [21;4;7] Output: 32 Explanation: 21 has 4 divisors: 1; 3; 7; 21 4 has 3 divisors: 1; 2; 4 7 has 2 divisors: 1; 7 The answer is the sum of divisors of 21 only. Example 2: Input: nums = [21;21] Output: 64 Example 3: Input: nums = [1;2;3;4;5] Output: 0 Constraints: 1 <= nums.length <= 104 1 <= nums[i] <= 105
Airbnb,1298,Maximum Candies You Can Get from Boxes,Hard,"String, Stack","You are given a string s that consists of lower case English letters and brackets. Reverse the strings in each pair of matching parentheses; starting from the innermost one. Your result should not contain any brackets. Example 1: Input: s = ""(abcd)"" Output: ""dcba"" Example 2: Input: s = ""(u(love)i)"" Output: ""iloveu"" Explanation: The substring ""love"" is reversed first; then the whole string is reversed. Example 3: Input: s = ""(ed(et(oc))el)"" Output: ""leetcode"" Explanation: First; we reverse the substring ""oc""; then ""etco""; and finally; the whole string. Constraints: 1 <= s.length <= 2000 s only contains lower case English characters and parentheses. It is guaranteed that all parentheses are balanced."
Airbnb,1557,Minimum Number of Vertices to Reach All Nodes,Med,"Hash Table, String, Bit Manipulation, Rolling Hash, Hash Function","Given a binary string s and an integer k; return true if every binary code of length k is a substring of s. Otherwise; return false. Example 1: Input: s = ""00110110""; k = 2 Output: true Explanation: The binary codes of length 2 are ""00""; ""01""; ""10"" and ""11"". They can be all found as substrings at indices 0; 1; 3 and 2 respectively. Example 2: Input: s = ""0110""; k = 1 Output: true Explanation: The binary codes of length 1 are ""0"" and ""1""; it is clear that both exist as a substring. Example 3: Input: s = ""0110""; k = 2 Output: false Explanation: The binary code ""00"" is of length 2 and does not exist in the array. Constraints: 1 <= s.length <= 5 * 105 s[i] is either '0' or '1'. 1 <= k <= 20"
Airbnb,1554,Strings Differ by One Character,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search",Given an undirected tree consisting of n vertices numbered from 0 to n-1; which has some apples in their vertices. You spend 1 second to walk over one edge of the tree. Return the minimum time in seconds you have to spend to collect all apples in the tree; starting at vertex 0 and coming back to this vertex. The edges of the undirected tree are given in the array edges; where edges[i] = [ai; bi] means that exists an edge connecting the vertices ai and bi. Additionally; there is a boolean array hasApple; where hasApple[i] = true means that vertex i has an apple; otherwise; it does not have any apple. Example 1: Input: n = 7; edges = [[0;1];[0;2];[1;4];[1;5];[2;3];[2;6]]; hasApple = [false;false;true;false;true;true;false] Output: 8 Explanation: The figure above represents the given tree where red vertices have an apple. One optimal path to collect all apples is shown by the green arrows. Example 2: Input: n = 7; edges = [[0;1];[0;2];[1;4];[1;5];[2;3];[2;6]]; hasApple = [false;false;true;false;false;true;false] Output: 6 Explanation: The figure above represents the given tree where red vertices have an apple. One optimal path to collect all apples is shown by the green arrows. Example 3: Input: n = 7; edges = [[0;1];[0;2];[1;4];[1;5];[2;3];[2;6]]; hasApple = [false;false;false;false;false;false;false] Output: 0 Constraints: 1 <= n <= 105 edges.length == n - 1 edges[i].length == 2 0 <= ai < bi <= n - 1 hasApple.length == n
Airbnb,2043,Simple Bank System,Med,"Array, Matrix, Simulation",You are given an m x n integer matrix grid​​​; where m and n are both even integers; and an integer k. The matrix is composed of several layers; which is shown in the below image; where each color is its own layer: A cyclic rotation of the matrix is done by cyclically rotating each layer in the matrix. To cyclically rotate a layer once; each element in the layer will take the place of the adjacent element in the counter-clockwise direction. An example rotation is shown below: Return the matrix after applying k cyclic rotations to it. Example 1: Input: grid = [[40;10];[30;20]]; k = 1 Output: [[10;20];[40;30]] Explanation: The figures above represent the grid at every state. Example 2: Input: grid = [[1;2;3;4];[5;6;7;8];[9;10;11;12];[13;14;15;16]]; k = 2 Output: [[3;4;8;12];[2;11;10;16];[1;7;6;15];[5;9;13;14]] Explanation: The figures above represent the grid at every state. Constraints: m == grid.length n == grid[i].length 2 <= m; n <= 50 Both m and n are even integers. 1 <= grid[i][j] <= 5000 1 <= k <= 109
Airbnb,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Airbnb,341,Flatten Nested List Iterator,Med,"Stack, Tree, Depth-First Search, Design, Queue, Iterator",You are given a nested list of integers nestedList. Each element is either an integer or a list whose elements may also be integers or other lists. Implement an iterator to flatten it. Implement the NestedIterator class: NestedIterator(List<NestedInteger> nestedList) Initializes the iterator with the nested list nestedList. int next() Returns the next integer in the nested list. boolean hasNext() Returns true if there are still some integers in the nested list and false otherwise. Your code will be tested with the following pseudocode: initialize iterator with nestedList res = [] while iterator.hasNext() append iterator.next() to the end of res return res If res matches the expected flattened list; then your code will be judged as correct. Example 1: Input: nestedList = [[1;1];2;[1;1]] Output: [1;1;2;1;1] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;1;2;1;1]. Example 2: Input: nestedList = [1;[4;[6]]] Output: [1;4;6] Explanation: By calling next repeatedly until hasNext returns false; the order of elements returned by next should be: [1;4;6]. Constraints: 1 <= nestedList.length <= 500 The values of the integers in the nested list is in the range [-106; 106].
Airbnb,348,Design Tic-Tac-Toe,Med,"Array, Hash Table, Design, Matrix, Simulation",
Airbnb,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Airbnb,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Airbnb,981,Time Based Key-Value Store,Med,"Array, String","You are given an array of n strings strs; all of the same length. The strings can be arranged such that there is one on each line; making a grid. For example; strs = [""abc""; ""bce""; ""cae""] can be arranged as follows: abc bce cae You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed); columns 0 ('a'; 'b'; 'c') and 2 ('c'; 'e'; 'e') are sorted; while column 1 ('b'; 'c'; 'a') is not; so you would delete column 1. Return the number of columns that you will delete. Example 1: Input: strs = [""cba"";""daf"";""ghi""] Output: 1 Explanation: The grid looks as follows: cba daf ghi Columns 0 and 2 are sorted; but column 1 is not; so you only need to delete 1 column. Example 2: Input: strs = [""a"";""b""] Output: 0 Explanation: The grid looks as follows: a b Column 0 is the only column and is sorted; so you will not delete any columns. Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: The grid looks as follows: zyx wvu tsr All 3 columns are not sorted; so you will delete all 3. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 1000 strs[i] consists of lowercase English letters."
Airbnb,1387,Sort Integers by The Power Value,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree","Given a binary tree with the following rules: root.val == 0 If treeNode.val == x and treeNode.left != null; then treeNode.left.val == 2 * x + 1 If treeNode.val == x and treeNode.right != null; then treeNode.right.val == 2 * x + 2 Now the binary tree is contaminated; which means all treeNode.val have been changed to -1. Implement the FindElements class: FindElements(TreeNode* root) Initializes the object with a contaminated binary tree and recovers it. bool find(int target) Returns true if the target value exists in the recovered binary tree. Example 1: Input [""FindElements"";""find"";""find""] [[[-1;null;-1]];[1];[2]] Output [null;false;true] Explanation FindElements findElements = new FindElements([-1;null;-1]); findElements.find(1); // return False findElements.find(2); // return True Example 2: Input [""FindElements"";""find"";""find"";""find""] [[[-1;-1;-1;-1;-1]];[1];[3];[5]] Output [null;true;true;false] Explanation FindElements findElements = new FindElements([-1;-1;-1;-1;-1]); findElements.find(1); // return True findElements.find(3); // return True findElements.find(5); // return False Example 3: Input [""FindElements"";""find"";""find"";""find"";""find""] [[[-1;null;-1;-1;null;-1]];[2];[3];[4];[5]] Output [null;true;false;false;true] Explanation FindElements findElements = new FindElements([-1;null;-1;-1;null;-1]); findElements.find(2); // return True findElements.find(3); // return False findElements.find(4); // return False findElements.find(5); // return True Constraints: TreeNode.val == -1 The height of the binary tree is less than or equal to 20 The total number of nodes is between [1; 104] Total calls of find() is between [1; 104] 0 <= target <= 106"
Airbnb,3076,Shortest Uncommon Substring in an Array,Med,,DataFrame players: +-------------+--------+ | Column Name | Type | +-------------+--------+ | player_id | int | | name | object | | age | int | | position | object | | ... | ... | +-------------+--------+ Write a solution to calculate and display the number of rows and columns of players. Return the result as an array: [number of rows; number of columns] The result format is in the following example. Example 1: Input: +-----------+----------+-----+-------------+--------------------+ | player_id | name | age | position | team | +-----------+----------+-----+-------------+--------------------+ | 846 | Mason | 21 | Forward | RealMadrid | | 749 | Riley | 30 | Winger | Barcelona | | 155 | Bob | 28 | Striker | ManchesterUnited | | 583 | Isabella | 32 | Goalkeeper | Liverpool | | 388 | Zachary | 24 | Midfielder | BayernMunich | | 883 | Ava | 23 | Defender | Chelsea | | 355 | Violet | 18 | Striker | Juventus | | 247 | Thomas | 27 | Striker | ParisSaint-Germain | | 761 | Jack | 33 | Midfielder | ManchesterCity | | 642 | Charlie | 36 | Center-back | Arsenal | +-----------+----------+-----+-------------+--------------------+ Output: [10; 5] Explanation: This DataFrame contains 10 rows and 5 columns.
Salesforce,1268,Search Suggestions System,Med,Database,Table: Users +----------------+---------+ | Column Name | Type | +----------------+---------+ | user_id | int | | join_date | date | | favorite_brand | varchar | +----------------+---------+ user_id is the primary key (column with unique values) of this table. This table has the info of the users of an online shopping website where users can sell and buy items. Table: Orders +---------------+---------+ | Column Name | Type | +---------------+---------+ | order_id | int | | order_date | date | | item_id | int | | buyer_id | int | | seller_id | int | +---------------+---------+ order_id is the primary key (column with unique values) of this table. item_id is a foreign key (reference column) to the Items table. buyer_id and seller_id are foreign keys to the Users table. Table: Items +---------------+---------+ | Column Name | Type | +---------------+---------+ | item_id | int | | item_brand | varchar | +---------------+---------+ item_id is the primary key (column with unique values) of this table. Write a solution to find for each user; the join date and the number of orders they made as a buyer in 2019. Return the result table in any order. The result format is in the following example. Example 1: Input: Users table: +---------+------------+----------------+ | user_id | join_date | favorite_brand | +---------+------------+----------------+ | 1 | 2018-01-01 | Lenovo | | 2 | 2018-02-09 | Samsung | | 3 | 2018-01-19 | LG | | 4 | 2018-05-21 | HP | +---------+------------+----------------+ Orders table: +----------+------------+---------+----------+-----------+ | order_id | order_date | item_id | buyer_id | seller_id | +----------+------------+---------+----------+-----------+ | 1 | 2019-08-01 | 4 | 1 | 2 | | 2 | 2018-08-02 | 2 | 1 | 3 | | 3 | 2019-08-03 | 3 | 2 | 3 | | 4 | 2018-08-04 | 1 | 4 | 2 | | 5 | 2018-08-04 | 1 | 3 | 4 | | 6 | 2019-08-05 | 2 | 2 | 4 | +----------+------------+---------+----------+-----------+ Items table: +---------+------------+ | item_id | item_brand | +---------+------------+ | 1 | Samsung | | 2 | Lenovo | | 3 | LG | | 4 | HP | +---------+------------+ Output: +-----------+------------+----------------+ | buyer_id | join_date | orders_in_2019 | +-----------+------------+----------------+ | 1 | 2018-01-01 | 1 | | 2 | 2018-02-09 | 2 | | 3 | 2018-01-19 | 0 | | 4 | 2018-05-21 | 0 | +-----------+------------+----------------+
Salesforce,139,Word Break,Med,"Array, Hash Table, String, Dynamic Programming, Trie, Memoization","Given a string s and a dictionary of strings wordDict; return true if s can be segmented into a space-separated sequence of one or more dictionary words. Note that the same word in the dictionary may be reused multiple times in the segmentation. Example 1: Input: s = ""leetcode""; wordDict = [""leet"";""code""] Output: true Explanation: Return true because ""leetcode"" can be segmented as ""leet code"". Example 2: Input: s = ""applepenapple""; wordDict = [""apple"";""pen""] Output: true Explanation: Return true because ""applepenapple"" can be segmented as ""apple pen apple"". Note that you are allowed to reuse a dictionary word. Example 3: Input: s = ""catsandog""; wordDict = [""cats"";""dog"";""sand"";""and"";""cat""] Output: false Constraints: 1 <= s.length <= 300 1 <= wordDict.length <= 1000 1 <= wordDict[i].length <= 20 s and wordDict[i] consist of only lowercase English letters. All the strings of wordDict are unique."
Salesforce,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Salesforce,1326,Minimum Number of Taps to Open to Water a Garden,Hard,"Array, Math, Binary Search, Prefix Sum",Given an integer array nums; return the sum of floor(nums[i] / nums[j]) for all pairs of indices 0 <= i; j < nums.length in the array. Since the answer may be too large; return it modulo 109 + 7. The floor() function returns the integer part of the division. Example 1: Input: nums = [2;5;9] Output: 10 Explanation: floor(2 / 5) = floor(2 / 9) = floor(5 / 9) = 0 floor(2 / 2) = floor(5 / 5) = floor(9 / 9) = 1 floor(5 / 2) = 2 floor(9 / 2) = 4 floor(9 / 5) = 1 We calculate the floor of the division for every pair of indices in the array then sum them up. Example 2: Input: nums = [7;7;7;7;7;7;7] Output: 49 Constraints: 1 <= nums.length <= 105 1 <= nums[i] <= 105
Salesforce,410,Split Array Largest Sum,Hard,"Array, Binary Search, Dynamic Programming, Greedy, Prefix Sum",Given an integer array nums and an integer k; split nums into k non-empty subarrays such that the largest sum of any subarray is minimized. Return the minimized largest sum of the split. A subarray is a contiguous part of the array. Example 1: Input: nums = [7;2;5;10;8]; k = 2 Output: 18 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [7;2;5] and [10;8]; where the largest sum among the two subarrays is only 18. Example 2: Input: nums = [1;2;3;4;5]; k = 2 Output: 9 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [1;2;3] and [4;5]; where the largest sum among the two subarrays is only 9. Constraints: 1 <= nums.length <= 1000 0 <= nums[i] <= 106 1 <= k <= min(50; nums.length)
Salesforce,924,Minimize Malware Spread,Hard,"Array, Hash Table, Binary Search, Sorting",Alice and Bob have a different total number of candies. You are given two integer arrays aliceSizes and bobSizes where aliceSizes[i] is the number of candies of the ith box of candy that Alice has and bobSizes[j] is the number of candies of the jth box of candy that Bob has. Since they are friends; they would like to exchange one candy box each so that after the exchange; they both have the same total amount of candy. The total amount of candy a person has is the sum of the number of candies in each box they have. Return an integer array answer where answer[0] is the number of candies in the box that Alice must exchange; and answer[1] is the number of candies in the box that Bob must exchange. If there are multiple answers; you may return any one of them. It is guaranteed that at least one answer exists. Example 1: Input: aliceSizes = [1;1]; bobSizes = [2;2] Output: [1;2] Example 2: Input: aliceSizes = [1;2]; bobSizes = [2;3] Output: [1;2] Example 3: Input: aliceSizes = [2]; bobSizes = [1;3] Output: [2;3] Constraints: 1 <= aliceSizes.length; bobSizes.length <= 104 1 <= aliceSizes[i]; bobSizes[j] <= 105 Alice and Bob have a different total number of candies. There will be at least one valid answer for the given input.
Salesforce,2957,Remove Adjacent Almost-Equal Characters,Med,,
Salesforce,3171,Find Subarray With Bitwise OR Closest to K,Hard,"Array, Greedy",You are given two arrays nums1 and nums2 consisting of positive integers. You have to replace all the 0's in both arrays with strictly positive integers such that the sum of elements of both arrays becomes equal. Return the minimum equal sum you can obtain; or -1 if it is impossible. Example 1: Input: nums1 = [3;2;0;1;0]; nums2 = [6;5;0] Output: 12 Explanation: We can replace 0's in the following way: - Replace the two 0's in nums1 with the values 2 and 4. The resulting array is nums1 = [3;2;2;1;4]. - Replace the 0 in nums2 with the value 1. The resulting array is nums2 = [6;5;1]. Both arrays have an equal sum of 12. It can be shown that it is the minimum sum we can obtain. Example 2: Input: nums1 = [2;0;2;0]; nums2 = [1;4] Output: -1 Explanation: It is impossible to make the sum of both arrays equal. Constraints: 1 <= nums1.length; nums2.length <= 105 0 <= nums1[i]; nums2[i] <= 106
Salesforce,895,Maximum Frequency Stack,Hard,"Array, Bit Manipulation, Breadth-First Search, Matrix","You are given an m x n grid grid where: '.' is an empty cell. '#' is a wall. '@' is the starting point. Lowercase letters represent keys. Uppercase letters represent locks. You start at the starting point and one move consists of walking one space in one of the four cardinal directions. You cannot walk outside the grid; or walk into a wall. If you walk over a key; you can pick it up and you cannot walk over a lock unless you have its corresponding key. For some 1 <= k <= 6; there is exactly one lowercase and one uppercase letter of the first k letters of the English alphabet in the grid. This means that there is exactly one key for each lock; and one lock for each key; and also that the letters used to represent the keys and locks were chosen in the same order as the English alphabet. Return the lowest number of moves to acquire all keys. If it is impossible; return -1. Example 1: Input: grid = [""@.a.."";""###.#"";""b.A.B""] Output: 8 Explanation: Note that the goal is to obtain all the keys not to open all the locks. Example 2: Input: grid = [""@..aA"";""..B#."";""....b""] Output: 6 Example 3: Input: grid = [""@Aa""] Output: -1 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 30 grid[i][j] is either an English letter; '.'; '#'; or '@'. There is exactly one '@' in the grid. The number of keys in the grid is in the range [1; 6]. Each key in the grid is unique. Each key in the grid has a matching lock."
Salesforce,1051,Height Checker,Easy,"Two Pointers, String, Binary Search, Greedy",
Salesforce,2296,Design a Text Editor,Hard,Database,
Salesforce,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Salesforce,1150,Check If a Number Is Majority Element in a Sorted Array,Easy,"Two Pointers, Binary Search, Stack, Tree, Depth-First Search, Binary Search Tree, Binary Tree",
Salesforce,1659,Maximize Grid Happiness,Hard,"Array, Two Pointers, Dynamic Programming, Greedy",You are given two sorted arrays of distinct integers nums1 and nums2. A valid path is defined as follows: Choose array nums1 or nums2 to traverse (from index-0). Traverse the current array from left to right. If you are reading any value that is present in nums1 and nums2 you are allowed to change your path to the other array. (Only one repeated value is considered in the valid path). The score is defined as the sum of unique values in a valid path. Return the maximum score you can obtain of all possible valid paths. Since the answer may be too large; return it modulo 109 + 7. Example 1: Input: nums1 = [2;4;5;8;10]; nums2 = [4;6;8;9] Output: 30 Explanation: Valid paths: [2;4;5;8;10]; [2;4;5;8;9]; [2;4;6;8;9]; [2;4;6;8;10]; (starting from nums1) [4;6;8;9]; [4;5;8;10]; [4;5;8;9]; [4;6;8;10] (starting from nums2) The maximum is obtained with the path in green [2;4;6;8;10]. Example 2: Input: nums1 = [1;3;5;7;9]; nums2 = [3;5;100] Output: 109 Explanation: Maximum sum is obtained with the path [1;3;5;100]. Example 3: Input: nums1 = [1;2;3;4;5]; nums2 = [6;7;8;9;10] Output: 40 Explanation: There are no common elements between nums1 and nums2. Maximum sum is obtained with the path [6;7;8;9;10]. Constraints: 1 <= nums1.length; nums2.length <= 105 1 <= nums1[i]; nums2[i] <= 107 nums1 and nums2 are strictly increasing.
Salesforce,1701,Average Waiting Time,Med,"Union Find, Graph",Alice and Bob have an undirected graph of n nodes and three types of edges: Type 1: Can be traversed by Alice only. Type 2: Can be traversed by Bob only. Type 3: Can be traversed by both Alice and Bob. Given an array edges where edges[i] = [typei; ui; vi] represents a bidirectional edge of type typei between nodes ui and vi; find the maximum number of edges you can remove so that after removing the edges; the graph can still be fully traversed by both Alice and Bob. The graph is fully traversed by Alice and Bob if starting from any node; they can reach all other nodes. Return the maximum number of edges you can remove; or return -1 if Alice and Bob cannot fully traverse the graph. Example 1: Input: n = 4; edges = [[3;1;2];[3;2;3];[1;1;3];[1;2;4];[1;1;2];[2;3;4]] Output: 2 Explanation: If we remove the 2 edges [1;1;2] and [1;1;3]. The graph will still be fully traversable by Alice and Bob. Removing any additional edge will not make it so. So the maximum number of edges we can remove is 2. Example 2: Input: n = 4; edges = [[3;1;2];[3;2;3];[1;1;4];[2;1;4]] Output: 0 Explanation: Notice that removing any edge will not make the graph fully traversable by Alice and Bob. Example 3: Input: n = 4; edges = [[3;2;3];[1;1;2];[2;3;4]] Output: -1 Explanation: In the current graph; Alice cannot reach node 4 from the other nodes. Likewise; Bob cannot reach 1. Therefore it's impossible to make the graph fully traversable. Constraints: 1 <= n <= 105 1 <= edges.length <= min(105; 3 * n * (n - 1) / 2) edges[i].length == 3 1 <= typei <= 3 1 <= ui < vi <= n All tuples (typei; ui; vi) are distinct.
Salesforce,2068,Check Whether Two Strings are Almost Equivalent,Easy,"Array, Hash Table, Bit Manipulation, Depth-First Search, Trie",There is a rooted tree consisting of n nodes numbered 0 to n - 1. Each node's number denotes its unique genetic value (i.e. the genetic value of node x is x). The genetic difference between two genetic values is defined as the bitwise-XOR of their values. You are given the integer array parents; where parents[i] is the parent for node i. If node x is the root of the tree; then parents[x] == -1. You are also given the array queries where queries[i] = [nodei; vali]. For each query i; find the maximum genetic difference between vali and pi; where pi is the genetic value of any node that is on the path between nodei and the root (including nodei and the root). More formally; you want to maximize vali XOR pi. Return an array ans where ans[i] is the answer to the ith query. Example 1: Input: parents = [-1;0;1;1]; queries = [[0;2];[3;2];[2;5]] Output: [2;3;7] Explanation: The queries are processed as follows: - [0;2]: The node with the maximum genetic difference is 0; with a difference of 2 XOR 0 = 2. - [3;2]: The node with the maximum genetic difference is 1; with a difference of 2 XOR 1 = 3. - [2;5]: The node with the maximum genetic difference is 2; with a difference of 5 XOR 2 = 7. Example 2: Input: parents = [3;7;-1;2;0;7;0;2]; queries = [[4;6];[1;15];[0;5]] Output: [6;14;7] Explanation: The queries are processed as follows: - [4;6]: The node with the maximum genetic difference is 0; with a difference of 6 XOR 0 = 6. - [1;15]: The node with the maximum genetic difference is 1; with a difference of 15 XOR 1 = 14. - [0;5]: The node with the maximum genetic difference is 2; with a difference of 5 XOR 2 = 7. Constraints: 2 <= parents.length <= 105 0 <= parents[i] <= parents.length - 1 for every node i that is not the root. parents[root] == -1 1 <= queries.length <= 3 * 104 0 <= nodei <= parents.length - 1 0 <= vali <= 2 * 105
Salesforce,2563,Count the Number of Fair Pairs,Med,"String, Binary Search","You are given a string; message; and a positive integer; limit. You must split message into one or more parts based on limit. Each resulting part should have the suffix ""<a/b>""; where ""b"" is to be replaced with the total number of parts and ""a"" is to be replaced with the index of the part; starting from 1 and going up to b. Additionally; the length of each resulting part (including its suffix) should be equal to limit; except for the last part whose length can be at most limit. The resulting parts should be formed such that when their suffixes are removed and they are all concatenated in order; they should be equal to message. Also; the result should contain as few parts as possible. Return the parts message would be split into as an array of strings. If it is impossible to split message as required; return an empty array. Example 1: Input: message = ""this is really a very awesome message""; limit = 9 Output: [""thi<1/14>"";""s i<2/14>"";""s r<3/14>"";""eal<4/14>"";""ly <5/14>"";""a v<6/14>"";""ery<7/14>"";"" aw<8/14>"";""eso<9/14>"";""me<10/14>"";"" m<11/14>"";""es<12/14>"";""sa<13/14>"";""ge<14/14>""] Explanation: The first 9 parts take 3 characters each from the beginning of message. The next 5 parts take 2 characters each to finish splitting message. In this example; each part; including the last; has length 9. It can be shown it is not possible to split message into less than 14 parts. Example 2: Input: message = ""short message""; limit = 15 Output: [""short mess<1/2>"";""age<2/2>""] Explanation: Under the given constraints; the string can be split into two parts: - The first part comprises of the first 10 characters; and has a length 15. - The next part comprises of the last 3 characters; and has a length 8. Constraints: 1 <= message.length <= 104 message consists only of lowercase English letters and ' '. 1 <= limit <= 104"
Salesforce,2866,Beautiful Towers II,Med,"Array, Sliding Window",You are given a 0-indexed integer array nums and an integer threshold. Find the length of the longest subarray of nums starting at index l and ending at index r (0 <= l <= r < nums.length) that satisfies the following conditions: nums[l] % 2 == 0 For all indices i in the range [l; r - 1]; nums[i] % 2 != nums[i + 1] % 2 For all indices i in the range [l; r]; nums[i] <= threshold Return an integer denoting the length of the longest such subarray. Note: A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [3;2;5;4]; threshold = 5 Output: 3 Explanation: In this example; we can select the subarray that starts at l = 1 and ends at r = 3 => [2;5;4]. This subarray satisfies the conditions. Hence; the answer is the length of the subarray; 3. We can show that 3 is the maximum possible achievable length. Example 2: Input: nums = [1;2]; threshold = 2 Output: 1 Explanation: In this example; we can select the subarray that starts at l = 1 and ends at r = 1 => [2]. It satisfies all the conditions and we can show that 1 is the maximum possible achievable length. Example 3: Input: nums = [2;3;4;5]; threshold = 4 Output: 3 Explanation: In this example; we can select the subarray that starts at l = 0 and ends at r = 2 => [2;3;4]. It satisfies all the conditions. Hence; the answer is the length of the subarray; 3. We can show that 3 is the maximum possible achievable length. Constraints: 1 <= nums.length <= 100 1 <= nums[i] <= 100 1 <= threshold <= 100
Salesforce,2865,Beautiful Towers I,Med,"Graph, Heap (Priority Queue), Shortest Path",
Salesforce,2946,Matrix Similarity After Cyclic Shifts,Easy,,
Salesforce,2992,Number of Self-Divisible Permutations,Med,,
Salesforce,3125,Maximum Number That Makes Result of Bitwise AND Zero,Med,,
Salesforce,3135,Equalize Strings by Adding or Removing Characters at Ends,Med,,
Salesforce,3197,Find the Minimum Area to Cover All Ones II,Hard,"Array, Hash Table, Bit Manipulation, Trie, Sliding Window",You are given a 0-indexed integer array nums. A pair of integers x and y is called a strong pair if it satisfies the condition: |x - y| <= min(x; y) You need to select two integers from nums such that they form a strong pair and their bitwise XOR is the maximum among all strong pairs in the array. Return the maximum XOR value out of all possible strong pairs in the array nums. Note that you can pick the same integer twice to form a pair. Example 1: Input: nums = [1;2;3;4;5] Output: 7 Explanation: There are 11 strong pairs in the array nums: (1; 1); (1; 2); (2; 2); (2; 3); (2; 4); (3; 3); (3; 4); (3; 5); (4; 4); (4; 5) and (5; 5). The maximum XOR possible from these pairs is 3 XOR 4 = 7. Example 2: Input: nums = [10;100] Output: 0 Explanation: There are 2 strong pairs in the array nums: (10; 10) and (100; 100). The maximum XOR possible from these pairs is 10 XOR 10 = 0 since the pair (100; 100) also gives 100 XOR 100 = 0. Example 3: Input: nums = [500;520;2500;3000] Output: 1020 Explanation: There are 6 strong pairs in the array nums: (500; 500); (500; 520); (520; 520); (2500; 2500); (2500; 3000) and (3000; 3000). The maximum XOR possible from these pairs is 500 XOR 520 = 1020 since the only other non-zero XOR value is 2500 XOR 3000 = 636. Constraints: 1 <= nums.length <= 5 * 104 1 <= nums[i] <= 220 - 1
Salesforce,3193,Count the Number of Inversions,Hard,"Array, Hash Table, Bit Manipulation, Trie, Sliding Window",You are given a 0-indexed integer array nums. A pair of integers x and y is called a strong pair if it satisfies the condition: |x - y| <= min(x; y) You need to select two integers from nums such that they form a strong pair and their bitwise XOR is the maximum among all strong pairs in the array. Return the maximum XOR value out of all possible strong pairs in the array nums. Note that you can pick the same integer twice to form a pair. Example 1: Input: nums = [1;2;3;4;5] Output: 7 Explanation: There are 11 strong pairs in the array nums: (1; 1); (1; 2); (2; 2); (2; 3); (2; 4); (3; 3); (3; 4); (3; 5); (4; 4); (4; 5) and (5; 5). The maximum XOR possible from these pairs is 3 XOR 4 = 7. Example 2: Input: nums = [10;100] Output: 0 Explanation: There are 2 strong pairs in the array nums: (10; 10) and (100; 100). The maximum XOR possible from these pairs is 10 XOR 10 = 0 since the pair (100; 100) also gives 100 XOR 100 = 0. Example 3: Input: nums = [5;6;25;30] Output: 7 Explanation: There are 6 strong pairs in the array nums: (5; 5); (5; 6); (6; 6); (25; 25); (25; 30) and (30; 30). The maximum XOR possible from these pairs is 25 XOR 30 = 7 since the only other non-zero XOR value is 5 XOR 6 = 3. Constraints: 1 <= nums.length <= 50 1 <= nums[i] <= 100
Salesforce,3195,Find the Minimum Area to Cover All Ones I,Med,"Two Pointers, String, Greedy","There are n balls on a table; each ball has a color black or white. You are given a 0-indexed binary string s of length n; where 1 and 0 represent black and white balls; respectively. In each step; you can choose two adjacent balls and swap them. Return the minimum number of steps to group all the black balls to the right and all the white balls to the left. Example 1: Input: s = ""101"" Output: 1 Explanation: We can group all the black balls to the right in the following way: - Swap s[0] and s[1]; s = ""011"". Initially; 1s are not grouped together; requiring at least 1 step to group them to the right. Example 2: Input: s = ""100"" Output: 2 Explanation: We can group all the black balls to the right in the following way: - Swap s[0] and s[1]; s = ""010"". - Swap s[1] and s[2]; s = ""001"". It can be proven that the minimum number of steps needed is 2. Example 3: Input: s = ""0111"" Output: 0 Explanation: All the black balls are already grouped to the right. Constraints: 1 <= n == s.length <= 105 s[i] is either '0' or '1'."
Salesforce,3200,Maximum Height of a Triangle,Easy,"Math, Dynamic Programming, Combinatorics","You are given an integer n. A string s is called good if it contains only lowercase English characters and it is possible to rearrange the characters of s such that the new string contains ""leet"" as a substring. For example: The string ""lteer"" is good because we can rearrange it to form ""leetr"" . ""letl"" is not good because we cannot rearrange it to contain ""leet"" as a substring. Return the total number of good strings of length n. Since the answer may be large; return it modulo 109 + 7. A substring is a contiguous sequence of characters within a string. Example 1: Input: n = 4 Output: 12 Explanation: The 12 strings which can be rearranged to have ""leet"" as a substring are: ""eelt""; ""eetl""; ""elet""; ""elte""; ""etel""; ""etle""; ""leet""; ""lete""; ""ltee""; ""teel""; ""tele""; and ""tlee"". Example 2: Input: n = 10 Output: 83943898 Explanation: The number of strings with length 10 which can be rearranged to have ""leet"" as a substring is 526083947580. Hence the answer is 526083947580 % (109 + 7) = 83943898. Constraints: 1 <= n <= 105"
Salesforce,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Salesforce,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Salesforce,526,Beautiful Arrangement,Med,"Array, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask",Suppose you have n integers labeled 1 through n. A permutation of those n integers perm (1-indexed) is considered a beautiful arrangement if for every i (1 <= i <= n); either of the following is true: perm[i] is divisible by i. i is divisible by perm[i]. Given an integer n; return the number of the beautiful arrangements that you can construct. Example 1: Input: n = 2 Output: 2 Explanation: The first beautiful arrangement is [1;2]: - perm[1] = 1 is divisible by i = 1 - perm[2] = 2 is divisible by i = 2 The second beautiful arrangement is [2;1]: - perm[1] = 2 is divisible by i = 1 - i = 2 is divisible by perm[2] = 1 Example 2: Input: n = 1 Output: 1 Constraints: 1 <= n <= 15
Salesforce,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Salesforce,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Salesforce,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Salesforce,1492,The kth Factor of n,Med,"Tree, Depth-First Search, Breadth-First Search",A company has n employees with a unique ID for each employee from 0 to n - 1. The head of the company is the one with headID. Each employee has one direct manager given in the manager array where manager[i] is the direct manager of the i-th employee; manager[headID] = -1. Also; it is guaranteed that the subordination relationships have a tree structure. The head of the company wants to inform all the company employees of an urgent piece of news. He will inform his direct subordinates; and they will inform their subordinates; and so on until all employees know about the urgent news. The i-th employee needs informTime[i] minutes to inform all of his direct subordinates (i.e.; After informTime[i] minutes; all his direct subordinates can start spreading the news). Return the number of minutes needed to inform all the employees about the urgent news. Example 1: Input: n = 1; headID = 0; manager = [-1]; informTime = [0] Output: 0 Explanation: The head of the company is the only employee in the company. Example 2: Input: n = 6; headID = 2; manager = [2;2;-1;2;2;2]; informTime = [0;0;1;0;0;0] Output: 1 Explanation: The head of the company with id = 2 is the direct manager of all the employees in the company and needs 1 minute to inform them all. The tree structure of the employees in the company is shown. Constraints: 1 <= n <= 105 0 <= headID < n manager.length == n 0 <= manager[i] < n manager[headID] == -1 informTime.length == n 0 <= informTime[i] <= 1000 informTime[i] == 0 if employee i has no subordinates. It is guaranteed that all the employees can be informed.
Salesforce,3313,Find the Last Marked Nodes in Tree,Hard,"Array, Dynamic Programming, Prefix Sum",You are given an array of integers nums with length n; and a positive odd integer k. Select exactly k disjoint subarrays sub1; sub2; ...; subk from nums such that the last element of subi appears before the first element of sub{i+1} for all 1 <= i <= k-1. The goal is to maximize their combined strength. The strength of the selected subarrays is defined as: strength = k * sum(sub1)- (k - 1) * sum(sub2) + (k - 2) * sum(sub3) - ... - 2 * sum(sub{k-1}) + sum(subk) where sum(subi) is the sum of the elements in the i-th subarray. Return the maximum possible strength that can be obtained from selecting exactly k disjoint subarrays from nums. Note that the chosen subarrays don't need to cover the entire array. Example 1: Input: nums = [1;2;3;-1;2]; k = 3 Output: 22 Explanation: The best possible way to select 3 subarrays is: nums[0..2]; nums[3..3]; and nums[4..4]. The strength is calculated as follows: strength = 3 * (1 + 2 + 3) - 2 * (-1) + 2 = 22 Example 2: Input: nums = [12;-2;-2;-2;-2]; k = 5 Output: 64 Explanation: The only possible way to select 5 disjoint subarrays is: nums[0..0]; nums[1..1]; nums[2..2]; nums[3..3]; and nums[4..4]. The strength is calculated as follows: strength = 5 * 12 - 4 * (-2) + 3 * (-2) - 2 * (-2) + (-2) = 64 Example 3: Input: nums = [-1;-2;-3]; k = 1 Output: -1 Explanation: The best possible way to select 1 subarray is: nums[0..0]. The strength is -1. Constraints: 1 <= n <= 104 -109 <= nums[i] <= 109 1 <= k <= n 1 <= n * k <= 106 k is odd.
Salesforce,115,Distinct Subsequences,Hard,"String, Dynamic Programming","Given two strings s and t; return the number of distinct subsequences of s which equals t. The test cases are generated so that the answer fits on a 32-bit signed integer. Example 1: Input: s = ""rabbbit""; t = ""rabbit"" Output: 3 Explanation: As shown below; there are 3 ways you can generate ""rabbit"" from s. rabbbit rabbbit rabbbit Example 2: Input: s = ""babgbag""; t = ""bag"" Output: 5 Explanation: As shown below; there are 5 ways you can generate ""bag"" from s. babgbag babgbag babgbag babgbag babgbag Constraints: 1 <= s.length; t.length <= 1000 s and t consist of English letters."
Salesforce,179,Largest Number,Med,"Array, String, Greedy, Sorting","Given a list of non-negative integers nums; arrange them such that they form the largest number and return it. Since the result may be very large; so you need to return a string instead of an integer. Example 1: Input: nums = [10;2] Output: ""210"" Example 2: Input: nums = [3;30;34;5;9] Output: ""9534330"" Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 109"
Salesforce,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Salesforce,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Salesforce,647,Palindromic Substrings,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the number of palindromic substrings in it. A string is a palindrome when it reads the same backward as forward. A substring is a contiguous sequence of characters within the string. Example 1: Input: s = ""abc"" Output: 3 Explanation: Three palindromic strings: ""a""; ""b""; ""c"". Example 2: Input: s = ""aaa"" Output: 6 Explanation: Six palindromic strings: ""a""; ""a""; ""a""; ""aa""; ""aa""; ""aaa"". Constraints: 1 <= s.length <= 1000 s consists of lowercase English letters."
Salesforce,713,Subarray Product Less Than K,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of integers nums and an integer k; return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k. Example 1: Input: nums = [10;5;2;6]; k = 100 Output: 8 Explanation: The 8 subarrays that have product less than 100 are: [10]; [5]; [2]; [6]; [10; 5]; [5; 2]; [2; 6]; [5; 2; 6] Note that [10; 5; 2] is not included as the product of 100 is not strictly less than k. Example 2: Input: nums = [1;2;3]; k = 0 Output: 0 Constraints: 1 <= nums.length <= 3 * 104 1 <= nums[i] <= 1000 0 <= k <= 106
Salesforce,12,Integer to Roman,Med,"Hash Table, Math, String","Seven different symbols represent Roman numerals with the following values: Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 Roman numerals are formed by appending the conversions of decimal place values from highest to lowest. Converting a decimal place value into a Roman numeral has the following rules: If the value does not start with 4 or 9; select the symbol of the maximal value that can be subtracted from the input; append that symbol to the result; subtract its value; and convert the remainder to a Roman numeral. If the value starts with 4 or 9 use the subtractive form representing one symbol subtracted from the following symbol; for example; 4 is 1 (I) less than 5 (V): IV and 9 is 1 (I) less than 10 (X): IX. Only the following subtractive forms are used: 4 (IV); 9 (IX); 40 (XL); 90 (XC); 400 (CD) and 900 (CM). Only powers of 10 (I; X; C; M) can be appended consecutively at most 3 times to represent multiples of 10. You cannot append 5 (V); 50 (L); or 500 (D) multiple times. If you need to append a symbol 4 times use the subtractive form. Given an integer; convert it to a Roman numeral. Example 1: Input: num = 3749 Output: ""MMMDCCXLIX"" Explanation: 3000 = MMM as 1000 (M) + 1000 (M) + 1000 (M) 700 = DCC as 500 (D) + 100 (C) + 100 (C) 40 = XL as 10 (X) less of 50 (L) 9 = IX as 1 (I) less of 10 (X) Note: 49 is not 1 (I) less of 50 (L) because the conversion is based on decimal places Example 2: Input: num = 58 Output: ""LVIII"" Explanation: 50 = L 8 = VIII Example 3: Input: num = 1994 Output: ""MCMXCIV"" Explanation: 1000 = M 900 = CM 90 = XC 4 = IV Constraints: 1 <= num <= 3999"
Salesforce,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Salesforce,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Salesforce,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Salesforce,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
Salesforce,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Salesforce,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Salesforce,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
Salesforce,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
Salesforce,532,K-diff Pairs in an Array,Med,"Array, Hash Table, Two Pointers, Binary Search, Sorting",Given an array of integers nums and an integer k; return the number of unique k-diff pairs in the array. A k-diff pair is an integer pair (nums[i]; nums[j]); where the following are true: 0 <= i; j < nums.length i != j |nums[i] - nums[j]| == k Notice that |val| denotes the absolute value of val. Example 1: Input: nums = [3;1;4;1;5]; k = 2 Output: 2 Explanation: There are two 2-diff pairs in the array; (1; 3) and (3; 5). Although we have two 1s in the input; we should only return the number of unique pairs. Example 2: Input: nums = [1;2;3;4;5]; k = 1 Output: 4 Explanation: There are four 1-diff pairs in the array; (1; 2); (2; 3); (3; 4) and (4; 5). Example 3: Input: nums = [1;3;1;5;4]; k = 0 Output: 1 Explanation: There is one 0-diff pair in the array; (1; 1). Constraints: 1 <= nums.length <= 104 -107 <= nums[i] <= 107 0 <= k <= 107
Salesforce,621,Task Scheduler,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting","You are given an array of CPU tasks; each labeled with a letter from A to Z; and a number n. Each CPU interval can be idle or allow the completion of one task. Tasks can be completed in any order; but there's a constraint: there has to be a gap of at least n intervals between two tasks with the same label. Return the minimum number of CPU intervals required to complete all tasks. Example 1: Input: tasks = [""A"";""A"";""A"";""B"";""B"";""B""]; n = 2 Output: 8 Explanation: A possible sequence is: A -> B -> idle -> A -> B -> idle -> A -> B. After completing task A; you must wait two intervals before doing A again. The same applies to task B. In the 3rd interval; neither A nor B can be done; so you idle. By the 4th interval; you can do A again as 2 intervals have passed. Example 2: Input: tasks = [""A"";""C"";""A"";""B"";""D"";""B""]; n = 1 Output: 6 Explanation: A possible sequence is: A -> B -> C -> D -> A -> B. With a cooling interval of 1; you can repeat a task after just one other task. Example 3: Input: tasks = [""A"";""A"";""A""; ""B"";""B"";""B""]; n = 3 Output: 10 Explanation: A possible sequence is: A -> B -> idle -> idle -> A -> B -> idle -> idle -> A -> B. There are only two types of tasks; A and B; which need to be separated by 3 intervals. This leads to idling twice between repetitions of these tasks. Constraints: 1 <= tasks.length <= 104 tasks[i] is an uppercase English letter. 0 <= n <= 100"
Salesforce,697,Degree of an Array,Easy,"Array, Hash Table",Given a non-empty array of non-negative integers nums; the degree of this array is defined as the maximum frequency of any one of its elements. Your task is to find the smallest possible length of a (contiguous) subarray of nums; that has the same degree as nums. Example 1: Input: nums = [1;2;2;3;1] Output: 2 Explanation: The input array has a degree of 2 because both elements 1 and 2 appear twice. Of the subarrays that have the same degree: [1; 2; 2; 3; 1]; [1; 2; 2; 3]; [2; 2; 3; 1]; [1; 2; 2]; [2; 2; 3]; [2; 2] The shortest length is 2. So return 2. Example 2: Input: nums = [1;2;2;3;1;4;2] Output: 6 Explanation: The degree is 3 because the element 2 is repeated 3 times. So [2;2;3;1;4;2] is the shortest subarray; therefore returning 6. Constraints: nums.length will be between 1 and 50;000. nums[i] will be an integer between 0 and 49;999.
Salesforce,1710,Maximum Units on a Truck,Easy,"Array, Greedy, Heap (Priority Queue), Ordered Set",You have k servers numbered from 0 to k-1 that are being used to handle multiple requests simultaneously. Each server has infinite computational capacity but cannot handle more than one request at a time. The requests are assigned to servers according to a specific algorithm: The ith (0-indexed) request arrives. If all servers are busy; the request is dropped (not handled at all). If the (i % k)th server is available; assign the request to that server. Otherwise; assign the request to the next available server (wrapping around the list of servers and starting from 0 if necessary). For example; if the ith server is busy; try to assign the request to the (i+1)th server; then the (i+2)th server; and so on. You are given a strictly increasing array arrival of positive integers; where arrival[i] represents the arrival time of the ith request; and another array load; where load[i] represents the load of the ith request (the time it takes to complete). Your goal is to find the busiest server(s). A server is considered busiest if it handled the most number of requests successfully among all the servers. Return a list containing the IDs (0-indexed) of the busiest server(s). You may return the IDs in any order. Example 1: Input: k = 3; arrival = [1;2;3;4;5]; load = [5;2;3;3;3] Output: [1] Explanation: All of the servers start out available. The first 3 requests are handled by the first 3 servers in order. Request 3 comes in. Server 0 is busy; so it's assigned to the next available server; which is 1. Request 4 comes in. It cannot be handled since all servers are busy; so it is dropped. Servers 0 and 2 handled one request each; while server 1 handled two requests. Hence server 1 is the busiest server. Example 2: Input: k = 3; arrival = [1;2;3;4]; load = [1;2;1;2] Output: [0] Explanation: The first 3 requests are handled by first 3 servers. Request 3 comes in. It is handled by server 0 since the server is available. Server 0 handled two requests; while servers 1 and 2 handled one request each. Hence server 0 is the busiest server. Example 3: Input: k = 3; arrival = [1;2;3]; load = [10;12;11] Output: [0;1;2] Explanation: Each server handles a single request; so they are all considered the busiest. Constraints: 1 <= k <= 105 1 <= arrival.length; load.length <= 105 arrival.length == load.length 1 <= arrival[i]; load[i] <= 109 arrival is strictly increasing.
Salesforce,2484,Count Palindromic Subsequences,Hard,Database,
Salesforce,2966,Divide Array Into Arrays With Max Difference,Med,,
Salesforce,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Salesforce,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Salesforce,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Salesforce,105,Construct Binary Tree from Preorder and Inorder Traversal,Med,"Array, Hash Table, Divide and Conquer, Tree, Binary Tree",Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree; construct and return the binary tree. Example 1: Input: preorder = [3;9;20;15;7]; inorder = [9;3;15;20;7] Output: [3;9;20;null;null;15;7] Example 2: Input: preorder = [-1]; inorder = [-1] Output: [-1] Constraints: 1 <= preorder.length <= 3000 inorder.length == preorder.length -3000 <= preorder[i]; inorder[i] <= 3000 preorder and inorder consist of unique values. Each value of inorder also appears in preorder. preorder is guaranteed to be the preorder traversal of the tree. inorder is guaranteed to be the inorder traversal of the tree.
Salesforce,116,Populating Next Right Pointers in Each Node,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given a perfect binary tree where all leaves are on the same level; and every parent has two children. The binary tree has the following definition: struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;6;7] Output: [1;#;2;3;#;4;5;6;7;#] Explanation: Given the above perfect binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 212 - 1]. -1000 <= Node.val <= 1000 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Salesforce,155,Min Stack,Med,"Stack, Design","Design a stack that supports push; pop; top; and retrieving the minimum element in constant time. Implement the MinStack class: MinStack() initializes the stack object. void push(int val) pushes the element val onto the stack. void pop() removes the element on the top of the stack. int top() gets the top element of the stack. int getMin() retrieves the minimum element in the stack. You must implement a solution with O(1) time complexity for each function. Example 1: Input [""MinStack"";""push"";""push"";""push"";""getMin"";""pop"";""top"";""getMin""] [[];[-2];[0];[-3];[];[];[];[]] Output [null;null;null;null;-3;null;0;-2] Explanation MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2 Constraints: -231 <= val <= 231 - 1 Methods pop; top and getMin operations will always be called on non-empty stacks. At most 3 * 104 calls will be made to push; pop; top; and getMin."
Salesforce,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Salesforce,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Salesforce,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Salesforce,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
Salesforce,423,Reconstruct Original Digits from English,Med,"Hash Table, Math, String","Given a string s containing an out-of-order English representation of digits 0-9; return the digits in ascending order. Example 1: Input: s = ""owoztneoer"" Output: ""012"" Example 2: Input: s = ""fviefuro"" Output: ""45"" Constraints: 1 <= s.length <= 105 s[i] is one of the characters [""e"";""g"";""f"";""i"";""h"";""o"";""n"";""s"";""r"";""u"";""t"";""w"";""v"";""x"";""z""]. s is guaranteed to be valid."
Salesforce,502,IPO,Hard,"Array, Greedy, Sorting, Heap (Priority Queue)",Suppose LeetCode will start its IPO soon. In order to sell a good price of its shares to Venture Capital; LeetCode would like to work on some projects to increase its capital before the IPO. Since it has limited resources; it can only finish at most k distinct projects before the IPO. Help LeetCode design the best way to maximize its total capital after finishing at most k distinct projects. You are given n projects where the ith project has a pure profit profits[i] and a minimum capital of capital[i] is needed to start it. Initially; you have w capital. When you finish a project; you will obtain its pure profit and the profit will be added to your total capital. Pick a list of at most k distinct projects from given projects to maximize your final capital; and return the final maximized capital. The answer is guaranteed to fit in a 32-bit signed integer. Example 1: Input: k = 2; w = 0; profits = [1;2;3]; capital = [0;1;1] Output: 4 Explanation: Since your initial capital is 0; you can only start the project indexed 0. After finishing it you will obtain profit 1 and your capital becomes 1. With capital 1; you can either start the project indexed 1 or the project indexed 2. Since you can choose at most 2 projects; you need to finish the project indexed 2 to get the maximum capital. Therefore; output the final maximized capital; which is 0 + 1 + 3 = 4. Example 2: Input: k = 3; w = 0; profits = [1;2;3]; capital = [0;1;2] Output: 6 Constraints: 1 <= k <= 105 0 <= w <= 109 n == profits.length n == capital.length 1 <= n <= 105 0 <= profits[i] <= 104 0 <= capital[i] <= 109
Salesforce,695,Max Area of Island,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island. Return the maximum area of an island in grid. If there is no island; return 0. Example 1: Input: grid = [[0;0;1;0;0;0;0;1;0;0;0;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;1;1;0;1;0;0;0;0;0;0;0;0];[0;1;0;0;1;1;0;0;1;0;1;0;0];[0;1;0;0;1;1;0;0;1;1;1;0;0];[0;0;0;0;0;0;0;0;0;0;1;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;0;0;0;0;0;0;1;1;0;0;0;0]] Output: 6 Explanation: The answer is not 11; because the island must be connected 4-directionally. Example 2: Input: grid = [[0;0;0;0;0;0;0;0]] Output: 0 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 50 grid[i][j] is either 0 or 1.
Salesforce,1315,Sum of Nodes with Even-Valued Grandparent,Med,,
Salesforce,1718,Construct the Lexicographically Largest Valid Sequence,Med,Database,
Salesforce,2035,Partition Array Into Two Arrays to Minimize Sum Difference,Hard,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given two m x n binary matrices grid1 and grid2 containing only 0's (representing water) and 1's (representing land). An island is a group of 1's connected 4-directionally (horizontal or vertical). Any cells outside of the grid are considered water cells. An island in grid2 is considered a sub-island if there is an island in grid1 that contains all the cells that make up this island in grid2. Return the number of islands in grid2 that are considered sub-islands. Example 1: Input: grid1 = [[1;1;1;0;0];[0;1;1;1;1];[0;0;0;0;0];[1;0;0;0;0];[1;1;0;1;1]]; grid2 = [[1;1;1;0;0];[0;0;1;1;1];[0;1;0;0;0];[1;0;1;1;0];[0;1;0;1;0]] Output: 3 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are three sub-islands. Example 2: Input: grid1 = [[1;0;1;0;1];[1;1;1;1;1];[0;0;0;0;0];[1;1;1;1;1];[1;0;1;0;1]]; grid2 = [[0;0;0;0;0];[1;1;1;1;1];[0;1;0;1;0];[0;1;0;1;0];[1;0;0;0;1]] Output: 2 Explanation: In the picture above; the grid on the left is grid1 and the grid on the right is grid2. The 1s colored red in grid2 are those considered to be part of a sub-island. There are two sub-islands. Constraints: m == grid1.length == grid2.length n == grid1[i].length == grid2[i].length 1 <= m; n <= 500 grid1[i][j] and grid2[i][j] are either 0 or 1.
Salesforce,2231,Largest Number After Digit Swaps by Parity,Easy,"Array, Two Pointers, String","Given an array of strings words; return the first palindromic string in the array. If there is no such string; return an empty string """". A string is palindromic if it reads the same forward and backward. Example 1: Input: words = [""abc"";""car"";""ada"";""racecar"";""cool""] Output: ""ada"" Explanation: The first string that is palindromic is ""ada"". Note that ""racecar"" is also palindromic; but it is not the first. Example 2: Input: words = [""notapalindrome"";""racecar""] Output: ""racecar"" Explanation: The first and only string that is palindromic is ""racecar"". Example 3: Input: words = [""def"";""ghi""] Output: """" Explanation: There are no palindromic strings; so the empty string is returned. Constraints: 1 <= words.length <= 100 1 <= words[i].length <= 100 words[i] consists only of lowercase English letters."
Salesforce,2964,Number of Divisible Triplet Sums,Med,,
Salesforce,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Salesforce,14,Longest Common Prefix,Easy,"String, Trie","Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix; return an empty string """". Example 1: Input: strs = [""flower"";""flow"";""flight""] Output: ""fl"" Example 2: Input: strs = [""dog"";""racecar"";""car""] Output: """" Explanation: There is no common prefix among the input strings. Constraints: 1 <= strs.length <= 200 0 <= strs[i].length <= 200 strs[i] consists of only lowercase English letters."
Salesforce,25,Reverse Nodes in k-Group,Hard,"Linked List, Recursion",Given the head of a linked list; reverse the nodes of the list k at a time; and return the modified list. k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes; in the end; should remain as it is. You may not alter the values in the list's nodes; only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4;5]; k = 2 Output: [2;1;4;3;5] Example 2: Input: head = [1;2;3;4;5]; k = 3 Output: [3;2;1;4;5] Constraints: The number of nodes in the list is n. 1 <= k <= n <= 5000 0 <= Node.val <= 1000 Follow-up: Can you solve the problem in O(1) extra memory space?
Salesforce,32,Longest Valid Parentheses,Hard,"String, Dynamic Programming, Stack","Given a string containing just the characters '(' and ')'; return the length of the longest valid (well-formed) parentheses substring. Example 1: Input: s = ""(()"" Output: 2 Explanation: The longest valid parentheses substring is ""()"". Example 2: Input: s = "")()())"" Output: 4 Explanation: The longest valid parentheses substring is ""()()"". Example 3: Input: s = """" Output: 0 Constraints: 0 <= s.length <= 3 * 104 s[i] is '('; or ')'."
Salesforce,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Salesforce,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Salesforce,44,Wildcard Matching,Hard,"String, Dynamic Programming, Greedy, Recursion","Given an input string (s) and a pattern (p); implement wildcard pattern matching with support for '?' and '*' where: '?' Matches any single character. '*' Matches any sequence of characters (including the empty sequence). The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""*"" Output: true Explanation: '*' matches any sequence. Example 3: Input: s = ""cb""; p = ""?a"" Output: false Explanation: '?' matches 'c'; but the second letter is 'a'; which does not match 'b'. Constraints: 0 <= s.length; p.length <= 2000 s contains only lowercase English letters. p contains only lowercase English letters; '?' or '*'."
Salesforce,75,Sort Colors,Med,"Array, Two Pointers, Sorting",Given an array nums with n objects colored red; white; or blue; sort them in-place so that objects of the same color are adjacent; with the colors in the order red; white; and blue. We will use the integers 0; 1; and 2 to represent the color red; white; and blue; respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2;0;2;1;1;0] Output: [0;0;1;1;2;2] Example 2: Input: nums = [2;0;1] Output: [0;1;2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0; 1; or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?
Salesforce,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Salesforce,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
Salesforce,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Salesforce,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Salesforce,218,The Skyline Problem,Hard,"Array, Divide and Conquer, Binary Indexed Tree, Segment Tree, Line Sweep, Heap (Priority Queue), Ordered Set","A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Given the locations and heights of all the buildings; return the skyline formed by these buildings collectively. The geometric information of each building is given in the array buildings where buildings[i] = [lefti; righti; heighti]: lefti is the x coordinate of the left edge of the ith building. righti is the x coordinate of the right edge of the ith building. heighti is the height of the ith building. You may assume all buildings are perfect rectangles grounded on an absolutely flat surface at height 0. The skyline should be represented as a list of ""key points"" sorted by their x-coordinate in the form [[x1;y1];[x2;y2];...]. Each key point is the left endpoint of some horizontal segment in the skyline except the last point in the list; which always has a y-coordinate 0 and is used to mark the skyline's termination where the rightmost building ends. Any ground between the leftmost and rightmost buildings should be part of the skyline's contour. Note: There must be no consecutive horizontal lines of equal height in the output skyline. For instance; [...;[2 3];[4 5];[7 5];[11 5];[12 7];...] is not acceptable; the three lines of height 5 should be merged into one in the final output as such: [...;[2 3];[4 5];[12 7];...] Example 1: Input: buildings = [[2;9;10];[3;7;15];[5;12;12];[15;20;10];[19;24;8]] Output: [[2;10];[3;15];[7;12];[12;0];[15;10];[20;8];[24;0]] Explanation: Figure A shows the buildings of the input. Figure B shows the skyline formed by those buildings. The red points in figure B represent the key points in the output list. Example 2: Input: buildings = [[0;2;3];[2;5;3]] Output: [[0;3];[5;0]] Constraints: 1 <= buildings.length <= 104 0 <= lefti < righti <= 231 - 1 1 <= heighti <= 231 - 1 buildings is sorted by lefti in non-decreasing order."
Salesforce,236,Lowest Common Ancestor of a Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",Given a binary tree; find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 1 Output: 3 Explanation: The LCA of nodes 5 and 1 is 3. Example 2: Input: root = [3;5;1;6;2;0;8;null;null;7;4]; p = 5; q = 4 Output: 5 Explanation: The LCA of nodes 5 and 4 is 5; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [1;2]; p = 1; q = 2 Output: 1 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the tree.
Salesforce,255,Verify Preorder Sequence in Binary Search Tree,Med,"Array, Stack, Tree, Binary Search Tree, Recursion, Monotonic Stack, Binary Tree",
Salesforce,261,Graph Valid Tree,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
Salesforce,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
Salesforce,322,Coin Change,Med,"Array, Dynamic Programming, Breadth-First Search",You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money. Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins; return -1. You may assume that you have an infinite number of each kind of coin. Example 1: Input: coins = [1;2;5]; amount = 11 Output: 3 Explanation: 11 = 5 + 5 + 1 Example 2: Input: coins = [2]; amount = 3 Output: -1 Example 3: Input: coins = [1]; amount = 0 Output: 0 Constraints: 1 <= coins.length <= 12 1 <= coins[i] <= 231 - 1 0 <= amount <= 104
Salesforce,378,Kth Smallest Element in a Sorted Matrix,Med,"Array, Binary Search, Sorting, Heap (Priority Queue), Matrix",Given an n x n matrix where each of the rows and columns is sorted in ascending order; return the kth smallest element in the matrix. Note that it is the kth smallest element in the sorted order; not the kth distinct element. You must find a solution with a memory complexity better than O(n2). Example 1: Input: matrix = [[1;5;9];[10;11;13];[12;13;15]]; k = 8 Output: 13 Explanation: The elements in the matrix are [1;5;9;10;11;12;13;13;15]; and the 8th smallest number is 13 Example 2: Input: matrix = [[-5]]; k = 1 Output: -5 Constraints: n == matrix.length == matrix[i].length 1 <= n <= 300 -109 <= matrix[i][j] <= 109 All the rows and columns of matrix are guaranteed to be sorted in non-decreasing order. 1 <= k <= n2 Follow up: Could you solve the problem with a constant memory (i.e.; O(1) memory complexity)? Could you solve the problem in O(n) time complexity? The solution may be too advanced for an interview but you may find reading this paper fun.
Salesforce,392,Is Subsequence,Easy,"Two Pointers, String, Dynamic Programming","Given two strings s and t; return true if s is a subsequence of t; or false otherwise. A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e.; ""ace"" is a subsequence of ""abcde"" while ""aec"" is not). Example 1: Input: s = ""abc""; t = ""ahbgdc"" Output: true Example 2: Input: s = ""axc""; t = ""ahbgdc"" Output: false Constraints: 0 <= s.length <= 100 0 <= t.length <= 104 s and t consist only of lowercase English letters. Follow up: Suppose there are lots of incoming s; say s1; s2; ...; sk where k >= 109; and you want to check one by one to see if t has its subsequence. In this scenario; how would you change your code?"
Salesforce,588,Design In-Memory File System,Hard,"Hash Table, String, Design, Trie, Sorting",
Salesforce,628,Maximum Product of Three Numbers,Easy,"Array, Math, Sorting",Given an integer array nums; find three numbers whose product is maximum and return the maximum product. Example 1: Input: nums = [1;2;3] Output: 6 Example 2: Input: nums = [1;2;3;4] Output: 24 Example 3: Input: nums = [-1;-2;-3] Output: -6 Constraints: 3 <= nums.length <= 104 -1000 <= nums[i] <= 1000
Salesforce,696,Count Binary Substrings,Easy,"Two Pointers, String","Given a binary string s; return the number of non-empty substrings that have the same number of 0's and 1's; and all the 0's and all the 1's in these substrings are grouped consecutively. Substrings that occur multiple times are counted the number of times they occur. Example 1: Input: s = ""00110011"" Output: 6 Explanation: There are 6 substrings that have equal number of consecutive 1's and 0's: ""0011""; ""01""; ""1100""; ""10""; ""0011""; and ""01"". Notice that some of these substrings repeat and are counted the number of times they occur. Also; ""00110011"" is not a valid substring because all the 0's (and 1's) are not grouped together. Example 2: Input: s = ""10101"" Output: 4 Explanation: There are 4 substrings: ""10""; ""01""; ""10""; ""01"" that have equal number of consecutive 1's and 0's. Constraints: 1 <= s.length <= 105 s[i] is either '0' or '1'."
Salesforce,739,Daily Temperatures,Med,"Array, Stack, Monotonic Stack",Given an array of integers temperatures represents the daily temperatures; return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible; keep answer[i] == 0 instead. Example 1: Input: temperatures = [73;74;75;71;69;72;76;73] Output: [1;1;4;2;1;1;0;0] Example 2: Input: temperatures = [30;40;50;60] Output: [1;1;1;0] Example 3: Input: temperatures = [30;60;90] Output: [1;1;0] Constraints: 1 <= temperatures.length <= 105 30 <= temperatures[i] <= 100
Salesforce,865,Smallest Subtree with all the Deepest Nodes,Med,"Backtracking, Interactive",
Salesforce,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Salesforce,1010,Pairs of Songs With Total Durations Divisible by 60,Med,"Hash Table, Math, Enumeration",Given three integers x; y; and bound; return a list of all the powerful integers that have a value less than or equal to bound. An integer is powerful if it can be represented as xi + yj for some integers i >= 0 and j >= 0. You may return the answer in any order. In your answer; each value should occur at most once. Example 1: Input: x = 2; y = 3; bound = 10 Output: [2;3;4;5;7;9;10] Explanation: 2 = 20 + 30 3 = 21 + 30 4 = 20 + 31 5 = 21 + 31 7 = 22 + 31 9 = 23 + 30 10 = 20 + 32 Example 2: Input: x = 3; y = 5; bound = 15 Output: [2;4;6;8;10;14] Constraints: 1 <= x; y <= 100 0 <= bound <= 106
Salesforce,1290,Convert Binary Number in a Linked List to Integer,Easy,"Array, Binary Search, Dynamic Programming, Sorting",Given two integer arrays arr1 and arr2; return the minimum number of operations (possibly zero) needed to make arr1 strictly increasing. In one operation; you can choose two indices 0 <= i < arr1.length and 0 <= j < arr2.length and do the assignment arr1[i] = arr2[j]. If there is no way to make arr1 strictly increasing; return -1. Example 1: Input: arr1 = [1;5;3;6;7]; arr2 = [1;3;2;4] Output: 1 Explanation: Replace 5 with 2; then arr1 = [1; 2; 3; 6; 7]. Example 2: Input: arr1 = [1;5;3;6;7]; arr2 = [4;3;1] Output: 2 Explanation: Replace 5 with 3 and then replace 3 with 4. arr1 = [1; 3; 4; 6; 7]. Example 3: Input: arr1 = [1;5;3;6;7]; arr2 = [1;6;3;3] Output: -1 Explanation: You can't make arr1 strictly increasing. Constraints: 1 <= arr1.length; arr2.length <= 2000 0 <= arr1[i]; arr2[i] <= 10^9
Salesforce,1297,Maximum Number of Occurrences of a Substring,Med,"Hash Table, String, Counting","Given a string text; you want to use the characters of text to form as many instances of the word ""balloon"" as possible. You can use each character in text at most once. Return the maximum number of instances that can be formed. Example 1: Input: text = ""nlaebolko"" Output: 1 Example 2: Input: text = ""loonbalxballpoon"" Output: 2 Example 3: Input: text = ""leetcode"" Output: 0 Constraints: 1 <= text.length <= 104 text consists of lower case English letters only. Note: This question is the same as 2287: Rearrange Characters to Make Target String."
Salesforce,2016,Maximum Difference Between Increasing Elements,Easy,"Array, Sorting",Given an integer array nums; your goal is to make all elements in nums equal. To complete one operation; follow these steps: Find the largest value in nums. Let its index be i (0-indexed) and its value be largest. If there are multiple elements with the largest value; pick the smallest i. Find the next largest value in nums strictly smaller than largest. Let its value be nextLargest. Reduce nums[i] to nextLargest. Return the number of operations to make all elements in nums equal. Example 1: Input: nums = [5;1;3] Output: 3 Explanation: It takes 3 operations to make all elements in nums equal: 1. largest = 5 at index 0. nextLargest = 3. Reduce nums[0] to 3. nums = [3;1;3]. 2. largest = 3 at index 0. nextLargest = 1. Reduce nums[0] to 1. nums = [1;1;3]. 3. largest = 3 at index 2. nextLargest = 1. Reduce nums[2] to 1. nums = [1;1;1]. Example 2: Input: nums = [1;1;1] Output: 0 Explanation: All elements in nums are already equal. Example 3: Input: nums = [1;1;2;2;3] Output: 4 Explanation: It takes 4 operations to make all elements in nums equal: 1. largest = 3 at index 4. nextLargest = 2. Reduce nums[4] to 2. nums = [1;1;2;2;2]. 2. largest = 2 at index 2. nextLargest = 1. Reduce nums[2] to 1. nums = [1;1;1;2;2]. 3. largest = 2 at index 3. nextLargest = 1. Reduce nums[3] to 1. nums = [1;1;1;1;2]. 4. largest = 2 at index 4. nextLargest = 1. Reduce nums[4] to 1. nums = [1;1;1;1;1]. Constraints: 1 <= nums.length <= 5 * 104 1 <= nums[i] <= 5 * 104
Salesforce,2592,Maximize Greatness of an Array,Med,"Array, Hash Table, Greedy, Counting",You are given two 0-indexed integer arrays nums1 and nums2; of equal length n. In one operation; you can swap the values of any two indices of nums1. The cost of this operation is the sum of the indices. Find the minimum total cost of performing the given operation any number of times such that nums1[i] != nums2[i] for all 0 <= i <= n - 1 after performing all the operations. Return the minimum total cost such that nums1 and nums2 satisfy the above condition. In case it is not possible; return -1. Example 1: Input: nums1 = [1;2;3;4;5]; nums2 = [1;2;3;4;5] Output: 10 Explanation: One of the ways we can perform the operations is: - Swap values at indices 0 and 3; incurring cost = 0 + 3 = 3. Now; nums1 = [4;2;3;1;5] - Swap values at indices 1 and 2; incurring cost = 1 + 2 = 3. Now; nums1 = [4;3;2;1;5]. - Swap values at indices 0 and 4; incurring cost = 0 + 4 = 4. Now; nums1 =[5;3;2;1;4]. We can see that for each index i; nums1[i] != nums2[i]. The cost required here is 10. Note that there are other ways to swap values; but it can be proven that it is not possible to obtain a cost less than 10. Example 2: Input: nums1 = [2;2;2;1;3]; nums2 = [1;2;2;3;3] Output: 10 Explanation: One of the ways we can perform the operations is: - Swap values at indices 2 and 3; incurring cost = 2 + 3 = 5. Now; nums1 = [2;2;1;2;3]. - Swap values at indices 1 and 4; incurring cost = 1 + 4 = 5. Now; nums1 = [2;3;1;2;2]. The total cost needed here is 10; which is the minimum possible. Example 3: Input: nums1 = [1;2;2]; nums2 = [1;2;2] Output: -1 Explanation: It can be shown that it is not possible to satisfy the given conditions irrespective of the number of operations we perform. Hence; we return -1. Constraints: n == nums1.length == nums2.length 1 <= n <= 105 1 <= nums1[i]; nums2[i] <= n
Salesforce,2,Add Two Numbers,Med,"Linked List, Math, Recursion",You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order; and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero; except the number 0 itself. Example 1: Input: l1 = [2;4;3]; l2 = [5;6;4] Output: [7;0;8] Explanation: 342 + 465 = 807. Example 2: Input: l1 = [0]; l2 = [0] Output: [0] Example 3: Input: l1 = [9;9;9;9;9;9;9]; l2 = [9;9;9;9] Output: [8;9;9;9;0;0;0;1] Constraints: The number of nodes in each linked list is in the range [1; 100]. 0 <= Node.val <= 9 It is guaranteed that the list represents a number that does not have leading zeros.
Salesforce,13,Roman to Integer,Easy,"Hash Table, Math, String","Roman numerals are represented by seven different symbols: I; V; X; L; C; D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example; 2 is written as II in Roman numeral; just two ones added together. 12 is written as XII; which is simply X + II. The number 27 is written as XXVII; which is XX + V + II. Roman numerals are usually written largest to smallest from left to right. However; the numeral for four is not IIII. Instead; the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine; which is written as IX. There are six instances where subtraction is used: I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral; convert it to an integer. Example 1: Input: s = ""III"" Output: 3 Explanation: III = 3. Example 2: Input: s = ""LVIII"" Output: 58 Explanation: L = 50; V= 5; III = 3. Example 3: Input: s = ""MCMXCIV"" Output: 1994 Explanation: M = 1000; CM = 900; XC = 90 and IV = 4. Constraints: 1 <= s.length <= 15 s contains only the characters ('I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M'). It is guaranteed that s is a valid roman numeral in the range [1; 3999]."
Salesforce,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Salesforce,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Salesforce,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Salesforce,48,Rotate Image,Med,"Array, Math, Matrix",You are given an n x n 2D matrix representing an image; rotate the image by 90 degrees (clockwise). You have to rotate the image in-place; which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [[7;4;1];[8;5;2];[9;6;3]] Example 2: Input: matrix = [[5;1;9;11];[2;4;8;10];[13;3;6;7];[15;14;12;16]] Output: [[15;13;2;5];[14;3;4;1];[12;6;8;9];[16;7;10;11]] Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000
Salesforce,51,N-Queens,Hard,"Array, Backtracking","The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n; return all distinct solutions to the n-queens puzzle. You may return the answer in any order. Each solution contains a distinct board configuration of the n-queens' placement; where 'Q' and '.' both indicate a queen and an empty space; respectively. Example 1: Input: n = 4 Output: [["".Q.."";""...Q"";""Q..."";""..Q.""];[""..Q."";""Q..."";""...Q"";"".Q..""]] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above Example 2: Input: n = 1 Output: [[""Q""]] Constraints: 1 <= n <= 9"
Salesforce,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Salesforce,64,Minimum Path Sum,Med,"Array, Dynamic Programming, Matrix",Given a m x n grid filled with non-negative numbers; find a path from top left to bottom right; which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1;3;1];[1;5;1];[4;2;1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. Example 2: Input: grid = [[1;2;3];[4;5;6]] Output: 12 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 200 0 <= grid[i][j] <= 200
Salesforce,72,Edit Distance,Med,"String, Dynamic Programming","Given two strings word1 and word2; return the minimum number of operations required to convert word1 to word2. You have the following three operations permitted on a word: Insert a character Delete a character Replace a character Example 1: Input: word1 = ""horse""; word2 = ""ros"" Output: 3 Explanation: horse -> rorse (replace 'h' with 'r') rorse -> rose (remove 'r') rose -> ros (remove 'e') Example 2: Input: word1 = ""intention""; word2 = ""execution"" Output: 5 Explanation: intention -> inention (remove 't') inention -> enention (replace 'i' with 'e') enention -> exention (replace 'n' with 'x') exention -> exection (replace 'n' with 'c') exection -> execution (insert 'u') Constraints: 0 <= word1.length; word2.length <= 500 word1 and word2 consist of lowercase English letters."
Salesforce,76,Minimum Window Substring,Hard,"Hash Table, String, Sliding Window","Given two strings s and t of lengths m and n respectively; return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring; return the empty string """". The testcases will be generated such that the answer is unique. Example 1: Input: s = ""ADOBECODEBANC""; t = ""ABC"" Output: ""BANC"" Explanation: The minimum window substring ""BANC"" includes 'A'; 'B'; and 'C' from string t. Example 2: Input: s = ""a""; t = ""a"" Output: ""a"" Explanation: The entire string s is the minimum window. Example 3: Input: s = ""a""; t = ""aa"" Output: """" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a'; return empty string. Constraints: m == s.length n == t.length 1 <= m; n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?"
Salesforce,78,Subsets,Med,"Array, Backtracking, Bit Manipulation",Given an integer array nums of unique elements; return all possible subsets (the power set). The solution set must not contain duplicate subsets. Return the solution in any order. Example 1: Input: nums = [1;2;3] Output: [[];[1];[2];[1;2];[3];[1;3];[2;3];[1;2;3]] Example 2: Input: nums = [0] Output: [[];[0]] Constraints: 1 <= nums.length <= 10 -10 <= nums[i] <= 10 All the numbers of nums are unique.
Salesforce,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Salesforce,114,Flatten Binary Tree to Linked List,Med,"Linked List, Stack, Tree, Depth-First Search, Binary Tree","Given the root of a binary tree; flatten the tree into a ""linked list"": The ""linked list"" should use the same TreeNode class where the right child pointer points to the next node in the list and the left child pointer is always null. The ""linked list"" should be in the same order as a pre-order traversal of the binary tree. Example 1: Input: root = [1;2;5;3;4;null;6] Output: [1;null;2;null;3;null;4;null;5;null;6] Example 2: Input: root = [] Output: [] Example 3: Input: root = [0] Output: [0] Constraints: The number of nodes in the tree is in the range [0; 2000]. -100 <= Node.val <= 100 Follow up: Can you flatten the tree in-place (with O(1) extra space)?"
Salesforce,120,Triangle,Med,"Array, Dynamic Programming",Given a triangle array; return the minimum path sum from top to bottom. For each step; you may move to an adjacent number of the row below. More formally; if you are on index i on the current row; you may move to either index i or index i + 1 on the next row. Example 1: Input: triangle = [[2];[3;4];[6;5;7];[4;1;8;3]] Output: 11 Explanation: The triangle looks like: 2 3 4 6 5 7 4 1 8 3 The minimum path sum from top to bottom is 2 + 3 + 5 + 1 = 11 (underlined above). Example 2: Input: triangle = [[-10]] Output: -10 Constraints: 1 <= triangle.length <= 200 triangle[0].length == 1 triangle[i].length == triangle[i - 1].length + 1 -104 <= triangle[i][j] <= 104 Follow up: Could you do this using only O(n) extra space; where n is the total number of rows in the triangle?
Salesforce,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Salesforce,151,Reverse Words in a String,Med,"Two Pointers, String","Given an input string s; reverse the order of the words. A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space. Return a string of the words in reverse order concatenated by a single space. Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces. Example 1: Input: s = ""the sky is blue"" Output: ""blue is sky the"" Example 2: Input: s = "" hello world "" Output: ""world hello"" Explanation: Your reversed string should not contain leading or trailing spaces. Example 3: Input: s = ""a good example"" Output: ""example good a"" Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string. Constraints: 1 <= s.length <= 104 s contains English letters (upper-case and lower-case); digits; and spaces ' '. There is at least one word in s. Follow-up: If the string data type is mutable in your language; can you solve it in-place with O(1) extra space?"
Salesforce,169,Majority Element,Easy,"Array, Hash Table, Divide and Conquer, Sorting, Counting",Given an array nums of size n; return the majority element. The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array. Example 1: Input: nums = [3;2;3] Output: 3 Example 2: Input: nums = [2;2;1;1;1;2;2] Output: 2 Constraints: n == nums.length 1 <= n <= 5 * 104 -109 <= nums[i] <= 109 Follow-up: Could you solve the problem in linear time and in O(1) space?
Salesforce,204,Count Primes,Med,"Array, Math, Enumeration, Number Theory",Given an integer n; return the number of prime numbers that are strictly less than n. Example 1: Input: n = 10 Output: 4 Explanation: There are 4 prime numbers less than 10; they are 2; 3; 5; 7. Example 2: Input: n = 0 Output: 0 Example 3: Input: n = 1 Output: 0 Constraints: 0 <= n <= 5 * 106
Salesforce,205,Isomorphic Strings,Easy,"Hash Table, String","Given two strings s and t; determine if they are isomorphic. Two strings s and t are isomorphic if the characters in s can be replaced to get t. All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character; but a character may map to itself. Example 1: Input: s = ""egg""; t = ""add"" Output: true Explanation: The strings s and t can be made identical by: Mapping 'e' to 'a'. Mapping 'g' to 'd'. Example 2: Input: s = ""foo""; t = ""bar"" Output: false Explanation: The strings s and t can not be made identical as 'o' needs to be mapped to both 'a' and 'r'. Example 3: Input: s = ""paper""; t = ""title"" Output: true Constraints: 1 <= s.length <= 5 * 104 t.length == s.length s and t consist of any valid ascii character."
Salesforce,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Salesforce,229,Majority Element II,Med,"Array, Hash Table, Sorting, Counting",Given an integer array of size n; find all elements that appear more than ⌊ n/3 ⌋ times. Example 1: Input: nums = [3;2;3] Output: [3] Example 2: Input: nums = [1] Output: [1] Example 3: Input: nums = [1;2] Output: [1;2] Constraints: 1 <= nums.length <= 5 * 104 -109 <= nums[i] <= 109 Follow up: Could you solve the problem in linear time and in O(1) space?
Salesforce,233,Number of Digit One,Hard,"Math, Dynamic Programming, Recursion",Given an integer n; count the total number of digit 1 appearing in all non-negative integers less than or equal to n. Example 1: Input: n = 13 Output: 6 Example 2: Input: n = 0 Output: 0 Constraints: 0 <= n <= 109
Salesforce,235,Lowest Common Ancestor of a Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given a binary search tree (BST); find the lowest common ancestor (LCA) node of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).” Example 1: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 8 Output: 6 Explanation: The LCA of nodes 2 and 8 is 6. Example 2: Input: root = [6;2;8;0;4;7;9;null;null;3;5]; p = 2; q = 4 Output: 2 Explanation: The LCA of nodes 2 and 4 is 2; since a node can be a descendant of itself according to the LCA definition. Example 3: Input: root = [2;1]; p = 2; q = 1 Output: 2 Constraints: The number of nodes in the tree is in the range [2; 105]. -109 <= Node.val <= 109 All Node.val are unique. p != q p and q will exist in the BST.
Salesforce,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Salesforce,241,Different Ways to Add Parentheses,Med,"Math, String, Dynamic Programming, Recursion, Memoization","Given a string expression of numbers and operators; return all possible results from computing all the different possible ways to group numbers and operators. You may return the answer in any order. The test cases are generated such that the output values fit in a 32-bit integer and the number of different results does not exceed 104. Example 1: Input: expression = ""2-1-1"" Output: [0;2] Explanation: ((2-1)-1) = 0 (2-(1-1)) = 2 Example 2: Input: expression = ""2*3-4*5"" Output: [-34;-14;-10;-10;10] Explanation: (2*(3-(4*5))) = -34 ((2*3)-(4*5)) = -14 ((2*(3-4))*5) = -10 (2*((3-4)*5)) = -10 (((2*3)-4)*5) = 10 Constraints: 1 <= expression.length <= 20 expression consists of digits and the operator '+'; '-'; and '*'. All the integer values in the input expression are in the range [0; 99]. The integer values in the input expression do not have a leading '-' or '+' denoting the sign."
Salesforce,277,Find the Celebrity,Med,"Two Pointers, Graph, Interactive",
Salesforce,286,Walls and Gates,Med,"Array, Breadth-First Search, Matrix",
Salesforce,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
Salesforce,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
Salesforce,354,Russian Doll Envelopes,Hard,"Array, Binary Search, Dynamic Programming, Sorting",You are given a 2D array of integers envelopes where envelopes[i] = [wi; hi] represents the width and the height of an envelope. One envelope can fit into another if and only if both the width and height of one envelope are greater than the other envelope's width and height. Return the maximum number of envelopes you can Russian doll (i.e.; put one inside the other). Note: You cannot rotate an envelope. Example 1: Input: envelopes = [[5;4];[6;4];[6;7];[2;3]] Output: 3 Explanation: The maximum number of envelopes you can Russian doll is 3 ([2;3] => [5;4] => [6;7]). Example 2: Input: envelopes = [[1;1];[1;1];[1;1]] Output: 1 Constraints: 1 <= envelopes.length <= 105 envelopes[i].length == 2 1 <= wi; hi <= 105
Salesforce,366,Find Leaves of Binary Tree,Med,"Tree, Depth-First Search, Binary Tree",
Salesforce,370,Range Addition,Med,"Array, Prefix Sum",
Salesforce,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Salesforce,394,Decode String,Med,"String, Stack, Recursion","Given an encoded string; return its decoded string. The encoding rule is: k[encoded_string]; where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer. You may assume that the input string is always valid; there are no extra white spaces; square brackets are well-formed; etc. Furthermore; you may assume that the original data does not contain any digits and that digits are only for those repeat numbers; k. For example; there will not be input like 3a or 2[4]. The test cases are generated so that the length of the output will never exceed 105. Example 1: Input: s = ""3[a]2[bc]"" Output: ""aaabcbc"" Example 2: Input: s = ""3[a2[c]]"" Output: ""accaccacc"" Example 3: Input: s = ""2[abc]3[cd]ef"" Output: ""abcabccdcdcdef"" Constraints: 1 <= s.length <= 30 s consists of lowercase English letters; digits; and square brackets '[]'. s is guaranteed to be a valid input. All the integers in s are in the range [1; 300]."
Salesforce,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Salesforce,450,Delete Node in a BST,Med,"Tree, Binary Search Tree, Binary Tree",Given a root node reference of a BST and a key; delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST. Basically; the deletion can be divided into two stages: Search for a node to remove. If the node is found; delete the node. Example 1: Input: root = [5;3;6;2;4;null;7]; key = 3 Output: [5;4;6;2;null;null;7] Explanation: Given key to delete is 3. So we find the node with value 3 and delete it. One valid answer is [5;4;6;2;null;null;7]; shown in the above BST. Please notice that another valid answer is [5;2;6;null;4;null;7] and it's also accepted. Example 2: Input: root = [5;3;6;2;4;null;7]; key = 0 Output: [5;3;6;2;4;null;7] Explanation: The tree does not contain a node with value = 0. Example 3: Input: root = []; key = 0 Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -105 <= Node.val <= 105 Each node has a unique value. root is a valid binary search tree. -105 <= key <= 105 Follow up: Could you solve it with time complexity O(height of tree)?
Salesforce,459,Repeated Substring Pattern,Easy,"String, String Matching","Given a string s; check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. Example 1: Input: s = ""abab"" Output: true Explanation: It is the substring ""ab"" twice. Example 2: Input: s = ""aba"" Output: false Example 3: Input: s = ""abcabcabcabc"" Output: true Explanation: It is the substring ""abc"" four times or the substring ""abcabc"" twice. Constraints: 1 <= s.length <= 104 s consists of lowercase English letters."
Salesforce,472,Concatenated Words,Hard,"Array, String, Dynamic Programming, Depth-First Search, Trie","Given an array of strings words (without duplicates); return all the concatenated words in the given list of words. A concatenated word is defined as a string that is comprised entirely of at least two shorter words (not necessarily distinct) in the given array. Example 1: Input: words = [""cat"";""cats"";""catsdogcats"";""dog"";""dogcatsdog"";""hippopotamuses"";""rat"";""ratcatdogcat""] Output: [""catsdogcats"";""dogcatsdog"";""ratcatdogcat""] Explanation: ""catsdogcats"" can be concatenated by ""cats""; ""dog"" and ""cats""; ""dogcatsdog"" can be concatenated by ""dog""; ""cats"" and ""dog""; ""ratcatdogcat"" can be concatenated by ""rat""; ""cat""; ""dog"" and ""cat"". Example 2: Input: words = [""cat"";""dog"";""catdog""] Output: [""catdog""] Constraints: 1 <= words.length <= 104 1 <= words[i].length <= 30 words[i] consists of only lowercase English letters. All the strings of words are unique. 1 <= sum(words[i].length) <= 105"
Salesforce,486,Predict the Winner,Med,"Array, Math, Dynamic Programming, Recursion, Game Theory",You are given an integer array nums. Two players are playing a game with this array: player 1 and player 2. Player 1 and player 2 take turns; with player 1 starting first. Both players start the game with a score of 0. At each turn; the player takes one of the numbers from either end of the array (i.e.; nums[0] or nums[nums.length - 1]) which reduces the size of the array by 1. The player adds the chosen number to their score. The game ends when there are no more elements in the array. Return true if Player 1 can win the game. If the scores of both players are equal; then player 1 is still the winner; and you should also return true. You may assume that both players are playing optimally. Example 1: Input: nums = [1;5;2] Output: false Explanation: Initially; player 1 can choose between 1 and 2. If he chooses 2 (or 1); then player 2 can choose from 1 (or 2) and 5. If player 2 chooses 5; then player 1 will be left with 1 (or 2). So; final score of player 1 is 1 + 2 = 3; and player 2 is 5. Hence; player 1 will never be the winner and you need to return false. Example 2: Input: nums = [1;5;233;7] Output: true Explanation: Player 1 first chooses 1. Then player 2 has to choose between 5 and 7. No matter which number player 2 choose; player 1 can choose 233. Finally; player 1 has more score (234) than player 2 (12); so you need to return True representing player1 can win. Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 107
Salesforce,494,Target Sum,Med,"Array, Dynamic Programming, Backtracking","You are given an integer array nums and an integer target. You want to build an expression out of nums by adding one of the symbols '+' and '-' before each integer in nums and then concatenate all the integers. For example; if nums = [2; 1]; you can add a '+' before 2 and a '-' before 1 and concatenate them to build the expression ""+2-1"". Return the number of different expressions that you can build; which evaluates to target. Example 1: Input: nums = [1;1;1;1;1]; target = 3 Output: 5 Explanation: There are 5 ways to assign symbols to make the sum of nums be target 3. -1 + 1 + 1 + 1 + 1 = 3 +1 - 1 + 1 + 1 + 1 = 3 +1 + 1 - 1 + 1 + 1 = 3 +1 + 1 + 1 - 1 + 1 = 3 +1 + 1 + 1 + 1 - 1 = 3 Example 2: Input: nums = [1]; target = 1 Output: 1 Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 1000 0 <= sum(nums[i]) <= 1000 -1000 <= target <= 1000"
Salesforce,557,Reverse Words in a String III,Easy,"Two Pointers, String","Given a string s; reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order. Example 1: Input: s = ""Let's take LeetCode contest"" Output: ""s'teL ekat edoCteeL tsetnoc"" Example 2: Input: s = ""Mr Ding"" Output: ""rM gniD"" Constraints: 1 <= s.length <= 5 * 104 s contains printable ASCII characters. s does not contain any leading or trailing spaces. There is at least one word in s. All the words in s are separated by a single space."
Salesforce,650,2 Keys Keyboard,Med,"Math, Dynamic Programming",There is only one character 'A' on the screen of a notepad. You can perform one of two operations on this notepad for each step: Copy All: You can copy all the characters present on the screen (a partial copy is not allowed). Paste: You can paste the characters which are copied last time. Given an integer n; return the minimum number of operations to get the character 'A' exactly n times on the screen. Example 1: Input: n = 3 Output: 3 Explanation: Initially; we have one character 'A'. In step 1; we use Copy All operation. In step 2; we use Paste operation to get 'AA'. In step 3; we use Paste operation to get 'AAA'. Example 2: Input: n = 1 Output: 0 Constraints: 1 <= n <= 1000
Salesforce,678,Valid Parenthesis String,Med,"String, Dynamic Programming, Stack, Greedy","Given a string s containing only three types of characters: '('; ')' and '*'; return true if s is valid. The following rules define a valid string: Any left parenthesis '(' must have a corresponding right parenthesis ')'. Any right parenthesis ')' must have a corresponding left parenthesis '('. Left parenthesis '(' must go before the corresponding right parenthesis ')'. '*' could be treated as a single right parenthesis ')' or a single left parenthesis '(' or an empty string """". Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""(*)"" Output: true Example 3: Input: s = ""(*))"" Output: true Constraints: 1 <= s.length <= 100 s[i] is '('; ')' or '*'."
Salesforce,692,Top K Frequent Words,Med,"Hash Table, String, Trie, Sorting, Heap (Priority Queue), Bucket Sort, Counting","Given an array of strings words and an integer k; return the k most frequent strings. Return the answer sorted by the frequency from highest to lowest. Sort the words with the same frequency by their lexicographical order. Example 1: Input: words = [""i"";""love"";""leetcode"";""i"";""love"";""coding""]; k = 2 Output: [""i"";""love""] Explanation: ""i"" and ""love"" are the two most frequent words. Note that ""i"" comes before ""love"" due to a lower alphabetical order. Example 2: Input: words = [""the"";""day"";""is"";""sunny"";""the"";""the"";""the"";""sunny"";""is"";""is""]; k = 4 Output: [""the"";""is"";""sunny"";""day""] Explanation: ""the""; ""is""; ""sunny"" and ""day"" are the four most frequent words; with the number of occurrence being 4; 3; 2 and 1 respectively. Constraints: 1 <= words.length <= 500 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. k is in the range [1; The number of unique words[i]] Follow-up: Could you solve it in O(n log(k)) time and O(n) extra space?"
Salesforce,724,Find Pivot Index,Easy,"Array, Prefix Sum",Given an array of integers nums; calculate the pivot index of this array. The pivot index is the index where the sum of all the numbers strictly to the left of the index is equal to the sum of all the numbers strictly to the index's right. If the index is on the left edge of the array; then the left sum is 0 because there are no elements to the left. This also applies to the right edge of the array. Return the leftmost pivot index. If no such index exists; return -1. Example 1: Input: nums = [1;7;3;6;5;6] Output: 3 Explanation: The pivot index is 3. Left sum = nums[0] + nums[1] + nums[2] = 1 + 7 + 3 = 11 Right sum = nums[4] + nums[5] = 5 + 6 = 11 Example 2: Input: nums = [1;2;3] Output: -1 Explanation: There is no index that satisfies the conditions in the problem statement. Example 3: Input: nums = [2;1;-1] Output: 0 Explanation: The pivot index is 0. Left sum = 0 (no elements to the left of index 0) Right sum = nums[1] + nums[2] = 1 + -1 = 0 Constraints: 1 <= nums.length <= 104 -1000 <= nums[i] <= 1000 Note: This question is the same as 1991: https://leetcode.com/problems/find-the-middle-index-in-array/
Salesforce,703,Kth Largest Element in a Stream,Easy,,
Salesforce,792,Number of Matching Subsequences,Med,"Array, Binary Search",Given an array of integers nums which is sorted in ascending order; and an integer target; write a function to search target in nums. If target exists; then return its index. Otherwise; return -1. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [-1;0;3;5;9;12]; target = 9 Output: 4 Explanation: 9 exists in nums and its index is 4 Example 2: Input: nums = [-1;0;3;5;9;12]; target = 2 Output: -1 Explanation: 2 does not exist in nums so return -1 Constraints: 1 <= nums.length <= 104 -104 < nums[i]; target < 104 All the integers in nums are unique. nums is sorted in ascending order.
Salesforce,831,Masking Personal Information,Med,"Array, Dynamic Programming, Prefix Sum",You are given an integer array nums and an integer k. You can partition the array into at most k non-empty adjacent subarrays. The score of a partition is the sum of the averages of each subarray. Note that the partition must use every integer in nums; and that the score is not necessarily an integer. Return the maximum score you can achieve of all the possible partitions. Answers within 10-6 of the actual answer will be accepted. Example 1: Input: nums = [9;1;2;3;9]; k = 3 Output: 20.00000 Explanation: The best choice is to partition nums into [9]; [1; 2; 3]; [9]. The answer is 9 + (1 + 2 + 3) / 3 + 9 = 20. We could have also partitioned nums into [9; 1]; [2]; [3; 9]; for example. That partition would lead to a score of 5 + 2 + 6 = 13; which is worse. Example 2: Input: nums = [1;2;3;4;5;6;7]; k = 4 Output: 20.50000 Constraints: 1 <= nums.length <= 100 1 <= nums[i] <= 104 1 <= k <= nums.length
Salesforce,876,Middle of the Linked List,Easy,"Array, Hash Table, Greedy, Sorting",Alice has some number of cards and she wants to rearrange the cards into groups so that each group is of size groupSize; and consists of groupSize consecutive cards. Given an integer array hand where hand[i] is the value written on the ith card and an integer groupSize; return true if she can rearrange the cards; or false otherwise. Example 1: Input: hand = [1;2;3;6;2;3;4;7;8]; groupSize = 3 Output: true Explanation: Alice's hand can be rearranged as [1;2;3];[2;3;4];[6;7;8] Example 2: Input: hand = [1;2;3;4;5]; groupSize = 4 Output: false Explanation: Alice's hand can not be rearranged into groups of 4. Constraints: 1 <= hand.length <= 104 0 <= hand[i] <= 109 1 <= groupSize <= hand.length Note: This question is the same as 1296: https://leetcode.com/problems/divide-array-in-sets-of-k-consecutive-numbers/
Salesforce,973,K Closest Points to Origin,Med,"String, Stack, Greedy, Queue","You are given two strings stamp and target. Initially; there is a string s of length target.length with all s[i] == '?'. In one turn; you can place stamp over s and replace every letter in the s with the corresponding letter from stamp. For example; if stamp = ""abc"" and target = ""abcba""; then s is ""?????"" initially. In one turn you can: place stamp at index 0 of s to obtain ""abc??""; place stamp at index 1 of s to obtain ""?abc?""; or place stamp at index 2 of s to obtain ""??abc"". Note that stamp must be fully contained in the boundaries of s in order to stamp (i.e.; you cannot place stamp at index 3 of s). We want to convert s to target using at most 10 * target.length turns. Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns; return an empty array. Example 1: Input: stamp = ""abc""; target = ""ababc"" Output: [0;2] Explanation: Initially s = ""?????"". - Place stamp at index 0 to get ""abc??"". - Place stamp at index 2 to get ""ababc"". [1;0;2] would also be accepted as an answer; as well as some other answers. Example 2: Input: stamp = ""abca""; target = ""aabcaca"" Output: [3;0;1] Explanation: Initially s = ""???????"". - Place stamp at index 3 to get ""???abca"". - Place stamp at index 0 to get ""abcabca"". - Place stamp at index 1 to get ""aabcaca"". Constraints: 1 <= stamp.length <= target.length <= 1000 stamp and target consist of lowercase English letters."
Salesforce,981,Time Based Key-Value Store,Med,"Array, String","You are given an array of n strings strs; all of the same length. The strings can be arranged such that there is one on each line; making a grid. For example; strs = [""abc""; ""bce""; ""cae""] can be arranged as follows: abc bce cae You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed); columns 0 ('a'; 'b'; 'c') and 2 ('c'; 'e'; 'e') are sorted; while column 1 ('b'; 'c'; 'a') is not; so you would delete column 1. Return the number of columns that you will delete. Example 1: Input: strs = [""cba"";""daf"";""ghi""] Output: 1 Explanation: The grid looks as follows: cba daf ghi Columns 0 and 2 are sorted; but column 1 is not; so you only need to delete 1 column. Example 2: Input: strs = [""a"";""b""] Output: 0 Explanation: The grid looks as follows: a b Column 0 is the only column and is sorted; so you will not delete any columns. Example 3: Input: strs = [""zyx"";""wvu"";""tsr""] Output: 3 Explanation: The grid looks as follows: zyx wvu tsr All 3 columns are not sorted; so you will delete all 3. Constraints: n == strs.length 1 <= n <= 100 1 <= strs[i].length <= 1000 strs[i] consists of lowercase English letters."
Salesforce,1032,Stream of Characters,Hard,"Array, String, Union Find, Graph","You are given an array of strings equations that represent relationships between variables where each string equations[i] is of length 4 and takes one of two different forms: ""xi==yi"" or ""xi!=yi"".Here; xi and yi are lowercase letters (not necessarily different) that represent one-letter variable names. Return true if it is possible to assign integers to variable names so as to satisfy all the given equations; or false otherwise. Example 1: Input: equations = [""a==b"";""b!=a""] Output: false Explanation: If we assign say; a = 1 and b = 1; then the first equation is satisfied; but not the second. There is no way to assign the variables to satisfy both equations. Example 2: Input: equations = [""b==a"";""a==b""] Output: true Explanation: We could assign a = 1 and b = 1 to satisfy both equations. Constraints: 1 <= equations.length <= 500 equations[i].length == 4 equations[i][0] is a lowercase letter. equations[i][1] is either '=' or '!'. equations[i][2] is '='. equations[i][3] is a lowercase letter."
Salesforce,1944,Number of Visible People in a Queue,Hard,"Array, String","A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each of the words consists of only uppercase and lowercase English letters (no punctuation). For example; ""Hello World""; ""HELLO""; and ""hello world hello world"" are all sentences. You are given a sentence s​​​​​​ and an integer k​​​​​​. You want to truncate s​​​​​​ such that it contains only the first k​​​​​​ words. Return s​​​​​​ after truncating it. Example 1: Input: s = ""Hello how are you Contestant""; k = 4 Output: ""Hello how are you"" Explanation: The words in s are [""Hello""; ""how"" ""are""; ""you""; ""Contestant""]. The first 4 words are [""Hello""; ""how""; ""are""; ""you""]. Hence; you should return ""Hello how are you"". Example 2: Input: s = ""What is the solution to this problem""; k = 4 Output: ""What is the solution"" Explanation: The words in s are [""What""; ""is"" ""the""; ""solution""; ""to""; ""this""; ""problem""]. The first 4 words are [""What""; ""is""; ""the""; ""solution""]. Hence; you should return ""What is the solution"". Example 3: Input: s = ""chopper is not a tanuki""; k = 5 Output: ""chopper is not a tanuki"" Constraints: 1 <= s.length <= 500 k is in the range [1; the number of words in s]. s consist of only lowercase and uppercase English letters and spaces. The words in s are separated by a single space. There are no leading or trailing spaces."
Salesforce,1283,Find the Smallest Divisor Given a Threshold,Med,String,"Given a date string in the form Day Month Year; where: Day is in the set {""1st""; ""2nd""; ""3rd""; ""4th""; ...; ""30th""; ""31st""}. Month is in the set {""Jan""; ""Feb""; ""Mar""; ""Apr""; ""May""; ""Jun""; ""Jul""; ""Aug""; ""Sep""; ""Oct""; ""Nov""; ""Dec""}. Year is in the range [1900; 2100]. Convert the date string to the format YYYY-MM-DD; where: YYYY denotes the 4 digit year. MM denotes the 2 digit month. DD denotes the 2 digit day. Example 1: Input: date = ""20th Oct 2052"" Output: ""2052-10-20"" Example 2: Input: date = ""6th Jun 1933"" Output: ""1933-06-06"" Example 3: Input: date = ""26th May 1960"" Output: ""1960-05-26"" Constraints: The given dates are guaranteed to be valid; so no error handling is necessary."
Salesforce,1381,Design a Stack With Increment Operation,Med,"Array, String, Dynamic Programming, Backtracking, Bit Manipulation, Bitmask","Given a list of words; list of single letters (might be repeating) and score of every character. Return the maximum score of any valid set of words formed by using the given letters (words[i] cannot be used two or more times). It is not necessary to use all characters in letters and each letter can only be used once. Score of letters 'a'; 'b'; 'c'; ... ;'z' is given by score[0]; score[1]; ... ; score[25] respectively. Example 1: Input: words = [""dog"";""cat"";""dad"";""good""]; letters = [""a"";""a"";""c"";""d"";""d"";""d"";""g"";""o"";""o""]; score = [1;0;9;5;0;0;3;0;0;0;0;0;0;0;2;0;0;0;0;0;0;0;0;0;0;0] Output: 23 Explanation: Score a=1; c=9; d=5; g=3; o=2 Given letters; we can form the words ""dad"" (5+1+5) and ""good"" (3+2+2+5) with a score of 23. Words ""dad"" and ""dog"" only get a score of 21. Example 2: Input: words = [""xxxz"";""ax"";""bx"";""cx""]; letters = [""z"";""a"";""b"";""c"";""x"";""x"";""x""]; score = [4;4;4;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;5;0;10] Output: 27 Explanation: Score a=4; b=4; c=4; x=5; z=10 Given letters; we can form the words ""ax"" (4+5); ""bx"" (4+5) and ""cx"" (4+5) with a score of 27. Word ""xxxz"" only get a score of 25. Example 3: Input: words = [""leetcode""]; letters = [""l"";""e"";""t"";""c"";""o"";""d""]; score = [0;0;1;1;1;0;0;0;0;0;0;1;0;0;1;0;0;0;0;1;0;0;0;0;0;0] Output: 0 Explanation: Letter ""e"" can only be used once. Constraints: 1 <= words.length <= 14 1 <= words[i].length <= 15 1 <= letters.length <= 100 letters[i].length == 1 score.length == 26 0 <= score[i] <= 10 words[i]; letters[i] contains only lower case English letters."
Salesforce,1552,Magnetic Force Between Two Balls,Med,"Array, Stack, Simulation","You are given an integer array target and an integer n. You have an empty stack with the two following operations: ""Push"": pushes an integer to the top of the stack. ""Pop"": removes the integer on the top of the stack. You also have a stream of the integers in the range [1; n]. Use the two stack operations to make the numbers in the stack (from the bottom to the top) equal to target. You should follow the following rules: If the stream of the integers is not empty; pick the next integer from the stream and push it to the top of the stack. If the stack is not empty; pop the integer at the top of the stack. If; at any moment; the elements in the stack (from the bottom to the top) are equal to target; do not read new integers from the stream and do not do more operations on the stack. Return the stack operations needed to build target following the mentioned rules. If there are multiple valid answers; return any of them. Example 1: Input: target = [1;3]; n = 3 Output: [""Push"";""Push"";""Pop"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Pop the integer on the top of the stack. s = [1]. Read 3 from the stream and push it to the stack. s = [1;3]. Example 2: Input: target = [1;2;3]; n = 3 Output: [""Push"";""Push"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Read 3 from the stream and push it to the stack. s = [1;2;3]. Example 3: Input: target = [1;2]; n = 4 Output: [""Push"";""Push""] Explanation: Initially the stack s is empty. The last element is the top of the stack. Read 1 from the stream and push it to the stack. s = [1]. Read 2 from the stream and push it to the stack. s = [1;2]. Since the stack (from the bottom to the top) is equal to target; we stop the stack operations. The answers that read integer 3 from the stream are not accepted. Constraints: 1 <= target.length <= 100 1 <= n <= 100 1 <= target[i] <= n target is strictly increasing."
Salesforce,1669,Merge In Between Linked Lists,Med,"Array, Dynamic Programming, Sorting",Given a wooden stick of length n units. The stick is labelled from 0 to n. For example; a stick of length 6 is labelled as follows: Given an integer array cuts where cuts[i] denotes a position you should perform a cut at. You should perform the cuts in order; you can change the order of the cuts as you wish. The cost of one cut is the length of the stick to be cut; the total cost is the sum of costs of all cuts. When you cut a stick; it will be split into two smaller sticks (i.e. the sum of their lengths is the length of the stick before the cut). Please refer to the first example for a better explanation. Return the minimum total cost of the cuts. Example 1: Input: n = 7; cuts = [1;3;4;5] Output: 16 Explanation: Using cuts order = [1; 3; 4; 5] as in the input leads to the following scenario: The first cut is done to a rod of length 7 so the cost is 7. The second cut is done to a rod of length 6 (i.e. the second part of the first cut); the third is done to a rod of length 4 and the last cut is to a rod of length 3. The total cost is 7 + 6 + 4 + 3 = 20. Rearranging the cuts to be [3; 5; 1; 4] for example will lead to a scenario with total cost = 16 (as shown in the example photo 7 + 4 + 3 + 2 = 16). Example 2: Input: n = 9; cuts = [5;6;1;4;2] Output: 22 Explanation: If you try the given cuts ordering the cost will be 25. There are much ordering with total cost <= 25; for example; the order [4; 6; 5; 2; 1] has total cost = 22 which is the minimum possible. Constraints: 2 <= n <= 106 1 <= cuts.length <= min(n - 1; 100) 1 <= cuts[i] <= n - 1 All the integers in cuts array are distinct.
Salesforce,2025,Maximum Number of Ways to Partition an Array,Hard,"Hash Table, String, Counting","You are given an array of strings words (0-indexed). In one operation; pick two distinct indices i and j; where words[i] is a non-empty string; and move any character from words[i] to any position in words[j]. Return true if you can make every string in words equal using any number of operations; and false otherwise. Example 1: Input: words = [""abc"";""aabc"";""bc""] Output: true Explanation: Move the first 'a' in words[1] to the front of words[2]; to make words[1] = ""abc"" and words[2] = ""abc"". All the strings are now equal to ""abc""; so return true. Example 2: Input: words = [""ab"";""a""] Output: false Explanation: It is impossible to make all the strings equal using the operation. Constraints: 1 <= words.length <= 100 1 <= words[i].length <= 100 words[i] consists of lowercase English letters."
Salesforce,2064,Minimized Maximum of Products Distributed to Any Store,Med,Database,
Salesforce,2355,Maximum Number of Books You Can Take,Hard,"Array, Sorting",Alice manages a company and has rented some floors of a building as office space. Alice has decided some of these floors should be special floors; used for relaxation only. You are given two integers bottom and top; which denote that Alice has rented all the floors from bottom to top (inclusive). You are also given the integer array special; where special[i] denotes a special floor that Alice has designated for relaxation. Return the maximum number of consecutive floors without a special floor. Example 1: Input: bottom = 2; top = 9; special = [4;6] Output: 3 Explanation: The following are the ranges (inclusive) of consecutive floors without a special floor: - (2; 3) with a total amount of 2 floors. - (5; 5) with a total amount of 1 floor. - (7; 9) with a total amount of 3 floors. Therefore; we return the maximum number which is 3 floors. Example 2: Input: bottom = 6; top = 8; special = [7;6;8] Output: 0 Explanation: Every floor rented is a special floor; so we return 0. Constraints: 1 <= special.length <= 105 1 <= bottom <= special[i] <= top <= 109 All the values of special are unique.
Salesforce,2472,Maximum Number of Non-overlapping Palindrome Substrings,Hard,"Array, Graph, Topological Sort, Matrix",You are given a positive integer k. You are also given: a 2D integer array rowConditions of size n where rowConditions[i] = [abovei; belowi]; and a 2D integer array colConditions of size m where colConditions[i] = [lefti; righti]. The two arrays contain integers from 1 to k. You have to build a k x k matrix that contains each of the numbers from 1 to k exactly once. The remaining cells should have the value 0. The matrix should also satisfy the following conditions: The number abovei should appear in a row that is strictly above the row at which the number belowi appears for all i from 0 to n - 1. The number lefti should appear in a column that is strictly left of the column at which the number righti appears for all i from 0 to m - 1. Return any matrix that satisfies the conditions. If no answer exists; return an empty matrix. Example 1: Input: k = 3; rowConditions = [[1;2];[3;2]]; colConditions = [[2;1];[3;2]] Output: [[3;0;0];[0;0;1];[0;2;0]] Explanation: The diagram above shows a valid example of a matrix that satisfies all the conditions. The row conditions are the following: - Number 1 is in row 1; and number 2 is in row 2; so 1 is above 2 in the matrix. - Number 3 is in row 0; and number 2 is in row 2; so 3 is above 2 in the matrix. The column conditions are the following: - Number 2 is in column 1; and number 1 is in column 2; so 2 is left of 1 in the matrix. - Number 3 is in column 0; and number 2 is in column 1; so 3 is left of 2 in the matrix. Note that there may be multiple correct answers. Example 2: Input: k = 3; rowConditions = [[1;2];[2;3];[3;1];[2;3]]; colConditions = [[2;1]] Output: [] Explanation: From the first two conditions; 3 has to be below 1 but the third conditions needs 3 to be above 1 to be satisfied. No matrix can satisfy all the conditions; so we return the empty matrix. Constraints: 2 <= k <= 400 1 <= rowConditions.length; colConditions.length <= 104 rowConditions[i].length == colConditions[i].length == 2 1 <= abovei; belowi; lefti; righti <= k abovei != belowi lefti != righti
Salesforce,2954,Count the Number of Infection Sequences,Hard,"Array, Hash Table, Sliding Window",You are given an integer array nums and two positive integers m and k. Return the maximum sum out of all almost unique subarrays of length k of nums. If no such subarray exists; return 0. A subarray of nums is almost unique if it contains at least m distinct elements. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [2;6;7;3;1;7]; m = 3; k = 4 Output: 18 Explanation: There are 3 almost unique subarrays of size k = 4. These subarrays are [2; 6; 7; 3]; [6; 7; 3; 1]; and [7; 3; 1; 7]. Among these subarrays; the one with the maximum sum is [2; 6; 7; 3] which has a sum of 18. Example 2: Input: nums = [5;9;9;2;4;5;4]; m = 1; k = 3 Output: 23 Explanation: There are 5 almost unique subarrays of size k. These subarrays are [5; 9; 9]; [9; 9; 2]; [9; 2; 4]; [2; 4; 5]; and [4; 5; 4]. Among these subarrays; the one with the maximum sum is [5; 9; 9] which has a sum of 23. Example 3: Input: nums = [1;2;1;2;1;2;1]; m = 3; k = 3 Output: 0 Explanation: There are no subarrays of size k = 3 that contain at least m = 3 distinct elements in the given array [1;2;1;2;1;2;1]. Therefore; no almost unique subarrays exist; and the maximum sum is 0. Constraints: 1 <= nums.length <= 2 * 104 1 <= m <= k <= nums.length 1 <= nums[i] <= 109
DoorDash,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
DoorDash,286,Walls and Gates,Med,"Array, Breadth-First Search, Matrix",
DoorDash,1235,Maximum Profit in Job Scheduling,Hard,,
DoorDash,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
DoorDash,826,Most Profit Assigning Work,Med,"Math, Dynamic Programming, Probability and Statistics",There are two types of soup: type A and type B. Initially; we have n ml of each type of soup. There are four kinds of operations: Serve 100 ml of soup A and 0 ml of soup B; Serve 75 ml of soup A and 25 ml of soup B; Serve 50 ml of soup A and 50 ml of soup B; and Serve 25 ml of soup A and 75 ml of soup B. When we serve some soup; we give it to someone; and we no longer have it. Each turn; we will choose from the four operations with an equal probability 0.25. If the remaining volume of soup is not enough to complete the operation; we will serve as much as possible. We stop once we no longer have some quantity of both types of soup. Note that we do not have an operation where all 100 ml's of soup B are used first. Return the probability that soup A will be empty first; plus half the probability that A and B become empty at the same time. Answers within 10-5 of the actual answer will be accepted. Example 1: Input: n = 50 Output: 0.62500 Explanation: If we choose the first two operations; A will become empty first. For the third operation; A and B will become empty at the same time. For the fourth operation; B will become empty first. So the total probability of A becoming empty first plus half the probability that A and B become empty at the same time; is 0.25 * (1 + 1 + 0.5 + 0) = 0.625. Example 2: Input: n = 100 Output: 0.71875 Constraints: 0 <= n <= 109
DoorDash,875,Koko Eating Bananas,Med,"Array, Two Pointers, Dynamic Programming, Enumeration",You may recall that an array arr is a mountain array if and only if: arr.length >= 3 There exists some index i (0-indexed) with 0 < i < arr.length - 1 such that: arr[0] < arr[1] < ... < arr[i - 1] < arr[i] arr[i] > arr[i + 1] > ... > arr[arr.length - 1] Given an integer array arr; return the length of the longest subarray; which is a mountain. Return 0 if there is no mountain subarray. Example 1: Input: arr = [2;1;4;7;3;2;5] Output: 5 Explanation: The largest mountain is [1;4;7;3;2] which has length 5. Example 2: Input: arr = [2;2;2] Output: 0 Explanation: There is no mountain. Constraints: 1 <= arr.length <= 104 0 <= arr[i] <= 104 Follow up: Can you solve it using only one pass? Can you solve it in O(1) space?
DoorDash,1166,Design File System,Med,"Array, Math, Dynamic Programming, Probability and Statistics",
DoorDash,1790,Check if One String Swap Can Make Strings Equal,Easy,"Hash Table, Two Pointers, Tree, Binary Tree",
DoorDash,1347,Minimum Number of Steps to Make Two Strings Anagram,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",
DoorDash,859,Buddy Strings,Easy,"Array, Linked List, Design, Queue","Design your implementation of the circular double-ended queue (deque). Implement the MyCircularDeque class: MyCircularDeque(int k) Initializes the deque with a maximum size of k. boolean insertFront() Adds an item at the front of Deque. Returns true if the operation is successful; or false otherwise. boolean insertLast() Adds an item at the rear of Deque. Returns true if the operation is successful; or false otherwise. boolean deleteFront() Deletes an item from the front of Deque. Returns true if the operation is successful; or false otherwise. boolean deleteLast() Deletes an item from the rear of Deque. Returns true if the operation is successful; or false otherwise. int getFront() Returns the front item from the Deque. Returns -1 if the deque is empty. int getRear() Returns the last item from Deque. Returns -1 if the deque is empty. boolean isEmpty() Returns true if the deque is empty; or false otherwise. boolean isFull() Returns true if the deque is full; or false otherwise. Example 1: Input [""MyCircularDeque""; ""insertLast""; ""insertLast""; ""insertFront""; ""insertFront""; ""getRear""; ""isFull""; ""deleteLast""; ""insertFront""; ""getFront""] [[3]; [1]; [2]; [3]; [4]; []; []; []; [4]; []] Output [null; true; true; true; false; 2; true; true; true; 4] Explanation MyCircularDeque myCircularDeque = new MyCircularDeque(3); myCircularDeque.insertLast(1); // return True myCircularDeque.insertLast(2); // return True myCircularDeque.insertFront(3); // return True myCircularDeque.insertFront(4); // return False; the queue is full. myCircularDeque.getRear(); // return 2 myCircularDeque.isFull(); // return True myCircularDeque.deleteLast(); // return True myCircularDeque.insertFront(4); // return True myCircularDeque.getFront(); // return 4 Constraints: 1 <= k <= 1000 0 <= value <= 1000 At most 2000 calls will be made to insertFront; insertLast; deleteFront; deleteLast; getFront; getRear; isEmpty; isFull."
DoorDash,1268,Search Suggestions System,Med,Database,Table: Users +----------------+---------+ | Column Name | Type | +----------------+---------+ | user_id | int | | join_date | date | | favorite_brand | varchar | +----------------+---------+ user_id is the primary key (column with unique values) of this table. This table has the info of the users of an online shopping website where users can sell and buy items. Table: Orders +---------------+---------+ | Column Name | Type | +---------------+---------+ | order_id | int | | order_date | date | | item_id | int | | buyer_id | int | | seller_id | int | +---------------+---------+ order_id is the primary key (column with unique values) of this table. item_id is a foreign key (reference column) to the Items table. buyer_id and seller_id are foreign keys to the Users table. Table: Items +---------------+---------+ | Column Name | Type | +---------------+---------+ | item_id | int | | item_brand | varchar | +---------------+---------+ item_id is the primary key (column with unique values) of this table. Write a solution to find for each user; the join date and the number of orders they made as a buyer in 2019. Return the result table in any order. The result format is in the following example. Example 1: Input: Users table: +---------+------------+----------------+ | user_id | join_date | favorite_brand | +---------+------------+----------------+ | 1 | 2018-01-01 | Lenovo | | 2 | 2018-02-09 | Samsung | | 3 | 2018-01-19 | LG | | 4 | 2018-05-21 | HP | +---------+------------+----------------+ Orders table: +----------+------------+---------+----------+-----------+ | order_id | order_date | item_id | buyer_id | seller_id | +----------+------------+---------+----------+-----------+ | 1 | 2019-08-01 | 4 | 1 | 2 | | 2 | 2018-08-02 | 2 | 1 | 3 | | 3 | 2019-08-03 | 3 | 2 | 3 | | 4 | 2018-08-04 | 1 | 4 | 2 | | 5 | 2018-08-04 | 1 | 3 | 4 | | 6 | 2019-08-05 | 2 | 2 | 4 | +----------+------------+---------+----------+-----------+ Items table: +---------+------------+ | item_id | item_brand | +---------+------------+ | 1 | Samsung | | 2 | Lenovo | | 3 | LG | | 4 | HP | +---------+------------+ Output: +-----------+------------+----------------+ | buyer_id | join_date | orders_in_2019 | +-----------+------------+----------------+ | 1 | 2018-01-01 | 1 | | 2 | 2018-02-09 | 2 | | 3 | 2018-01-19 | 0 | | 4 | 2018-05-21 | 0 | +-----------+------------+----------------+
DoorDash,658,Find K Closest Elements,Med,"Array, Two Pointers, Binary Search, Sliding Window, Sorting, Heap (Priority Queue)",Given a sorted integer array arr; two integers k and x; return the k closest integers to x in the array. The result should also be sorted in ascending order. An integer a is closer to x than an integer b if: |a - x| < |b - x|; or |a - x| == |b - x| and a < b Example 1: Input: arr = [1;2;3;4;5]; k = 4; x = 3 Output: [1;2;3;4] Example 2: Input: arr = [1;1;2;3;4;5]; k = 4; x = -1 Output: [1;1;2;3] Constraints: 1 <= k <= arr.length 1 <= arr.length <= 104 arr is sorted in ascending order. -104 <= arr[i]; x <= 104
DoorDash,1779,Find Nearest Point That Has the Same X or Y Coordinate,Easy,Database,
DoorDash,1834,Single-Threaded CPU,Med,"Array, Hash Table, Greedy",On a social network consisting of m users and some friendships between users; two users can communicate with each other if they know a common language. You are given an integer n; an array languages; and an array friendships where: There are n languages numbered 1 through n; languages[i] is the set of languages the i​​​​​​th​​​​ user knows; and friendships[i] = [u​​​​​​i​​​; v​​​​​​i] denotes a friendship between the users u​​​​​​​​​​​i​​​​​ and vi. You can choose one language and teach it to some users so that all friends can communicate with each other. Return the minimum number of users you need to teach. Note that friendships are not transitive; meaning if x is a friend of y and y is a friend of z; this doesn't guarantee that x is a friend of z. Example 1: Input: n = 2; languages = [[1];[2];[1;2]]; friendships = [[1;2];[1;3];[2;3]] Output: 1 Explanation: You can either teach user 1 the second language or user 2 the first language. Example 2: Input: n = 3; languages = [[2];[1;3];[1;2];[3]]; friendships = [[1;4];[1;2];[3;4];[2;3]] Output: 2 Explanation: Teach the third language to users 1 and 3; yielding two users to teach. Constraints: 2 <= n <= 500 languages.length == m 1 <= m <= 500 1 <= languages[i].length <= n 1 <= languages[i][j] <= n 1 <= u​​​​​​i < v​​​​​​i <= languages.length 1 <= friendships.length <= 500 All tuples (u​​​​​i; v​​​​​​i) are unique languages[i] contains only unique values
DoorDash,772,Basic Calculator III,Hard,"Array, Divide and Conquer, Tree, Matrix",Given a n * n matrix grid of 0's and 1's only. We want to represent grid with a Quad-Tree. Return the root of the Quad-Tree representing grid. A Quad-Tree is a tree data structure in which each internal node has exactly four children. Besides; each node has two attributes: val: True if the node represents a grid of 1's or False if the node represents a grid of 0's. Notice that you can assign the val to True or False when isLeaf is False; and both are accepted in the answer. isLeaf: True if the node is a leaf node on the tree or False if the node has four children. class Node { public boolean val; public boolean isLeaf; public Node topLeft; public Node topRight; public Node bottomLeft; public Node bottomRight; } We can construct a Quad-Tree from a two-dimensional area using the following steps: If the current grid has the same value (i.e all 1's or all 0's) set isLeaf True and set val to the value of the grid and set the four children to Null and stop. If the current grid has different values; set isLeaf to False and set val to any value and divide the current grid into four sub-grids as shown in the photo. Recurse for each of the children with the proper sub-grid. If you want to know more about the Quad-Tree; you can refer to the wiki. Quad-Tree format: You don't need to read this section for solving the problem. This is only if you want to understand the output format here. The output represents the serialized format of a Quad-Tree using level order traversal; where null signifies a path terminator where no node exists below. It is very similar to the serialization of the binary tree. The only difference is that the node is represented as a list [isLeaf; val]. If the value of isLeaf or val is True we represent it as 1 in the list [isLeaf; val] and if the value of isLeaf or val is False we represent it as 0. Example 1: Input: grid = [[0;1];[1;0]] Output: [[0;1];[1;0];[1;1];[1;1];[1;0]] Explanation: The explanation of this example is shown below: Notice that 0 represents False and 1 represents True in the photo representing the Quad-Tree. Example 2: Input: grid = [[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;1;1;1;1];[1;1;1;1;1;1;1;1];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0];[1;1;1;1;0;0;0;0]] Output: [[0;1];[1;1];[0;1];[1;1];[1;0];null;null;null;null;[1;0];[1;0];[1;1];[1;1]] Explanation: All values in the grid are not the same. We divide the grid into four sub-grids. The topLeft; bottomLeft and bottomRight each has the same value. The topRight have different values so we divide it into 4 sub-grids where each has the same value. Explanation is shown in the photo below: Constraints: n == grid.length == grid[i].length n == 2x where 0 <= x <= 6
DoorDash,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
DoorDash,1905,Count Sub Islands,Med,"Hash Table, Linked List, Design, Doubly-Linked List","There is an authentication system that works with authentication tokens. For each session; the user will receive a new authentication token that will expire timeToLive seconds after the currentTime. If the token is renewed; the expiry time will be extended to expire timeToLive seconds after the (potentially different) currentTime. Implement the AuthenticationManager class: AuthenticationManager(int timeToLive) constructs the AuthenticationManager and sets the timeToLive. generate(string tokenId; int currentTime) generates a new token with the given tokenId at the given currentTime in seconds. renew(string tokenId; int currentTime) renews the unexpired token with the given tokenId at the given currentTime in seconds. If there are no unexpired tokens with the given tokenId; the request is ignored; and nothing happens. countUnexpiredTokens(int currentTime) returns the number of unexpired tokens at the given currentTime. Note that if a token expires at time t; and another action happens on time t (renew or countUnexpiredTokens); the expiration takes place before the other actions. Example 1: Input [""AuthenticationManager""; ""renew""; ""generate""; ""countUnexpiredTokens""; ""generate""; ""renew""; ""renew""; ""countUnexpiredTokens""] [[5]; [""aaa""; 1]; [""aaa""; 2]; [6]; [""bbb""; 7]; [""aaa""; 8]; [""bbb""; 10]; [15]] Output [null; null; null; 1; null; null; null; 0] Explanation AuthenticationManager authenticationManager = new AuthenticationManager(5); // Constructs the AuthenticationManager with timeToLive = 5 seconds. authenticationManager.renew(""aaa""; 1); // No token exists with tokenId ""aaa"" at time 1; so nothing happens. authenticationManager.generate(""aaa""; 2); // Generates a new token with tokenId ""aaa"" at time 2. authenticationManager.countUnexpiredTokens(6); // The token with tokenId ""aaa"" is the only unexpired one at time 6; so return 1. authenticationManager.generate(""bbb""; 7); // Generates a new token with tokenId ""bbb"" at time 7. authenticationManager.renew(""aaa""; 8); // The token with tokenId ""aaa"" expired at time 7; and 8 >= 7; so at time 8 the renew request is ignored; and nothing happens. authenticationManager.renew(""bbb""; 10); // The token with tokenId ""bbb"" is unexpired at time 10; so the renew request is fulfilled and now the token will expire at time 15. authenticationManager.countUnexpiredTokens(15); // The token with tokenId ""bbb"" expires at time 15; and the token with tokenId ""aaa"" expired at time 7; so currently no token is unexpired; so return 0. Constraints: 1 <= timeToLive <= 108 1 <= currentTime <= 108 1 <= tokenId.length <= 5 tokenId consists only of lowercase letters. All calls to generate will contain unique values of tokenId. The values of currentTime across all the function calls will be strictly increasing. At most 2000 calls will be made to all functions combined."
DoorDash,556,Next Greater Element III,Med,"Math, Two Pointers, String",Given a positive integer n; find the smallest integer which has exactly the same digits existing in the integer n and is greater in value than n. If no such positive integer exists; return -1. Note that the returned integer should fit in 32-bit integer; if there is a valid answer but it does not fit in 32-bit integer; return -1. Example 1: Input: n = 12 Output: 21 Example 2: Input: n = 21 Output: -1 Constraints: 1 <= n <= 231 - 1
DoorDash,827,Making A Large Island,Hard,"Array, Two Pointers, String","Sometimes people repeat letters to represent extra feeling. For example: ""hello"" -> ""heeellooo"" ""hi"" -> ""hiiii"" In these strings like ""heeellooo""; we have groups of adjacent letters that are all the same: ""h""; ""eee""; ""ll""; ""ooo"". You are given a string s and an array of query strings words. A query word is stretchy if it can be made to be equal to s by any number of applications of the following extension operation: choose a group consisting of characters c; and add some number of characters c to the group so that the size of the group is three or more. For example; starting with ""hello""; we could do an extension on the group ""o"" to get ""hellooo""; but we cannot get ""helloo"" since the group ""oo"" has a size less than three. Also; we could do another extension like ""ll"" -> ""lllll"" to get ""helllllooo"". If s = ""helllllooo""; then the query word ""hello"" would be stretchy because of these two extension operations: query = ""hello"" -> ""hellooo"" -> ""helllllooo"" = s. Return the number of query strings that are stretchy. Example 1: Input: s = ""heeellooo""; words = [""hello""; ""hi""; ""helo""] Output: 1 Explanation: We can extend ""e"" and ""o"" in the word ""hello"" to get ""heeellooo"". We can't extend ""helo"" to get ""heeellooo"" because the group ""ll"" is not size 3 or more. Example 2: Input: s = ""zzzzzyyyyy""; words = [""zzyy"";""zy"";""zyy""] Output: 3 Constraints: 1 <= s.length; words.length <= 100 1 <= words[i].length <= 100 s and words[i] consist of lowercase letters."
DoorDash,317,Shortest Distance from All Buildings,Hard,"Array, Breadth-First Search, Matrix",
DoorDash,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
DoorDash,1359,Count All Valid Pickup and Delivery Options,Hard,"Math, Backtracking, Bit Manipulation",Given 2 integers n and start. Your task is return any permutation p of (0;1;2.....;2^n -1) such that : p[0] = start p[i] and p[i+1] differ by only one bit in their binary representation. p[0] and p[2^n -1] must also differ by only one bit in their binary representation. Example 1: Input: n = 2; start = 3 Output: [3;2;0;1] Explanation: The binary representation of the permutation is (11;10;00;01). All the adjacent element differ by one bit. Another valid permutation is [3;1;0;2] Example 2: Input: n = 3; start = 2 Output: [2;6;7;5;4;0;1;3] Explanation: The binary representation of the permutation is (010;110;111;101;100;000;001;011). Constraints: 1 <= n <= 16 0 <= start < 2 ^ n
DoorDash,621,Task Scheduler,Med,"Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting","You are given an array of CPU tasks; each labeled with a letter from A to Z; and a number n. Each CPU interval can be idle or allow the completion of one task. Tasks can be completed in any order; but there's a constraint: there has to be a gap of at least n intervals between two tasks with the same label. Return the minimum number of CPU intervals required to complete all tasks. Example 1: Input: tasks = [""A"";""A"";""A"";""B"";""B"";""B""]; n = 2 Output: 8 Explanation: A possible sequence is: A -> B -> idle -> A -> B -> idle -> A -> B. After completing task A; you must wait two intervals before doing A again. The same applies to task B. In the 3rd interval; neither A nor B can be done; so you idle. By the 4th interval; you can do A again as 2 intervals have passed. Example 2: Input: tasks = [""A"";""C"";""A"";""B"";""D"";""B""]; n = 1 Output: 6 Explanation: A possible sequence is: A -> B -> C -> D -> A -> B. With a cooling interval of 1; you can repeat a task after just one other task. Example 3: Input: tasks = [""A"";""A"";""A""; ""B"";""B"";""B""]; n = 3 Output: 10 Explanation: A possible sequence is: A -> B -> idle -> idle -> A -> B -> idle -> idle -> A -> B. There are only two types of tasks; A and B; which need to be separated by 3 intervals. This leads to idling twice between repetitions of these tasks. Constraints: 1 <= tasks.length <= 104 tasks[i] is an uppercase English letter. 0 <= n <= 100"
DoorDash,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
DoorDash,986,Interval List Intersections,Med,"Array, String, Enumeration","Given an array arr of 4 digits; find the latest 24-hour time that can be made using each digit exactly once. 24-hour times are formatted as ""HH:MM""; where HH is between 00 and 23; and MM is between 00 and 59. The earliest 24-hour time is 00:00; and the latest is 23:59. Return the latest 24-hour time in ""HH:MM"" format. If no valid time can be made; return an empty string. Example 1: Input: arr = [1;2;3;4] Output: ""23:41"" Explanation: The valid 24-hour times are ""12:34""; ""12:43""; ""13:24""; ""13:42""; ""14:23""; ""14:32""; ""21:34""; ""21:43""; ""23:14""; and ""23:41"". Of these times; ""23:41"" is the latest. Example 2: Input: arr = [5;5;5;5] Output: """" Explanation: There are no valid 24-hour times as ""55:55"" is not valid. Constraints: arr.length == 4 0 <= arr[i] <= 9"
DoorDash,1173,Immediate Food Delivery I,Easy,Database,
DoorDash,1174,Immediate Food Delivery II,Med,Database,Table: Product +--------------+---------+ | Column Name | Type | +--------------+---------+ | product_id | int | | product_name | varchar | | unit_price | int | +--------------+---------+ product_id is the primary key (column with unique values) of this table. Each row of this table indicates the name and the price of each product. Table: Sales +-------------+---------+ | Column Name | Type | +-------------+---------+ | seller_id | int | | product_id | int | | buyer_id | int | | sale_date | date | | quantity | int | | price | int | +-------------+---------+ This table can have duplicate rows. product_id is a foreign key (reference column) to the Product table. Each row of this table contains some information about one sale. Write a solution to report the products that were only sold in the first quarter of 2019. That is; between 2019-01-01 and 2019-03-31 inclusive. Return the result table in any order. The result format is in the following example. Example 1: Input: Product table: +------------+--------------+------------+ | product_id | product_name | unit_price | +------------+--------------+------------+ | 1 | S8 | 1000 | | 2 | G4 | 800 | | 3 | iPhone | 1400 | +------------+--------------+------------+ Sales table: +-----------+------------+----------+------------+----------+-------+ | seller_id | product_id | buyer_id | sale_date | quantity | price | +-----------+------------+----------+------------+----------+-------+ | 1 | 1 | 1 | 2019-01-21 | 2 | 2000 | | 1 | 2 | 2 | 2019-02-17 | 1 | 800 | | 2 | 2 | 3 | 2019-06-02 | 1 | 800 | | 3 | 3 | 4 | 2019-05-13 | 2 | 2800 | +-----------+------------+----------+------------+----------+-------+ Output: +-------------+--------------+ | product_id | product_name | +-------------+--------------+ | 1 | S8 | +-------------+--------------+ Explanation: The product with id 1 was only sold in the spring of 2019. The product with id 2 was sold in the spring of 2019 but was also sold after the spring of 2019. The product with id 3 was sold after spring 2019. We return only product 1 as it is the product that was only sold in the spring of 2019.
DoorDash,208,Implement Trie (Prefix Tree),Med,"Hash Table, String, Design, Trie","A trie (pronounced as ""try"") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure; such as autocomplete and spellchecker. Implement the Trie class: Trie() Initializes the trie object. void insert(String word) Inserts the string word into the trie. boolean search(String word) Returns true if the string word is in the trie (i.e.; was inserted before); and false otherwise. boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix; and false otherwise. Example 1: Input [""Trie""; ""insert""; ""search""; ""search""; ""startsWith""; ""insert""; ""search""] [[]; [""apple""]; [""apple""]; [""app""]; [""app""]; [""app""]; [""app""]] Output [null; null; true; false; true; null; true] Explanation Trie trie = new Trie(); trie.insert(""apple""); trie.search(""apple""); // return True trie.search(""app""); // return False trie.startsWith(""app""); // return True trie.insert(""app""); trie.search(""app""); // return True Constraints: 1 <= word.length; prefix.length <= 2000 word and prefix consist only of lowercase English letters. At most 3 * 104 calls in total will be made to insert; search; and startsWith."
DoorDash,296,Best Meeting Point,Hard,"Array, Math, Sorting, Matrix",
DoorDash,2565,Subsequence With the Minimum Score,Hard,"Array, Two Pointers, Greedy",
DoorDash,2611,Mice and Cheese,Med,,
DoorDash,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
DoorDash,227,Basic Calculator II,Med,"Math, String, Stack","Given a string s which represents an expression; evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231; 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""3+2*2"" Output: 7 Example 2: Input: s = "" 3/2 "" Output: 1 Example 3: Input: s = "" 3+5 / 2 "" Output: 5 Constraints: 1 <= s.length <= 3 * 105 s consists of integers and operators ('+'; '-'; '*'; '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0; 231 - 1]. The answer is guaranteed to fit in a 32-bit integer."
DoorDash,987,Vertical Order Traversal of a Binary Tree,Hard,"Array, Queue, Sorting, Simulation",You are given an integer array deck. There is a deck of cards where every card has a unique integer. The integer on the ith card is deck[i]. You can order the deck in any order you want. Initially; all the cards start face down (unrevealed) in one deck. You will do the following steps repeatedly until all cards are revealed: Take the top card of the deck; reveal it; and take it out of the deck. If there are still cards in the deck then put the next top card of the deck at the bottom of the deck. If there are still unrevealed cards; go back to step 1. Otherwise; stop. Return an ordering of the deck that would reveal the cards in increasing order. Note that the first entry in the answer is considered to be the top of the deck. Example 1: Input: deck = [17;13;11;2;3;5;7] Output: [2;13;3;11;5;17;7] Explanation: We get the deck in the order [17;13;11;2;3;5;7] (this order does not matter); and reorder it. After reordering; the deck starts as [2;13;3;11;5;17;7]; where 2 is the top of the deck. We reveal 2; and move 13 to the bottom. The deck is now [3;11;5;17;7;13]. We reveal 3; and move 11 to the bottom. The deck is now [5;17;7;13;11]. We reveal 5; and move 17 to the bottom. The deck is now [7;13;11;17]. We reveal 7; and move 13 to the bottom. The deck is now [11;17;13]. We reveal 11; and move 17 to the bottom. The deck is now [13;17]. We reveal 13; and move 17 to the bottom. The deck is now [17]. We reveal 17. Since all the cards revealed are in increasing order; the answer is correct. Example 2: Input: deck = [1;1000] Output: [1;1000] Constraints: 1 <= deck.length <= 1000 1 <= deck[i] <= 106 All the values of deck are unique.
DoorDash,2049,Count Nodes With the Highest Score,Med,"Array, Greedy, Sorting",You are playing a video game where you are defending your city from a group of n monsters. You are given a 0-indexed integer array dist of size n; where dist[i] is the initial distance in kilometers of the ith monster from the city. The monsters walk toward the city at a constant speed. The speed of each monster is given to you in an integer array speed of size n; where speed[i] is the speed of the ith monster in kilometers per minute. You have a weapon that; once fully charged; can eliminate a single monster. However; the weapon takes one minute to charge. The weapon is fully charged at the very start. You lose when any monster reaches your city. If a monster reaches the city at the exact moment the weapon is fully charged; it counts as a loss; and the game ends before you can use your weapon. Return the maximum number of monsters that you can eliminate before you lose; or n if you can eliminate all the monsters before they reach the city. Example 1: Input: dist = [1;3;4]; speed = [1;1;1] Output: 3 Explanation: In the beginning; the distances of the monsters are [1;3;4]. You eliminate the first monster. After a minute; the distances of the monsters are [X;2;3]. You eliminate the second monster. After a minute; the distances of the monsters are [X;X;2]. You eliminate the third monster. All 3 monsters can be eliminated. Example 2: Input: dist = [1;1;2;3]; speed = [1;1;1;1] Output: 1 Explanation: In the beginning; the distances of the monsters are [1;1;2;3]. You eliminate the first monster. After a minute; the distances of the monsters are [X;0;1;2]; so you lose. You can only eliminate 1 monster. Example 3: Input: dist = [3;2;4]; speed = [5;3;2] Output: 1 Explanation: In the beginning; the distances of the monsters are [3;2;4]. You eliminate the first monster. After a minute; the distances of the monsters are [X;0;2]; so you lose. You can only eliminate 1 monster. Constraints: n == dist.length == speed.length 1 <= n <= 105 1 <= dist[i]; speed[i] <= 105
DoorDash,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
DoorDash,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
DoorDash,778,Swim in Rising Water,Hard,"Hash Table, String, Greedy, Sorting, Heap (Priority Queue), Counting","Given a string s; rearrange the characters of s so that any two adjacent characters are not the same. Return any possible rearrangement of s or return """" if not possible. Example 1: Input: s = ""aab"" Output: ""aba"" Example 2: Input: s = ""aaab"" Output: """" Constraints: 1 <= s.length <= 500 s consists of lowercase English letters."
DoorDash,1944,Number of Visible People in a Queue,Hard,"Array, String","A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each of the words consists of only uppercase and lowercase English letters (no punctuation). For example; ""Hello World""; ""HELLO""; and ""hello world hello world"" are all sentences. You are given a sentence s​​​​​​ and an integer k​​​​​​. You want to truncate s​​​​​​ such that it contains only the first k​​​​​​ words. Return s​​​​​​ after truncating it. Example 1: Input: s = ""Hello how are you Contestant""; k = 4 Output: ""Hello how are you"" Explanation: The words in s are [""Hello""; ""how"" ""are""; ""you""; ""Contestant""]. The first 4 words are [""Hello""; ""how""; ""are""; ""you""]. Hence; you should return ""Hello how are you"". Example 2: Input: s = ""What is the solution to this problem""; k = 4 Output: ""What is the solution"" Explanation: The words in s are [""What""; ""is"" ""the""; ""solution""; ""to""; ""this""; ""problem""]. The first 4 words are [""What""; ""is""; ""the""; ""solution""]. Hence; you should return ""What is the solution"". Example 3: Input: s = ""chopper is not a tanuki""; k = 5 Output: ""chopper is not a tanuki"" Constraints: 1 <= s.length <= 500 k is in the range [1; the number of words in s]. s consist of only lowercase and uppercase English letters and spaces. The words in s are separated by a single space. There are no leading or trailing spaces."
DoorDash,84,Largest Rectangle in Histogram,Hard,"Array, Stack, Monotonic Stack",Given an array of integers heights representing the histogram's bar height where the width of each bar is 1; return the area of the largest rectangle in the histogram. Example 1: Input: heights = [2;1;5;6;2;3] Output: 10 Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area; which has an area = 10 units. Example 2: Input: heights = [2;4] Output: 4 Constraints: 1 <= heights.length <= 105 0 <= heights[i] <= 104
DoorDash,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
DoorDash,211,Design Add and Search Words Data Structure,Med,"String, Depth-First Search, Design, Trie","Design a data structure that supports adding new words and finding if a string matches any previously added string. Implement the WordDictionary class: WordDictionary() Initializes the object. void addWord(word) Adds word to the data structure; it can be matched later. bool search(word) Returns true if there is any string in the data structure that matches word or false otherwise. word may contain dots '.' where dots can be matched with any letter. Example: Input [""WordDictionary"";""addWord"";""addWord"";""addWord"";""search"";""search"";""search"";""search""] [[];[""bad""];[""dad""];[""mad""];[""pad""];[""bad""];["".ad""];[""b..""]] Output [null;null;null;null;false;true;true;true] Explanation WordDictionary wordDictionary = new WordDictionary(); wordDictionary.addWord(""bad""); wordDictionary.addWord(""dad""); wordDictionary.addWord(""mad""); wordDictionary.search(""pad""); // return False wordDictionary.search(""bad""); // return True wordDictionary.search("".ad""); // return True wordDictionary.search(""b..""); // return True Constraints: 1 <= word.length <= 25 word in addWord consists of lowercase English letters. word in search consist of '.' or lowercase English letters. There will be at most 2 dots in word for search queries. At most 104 calls will be made to addWord and search."
DoorDash,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
DoorDash,588,Design In-Memory File System,Hard,"Hash Table, String, Design, Trie, Sorting",
DoorDash,164,Maximum Gap,Med,"Array, Sorting, Bucket Sort, Radix Sort",Given an integer array nums; return the maximum difference between two successive elements in its sorted form. If the array contains less than two elements; return 0. You must write an algorithm that runs in linear time and uses linear extra space. Example 1: Input: nums = [3;6;9;1] Output: 3 Explanation: The sorted form of the array is [1;3;6;9]; either (3;6) or (6;9) has the maximum difference 3. Example 2: Input: nums = [10] Output: 0 Explanation: The array contains less than 2 elements; therefore return 0. Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 109
DoorDash,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
DoorDash,1730,Shortest Path to Get Food,Med,"Array, Binary Search, Sorting",You are given an array nums of non-negative integers. nums is considered special if there exists a number x such that there are exactly x numbers in nums that are greater than or equal to x. Notice that x does not have to be an element in nums. Return x if the array is special; otherwise; return -1. It can be proven that if nums is special; the value for x is unique. Example 1: Input: nums = [3;5] Output: 2 Explanation: There are 2 values (3 and 5) that are greater than or equal to 2. Example 2: Input: nums = [0;0] Output: -1 Explanation: No numbers fit the criteria for x. If x = 0; there should be 0 numbers >= x; but there are 2. If x = 1; there should be 1 number >= x; but there are 0. If x = 2; there should be 2 numbers >= x; but there are 0. x cannot be greater since there are only 2 numbers in nums. Example 3: Input: nums = [0;4;3;0;4] Output: 3 Explanation: There are 3 values that are greater than or equal to 3. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 1000
DoorDash,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
DoorDash,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
DoorDash,45,Jump Game II,Med,"Array, Dynamic Programming, Greedy",You are given a 0-indexed array of integers nums of length n. You are initially positioned at nums[0]. Each element nums[i] represents the maximum length of a forward jump from index i. In other words; if you are at nums[i]; you can jump to any nums[i + j] where: 0 <= j <= nums[i] and i + j < n Return the minimum number of jumps to reach nums[n - 1]. The test cases are generated such that you can reach nums[n - 1]. Example 1: Input: nums = [2;3;1;1;4] Output: 2 Explanation: The minimum number of jumps to reach the last index is 2. Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [2;3;0;1;4] Output: 2 Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 1000 It's guaranteed that you can reach nums[n - 1].
DoorDash,212,Word Search II,Hard,"Array, String, Backtracking, Trie, Matrix","Given an m x n board of characters and a list of strings words; return all words on the board. Each word must be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once in a word. Example 1: Input: board = [[""o"";""a"";""a"";""n""];[""e"";""t"";""a"";""e""];[""i"";""h"";""k"";""r""];[""i"";""f"";""l"";""v""]]; words = [""oath"";""pea"";""eat"";""rain""] Output: [""eat"";""oath""] Example 2: Input: board = [[""a"";""b""];[""c"";""d""]]; words = [""abcb""] Output: [] Constraints: m == board.length n == board[i].length 1 <= m; n <= 12 board[i][j] is a lowercase English letter. 1 <= words.length <= 3 * 104 1 <= words[i].length <= 10 words[i] consists of lowercase English letters. All the strings of words are unique."
DoorDash,277,Find the Celebrity,Med,"Two Pointers, Graph, Interactive",
DoorDash,542,01 Matrix,Med,"Array, Dynamic Programming, Breadth-First Search, Matrix",Given an m x n binary matrix mat; return the distance of the nearest 0 for each cell. The distance between two adjacent cells is 1. Example 1: Input: mat = [[0;0;0];[0;1;0];[0;0;0]] Output: [[0;0;0];[0;1;0];[0;0;0]] Example 2: Input: mat = [[0;0;0];[0;1;0];[1;1;1]] Output: [[0;0;0];[0;1;0];[1;2;1]] Constraints: m == mat.length n == mat[i].length 1 <= m; n <= 104 1 <= m * n <= 104 mat[i][j] is either 0 or 1. There is at least one 0 in mat.
DoorDash,695,Max Area of Island,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n binary matrix grid. An island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. The area of an island is the number of cells with a value 1 in the island. Return the maximum area of an island in grid. If there is no island; return 0. Example 1: Input: grid = [[0;0;1;0;0;0;0;1;0;0;0;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;1;1;0;1;0;0;0;0;0;0;0;0];[0;1;0;0;1;1;0;0;1;0;1;0;0];[0;1;0;0;1;1;0;0;1;1;1;0;0];[0;0;0;0;0;0;0;0;0;0;1;0;0];[0;0;0;0;0;0;0;1;1;1;0;0;0];[0;0;0;0;0;0;0;1;1;0;0;0;0]] Output: 6 Explanation: The answer is not 11; because the island must be connected 4-directionally. Example 2: Input: grid = [[0;0;0;0;0;0;0;0]] Output: 0 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 50 grid[i][j] is either 0 or 1.
DoorDash,1011,Capacity To Ship Packages Within D Days,Med,"Tree, Depth-First Search, Binary Tree",You are given the root of a binary tree with n nodes; where each node is uniquely assigned a value from 1 to n. You are also given a sequence of n values voyage; which is the desired pre-order traversal of the binary tree. Any node in the binary tree can be flipped by swapping its left and right subtrees. For example; flipping node 1 will have the following effect: Flip the smallest number of nodes so that the pre-order traversal of the tree matches voyage. Return a list of the values of all flipped nodes. You may return the answer in any order. If it is impossible to flip the nodes in the tree to make the pre-order traversal match voyage; return the list [-1]. Example 1: Input: root = [1;2]; voyage = [2;1] Output: [-1] Explanation: It is impossible to flip the nodes such that the pre-order traversal matches voyage. Example 2: Input: root = [1;2;3]; voyage = [1;3;2] Output: [1] Explanation: Flipping node 1 swaps nodes 2 and 3; so the pre-order traversal matches voyage. Example 3: Input: root = [1;2;3]; voyage = [1;2;3] Output: [] Explanation: The tree's pre-order traversal already matches voyage; so no nodes need to be flipped. Constraints: The number of nodes in the tree is n. n == voyage.length 1 <= n <= 100 1 <= Node.val; voyage[i] <= n All the values in the tree are unique. All the values in voyage are unique.
DoorDash,1143,Longest Common Subsequence,Med,"Array, Hash Table, Binary Search, Matrix, Counting",
DoorDash,36,Valid Sudoku,Med,"Array, Hash Table, Matrix","Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules: Each row must contain the digits 1-9 without repetition. Each column must contain the digits 1-9 without repetition. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition. Note: A Sudoku board (partially filled) could be valid but is not necessarily solvable. Only the filled cells need to be validated according to the mentioned rules. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: true Example 2: Input: board = [[""8"";""3"";""."";""."";""7"";""."";""."";""."";"".""] ;[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""] ;[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""] ;[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""] ;[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""] ;[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""] ;[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""] ;[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""] ;[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: false Explanation: Same as Example 1; except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box; it is invalid. Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit 1-9 or '.'."
DoorDash,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
DoorDash,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
DoorDash,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
DoorDash,253,Meeting Rooms II,Med,"Array, Two Pointers, Greedy, Sorting, Heap (Priority Queue), Prefix Sum",
DoorDash,283,Move Zeroes,Easy,"Array, Two Pointers",Given an integer array nums; move all 0's to the end of it while maintaining the relative order of the non-zero elements. Note that you must do this in-place without making a copy of the array. Example 1: Input: nums = [0;1;0;3;12] Output: [1;3;12;0;0] Example 2: Input: nums = [0] Output: [0] Constraints: 1 <= nums.length <= 104 -231 <= nums[i] <= 231 - 1 Follow up: Could you minimize the total number of operations done?
DoorDash,314,Binary Tree Vertical Order Traversal,Med,"Hash Table, Tree, Depth-First Search, Breadth-First Search, Sorting, Binary Tree",
DoorDash,347,Top K Frequent Elements,Med,"Array, Hash Table, Divide and Conquer, Sorting, Heap (Priority Queue), Bucket Sort, Counting, Quickselect",Given an integer array nums and an integer k; return the k most frequent elements. You may return the answer in any order. Example 1: Input: nums = [1;1;1;2;2;3]; k = 2 Output: [1;2] Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 k is in the range [1; the number of unique elements in the array]. It is guaranteed that the answer is unique. Follow up: Your algorithm's time complexity must be better than O(n log n); where n is the array's size.
DoorDash,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
DoorDash,547,Number of Provinces,Med,"Depth-First Search, Breadth-First Search, Union Find, Graph",There are n cities. Some of them are connected; while some are not. If city a is connected directly with city b; and city b is connected directly with city c; then city a is connected indirectly with city c. A province is a group of directly or indirectly connected cities and no other cities outside of the group. You are given an n x n matrix isConnected where isConnected[i][j] = 1 if the ith city and the jth city are directly connected; and isConnected[i][j] = 0 otherwise. Return the total number of provinces. Example 1: Input: isConnected = [[1;1;0];[1;1;0];[0;0;1]] Output: 2 Example 2: Input: isConnected = [[1;0;0];[0;1;0];[0;0;1]] Output: 3 Constraints: 1 <= n <= 200 n == isConnected.length n == isConnected[i].length isConnected[i][j] is 1 or 0. isConnected[i][i] == 1 isConnected[i][j] == isConnected[j][i]
DoorDash,759,Employee Free Time,Hard,"Array, Greedy, Sorting",You are given a 2D integer array intervals where intervals[i] = [starti; endi] represents all the integers from starti to endi inclusively. A containing set is an array nums where each interval from intervals has at least two integers in nums. For example; if intervals = [[1;3]; [3;7]; [8;9]]; then [1;2;4;7;8;9] and [2;3;4;8;9] are containing sets. Return the minimum possible size of a containing set. Example 1: Input: intervals = [[1;3];[3;7];[8;9]] Output: 5 Explanation: let nums = [2; 3; 4; 8; 9]. It can be shown that there cannot be any containing array of size 4. Example 2: Input: intervals = [[1;3];[1;4];[2;5];[3;5]] Output: 3 Explanation: let nums = [2; 3; 4]. It can be shown that there cannot be any containing array of size 2. Example 3: Input: intervals = [[1;2];[2;3];[2;4];[4;5]] Output: 5 Explanation: let nums = [1; 2; 3; 4; 5]. It can be shown that there cannot be any containing array of size 4. Constraints: 1 <= intervals.length <= 3000 intervals[i].length == 2 0 <= starti < endi <= 108
DoorDash,1152,Analyze User Website Visit Pattern,Med,"Greedy, Heap (Priority Queue)",
DoorDash,1383,Maximum Performance of a Team,Hard,Math,
DoorDash,1472,Design Browser History,Med,"Hash Table, String, Counting","You are given a string s. Reorder the string using the following algorithm: Remove the smallest character from s and append it to the result. Remove the smallest character from s that is greater than the last appended character; and append it to the result. Repeat step 2 until no more characters can be removed. Remove the largest character from s and append it to the result. Remove the largest character from s that is smaller than the last appended character; and append it to the result. Repeat step 5 until no more characters can be removed. Repeat steps 1 through 6 until all characters from s have been removed. If the smallest or largest character appears more than once; you may choose any occurrence to append to the result. Return the resulting string after reordering s using this algorithm. Example 1: Input: s = ""aaaabbbbcccc"" Output: ""abccbaabccba"" Explanation: After steps 1; 2 and 3 of the first iteration; result = ""abc"" After steps 4; 5 and 6 of the first iteration; result = ""abccba"" First iteration is done. Now s = ""aabbcc"" and we go back to step 1 After steps 1; 2 and 3 of the second iteration; result = ""abccbaabc"" After steps 4; 5 and 6 of the second iteration; result = ""abccbaabccba"" Example 2: Input: s = ""rat"" Output: ""art"" Explanation: The word ""rat"" becomes ""art"" after re-ordering it with the mentioned algorithm. Constraints: 1 <= s.length <= 500 s consists of only lowercase English letters."
DoorDash,1522,Diameter of N-Ary Tree,Med,"Array, Math, Dynamic Programming, Game Theory","Alice and Bob continue their games with piles of stones. There are several stones arranged in a row; and each stone has an associated value which is an integer given in the array stoneValue. Alice and Bob take turns; with Alice starting first. On each player's turn; that player can take 1; 2; or 3 stones from the first remaining stones in the row. The score of each player is the sum of the values of the stones taken. The score of each player is 0 initially. The objective of the game is to end with the highest score; and the winner is the player with the highest score and there could be a tie. The game continues until all the stones have been taken. Assume Alice and Bob play optimally. Return ""Alice"" if Alice will win; ""Bob"" if Bob will win; or ""Tie"" if they will end the game with the same score. Example 1: Input: stoneValue = [1;2;3;7] Output: ""Bob"" Explanation: Alice will always lose. Her best move will be to take three piles and the score become 6. Now the score of Bob is 7 and Bob wins. Example 2: Input: stoneValue = [1;2;3;-9] Output: ""Alice"" Explanation: Alice must choose all the three piles at the first move to win and leave Bob with negative score. If Alice chooses one pile her score will be 1 and the next move Bob's score becomes 5. In the next move; Alice will take the pile with value = -9 and lose. If Alice chooses two piles her score will be 3 and the next move Bob's score becomes 3. In the next move; Alice will take the pile with value = -9 and also lose. Remember that both play optimally so here Alice will choose the scenario that makes her win. Example 3: Input: stoneValue = [1;2;3;6] Output: ""Tie"" Explanation: Alice cannot win this game. She can end the game in a draw if she decided to choose all the first three piles; otherwise she will lose. Constraints: 1 <= stoneValue.length <= 5 * 104 -1000 <= stoneValue[i] <= 1000"
DoorDash,1804,Implement Trie II (Prefix Tree),Med,"String, Greedy","You are given a binary string binary consisting of only 0's or 1's. You can apply each of the following operations any number of times: Operation 1: If the number contains the substring ""00""; you can replace it with ""10"". For example; ""00010"" -> ""10010"" Operation 2: If the number contains the substring ""10""; you can replace it with ""01"". For example; ""00010"" -> ""00001"" Return the maximum binary string you can obtain after any number of operations. Binary string x is greater than binary string y if x's decimal representation is greater than y's decimal representation. Example 1: Input: binary = ""000110"" Output: ""111011"" Explanation: A valid transformation sequence can be: ""000110"" -> ""000101"" ""000101"" -> ""100101"" ""100101"" -> ""110101"" ""110101"" -> ""110011"" ""110011"" -> ""111011"" Example 2: Input: binary = ""01"" Output: ""01"" Explanation: ""01"" cannot be transformed any further. Constraints: 1 <= binary.length <= 105 binary consist of '0' and '1'."
DoorDash,2065,Maximum Path Quality of a Graph,Hard,"Array, Depth-First Search, Union Find, Graph",
DoorDash,2185,Counting Words With a Given Prefix,Easy,Database,
DoorDash,2365,Task Scheduler II,Med,String,"Given a string s and a character letter; return the percentage of characters in s that equal letter rounded down to the nearest whole percent. Example 1: Input: s = ""foobar""; letter = ""o"" Output: 33 Explanation: The percentage of characters in s that equal the letter 'o' is 2 / 6 * 100% = 33% when rounded down; so we return 33. Example 2: Input: s = ""jjjj""; letter = ""k"" Output: 0 Explanation: The percentage of characters in s that equal the letter 'k' is 0%; so we return 0. Constraints: 1 <= s.length <= 100 s consists of lowercase English letters. letter is a lowercase English letter."
Goldman Sachs,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Goldman Sachs,1041,Robot Bounded In Circle,Med,"Array, Matrix, Simulation","You are given an 8 x 8 matrix representing a chessboard. There is exactly one white rook represented by 'R'; some number of white bishops 'B'; and some number of black pawns 'p'. Empty squares are represented by '.'. A rook can move any number of squares horizontally or vertically (up; down; left; right) until it reaches another piece or the edge of the board. A rook is attacking a pawn if it can move to the pawn's square in one move. Note: A rook cannot move through other pieces; such as bishops or pawns. This means a rook cannot attack a pawn if there is another piece blocking the path. Return the number of pawns the white rook is attacking. Example 1: Input: board = [[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""."";""."";""."";""R"";""."";""."";""."";""p""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""]] Output: 3 Explanation: In this example; the rook is attacking all the pawns. Example 2: Input: board = [[""."";""."";""."";""."";""."";""."";"".""];[""."";""p"";""p"";""p"";""p"";""p"";""."";"".""];[""."";""p"";""p"";""B"";""p"";""p"";""."";"".""];[""."";""p"";""B"";""R"";""B"";""p"";""."";"".""];[""."";""p"";""p"";""B"";""p"";""p"";""."";"".""];[""."";""p"";""p"";""p"";""p"";""p"";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""]] Output: 0 Explanation: The bishops are blocking the rook from attacking any of the pawns. Example 3: Input: board = [[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""p"";""p"";""."";""R"";""."";""p"";""B"";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""];[""."";""."";""."";""B"";""."";""."";""."";"".""];[""."";""."";""."";""p"";""."";""."";""."";"".""];[""."";""."";""."";""."";""."";""."";""."";"".""]] Output: 3 Explanation: The rook is attacking the pawns at positions b5; d6; and f5. Constraints: board.length == 8 board[i].length == 8 board[i][j] is either 'R'; '.'; 'B'; or 'p' There is exactly one cell with board[i][j] == 'R'"
Goldman Sachs,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Goldman Sachs,166,Fraction to Recurring Decimal,Med,"Hash Table, Math, String","Given two integers representing the numerator and denominator of a fraction; return the fraction in string format. If the fractional part is repeating; enclose the repeating part in parentheses. If multiple answers are possible; return any of them. It is guaranteed that the length of the answer string is less than 104 for all the given inputs. Example 1: Input: numerator = 1; denominator = 2 Output: ""0.5"" Example 2: Input: numerator = 2; denominator = 1 Output: ""2"" Example 3: Input: numerator = 4; denominator = 333 Output: ""0.(012)"" Constraints: -231 <= numerator; denominator <= 231 - 1 denominator != 0"
Goldman Sachs,387,First Unique Character in a String,Easy,"Hash Table, String, Queue, Counting","Given a string s; find the first non-repeating character in it and return its index. If it does not exist; return -1. Example 1: Input: s = ""leetcode"" Output: 0 Explanation: The character 'l' at index 0 is the first character that does not occur at any other index. Example 2: Input: s = ""loveleetcode"" Output: 2 Example 3: Input: s = ""aabb"" Output: -1 Constraints: 1 <= s.length <= 105 s consists of only lowercase English letters."
Goldman Sachs,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Goldman Sachs,780,Reaching Points,Hard,"Array, Stack, Greedy, Sorting, Monotonic Stack",You are given an integer array arr of length n that represents a permutation of the integers in the range [0; n - 1]. We split arr into some number of chunks (i.e.; partitions); and individually sort each chunk. After concatenating them; the result should equal the sorted array. Return the largest number of chunks we can make to sort the array. Example 1: Input: arr = [4;3;2;1;0] Output: 1 Explanation: Splitting into two or more chunks will not return the required result. For example; splitting into [4; 3]; [2; 1; 0] will result in [3; 4; 0; 1; 2]; which isn't sorted. Example 2: Input: arr = [1;0;2;3;4] Output: 4 Explanation: We can split into two chunks; such as [1; 0]; [2; 3; 4]. However; splitting into [1; 0]; [2]; [3]; [4] is the highest number of chunks possible. Constraints: n == arr.length 1 <= n <= 10 0 <= arr[i] < n All the elements of arr are unique.
Goldman Sachs,1086,High Five,Easy,"Math, Dynamic Programming, Brainteaser, Game Theory",Alice and Bob take turns playing a game; with Alice starting first. Initially; there is a number n on the chalkboard. On each player's turn; that player makes a move consisting of: Choosing any x with 0 < x < n and n % x == 0. Replacing the number n on the chalkboard with n - x. Also; if a player cannot make a move; they lose the game. Return true if and only if Alice wins the game; assuming both players play optimally. Example 1: Input: n = 2 Output: true Explanation: Alice chooses 1; and Bob has no more moves. Example 2: Input: n = 3 Output: false Explanation: Alice chooses 1; Bob chooses 1; and Alice has no more moves. Constraints: 1 <= n <= 1000
Goldman Sachs,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Goldman Sachs,844,Backspace String Compare,Easy,,
Goldman Sachs,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Goldman Sachs,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Goldman Sachs,1010,Pairs of Songs With Total Durations Divisible by 60,Med,"Hash Table, Math, Enumeration",Given three integers x; y; and bound; return a list of all the powerful integers that have a value less than or equal to bound. An integer is powerful if it can be represented as xi + yj for some integers i >= 0 and j >= 0. You may return the answer in any order. In your answer; each value should occur at most once. Example 1: Input: x = 2; y = 3; bound = 10 Output: [2;3;4;5;7;9;10] Explanation: 2 = 20 + 30 3 = 21 + 30 4 = 20 + 31 5 = 21 + 31 7 = 22 + 31 9 = 23 + 30 10 = 20 + 32 Example 2: Input: x = 3; y = 5; bound = 15 Output: [2;4;6;8;10;14] Constraints: 1 <= x; y <= 100 0 <= bound <= 106
Goldman Sachs,443,String Compression,Med,"Two Pointers, String","Given an array of characters chars; compress it using the following algorithm: Begin with an empty string s. For each group of consecutive repeating characters in chars: If the group's length is 1; append the character to s. Otherwise; append the character followed by the group's length. The compressed string s should not be returned separately; but instead; be stored in the input character array chars. Note that group lengths that are 10 or longer will be split into multiple characters in chars. After you are done modifying the input array; return the new length of the array. You must write an algorithm that uses only constant extra space. Example 1: Input: chars = [""a"";""a"";""b"";""b"";""c"";""c"";""c""] Output: Return 6; and the first 6 characters of the input array should be: [""a"";""2"";""b"";""2"";""c"";""3""] Explanation: The groups are ""aa""; ""bb""; and ""ccc"". This compresses to ""a2b2c3"". Example 2: Input: chars = [""a""] Output: Return 1; and the first character of the input array should be: [""a""] Explanation: The only group is ""a""; which remains uncompressed since it's a single character. Example 3: Input: chars = [""a"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b"";""b""] Output: Return 4; and the first 4 characters of the input array should be: [""a"";""b"";""1"";""2""]. Explanation: The groups are ""a"" and ""bbbbbbbbbbbb"". This compresses to ""ab12"". Constraints: 1 <= chars.length <= 2000 chars[i] is a lowercase English letter; uppercase English letter; digit; or symbol."
Goldman Sachs,1823,Find the Winner of the Circular Game,Med,"String, Counting","You are given a string s of even length. Split this string into two halves of equal lengths; and let a be the first half and b be the second half. Two strings are alike if they have the same number of vowels ('a'; 'e'; 'i'; 'o'; 'u'; 'A'; 'E'; 'I'; 'O'; 'U'). Notice that s contains uppercase and lowercase letters. Return true if a and b are alike. Otherwise; return false. Example 1: Input: s = ""book"" Output: true Explanation: a = ""bo"" and b = ""ok"". a has 1 vowel and b has 1 vowel. Therefore; they are alike. Example 2: Input: s = ""textbook"" Output: false Explanation: a = ""text"" and b = ""book"". a has 1 vowel whereas b has 2. Therefore; they are not alike. Notice that the vowel o is counted twice. Constraints: 2 <= s.length <= 1000 s.length is even. s consists of uppercase and lowercase letters."
Goldman Sachs,2484,Count Palindromic Subsequences,Hard,Database,
Goldman Sachs,1,Two Sum,Easy,"Array, Hash Table",Given an array of integers nums and an integer target; return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution; and you may not use the same element twice. You can return the answer in any order. Example 1: Input: nums = [2;7;11;15]; target = 9 Output: [0;1] Explanation: Because nums[0] + nums[1] == 9; we return [0; 1]. Example 2: Input: nums = [3;2;4]; target = 6 Output: [1;2] Example 3: Input: nums = [3;3]; target = 6 Output: [0;1] Constraints: 2 <= nums.length <= 104 -109 <= nums[i] <= 109 -109 <= target <= 109 Only one valid answer exists. Follow-up: Can you come up with an algorithm that is less than O(n2) time complexity?
Goldman Sachs,64,Minimum Path Sum,Med,"Array, Dynamic Programming, Matrix",Given a m x n grid filled with non-negative numbers; find a path from top left to bottom right; which minimizes the sum of all numbers along its path. Note: You can only move either down or right at any point in time. Example 1: Input: grid = [[1;3;1];[1;5;1];[4;2;1]] Output: 7 Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum. Example 2: Input: grid = [[1;2;3];[4;5;6]] Output: 12 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 200 0 <= grid[i][j] <= 200
Goldman Sachs,153,Find Minimum in Rotated Sorted Array,Med,"Array, Binary Search",Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example; the array nums = [0;1;2;4;5;6;7] might become: [4;5;6;7;0;1;2] if it was rotated 4 times. [0;1;2;4;5;6;7] if it was rotated 7 times. Notice that rotating an array [a[0]; a[1]; a[2]; ...; a[n-1]] 1 time results in the array [a[n-1]; a[0]; a[1]; a[2]; ...; a[n-2]]. Given the sorted rotated array nums of unique elements; return the minimum element of this array. You must write an algorithm that runs in O(log n) time. Example 1: Input: nums = [3;4;5;1;2] Output: 1 Explanation: The original array was [1;2;3;4;5] rotated 3 times. Example 2: Input: nums = [4;5;6;7;0;1;2] Output: 0 Explanation: The original array was [0;1;2;4;5;6;7] and it was rotated 4 times. Example 3: Input: nums = [11;13;15;17] Output: 11 Explanation: The original array was [11;13;15;17] and it was rotated 4 times. Constraints: n == nums.length 1 <= n <= 5000 -5000 <= nums[i] <= 5000 All the integers of nums are unique. nums is sorted and rotated between 1 and n times.
Goldman Sachs,647,Palindromic Substrings,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the number of palindromic substrings in it. A string is a palindrome when it reads the same backward as forward. A substring is a contiguous sequence of characters within the string. Example 1: Input: s = ""abc"" Output: 3 Explanation: Three palindromic strings: ""a""; ""b""; ""c"". Example 2: Input: s = ""aaa"" Output: 6 Explanation: Six palindromic strings: ""a""; ""a""; ""a""; ""aa""; ""aa""; ""aaa"". Constraints: 1 <= s.length <= 1000 s consists of lowercase English letters."
Goldman Sachs,688,Knight Probability in Chessboard,Med,Dynamic Programming,On an n x n chessboard; a knight starts at the cell (row; column) and attempts to make exactly k moves. The rows and columns are 0-indexed; so the top-left cell is (0; 0); and the bottom-right cell is (n - 1; n - 1). A chess knight has eight possible moves it can make; as illustrated below. Each move is two cells in a cardinal direction; then one cell in an orthogonal direction. Each time the knight is to move; it chooses one of eight possible moves uniformly at random (even if the piece would go off the chessboard) and moves there. The knight continues moving until it has made exactly k moves or has moved off the chessboard. Return the probability that the knight remains on the board after it has stopped moving. Example 1: Input: n = 3; k = 2; row = 0; column = 0 Output: 0.06250 Explanation: There are two moves (to (1;2); (2;1)) that will keep the knight on the board. From each of those positions; there are also two moves that will keep the knight on the board. The total probability the knight stays on the board is 0.0625. Example 2: Input: n = 1; k = 0; row = 0; column = 0 Output: 1.00000 Constraints: 1 <= n <= 25 0 <= k <= 100 0 <= row; column <= n - 1
Goldman Sachs,2513,Minimize the Maximum of Two Arrays,Med,"Array, Binary Search, Divide and Conquer, Binary Indexed Tree, Segment Tree, Merge Sort, Ordered Set",You are given two 0-indexed integer arrays nums1 and nums2; each of size n; and an integer diff. Find the number of pairs (i; j) such that: 0 <= i < j <= n - 1 and nums1[i] - nums1[j] <= nums2[i] - nums2[j] + diff. Return the number of pairs that satisfy the conditions. Example 1: Input: nums1 = [3;2;5]; nums2 = [2;2;1]; diff = 1 Output: 3 Explanation: There are 3 pairs that satisfy the conditions: 1. i = 0; j = 1: 3 - 2 <= 2 - 2 + 1. Since i < j and 1 <= 1; this pair satisfies the conditions. 2. i = 0; j = 2: 3 - 5 <= 2 - 1 + 1. Since i < j and -2 <= 2; this pair satisfies the conditions. 3. i = 1; j = 2: 2 - 5 <= 2 - 1 + 1. Since i < j and -3 <= 2; this pair satisfies the conditions. Therefore; we return 3. Example 2: Input: nums1 = [3;-1]; nums2 = [-2;2]; diff = -1 Output: 0 Explanation: Since there does not exist any pair that satisfies the conditions; we return 0. Constraints: n == nums1.length == nums2.length 2 <= n <= 105 -104 <= nums1[i]; nums2[i] <= 104 -104 <= diff <= 104
Goldman Sachs,3167,Better Compression of String,Med,,
Goldman Sachs,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Goldman Sachs,1507,Reformat Date,Easy,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix",You are given an m x n grid. Each cell of grid represents a street. The street of grid[i][j] can be: 1 which means a street connecting the left cell and the right cell. 2 which means a street connecting the upper cell and the lower cell. 3 which means a street connecting the left cell and the lower cell. 4 which means a street connecting the right cell and the lower cell. 5 which means a street connecting the left cell and the upper cell. 6 which means a street connecting the right cell and the upper cell. You will initially start at the street of the upper-left cell (0; 0). A valid path in the grid is a path that starts from the upper left cell (0; 0) and ends at the bottom-right cell (m - 1; n - 1). The path should only follow the streets. Notice that you are not allowed to change any street. Return true if there is a valid path in the grid or false otherwise. Example 1: Input: grid = [[2;4;3];[6;5;2]] Output: true Explanation: As shown you can start at cell (0; 0) and visit all the cells of the grid to reach (m - 1; n - 1). Example 2: Input: grid = [[1;2;1];[1;2;1]] Output: false Explanation: As shown you the street at cell (0; 0) is not connected with any street of any other cell and you will get stuck at cell (0; 0) Example 3: Input: grid = [[1;1;2]] Output: false Explanation: You will get stuck at cell (0; 1) and you cannot reach cell (0; 2). Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 1 <= grid[i][j] <= 6
Goldman Sachs,91,Decode Ways,Med,"String, Dynamic Programming","You have intercepted a secret message encoded as a string of numbers. The message is decoded via the following mapping: ""1"" -> 'A' ""2"" -> 'B' ... ""25"" -> 'Y' ""26"" -> 'Z' However; while decoding the message; you realize that there are many different ways you can decode the message because some codes are contained in other codes (""2"" and ""5"" vs ""25""). For example; ""11106"" can be decoded into: ""AAJF"" with the grouping (1; 1; 10; 6) ""KJF"" with the grouping (11; 10; 6) The grouping (1; 11; 06) is invalid because ""06"" is not a valid code (only ""6"" is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits; return the number of ways to decode it. If the entire string cannot be decoded in any valid way; return 0. The test cases are generated so that the answer fits in a 32-bit integer. Example 1: Input: s = ""12"" Output: 2 Explanation: ""12"" could be decoded as ""AB"" (1 2) or ""L"" (12). Example 2: Input: s = ""226"" Output: 3 Explanation: ""226"" could be decoded as ""BZ"" (2 26); ""VF"" (22 6); or ""BBF"" (2 2 6). Example 3: Input: s = ""06"" Output: 0 Explanation: ""06"" cannot be mapped to ""F"" because of the leading zero (""6"" is different from ""06""). In this case; the string is not a valid encoding; so return 0. Constraints: 1 <= s.length <= 100 s contains only digits and may contain leading zero(s)."
Goldman Sachs,2097,Valid Arrangement of Pairs,Hard,Database,
Goldman Sachs,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Goldman Sachs,862,Shortest Subarray with Sum at Least K,Hard,"Array, Hash Table, String, Sorting","You are given a 0-indexed string s that you must perform k replacement operations on. The replacement operations are given as three 0-indexed parallel arrays; indices; sources; and targets; all of length k. To complete the ith replacement operation: Check if the substring sources[i] occurs at index indices[i] in the original string s. If it does not occur; do nothing. Otherwise if it does occur; replace that substring with targets[i]. For example; if s = ""abcd""; indices[i] = 0; sources[i] = ""ab""; and targets[i] = ""eee""; then the result of this replacement will be ""eeecd"". All replacement operations must occur simultaneously; meaning the replacement operations should not affect the indexing of each other. The testcases will be generated such that the replacements will not overlap. For example; a testcase with s = ""abc""; indices = [0; 1]; and sources = [""ab"";""bc""] will not be generated because the ""ab"" and ""bc"" replacements overlap. Return the resulting string after performing all replacement operations on s. A substring is a contiguous sequence of characters in a string. Example 1: Input: s = ""abcd""; indices = [0; 2]; sources = [""a""; ""cd""]; targets = [""eee""; ""ffff""] Output: ""eeebffff"" Explanation: ""a"" occurs at index 0 in s; so we replace it with ""eee"". ""cd"" occurs at index 2 in s; so we replace it with ""ffff"". Example 2: Input: s = ""abcd""; indices = [0; 2]; sources = [""ab"";""ec""]; targets = [""eee"";""ffff""] Output: ""eeecd"" Explanation: ""ab"" occurs at index 0 in s; so we replace it with ""eee"". ""ec"" does not occur at index 2 in s; so we do nothing. Constraints: 1 <= s.length <= 1000 k == indices.length == sources.length == targets.length 1 <= k <= 100 0 <= indexes[i] < s.length 1 <= sources[i].length; targets[i].length <= 50 s consists of only lowercase English letters. sources[i] and targets[i] consist of only lowercase English letters."
Goldman Sachs,2438,Range Product Queries of Powers,Med,"Depth-First Search, Graph",You are given a directed graph of n nodes numbered from 0 to n - 1; where each node has at most one outgoing edge. The graph is represented with a given 0-indexed array edges of size n; indicating that there is a directed edge from node i to node edges[i]. If there is no outgoing edge from i; then edges[i] == -1. You are also given two integers node1 and node2. Return the index of the node that can be reached from both node1 and node2; such that the maximum between the distance from node1 to that node; and from node2 to that node is minimized. If there are multiple answers; return the node with the smallest index; and if no possible answer exists; return -1. Note that edges may contain cycles. Example 1: Input: edges = [2;2;3;-1]; node1 = 0; node2 = 1 Output: 2 Explanation: The distance from node 0 to node 2 is 1; and the distance from node 1 to node 2 is 1. The maximum of those two distances is 1. It can be proven that we cannot get a node with a smaller maximum distance than 1; so we return node 2. Example 2: Input: edges = [1;2;-1]; node1 = 0; node2 = 2 Output: 2 Explanation: The distance from node 0 to node 2 is 2; and the distance from node 2 to itself is 0. The maximum of those two distances is 2. It can be proven that we cannot get a node with a smaller maximum distance than 2; so we return node 2. Constraints: n == edges.length 2 <= n <= 105 -1 <= edges[i] < n edges[i] != i 0 <= node1; node2 < n
Goldman Sachs,300,Longest Increasing Subsequence,Med,"Array, Binary Search, Dynamic Programming",Given an integer array nums; return the length of the longest strictly increasing subsequence. Example 1: Input: nums = [10;9;2;5;3;7;101;18] Output: 4 Explanation: The longest increasing subsequence is [2;3;7;101]; therefore the length is 4. Example 2: Input: nums = [0;1;0;3;2;3] Output: 4 Example 3: Input: nums = [7;7;7;7;7;7;7] Output: 1 Constraints: 1 <= nums.length <= 2500 -104 <= nums[i] <= 104 Follow up: Can you come up with an algorithm that runs in O(n log(n)) time complexity?
Goldman Sachs,1116,Print Zero Even Odd,Med,"Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given the root of a binary tree; the level of its root is 1; the level of its children is 2; and so on. Return the smallest level x such that the sum of all the values of nodes at level x is maximal. Example 1: Input: root = [1;7;0;7;-8;null;null] Output: 2 Explanation: Level 1 sum = 1. Level 2 sum = 7 + 0 = 7. Level 3 sum = 7 + -8 = -1. So we return the level with the maximum sum which is level 2. Example 2: Input: root = [989;null;10250;98693;-89388;null;null;null;-32127] Output: 2 Constraints: The number of nodes in the tree is in the range [1; 104]. -105 <= Node.val <= 105
Goldman Sachs,2087,Minimum Cost Homecoming of a Robot in a Grid,Med,Database,Table: Signups +----------------+----------+ | Column Name | Type | +----------------+----------+ | user_id | int | | time_stamp | datetime | +----------------+----------+ user_id is the column of unique values for this table. Each row contains information about the signup time for the user with ID user_id. Table: Confirmations +----------------+----------+ | Column Name | Type | +----------------+----------+ | user_id | int | | time_stamp | datetime | | action | ENUM | +----------------+----------+ (user_id; time_stamp) is the primary key (combination of columns with unique values) for this table. user_id is a foreign key (reference column) to the Signups table. action is an ENUM (category) of the type ('confirmed'; 'timeout') Each row of this table indicates that the user with ID user_id requested a confirmation message at time_stamp and that confirmation message was either confirmed ('confirmed') or expired without confirming ('timeout'). The confirmation rate of a user is the number of 'confirmed' messages divided by the total number of requested confirmation messages. The confirmation rate of a user that did not request any confirmation messages is 0. Round the confirmation rate to two decimal places. Write a solution to find the confirmation rate of each user. Return the result table in any order. The result format is in the following example. Example 1: Input: Signups table: +---------+---------------------+ | user_id | time_stamp | +---------+---------------------+ | 3 | 2020-03-21 10:16:13 | | 7 | 2020-01-04 13:57:59 | | 2 | 2020-07-29 23:09:44 | | 6 | 2020-12-09 10:39:37 | +---------+---------------------+ Confirmations table: +---------+---------------------+-----------+ | user_id | time_stamp | action | +---------+---------------------+-----------+ | 3 | 2021-01-06 03:30:46 | timeout | | 3 | 2021-07-14 14:00:00 | timeout | | 7 | 2021-06-12 11:57:29 | confirmed | | 7 | 2021-06-13 12:58:28 | confirmed | | 7 | 2021-06-14 13:59:27 | confirmed | | 2 | 2021-01-22 00:00:00 | confirmed | | 2 | 2021-02-28 23:59:59 | timeout | +---------+---------------------+-----------+ Output: +---------+-------------------+ | user_id | confirmation_rate | +---------+-------------------+ | 6 | 0.00 | | 3 | 0.00 | | 7 | 1.00 | | 2 | 0.50 | +---------+-------------------+ Explanation: User 6 did not request any confirmation messages. The confirmation rate is 0. User 3 made 2 requests and both timed out. The confirmation rate is 0. User 7 made 3 requests and all were confirmed. The confirmation rate is 1. User 2 made 2 requests where one was confirmed and the other timed out. The confirmation rate is 1 / 2 = 0.5.
Goldman Sachs,2154,Keep Multiplying Found Values by Two,Easy,"String, Greedy","You are given a string s consisting of n characters which are either 'X' or 'O'. A move is defined as selecting three consecutive characters of s and converting them to 'O'. Note that if a move is applied to the character 'O'; it will stay the same. Return the minimum number of moves required so that all the characters of s are converted to 'O'. Example 1: Input: s = ""XXX"" Output: 1 Explanation: XXX -> OOO We select all the 3 characters and convert them in one move. Example 2: Input: s = ""XXOX"" Output: 2 Explanation: XXOX -> OOOX -> OOOO We select the first 3 characters in the first move; and convert them to 'O'. Then we select the last 3 characters and convert them so that the final string contains all 'O's. Example 3: Input: s = ""OOOO"" Output: 0 Explanation: There are no 'X's in s to convert. Constraints: 3 <= s.length <= 1000 s[i] is either 'X' or 'O'."
Goldman Sachs,2420,Find All Good Indices,Med,"Array, Tree, Depth-First Search, Breadth-First Search",
Goldman Sachs,3168,Minimum Number of Chairs in a Waiting Room,Easy,,
Goldman Sachs,5,Longest Palindromic Substring,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the longest palindromic substring in s. Example 1: Input: s = ""babad"" Output: ""bab"" Explanation: ""aba"" is also a valid answer. Example 2: Input: s = ""cbbd"" Output: ""bb"" Constraints: 1 <= s.length <= 1000 s consist of only digits and English letters."
Goldman Sachs,33,Search in Rotated Sorted Array,Med,"Array, Binary Search",There is an integer array nums sorted in ascending order (with distinct values). Prior to being passed to your function; nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k]; nums[k+1]; ...; nums[n-1]; nums[0]; nums[1]; ...; nums[k-1]] (0-indexed). For example; [0;1;2;4;5;6;7] might be rotated at pivot index 3 and become [4;5;6;7;0;1;2]. Given the array nums after the possible rotation and an integer target; return the index of target if it is in nums; or -1 if it is not in nums. You must write an algorithm with O(log n) runtime complexity. Example 1: Input: nums = [4;5;6;7;0;1;2]; target = 0 Output: 4 Example 2: Input: nums = [4;5;6;7;0;1;2]; target = 3 Output: -1 Example 3: Input: nums = [1]; target = 0 Output: -1 Constraints: 1 <= nums.length <= 5000 -104 <= nums[i] <= 104 All values of nums are unique. nums is an ascending array that is possibly rotated. -104 <= target <= 104
Goldman Sachs,931,Minimum Falling Path Sum,Med,"Hash Table, Stack, Design, Ordered Set","Design a stack-like data structure to push elements to the stack and pop the most frequent element from the stack. Implement the FreqStack class: FreqStack() constructs an empty frequency stack. void push(int val) pushes an integer val onto the top of the stack. int pop() removes and returns the most frequent element in the stack. If there is a tie for the most frequent element; the element closest to the stack's top is removed and returned. Example 1: Input [""FreqStack""; ""push""; ""push""; ""push""; ""push""; ""push""; ""push""; ""pop""; ""pop""; ""pop""; ""pop""] [[]; [5]; [7]; [5]; [7]; [4]; [5]; []; []; []; []] Output [null; null; null; null; null; null; null; 5; 7; 5; 4] Explanation FreqStack freqStack = new FreqStack(); freqStack.push(5); // The stack is [5] freqStack.push(7); // The stack is [5;7] freqStack.push(5); // The stack is [5;7;5] freqStack.push(7); // The stack is [5;7;5;7] freqStack.push(4); // The stack is [5;7;5;7;4] freqStack.push(5); // The stack is [5;7;5;7;4;5] freqStack.pop(); // return 5; as 5 is the most frequent. The stack becomes [5;7;5;7;4]. freqStack.pop(); // return 7; as 5 and 7 is the most frequent; but 7 is closest to the top. The stack becomes [5;7;5;4]. freqStack.pop(); // return 5; as 5 is the most frequent. The stack becomes [5;7;4]. freqStack.pop(); // return 4; as 4; 5 and 7 is the most frequent; but 4 is closest to the top. The stack becomes [5;7]. Constraints: 0 <= val <= 109 At most 2 * 104 calls will be made to push and pop. It is guaranteed that there will be at least one element in the stack before calling pop."
Goldman Sachs,1109,Corporate Flight Bookings,Med,,
Goldman Sachs,2191,Sort the Jumbled Numbers,Med,"String, Dynamic Programming, Greedy","You are given a 0-indexed string hamsters where hamsters[i] is either: 'H' indicating that there is a hamster at index i; or '.' indicating that index i is empty. You will add some number of food buckets at the empty indices in order to feed the hamsters. A hamster can be fed if there is at least one food bucket to its left or to its right. More formally; a hamster at index i can be fed if you place a food bucket at index i - 1 and/or at index i + 1. Return the minimum number of food buckets you should place at empty indices to feed all the hamsters or -1 if it is impossible to feed all of them. Example 1: Input: hamsters = ""H..H"" Output: 2 Explanation: We place two food buckets at indices 1 and 2. It can be shown that if we place only one food bucket; one of the hamsters will not be fed. Example 2: Input: hamsters = "".H.H."" Output: 1 Explanation: We place one food bucket at index 2. Example 3: Input: hamsters = "".HHH."" Output: -1 Explanation: If we place a food bucket at every empty index as shown; the hamster at index 2 will not be able to eat. Constraints: 1 <= hamsters.length <= 105 hamsters[i] is either'H' or '.'."
Goldman Sachs,1427,Perform String Shifts,Easy,"Tree, Depth-First Search, Binary Search Tree, Sorting, Binary Tree",Given two binary search trees root1 and root2; return a list containing all the integers from both trees sorted in ascending order. Example 1: Input: root1 = [2;1;4]; root2 = [1;0;3] Output: [0;1;1;2;3;4] Example 2: Input: root1 = [1;null;8]; root2 = [8;1] Output: [1;1;8;8] Constraints: The number of nodes in each tree is in the range [0; 5000]. -105 <= Node.val <= 105
Goldman Sachs,1413,Minimum Value to Get Positive Step by Step Sum,Easy,"Array, Binary Search, Matrix, Prefix Sum",Given a m x n matrix mat and an integer threshold; return the maximum side-length of a square with a sum less than or equal to threshold or return 0 if there is no such square. Example 1: Input: mat = [[1;1;3;2;4;3;2];[1;1;3;2;4;3;2];[1;1;3;2;4;3;2]]; threshold = 4 Output: 2 Explanation: The maximum side length of square with sum less than 4 is 2 as shown. Example 2: Input: mat = [[2;2;2;2;2];[2;2;2;2;2];[2;2;2;2;2];[2;2;2;2;2];[2;2;2;2;2]]; threshold = 1 Output: 0 Constraints: m == mat.length n == mat[i].length 1 <= m; n <= 300 0 <= mat[i][j] <= 104 0 <= threshold <= 105
Goldman Sachs,1750,Minimum Length of String After Deleting Similar Ends,Med,"Hash Table, Tree, Depth-First Search, Binary Tree, Counting",
Goldman Sachs,1771,Maximize Palindrome Length From Subsequences,Hard,"Array, Math, Binary Search, Greedy, Sorting, Heap (Priority Queue)",You have an inventory of different colored balls; and there is a customer that wants orders balls of any color. The customer weirdly values the colored balls. Each colored ball's value is the number of balls of that color you currently have in your inventory. For example; if you own 6 yellow balls; the customer would pay 6 for the first yellow ball. After the transaction; there are only 5 yellow balls left; so the next yellow ball is then valued at 5 (i.e.; the value of the balls decreases as you sell more to the customer). You are given an integer array; inventory; where inventory[i] represents the number of balls of the ith color that you initially own. You are also given an integer orders; which represents the total number of balls that the customer wants. You can sell the balls in any order. Return the maximum total value that you can attain after selling orders colored balls. As the answer may be too large; return it modulo 109 + 7. Example 1: Input: inventory = [2;5]; orders = 4 Output: 14 Explanation: Sell the 1st color 1 time (2) and the 2nd color 3 times (5 + 4 + 3). The maximum total value is 2 + 5 + 4 + 3 = 14. Example 2: Input: inventory = [3;5]; orders = 6 Output: 19 Explanation: Sell the 1st color 2 times (3 + 2) and the 2nd color 4 times (5 + 4 + 3 + 2). The maximum total value is 3 + 2 + 5 + 4 + 3 + 2 = 19. Constraints: 1 <= inventory.length <= 105 1 <= inventory[i] <= 109 1 <= orders <= min(sum(inventory[i]); 109)
Goldman Sachs,2266,Count Number of Texts,Med,"Math, Enumeration",A generic microwave supports cooking times for: at least 1 second. at most 99 minutes and 99 seconds. To set the cooking time; you push at most four digits. The microwave normalizes what you push as four digits by prepending zeroes. It interprets the first two digits as the minutes and the last two digits as the seconds. It then adds them up as the cooking time. For example; You push 9 5 4 (three digits). It is normalized as 0954 and interpreted as 9 minutes and 54 seconds. You push 0 0 0 8 (four digits). It is interpreted as 0 minutes and 8 seconds. You push 8 0 9 0. It is interpreted as 80 minutes and 90 seconds. You push 8 1 3 0. It is interpreted as 81 minutes and 30 seconds. You are given integers startAt; moveCost; pushCost; and targetSeconds. Initially; your finger is on the digit startAt. Moving the finger above any specific digit costs moveCost units of fatigue. Pushing the digit below the finger once costs pushCost units of fatigue. There can be multiple ways to set the microwave to cook for targetSeconds seconds but you are interested in the way with the minimum cost. Return the minimum cost to set targetSeconds seconds of cooking time. Remember that one minute consists of 60 seconds. Example 1: Input: startAt = 1; moveCost = 2; pushCost = 1; targetSeconds = 600 Output: 6 Explanation: The following are the possible ways to set the cooking time. - 1 0 0 0; interpreted as 10 minutes and 0 seconds. The finger is already on digit 1; pushes 1 (with cost 1); moves to 0 (with cost 2); pushes 0 (with cost 1); pushes 0 (with cost 1); and pushes 0 (with cost 1). The cost is: 1 + 2 + 1 + 1 + 1 = 6. This is the minimum cost. - 0 9 6 0; interpreted as 9 minutes and 60 seconds. That is also 600 seconds. The finger moves to 0 (with cost 2); pushes 0 (with cost 1); moves to 9 (with cost 2); pushes 9 (with cost 1); moves to 6 (with cost 2); pushes 6 (with cost 1); moves to 0 (with cost 2); and pushes 0 (with cost 1). The cost is: 2 + 1 + 2 + 1 + 2 + 1 + 2 + 1 = 12. - 9 6 0; normalized as 0960 and interpreted as 9 minutes and 60 seconds. The finger moves to 9 (with cost 2); pushes 9 (with cost 1); moves to 6 (with cost 2); pushes 6 (with cost 1); moves to 0 (with cost 2); and pushes 0 (with cost 1). The cost is: 2 + 1 + 2 + 1 + 2 + 1 = 9. Example 2: Input: startAt = 0; moveCost = 1; pushCost = 2; targetSeconds = 76 Output: 6 Explanation: The optimal way is to push two digits: 7 6; interpreted as 76 seconds. The finger moves to 7 (with cost 1); pushes 7 (with cost 2); moves to 6 (with cost 1); and pushes 6 (with cost 2). The total cost is: 1 + 2 + 1 + 2 = 6 Note other possible ways are 0076; 076; 0116; and 116; but none of them produces the minimum cost. Constraints: 0 <= startAt <= 9 1 <= moveCost; pushCost <= 105 1 <= targetSeconds <= 6039
Goldman Sachs,2300,Successful Pairs of Spells and Potions,Med,"Hash Table, String, Greedy, Heap (Priority Queue), Counting","You are given a string s and an integer repeatLimit. Construct a new string repeatLimitedString using the characters of s such that no letter appears more than repeatLimit times in a row. You do not have to use all characters from s. Return the lexicographically largest repeatLimitedString possible. A string a is lexicographically larger than a string b if in the first position where a and b differ; string a has a letter that appears later in the alphabet than the corresponding letter in b. If the first min(a.length; b.length) characters do not differ; then the longer string is the lexicographically larger one. Example 1: Input: s = ""cczazcc""; repeatLimit = 3 Output: ""zzcccac"" Explanation: We use all of the characters from s to construct the repeatLimitedString ""zzcccac"". The letter 'a' appears at most 1 time in a row. The letter 'c' appears at most 3 times in a row. The letter 'z' appears at most 2 times in a row. Hence; no letter appears more than repeatLimit times in a row and the string is a valid repeatLimitedString. The string is the lexicographically largest repeatLimitedString possible so we return ""zzcccac"". Note that the string ""zzcccca"" is lexicographically larger but the letter 'c' appears more than 3 times in a row; so it is not a valid repeatLimitedString. Example 2: Input: s = ""aababab""; repeatLimit = 2 Output: ""bbabaa"" Explanation: We use only some of the characters from s to construct the repeatLimitedString ""bbabaa"". The letter 'a' appears at most 2 times in a row. The letter 'b' appears at most 2 times in a row. Hence; no letter appears more than repeatLimit times in a row and the string is a valid repeatLimitedString. The string is the lexicographically largest repeatLimitedString possible so we return ""bbabaa"". Note that the string ""bbabaaa"" is lexicographically larger but the letter 'a' appears more than 2 times in a row; so it is not a valid repeatLimitedString. Constraints: 1 <= repeatLimit <= s.length <= 105 s consists of lowercase English letters."
Goldman Sachs,2446,Determine if Two Events Have Conflict,Easy,Database,
Goldman Sachs,2550,Count Collisions of Monkeys on a Polygon,Med,"Array, String","You are given two string arrays; queries and dictionary. All words in each array comprise of lowercase English letters and have the same length. In one edit you can take a word from queries; and change any letter in it to any other letter. Find all words from queries that; after a maximum of two edits; equal some word from dictionary. Return a list of all words from queries; that match with some word from dictionary after a maximum of two edits. Return the words in the same order they appear in queries. Example 1: Input: queries = [""word"";""note"";""ants"";""wood""]; dictionary = [""wood"";""joke"";""moat""] Output: [""word"";""note"";""wood""] Explanation: - Changing the 'r' in ""word"" to 'o' allows it to equal the dictionary word ""wood"". - Changing the 'n' to 'j' and the 't' to 'k' in ""note"" changes it to ""joke"". - It would take more than 2 edits for ""ants"" to equal a dictionary word. - ""wood"" can remain unchanged (0 edits) and match the corresponding dictionary word. Thus; we return [""word"";""note"";""wood""]. Example 2: Input: queries = [""yes""]; dictionary = [""not""] Output: [] Explanation: Applying any two edits to ""yes"" cannot make it equal to ""not"". Thus; we return an empty array. Constraints: 1 <= queries.length; dictionary.length <= 100 n == queries[i].length == dictionary[j].length 1 <= n <= 100 All queries[i] and dictionary[j] are composed of lowercase English letters."
Goldman Sachs,3001,Minimum Moves to Capture The Queen,Med,"Array, Math, Stack, Greedy, Monotonic Stack, Number Theory",You are given an array nums of n positive integers and an integer k. Initially; you start with a score of 1. You have to maximize your score by applying the following operation at most k times: Choose any non-empty subarray nums[l; ...; r] that you haven't chosen previously. Choose an element x of nums[l; ...; r] with the highest prime score. If multiple such elements exist; choose the one with the smallest index. Multiply your score by x. Here; nums[l; ...; r] denotes the subarray of nums starting at index l and ending at the index r; both ends being inclusive. The prime score of an integer x is equal to the number of distinct prime factors of x. For example; the prime score of 300 is 3 since 300 = 2 * 2 * 3 * 5 * 5. Return the maximum possible score after applying at most k operations. Since the answer may be large; return it modulo 109 + 7. Example 1: Input: nums = [8;3;9;3;8]; k = 2 Output: 81 Explanation: To get a score of 81; we can apply the following operations: - Choose subarray nums[2; ...; 2]. nums[2] is the only element in this subarray. Hence; we multiply the score by nums[2]. The score becomes 1 * 9 = 9. - Choose subarray nums[2; ...; 3]. Both nums[2] and nums[3] have a prime score of 1; but nums[2] has the smaller index. Hence; we multiply the score by nums[2]. The score becomes 9 * 9 = 81. It can be proven that 81 is the highest score one can obtain. Example 2: Input: nums = [19;12;14;6;10;18]; k = 3 Output: 4788 Explanation: To get a score of 4788; we can apply the following operations: - Choose subarray nums[0; ...; 0]. nums[0] is the only element in this subarray. Hence; we multiply the score by nums[0]. The score becomes 1 * 19 = 19. - Choose subarray nums[5; ...; 5]. nums[5] is the only element in this subarray. Hence; we multiply the score by nums[5]. The score becomes 19 * 18 = 342. - Choose subarray nums[2; ...; 3]. Both nums[2] and nums[3] have a prime score of 2; but nums[2] has the smaller index. Hence; we multipy the score by nums[2]. The score becomes 342 * 14 = 4788. It can be proven that 4788 is the highest score one can obtain. Constraints: 1 <= nums.length == n <= 105 1 <= nums[i] <= 105 1 <= k <= min(n * (n + 1) / 2; 109)
Goldman Sachs,3,Longest Substring Without Repeating Characters,Med,"Hash Table, String, Sliding Window","Given a string s; find the length of the longest substring without repeating characters. Example 1: Input: s = ""abcabcbb"" Output: 3 Explanation: The answer is ""abc""; with the length of 3. Example 2: Input: s = ""bbbbb"" Output: 1 Explanation: The answer is ""b""; with the length of 1. Example 3: Input: s = ""pwwkew"" Output: 3 Explanation: The answer is ""wke""; with the length of 3. Notice that the answer must be a substring; ""pwke"" is a subsequence and not a substring. Constraints: 0 <= s.length <= 5 * 104 s consists of English letters; digits; symbols and spaces."
Goldman Sachs,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Goldman Sachs,706,Design HashMap,Easy,,
Goldman Sachs,2933,High-Access Employees,Med,,
Goldman Sachs,50,"Pow(x, n)",Med,"Math, Recursion",Implement pow(x; n); which calculates x raised to the power n (i.e.; xn). Example 1: Input: x = 2.00000; n = 10 Output: 1024.00000 Example 2: Input: x = 2.10000; n = 3 Output: 9.26100 Example 3: Input: x = 2.00000; n = -2 Output: 0.25000 Explanation: 2-2 = 1/22 = 1/4 = 0.25 Constraints: -100.0 < x < 100.0 -231 <= n <= 231-1 n is an integer. Either x is not zero or n > 0. -104 <= xn <= 104
Goldman Sachs,53,Maximum Subarray,Med,"Array, Divide and Conquer, Dynamic Programming",Given an integer array nums; find the subarray with the largest sum; and return its sum. Example 1: Input: nums = [-2;1;-3;4;-1;2;1;-5;4] Output: 6 Explanation: The subarray [4;-1;2;1] has the largest sum 6. Example 2: Input: nums = [1] Output: 1 Explanation: The subarray [1] has the largest sum 1. Example 3: Input: nums = [5;4;-1;7;8] Output: 23 Explanation: The subarray [5;4;-1;7;8] has the largest sum 23. Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution using the divide and conquer approach; which is more subtle.
Goldman Sachs,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Goldman Sachs,326,Power of Three,Easy,"Math, Recursion",Given an integer n; return true if it is a power of three. Otherwise; return false. An integer n is a power of three; if there exists an integer x such that n == 3x. Example 1: Input: n = 27 Output: true Explanation: 27 = 33 Example 2: Input: n = 0 Output: false Explanation: There is no x where 3x = 0. Example 3: Input: n = -1 Output: false Explanation: There is no x where 3x = (-1). Constraints: -231 <= n <= 231 - 1 Follow up: Could you solve it without loops/recursion?
Goldman Sachs,55,Jump Game,Med,"Array, Dynamic Programming, Greedy",You are given an integer array nums. You are initially positioned at the array's first index; and each element in the array represents your maximum jump length at that position. Return true if you can reach the last index; or false otherwise. Example 1: Input: nums = [2;3;1;1;4] Output: true Explanation: Jump 1 step from index 0 to 1; then 3 steps to the last index. Example 2: Input: nums = [3;2;1;0;4] Output: false Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0; which makes it impossible to reach the last index. Constraints: 1 <= nums.length <= 104 0 <= nums[i] <= 105
Goldman Sachs,56,Merge Intervals,Med,"Array, Sorting",Given an array of intervals where intervals[i] = [starti; endi]; merge all overlapping intervals; and return an array of the non-overlapping intervals that cover all the intervals in the input. Example 1: Input: intervals = [[1;3];[2;6];[8;10];[15;18]] Output: [[1;6];[8;10];[15;18]] Explanation: Since intervals [1;3] and [2;6] overlap; merge them into [1;6]. Example 2: Input: intervals = [[1;4];[4;5]] Output: [[1;5]] Explanation: Intervals [1;4] and [4;5] are considered overlapping. Constraints: 1 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 104
Goldman Sachs,141,Linked List Cycle,Easy,"Hash Table, Linked List, Two Pointers",Given head; the head of a linked list; determine if the linked list has a cycle in it. There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internally; pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter. Return true if there is a cycle in the linked list. Otherwise; return false. Example 1: Input: head = [3;2;0;-4]; pos = 1 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 1st node (0-indexed). Example 2: Input: head = [1;2]; pos = 0 Output: true Explanation: There is a cycle in the linked list; where the tail connects to the 0th node. Example 3: Input: head = [1]; pos = -1 Output: false Explanation: There is no cycle in the linked list. Constraints: The number of the nodes in the list is in the range [0; 104]. -105 <= Node.val <= 105 pos is -1 or a valid index in the linked-list. Follow up: Can you solve it using O(1) (i.e. constant) memory?
Goldman Sachs,657,Robot Return to Origin,Easy,"String, Simulation","There is a robot starting at the position (0; 0); the origin; on a 2D plane. Given a sequence of its moves; judge if this robot ends up at (0; 0) after it completes its moves. You are given a string moves that represents the move sequence of the robot where moves[i] represents its ith move. Valid moves are 'R' (right); 'L' (left); 'U' (up); and 'D' (down). Return true if the robot returns to the origin after it finishes all of its moves; or false otherwise. Note: The way that the robot is ""facing"" is irrelevant. 'R' will always make the robot move to the right once; 'L' will always make it move left; etc. Also; assume that the magnitude of the robot's movement is the same for each move. Example 1: Input: moves = ""UD"" Output: true Explanation: The robot moves up once; and then down once. All moves have the same magnitude; so it ended up at the origin where it started. Therefore; we return true. Example 2: Input: moves = ""LL"" Output: false Explanation: The robot moves left twice. It ends up two ""moves"" to the left of the origin. We return false because it is not at the origin at the end of its moves. Constraints: 1 <= moves.length <= 2 * 104 moves only contains the characters 'U'; 'D'; 'L' and 'R'."
Goldman Sachs,1832,Check if the Sentence Is Pangram,Easy,"Array, Hash Table, Binary Search, Greedy",You are given an array target that consists of distinct integers and another integer array arr that can have duplicates. In one operation; you can insert any integer at any position in arr. For example; if arr = [1;4;1;2]; you can add 3 in the middle and make it [1;4;3;1;2]. Note that you can insert the integer at the very beginning or end of the array. Return the minimum number of operations needed to make target a subsequence of arr. A subsequence of an array is a new array generated from the original array by deleting some elements (possibly none) without changing the remaining elements' relative order. For example; [2;7;4] is a subsequence of [4;2;3;7;2;1;4] (the underlined elements); while [2;4;2] is not. Example 1: Input: target = [5;1;3]; arr = [9;4;2;3;4] Output: 2 Explanation: You can add 5 and 1 in such a way that makes arr = [5;9;4;1;2;3;4]; then target will be a subsequence of arr. Example 2: Input: target = [6;4;8;1;3;2]; arr = [4;7;6;2;3;8;6;1] Output: 3 Constraints: 1 <= target.length; arr.length <= 105 1 <= target[i]; arr[i] <= 109 target contains no duplicates.
Goldman Sachs,2375,Construct Smallest Number From DI String,Med,"Array, Breadth-First Search, Graph, Heap (Priority Queue), Matrix, Shortest Path",You are given a 0-indexed 2D integer array grid of size m x n. Each cell has one of two values: 0 represents an empty cell; 1 represents an obstacle that may be removed. You can move up; down; left; or right from and to an empty cell. Return the minimum number of obstacles to remove so you can move from the upper left corner (0; 0) to the lower right corner (m - 1; n - 1). Example 1: Input: grid = [[0;1;1];[1;1;0];[1;1;0]] Output: 2 Explanation: We can remove the obstacles at (0; 1) and (0; 2) to create a path from (0; 0) to (2; 2). It can be shown that we need to remove at least 2 obstacles; so we return 2. Note that there may be other ways to remove 2 obstacles to create a path. Example 2: Input: grid = [[0;1;0;0;0];[0;1;0;1;0];[0;0;0;1;0]] Output: 0 Explanation: We can move from (0; 0) to (2; 4) without removing any obstacles; so we return 0. Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 105 2 <= m * n <= 105 grid[i][j] is either 0 or 1. grid[0][0] == grid[m - 1][n - 1] == 0
Goldman Sachs,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Goldman Sachs,74,Search a 2D Matrix,Med,"Array, Binary Search, Matrix",You are given an m x n integer matrix matrix with the following two properties: Each row is sorted in non-decreasing order. The first integer of each row is greater than the last integer of the previous row. Given an integer target; return true if target is in matrix or false otherwise. You must write a solution in O(log(m * n)) time complexity. Example 1: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 3 Output: true Example 2: Input: matrix = [[1;3;5;7];[10;11;16;20];[23;30;34;60]]; target = 13 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 100 -104 <= matrix[i][j]; target <= 104
Goldman Sachs,238,Product of Array Except Self,Med,"Array, Prefix Sum",Given an integer array nums; return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i]. The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. You must write an algorithm that runs in O(n) time and without using the division operation. Example 1: Input: nums = [1;2;3;4] Output: [24;12;8;6] Example 2: Input: nums = [-1;1;0;-3;3] Output: [0;0;9;0;0] Constraints: 2 <= nums.length <= 105 -30 <= nums[i] <= 30 The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer. Follow up: Can you solve the problem in O(1) extra space complexity? (The output array does not count as extra space for space complexity analysis.)
Goldman Sachs,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
Goldman Sachs,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Goldman Sachs,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Goldman Sachs,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Goldman Sachs,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Goldman Sachs,1356,Sort Integers by The Number of 1 Bits,Easy,"Two Pointers, String, Greedy, Binary Indexed Tree","You are given a string s consisting only of lowercase English letters. In one move; you can select any two adjacent characters of s and swap them. Return the minimum number of moves needed to make s a palindrome. Note that the input will be generated such that s can always be converted to a palindrome. Example 1: Input: s = ""aabb"" Output: 2 Explanation: We can obtain two palindromes from s; ""abba"" and ""baab"". - We can obtain ""abba"" from s in 2 moves: ""aabb"" -> ""abab"" -> ""abba"". - We can obtain ""baab"" from s in 2 moves: ""aabb"" -> ""abab"" -> ""baab"". Thus; the minimum number of moves needed to make s a palindrome is 2. Example 2: Input: s = ""letelt"" Output: 2 Explanation: One of the palindromes we can obtain from s in 2 moves is ""lettel"". One of the ways we can obtain it is ""letelt"" -> ""letetl"" -> ""lettel"". Other palindromes such as ""tleelt"" can also be obtained in 2 moves. It can be shown that it is not possible to obtain a palindrome in less than 2 moves. Constraints: 1 <= s.length <= 2000 s consists only of lowercase English letters. s can be converted to a palindrome using a finite number of moves."
Goldman Sachs,1395,Count Number of Teams,Med,"Array, Math, Geometry",On a 2D plane; there are n points with integer coordinates points[i] = [xi; yi]. Return the minimum time in seconds to visit all the points in the order given by points. You can move according to these rules: In 1 second; you can either: move vertically by one unit; move horizontally by one unit; or move diagonally sqrt(2) units (in other words; move one unit vertically then one unit horizontally in 1 second). You have to visit the points in the same order as they appear in the array. You are allowed to pass through points that appear later in the order; but these do not count as visits. Example 1: Input: points = [[1;1];[3;4];[-1;0]] Output: 7 Explanation: One optimal path is [1;1] -> [2;2] -> [3;3] -> [3;4] -> [2;3] -> [1;2] -> [0;1] -> [-1;0] Time from [1;1] to [3;4] = 3 seconds Time from [3;4] to [-1;0] = 4 seconds Total time = 7 seconds Example 2: Input: points = [[3;2];[-2;2]] Output: 5 Constraints: points.length == n 1 <= n <= 100 points[i].length == 2 -1000 <= points[i][0]; points[i][1] <= 1000
Goldman Sachs,8,String to Integer (atoi),Med,String,"Implement the myAtoi(string s) function; which converts a string to a 32-bit signed integer. The algorithm for myAtoi(string s) is as follows: Whitespace: Ignore any leading whitespace ("" ""). Signedness: Determine the sign by checking if the next character is '-' or '+'; assuming positivity if neither present. Conversion: Read the integer by skipping leading zeros until a non-digit character is encountered or the end of the string is reached. If no digits were read; then the result is 0. Rounding: If the integer is out of the 32-bit signed integer range [-231; 231 - 1]; then round the integer to remain in the range. Specifically; integers less than -231 should be rounded to -231; and integers greater than 231 - 1 should be rounded to 231 - 1. Return the integer as the final result. Example 1: Input: s = ""42"" Output: 42 Explanation: The underlined characters are what is read in and the caret is the current reader position. Step 1: ""42"" (no characters read because there is no leading whitespace) ^ Step 2: ""42"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""42"" (""42"" is read in) ^ Example 2: Input: s = "" -042"" Output: -42 Explanation: Step 1: "" -042"" (leading whitespace is read and ignored) ^ Step 2: "" -042"" ('-' is read; so the result should be negative) ^ Step 3: "" -042"" (""042"" is read in; leading zeros ignored in the result) ^ Example 3: Input: s = ""1337c0d3"" Output: 1337 Explanation: Step 1: ""1337c0d3"" (no characters read because there is no leading whitespace) ^ Step 2: ""1337c0d3"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""1337c0d3"" (""1337"" is read in; reading stops because the next character is a non-digit) ^ Example 4: Input: s = ""0-1"" Output: 0 Explanation: Step 1: ""0-1"" (no characters read because there is no leading whitespace) ^ Step 2: ""0-1"" (no characters read because there is neither a '-' nor '+') ^ Step 3: ""0-1"" (""0"" is read in; reading stops because the next character is a non-digit) ^ Example 5: Input: s = ""words and 987"" Output: 0 Explanation: Reading stops at the first non-digit character 'w'. Constraints: 0 <= s.length <= 200 s consists of English letters (lower-case and upper-case); digits (0-9); ' '; '+'; '-'; and '.'."
Goldman Sachs,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Goldman Sachs,51,N-Queens,Hard,"Array, Backtracking","The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n; return all distinct solutions to the n-queens puzzle. You may return the answer in any order. Each solution contains a distinct board configuration of the n-queens' placement; where 'Q' and '.' both indicate a queen and an empty space; respectively. Example 1: Input: n = 4 Output: [["".Q.."";""...Q"";""Q..."";""..Q.""];[""..Q."";""Q..."";""...Q"";"".Q..""]] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above Example 2: Input: n = 1 Output: [[""Q""]] Constraints: 1 <= n <= 9"
Goldman Sachs,119,Pascal's Triangle II,Easy,"Array, Dynamic Programming",Given an integer rowIndex; return the rowIndexth (0-indexed) row of the Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: rowIndex = 3 Output: [1;3;3;1] Example 2: Input: rowIndex = 0 Output: [1] Example 3: Input: rowIndex = 1 Output: [1;1] Constraints: 0 <= rowIndex <= 33 Follow up: Could you optimize your algorithm to use only O(rowIndex) extra space?
Goldman Sachs,134,Gas Station,Med,"Array, Greedy",There are n gas stations along a circular route; where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i + 1)th station. You begin the journey with an empty tank at one of the gas stations. Given two integer arrays gas and cost; return the starting gas station's index if you can travel around the circuit once in the clockwise direction; otherwise return -1. If there exists a solution; it is guaranteed to be unique. Example 1: Input: gas = [1;2;3;4;5]; cost = [3;4;5;1;2] Output: 3 Explanation: Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 4. Your tank = 4 - 1 + 5 = 8 Travel to station 0. Your tank = 8 - 2 + 1 = 7 Travel to station 1. Your tank = 7 - 3 + 2 = 6 Travel to station 2. Your tank = 6 - 4 + 3 = 5 Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. Therefore; return 3 as the starting index. Example 2: Input: gas = [2;3;4]; cost = [3;4;3] Output: -1 Explanation: You can't start at station 0 or 1; as there is not enough gas to travel to the next station. Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 Travel to station 0. Your tank = 4 - 3 + 2 = 3 Travel to station 1. Your tank = 3 - 3 + 3 = 3 You cannot travel back to station 2; as it requires 4 unit of gas but you only have 3. Therefore; you can't travel around the circuit once no matter where you start. Constraints: n == gas.length == cost.length 1 <= n <= 105 0 <= gas[i]; cost[i] <= 104
Goldman Sachs,135,Candy,Hard,"Array, Greedy",There are n children standing in a line. Each child is assigned a rating value given in the integer array ratings. You are giving candies to these children subjected to the following requirements: Each child must have at least one candy. Children with a higher rating get more candies than their neighbors. Return the minimum number of candies you need to have to distribute the candies to the children. Example 1: Input: ratings = [1;0;2] Output: 5 Explanation: You can allocate to the first; second and third child with 2; 1; 2 candies respectively. Example 2: Input: ratings = [1;2;2] Output: 4 Explanation: You can allocate to the first; second and third child with 1; 2; 1 candies respectively. The third child gets 1 candy because it satisfies the above two conditions. Constraints: n == ratings.length 1 <= n <= 2 * 104 0 <= ratings[i] <= 2 * 104
Goldman Sachs,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Goldman Sachs,209,Minimum Size Subarray Sum,Med,"Array, Binary Search, Sliding Window, Prefix Sum",Given an array of positive integers nums and a positive integer target; return the minimal length of a subarray whose sum is greater than or equal to target. If there is no such subarray; return 0 instead. Example 1: Input: target = 7; nums = [2;3;1;2;4;3] Output: 2 Explanation: The subarray [4;3] has the minimal length under the problem constraint. Example 2: Input: target = 4; nums = [1;4;4] Output: 1 Example 3: Input: target = 11; nums = [1;1;1;1;1;1;1;1] Output: 0 Constraints: 1 <= target <= 109 1 <= nums.length <= 105 1 <= nums[i] <= 104 Follow up: If you have figured out the O(n) solution; try coding another solution of which the time complexity is O(n log(n)).
Goldman Sachs,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Goldman Sachs,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Goldman Sachs,41,First Missing Positive,Hard,"Array, Hash Table",Given an unsorted integer array nums. Return the smallest positive integer that is not present in nums. You must implement an algorithm that runs in O(n) time and uses O(1) auxiliary space. Example 1: Input: nums = [1;2;0] Output: 3 Explanation: The numbers in the range [1;2] are all in the array. Example 2: Input: nums = [3;4;-1;1] Output: 2 Explanation: 1 is in the array but 2 is missing. Example 3: Input: nums = [7;8;9;11;12] Output: 1 Explanation: The smallest positive integer 1 is missing. Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1
Goldman Sachs,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Goldman Sachs,97,Interleaving String,Med,"String, Dynamic Programming","Given strings s1; s2; and s3; find whether s3 is formed by an interleaving of s1 and s2. An interleaving of two strings s and t is a configuration where s and t are divided into n and m substrings respectively; such that: s = s1 + s2 + ... + sn t = t1 + t2 + ... + tm |n - m| <= 1 The interleaving is s1 + t1 + s2 + t2 + s3 + t3 + ... or t1 + s1 + t2 + s2 + t3 + s3 + ... Note: a + b is the concatenation of strings a and b. Example 1: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbcbcac"" Output: true Explanation: One way to obtain s3 is: Split s1 into s1 = ""aa"" + ""bc"" + ""c""; and s2 into s2 = ""dbbc"" + ""a"". Interleaving the two splits; we get ""aa"" + ""dbbc"" + ""bc"" + ""a"" + ""c"" = ""aadbbcbcac"". Since s3 can be obtained by interleaving s1 and s2; we return true. Example 2: Input: s1 = ""aabcc""; s2 = ""dbbca""; s3 = ""aadbbbaccc"" Output: false Explanation: Notice how it is impossible to interleave s2 with any other string to obtain s3. Example 3: Input: s1 = """"; s2 = """"; s3 = """" Output: true Constraints: 0 <= s1.length; s2.length <= 100 0 <= s3.length <= 200 s1; s2; and s3 consist of lowercase English letters. Follow up: Could you solve it using only O(s2.length) additional memory space?"
Goldman Sachs,118,Pascal's Triangle,Easy,"Array, Dynamic Programming",Given an integer numRows; return the first numRows of Pascal's triangle. In Pascal's triangle; each number is the sum of the two numbers directly above it as shown: Example 1: Input: numRows = 5 Output: [[1];[1;1];[1;2;1];[1;3;3;1];[1;4;6;4;1]] Example 2: Input: numRows = 1 Output: [[1]] Constraints: 1 <= numRows <= 30
Goldman Sachs,143,Reorder List,Med,"Linked List, Two Pointers, Stack, Recursion",You are given the head of a singly linked-list. The list can be represented as: L0 → L1 → … → Ln - 1 → Ln Reorder the list to be on the following form: L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → … You may not modify the values in the list's nodes. Only nodes themselves may be changed. Example 1: Input: head = [1;2;3;4] Output: [1;4;2;3] Example 2: Input: head = [1;2;3;4;5] Output: [1;5;2;4;3] Constraints: The number of nodes in the list is in the range [1; 5 * 104]. 1 <= Node.val <= 1000
Goldman Sachs,152,Maximum Product Subarray,Med,"Array, Dynamic Programming",Given an integer array nums; find a subarray that has the largest product; and return the product. The test cases are generated so that the answer will fit in a 32-bit integer. Example 1: Input: nums = [2;3;-2;4] Output: 6 Explanation: [2;3] has the largest product 6. Example 2: Input: nums = [-2;0;-1] Output: 0 Explanation: The result cannot be 2; because [-2;-1] is not a subarray. Constraints: 1 <= nums.length <= 2 * 104 -10 <= nums[i] <= 10 The product of any subarray of nums is guaranteed to fit in a 32-bit integer.
Goldman Sachs,160,Intersection of Two Linked Lists,Easy,"Hash Table, Linked List, Two Pointers",Given the heads of two singly linked-lists headA and headB; return the node at which the two lists intersect. If the two linked lists have no intersection at all; return null. For example; the following two linked lists begin to intersect at node c1: The test cases are generated such that there are no cycles anywhere in the entire linked structure. Note that the linked lists must retain their original structure after the function returns. Custom Judge: The inputs to the judge are given as follows (your program is not given these inputs): intersectVal - The value of the node where the intersection occurs. This is 0 if there is no intersected node. listA - The first linked list. listB - The second linked list. skipA - The number of nodes to skip ahead in listA (starting from the head) to get to the intersected node. skipB - The number of nodes to skip ahead in listB (starting from the head) to get to the intersected node. The judge will then create the linked structure based on these inputs and pass the two heads; headA and headB to your program. If you correctly return the intersected node; then your solution will be accepted. Example 1: Input: intersectVal = 8; listA = [4;1;8;4;5]; listB = [5;6;1;8;4;5]; skipA = 2; skipB = 3 Output: Intersected at '8' Explanation: The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [4;1;8;4;5]. From the head of B; it reads as [5;6;1;8;4;5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B. - Note that the intersected node's value is not 1 because the nodes with value 1 in A and B (2nd node in A and 3rd node in B) are different node references. In other words; they point to two different locations in memory; while the nodes with value 8 in A and B (3rd node in A and 4th node in B) point to the same location in memory. Example 2: Input: intersectVal = 2; listA = [1;9;1;2;4]; listB = [3;2;4]; skipA = 3; skipB = 1 Output: Intersected at '2' Explanation: The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A; it reads as [1;9;1;2;4]. From the head of B; it reads as [3;2;4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B. Example 3: Input: intersectVal = 0; listA = [2;6;4]; listB = [1;5]; skipA = 3; skipB = 2 Output: No intersection Explanation: From the head of A; it reads as [2;6;4]. From the head of B; it reads as [1;5]. Since the two lists do not intersect; intersectVal must be 0; while skipA and skipB can be arbitrary values. Explanation: The two lists do not intersect; so return null. Constraints: The number of nodes of listA is in the m. The number of nodes of listB is in the n. 1 <= m; n <= 3 * 104 1 <= Node.val <= 105 0 <= skipA <= m 0 <= skipB <= n intersectVal is 0 if listA and listB do not intersect. intersectVal == listA[skipA] == listB[skipB] if listA and listB intersect. Follow up: Could you write a solution that runs in O(m + n) time and use only O(1) memory?
Goldman Sachs,189,Rotate Array,Med,"Array, Math, Two Pointers",Given an integer array nums; rotate the array to the right by k steps; where k is non-negative. Example 1: Input: nums = [1;2;3;4;5;6;7]; k = 3 Output: [5;6;7;1;2;3;4] Explanation: rotate 1 steps to the right: [7;1;2;3;4;5;6] rotate 2 steps to the right: [6;7;1;2;3;4;5] rotate 3 steps to the right: [5;6;7;1;2;3;4] Example 2: Input: nums = [-1;-100;3;99]; k = 2 Output: [3;99;-1;-100] Explanation: rotate 1 steps to the right: [99;-1;-100;3] rotate 2 steps to the right: [3;99;-1;-100] Constraints: 1 <= nums.length <= 105 -231 <= nums[i] <= 231 - 1 0 <= k <= 105 Follow up: Try to come up with as many solutions as you can. There are at least three different ways to solve this problem. Could you do it in-place with O(1) extra space?
Goldman Sachs,215,Kth Largest Element in an Array,Med,"Array, Divide and Conquer, Sorting, Heap (Priority Queue), Quickselect",Given an integer array nums and an integer k; return the kth largest element in the array. Note that it is the kth largest element in the sorted order; not the kth distinct element. Can you solve it without sorting? Example 1: Input: nums = [3;2;1;5;6;4]; k = 2 Output: 5 Example 2: Input: nums = [3;2;3;1;2;4;5;5;6]; k = 4 Output: 4 Constraints: 1 <= k <= nums.length <= 105 -104 <= nums[i] <= 104
Goldman Sachs,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Goldman Sachs,268,Missing Number,Easy,"Array, Hash Table, Math, Binary Search, Bit Manipulation, Sorting",Given an array nums containing n distinct numbers in the range [0; n]; return the only number in the range that is missing from the array. Example 1: Input: nums = [3;0;1] Output: 2 Explanation: n = 3 since there are 3 numbers; so all numbers are in the range [0;3]. 2 is the missing number in the range since it does not appear in nums. Example 2: Input: nums = [0;1] Output: 2 Explanation: n = 2 since there are 2 numbers; so all numbers are in the range [0;2]. 2 is the missing number in the range since it does not appear in nums. Example 3: Input: nums = [9;6;4;2;3;5;7;0;1] Output: 8 Explanation: n = 9 since there are 9 numbers; so all numbers are in the range [0;9]. 8 is the missing number in the range since it does not appear in nums. Constraints: n == nums.length 1 <= n <= 104 0 <= nums[i] <= n All the numbers of nums are unique. Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?
Goldman Sachs,421,Maximum XOR of Two Numbers in an Array,Med,"Array, Hash Table, Bit Manipulation, Trie",Given an integer array nums; return the maximum result of nums[i] XOR nums[j]; where 0 <= i <= j < n. Example 1: Input: nums = [3;10;5;25;2;8] Output: 28 Explanation: The maximum result is 5 XOR 25 = 28. Example 2: Input: nums = [14;70;53;83;49;91;36;80;92;51;66;70] Output: 127 Constraints: 1 <= nums.length <= 2 * 105 0 <= nums[i] <= 231 - 1
Goldman Sachs,696,Count Binary Substrings,Easy,"Two Pointers, String","Given a binary string s; return the number of non-empty substrings that have the same number of 0's and 1's; and all the 0's and all the 1's in these substrings are grouped consecutively. Substrings that occur multiple times are counted the number of times they occur. Example 1: Input: s = ""00110011"" Output: 6 Explanation: There are 6 substrings that have equal number of consecutive 1's and 0's: ""0011""; ""01""; ""1100""; ""10""; ""0011""; and ""01"". Notice that some of these substrings repeat and are counted the number of times they occur. Also; ""00110011"" is not a valid substring because all the 0's (and 1's) are not grouped together. Example 2: Input: s = ""10101"" Output: 4 Explanation: There are 4 substrings: ""10""; ""01""; ""10""; ""01"" that have equal number of consecutive 1's and 0's. Constraints: 1 <= s.length <= 105 s[i] is either '0' or '1'."
Goldman Sachs,845,Longest Mountain in Array,Med,,
Goldman Sachs,1190,Reverse Substrings Between Each Pair of Parentheses,Med,"Array, Hash Table, String, Tree, Depth-First Search, Breadth-First Search",
Goldman Sachs,1306,Jump Game III,Med,"Array, Sorting",Given an array of distinct integers arr; find all pairs of elements with the minimum absolute difference of any two elements. Return a list of pairs in ascending order(with respect to pairs); each pair [a; b] follows a; b are from arr a < b b - a equals to the minimum absolute difference of any two elements in arr Example 1: Input: arr = [4;2;1;3] Output: [[1;2];[2;3];[3;4]] Explanation: The minimum absolute difference is 1. List all pairs with difference equal to 1 in ascending order. Example 2: Input: arr = [1;3;6;10;15] Output: [[1;3]] Example 3: Input: arr = [3;8;-10;23;19;-4;-14;27] Output: [[-14;-10];[19;23];[23;27]] Constraints: 2 <= arr.length <= 105 -106 <= arr[i] <= 106
Citadel,2771,Longest Non-decreasing Subarray From Two Arrays,Med,,
Citadel,124,Binary Tree Maximum Path Sum,Hard,"Dynamic Programming, Tree, Depth-First Search, Binary Tree",A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root. The path sum of a path is the sum of the node's values in the path. Given the root of a binary tree; return the maximum path sum of any non-empty path. Example 1: Input: root = [1;2;3] Output: 6 Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6. Example 2: Input: root = [-10;9;20;null;null;15;7] Output: 42 Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42. Constraints: The number of nodes in the tree is in the range [1; 3 * 104]. -1000 <= Node.val <= 1000
Citadel,740,Delete and Earn,Med,"Array, Hash Table, Dynamic Programming",You are given an integer array nums. You want to maximize the number of points you get by performing the following operation any number of times: Pick any nums[i] and delete it to earn nums[i] points. Afterwards; you must delete every element equal to nums[i] - 1 and every element equal to nums[i] + 1. Return the maximum number of points you can earn by applying the above operation some number of times. Example 1: Input: nums = [3;4;2] Output: 6 Explanation: You can perform the following operations: - Delete 4 to earn 4 points. Consequently; 3 is also deleted. nums = [2]. - Delete 2 to earn 2 points. nums = []. You earn a total of 6 points. Example 2: Input: nums = [2;2;3;3;3;4] Output: 9 Explanation: You can perform the following operations: - Delete a 3 to earn 3 points. All 2's and 4's are also deleted. nums = [3;3]. - Delete a 3 again to earn 3 points. nums = [3]. - Delete a 3 once more to earn 3 points. nums = []. You earn a total of 9 points. Constraints: 1 <= nums.length <= 2 * 104 1 <= nums[i] <= 104
Citadel,1197,Minimum Knight Moves,Med,"String, Stack, Recursion","A boolean expression is an expression that evaluates to either true or false. It can be in one of the following shapes: 't' that evaluates to true. 'f' that evaluates to false. '!(subExpr)' that evaluates to the logical NOT of the inner expression subExpr. '&(subExpr1; subExpr2; ...; subExprn)' that evaluates to the logical AND of the inner expressions subExpr1; subExpr2; ...; subExprn where n >= 1. '|(subExpr1; subExpr2; ...; subExprn)' that evaluates to the logical OR of the inner expressions subExpr1; subExpr2; ...; subExprn where n >= 1. Given a string expression that represents a boolean expression; return the evaluation of that expression. It is guaranteed that the given expression is valid and follows the given rules. Example 1: Input: expression = ""&(|(f))"" Output: false Explanation: First; evaluate |(f) --> f. The expression is now ""&(f)"". Then; evaluate &(f) --> f. The expression is now ""f"". Finally; return false. Example 2: Input: expression = ""|(f;f;f;t)"" Output: true Explanation: The evaluation of (false OR false OR false OR true) is true. Example 3: Input: expression = ""!(&(f;t))"" Output: true Explanation: First; evaluate &(f;t) --> (false AND true) --> false --> f. The expression is now ""!(f)"". Then; evaluate !(f) --> NOT false --> true. We return true. Constraints: 1 <= expression.length <= 2 * 104 expression[i] is one following characters: '('; ')'; '&'; '|'; '!'; 't'; 'f'; and ';'."
Citadel,2918,Minimum Equal Sum of Two Arrays After Replacing Zeros,Med,"Stack, Tree, Depth-First Search, Binary Tree",
Citadel,2361,Minimum Costs Using the Train Line,Hard,"String, Simulation","You are given a string s consisting of digits and an integer k. A round can be completed if the length of s is greater than k. In one round; do the following: Divide s into consecutive groups of size k such that the first k characters are in the first group; the next k characters are in the second group; and so on. Note that the size of the last group can be smaller than k. Replace each group of s with a string representing the sum of all its digits. For example; ""346"" is replaced with ""13"" because 3 + 4 + 6 = 13. Merge consecutive groups together to form a new string. If the length of the string is greater than k; repeat from step 1. Return s after all rounds have been completed. Example 1: Input: s = ""11111222223""; k = 3 Output: ""135"" Explanation: - For the first round; we divide s into groups of size 3: ""111""; ""112""; ""222""; and ""23"". ​​​​​Then we calculate the digit sum of each group: 1 + 1 + 1 = 3; 1 + 1 + 2 = 4; 2 + 2 + 2 = 6; and 2 + 3 = 5. So; s becomes ""3"" + ""4"" + ""6"" + ""5"" = ""3465"" after the first round. - For the second round; we divide s into ""346"" and ""5"". Then we calculate the digit sum of each group: 3 + 4 + 6 = 13; 5 = 5. So; s becomes ""13"" + ""5"" = ""135"" after second round. Now; s.length <= k; so we return ""135"" as the answer. Example 2: Input: s = ""00000000""; k = 3 Output: ""000"" Explanation: We divide s into ""000""; ""000""; and ""00"". Then we calculate the digit sum of each group: 0 + 0 + 0 = 0; 0 + 0 + 0 = 0; and 0 + 0 = 0. s becomes ""0"" + ""0"" + ""0"" = ""000""; whose length is equal to k; so we return ""000"". Constraints: 1 <= s.length <= 100 2 <= k <= 100 s consists of digits only."
Citadel,460,LFU Cache,Hard,"Hash Table, Linked List, Design, Doubly-Linked List","Design and implement a data structure for a Least Frequently Used (LFU) cache. Implement the LFUCache class: LFUCache(int capacity) Initializes the object with the capacity of the data structure. int get(int key) Gets the value of the key if the key exists in the cache. Otherwise; returns -1. void put(int key; int value) Update the value of the key if present; or inserts the key if not already present. When the cache reaches its capacity; it should invalidate and remove the least frequently used key before inserting a new item. For this problem; when there is a tie (i.e.; two or more keys with the same frequency); the least recently used key would be invalidated. To determine the least frequently used key; a use counter is maintained for each key in the cache. The key with the smallest use counter is the least frequently used key. When a key is first inserted into the cache; its use counter is set to 1 (due to the put operation). The use counter for a key in the cache is incremented either a get or put operation is called on it. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LFUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [3]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; 3; null; -1; 3; 4] Explanation // cnt(x) = the use counter for key x // cache=[] will show the last used order for tiebreakers (leftmost element is most recent) LFUCache lfu = new LFUCache(2); lfu.put(1; 1); // cache=[1;_]; cnt(1)=1 lfu.put(2; 2); // cache=[2;1]; cnt(2)=1; cnt(1)=1 lfu.get(1); // return 1 // cache=[1;2]; cnt(2)=1; cnt(1)=2 lfu.put(3; 3); // 2 is the LFU key because cnt(2)=1 is the smallest; invalidate 2. // cache=[3;1]; cnt(3)=1; cnt(1)=2 lfu.get(2); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;1]; cnt(3)=2; cnt(1)=2 lfu.put(4; 4); // Both 1 and 3 have the same cnt; but 1 is LRU; invalidate 1. // cache=[4;3]; cnt(4)=1; cnt(3)=2 lfu.get(1); // return -1 (not found) lfu.get(3); // return 3 // cache=[3;4]; cnt(4)=1; cnt(3)=3 lfu.get(4); // return 4 // cache=[4;3]; cnt(4)=2; cnt(3)=3 Constraints: 1 <= capacity <= 104 0 <= key <= 105 0 <= value <= 109 At most 2 * 105 calls will be made to get and put."
Citadel,2533,Number of Good Binary Strings,Med,"Array, Bit Manipulation, Brainteaser",You are given two 0-indexed arrays; nums1 and nums2; consisting of non-negative integers. There exists another array; nums3; which contains the bitwise XOR of all pairings of integers between nums1 and nums2 (every integer in nums1 is paired with every integer in nums2 exactly once). Return the bitwise XOR of all integers in nums3. Example 1: Input: nums1 = [2;1;3]; nums2 = [10;2;5;0] Output: 13 Explanation: A possible nums3 array is [8;0;7;2;11;3;4;1;9;1;6;3]. The bitwise XOR of all these numbers is 13; so we return 13. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 0 Explanation: All possible pairs of bitwise XORs are nums1[0] ^ nums2[0]; nums1[0] ^ nums2[1]; nums1[1] ^ nums2[0]; and nums1[1] ^ nums2[1]. Thus; one possible nums3 array is [2;5;1;6]. 2 ^ 5 ^ 1 ^ 6 = 0; so we return 0. Constraints: 1 <= nums1.length; nums2.length <= 105 0 <= nums1[i]; nums2[j] <= 109
Citadel,2702,Minimum Operations to Make Numbers Non-positive,Hard,"Array, Binary Search, Greedy, Sorting",
Citadel,3186,Maximum Total Damage With Spell Casting,Med,Array,You are given a 0-indexed array nums of integers. A triplet of indices (i; j; k) is a mountain if: i < j < k nums[i] < nums[j] and nums[k] < nums[j] Return the minimum possible sum of a mountain triplet of nums. If no such triplet exists; return -1. Example 1: Input: nums = [8;6;1;5;3] Output: 9 Explanation: Triplet (2; 3; 4) is a mountain triplet of sum 9 since: - 2 < 3 < 4 - nums[2] < nums[3] and nums[4] < nums[3] And the sum of this triplet is nums[2] + nums[3] + nums[4] = 9. It can be shown that there are no mountain triplets with a sum of less than 9. Example 2: Input: nums = [5;4;8;7;10;2] Output: 13 Explanation: Triplet (1; 3; 5) is a mountain triplet of sum 13 since: - 1 < 3 < 5 - nums[1] < nums[3] and nums[5] < nums[3] And the sum of this triplet is nums[1] + nums[3] + nums[5] = 13. It can be shown that there are no mountain triplets with a sum of less than 13. Example 3: Input: nums = [6;5;4;3;4;5] Output: -1 Explanation: It can be shown that there are no mountain triplets in nums. Constraints: 3 <= nums.length <= 105 1 <= nums[i] <= 108
Citadel,718,Maximum Length of Repeated Subarray,Med,"Array, Binary Search, Dynamic Programming, Sliding Window, Rolling Hash, Hash Function",Given two integer arrays nums1 and nums2; return the maximum length of a subarray that appears in both arrays. Example 1: Input: nums1 = [1;2;3;2;1]; nums2 = [3;2;1;4;7] Output: 3 Explanation: The repeated subarray with maximum length is [3;2;1]. Example 2: Input: nums1 = [0;0;0;0;0]; nums2 = [0;0;0;0;0] Output: 5 Explanation: The repeated subarray with maximum length is [0;0;0;0;0]. Constraints: 1 <= nums1.length; nums2.length <= 1000 0 <= nums1[i]; nums2[i] <= 100
Citadel,1515,Best Position for a Service Centre,Hard,"Math, Greedy",Given an integer k; return the minimum number of Fibonacci numbers whose sum is equal to k. The same Fibonacci number can be used multiple times. The Fibonacci numbers are defined as: F1 = 1 F2 = 1 Fn = Fn-1 + Fn-2 for n > 2. It is guaranteed that for the given constraints we can always find such Fibonacci numbers that sum up to k. Example 1: Input: k = 7 Output: 2 Explanation: The Fibonacci numbers are: 1; 1; 2; 3; 5; 8; 13; ... For k = 7 we can use 2 + 5 = 7. Example 2: Input: k = 10 Output: 2 Explanation: For k = 10 we can use 2 + 8 = 10. Example 3: Input: k = 19 Output: 3 Explanation: For k = 19 we can use 1 + 5 + 13 = 19. Constraints: 1 <= k <= 109
Citadel,974,Subarray Sums Divisible by K,Med,"Array, String, Sorting","You are given an array of logs. Each log is a space-delimited string of words; where the first word is the identifier. There are two types of logs: Letter-logs: All words (except the identifier) consist of lowercase English letters. Digit-logs: All words (except the identifier) consist of digits. Reorder these logs so that: The letter-logs come before all digit-logs. The letter-logs are sorted lexicographically by their contents. If their contents are the same; then sort them lexicographically by their identifiers. The digit-logs maintain their relative ordering. Return the final order of the logs. Example 1: Input: logs = [""dig1 8 1 5 1"";""let1 art can"";""dig2 3 6"";""let2 own kit dig"";""let3 art zero""] Output: [""let1 art can"";""let3 art zero"";""let2 own kit dig"";""dig1 8 1 5 1"";""dig2 3 6""] Explanation: The letter-log contents are all different; so their ordering is ""art can""; ""art zero""; ""own kit dig"". The digit-logs have a relative order of ""dig1 8 1 5 1""; ""dig2 3 6"". Example 2: Input: logs = [""a1 9 2 3 1"";""g1 act car"";""zo4 4 7"";""ab1 off key dog"";""a8 act zoo""] Output: [""g1 act car"";""a8 act zoo"";""ab1 off key dog"";""a1 9 2 3 1"";""zo4 4 7""] Constraints: 1 <= logs.length <= 100 3 <= logs[i].length <= 100 All the tokens of logs[i] are separated by a single space. logs[i] is guaranteed to have an identifier and at least one word after the identifier."
Citadel,2661,First Completely Painted Row or Column,Med,"Array, Hash Table, Math, Greedy",You are given a 0-indexed integer array nums and an integer value. In one operation; you can add or subtract value from any element of nums. For example; if nums = [1;2;3] and value = 2; you can choose to subtract value from nums[0] to make nums = [-1;2;3]. The MEX (minimum excluded) of an array is the smallest missing non-negative integer in it. For example; the MEX of [-1;2;3] is 0 while the MEX of [1;0;3] is 2. Return the maximum MEX of nums after applying the mentioned operation any number of times. Example 1: Input: nums = [1;-10;7;13;6;8]; value = 5 Output: 4 Explanation: One can achieve this result by applying the following operations: - Add value to nums[1] twice to make nums = [1;0;7;13;6;8] - Subtract value from nums[2] once to make nums = [1;0;2;13;6;8] - Subtract value from nums[3] twice to make nums = [1;0;2;3;6;8] The MEX of nums is 4. It can be shown that 4 is the maximum MEX we can achieve. Example 2: Input: nums = [1;-10;7;13;6;8]; value = 7 Output: 2 Explanation: One can achieve this result by applying the following operation: - subtract value from nums[2] once to make nums = [1;-10;0;13;6;8] The MEX of nums is 2. It can be shown that 2 is the maximum MEX we can achieve. Constraints: 1 <= nums.length; value <= 105 -109 <= nums[i] <= 109
Citadel,146,LRU Cache,Med,"Hash Table, Linked List, Design, Doubly-Linked List","Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists; otherwise return -1. void put(int key; int value) Update the value of the key if the key exists. Otherwise; add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation; evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input [""LRUCache""; ""put""; ""put""; ""get""; ""put""; ""get""; ""put""; ""get""; ""get""; ""get""] [[2]; [1; 1]; [2; 2]; [1]; [3; 3]; [2]; [4; 4]; [1]; [3]; [4]] Output [null; null; null; 1; null; -1; null; -1; 3; 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1; 1); // cache is {1=1} lRUCache.put(2; 2); // cache is {1=1; 2=2} lRUCache.get(1); // return 1 lRUCache.put(3; 3); // LRU key was 2; evicts key 2; cache is {1=1; 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4; 4); // LRU key was 1; evicts key 1; cache is {4=4; 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put."
Citadel,647,Palindromic Substrings,Med,"Two Pointers, String, Dynamic Programming","Given a string s; return the number of palindromic substrings in it. A string is a palindrome when it reads the same backward as forward. A substring is a contiguous sequence of characters within the string. Example 1: Input: s = ""abc"" Output: 3 Explanation: Three palindromic strings: ""a""; ""b""; ""c"". Example 2: Input: s = ""aaa"" Output: 6 Explanation: Six palindromic strings: ""a""; ""a""; ""a""; ""aa""; ""aa""; ""aaa"". Constraints: 1 <= s.length <= 1000 s consists of lowercase English letters."
Citadel,150,Evaluate Reverse Polish Notation,Med,"Array, Math, Stack","You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression. Return an integer that represents the value of the expression. Note that: The valid operators are '+'; '-'; '*'; and '/'. Each operand may be an integer or another expression. The division between two integers always truncates toward zero. There will not be any division by zero. The input represents a valid arithmetic expression in a reverse polish notation. The answer and all the intermediate calculations can be represented in a 32-bit integer. Example 1: Input: tokens = [""2"";""1"";""+"";""3"";""*""] Output: 9 Explanation: ((2 + 1) * 3) = 9 Example 2: Input: tokens = [""4"";""13"";""5"";""/"";""+""] Output: 6 Explanation: (4 + (13 / 5)) = 6 Example 3: Input: tokens = [""10"";""6"";""9"";""3"";""+"";""-11"";""*"";""/"";""*"";""17"";""+"";""5"";""+""] Output: 22 Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 = ((10 * (6 / (12 * -11))) + 17) + 5 = ((10 * (6 / -132)) + 17) + 5 = ((10 * 0) + 17) + 5 = (0 + 17) + 5 = 17 + 5 = 22 Constraints: 1 <= tokens.length <= 104 tokens[i] is either an operator: ""+""; ""-""; ""*""; or ""/""; or an integer in the range [-200; 200]."
Citadel,1048,Longest String Chain,Med,"Math, Stack, Simulation",The factorial of a positive integer n is the product of all positive integers less than or equal to n. For example; factorial(10) = 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1. We make a clumsy factorial using the integers in decreasing order by swapping out the multiply operations for a fixed rotation of operations with multiply '*'; divide '/'; add '+'; and subtract '-' in this order. For example; clumsy(10) = 10 * 9 / 8 + 7 - 6 * 5 / 4 + 3 - 2 * 1. However; these operations are still applied using the usual order of operations of arithmetic. We do all multiplication and division steps before any addition or subtraction steps; and multiplication and division steps are processed left to right. Additionally; the division that we use is floor division such that 10 * 9 / 8 = 90 / 8 = 11. Given an integer n; return the clumsy factorial of n. Example 1: Input: n = 4 Output: 7 Explanation: 7 = 4 * 3 / 2 + 1 Example 2: Input: n = 10 Output: 12 Explanation: 12 = 10 * 9 / 8 + 7 - 6 * 5 / 4 + 3 - 2 * 1 Constraints: 1 <= n <= 104
Citadel,121,Best Time to Buy and Sell Stock,Easy,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit; return 0. Example 1: Input: prices = [7;1;5;3;6;4] Output: 5 Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6); profit = 6-1 = 5. Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell. Example 2: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transactions are done and the max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 104
Citadel,122,Best Time to Buy and Sell Stock II,Med,"Array, Dynamic Programming, Greedy",You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day; you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However; you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. Example 1: Input: prices = [7;1;5;3;6;4] Output: 7 Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5); profit = 5-1 = 4. Then buy on day 4 (price = 3) and sell on day 5 (price = 6); profit = 6-3 = 3. Total profit is 4 + 3 = 7. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Total profit is 4. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: There is no way to make a positive profit; so we never buy the stock to achieve the maximum profit of 0. Constraints: 1 <= prices.length <= 3 * 104 0 <= prices[i] <= 104
Citadel,297,Serialize and Deserialize Binary Tree,Hard,"String, Tree, Depth-First Search, Breadth-First Search, Design, Binary Tree",Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer; or transmitted across a network connection link to be reconstructed later in the same or another computer environment. Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure. Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format; so please be creative and come up with different approaches yourself. Example 1: Input: root = [1;2;3;null;null;4;5] Output: [1;2;3;null;null;4;5] Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 104]. -1000 <= Node.val <= 1000
Citadel,239,Sliding Window Maximum,Hard,"Array, Queue, Sliding Window, Heap (Priority Queue), Monotonic Queue",You are given an array of integers nums; there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window. Example 1: Input: nums = [1;3;-1;-3;5;3;6;7]; k = 3 Output: [3;3;5;5;6;7] Explanation: Window position Max --------------- ----- [1 3 -1] -3 5 3 6 7 3 1 [3 -1 -3] 5 3 6 7 3 1 3 [-1 -3 5] 3 6 7 5 1 3 -1 [-3 5 3] 6 7 5 1 3 -1 -3 [5 3 6] 7 6 1 3 -1 -3 5 [3 6 7] 7 Example 2: Input: nums = [1]; k = 1 Output: [1] Constraints: 1 <= nums.length <= 105 -104 <= nums[i] <= 104 1 <= k <= nums.length
Citadel,287,Find the Duplicate Number,Med,"Array, Two Pointers, Binary Search, Bit Manipulation",Given an array of integers nums containing n + 1 integers where each integer is in the range [1; n] inclusive. There is only one repeated number in nums; return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Example 1: Input: nums = [1;3;4;2;2] Output: 2 Example 2: Input: nums = [3;1;3;4;2] Output: 3 Example 3: Input: nums = [3;3;3;3;3] Output: 3 Constraints: 1 <= n <= 105 nums.length == n + 1 1 <= nums[i] <= n All the integers in nums appear only once except for precisely one integer which appears two or more times. Follow up: How can we prove that at least one duplicate number must exist in nums? Can you solve the problem in linear runtime complexity?
Citadel,10,Regular Expression Matching,Hard,"String, Dynamic Programming, Recursion","Given an input string s and a pattern p; implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = ""aa""; p = ""a"" Output: false Explanation: ""a"" does not match the entire string ""aa"". Example 2: Input: s = ""aa""; p = ""a*"" Output: true Explanation: '*' means zero or more of the preceding element; 'a'. Therefore; by repeating 'a' once; it becomes ""aa"". Example 3: Input: s = ""ab""; p = "".*"" Output: true Explanation: "".*"" means ""zero or more (*) of any character (.)"". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase English letters; '.'; and '*'. It is guaranteed for each appearance of the character '*'; there will be a previous valid character to match."
Citadel,37,Sudoku Solver,Hard,"Array, Hash Table, Backtracking, Matrix","Write a program to solve a Sudoku puzzle by filling the empty cells. A sudoku solution must satisfy all of the following rules: Each of the digits 1-9 must occur exactly once in each row. Each of the digits 1-9 must occur exactly once in each column. Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid. The '.' character indicates empty cells. Example 1: Input: board = [[""5"";""3"";""."";""."";""7"";""."";""."";""."";"".""];[""6"";""."";""."";""1"";""9"";""5"";""."";""."";"".""];[""."";""9"";""8"";""."";""."";""."";""."";""6"";"".""];[""8"";""."";""."";""."";""6"";""."";""."";""."";""3""];[""4"";""."";""."";""8"";""."";""3"";""."";""."";""1""];[""7"";""."";""."";""."";""2"";""."";""."";""."";""6""];[""."";""6"";""."";""."";""."";""."";""2"";""8"";"".""];[""."";""."";""."";""4"";""1"";""9"";""."";""."";""5""];[""."";""."";""."";""."";""8"";""."";""."";""7"";""9""]] Output: [[""5"";""3"";""4"";""6"";""7"";""8"";""9"";""1"";""2""];[""6"";""7"";""2"";""1"";""9"";""5"";""3"";""4"";""8""];[""1"";""9"";""8"";""3"";""4"";""2"";""5"";""6"";""7""];[""8"";""5"";""9"";""7"";""6"";""1"";""4"";""2"";""3""];[""4"";""2"";""6"";""8"";""5"";""3"";""7"";""9"";""1""];[""7"";""1"";""3"";""9"";""2"";""4"";""8"";""5"";""6""];[""9"";""6"";""1"";""5"";""3"";""7"";""2"";""8"";""4""];[""2"";""8"";""7"";""4"";""1"";""9"";""6"";""3"";""5""];[""3"";""4"";""5"";""2"";""8"";""6"";""1"";""7"";""9""]] Explanation: The input board is shown above and the only valid solution is shown below: Constraints: board.length == 9 board[i].length == 9 board[i][j] is a digit or '.'. It is guaranteed that the input board has only one solution."
Citadel,46,Permutations,Med,"Array, Backtracking",Given an array nums of distinct integers; return all the possible permutations. You can return the answer in any order. Example 1: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Example 2: Input: nums = [0;1] Output: [[0;1];[1;0]] Example 3: Input: nums = [1] Output: [[1]] Constraints: 1 <= nums.length <= 6 -10 <= nums[i] <= 10 All the integers of nums are unique.
Citadel,98,Validate Binary Search Tree,Med,"Tree, Depth-First Search, Binary Search Tree, Binary Tree",Given the root of a binary tree; determine if it is a valid binary search tree (BST). A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees. Example 1: Input: root = [2;1;3] Output: true Example 2: Input: root = [5;1;4;null;null;3;6] Output: false Explanation: The root node's value is 5 but its right child's value is 4. Constraints: The number of nodes in the tree is in the range [1; 104]. -231 <= Node.val <= 231 - 1
Citadel,295,Find Median from Data Stream,Hard,"Two Pointers, Design, Sorting, Heap (Priority Queue), Data Stream","The median is the middle value in an ordered integer list. If the size of the list is even; there is no middle value; and the median is the mean of the two middle values. For example; for arr = [2;3;4]; the median is 3. For example; for arr = [2;3]; the median is (2 + 3) / 2 = 2.5. Implement the MedianFinder class: MedianFinder() initializes the MedianFinder object. void addNum(int num) adds the integer num from the data stream to the data structure. double findMedian() returns the median of all elements so far. Answers within 10-5 of the actual answer will be accepted. Example 1: Input [""MedianFinder""; ""addNum""; ""addNum""; ""findMedian""; ""addNum""; ""findMedian""] [[]; [1]; [2]; []; [3]; []] Output [null; null; null; 1.5; null; 2.0] Explanation MedianFinder medianFinder = new MedianFinder(); medianFinder.addNum(1); // arr = [1] medianFinder.addNum(2); // arr = [1; 2] medianFinder.findMedian(); // return 1.5 (i.e.; (1 + 2) / 2) medianFinder.addNum(3); // arr[1; 2; 3] medianFinder.findMedian(); // return 2.0 Constraints: -105 <= num <= 105 There will be at least one element in the data structure before calling findMedian. At most 5 * 104 calls will be made to addNum and findMedian. Follow up: If all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution? If 99% of all integer numbers from the stream are in the range [0; 100]; how would you optimize your solution?"
Citadel,489,Robot Room Cleaner,Hard,"Array, Math, Dynamic Programming, Combinatorics","Bob is standing at cell (0; 0); and he wants to reach destination: (row; column). He can only travel right and down. You are going to help Bob by providing instructions for him to reach destination. The instructions are represented as a string; where each character is either: 'H'; meaning move horizontally (go right); or 'V'; meaning move vertically (go down). Multiple instructions will lead Bob to destination. For example; if destination is (2; 3); both ""HHHVV"" and ""HVHVH"" are valid instructions. However; Bob is very picky. Bob has a lucky number k; and he wants the kth lexicographically smallest instructions that will lead him to destination. k is 1-indexed. Given an integer array destination and an integer k; return the kth lexicographically smallest instructions that will take Bob to destination. Example 1: Input: destination = [2;3]; k = 1 Output: ""HHHVV"" Explanation: All the instructions that reach (2; 3) in lexicographic order are as follows: [""HHHVV""; ""HHVHV""; ""HHVVH""; ""HVHHV""; ""HVHVH""; ""HVVHH""; ""VHHHV""; ""VHHVH""; ""VHVHH""; ""VVHHH""]. Example 2: Input: destination = [2;3]; k = 2 Output: ""HHVHV"" Example 3: Input: destination = [2;3]; k = 3 Output: ""HHVVH"" Constraints: destination.length == 2 1 <= row; column <= 15 1 <= k <= nCr(row + column; row); where nCr(a; b) denotes a choose b​​​​​."
Citadel,2958,Length of Longest Subarray With at Most K Frequency,Med,,
Citadel,23,Merge k Sorted Lists,Hard,"Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort",You are given an array of k linked-lists lists; each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1;4;5];[1;3;4];[2;6]] Output: [1;1;2;3;4;4;5;6] Explanation: The linked-lists are: [ 1->4->5; 1->3->4; 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.
Citadel,42,Trapping Rain Water,Hard,"Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack",Given n non-negative integers representing an elevation map where the width of each bar is 1; compute how much water it can trap after raining. Example 1: Input: height = [0;1;0;2;1;0;1;3;2;1;2;1] Output: 6 Explanation: The above elevation map (black section) is represented by array [0;1;0;2;1;0;1;3;2;1;2;1]. In this case; 6 units of rain water (blue section) are being trapped. Example 2: Input: height = [4;2;0;3;2;5] Output: 9 Constraints: n == height.length 1 <= n <= 2 * 104 0 <= height[i] <= 105
Citadel,49,Group Anagrams,Med,"Array, Hash Table, String, Sorting","Given an array of strings strs; group the anagrams together. You can return the answer in any order. Example 1: Input: strs = [""eat"";""tea"";""tan"";""ate"";""nat"";""bat""] Output: [[""bat""];[""nat"";""tan""];[""ate"";""eat"";""tea""]] Explanation: There is no string in strs that can be rearranged to form ""bat"". The strings ""nat"" and ""tan"" are anagrams as they can be rearranged to form each other. The strings ""ate""; ""eat""; and ""tea"" are anagrams as they can be rearranged to form each other. Example 2: Input: strs = [""""] Output: [[""""]] Example 3: Input: strs = [""a""] Output: [[""a""]] Constraints: 1 <= strs.length <= 104 0 <= strs[i].length <= 100 strs[i] consists of lowercase English letters."
Citadel,51,N-Queens,Hard,"Array, Backtracking","The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other. Given an integer n; return all distinct solutions to the n-queens puzzle. You may return the answer in any order. Each solution contains a distinct board configuration of the n-queens' placement; where 'Q' and '.' both indicate a queen and an empty space; respectively. Example 1: Input: n = 4 Output: [["".Q.."";""...Q"";""Q..."";""..Q.""];[""..Q."";""Q..."";""...Q"";"".Q..""]] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above Example 2: Input: n = 1 Output: [[""Q""]] Constraints: 1 <= n <= 9"
Citadel,200,Number of Islands,Med,"Array, Depth-First Search, Breadth-First Search, Union Find, Matrix","Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water); return the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water. Example 1: Input: grid = [ [""1"";""1"";""1"";""1"";""0""]; [""1"";""1"";""0"";""1"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""0"";""0"";""0""] ] Output: 1 Example 2: Input: grid = [ [""1"";""1"";""0"";""0"";""0""]; [""1"";""1"";""0"";""0"";""0""]; [""0"";""0"";""1"";""0"";""0""]; [""0"";""0"";""0"";""1"";""1""] ] Output: 3 Constraints: m == grid.length n == grid[i].length 1 <= m; n <= 300 grid[i][j] is '0' or '1'."
Citadel,221,Maximal Square,Med,"Array, Dynamic Programming, Matrix","Given an m x n binary matrix filled with 0's and 1's; find the largest square containing only 1's and return its area. Example 1: Input: matrix = [[""1"";""0"";""1"";""0"";""0""];[""1"";""0"";""1"";""1"";""1""];[""1"";""1"";""1"";""1"";""1""];[""1"";""0"";""0"";""1"";""0""]] Output: 4 Example 2: Input: matrix = [[""0"";""1""];[""1"";""0""]] Output: 1 Example 3: Input: matrix = [[""0""]] Output: 0 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 300 matrix[i][j] is '0' or '1'."
Citadel,399,Evaluate Division,Med,"Array, String, Depth-First Search, Breadth-First Search, Union Find, Graph, Shortest Path","You are given an array of variable pairs equations and an array of real numbers values; where equations[i] = [Ai; Bi] and values[i] represent the equation Ai / Bi = values[i]. Each Ai or Bi is a string that represents a single variable. You are also given some queries; where queries[j] = [Cj; Dj] represents the jth query where you must find the answer for Cj / Dj = ?. Return the answers to all queries. If a single answer cannot be determined; return -1.0. Note: The input is always valid. You may assume that evaluating the queries will not result in division by zero and that there is no contradiction. Note: The variables that do not occur in the list of equations are undefined; so the answer cannot be determined for them. Example 1: Input: equations = [[""a"";""b""];[""b"";""c""]]; values = [2.0;3.0]; queries = [[""a"";""c""];[""b"";""a""];[""a"";""e""];[""a"";""a""];[""x"";""x""]] Output: [6.00000;0.50000;-1.00000;1.00000;-1.00000] Explanation: Given: a / b = 2.0; b / c = 3.0 queries are: a / c = ?; b / a = ?; a / e = ?; a / a = ?; x / x = ? return: [6.0; 0.5; -1.0; 1.0; -1.0 ] note: x is undefined => -1.0 Example 2: Input: equations = [[""a"";""b""];[""b"";""c""];[""bc"";""cd""]]; values = [1.5;2.5;5.0]; queries = [[""a"";""c""];[""c"";""b""];[""bc"";""cd""];[""cd"";""bc""]] Output: [3.75000;0.40000;5.00000;0.20000] Example 3: Input: equations = [[""a"";""b""]]; values = [0.5]; queries = [[""a"";""b""];[""b"";""a""];[""a"";""c""];[""x"";""y""]] Output: [0.50000;2.00000;-1.00000;-1.00000] Constraints: 1 <= equations.length <= 20 equations[i].length == 2 1 <= Ai.length; Bi.length <= 5 values.length == equations.length 0.0 < values[i] <= 20.0 1 <= queries.length <= 20 queries[i].length == 2 1 <= Cj.length; Dj.length <= 5 Ai; Bi; Cj; Dj consist of lower case English letters and digits."
Citadel,642,Design Search Autocomplete System,Hard,"String, Depth-First Search, Design, Trie, Sorting, Heap (Priority Queue), Data Stream",
Citadel,765,Couples Holding Hands,Hard,"String, Tree, Depth-First Search, Breadth-First Search",
Citadel,622,Design Circular Queue,Med,,
Citadel,994,Rotting Oranges,Med,"Array, Hash Table, Math, Bit Manipulation",There are 8 prison cells in a row and each cell is either occupied or vacant. Each day; whether the cell is occupied or vacant changes according to the following rules: If a cell has two adjacent neighbors that are both occupied or both vacant; then the cell becomes occupied. Otherwise; it becomes vacant. Note that because the prison is a row; the first and the last cells in the row can't have two adjacent neighbors. You are given an integer array cells where cells[i] == 1 if the ith cell is occupied and cells[i] == 0 if the ith cell is vacant; and you are given an integer n. Return the state of the prison after n days (i.e.; n such changes described above). Example 1: Input: cells = [0;1;0;1;1;0;0;1]; n = 7 Output: [0;0;1;1;0;0;0;0] Explanation: The following table summarizes the state of the prison on each day: Day 0: [0; 1; 0; 1; 1; 0; 0; 1] Day 1: [0; 1; 1; 0; 0; 0; 0; 0] Day 2: [0; 0; 0; 0; 1; 1; 1; 0] Day 3: [0; 1; 1; 0; 0; 1; 0; 0] Day 4: [0; 0; 0; 0; 0; 1; 0; 0] Day 5: [0; 1; 1; 1; 0; 1; 0; 0] Day 6: [0; 0; 1; 0; 1; 1; 0; 0] Day 7: [0; 0; 1; 1; 0; 0; 0; 0] Example 2: Input: cells = [1;0;0;1;0;0;1;0]; n = 1000000000 Output: [0;0;1;1;1;1;1;0] Constraints: cells.length == 8 cells[i] is either 0 or 1. 1 <= n <= 109
Citadel,1268,Search Suggestions System,Med,Database,Table: Users +----------------+---------+ | Column Name | Type | +----------------+---------+ | user_id | int | | join_date | date | | favorite_brand | varchar | +----------------+---------+ user_id is the primary key (column with unique values) of this table. This table has the info of the users of an online shopping website where users can sell and buy items. Table: Orders +---------------+---------+ | Column Name | Type | +---------------+---------+ | order_id | int | | order_date | date | | item_id | int | | buyer_id | int | | seller_id | int | +---------------+---------+ order_id is the primary key (column with unique values) of this table. item_id is a foreign key (reference column) to the Items table. buyer_id and seller_id are foreign keys to the Users table. Table: Items +---------------+---------+ | Column Name | Type | +---------------+---------+ | item_id | int | | item_brand | varchar | +---------------+---------+ item_id is the primary key (column with unique values) of this table. Write a solution to find for each user; the join date and the number of orders they made as a buyer in 2019. Return the result table in any order. The result format is in the following example. Example 1: Input: Users table: +---------+------------+----------------+ | user_id | join_date | favorite_brand | +---------+------------+----------------+ | 1 | 2018-01-01 | Lenovo | | 2 | 2018-02-09 | Samsung | | 3 | 2018-01-19 | LG | | 4 | 2018-05-21 | HP | +---------+------------+----------------+ Orders table: +----------+------------+---------+----------+-----------+ | order_id | order_date | item_id | buyer_id | seller_id | +----------+------------+---------+----------+-----------+ | 1 | 2019-08-01 | 4 | 1 | 2 | | 2 | 2018-08-02 | 2 | 1 | 3 | | 3 | 2019-08-03 | 3 | 2 | 3 | | 4 | 2018-08-04 | 1 | 4 | 2 | | 5 | 2018-08-04 | 1 | 3 | 4 | | 6 | 2019-08-05 | 2 | 2 | 4 | +----------+------------+---------+----------+-----------+ Items table: +---------+------------+ | item_id | item_brand | +---------+------------+ | 1 | Samsung | | 2 | Lenovo | | 3 | LG | | 4 | HP | +---------+------------+ Output: +-----------+------------+----------------+ | buyer_id | join_date | orders_in_2019 | +-----------+------------+----------------+ | 1 | 2018-01-01 | 1 | | 2 | 2018-02-09 | 2 | | 3 | 2018-01-19 | 0 | | 4 | 2018-05-21 | 0 | +-----------+------------+----------------+
Citadel,4,Median of Two Sorted Arrays,Hard,"Array, Binary Search, Divide and Conquer",Given two sorted arrays nums1 and nums2 of size m and n respectively; return the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)). Example 1: Input: nums1 = [1;3]; nums2 = [2] Output: 2.00000 Explanation: merged array = [1;2;3] and median is 2. Example 2: Input: nums1 = [1;2]; nums2 = [3;4] Output: 2.50000 Explanation: merged array = [1;2;3;4] and median is (2 + 3) / 2 = 2.5. Constraints: nums1.length == m nums2.length == n 0 <= m <= 1000 0 <= n <= 1000 1 <= m + n <= 2000 -106 <= nums1[i]; nums2[i] <= 106
Citadel,17,Letter Combinations of a Phone Number,Med,"Hash Table, String, Backtracking","Given a string containing digits from 2-9 inclusive; return all possible letter combinations that the number could represent. Return the answer in any order. A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. Example 1: Input: digits = ""23"" Output: [""ad"";""ae"";""af"";""bd"";""be"";""bf"";""cd"";""ce"";""cf""] Example 2: Input: digits = """" Output: [] Example 3: Input: digits = ""2"" Output: [""a"";""b"";""c""] Constraints: 0 <= digits.length <= 4 digits[i] is a digit in the range ['2'; '9']."
Citadel,39,Combination Sum,Med,"Array, Backtracking",Given an array of distinct integers candidates and a target integer target; return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order. The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency of at least one of the chosen numbers is different. The test cases are generated such that the number of unique combinations that sum up to target is less than 150 combinations for the given input. Example 1: Input: candidates = [2;3;6;7]; target = 7 Output: [[2;2;3];[7]] Explanation: 2 and 3 are candidates; and 2 + 2 + 3 = 7. Note that 2 can be used multiple times. 7 is a candidate; and 7 = 7. These are the only two combinations. Example 2: Input: candidates = [2;3;5]; target = 8 Output: [[2;2;2;2];[2;3;3];[3;5]] Example 3: Input: candidates = [2]; target = 1 Output: [] Constraints: 1 <= candidates.length <= 30 2 <= candidates[i] <= 40 All elements of candidates are distinct. 1 <= target <= 40
Citadel,123,Best Time to Buy and Sell Stock III,Hard,"Array, Dynamic Programming",You are given an array prices where prices[i] is the price of a given stock on the ith day. Find the maximum profit you can achieve. You may complete at most two transactions. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: prices = [3;3;5;0;0;3;1;4] Output: 6 Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Then buy on day 7 (price = 1) and sell on day 8 (price = 4); profit = 4-1 = 3. Example 2: Input: prices = [1;2;3;4;5] Output: 4 Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5); profit = 5-1 = 4. Note that you cannot buy on day 1; buy on day 2 and sell them later; as you are engaging multiple transactions at the same time. You must sell before buying again. Example 3: Input: prices = [7;6;4;3;1] Output: 0 Explanation: In this case; no transaction is done; i.e. max profit = 0. Constraints: 1 <= prices.length <= 105 0 <= prices[i] <= 105
Citadel,188,Best Time to Buy and Sell Stock IV,Hard,"Array, Dynamic Programming",You are given an integer array prices where prices[i] is the price of a given stock on the ith day; and an integer k. Find the maximum profit you can achieve. You may complete at most k transactions: i.e. you may buy at most k times and sell at most k times. Note: You may not engage in multiple transactions simultaneously (i.e.; you must sell the stock before you buy again). Example 1: Input: k = 2; prices = [2;4;1] Output: 2 Explanation: Buy on day 1 (price = 2) and sell on day 2 (price = 4); profit = 4-2 = 2. Example 2: Input: k = 2; prices = [3;2;6;5;0;3] Output: 7 Explanation: Buy on day 2 (price = 2) and sell on day 3 (price = 6); profit = 6-2 = 4. Then buy on day 5 (price = 0) and sell on day 6 (price = 3); profit = 3-0 = 3. Constraints: 1 <= k <= 100 1 <= prices.length <= 1000 0 <= prices[i] <= 1000
Citadel,198,House Robber,Med,"Array, Dynamic Programming",You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed; the only constraint stopping you from robbing each of them is that adjacent houses have security systems connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given an integer array nums representing the amount of money of each house; return the maximum amount of money you can rob tonight without alerting the police. Example 1: Input: nums = [1;2;3;1] Output: 4 Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3). Total amount you can rob = 1 + 3 = 4. Example 2: Input: nums = [2;7;9;3;1] Output: 12 Explanation: Rob house 1 (money = 2); rob house 3 (money = 9) and rob house 5 (money = 1). Total amount you can rob = 2 + 9 + 1 = 12. Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 400
Citadel,207,Course Schedule,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return true if you can finish all courses. Otherwise; return false. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: true Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. Example 2: Input: numCourses = 2; prerequisites = [[1;0];[0;1]] Output: false Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0; and to take course 0 you should also have finished course 1. So it is impossible. Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= 5000 prerequisites[i].length == 2 0 <= ai; bi < numCourses All the pairs prerequisites[i] are unique.
Citadel,208,Implement Trie (Prefix Tree),Med,"Hash Table, String, Design, Trie","A trie (pronounced as ""try"") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure; such as autocomplete and spellchecker. Implement the Trie class: Trie() Initializes the trie object. void insert(String word) Inserts the string word into the trie. boolean search(String word) Returns true if the string word is in the trie (i.e.; was inserted before); and false otherwise. boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix; and false otherwise. Example 1: Input [""Trie""; ""insert""; ""search""; ""search""; ""startsWith""; ""insert""; ""search""] [[]; [""apple""]; [""apple""]; [""app""]; [""app""]; [""app""]; [""app""]] Output [null; null; true; false; true; null; true] Explanation Trie trie = new Trie(); trie.insert(""apple""); trie.search(""apple""); // return True trie.search(""app""); // return False trie.startsWith(""app""); // return True trie.insert(""app""); trie.search(""app""); // return True Constraints: 1 <= word.length; prefix.length <= 2000 word and prefix consist only of lowercase English letters. At most 3 * 104 calls in total will be made to insert; search; and startsWith."
Citadel,269,Alien Dictionary,Hard,"Array, String, Depth-First Search, Breadth-First Search, Graph, Topological Sort",
Citadel,279,Perfect Squares,Med,"Math, Dynamic Programming, Breadth-First Search",Given an integer n; return the least number of perfect square numbers that sum to n. A perfect square is an integer that is the square of an integer; in other words; it is the product of some integer with itself. For example; 1; 4; 9; and 16 are perfect squares while 3 and 11 are not. Example 1: Input: n = 12 Output: 3 Explanation: 12 = 4 + 4 + 4. Example 2: Input: n = 13 Output: 2 Explanation: 13 = 4 + 9. Constraints: 1 <= n <= 104
Citadel,310,Minimum Height Trees,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",A tree is an undirected graph in which any two vertices are connected by exactly one path. In other words; any connected graph without simple cycles is a tree. Given a tree of n nodes labelled from 0 to n - 1; and an array of n - 1 edges where edges[i] = [ai; bi] indicates that there is an undirected edge between the two nodes ai and bi in the tree; you can choose any node of the tree as the root. When you select a node x as the root; the result tree has height h. Among all possible rooted trees; those with minimum height (i.e. min(h)) are called minimum height trees (MHTs). Return a list of all MHTs' root labels. You can return the answer in any order. The height of a rooted tree is the number of edges on the longest downward path between the root and a leaf. Example 1: Input: n = 4; edges = [[1;0];[1;2];[1;3]] Output: [1] Explanation: As shown; the height of the tree is 1 when the root is the node with label 1 which is the only MHT. Example 2: Input: n = 6; edges = [[3;0];[3;1];[3;2];[3;4];[5;4]] Output: [3;4] Constraints: 1 <= n <= 2 * 104 edges.length == n - 1 0 <= ai; bi < n ai != bi All the pairs (ai; bi) are distinct. The given input is guaranteed to be a tree and there will be no repeated edges.
Citadel,329,Longest Increasing Path in a Matrix,Hard,"Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph, Topological Sort, Memoization, Matrix",Given an m x n integers matrix; return the length of the longest increasing path in matrix. From each cell; you can either move in four directions: left; right; up; or down. You may not move diagonally or move outside the boundary (i.e.; wrap-around is not allowed). Example 1: Input: matrix = [[9;9;4];[6;6;8];[2;1;1]] Output: 4 Explanation: The longest increasing path is [1; 2; 6; 9]. Example 2: Input: matrix = [[3;4;5];[3;2;6];[2;2;1]] Output: 4 Explanation: The longest increasing path is [3; 4; 5; 6]. Moving diagonally is not allowed. Example 3: Input: matrix = [[1]] Output: 1 Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 200 0 <= matrix[i][j] <= 231 - 1
Citadel,412,Fizz Buzz,Easy,"Math, String, Simulation","Given an integer n; return a string array answer (1-indexed) where: answer[i] == ""FizzBuzz"" if i is divisible by 3 and 5. answer[i] == ""Fizz"" if i is divisible by 3. answer[i] == ""Buzz"" if i is divisible by 5. answer[i] == i (as a string) if none of the above conditions are true. Example 1: Input: n = 3 Output: [""1"";""2"";""Fizz""] Example 2: Input: n = 5 Output: [""1"";""2"";""Fizz"";""4"";""Buzz""] Example 3: Input: n = 15 Output: [""1"";""2"";""Fizz"";""4"";""Buzz"";""Fizz"";""7"";""8"";""Fizz"";""Buzz"";""11"";""Fizz"";""13"";""14"";""FizzBuzz""] Constraints: 1 <= n <= 104"
Citadel,631,Design Excel Sum Formula,Hard,"Array, Graph, Design, Topological Sort, Matrix",
Citadel,782,Transform to Chessboard,Hard,"Hash Table, String","You're given strings jewels representing the types of stones that are jewels; and stones representing the stones you have. Each character in stones is a type of stone you have. You want to know how many of the stones you have are also jewels. Letters are case sensitive; so ""a"" is considered a different type of stone from ""A"". Example 1: Input: jewels = ""aA""; stones = ""aAAbbbb"" Output: 3 Example 2: Input: jewels = ""z""; stones = ""ZZ"" Output: 0 Constraints: 1 <= jewels.length; stones.length <= 50 jewels and stones consist of only English letters. All the characters of jewels are unique."
Citadel,2466,Count Ways To Build Good Strings,Med,"Array, Union Find, Prefix Sum, Ordered Set",You are given two 0-indexed integer arrays nums and removeQueries; both of length n. For the ith query; the element in nums at the index removeQueries[i] is removed; splitting nums into different segments. A segment is a contiguous sequence of positive integers in nums. A segment sum is the sum of every element in a segment. Return an integer array answer; of length n; where answer[i] is the maximum segment sum after applying the ith removal. Note: The same index will not be removed more than once. Example 1: Input: nums = [1;2;5;6;1]; removeQueries = [0;3;2;4;1] Output: [14;7;2;2;0] Explanation: Using 0 to indicate a removed element; the answer is as follows: Query 1: Remove the 0th element; nums becomes [0;2;5;6;1] and the maximum segment sum is 14 for segment [2;5;6;1]. Query 2: Remove the 3rd element; nums becomes [0;2;5;0;1] and the maximum segment sum is 7 for segment [2;5]. Query 3: Remove the 2nd element; nums becomes [0;2;0;0;1] and the maximum segment sum is 2 for segment [2]. Query 4: Remove the 4th element; nums becomes [0;2;0;0;0] and the maximum segment sum is 2 for segment [2]. Query 5: Remove the 1st element; nums becomes [0;0;0;0;0] and the maximum segment sum is 0; since there are no segments. Finally; we return [14;7;2;2;0]. Example 2: Input: nums = [3;2;11;1]; removeQueries = [3;2;1;0] Output: [16;5;3;0] Explanation: Using 0 to indicate a removed element; the answer is as follows: Query 1: Remove the 3rd element; nums becomes [3;2;11;0] and the maximum segment sum is 16 for segment [3;2;11]. Query 2: Remove the 2nd element; nums becomes [3;2;0;0] and the maximum segment sum is 5 for segment [3;2]. Query 3: Remove the 1st element; nums becomes [3;0;0;0] and the maximum segment sum is 3 for segment [3]. Query 4: Remove the 0th element; nums becomes [0;0;0;0] and the maximum segment sum is 0; since there are no segments. Finally; we return [16;5;3;0]. Constraints: n == nums.length == removeQueries.length 1 <= n <= 105 1 <= nums[i] <= 109 0 <= removeQueries[i] < n All the values of removeQueries are unique.
Citadel,11,Container With Most Water,Med,"Array, Two Pointers, Greedy",You are given an integer array height of length n. There are n vertical lines drawn such that the two endpoints of the ith line are (i; 0) and (i; height[i]). Find two lines that together with the x-axis form a container; such that the container contains the most water. Return the maximum amount of water a container can store. Notice that you may not slant the container. Example 1: Input: height = [1;8;6;2;5;4;8;3;7] Output: 49 Explanation: The above vertical lines are represented by array [1;8;6;2;5;4;8;3;7]. In this case; the max area of water (blue section) the container can contain is 49. Example 2: Input: height = [1;1] Output: 1 Constraints: n == height.length 2 <= n <= 105 0 <= height[i] <= 104
Citadel,13,Roman to Integer,Easy,"Hash Table, Math, String","Roman numerals are represented by seven different symbols: I; V; X; L; C; D and M. Symbol Value I 1 V 5 X 10 L 50 C 100 D 500 M 1000 For example; 2 is written as II in Roman numeral; just two ones added together. 12 is written as XII; which is simply X + II. The number 27 is written as XXVII; which is XX + V + II. Roman numerals are usually written largest to smallest from left to right. However; the numeral for four is not IIII. Instead; the number four is written as IV. Because the one is before the five we subtract it making four. The same principle applies to the number nine; which is written as IX. There are six instances where subtraction is used: I can be placed before V (5) and X (10) to make 4 and 9. X can be placed before L (50) and C (100) to make 40 and 90. C can be placed before D (500) and M (1000) to make 400 and 900. Given a roman numeral; convert it to an integer. Example 1: Input: s = ""III"" Output: 3 Explanation: III = 3. Example 2: Input: s = ""LVIII"" Output: 58 Explanation: L = 50; V= 5; III = 3. Example 3: Input: s = ""MCMXCIV"" Output: 1994 Explanation: M = 1000; CM = 900; XC = 90 and IV = 4. Constraints: 1 <= s.length <= 15 s contains only the characters ('I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M'). It is guaranteed that s is a valid roman numeral in the range [1; 3999]."
Citadel,15,3Sum,Med,"Array, Two Pointers, Sorting",Given an integer array nums; return all the triplets [nums[i]; nums[j]; nums[k]] such that i != j; i != k; and j != k; and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets. Example 1: Input: nums = [-1;0;1;2;-1;-4] Output: [[-1;-1;2];[-1;0;1]] Explanation: nums[0] + nums[1] + nums[2] = (-1) + 0 + 1 = 0. nums[1] + nums[2] + nums[4] = 0 + 1 + (-1) = 0. nums[0] + nums[3] + nums[4] = (-1) + 2 + (-1) = 0. The distinct triplets are [-1;0;1] and [-1;-1;2]. Notice that the order of the output and the order of the triplets does not matter. Example 2: Input: nums = [0;1;1] Output: [] Explanation: The only possible triplet does not sum up to 0. Example 3: Input: nums = [0;0;0] Output: [[0;0;0]] Explanation: The only possible triplet sums up to 0. Constraints: 3 <= nums.length <= 3000 -105 <= nums[i] <= 105
Citadel,20,Valid Parentheses,Easy,"String, Stack","Given a string s containing just the characters '('; ')'; '{'; '}'; '[' and ']'; determine if the input string is valid. An input string is valid if: Open brackets must be closed by the same type of brackets. Open brackets must be closed in the correct order. Every close bracket has a corresponding open bracket of the same type. Example 1: Input: s = ""()"" Output: true Example 2: Input: s = ""()[]{}"" Output: true Example 3: Input: s = ""(]"" Output: false Example 4: Input: s = ""([])"" Output: true Constraints: 1 <= s.length <= 104 s consists of parentheses only '()[]{}'."
Citadel,31,Next Permutation,Med,"Array, Two Pointers",A permutation of an array of integers is an arrangement of its members into a sequence or linear order. For example; for arr = [1;2;3]; the following are all the permutations of arr: [1;2;3]; [1;3;2]; [2; 1; 3]; [2; 3; 1]; [3;1;2]; [3;2;1]. The next permutation of an array of integers is the next lexicographically greater permutation of its integer. More formally; if all the permutations of the array are sorted in one container according to their lexicographical order; then the next permutation of that array is the permutation that follows it in the sorted container. If such arrangement is not possible; the array must be rearranged as the lowest possible order (i.e.; sorted in ascending order). For example; the next permutation of arr = [1;2;3] is [1;3;2]. Similarly; the next permutation of arr = [2;3;1] is [3;1;2]. While the next permutation of arr = [3;2;1] is [1;2;3] because [3;2;1] does not have a lexicographical larger rearrangement. Given an array of integers nums; find the next permutation of nums. The replacement must be in place and use only constant extra memory. Example 1: Input: nums = [1;2;3] Output: [1;3;2] Example 2: Input: nums = [3;2;1] Output: [1;2;3] Example 3: Input: nums = [1;1;5] Output: [1;5;1] Constraints: 1 <= nums.length <= 100 0 <= nums[i] <= 100
Citadel,47,Permutations II,Med,"Array, Backtracking",Given a collection of numbers; nums; that might contain duplicates; return all possible unique permutations in any order. Example 1: Input: nums = [1;1;2] Output: [[1;1;2]; [1;2;1]; [2;1;1]] Example 2: Input: nums = [1;2;3] Output: [[1;2;3];[1;3;2];[2;1;3];[2;3;1];[3;1;2];[3;2;1]] Constraints: 1 <= nums.length <= 8 -10 <= nums[i] <= 10
Citadel,54,Spiral Matrix,Med,"Array, Matrix, Simulation",Given an m x n matrix; return all elements of the matrix in spiral order. Example 1: Input: matrix = [[1;2;3];[4;5;6];[7;8;9]] Output: [1;2;3;6;9;8;7;4;5] Example 2: Input: matrix = [[1;2;3;4];[5;6;7;8];[9;10;11;12]] Output: [1;2;3;4;8;12;11;10;9;5;6;7] Constraints: m == matrix.length n == matrix[i].length 1 <= m; n <= 10 -100 <= matrix[i][j] <= 100
Citadel,62,Unique Paths,Med,"Math, Dynamic Programming, Combinatorics",There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e.; grid[0][0]). The robot tries to move to the bottom-right corner (i.e.; grid[m - 1][n - 1]). The robot can only move either down or right at any point in time. Given the two integers m and n; return the number of possible unique paths that the robot can take to reach the bottom-right corner. The test cases are generated so that the answer will be less than or equal to 2 * 109. Example 1: Input: m = 3; n = 7 Output: 28 Example 2: Input: m = 3; n = 2 Output: 3 Explanation: From the top-left corner; there are a total of 3 ways to reach the bottom-right corner: 1. Right -> Down -> Down 2. Down -> Down -> Right 3. Down -> Right -> Down Constraints: 1 <= m; n <= 100
Citadel,69,Sqrt(x),Easy,"Math, Binary Search",Given a non-negative integer x; return the square root of x rounded down to the nearest integer. The returned integer should be non-negative as well. You must not use any built-in exponent function or operator. For example; do not use pow(x; 0.5) in c++ or x ** 0.5 in python. Example 1: Input: x = 4 Output: 2 Explanation: The square root of 4 is 2; so we return 2. Example 2: Input: x = 8 Output: 2 Explanation: The square root of 8 is 2.82842...; and since we round it down to the nearest integer; 2 is returned. Constraints: 0 <= x <= 231 - 1
Citadel,70,Climbing Stairs,Easy,"Math, Dynamic Programming, Memoization",You are climbing a staircase. It takes n steps to reach the top. Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top? Example 1: Input: n = 2 Output: 2 Explanation: There are two ways to climb to the top. 1. 1 step + 1 step 2. 2 steps Example 2: Input: n = 3 Output: 3 Explanation: There are three ways to climb to the top. 1. 1 step + 1 step + 1 step 2. 1 step + 2 steps 3. 2 steps + 1 step Constraints: 1 <= n <= 45
Citadel,71,Simplify Path,Med,"String, Stack","You are given an absolute path for a Unix-style file system; which always begins with a slash '/'. Your task is to transform this absolute path into its simplified canonical path. The rules of a Unix-style file system are as follows: A single period '.' represents the current directory. A double period '..' represents the previous/parent directory. Multiple consecutive slashes such as '//' and '///' are treated as a single slash '/'. Any sequence of periods that does not match the rules above should be treated as a valid directory or file name. For example; '...' and '....' are valid directory or file names. The simplified canonical path should follow these rules: The path must start with a single slash '/'. Directories within the path must be separated by exactly one slash '/'. The path must not end with a slash '/'; unless it is the root directory. The path must not have any single or double periods ('.' and '..') used to denote current or parent directories. Return the simplified canonical path. Example 1: Input: path = ""/home/"" Output: ""/home"" Explanation: The trailing slash should be removed. Example 2: Input: path = ""/home//foo/"" Output: ""/home/foo"" Explanation: Multiple consecutive slashes are replaced by a single one. Example 3: Input: path = ""/home/user/Documents/../Pictures"" Output: ""/home/user/Pictures"" Explanation: A double period "".."" refers to the directory up a level (the parent directory). Example 4: Input: path = ""/../"" Output: ""/"" Explanation: Going one level up from the root directory is not possible. Example 5: Input: path = ""/.../a/../b/c/../d/./"" Output: ""/.../b/d"" Explanation: ""..."" is a valid name for a directory in this problem. Constraints: 1 <= path.length <= 3000 path consists of English letters; digits; period '.'; slash '/' or '_'. path is a valid absolute Unix path."
Citadel,79,Word Search,Med,"Array, String, Backtracking, Matrix","Given an m x n grid of characters board and a string word; return true if word exists in the grid. The word can be constructed from letters of sequentially adjacent cells; where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCCED"" Output: true Example 2: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""SEE"" Output: true Example 3: Input: board = [[""A"";""B"";""C"";""E""];[""S"";""F"";""C"";""S""];[""A"";""D"";""E"";""E""]]; word = ""ABCB"" Output: false Constraints: m == board.length n = board[i].length 1 <= m; n <= 6 1 <= word.length <= 15 board and word consists of only lowercase and uppercase English letters. Follow up: Could you use search pruning to make your solution faster with a larger board?"
Citadel,116,Populating Next Right Pointers in Each Node,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",You are given a perfect binary tree where all leaves are on the same level; and every parent has two children. The binary tree has the following definition: struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;6;7] Output: [1;#;2;3;#;4;5;6;7;#] Explanation: Given the above perfect binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 212 - 1]. -1000 <= Node.val <= 1000 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Citadel,117,Populating Next Right Pointers in Each Node II,Med,"Linked List, Tree, Depth-First Search, Breadth-First Search, Binary Tree",Given a binary tree struct Node { int val; Node *left; Node *right; Node *next; } Populate each next pointer to point to its next right node. If there is no next right node; the next pointer should be set to NULL. Initially; all next pointers are set to NULL. Example 1: Input: root = [1;2;3;4;5;null;7] Output: [1;#;2;3;#;4;5;7;#] Explanation: Given the above binary tree (Figure A); your function should populate each next pointer to point to its next right node; just like in Figure B. The serialized output is in level order as connected by the next pointers; with '#' signifying the end of each level. Example 2: Input: root = [] Output: [] Constraints: The number of nodes in the tree is in the range [0; 6000]. -100 <= Node.val <= 100 Follow-up: You may only use constant extra space. The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.
Citadel,126,Word Ladder II,Hard,"Hash Table, String, Backtracking, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return all the shortest transformation sequences from beginWord to endWord; or an empty list if no such sequence exists. Each sequence should be returned as a list of the words [beginWord; s1; s2; ...; sk]. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: [[""hit"";""hot"";""dot"";""dog"";""cog""];[""hit"";""hot"";""lot"";""log"";""cog""]] Explanation: There are 2 shortest transformation sequences: ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> ""cog"" ""hit"" -> ""hot"" -> ""lot"" -> ""log"" -> ""cog"" Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: [] Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 5 endWord.length == beginWord.length 1 <= wordList.length <= 500 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique. The sum of all shortest transformation sequences does not exceed 105."
Citadel,127,Word Ladder,Hard,"Hash Table, String, Breadth-First Search","A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that: Every adjacent pair of words differs by a single letter. Every si for 1 <= i <= k is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words; beginWord and endWord; and a dictionary wordList; return the number of words in the shortest transformation sequence from beginWord to endWord; or 0 if no such sequence exists. Example 1: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log"";""cog""] Output: 5 Explanation: One shortest transformation sequence is ""hit"" -> ""hot"" -> ""dot"" -> ""dog"" -> cog""; which is 5 words long. Example 2: Input: beginWord = ""hit""; endWord = ""cog""; wordList = [""hot"";""dot"";""dog"";""lot"";""log""] Output: 0 Explanation: The endWord ""cog"" is not in wordList; therefore there is no valid transformation sequence. Constraints: 1 <= beginWord.length <= 10 endWord.length == beginWord.length 1 <= wordList.length <= 5000 wordList[i].length == beginWord.length beginWord; endWord; and wordList[i] consist of lowercase English letters. beginWord != endWord All the words in wordList are unique."
Citadel,210,Course Schedule II,Med,"Depth-First Search, Breadth-First Search, Graph, Topological Sort",There are a total of numCourses courses you have to take; labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai; bi] indicates that you must take course bi first if you want to take course ai. For example; the pair [0; 1]; indicates that to take course 0 you have to first take course 1. Return the ordering of courses you should take to finish all courses. If there are many valid answers; return any of them. If it is impossible to finish all courses; return an empty array. Example 1: Input: numCourses = 2; prerequisites = [[1;0]] Output: [0;1] Explanation: There are a total of 2 courses to take. To take course 1 you should have finished course 0. So the correct course order is [0;1]. Example 2: Input: numCourses = 4; prerequisites = [[1;0];[2;0];[3;1];[3;2]] Output: [0;2;1;3] Explanation: There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0;1;2;3]. Another correct ordering is [0;2;1;3]. Example 3: Input: numCourses = 1; prerequisites = [] Output: [0] Constraints: 1 <= numCourses <= 2000 0 <= prerequisites.length <= numCourses * (numCourses - 1) prerequisites[i].length == 2 0 <= ai; bi < numCourses ai != bi All the pairs [ai; bi] are distinct.
Citadel,218,The Skyline Problem,Hard,"Array, Divide and Conquer, Binary Indexed Tree, Segment Tree, Line Sweep, Heap (Priority Queue), Ordered Set","A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Given the locations and heights of all the buildings; return the skyline formed by these buildings collectively. The geometric information of each building is given in the array buildings where buildings[i] = [lefti; righti; heighti]: lefti is the x coordinate of the left edge of the ith building. righti is the x coordinate of the right edge of the ith building. heighti is the height of the ith building. You may assume all buildings are perfect rectangles grounded on an absolutely flat surface at height 0. The skyline should be represented as a list of ""key points"" sorted by their x-coordinate in the form [[x1;y1];[x2;y2];...]. Each key point is the left endpoint of some horizontal segment in the skyline except the last point in the list; which always has a y-coordinate 0 and is used to mark the skyline's termination where the rightmost building ends. Any ground between the leftmost and rightmost buildings should be part of the skyline's contour. Note: There must be no consecutive horizontal lines of equal height in the output skyline. For instance; [...;[2 3];[4 5];[7 5];[11 5];[12 7];...] is not acceptable; the three lines of height 5 should be merged into one in the final output as such: [...;[2 3];[4 5];[12 7];...] Example 1: Input: buildings = [[2;9;10];[3;7;15];[5;12;12];[15;20;10];[19;24;8]] Output: [[2;10];[3;15];[7;12];[12;0];[15;10];[20;8];[24;0]] Explanation: Figure A shows the buildings of the input. Figure B shows the skyline formed by those buildings. The red points in figure B represent the key points in the output list. Example 2: Input: buildings = [[0;2;3];[2;5;3]] Output: [[0;3];[5;0]] Constraints: 1 <= buildings.length <= 104 0 <= lefti < righti <= 231 - 1 1 <= heighti <= 231 - 1 buildings is sorted by lefti in non-decreasing order."
Citadel,224,Basic Calculator,Hard,"Math, String, Stack, Recursion","Given a string s representing a valid expression; implement a basic calculator to evaluate it; and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions; such as eval(). Example 1: Input: s = ""1 + 1"" Output: 2 Example 2: Input: s = "" 2-1 + 2 "" Output: 3 Example 3: Input: s = ""(1+(4+5+2)-3)+(6+8)"" Output: 23 Constraints: 1 <= s.length <= 3 * 105 s consists of digits; '+'; '-'; '('; ')'; and ' '. s represents a valid expression. '+' is not used as a unary operation (i.e.; ""+1"" and ""+(2 + 3)"" is invalid). '-' could be used as a unary operation (i.e.; ""-1"" and ""-(2 + 3)"" is valid). There will be no two consecutive operators in the input. Every number and running calculation will fit in a signed 32-bit integer."
Citadel,240,Search a 2D Matrix II,Med,"Array, Binary Search, Divide and Conquer, Matrix",Write an efficient algorithm that searches for a value target in an m x n integer matrix matrix. This matrix has the following properties: Integers in each row are sorted in ascending from left to right. Integers in each column are sorted in ascending from top to bottom. Example 1: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 5 Output: true Example 2: Input: matrix = [[1;4;7;11;15];[2;5;8;12;19];[3;6;9;16;22];[10;13;14;17;24];[18;21;23;26;30]]; target = 20 Output: false Constraints: m == matrix.length n == matrix[i].length 1 <= n; m <= 300 -109 <= matrix[i][j] <= 109 All the integers in each row are sorted in ascending order. All the integers in each column are sorted in ascending order. -109 <= target <= 109
Citadel,346,Moving Average from Data Stream,Easy,"Array, Design, Queue, Data Stream",
Citadel,380,Insert Delete GetRandom O(1),Med,"Array, Hash Table, Math, Design, Randomized","Implement the RandomizedSet class: RandomizedSet() Initializes the RandomizedSet object. bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present; false otherwise. bool remove(int val) Removes an item val from the set if present. Returns true if the item was present; false otherwise. int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned. You must implement the functions of the class such that each function works in average O(1) time complexity. Example 1: Input [""RandomizedSet""; ""insert""; ""remove""; ""insert""; ""getRandom""; ""remove""; ""insert""; ""getRandom""] [[]; [1]; [2]; [2]; []; [1]; [2]; []] Output [null; true; false; true; 2; true; false; 2] Explanation RandomizedSet randomizedSet = new RandomizedSet(); randomizedSet.insert(1); // Inserts 1 to the set. Returns true as 1 was inserted successfully. randomizedSet.remove(2); // Returns false as 2 does not exist in the set. randomizedSet.insert(2); // Inserts 2 to the set; returns true. Set now contains [1;2]. randomizedSet.getRandom(); // getRandom() should return either 1 or 2 randomly. randomizedSet.remove(1); // Removes 1 from the set; returns true. Set now contains [2]. randomizedSet.insert(2); // 2 was already in the set; so return false. randomizedSet.getRandom(); // Since 2 is the only number in the set; getRandom() will always return 2. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Citadel,381,Insert Delete GetRandom O(1) - Duplicates allowed,Hard,"Array, Hash Table, Math, Design, Randomized","RandomizedCollection is a data structure that contains a collection of numbers; possibly duplicates (i.e.; a multiset). It should support inserting and removing specific elements and also reporting a random element. Implement the RandomizedCollection class: RandomizedCollection() Initializes the empty RandomizedCollection object. bool insert(int val) Inserts an item val into the multiset; even if the item is already present. Returns true if the item is not present; false otherwise. bool remove(int val) Removes an item val from the multiset if present. Returns true if the item is present; false otherwise. Note that if val has multiple occurrences in the multiset; we only remove one of them. int getRandom() Returns a random element from the current multiset of elements. The probability of each element being returned is linearly related to the number of the same values the multiset contains. You must implement the functions of the class such that each function works on average O(1) time complexity. Note: The test cases are generated such that getRandom will only be called if there is at least one item in the RandomizedCollection. Example 1: Input [""RandomizedCollection""; ""insert""; ""insert""; ""insert""; ""getRandom""; ""remove""; ""getRandom""] [[]; [1]; [1]; [2]; []; [1]; []] Output [null; true; false; true; 2; true; 1] Explanation RandomizedCollection randomizedCollection = new RandomizedCollection(); randomizedCollection.insert(1); // return true since the collection does not contain 1. // Inserts 1 into the collection. randomizedCollection.insert(1); // return false since the collection contains 1. // Inserts another 1 into the collection. Collection now contains [1;1]. randomizedCollection.insert(2); // return true since the collection does not contain 2. // Inserts 2 into the collection. Collection now contains [1;1;2]. randomizedCollection.getRandom(); // getRandom should: // - return 1 with probability 2/3; or // - return 2 with probability 1/3. randomizedCollection.remove(1); // return true since the collection contains 1. // Removes 1 from the collection. Collection now contains [1;2]. randomizedCollection.getRandom(); // getRandom should return 1 or 2; both equally likely. Constraints: -231 <= val <= 231 - 1 At most 2 * 105 calls in total will be made to insert; remove; and getRandom. There will be at least one element in the data structure when getRandom is called."
Citadel,486,Predict the Winner,Med,"Array, Math, Dynamic Programming, Recursion, Game Theory",You are given an integer array nums. Two players are playing a game with this array: player 1 and player 2. Player 1 and player 2 take turns; with player 1 starting first. Both players start the game with a score of 0. At each turn; the player takes one of the numbers from either end of the array (i.e.; nums[0] or nums[nums.length - 1]) which reduces the size of the array by 1. The player adds the chosen number to their score. The game ends when there are no more elements in the array. Return true if Player 1 can win the game. If the scores of both players are equal; then player 1 is still the winner; and you should also return true. You may assume that both players are playing optimally. Example 1: Input: nums = [1;5;2] Output: false Explanation: Initially; player 1 can choose between 1 and 2. If he chooses 2 (or 1); then player 2 can choose from 1 (or 2) and 5. If player 2 chooses 5; then player 1 will be left with 1 (or 2). So; final score of player 1 is 1 + 2 = 3; and player 2 is 5. Hence; player 1 will never be the winner and you need to return false. Example 2: Input: nums = [1;5;233;7] Output: true Explanation: Player 1 first chooses 1. Then player 2 has to choose between 5 and 7. No matter which number player 2 choose; player 1 can choose 233. Finally; player 1 has more score (234) than player 2 (12); so you need to return True representing player1 can win. Constraints: 1 <= nums.length <= 20 0 <= nums[i] <= 107
Citadel,560,Subarray Sum Equals K,Med,"Array, Hash Table, Prefix Sum",Given an array of integers nums and an integer k; return the total number of subarrays whose sum equals to k. A subarray is a contiguous non-empty sequence of elements within an array. Example 1: Input: nums = [1;1;1]; k = 2 Output: 2 Example 2: Input: nums = [1;2;3]; k = 3 Output: 2 Constraints: 1 <= nums.length <= 2 * 104 -1000 <= nums[i] <= 1000 -107 <= k <= 107
Citadel,688,Knight Probability in Chessboard,Med,Dynamic Programming,On an n x n chessboard; a knight starts at the cell (row; column) and attempts to make exactly k moves. The rows and columns are 0-indexed; so the top-left cell is (0; 0); and the bottom-right cell is (n - 1; n - 1). A chess knight has eight possible moves it can make; as illustrated below. Each move is two cells in a cardinal direction; then one cell in an orthogonal direction. Each time the knight is to move; it chooses one of eight possible moves uniformly at random (even if the piece would go off the chessboard) and moves there. The knight continues moving until it has made exactly k moves or has moved off the chessboard. Return the probability that the knight remains on the board after it has stopped moving. Example 1: Input: n = 3; k = 2; row = 0; column = 0 Output: 0.06250 Explanation: There are two moves (to (1;2); (2;1)) that will keep the knight on the board. From each of those positions; there are also two moves that will keep the knight on the board. The total probability the knight stays on the board is 0.0625. Example 2: Input: n = 1; k = 0; row = 0; column = 0 Output: 1.00000 Constraints: 1 <= n <= 25 0 <= k <= 100 0 <= row; column <= n - 1
Citadel,735,Asteroid Collision,Med,"Array, Stack, Simulation",We are given an array asteroids of integers representing asteroids in a row. For each asteroid; the absolute value represents its size; and the sign represents its direction (positive meaning right; negative meaning left). Each asteroid moves at the same speed. Find out the state of the asteroids after all collisions. If two asteroids meet; the smaller one will explode. If both are the same size; both will explode. Two asteroids moving in the same direction will never meet. Example 1: Input: asteroids = [5;10;-5] Output: [5;10] Explanation: The 10 and -5 collide resulting in 10. The 5 and 10 never collide. Example 2: Input: asteroids = [8;-8] Output: [] Explanation: The 8 and -8 collide exploding each other. Example 3: Input: asteroids = [10;2;-5] Output: [10] Explanation: The 2 and -5 collide resulting in -5. The 10 and -5 collide resulting in 10. Constraints: 2 <= asteroids.length <= 104 -1000 <= asteroids[i] <= 1000 asteroids[i] != 0
Citadel,767,Reorganize String,Med,"Math, Bit Manipulation",Given two integers left and right; return the count of numbers in the inclusive range [left; right] having a prime number of set bits in their binary representation. Recall that the number of set bits an integer has is the number of 1's present when written in binary. For example; 21 written in binary is 10101; which has 3 set bits. Example 1: Input: left = 6; right = 10 Output: 4 Explanation: 6 -> 110 (2 set bits; 2 is prime) 7 -> 111 (3 set bits; 3 is prime) 8 -> 1000 (1 set bit; 1 is not prime) 9 -> 1001 (2 set bits; 2 is prime) 10 -> 1010 (2 set bits; 2 is prime) 4 numbers have a prime number of set bits. Example 2: Input: left = 10; right = 15 Output: 5 Explanation: 10 -> 1010 (2 set bits; 2 is prime) 11 -> 1011 (3 set bits; 3 is prime) 12 -> 1100 (2 set bits; 2 is prime) 13 -> 1101 (3 set bits; 3 is prime) 14 -> 1110 (3 set bits; 3 is prime) 15 -> 1111 (4 set bits; 4 is not prime) 5 numbers have a prime number of set bits. Constraints: 1 <= left <= right <= 106 0 <= right - left <= 104
Citadel,815,Bus Routes,Hard,Dynamic Programming,We stack glasses in a pyramid; where the first row has 1 glass; the second row has 2 glasses; and so on until the 100th row. Each glass holds one cup of champagne. Then; some champagne is poured into the first glass at the top. When the topmost glass is full; any excess liquid poured will fall equally to the glass immediately to the left and right of it. When those glasses become full; any excess champagne will fall equally to the left and right of those glasses; and so on. (A glass at the bottom row has its excess champagne fall on the floor.) For example; after one cup of champagne is poured; the top most glass is full. After two cups of champagne are poured; the two glasses on the second row are half full. After three cups of champagne are poured; those two cups become full - there are 3 full glasses total now. After four cups of champagne are poured; the third row has the middle glass half full; and the two outside glasses are a quarter full; as pictured below. Now after pouring some non-negative integer cups of champagne; return how full the jth glass in the ith row is (both i and j are 0-indexed.) Example 1: Input: poured = 1; query_row = 1; query_glass = 1 Output: 0.00000 Explanation: We poured 1 cup of champange to the top glass of the tower (which is indexed as (0; 0)). There will be no excess liquid so all the glasses under the top glass will remain empty. Example 2: Input: poured = 2; query_row = 1; query_glass = 1 Output: 0.50000 Explanation: We poured 2 cups of champange to the top glass of the tower (which is indexed as (0; 0)). There is one cup of excess liquid. The glass indexed as (1; 0) and the glass indexed as (1; 1) will share the excess liquid equally; and each will get half cup of champange. Example 3: Input: poured = 100000009; query_row = 33; query_glass = 17 Output: 1.00000 Constraints: 0 <= poured <= 109 0 <= query_glass <= query_row < 100
Citadel,1143,Longest Common Subsequence,Med,"Array, Hash Table, Binary Search, Matrix, Counting",
Citadel,1203,Sort Items by Groups Respecting Dependencies,Hard,Concurrency,"Suppose we have a class: public class Foo { public void first() { print(""first""); } public void second() { print(""second""); } public void third() { print(""third""); } } The same instance of Foo will be passed to three different threads. Thread A will call first(); thread B will call second(); and thread C will call third(). Design a mechanism and modify the program to ensure that second() is executed after first(); and third() is executed after second(). Note: We do not know how the threads will be scheduled in the operating system; even though the numbers in the input seem to imply the ordering. The input format you see is mainly to ensure our tests' comprehensiveness. Example 1: Input: nums = [1;2;3] Output: ""firstsecondthird"" Explanation: There are three threads being fired asynchronously. The input [1;2;3] means thread A calls first(); thread B calls second(); and thread C calls third(). ""firstsecondthird"" is the correct output. Example 2: Input: nums = [1;3;2] Output: ""firstsecondthird"" Explanation: The input [1;3;2] means thread A calls first(); thread B calls third(); and thread C calls second(). ""firstsecondthird"" is the correct output. Constraints: nums is a permutation of [1; 2; 3]."
Citadel,1670,Design Front Middle Back Queue,Med,Database,Table: Patients +--------------+---------+ | Column Name | Type | +--------------+---------+ | patient_id | int | | patient_name | varchar | | conditions | varchar | +--------------+---------+ patient_id is the primary key (column with unique values) for this table. 'conditions' contains 0 or more code separated by spaces. This table contains information of the patients in the hospital. Write a solution to find the patient_id; patient_name; and conditions of the patients who have Type I Diabetes. Type I Diabetes always starts with DIAB1 prefix. Return the result table in any order. The result format is in the following example. Example 1: Input: Patients table: +------------+--------------+--------------+ | patient_id | patient_name | conditions | +------------+--------------+--------------+ | 1 | Daniel | YFEV COUGH | | 2 | Alice | | | 3 | Bob | DIAB100 MYOP | | 4 | George | ACNE DIAB100 | | 5 | Alain | DIAB201 | +------------+--------------+--------------+ Output: +------------+--------------+--------------+ | patient_id | patient_name | conditions | +------------+--------------+--------------+ | 3 | Bob | DIAB100 MYOP | | 4 | George | ACNE DIAB100 | +------------+--------------+--------------+ Explanation: Bob and George both have a condition that starts with DIAB1.
Citadel,1884,Egg Drop With 2 Eggs and N Floors,Med,String,"You are given a string s consisting only of the characters '0' and '1'. In one operation; you can change any '0' to '1' or vice versa. The string is called alternating if no two adjacent characters are equal. For example; the string ""010"" is alternating; while the string ""0100"" is not. Return the minimum number of operations needed to make s alternating. Example 1: Input: s = ""0100"" Output: 1 Explanation: If you change the last character to '1'; s will be ""0101""; which is alternating. Example 2: Input: s = ""10"" Output: 0 Explanation: s is already alternating. Example 3: Input: s = ""1111"" Output: 2 Explanation: You need two operations to reach ""0101"" or ""1010"". Constraints: 1 <= s.length <= 104 s[i] is either '0' or '1'."
Citadel,2044,Count Number of Maximum Bitwise-OR Subsets,Med,"Hash Table, String, Bit Manipulation, Prefix Sum","A wonderful string is a string where at most one letter appears an odd number of times. For example; ""ccjjc"" and ""abab"" are wonderful; but ""ab"" is not. Given a string word that consists of the first ten lowercase English letters ('a' through 'j'); return the number of wonderful non-empty substrings in word. If the same substring appears multiple times in word; then count each occurrence separately. A substring is a contiguous sequence of characters in a string. Example 1: Input: word = ""aba"" Output: 4 Explanation: The four wonderful substrings are underlined below: - ""aba"" -> ""a"" - ""aba"" -> ""b"" - ""aba"" -> ""a"" - ""aba"" -> ""aba"" Example 2: Input: word = ""aabb"" Output: 9 Explanation: The nine wonderful substrings are underlined below: - ""aabb"" -> ""a"" - ""aabb"" -> ""aa"" - ""aabb"" -> ""aab"" - ""aabb"" -> ""aabb"" - ""aabb"" -> ""a"" - ""aabb"" -> ""abb"" - ""aabb"" -> ""b"" - ""aabb"" -> ""bb"" - ""aabb"" -> ""b"" Example 3: Input: word = ""he"" Output: 2 Explanation: The two wonderful substrings are underlined below: - ""he"" -> ""h"" - ""he"" -> ""e"" Constraints: 1 <= word.length <= 105 word consists of lowercase English letters from 'a' to 'j'."
Citadel,2050,Parallel Courses III,Hard,"Math, Recursion","A digit string is good if the digits (0-indexed) at even indices are even and the digits at odd indices are prime (2; 3; 5; or 7). For example; ""2582"" is good because the digits (2 and 8) at even positions are even and the digits (5 and 2) at odd positions are prime. However; ""3245"" is not good because 3 is at an even index but is not even. Given an integer n; return the total number of good digit strings of length n. Since the answer may be large; return it modulo 109 + 7. A digit string is a string consisting of digits 0 through 9 that may contain leading zeros. Example 1: Input: n = 1 Output: 5 Explanation: The good numbers of length 1 are ""0""; ""2""; ""4""; ""6""; ""8"". Example 2: Input: n = 4 Output: 400 Example 3: Input: n = 50 Output: 564908303 Constraints: 1 <= n <= 1015"
Citadel,2402,Meeting Rooms III,Hard,"Array, Math, Bit Manipulation",You are given a 0-indexed integer array nums. In one operation; select any non-negative integer x and an index i; then update nums[i] to be equal to nums[i] AND (nums[i] XOR x). Note that AND is the bitwise AND operation and XOR is the bitwise XOR operation. Return the maximum possible bitwise XOR of all elements of nums after applying the operation any number of times. Example 1: Input: nums = [3;2;4;6] Output: 7 Explanation: Apply the operation with x = 4 and i = 3; num[3] = 6 AND (6 XOR 4) = 6 AND 2 = 2. Now; nums = [3; 2; 4; 2] and the bitwise XOR of all the elements = 3 XOR 2 XOR 4 XOR 2 = 7. It can be shown that 7 is the maximum possible bitwise XOR. Note that other operations may be used to achieve a bitwise XOR of 7. Example 2: Input: nums = [1;2;3;9;2] Output: 11 Explanation: Apply the operation zero times. The bitwise XOR of all the elements = 1 XOR 2 XOR 3 XOR 9 XOR 2 = 11. It can be shown that 11 is the maximum possible bitwise XOR. Constraints: 1 <= nums.length <= 105 0 <= nums[i] <= 108