comefrom: <awangdev>219. Contains Duplicate II_1.java
code: public boolean containsNearbyDuplicate(int[] nums, int k) {
          if (nums == null || nums.length == 0 || k <= 0) {
              return false;
          }
          Set<Integer> set = new HashSet<>();
          for (int i = 0; i < nums.length; i++) {
              if (i > k) {
                  set.remove(nums[i - k - 1]);
              }
              if (!set.add(nums[i])) {
                  return true;
              }
          }
          return false;
      }
masked: public boolean var_0 ( int [ ] var_1 , int var_2 ) {
    if ( var_1 == null || var_1 . length == 0 || var_2 <= 0 ) {
      return false ;
    }
    Set < Integer > var_9 = new HashSet < > ( ) ;
    for ( int var_10 = 0 ;
    var_10 < var_1 . length ;
    var_10 ++ ) {
      if ( var_10 > var_2 ) {
        var_9 . remove ( var_1 [ var_10 - var_2 - 1 ] ) ;
      }
      if ( ! var_9 . add ( var_1 [ var_10 ] ) ) {
        return true ;
      }
    }
    return false ;
  }
  