comefrom: <awangdev>448. Find All Numbers Disappeared in an Array_2.java
code: public List<Integer> findDisappearedNumbers(int[] nums) {
          final List<Integer> rst = new ArrayList<Integer>();
          if (nums == null || nums.length == 0) return rst;
              
          for (int i = 0; i < nums.length; i++) {
              int desiredIndex = Math.abs(nums[i]) - 1;
              nums[desiredIndex] = -Math.abs(nums[desiredIndex]); 
          }
  
          for (int i = 0; i < nums.length; i++) {
              if (nums[i] > 0) rst.add(i + 1);
          }
          
          return rst;
      }
masked: public List < Integer > var_0 ( int [ ] var_1 ) {
    final List < Integer > var_2 = new ArrayList < Integer > ( ) ;
    if ( var_1 == null || var_1 . length == 0 ) return var_2 ;
    for ( int var_3 = 0 ;
    var_3 < var_1 . length ;
    var_3 ++ ) {
      int var_4 = Math . abs ( var_1 [ var_3 ] ) - 1 ;
      var_1 [ var_4 ] = - Math . abs ( var_1 [ var_4 ] ) ;
    }
    for ( int var_3 = 0 ;
    var_3 < var_1 . length ;
    var_3 ++ ) {
      if ( var_1 [ var_3 ] > 0 ) var_2 . add ( var_3 + 1 ) ;
    }
    return var_2 ;
  }
  