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Find All Numbers Disappeared in an Array

Tags : array, leetcode, cpp, easy

Problem Statement - link #

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.

Examples #

Example 1:

Input: nums = [4,3,2,7,8,2,3,1]
Output: [5,6]

Example 2:

Input: nums = [1,1]
Output: [2]

Constraints #

Solutions #

class Solution {
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
      sort(nums.begin(), nums.end());
      vector<int> res;
      int k=1;
      for(int i=0; i<nums.size(); i++){
        
        if(k==nums[i]) k++;
        else if(k<nums[i]) {
          while(k<nums[i]){
             res.push_back(k);
             k++;
          }
          k++;
        }
        
      }
      
      while(k<=nums.size()) {
             res.push_back(k);
             k++;
          }
      return res;
    }
};