Find All Duplicates in an Array

 https://leetcode.com/problems/find-all-duplicates-in-an-array/discuss/775798/c%2B%2B-Four-Solution-or-O-(N*N)-to-greater-O(N)-or-Explain-All

 

class Solution {
public:
    vector<int> findDuplicates(vector<int>& nums) {
        unordered_map<int,int>m;
        vector<int>ans;
        for(int i=0;i<nums.size();i++){
            m[nums[i]]++;
        }
        for(auto it:m){
            if(it.second>=2){
                ans.push_back(it.first);
            }
        }
        return ans;
    }
};