136.SingleNumber.cpp

#include<bits/stdc++.h>
using namespace std;

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        
        unordered_map<int,int>mp;
        
        for(auto x : nums)
        {
            mp[x]++;
        }
        
        for(auto x : mp)
        {
            if(x.second==1)
                return x.first;
        }
        
        return -1;
        
    }
};