1.TwoSum[Optimized].cpp

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

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {

            int i=0;
            unordered_map<int,int> mp;
            for(i=0;i<nums.size();i++)
            {
                if(mp.find(target-nums[i])!=mp.end())
                {
                    return {mp[target-nums[i]],i};
                }
                mp[nums[i]]=i;
            }
        
            return {};
                
    }    
        
};