1. Two Sum

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
//         int n = nums.size();
//         for(int i = 0 ; i < n-1 ; i++)       //bruteforce
//             for(int j = i +1 ; j < n ; j++ )
//                 if(nums[i] + nums[j] == target)
//                     return {i , j};
//             return {};
        
////////////////////////////////////
        
        map<int,int> m;     //second approach (slower then third approach)
        vector<int> ans;
        for(int i=0;i<nums.size();i++)
        {
            if(m.find(target-nums[i]) != m.end()){
                ans = {i, m[target-nums[i]]};
                return ans;
            }
            m[nums[i]] = i;
        }
        return ans;   
/*Runtime: 26 ms, faster than 60.72% of C++ online submissions for Two Sum.
Memory Usage: 11.2 MB, less than 21.04% of C++ online submissions for Two Sum.*/
        
////////////////////////////////////
        
    //     vector<pair<int,int>> v;        //sanchi approach
    //     for(int i=0;i<nums.size();i++)
    //     {
    //         v.push_back({nums[i],i});
    //     }
    //     vector<int> res;
    //     sort(v.begin(),v.end());
    //     auto itr1=v.begin();
    //     auto itr2=v.end()-1;
    //     while(itr1!=itr2){
    //         if((itr1->first+itr2->first)==target)
    //         {
    //             res.push_back(itr1->second);
    //             res.push_back(itr2->second);
    //             break;
    //         }
    //         if((itr1->first+itr2->first)<target)
    //             itr1++;
    //         else 
    //             itr2--;
    //     }
    //     return res;
/*Runtime: 6 ms, faster than 99.12% of C++ online submissions for Two Sum.
Memory Usage: 11.1 MB, less than 23.14% of C++ online submissions for Two Sum.*/
    }
};