1. Two Sum [Leetcode][C++]

class Solution { public: vector<int> twoSum(vector<int>& nums, int target) { //Brute Force Solution TimeO(N^2) & Auxiliary Space O(1) int length=nums.size(); for(int i=0;i<length;i++){ for(int j=i+1;j<length;j++){ if(nums[i]+nums[j]==target){ return {i,j}; } } } return {}; } }; 

class Solution { public: vector<int> twoSum(vector<int>& nums, int target){ //Efficient Solution TimeO(N) & Auxiliary Space O(N) int length=nums.size(); unordered_map<int,int> map; for(auto i=0;i<length;i++){ if(map.find(target-nums[i])!=map.end()){ return {i,map[target-nums[i]]}; } map[nums[i]]=i; } return {}; } };