lleetcode 1 two sum c++

Problem describe:https://leetcode.com/problems/two-sum/

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1]

AC code :

1.Bruth Algorithm

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> res;
        for(int i = 0;i < nums.size();i++)
            for(int j = i + 1;j < nums.size();j++)
                if(nums[i]+nums[j]==target)
                {
                    res.push_back(i);
                    res.push_back(j);
                }
        return res;
                    
    }
};

2.Hashmap

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> res;
        unordered_map<int,int> map;
        for(int i = 0; i < nums.size();i++)
        {
            map[nums[i]] = i;
        }
        for(int i = 0;i < nums.size();i++)
        {
            int left = target - nums[i];
            if(map.count(left) && i <  map[left])
            {
                res.push_back(i);
                res.push_back(map[left]);
            }        
        } 
        return res;
    }
};