(1)Two Sum - O(n^2)

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