class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector <int> soln;
        unordered_map <int, int> fax;
        for(int i(0);i<nums.size(); i++){
            if(fax.find(target-nums[i])!=fax.end()){
                soln.insert(soln.end(), {i, fax[target-nums[i]]});
            }
            fax[nums[i]]=i;
        }
        return soln;
    }
};