Leetcode#1 Two Sum

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