1两数之和

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        map<int, int> m;
        vector<int> ans;
        int i = 0;
        for (auto num : nums) {
            if (m.find(num) != m.end()) {
                ans.push_back(m[num]);
                ans.push_back(i);
                return ans;
            }
            else {
                m.insert(make_pair(target - num, i));
            }
            i++;
        }
        return ans;
    }
};