Leetcode：1. Two Sum

class Solution {public:    vector<int> twoSum(vector<int>& nums, int target) {        int n = nums.size();        vector<int> res;        for(int i = 0; i < n-1; 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;                }