每天一算：Two Sum

 1// 1. Two Sum
 2// https://leetcode.com/problems/two-sum/description/
 3// 时间复杂度：O(n)
 4// 空间复杂度：O(n)
 5class Solution {
 6public:
 7    vector<int> twoSum(vector<int>& nums, int target) {
 8
 9        unordered_map<int,int> record;
10        for(int i = 0 ; i < nums.size() ; i ++){
11
12            int complement = target - nums[i];
13            if(record.find(complement) != record.end()){
14                int res[] = {i, record[complement]};
15                return vector<int>(res, res + 2);
16            }
17
18            record[nums[i]] = i;
19        }
20    }
21};