leetcode(1)--两数之和

（1）暴力求解

class Solution { public:     vector<int> twoSum(vector<int>& nums, int target) {     vector<int>out;     for(int i = 0; i < nums.size() - 1; i++)         {             for(int j = i + 1; j < nums.size();j++)                 {                     if(nums[i]+nums[j] == target)                     {                         out.push_back(i);                         out.push_back(j);                     }                 }         }         return  out;     } };

（2）一次哈希

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