## 题目地址 
https://leetcode-cn.com/problems/two-sum/ 

## 思路 

## 一般解法 

代码：

```C++
```

## 优化解法 

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

```

```
class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        std::map <int,int> map;
        for(int i = 0; i < nums.size(); i++) {
            auto iter = map.find(target - nums[i]);
            if(iter != map.end()) {
                return {iter->second,i};
            }
            map[nums[i]] = i;
        }
        return {};
    }
};
```

```
class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        std::unordered_map <int,int> map;
        for(int i = 0; i < nums.size(); i++) {
            auto iter = map.find(target - nums[i]);
            if(iter != map.end()) {
                return {iter->second, i};
                break;
            }
            map.emplace(nums[i], i);
        }
        return {};
    }
};
```
## 代码

```C++

```