第一版：

class Solution
{
    
    
public:
    vector<int> twoSum(vector<int> &nums, int target)
    {
    
    
        vector<int> res;
        map<int, int> myMap;
        for (int i = 0; i < nums.size(); i++)
        {
    
    
            if (myMap.find(target - nums[i]) != myMap.end())
            {
    
    
                // 说明有
                res.push_back(i);
                res.push_back(myMap[target - nums[i]]);
                return res;
            }
            else
            {
    
    
                myMap.insert({
    
    nums[i], i});
            }
        }
        return res;
    }
};

第二版：

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