1两数之和

#include
#include
#include
using namespace std;
class Solution1{      //暴力枚举法
public:
    vector twoSum(vector& nums, int target) {
        for (int i = 0; i  twoSum(vector& nums, int target) {
        unordered_maphashtable;
        for (int i = 0; i < nums.size(); i++)
        {
            auto it = hashtable.find(target - nums[i]);//it是迭代器，完整写法为unordered_map::iterator，用auto代替
            if (it != hashtable.end()) //end()指向最后一个元素后一位，这里是判断是否到尾部
            {
                return{it->second,i};//如果哈希表中查找到结果，输出
            }
            hashtable[nums[i]] = i;//哈希表中没有查找到结果，写入哈希表
        }
        return{};
    }
};//时间复杂度O(n),空间复杂度O(n)
int main()
{
    vectorarr = {2, 7, 11, 15};
    int target = 9;
    Solution1 test1;
    cout << "[" << test1.twoSum(arr,target )[0] << "," << test1.twoSum(arr, target)[1] << "]" << endl;
    Solution2 test2;
    cout << "[" << test2.twoSum(arr, target)[0] << "," << test2.twoSum(arr, target)[1] << "]" << endl;
    return 0;
}