leetcode 1.TwoSum--hashmap

/*
leetcode 001 TwoSum
题目大意：从给定的一组数中找到两个数的和为target.返回两个数的序号，假设每次输入只有一组解
解题思路：
1、暴力搜索：对于每个数去找后面和它的和为target的数，如果找到了就返回
我好像第一次提交用暴力搜索竟然过了。
2、hash：先进行hash映射，为 ，对于每一个数，可以在O(1)的时间找到
*/

#include 
#include 
#include 
#include 
using namespace std;

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

    //hash
    vector<int> twoSum1(vector<int>& nums, int target)
    {
        unordered_map<int, int> mapping;            //hash map
        vector<int> result;                         //result
        for (size_t i = 0; i < nums.size(); ++i)    //O(n)：进行hash
        {
            mapping[nums[i]] = i;
        }
        for (size_t i = 0; i < nums.size(); ++i)
        {
            const int gap = target - nums[i];                           //找到这个数
            if (mapping.find(gap) != mapping.end() && mapping[gap]!=i)  //找到了，O(1)
            {
                result.push_back(i + 1);                                //index 1
                result.push_back(mapping[gap] + 1);                     //index 2
                break;
            }
        }
        return result;
    }
};

void test_twoSum()
{
    Solution sol;
    vector<int> index;
    vector<int> nums{4,71,15,3,9,17,13,25,1,33,0};
    int target = 30;
    index = sol.twoSum(nums, target);
    //输出
    for (auto i : index)
    {
        cout << i << " ";
    }
    cout << endl;
}

void test_twoSum1()
{
    Solution sol;
    vector<int> index;
    vector<int> nums{ 4,71,15,3,9,17,13,25,1,33,0 };
    int target = 30;
    index = sol.twoSum1(nums, target);
    //输出
    for (auto i : index)
    {
        cout << i << " ";
    }
    cout << endl;
}

int main()
{
    test_twoSum();

    return 0;
}