两数之和

方法一 暴力法

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        for(int i=0;i<nums.size();i++)
        {
            for(int j=0;j<nums.size();j++)
            {
                if(nums[j]==target-nums[i])
                {
                    //vector<int> a;        使用尾部追加
                    //a.push_back(i);
                    //a.push_back(j);
                    vector<int> a={i,j};    //直接声明初始化
                    return a;
                    
                }
            }
        }
    }
};

方法二  哈希法

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