leetcode(1)--兩數之和

（1）暴力求解

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

（2）一次哈希

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