LeetCode-Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

首先想到的是暴力求解算法，交上去竟然过了。

代码：

vector<int> twoSum(vector<int>& nums, int target) {
        int len = nums.size();
        vector<int> tmp;
        for(int i=0;i<len;i++){
            for(int j=i+1;j<len;j++){
                if(nums[i]+nums[j]==target){
                    tmp.push_back(i);
                    tmp.push_back(j);
                    return tmp;
                }
            }
        }
    }

优化一下，使用map，

代码：

   vector<int> twoSum(vector<int>& nums, int target) {
        map<int,int> tmp;
        vector<int> res;
        for(int i=0;i<nums.size();i++){
            tmp[nums[i]] = i;
        }
        for(int i=0;i<nums.size();i++){
            int s = target-nums[i];
            if(tmp.find(s)!=tmp.end()&&tmp.at(s)!=i){
                res.push_back(i);
                res.push_back(tmp[s]);
                return res;
            }
        }
}

做的过程中，还顺便学习了一下map。

https://blog.youkuaiyun.com/seanyxie/article/details/5804974

https://blog.youkuaiyun.com/u010025211/article/details/46653519