题解 | #两数之和#

class Solution {
public:
    /**
     * 
     * @param numbers int整型vector 
     * @param target int整型 
     * @return int整型vector
     */
    //暴力解题法
    vector<int> TraverseSum(vector<int>& numbers, int target){
        vector<int> res;
        for(int i=0; i<=numbers.size()-2; i++){
            for(int j=i+1; j<=numbers.size()-1; j++){
                if (numbers[i] + numbers[j] == target){
                    res.push_back(i+1);
                    res.push_back(j+1);
                }
            }
        }
        return res;
    }
    
    //哈希函数解题法
    vector<int> hashSum(vector<int>& numbers, int target){
        vector<int> res;
        unordered_map<int, int> hash; //key:值， value:下标
        for(int i=0; i<numbers.size(); i++){
            int j = target-numbers[i];
            if(hash[j]){
                //已经存了两个加数中的另一个
                res.push_back(hash[j]);
                res.push_back(i+1);
                break;
            }else{
                hash[numbers[i]] = i+1;
            }
        }
        return res;
    }
    
    vector<int> twoSum(vector<int>& numbers, int target){
        vector<int> res;
        // 暴力解题法： res = TraverseSum(numbers, target);
        res = hashSum(numbers, target);
        return res;
    }
};