stl库太强了(wawawa)

class Solution {
public:
    vector<vector<int>> mergeSimilarItems(vector<vector<int>>& items1, vector<vector<int>>& items2) {
        map<int,int> hash;//map插入时就是有序的
        for(auto& p : items1 ) hash[p[0]] += p[1];
        for(auto& p : items2 ) hash[p[0]] += p[1];
        vector<vector<int>> res;
        for(auto& [k, v]: hash)
           res.push_back({k,v});
        return res;
    }
};