2363. Merge Similar Items

You are given two 2D integer arrays, items1 and items2, representing two sets of items. Each array items has the following properties:

• items[i] = [valuei, weighti] where valuei represents the value and weighti represents the weight of the ith item.
• The value of each item in items is unique.

Return a 2D integer array ret where ret[i] = [valuei, weighti], with weighti being the sum of weights of all items with value valuei.

Note: ret should be returned in ascending order by value.

class Solution {
public:
    vector<vector<int>> mergeSimilarItems(vector<vector<int>>& items1, vector<vector<int>>& items2) {
        unordered_map<int, int> mp;
        for(auto& A : items1) {
            mp[A[0]] += A[1];
        }
        for(auto& A : items2) {
            mp[A[0]] += A[1];
        }
        vector<vector<int>> res;
        for(auto [k,v] : mp) res.push_back({k,v});
        sort(begin(res), end(res));
        return res;
    }
};