Problem

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.

Example 1:

Input: items1 = [[1,1],[4,5],[3,8]], items2 = [[3,1],[1,5]] Output: [[1,6],[3,9],[4,5]] Explanation: The item with value = 1 occurs in items1 with weight = 1 and in items2 with weight = 5, total weight = 1 + 5 = 6. The item with value = 3 occurs in items1 with weight = 8 and in items2 with weight = 1, total weight = 8 + 1 = 9. The item with value = 4 occurs in items1 with weight = 5, total weight = 5.
Therefore, we return [[1,6],[3,9],[4,5]].

Example 2:

Input: items1 = [[1,1],[3,2],[2,3]], items2 = [[2,1],[3,2],[1,3]] Output: [[1,4],[2,4],[3,4]] Explanation: The item with value = 1 occurs in items1 with weight = 1 and in items2 with weight = 3, total weight = 1 + 3 = 4. The item with value = 2 occurs in items1 with weight = 3 and in items2 with weight = 1, total weight = 3 + 1 = 4. The item with value = 3 occurs in items1 with weight = 2 and in items2 with weight = 2, total weight = 2 + 2 = 4. Therefore, we return [[1,4],[2,4],[3,4]].

Example 3:

Input: items1 = [[1,3],[2,2]], items2 = [[7,1],[2,2],[1,4]] Output: [[1,7],[2,4],[7,1]] Explanation: The item with value = 1 occurs in items1 with weight = 3 and in items2 with weight = 4, total weight = 3 + 4 = 7. The item with value = 2 occurs in items1 with weight = 2 and in items2 with weight = 2, total weight = 2 + 2 = 4. The item with value = 7 occurs in items2 with weight = 1, total weight = 1. Therefore, we return [[1,7],[2,4],[7,1]].

Constraints:

1 <= items1.length, items2.length <= 1000 items1[i].length == items2[i].length == 2 1 <= valuei, weighti <= 1000 Each valuei in items1 is unique. Each valuei in items2 is unique.

Pre analysis

Will create a hash object and then iterate over the items to get the sum of weight. Return the list from Hash.

Another solution

var mergeSimilarItems = function (items1, items2) {
  let ans = {},
    items = [...items1, ...items2];
  for (let [x, y] of items) {
    if (ans[x]) ans[x] += y;
    else ans[x] = y;
  }
  return Object.entries(ans);
};