2363. Merge Similar Items

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.

Solution (Java)

class Solution {
    public List<List<Integer>> mergeSimilarItems(int[][] arr1, int[][] arr2) {
        int[] cache = new int[1001];
        for (int[] num : arr1) {
            cache[num[0]] += num[1];
        }
        for (int[] num : arr2) {
            cache[num[0]] += num[1];
        }
        List<List<Integer>> result = new ArrayList<>();
        for (int i = 0; i < cache.length; i++) {
            int weight = cache[i];
            if (weight > 0) {
                int value = i;
                result.add(Arrays.asList(value, weight));
            }
        }
        return result;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).