leetcode-2363-easy

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.

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.

思路一：用 TreeSet 存储 key，用 map 存储二维数组，最后遍历 TreeSet。看了一下评论区，发现直接用 TreeMap 就可以实现存储有序的值，可以省去 TreeSet

public List<List<Integer>> mergeSimilarItems(int[][] items1, int[][] items2) {
    List<List<Integer>> result = new ArrayList<>();

    Set<Integer> keys = new TreeSet<>();
    Map<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < items1.length; i++) {
        keys.add(items1[i][0]);
        int finalI = i;
        map.compute(items1[i][0], (k, v) -> v == null ? items1[finalI][1] : v + items1[finalI][1]);
    }
    for (int i = 0; i < items2.length; i++) {
        int finalI = i;
        keys.add(items2[i][0]);
        map.compute(items2[i][0], (k, v) -> v == null ? items2[finalI][1] : v + items2[finalI][1]);
    }

    for (Integer key : keys) {
        List<Integer> list = new ArrayList<>();
        list.add(key);
        list.add(map.get(key));
        result.add(list);
    }

    return result;
}