Merge Two 2D Arrays by Summing Values

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Question

Approach

For my approach, I use a dictionary to store the sum of values for each unique id. I iterate through both nums1 and nums2, adding their values to the dictionary. After processing both arrays, I convert the dictionary into a sorted list of lists.

Implementation

class Solution:
    def mergeArrays(self, nums1: List[List[int]], nums2: List[List[int]]) -> List[List[int]]:
        merged_dict = {}
        
        for id_, val in nums1:
            merged_dict[id_] = merged_dict.get(id_, 0) + val
        
        for id_, val in nums2:
            merged_dict[id_] = merged_dict.get(id_, 0) + val
        
        result = sorted([[id_, val] for id_, val in merged_dict.items()])
        
        return result

Complexities

• Time: O(n + m) since each array is processed once
• Space: O(n + m) due to storing unique ids in the dictionary before sorting