Problem of The Day: Apply Operations to an Array

Problem Statement

My Solution

class Solution:
    def mergeArrays(self, nums1: List[List[int]], nums2: List[List[int]]) -> List[List[int]]:
        hash_map = defaultdict(list)
        for idx, val in nums1:
            hash_map[idx].append(val)
        for idx, val in nums2:
            hash_map[idx].append(val)
        res = []
        for idx, vals in hash_map.items():
            res.append([idx, sum(vals)])
        return sorted(res)

Editorial

Approach 1: HashMap

class Solution:
    def mergeArrays(
        self, nums1: List[List[int]], nums2: List[List[int]]
    ) -> List[List[int]]:
        key_to_sum = {}

        # Copying the array nums1 to the map.
        for nums in nums1:
            key_to_sum[nums[0]] = nums[1]

        # Adding the values to existing keys or create new entries.
        for nums in nums2:
            key_to_sum[nums[0]] = key_to_sum.get(nums[0], 0) + nums[1]

        merged_array = []
        for key, value in sorted(key_to_sum.items()):
            merged_array.append([key, value])

        return merged_array

Approach 2: Two Pointers

class Solution:
    def mergeArrays(
        self, nums1: list[list[int]], nums2: list[list[int]]
    ) -> list[list[int]]:
        N1, N2 = len(nums1), len(nums2)
        ptr1, ptr2 = 0, 0

        merged_array = []
        while ptr1 < N1 and ptr2 < N2:
            # If the id is same, add the values and insert to the result.
            # Increment both pointers.
            if nums1[ptr1][0] == nums2[ptr2][0]:
                merged_array.append(
                    [nums1[ptr1][0], nums1[ptr1][1] + nums2[ptr2][1]]
                )
                ptr1 += 1
                ptr2 += 1
            elif nums1[ptr1][0] < nums2[ptr2][0]:
                # If the id in nums1 is smaller, add it to result and increment the pointer
                merged_array.append(nums1[ptr1])
                ptr1 += 1
            else:
                # If the id in nums2 is smaller, add it to result and increment the pointer
                merged_array.append(nums2[ptr2])
                ptr2 += 1

        # If pairs are remaining in the nums1, then add them to the result.
        while ptr1 < N1:
            merged_array.append(nums1[ptr1])
            ptr1 += 1

        # If pairs are remaining in the nums2, then add them to the result.
        while ptr2 < N2:
            merged_array.append(nums2[ptr2])
            ptr2 += 1

        return merged_array