Merge Sorted Array

김견지·2025년 3월 16일

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Question

You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and nums2 respectively.

Merge nums1 and nums2 into a single array sorted in non-decreasing order.

The final sorted array should not be returned by the function, but instead be stored inside the array nums1. To accommodate this, nums1 has a length of m + n, where the first m elements denote the elements that should be merged, and the last n elements are set to 0 and should be ignored. nums2 has a length of n.

Example 1:
Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
Output: [1,2,2,3,5,6]
Explanation: The arrays we are merging are [1,2,3] and [2,5,6].
The result of the merge is [1,2,2,3,5,6] with the underlined elements coming from nums1.

Example 2:
Input: nums1 = [1], m = 1, nums2 = [], n = 0
Output: [1]
Explanation: The arrays we are merging are [1] and [].
The result of the merge is [1].

Example 3:
Input: nums1 = [0], m = 0, nums2 = [1], n = 1
Output: [1]
Explanation: The arrays we are merging are [] and [1].
The result of the merge is [1].
Note that because m = 0, there are no elements in nums1. The 0 is only there to ensure the merge result can fit in nums1.

Constraints:
nums1.length == m + n
nums2.length == n
0 <= m, n <= 200
1 <= m + n <= 200
-109 <= nums1[i], nums2[j] <= 109

My Solutioin

Code

class Solution:
    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        """
        Do not return anything, modify nums1 in-place instead.
        """
        if n != 0:
            del nums1[-1 * n:]
            
        i = 0
        while len(nums2) > 0:
            if i >= len(nums1):
                nums1 += nums2
                break
            if nums1[i] > nums2[0]:
                nums1.insert(i, nums2.pop(0))
            i += 1

        return

Using while len(nums2) > 0 and pop was decent idea but I should've consider edege cases like

n == 0
nums2 elements at the end of result
0 is included in nums1

And indexing of nums1 was a bit confusing.

Feedback

Python Grammar

del

When you want to delete part of (or whole) array.

del mylist  # to delete whole array
del mylist[-2:]  # to delete partially

pop()

value = mylist.pop(index). # if you want to pop with index

insert()

Insert value with index.

mylist.insert(index, value)

Better Solution?

lightest Sol.

class Solution:
    def merge(self, nums1: List[int], m: int, nums2: List[int], n: int) -> None:
        """
        Do not return anything, modify nums1 in-place instead.
        """
        for j in range(n):
            nums1[m+j] = nums2[j]
        nums1.sort()

Didn't know what .sort() do exactly when in comes to array memory, that I avoided to use it.