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Merge Sorted Array

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.

Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3

Output: [1,2,2,3,5,6]

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.

Input: nums1 = [1], m = 1, nums2 = [], n = 0

Output: [1]

The arrays we are merging are [1] and []. The result of the merge is [1].

Input: nums1 = [0], m = 0, nums2 = [1], n = 1

Output: [1]

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

Clarify the problem

What are some questions you'd ask an interviewer?

Understand the problem

Which approach is most efficient for merging two sorted arrays in-place?
Start from the beginning of both arrays and shift elements as needed
Create a new array, merge both arrays into it, then copy back to nums1
Start from the end of both arrays and fill nums1 from back to front
Use a min-heap to merge elements from both arrays

Take a moment to understand the problem and think of your approach before you start coding.