Merge Sorted Array

Problem

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 nums1. nums1 has length m + n — the first m elements are the ones to merge, the last n slots are 0 and should be ignored.

Input / Output Format

Input: nums1 (length m+n), m, nums2 (length n), n. Output: None — nums1 mutated in-place.

Examples

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]

Example 2

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

Approach Hints

• Reverse Two Pointers (in-place) — Pointers i = m-1, j = n-1, k = m+n-1. Fill nums1 from the back: whichever of nums1[i] / nums2[j] is larger goes to nums1[k]. Avoids overwriting unread nums1 values. Time: O(m+n), Space: O(1).
• Front-merge requires a buffer → O(m+n) space.
• After loop, leftover nums2 elements still need to be copied; leftover nums1 elements are already in place.