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8. Merge Sorted Array

easyAsked at Indeed

Merge two sorted arrays in place — Indeed's two-pointer pattern that maps directly to combining ranked job lists from multiple shards.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

Given two sorted arrays nums1 (size m+n) and nums2 (size n), merge nums2 into nums1 in place so nums1 becomes sorted. The first m elements of nums1 are the data and the last n slots are zero placeholders.

Constraints

  • 0 <= m, n <= 200
  • 1 <= m + n <= 200
  • -10^9 <= nums1[i], nums2[i] <= 10^9

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]

Approaches

1. Concat and sort

Splice nums2 into nums1 then sort.

Time
O((m+n) log(m+n))
Space
O(1)
nums1.splice(m, n, ...nums2);
nums1.sort((a,b)=>a-b);

Tradeoff:

2. Reverse two pointers

Fill nums1 from the back so writes never clobber unread data.

Time
O(m+n)
Space
O(1)
function merge(nums1, m, nums2, n) {
  let i = m - 1, j = n - 1, k = m + n - 1;
  while (j >= 0) {
    if (i >= 0 && nums1[i] > nums2[j]) nums1[k--] = nums1[i--];
    else nums1[k--] = nums2[j--];
  }
}

Tradeoff:

Indeed-specific tips

Indeed expects you to call out why merging from the back avoids overwrites — they apply the same trick when stitching pre-sorted job-feed shards into a single ranked window.

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Output

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