Skip to main content

8. Merge Sorted Array

easyAsked at Activision

Merge nums2 into nums1 in-place with both arrays already sorted — Activision uses this to verify reverse-pointer fluency on session telemetry merges.

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

Problem

You are given two sorted arrays nums1 (size m+n) and nums2 (size n). Merge nums2 into nums1 in non-decreasing order, in-place.

Constraints

  • nums1.length == m + n
  • nums2.length == n
  • 0 <= m,n <= 200
  • 1 <= m+n

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. Concatenate and sort

Copy nums2 onto the tail and sort.

Time
O((m+n) log(m+n))
Space
O(1)
for (let i=0;i<n;i++) nums1[m+i] = nums2[i];
nums1.sort((a,b)=>a-b);

Tradeoff:

2. Three-pointer reverse merge

Fill from the back so we never overwrite unread nums1 cells.

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:

Activision-specific tips

Activision specifically asks why you fill from the back — the answer signals you understand stable, allocation-free merges they use in match-result aggregation.

Solve it now

Free. No sign-up. Python and JavaScript run instantly in your browser.

Output

Press Run or Cmd+Enter to execute

Practice these live with InterviewChamp.AI

Drill Merge Sorted Array and other Activision interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →