Skip to main content

8. Merge Sorted Array

easyAsked at Booking

Merge two sorted arrays in-place — Booking tests this to see if you can fold a supplier price update into the master availability array without extra memory.

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

Problem

Given two sorted arrays nums1 (size m+n, with trailing zeros) and nums2 (size n), merge nums2 into nums1 as one sorted array in-place.

Constraints

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

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. Brute force concat-sort

Copy nums2 into nums1 and call 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 pointers from the back

Compare from the back and write into the tail — avoids overwriting unread 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:

Booking-specific tips

Booking handles supplier-fanout merges constantly — explain how the from-the-back pointer pattern avoids the doubled buffer you would need at supplier scale.

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 Booking interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →