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8. Merge Sorted Array

easyAsked at Coupang

Merge two sorted arrays in-place, mirroring how Coupang merges sorted delivery slot batches for same-day routing.

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

Problem

You are given two sorted integer arrays nums1 and nums2, and integers m and n representing the number of elements in each. Merge nums2 into nums1 as one sorted array in-place. nums1 has length m+n with the last n slots set to 0.

Constraints

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

Copy nums2 into nums1 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. Two pointers from end

Walk both arrays from their tails and write the larger element to nums1's end. Avoids overwriting unread elements.

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:

Coupang-specific tips

Coupang merges sorted delivery-window batches constantly for Rocket Delivery dispatch; show you can do it in-place without re-sorting the union.

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Output

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