Skip to main content

4. Remove Duplicates from Sorted Array

easyAsked at Zoom

Remove duplicates in-place from a sorted array so each element appears once.

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

Problem

Given a sorted array nums, remove the duplicates in-place such that each unique element appears only once. Return k, the number of unique elements. The first k elements of nums should hold the unique values in order.

Constraints

  • 1 <= nums.length <= 3 * 10^4
  • Sorted non-decreasing
  • Modify in-place, O(1) extra space

Examples

Example 1

Input
nums=[1,1,2]
Output
2, nums=[1,2,_]

Example 2

Input
nums=[0,0,1,1,1,2,2,3,3,4]
Output
5, nums=[0,1,2,3,4,_,_,_,_,_]

Approaches

1. Set then copy

Build a Set, copy back.

Time
O(n)
Space
O(n)
const u=[...new Set(nums)]; for(let i=0;i<u.length;i++) nums[i]=u[i]; return u.length;

Tradeoff:

2. Two-pointer in-place

Use a write-pointer that advances only when the next read differs. O(1) extra space.

Time
O(n)
Space
O(1)
function removeDuplicates(nums) {
  if (nums.length === 0) return 0;
  let k = 1;
  for (let i = 1; i < nums.length; i++) {
    if (nums[i] !== nums[i - 1]) {
      nums[k++] = nums[i];
    }
  }
  return k;
}

Tradeoff:

Zoom-specific tips

Zoom values in-place mutation patterns because the SDK frequently rewrites participant arrays in audio-mix buffers where allocations would jitter the frame budget.

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 Remove Duplicates from Sorted Array and other Zoom interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →