Skip to main content

5. Remove Element

easyAsked at Unity

Remove all occurrences of a value from an array in place. Unity uses this to test entity-list compaction patterns.

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

Problem

Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. Return the number of elements not equal to val; the relative order is not required.

Constraints

  • 0 <= nums.length <= 100
  • 0 <= nums[i], val <= 50

Examples

Example 1

Input
nums=[3,2,2,3], val=3
Output
2, nums=[2,2,_,_]

Example 2

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

Approaches

1. Filter copy

Allocate new array of non-val values then copy back.

Time
O(n)
Space
O(n)
const kept = nums.filter(x=>x!==val);
for (let i=0;i<kept.length;i++) nums[i]=kept[i];
return kept.length;

Tradeoff:

2. Two-pointer compaction

Write pointer keeps non-val values, read pointer scans the array.

Time
O(n)
Space
O(1)
function removeElement(nums, val) {
  let w = 0;
  for (let r=0;r<nums.length;r++) {
    if (nums[r] !== val) nums[w++] = nums[r];
  }
  return w;
}

Tradeoff:

Unity-specific tips

Unity frames this as despawn-and-compact for active entity lists where allocating a parallel array breaks 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 Element and other Unity interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →