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5. Remove Element

easyAsked at Roblox

Remove all occurrences of a target value from an array in-place.

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

Problem

Given an integer array nums and an integer val, remove every occurrence of val in-place. Return the number of elements that are not equal to val; the first k slots of nums must contain those elements.

Constraints

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

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, nums = [0,1,3,0,4,_,_,_]

Approaches

1. Filter and copy

Build a filtered array then copy back.

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

Tradeoff:

2. Two-pointer overwrite

Slow pointer marks next write slot; skip matches.

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

Tradeoff:

Roblox-specific tips

Roblox interviewers often follow up by asking how you would extend this to filter despawned entities from a per-frame physics list.

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Output

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