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5. Remove Element

easyAsked at Canva

Remove all occurrences of a value in place — Canva uses this to test how cleanly you mutate arrays, like removing deleted layers from a render queue.

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. The order of elements may be changed; return the count k of remaining elements.

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 then copy

Build a filtered array and assign back.

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

Tradeoff:

2. Two-pointer overwrite

Write pointer trails the read pointer; overwrite only when the read value should be kept.

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:

Canva-specific tips

Canva expects you to call out edge cases like empty arrays and all-matching arrays, because the editor's element pipeline must survive bulk-delete operations.

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Output

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