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5. Remove Element

easyAsked at Tesla

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

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

Problem

Given an integer array nums and a value val, remove all instances of val in-place and return the new length k. The first k elements of nums must hold the kept values; the order of remaining elements can change.

Constraints

  • 0 <= nums.length <= 100
  • 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

Approaches

1. Filter and copy back

Build new array, then overwrite.

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 overwrite

Write pointer advances only when value differs from val.

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:

Tesla-specific tips

Tesla embedded interviews like the in-place variant — same pattern as cleaning invalid sensor readings from a fixed-size buffer without realloc.

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Output

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