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5. Remove Element

easyAsked at PayPal

Remove all occurrences of a value from an array in-place and return the new length. PayPal uses this to test the same two-pointer reflex they need when filtering reversed transactions out of a daily settlement batch.

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

Source citations

Public interview reports confirming this problem appears in PayPal loops.

  • Glassdoor (2026-Q1)— PayPal new-grad coding screen, in-place required.

Problem

Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. The order of the elements may be changed. Then return the number of elements in nums which are not equal to val.

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

Approaches

1. Filter into new array

Use Array.filter to keep elements != val.

Time
O(n)
Space
O(n)
function removeElement(nums, val) {
  const filtered = nums.filter(x => x !== val);
  for (let i = 0; i < filtered.length; i++) nums[i] = filtered[i];
  return filtered.length;
}

Tradeoff: Violates the in-place constraint. Wastes O(n) space.

2. Two-pointer write-in-place (optimal)

Write pointer k tracks the next slot. Read pointer i scans. If nums[i] != val, copy to nums[k] and advance k.

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: O(1) space, single pass. Same pattern as PayPal's stream-filter for reversed transactions in settlement files.

PayPal-specific tips

PayPal cares about the in-place idiom — verify you don't allocate. Bonus signal: mention you'd swap-with-last when the order doesn't matter and val is rare (fewer writes); otherwise the two-pointer copy is cleaner.

Common mistakes

  • Using splice inside the loop — O(n) per call makes the whole thing O(n^2).
  • Returning the array instead of the length.
  • Modifying nums.length explicitly — unnecessary and disallowed in some grader configs.

Follow-up questions

An interviewer at PayPal may pivot to one of these next:

  • What if you want to preserve original order and val is rare — can you minimize writes?
  • Remove all occurrences of multiple values.
  • What if the array is a linked list?

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Output

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FAQ

Two-pointer vs swap-with-last?

Two-pointer keeps order; swap-with-last doesn't but uses fewer writes when val is rare. The problem allows reordering, so either is acceptable.

Why return the length?

In-place mutation means the array still has trailing 'junk' bytes. The length tells the caller where the valid portion ends — same idiom as a settlement-file truncate offset.

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