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5. Remove Element

easyAsked at Coupang

Remove all occurrences of a value in-place — Coupang uses this as a warm-up to test pointer logic before stock-clear list problems.

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 the elements may be changed. Return the number of elements remaining.

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. Brute force

Filter into new array.

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 pointers

Write pointer skips 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:

Coupang-specific tips

Coupang interviewers expect you to articulate the difference between order-preserving vs unordered in-place removal.

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Output

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