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5. Remove Element

easyAsked at Yelp

Filter out target values from an array in-place — Yelp uses this to test the same buffer-compaction logic that strips flagged reviews from a result page.

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

Problem

Given an array nums and an integer val, remove all occurrences of val in-place. Return the new length k; the first k elements of nums must contain the kept values in any order.

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

Approaches

1. Filter + copy

Filter into a new array, copy back.

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 pointers

Write index lags read index; only write non-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:

Yelp-specific tips

Yelp wants O(1) extra memory and will pivot to asking how this generalizes to filtering policy-violating reviews from a paginated business page.

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Output

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