Skip to main content

5. Remove Element

easyAsked at Lyft

Strip all instances of a value from an array in-place.

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 and return the new length k. The first k elements should contain everything that is NOT val (order does not matter).

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

Approaches

1. Filter copy

Build a new array of non-val elements.

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

Tradeoff:

2. Two pointer overwrite

Write pointer advances only when value is kept; read pointer scans whole array.

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:

Lyft-specific tips

Lyft phrases this as 'expire cancelled rides from a list without reallocating' — describe the write pointer using domain language to score bonus signal.

Solve it now

Free. No sign-up. Python and JavaScript run instantly in your browser.

Output

Press Run or Cmd+Enter to execute

Practice these live with InterviewChamp.AI

Drill Remove Element and other Lyft interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →