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5. Remove Element

easyAsked at Zoom

Remove all instances of a value in-place and return the new length.

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

Problem

Given an array nums and a value val, remove all instances of val in-place. The order of the remaining elements may change. Return the new length k.

Constraints

  • 0 <= nums.length <= 100
  • 0 <= nums[i], 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=[0,1,3,0,4,_,_,_]

Approaches

1. Filter into new array

Filter then copy back.

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

Tradeoff:

2. Two-pointer overwrite

Maintain a write index that only advances when the element is kept.

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:

Zoom-specific tips

Zoom interviewers like seeing zero-allocation rewrites — they map directly to the SDK's in-place participant filtering when subscribers drop off mid-call.

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Output

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