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5. Remove Element

easyAsked at DigitalOcean

Remove all instances of a target value in-place — DigitalOcean uses this to assess filtering primitives that resemble pruning evicted droplet metrics from a sliding-window batch.

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

Problem

Given an array nums and a value val, remove all instances of that value in-place and return the new length. The order of elements may change, and you must do it with O(1) extra memory.

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

Approaches

1. Filter to new array

Build a list excluding val, copy back.

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 index advances only when current value is not val; skip otherwise.

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];
      k++;
    }
  }
  return k;
}

Tradeoff:

DigitalOcean-specific tips

DigitalOcean expects in-place writes here because their hot-path metric filters cannot afford an allocation per droplet sample.

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Output

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