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5. Remove Element

easyAsked at Dropbox

Remove all occurrences of a value in place; Dropbox uses it to test in-place compaction patterns relevant to garbage-collecting stale chunk references.

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

Problem

Given an integer array and a value val, remove all occurrences of val in place. Return the new length k; the first k positions of nums should contain the kept elements.

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. Brute force

Filter into a new array and 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-pointer in place

Advance read index across nums; write to k only when value is kept. O(1) memory.

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:

Dropbox-specific tips

Dropbox grades on whether you ask 'does order matter?' — if not, a swap-from-end variant cuts writes in half and they like that micro-optimization.

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Output

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