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5. Remove Element

easyAsked at N26

Remove all instances of a given value from an array in-place. N26 reframes this as filtering reversed transactions out of a daily settlement batch.

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

Problem

Given an integer array nums and an integer val, remove all occurrences of val from nums in-place. Return the number of elements that are not equal to val; the first k elements should hold the kept values.

Constraints

  • 0 <= nums.length <= 100
  • 0 <= nums[i], val <= 50
  • Order of remaining elements may change

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. Splice loop

Remove each occurrence with array splice.

Time
O(n^2)
Space
O(1)
for (let i=nums.length-1;i>=0;i--)
  if (nums[i]===val) nums.splice(i,1);
return nums.length;

Tradeoff:

2. Two-pointer write index

Write pointer advances only on keepers.

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:

N26-specific tips

N26 reviewers value confirming whether order matters before optimizing; for ledger lines order is usually load-bearing, so call that assumption out.

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Output

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