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5. Remove Element

easyAsked at Nubank

Filter out cancelled-transaction codes in place to simplify a reconciliation feed.

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

Problem

Given an integer array nums and a value val, remove all occurrences of val in-place. Return the number of elements that are not equal to val; the first k slots must contain those elements.

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

Approaches

1. Filter copy

Allocate a new array of kept values.

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 pointer skips val; copy in place.

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:

Nubank-specific tips

Nubank weighs your ability to reason about idempotent in-place mutations the same way you would when rewriting a posted-but-cancelled ledger entry.

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Output

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