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5. Remove Element

easyAsked at Ramp

In-place remove all occurrences of a value from an array; return the new length.

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

Problem

Given an array nums and a value val, remove all occurrences of val in-place. Return the count of remaining elements; the first k positions of nums must hold them in any order.

Constraints

  • 0 <= nums.length <= 100
  • 0 <= nums[i] <= 50
  • 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, nums=[0,1,4,0,3,_,_,_]

Approaches

1. Filter to new array

Build filtered copy, write 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

Slow pointer tracks write position; fast scans. Write only non-val elements. O(1) extra space.

Time
O(n)
Space
O(1)
function removeElement(nums, val) {
  let slow = 0;
  for (let fast = 0; fast < nums.length; fast++) {
    if (nums[fast] !== val) {
      nums[slow] = nums[fast];
      slow++;
    }
  }
  return slow;
}

Tradeoff:

Ramp-specific tips

Ramp asks this as a precursor to filtering disputed transactions out of a ledger batch in place, so be ready to discuss preserving relative order for audit logs.

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Output

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