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5. Remove Element

easyAsked at Riot Games

Filter an array in place by value — Riot uses this to test write-pointer mechanics before anti-cheat blacklist filtering questions.

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

Problem

Given an integer array and a value val, remove all occurrences of val in place and return the new length. Order of the remaining elements may change.

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 into new array

Build a new array of survivors then copy back.

Time
O(n)
Space
O(n)
const keep = nums.filter(x=>x!==val);
for (let i=0;i<keep.length;i++) nums[i]=keep[i];
return keep.length;

Tradeoff:

2. Two-pointer overwrite

Advance a write index only for survivors.

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

Tradeoff:

Riot Games-specific tips

Riot anti-cheat filters player events with the same write-pointer technique to drop banned actors without reshuffling the broadcast buffer mid server tick.

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Output

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