Filter elements from array

85.6% acceptance

Mar 2, 2026

811

109

Given an integer array arr and a filtering function fn, return a filtered array filteredArr. The fn function takes one or two arguments: arr[i] - number from the arr i - index of arr[i] filteredArr should only contain the elements from the arr for which the expression fn(arr[i], i) evaluates to a truthy value. A truthy value is a value where Boolean(value) returns true. Please solve it without the built-in Array.filter method.

Solution

TypeScript

Time O(n)

Space O(1)

LeetCode

solution.ts

type Fn = (n: number, i: number) => any;

function filter(arr: number[], fn: Fn): number[] {
  const result: number[] = [];
  for (let i = 0; i < arr.length; i++) {
  if (fn(arr[i], i)) result.push(arr[i]);
  }
  return result;
}