Apply transform over each element in array

86.2% acceptance

Mar 2, 2026

912

120

Given an integer array arr and a mapping function fn, return a new array with a transformation applied to each element. The returned array should be created such that returnedArray[i] = fn(arr[i], i). Please solve it without the built-in Array.map method.

Solution

TypeScript

Time O(n)

Space O(1)

LeetCode

solution.ts

function map(arr: number[], fn: (n: number, i: number) => number): number[] {
  const result: number[] = new Array(arr.length);
  for (let i = 0; i < arr.length; i++) {
  result[i] = fn(arr[i], i);
  }
  return result;
}