Problem

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.

Examples

Example 1:

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Input:
arr = [1,2,3], fn = function plusone(n) { return n + 1; }
Output:
 [2,3,4]
Explanation:
const newArray = map(arr, plusone); // [2,3,4]
The function increases each value in the array by one.

Example 2:

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Input:
arr = [1,2,3], fn = function plusI(n, i) { return n + i; }
Output:
 [1,3,5]
Explanation: The function increases each value by the index it resides in.

Example 3:

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Input:
arr = [10,20,30], fn = function constant() { return 42; }
Output:
 [42,42,42]
Explanation: The function always returns 42.

Solution

Method 1 - Using for loop and auxiliary array

Code

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var map = function(arr, fn) {
  const transformedArr = [];
  for (let i = 0; i < arr.length; i++) {
    transformedArr[i] = fn(arr[i], i);
  }
  return transformedArr;
};

Complexity

  • Time: O(n)
  • Space: O(n)

Method 2 - Using for loop and update array in place

Code

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var map = function(arr, fn) {
    for (let i = 0; i < arr.length; ++i) {
        arr[i] = fn(arr[i], i);
    }
    return arr;
};

Complexity

  • Time: O(n)
  • Space: O(1)