Apply Transform Over Each Element in Array | #2635 | LeetCode Solution

Problem : Apply Transform Over Each Element in Array | #2635 | LeetCode

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.

Example 1:

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:

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:

Input: arr = [10,20,30], fn = function constant() { return 42; }

Output: [42,42,42]

Explanation: The function always returns 42.

Solution:

        /**

     * @param {number[]} arr

     * @param {Function} fn

     * @return {number[]}

     */

    var map = function(arr, fn) {

        returnedArray = []

        for (let i =0; i<arr.length; i++){

            returnedArray[i] = fn(arr[i], i)

        }

        return returnedArray

    };

Explanation:

This code defines a JavaScript function called `map` that mimics the behaviour of the built-in `Array.prototype.map()` method. The `map` function takes two arguments: an array (`arr`) and a callback function (`fn`). It applies the callback function to each element of the input array and returns a new array containing the results of those function calls.

Here's a step-by-step explanation of the code:

1. Function Definition:

a. The `map` function is defined with two parameters: `arr` (an array) and `fn` (a callback function).

2. Initialise an Empty Array:

a. Inside the `map` function, an empty array called `returnedArray` is initialised. This array will store the results of applying the callback function to each element of the input array.

3. Loop Over the Input Array:

a. A `for` loop is used to iterate through each element of the input array, `arr`. The loop variable `i` is initialised to 0.

b. The loop continues as long as `i` is less than the length of the input array (`arr.length`).

4. Apply the Callback Function:

a. Inside the loop, the callback function `fn` is called with two arguments:

b. The current element of the input array (`arr[i]`).

c. The index of the current element (`i`).

d. The result of calling the callback function is stored in the `returnedArray` at the same index, `i`.

5. Return the New Array:

a. After the loop completes, the `map` function returns the `returnedArray`, which now contains the results of applying the callback function to each element of the input array.