JavaScript Coding Challenge: "Beautiful Days at the Movies"

JCC Beautiful Days at the Movies Image

It's Friday, so it's time to get comfortable, weekend is coming 🙌, and for today we have a very easy JCC (JavaScript Coding Challenge)!

Here is another easy, and beautiful 😇 challenge from HackerRank:

Lily likes to play games with integers. She has created a new game where she determines the difference between a number and its reverse. For instance, given the number 12, its reverse is 21. Their difference is 9. The number 120 reversed is 21, and their difference is 99.

She decides to apply her game to decision making. She will look at a numbered range of days and will only go to a movie on a beautiful day.

Given a range of numbered days,[i...j] and a number k, determine the number of days in the range that are beautiful. Beautiful numbers are defined as numbers where |i - reverse(i)| is evenly divisible by k. If a day's value is a beautiful number, it is a beautiful day. Print the number of beautiful days in the range.

Function Description

Create a beautifulDays function. It must return the number of beautiful days in the range.

beautifulDays has the following parameters:

  • i: the starting day number
  • j: the ending day number
  • k: the divisor

Isn't this challenge beautiful? 😇

The solution

Let's break the problem into smaller pieces. We'll have to:

  1. Loop through all the numbers from i to j
  2. Get the difference between the number and its reverse
  3. Determine if the difference is evenly divisible by k
  4. Count the beautiful numbers
  5. Return the count
function beautifulDays(i, j, k) {
    let count = 0;
    // Step 1.
    for (let x = i; x <= j; x++) {
        // Step 4.
        if (isBeautifulDay(x, k)) {
    // Step 5.
    return count;

function isBeautifulDay(x, k) {
    // Step 3.
    return differenceOfReverse(x) % k === 0;

function differenceOfReverse(x) {
    let reversedX = parseInt(
    // Step 2.
    return Math.abs(x - reversedX);

I decided to split the solution in multiple functions. It's easier to understand what's going on this way.

Everything from the code above is pretty clear, but I do want to go over how we reverse the number.

Let's work on an example number, let's say: 120. So we have: let x = 120;.

Convert it to a string

x.toString(); // result: '120'

Split the string into an array of characters

x.toString().split(''); // result: ['1', '2', '0']

Reverse the array

    .reverse(); // result: ['0', '2', '1']

Join the characres from te array back to a string

    .join(''); // result: '021'

Convert the string back to a number

); // result: 21

Voila! We have the reversed number!


Nothing fancy for today, but at the same time we had a chance to complete a challenge.

REMEMBER: even if you don't work a lot in a day for your dream, it's important to do something EVERY SINGLE DAY! Keep moving forward everyday even if it's only a single small step! 😉 These small steps will pile up in something big one day!

Tagged with javascript, challenge, beginner, hackerrank, array, split, reverse, join