lucarampi/sum-21-challenge

Why I did this? 🤷🏻‍♂️

I applied for a job and I needed to resolve a challenge using only JavaSacript. Unfortunately, I couldn't find the bug before the deadline (about 40 minutes) and I got very upset. So I did what every programmer would do: I took that personal. I spent a few more minutes figuring out the bug and fixing it.

I'm learning Next.js so I thought "Should I make a simple app to train what I've already learned?" Why not?. Btw it was useful to remind a bit of Bootstrap...

The challenge 💡

I don't remember the exact question, but I'm sure you will get the idea.
The user should select a number (between 0-9). From that, the program should generate a new 4-digit number by repeating the user input. Here is an example:

	userInput = 3;
	newNumber = 3333;

New it should create an array that contains every number that the sum of all its digits should be equal to 21 (basically we need to decompose the numbers and sum). With that said we will have (using the newNumber variable above as reference) the result:

	resultArray = [1299, 1389, 1398, ..., 3297]

ps.: Because this is impossible to occur with the numbers 0 and 1 I excluded them (0993 is not valid).

Note: I couldn't find the exact link but it was on HackerRank.

Some code 👨‍💻

First of all we need to convert the user input into a 4-digit number:

function  convertToMaxValue(value: number) {
	return  `${value}${value}${value}${value}`;
	//note that the returned value is a string
}

We also need to check if all the selected numbers fill the 21-sum requirement. This function will be called later.

function check_number(checking_number: number) {
	const number_array = Array.from(checking_number.toString().split(""));
	const sum = Number(
		number_array.reduce((acc, currVal) => {
			return acc + Number(currVal);
			}, 0)
		);
	if (sum == 21) {
		return true;
	    }
	return false;
}

Once we've done that we are ready to go end get our answer.

In first place we generate an Array with all the positive numbers up to the max possible value (which is that 4-digit). You might notice that a filter removes all non-4-digit numbers whitch was our first objective.

function  generate_numbers(max: string): number[] {
	const  max_number_possible  =  Number(max);
	const  all_numbers_array  =  Array.from(Array(max_number_possible  +  1).keys())
		.filter((number) =>  number.toString().length  ==  LENGTH);
	const  result_array  = all_numbers_array.filter(check_number);
	return  result_array;
}

In the end, we have our result array with all numbers that respect all the requirements. You can check this code working by clicking here

My Linked-in: Luca Alfaro Rampinelli