software-internship-assessment

A coding assessment to be done by ENPICOM software engineering internship candidates

Intro

Hello there! First of all, congratulations - if you're asked to complete this assessment, it means we believe you're a promising internship candidate. However, programming skill is hard to judge by just talking, so we would like to ask you to complete this small programming challenge.

Please do not spend too much time on this - it should only take an hour or two.

General instructions

We would like to ask you to complete this assignment using the TypeScript language, since this is our main application development language at ENPICOM. For running TypeScript code without having to compile it to JavaScript first, we recommend ts-node.

To get started, please make a fork of this Git repository, and commit + push your code to the fork. When you have finished the assignment and made sure it works correctly, just send us the link to the repository you used.

For this assignment, please create a command line application implementing the algorithm described in the next section. This application should:

• print a message asking for the user to input a credit card number
• accept a single string of text on STDIN (read until the end)
• exit with status 0 if the provided string is valid according to the algorithm
• exit with status 42 otherwise

To help you out, we have provided a set of test cases to validate your implementation. To run these tests, you will need Node.js installed - if you do not have it installed, you can download it at that link for your OS.

You can run the tests from the root of the repository as follows:

$ node tests.js '<your-application-command>'

For example, if you use ts-node to run your application, this would be something like:

$ node tests.js 'ts-node luhn.ts'

Algorithm description

Given a number determine whether or not it is valid per the Luhn formula.

The Luhn algorithm is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers.

The task is to check if a given string is valid.

Validating a Number

Strings of length 1 or less are not valid. Spaces are allowed in the input, but they should be stripped before checking. All other non-digit characters are disallowed.

Example 1: valid credit card number

4539 1488 0343 6467

The first step of the Luhn algorithm is to double every second digit, starting from the right. We will be doubling

4_3_ 1_8_ 0_4_ 6_6_

If doubling the number results in a number greater than 9 then subtract 9 from the product. The results of our doubling:

8569 2478 0383 3437

Then sum all of the digits:

8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80

If the sum is evenly divisible by 10, then the number is valid. This number is valid!

Example 2: invalid credit card number

8273 1232 7352 0569

Double the second digits, starting from the right

7253 2262 5312 0539

Sum the digits

7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57

57 is not evenly divisible by 10, so this number is not valid.