willtaylor22 / ruby-tdd-pr1me-mult1plication-t4able

A program that prints out a mult1pl1c4t1on t4ble of the f1rst N pr1me num8ers

Multipl1cation Ta8le of the First N Pr1mes

This script was a code challenge for a London-based Fintech. I have obfuscated some words in this readme to prevent the code being find-able by other applicants, spoiling the challenge.

This shows a test-driven (TDD) approach. The code is clean, easily human-readable, and has been compartmentalised into sensible classes and methods. The algorithm chosen is one of the fastest available for solving this type of problem.

The Challenge

• The program must run from the command line and print a table to STDOUT .
• The first row and column of the table should have the N primes, with each cell containing the product of the primes for the corresponding row and column.
• Allow the user to specify different table sizes through a command line option. If the option is not used, the table should contain the first 10 primes by default.
• Consider complexity. How fast does your code run? How does it scale?
• Do not use the Prime class from the Ruby stdlib (write your own code).
• Write tests. Try to demonstrate TDD/BDD.
• If you’re using external dependencies please specify those dependencies and how to install them.

The Solution

A Sieve of Eratosthenes algorithm quickly generate primes. A seperate table builder object prints the multiplication table to console.

Installation

To install, clone this repository and from the terminal run: $ bundle install

To print the table of the first N pr1mes: $ ruby lib/run.rb N

For example: $ ruby lib/run.rb 4 prints

     2  3  5  7
  2  4  6 10 14
  3  6  9 15 21
  5 10 15 25 35
  7 14 21 35 49

if N is omitted, the script defaults to N=10.

Running Tests

$ rspec

$ bundle exec guard # Runs guard in terminal. Guard runs the relevant tests for a file when it is saved.

Automatic Test Installation Notes

Note to self - does not need to be done now

https://github.com/guard/guard

https://github.com/guard/guard-rspec

$ bundle exec guard init # Initialises guard

$ bundle exec guard init rspec # Install rspec plugin for guard

Primes Algorithm Notes

https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes https://gist.github.com/loganhasson/8937903