pk-nb / rps

Rock Paper Scissors

This is a programming exercise for use when pairing with developer applicants, borrowed from Ruby Quiz.

Setup

To run, add two or more subclasses of Player to the players directory (or simply check out the default-players branch) and run rake.

I've been having candidates create their own basic players (RockPlayer, PaperPlayer, RandomPlayer), and then having them suggest and implement more complicated options.

Synopsis

Your task is to build a strategy for playing the game of Paper Rock Scissors against all manner of opponents. The question here is if you can adapt to an opponent's strategy and seize the advantage, while he is doing the same to you of course.

If you're not familiar with this childhood game, it's very simple. Both players choose one of three items at the same time: Paper, a Rock, or Scissors. A "winner" is chosen by the following rules:

Paper covers a Rock.      (Paper beats a Rock.)
Scissors cut Paper.       (Scissors beat Paper.)
A Rock smashes Scissors.  (A Rock beats Scissors.)
Anything else is a "draw".

Defining a player for straight forward. I'm providing a class you can just inherit from:

class YourPlayer < Player
  def initialize( opponent )
    # optional
    #
    # called at the start of a match verses opponent
    # opponent = String of opponent's class name
    #
    # Player's constructor sets @opponent
  end

  def choose
    # required
    #
    # return your choice of :paper, :rock or :scissors
  end

  def result( you, them, win_lose_or_draw )
    # optional
    #
    # called after each choice you make to give feedback
    # you              = your choice
    # them             = opponent's choice
    # win_lose_or_draw = :win, :lose or :draw, your result
  end
end

We'll need some rules for defining players, to make it easy for all our strategies to play against each other:

• Player subclasses reside in the players directory
• One file per player (e.g. players/rock_player.rb -> RockPlayer)

Pairing

Set up a shared server with some basic dependencies:

apt-get install -y ruby2.0 git vim screen
sudo gem install rake

Create a user account to share (e.g. pairing) and set up a screen session:

screen -S rps

Have the other person SSH as the same user and connect to your running screen session:

screen -x

The other person's screen will update when you make changes and vice versa. To quickly get the results of the game, you can just type :!rake from within vim.