Monty Hall empirical proof

monty.rb

require 'test/unit'

# Read about the problem and mathematical proof here:
# http://www.greenteapress.com/thinkbayes/html/thinkbayes002.html#sec15

class MontyHall
  include Test::Unit::Assertions

  NUM_DOORS = 3

  # @return [Boolean] whether player won
  def play
    winning_door = rand(NUM_DOORS)
    player_first_choice = rand(NUM_DOORS)
    opened_empty_door = open_empty_door(winning_door, player_first_choice)
    assert_not_equal winning_door, opened_empty_door
    assert_not_equal player_first_choice, opened_empty_door
    player_second_choice = second_choice(player_first_choice, opened_empty_door)
    return (player_second_choice == winning_door)
  end
end

# basic Monty Hall rules, player always switches doors
class MontyHallStandard < MontyHall
  def open_empty_door(winning_door, player_first_choice)
    ((0...NUM_DOORS).to_a - [winning_door, player_first_choice]).sample
  end

  # always switch doors
  def second_choice(player_first_choice, opened_empty_door)
    ((0...NUM_DOORS).to_a - [player_first_choice, opened_empty_door]).sample
  end
end

class MontyHallAlwaysB < MontyHallStandard
  PREFERRED_DOOR = 1

  def open_empty_door(winning_door, player_first_choice)
    forbidden_doors = [winning_door, player_first_choice]
    if forbidden_doors.include?(PREFERRED_DOOR)
      super
    else
      PREFERRED_DOOR
    end
  end
end

class  MontyHallAlwaysBPlayerStick < MontyHallAlwaysB
  def second_choice(player_first_choice, opened_empty_door)
    opened_empty_door == PREFERRED_DOOR ? player_first_choice : super
  end
end

attempts = 10000
# game = MontyHallStandard.new
# game = MontyHallAlwaysB.new
game = MontyHallAlwaysBPlayerStick.new
successes = attempts.times.count { game.play }
success_rate = successes.to_f/attempts
puts "player success rate #{success_rate} in #{attempts} attempts"