oli.rb

#!/usr/bin/env ruby
# Monty Hall problem proof http://en.wikipedia.org/wiki/Monty_Hall_problem
module Monty
  PLAYERS_WITH_POLICY = { jimmy: :switch, jasper: :stick, johnson: :random }
  DOORS               = [:goat, :goat, :ferrari]
  COUNT               = Integer(ARGV[0] || 100000)

  class << self
    def win?(policy)
      doors        = DOORS.dup.shuffle
      first_choice = doors.pop

      remove_goat! doors

      final_choice = case policy
                     when :stick then first_choice
                     when :switch then doors.sample
                     when :random then [true, false].sample ? first_choice : doors.sample
                     end

      final_choice == :ferrari ? true : false
    end

    def remove_goat!(doors)
      doors.slice!(doors.index(:goat))
    end

    def present(results_hash)
      results_hash.each do |player, wins|
        win_percentage = ((wins / COUNT) * 100.0).round(2)
        puts "#{player.capitalize} used strategy #{PLAYERS_WITH_POLICY[player]} and won #{win_percentage}% of his #{COUNT} games"
      end
    end

    def play
      PLAYERS_WITH_POLICY.inject(Hash.new(0.0)) do |results, (player, policy)|
        COUNT.times { results[player] += 1 if win?(policy) }
        results
      end
    end
  end
end

Monty.present Monty.play

$ time ruby oli.rb 10000000

Jimmy used strategy switch and won 66.66% of his 10000000 games
Jasper used strategy stick and won 33.35% of his 10000000 games
Johnson used strategy random and won 50.02% of his 10000000 games

real        1m34.006s
user        1m33.934s
sys         0m0.174s