Paradox Monty-Hall

gistfile1.txt

#! /usr/bin/env ruby

require 'logger'
require 'pp'

class ThreeBoxGame

  def initialize(options = {})
    @double_choice  = options[:double_choice] || false
    @boxes          = %w(1 2 3)
    @box_with_price = @boxes.shuffle.first
    @user_choice    = @boxes.shuffle.first
    @logger         = Logger.new(STDOUT)
    @logger.level   = options[:log_level] || Logger::FATAL
    status
  end

  def win?
    status
    remove_one_box_and_redefine_choice if @double_choice
    status
    @box_with_price == @user_choice
  end


  private

  def remove_one_box_and_redefine_choice
    box_to_remove = (@boxes - [ @box_with_price ]).shuffle.first
    @boxes.delete(box_to_remove)
    @user_choice = (@boxes - [ @user_choice ]).first
  end

  def status
    @logger.debug "boxes: #{@boxes}"
    @logger.debug "user_choice: #{@user_choice}"
    @logger.debug "box_with_price: #{@box_with_price}"
  end

end

# puts ThreeBoxGame.new(double_choice: false).win? ? "Win!" : "Lose!"

results = {
  :single => { :win => 0, :lose => 0 },
  :double => { :win => 0, :lose => 0 }
}

count_of_tests = 50_000

count_of_tests.times do
  if ThreeBoxGame.new(double_choice: false).win?
    results[:single][:win] += 1
  else
    results[:single][:lose] += 1
  end

  if ThreeBoxGame.new(double_choice: true).win?
    results[:double][:win] += 1
  else
    results[:double][:lose] += 1
  end
end

results[:double][:probability] = results[:double][:win].to_f / count_of_tests
results[:single][:probability] = results[:single][:win].to_f / count_of_tests

pp results