the_three_doors.rb

class Array
  def sum; inject( nil ) { |sum,x| sum ? sum+x : x }; end
  def mean; sum / size; end
  def random; self[rand(size)]; end
end

class TheThreeDoors
  attr_accessor :prize, :strategy, :revealed, :picked, :final_selection

  def initialize strategy
    @prize = rand(3) + 1
    @strategy = strategy
  end

  def pick_one(num)
    @picked = num
  end

  def reveal!
    doors = [1,2,3]
    doors.delete(@prize)
    doors.delete(@picked)
    @revealed = doors.random
  end

  def run_strategy
    if strategy == :switch
      @final_selection = [1,2,3].select{|door| door != @picked && door != @revealed}.first
    else
      @final_selection = @picked
    end
  end
  
  def win
    if @final_selection == @prize
      return 1.0
    else
      return 0.0
    end
  end
end



wins = []
10000.times do |trial|
  doors = TheThreeDoors.new(:switch)
  doors.pick_one rand(3)+1

  
  doors.reveal!
  # puts "run the strategy!!"
  doors.run_strategy
  
  # puts "we picked #{doors.picked}"
  # puts "winning door #{doors.prize}"
  # puts "reveal a wrong door: #{doors.revealed}"
  # puts "final selectio: #{doors.final_selection}"
  # puts ""
  
  wins << doors.win
  
  # puts "the prize is #{doors.prize}"
  # puts "\n"
end

puts "we won #{wins.mean} times"