Monty.rb

#Monty Hall Dilemma
class Monty
  def initialize(i)
    @door = [:goat, :goat, :car]
    @trial_time = i
  end

  def first_choice
    return rand(@door.size)
  end

  def open_index(player_index)
    index = [0,1,2]
    index.delete(player_index)
    return @door[index[0]] == :goat ? index[0] : index[1]
  end

  def try(change = false)
    index = [0,1,2]
    @door.shuffle!
    player_index = first_choice
    if change
      index.delete(player_index)
      i = open_index(player_index)
      index.delete(i)
      player_index = index[0]
    end
    return @door[player_index] == :car ? 1 : 0
  end

  def sim(flag)
    sum = 0.0
    @trial_time.times do
      sum += try(flag)
    end
    puts "change:#{flag} => #{sum/@trial_time*100}%"
  end
end


if $0 == __FILE__
  m = Monty.new(100000)
  m.sim(change = false)
  m.sim(change = true)
end