Simulate the Monty Hall problem in Ruby

monty_hall.rb

class MontyHall
  DOORS = 0..2

  def initialize
    @car = rand(DOORS)
  end

  def pick
    @pick = rand(DOORS)
  end

  def reveal
    @reveal = rand(DOORS)
    while @reveal == @car || @reveal == @pick
      @reveal = rand(DOORS)
    end
  end

  def stay_wins? # 33%
    @car == @pick
  end

  def new_pick_wins? # 50%
    new_pick = closed_doors[rand(2)]
    new_pick == @car
  end

  def switch_wins? # 66%
    @pick != @car #&& @reveal != @car
  end

  def closed_doors
    DOORS.to_a - [@reveal]
  end

  def self.simulate(n)
    switch_wins, stay_wins, new_pick_wins = 0, 0, 0
    n.times do
      game = MontyHall.new
      game.pick
      game.reveal
      stay_wins     += 1 if game.stay_wins?
      switch_wins   += 1 if game.switch_wins?
      new_pick_wins += 1 if game.new_pick_wins?
    end

    puts "stay_wins     = #{1.0 * stay_wins / n}"
    puts "new_pick_wins = #{1.0 * new_pick_wins / n}"
    puts "switch_wins   = #{1.0 * switch_wins / n}"

    # stay_wins     = 0.333176
    # new_pick_wins = 0.500569
    # switch_wins   = 0.666824

  end
end

MontyHall.simulate 1_000_000