Monty Hall Problem Simulator

monty_hall.rb

number_of_doors = 3
monty_is_random = false
switch_choice = true
number_of_simulations = 10000

# number_of_correct_initial_guesses = 0
number_of_times_monty_accidentally_exposes_car = 0
number_of_wins = 0

doors = (1..number_of_doors).inject({}){|h,i| h[i] = nil; h }
# => {1=>nil, 2=>nil, 3=>nil}
door_with_car_behind_it = rand(number_of_doors) + 1
doors[door_with_car_behind_it] = "CAR"
doors.keys.each{|door_number| doors[door_number] ||= "Camel" }
# => (eg.) {1=>"CAR", 2=>"Camel", 3=>"Camel"}
number_of_simulations.times do
  first_guess = rand(number_of_doors) + 1
  montys_remaining_choices = doors.keys - [first_guess]
  if monty_is_random
    exposed = false
    while montys_remaining_choices.size > 1 && !exposed
      montys_door = montys_remaining_choices[rand(montys_remaining_choices.size)]
      if doors[montys_door] == "CAR"
        number_of_times_monty_accidentally_exposes_car += 1
        exposed = true
      else
        montys_remaining_choices -= [montys_door]
      end
    end
    next if exposed
  else
    if doors[first_guess] == "CAR"
      # Just choose any of the remaining doors to keep closed, might as well be the first
      montys_remaining_choices = montys_remaining_choices[0..0]
    else
      # Keep the CAR door closed
      montys_remaining_choices = [door_with_car_behind_it]
    end
  end
  raise "Oops" unless montys_remaining_choices.size == 1
  if switch_choice
    new_guess = montys_remaining_choices[0]
  else
    new_guess = first_guess
  end
  if doors[new_guess] == "CAR"
    number_of_wins += 1
  end
end

percent_of_all = (number_of_wins.to_f / number_of_simulations)*100
percent_of_valid = (number_of_wins.to_f / (number_of_simulations - number_of_times_monty_accidentally_exposes_car))*100
puts "Player won #{number_of_wins} times or #{percent_of_all.round(1)}% of all simulations.\n" +
     "Monty accidentally exposed the car #{number_of_times_monty_accidentally_exposes_car} times.\n" +
     "Therefore player won #{percent_of_valid.round(1)}% of valid simulations"