A demo proving the Monty Hall problem, in Ruby

Monty Hall

TRIES = 1000
successes = 0.0
1.upto(TRIES) do
  doors = [:goat, :goat, :goat]


  # put a car behind a random door
  doors[(rand * 3).to_i] = :car

  puts "1: #{doors[0]}"
  puts "2: #{doors[1]}"
  puts "3: #{doors[2]}"

  # pick a door at random
  choice = (rand * 3).to_i

  puts "Chose door ##{choice + 1}..."

  #open one of the other doors that has a goat, at random
  other_doors_with_no_car_indices = (doors.each_with_index.map{ |e, i| i}).reject{|i| i == choice || doors[i] == :car}
  open_door_index = other_doors_with_no_car_indices[(rand * other_doors_with_no_car_indices.length).to_i]

  puts "Host reveals a goat behind door ##{open_door_index + 1}..."

  #switch to the remaining door
  indices = [0, 1, 2]
  indices.delete(choice)
  indices.delete(open_door_index)
  final_door_index = indices.first

  puts "Switching to door ##{final_door_index + 1}...found a #{doors[final_door_index]}."
  if doors[final_door_index] == :car
    puts "WIN!"
    successes += 1
  else
    puts "FAIL."
  end
end

puts "-------------"
puts "Succeeded by switching in #{successes} out of #{TRIES} tries."
puts "Sucess rate: #{successes / TRIES * 100.0}%"