monty_hall.rb

# Should the contestant switch to the other door?
@switch = true
 
@wins = 0; @losses = 0
100000.times do
  # Hide the car
  car_behind = rand(3)
 
  # Contestant picks a door
  contestant_pick = rand(3)
 
  # Host opens a door that does not have the prize and is not the contestant's pick
  openable_doors = [0,1,2].delete_if{|x| x == contestant_pick or x == car_behind}
  host_opens = openable_doors[rand(openable_doors.size)]
 
  # Switch to the other door?
  if @switch
    new_pick = nil
    3.times{|i| new_pick = i if i != contestant_pick and i != host_opens}
    contestant_pick = new_pick
  end
 
  # See if the contestant won
  car_behind == contestant_pick ? @wins += 1 : @losses += 1
end
 
puts "#{@wins} wins and #{@losses} losses (#{@wins.to_f / (@wins + @losses)}% win)"