A Ruby simulation of the Monty Hall problem.

monty.rb

# This program simulates the Monty Hall problem (https://en.wikipedia.org/wiki/Monty_Hall_problem).
# Specifically, it counts how often the contestant wins by switching doors when given the choice
# by the game show host.

def contestant_wins?
  doors = [:car, :goat, :goat]
  indexes = 0...doors.size
  player_first_choice = rand(doors.size)
  host_choice = (indexes.select {|i| i != player_first_choice && doors[i] == :goat}).sample
  player_second_choice = indexes.find {|i| i != player_first_choice && i != host_choice}
  doors[player_second_choice] == :car
end

experiments = 10_000_000
wins = 0
experiments.times {wins += 1 if contestant_wins?}

puts "Relative frequency of winning when switching doors: #{wins.to_f/experiments.to_f}"