three gates

3gates.rb

require 'securerandom'

def seed
  SecureRandom.uuid.gsub(/[-a-z]/,"").to_i
end

total = 10000
rights = 0

(1..total).each do
  # gen a random doors
  doors = [false, false, false]
  doors[Random.new(seed).rand(3)] = true

  # choose a door
  rights += 1 if doors[Random.new(seed).rand(3)]
end

puts "insist: rights: #{rights}, probability: #{rights.to_f / total}."

rights = 0

(1..total).each do
  # gen a random doors
  doors = [false, false, false]
  doors[Random.new(seed).rand(3)] = true
  indexes = [0, 1, 2]

  # choose a door
  c = Random.new(seed).rand(3)

  # remove a wrong door
  indexes.delete c
  until indexes.length == 1
    i = Random.new(seed).rand(3)
    indexes.delete i unless doors[i]
  end
  rights += 1 if doors[indexes[0]]
end

puts "change: rights #{rights}, probability: #{rights.to_f / total}."