From: Ruby Quiz <james@...>
Date: 2006-03-30T00:06:34+09:00
Subject: [QUIZ] alarm.rb (#73)

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#!/usr/bin/env ruby -w

#
# Stephen Waits <steve@waits.net>
#

class AlarmKeypad

	# init a keypad, with length of security code, and the code's stop digits
	def initialize(code_length = 4, stop_digits = [1,2,3])
		# remember the length of the security code
		@code_length = code_length

		# and which digits cause a code to be checked
		@stop_digits = stop_digits

		# and reset our data structures to 0
		clear
	end

		
	# reset keypad to initial state
	def clear
		# an array of each code and how many times it's been entered
		@codes       = Array.new(10**@code_length,0)

		# last N+1 keypad button presses
		@key_history = []

		# total number of keypad button presses
		@key_presses = 0
	end

		
	# press a single digit
	def press(digit)
		# add digit to key history
		@key_history.shift while @key_history.size > @code_length
		@key_history << digit
		@key_presses += 1

		# see if we just tested a code
		if @stop_digits.include?(@key_history.last) and
		   @key_history.length > @code_length
			@codes[@key_history[0,@code_length].join.to_i] += 1
		end
	end

	# find out if every code had been tested
	def fully_tested?
		not @codes.include?(0)
	end

	# find out if an individual code has been tested
	# NOTE: an actual keypad obviously doesn't offer this functionality;
	#       but, it's useful and convenient (and might save duplication)
	def tested?(code)
		@codes[code] > 0
	end

	# output a summary
	def summarize
		tested          = @codes.select { |c| c > 0 }.size
		tested_multiple = @codes.select { |c| c > 1 }.size

		puts "Search space exhausted." if fully_tested?
		puts "Tested #{tested} of #{@codes.size} codes " + 
		     "in #{@key_presses} keystrokes."
		puts "#{tested_multiple} codes were tested more than once."
	end
end

if $0 == __FILE__
	# a random button presser, 3 digit codes
	a = AlarmKeypad.new(3)
	a.press( rand(10) ) until a.fully_tested?
	a.summarize

	# sequential code entry, 4 digit codes
	a = AlarmKeypad.new(4)
	("0000".."9999").each do |c|
		next if a.tested?(c.to_i)
		c.split(//).each { |d| a.press(d.to_i) }
		a.press(rand(3)+1)
	end
	a.summarize

	# sequential code entry, 5 digit codes, only [1] as a stop digit
	a = AlarmKeypad.new(5,[1])
	("00000".."99999").each do |c|
		next if a.tested?(c.to_i)
		c.split(//).each { |d| a.press(d.to_i) }
		a.press(1)
	end
	a.summarize
end