From: Daniel Martin <martin@...>
Date: 2007-08-14T21:37:51+09:00
Subject: Re: [QUIZ] Cellular Automata (#134)

I didn't have much time this weekend, but I had a bit more than
previous weeks, so here's my solution.  The goal here was "minimal
coding".  As a result, the rule-evaluation statement could charitably
be described as "terse".  It just does X's and spaces as in the quiz
description.

#!ruby
require 'optparse'

rule = 30
initial_pattern = '1'
steps = 10
OptionParser.new do |opts|
  opts.banner = "Usage: ca.rb [opts]"
  opts.on("-r", "--rule N", Integer, "Rule number") do |n|
    rule = n
  end
  opts.on("-s", "--states N", Integer,
                "Number of states (default 10)") do |s|
    steps = s
  end
  opts.on("-c", "--cells BITSTRING", String,
                "Initial cell pattern as 0s and 1s") do |s|
    initial_pattern = s
  end
end.parse!

# This ensures some padding for those nasty odd rules
pattern = '0' * steps + initial_pattern + '0' * steps;
(steps-1).times {
  puts pattern.tr('01',' X')
  ppat = pattern[0,1] + pattern + pattern[-1,1]
  pattern = (1..pattern.size).inject(""){|s,i|
    s << ((rule >> [ppat[i-1,3]].pack('b3')[0])&1).to_s
  }
}
puts pattern.tr('01',' X')

__END__

-- 
s=%q(  Daniel Martin -- martin@snowplow.org
       puts "s=%q(#{s})",s.to_a.last       )
       puts "s=%q(#{s})",s.to_a.last