From: Denis Hennessy <denis@...>
Date: 2008-01-14T05:15:19+09:00
Subject: Re: [QUIZ] Counting Cards (#152)

This week's puzzle had two challenges:

1. Implement a simple card counting scheme.
2. Present a simulated card deal to the user to help him develop the  
counting technique.

The real challenge is the second part. I ruled out the card names  
(3d,As,Tc...) and the ascii art options which left me needing a way of  
display proper graphic card images. I had a brief look at some gui  
toolkits (shoes, tk, ...) but in the end decided on a browser-based  
approach. I made a simple rails app and used an ajax request to update  
the training page. If anyone wants to try it, download http://www.hennessynet.com/counter.tar.gz 
   and unpack it into a temporary directory. Then run ./script/server  
and browse to http://localhost:3000/card_counter

The card counting algorithm is implemented first. The Counter class  
contains both the shuffled shoe as well as the running count.

card_counter.rb:
CARDS = %w{A K Q J T 9 8 7 6 5 4 3 2}
SUITS = %w{c s h d}

class Counter
   def initialize(decks)
     @count = 4 - 4*decks
     @shoe = []
     decks.times do
       CARDS.each do |c|
         SUITS.each do |s|
           @shoe << c.to_s + s.to_s
         end
       end
     end
     size = 52*decks
     size.times do |i|
       j = rand(size)
       @shoe[i],@shoe[j] = @shoe[j],@shoe[i]
     end
   end

   def deal
     card = @shoe.pop
     @count += 1 if "234567".include? card[0,1].to_s
     @count -= 1 if "TJQKA".include? card[0,1].to_s
     card
   end

   def count
     @count
   end

   def size
     @shoe.size
   end
end

Then I made a rails app with a controller called  
card_counter_controller.rb and a web page (practice.html.erb) to 'run'  
the training. The interesting bit is the periodically_call_remote()  
call which gets a new set of cards every n seconds and displays them  
to the user. A pause button suspends the dealing and displays the  
current count. I found a free set of card images at http://www.jfitz.com/cards/

card_counter_controller.rb:
require 'card_counter'

class CardCounterController < ApplicationController

   def practice
     session[:counter] = Counter.new params[:decks].to_i
     session[:min] = params[:min].to_i
     session[:max] = params[:max].to_i
     session[:delay] = params[:delay].to_i
   end

   def deal
     min = session[:min]
     max = session[:max]
     counter = session[:counter]
     max = counter.size if counter.size<max
     min = max if max < min
     count = min + rand(max-min+1)
     text = ""
     text = "Shoe complete" if count == 0
     count.times do
       card = session[:counter].deal
       text += "<img src='/images/#{card_index(card)}.png' width='72'  
height='96'/>\n"
     end
     text += "<p id='count' style='visibility: hidden'>Count is  
#{counter.count}</p>"
     render :text => text
   end

   # Convert card name ("6d", "Qs"...) to image index where 1=Ac,2=As, 
3=Ah,4=Ad,5=Kc and so on
   def card_index(card)
     c = CARDS.index card[0,1].to_s
     s = SUITS.index card[1,1].to_s
     c * 4 + s + 1
   end
end


practice.html.erb:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
   "http://www.w3.org/TR/2000/REC-xhtml1-20000126/DTD/xhtml1- 
strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
   <meta http-equiv="content-type" content="text/html; charset=utf-8" />
   <%= javascript_include_tag :defaults %>
   <title>Practice Card Counting</title>
   <script type="text/javascript">
   //<![CDATA[
   paused = false;
   function pause() {
     paused = !paused;
     if (paused) {
       $('count').setStyle('visibility: visible');
       $('pause').update('Continue')
     } else {
       $('pause').update('Pause')
     }
   }
   //]]>
   </script>
</head>
<body>
   <a id='pause' href="#" onClick="pause()">Pause</a>
   <div id="cards"></div>

   <%= periodically_call_remote(
   :condition => "paused == false",
   :update => "cards",
   :frequency => session[:delay],
   :url => { :action => "deal" }) %>
</body>
</html>

Enjoy,
Denis
>