Have you seen the sudoku puzzles that are being published in the Daily Telegraph and (I think) the Los Angeles times? There's a whole group of addicts out there and helper and forum web sites too. Lisa pointed the puzzle out to me recently (no, she's not an addict!) with the thought of providing a helper spreadsheet and wondered what I could do on algorithms.

The puzzle is easily explained. You're given a 9 x 9 grid of cells with some of them already filled in with a single digit in the range 1 to 9 and you have to complete the puzzle by adding further 1 to 9 digits such that each row, each column and each cluster of 9 cells contains each digit just once. Here's a blank board:

on which I've numbered the cells just for reference.

Here's that same game board completed. I filled in the numbers that you now see in red on the form above (try it out if you like) and when I submitted it to my program, it completed the other cells ... in this example right through to a complete solution.

I've not personally spent a huge amount of time on this - just played with the algorithms and I think that my program will solve most (but not all) puzzles. Furthermore, it's what I describe as a "spike solution" - the code is poorly written as it grew during my research. Bits of code are duplicated (I should have used a loop or functions), documentation and comments are lacking, and it's pretty poorly inset. You can see the code in this shocking state if you like and rightly criticise me. My defence is that it's a spike solution - a proof of context that needs re-engineering.

Two questions

Have I provided a "helper" or a "cheat"? Is a program such as this one a helper in the spirit of the game, or does it go to far and provide an unfair advantage? If that's the case, where's the limit?

Should I publish code like this? I'm quite happy with my spike solution and I don't think it opens any security holes on our site. So should I say "hey - look at this and use it if you like", should I publish it with a copyright statement, or should I be ashamed of myself for even typing code this p*sspoor in the first place?


Two more sample solutions - tests of my algorithm (I'll come back and replace one with a demo of what happens when someone submits a puzzle that can't be fully resolved).

(written 2005-06-23, updated 2008-06-06)

 H112 - PHP - Further Web Page and Network Handling
  [220] When to use Frames - (2005-02-19)
  [314] What language is this written in? - (2005-05-17)
  [345] Spotting a denial of service attack - (2005-06-12)
  [372] Time calculation in PHP - (2005-07-08)
  [376] What brings people to my web site? - (2005-07-13)
  [410] Reading a news or blog feed (RSS) in your PHP page - (2005-08-12)
  [425] Caching an XML feed - (2005-08-26)
  [443] Server side scripting of styles to suit the browser - (2005-09-12)
  [451] Accessing a page via POST from within a PHP script - (2005-09-26)
  [484] Setting the file name for a downloaded document - (2005-11-03)
  [537] Daily Image Santafied - (2005-12-22)
  [542] Morning image, afternoon image - (2005-12-26)
  [565] Using PHP to output images, XML, Style sheets, etc - (2006-01-15)
  [603] PHP - setting sort order with an associative array - (2006-02-13)
  [675] Adding PHP tags to an old cgi program - (2006-04-08)
  [767] Finding the language preference of a web site visitor - (2006-06-18)
  [789] Hot answers in PHP - (2006-07-02)
  [847] Image maps for navigation - a straightforward example - (2006-08-28)
  [904] Of course I'll tell you by email - (2006-10-25)
  [936] Global, Superglobal, Session variables - scope and persistance in PHP - (2006-11-21)
  [1009] Passing GET parameters through Apache mod_rewrite - (2006-12-27)
  [1114] PHP Image upload script - (2007-03-21)
  [1183] Improving searches - from OR to AND? - (2007-05-11)
  [1187] Updating a page strictly every minute (PHP, Perl) - (2007-05-14)
  [1210] PHP header() function - uses and new restrictions - (2007-05-30)
  [1355] .php or .html extension? Morally Static Pages - (2007-09-17)
  [1379] Simple page password protection - PHP - (2007-10-04)
  [1485] Copyright and theft of images, bandwidth and members. - (2007-12-26)
  [1495] Single login and single threaded models - Java and PHP - (2008-01-04)
  [1496] PHP / Web 2 logging - (2008-01-06)
  [1505] Script to present commonly used images - PHP - (2008-01-13)
  [1515] Keeping staff up to date on hotel room status - (2008-01-22)
  [1518] Downloading data for use in Excel (from PHP / MySQL) - (2008-01-25)
  [1549] http, https and ajp - comparison and choice - (2008-02-22)
  [2632] Shipping a test harness with your class in PHP - (2010-02-12)
  [2679] How to build a test harness into your PHP - (2010-03-16)
  [2729] Uploading a document or image to its own URL via a browser - (2010-04-18)
  [2918] Downloading a report from the web for further local analysis - (2010-08-13)
  [3036] Sending out an email containing HTML from within a PHP page - (2010-11-07)
  [3432] 3 digit HTTP status codes - what are they, which are most common, which should be a concern? - (2011-09-11)
  [3540] Easy session example in PHP - keeping each customers data apart - (2011-12-06)
  [3568] Telling which ServerAlias your visitor used - useful during merging domains - (2012-01-04)
  [3918] Multiple page web applications - maintaining state - PHP - (2012-11-10)
  [4070] Passing variable between PHP pages - hidden fields, cookies and sessions - (2013-04-26)
  [4483] Moving from mysql to mysqli - simple worked example - (2015-05-03)

G906 - Well House Consultants - Programming Standards
  [148] Programming in isolation - (2004-12-11)
  [272] More to programming than just programming - (2005-04-08)
  [343] Should I use structured or object oriented? - (2005-06-10)
  [945] Code quality counts - (2006-11-26)
  [1596] Selling curry to the chinese takeaway - (2008-03-31)
  [1679] PHP - Sanitised application principles for security and useability - (2008-06-16)
  [1852] Perl and Blackberries - (2008-10-23)
  [2322] Looking for a practical standards course - (2009-08-05)
  [2363] Alpaca Case or Camel Case - (2009-08-16)
  [2364] Getting it right from the start - new programmers - (2009-08-17)
  [3685] Programming Standards in Lua - (2012-04-06)

A211 - Web Application Design and Deployment
  [23] Skills and responsibilities - (2004-08-22)
  [659] Web Application Components - (2006-03-28)
  [1198] From Web to Web 2 - (2007-05-21)
  [1256] What country are you in? How we find out on our web site - (2007-07-03)
  [1351] Compressing web pages sent out from server. Is it worth it? - (2007-09-14)
  [1545] Letting new visitors know we provide training courses - (2008-02-19)
  [1547] New bathing idea for hotels from Hotelympia - (2008-02-20)
  [1798] What does an browser understand? What does an HTML document contain? - (2008-09-15)
  [2072] Copyright, Portability and other nontechnical web site issues - (2009-03-09)
  [3532] Sharing the user experience - designing a form with the customer in mind - (2011-11-29)

Back to Context in Perl

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Forward to Where do Perl modules load from

Spring turns to Summer
Chicken soup without the religion
Use standard Perl modules
Where do Perl modules load from
Sudoku helper or sudoku cheat
Context in Perl
Ballooning from Bath
Wimbledon Neck
Improved mining techniques!
Is photoajustment an addiction?