All About Interop : Sudoku

Sudoku Generator and Solver in C#

DotNetInterop — Sat, 15 Mar 2008 01:41:00 GMT

Seems like building a Sudoku application is almost a compulsory thing for programmers these days.

I've written about my prior efforts. Here's an update. Rather than force you all to use the XBAP I published last year, here's a standalone WPF app. C# Source and EXE include.

It uses the DLX (Dancing Links) algorithm from Donald Knuth.

Pretty speedy. It is a WPF app, but there are no fancy WPF graphics. It just generates a table, and that's about it. This one is handy if you like to do Sudoku on paper. I've uses this app to generate and print out puzzles that I can do with my kids.

Source: http://cid-842434ebe9688900.skydrive.live.com/self.aspx/Games/Sudoku-1.0-source.zip
EXE: http://cid-842434ebe9688900.skydrive.live.com/self.aspx/Games/Sudoku.exe

Cheers!

Sudoku Toy redux - using C# DancingLinks Engine

DotNetInterop — Thu, 07 Jun 2007 21:22:00 GMT

A while back I posted a toy app that generates (and optionally solves) a Sudoku puzzle. It was under the rubric of Interop because the inner engine of this toy used an implementation of the Dancing Links engine for Sudoku, built in Java. The original Dancing Links algorithm was proposed by Donald Knuth; I found a Java engine that produced a string representation of a valid puzzle. I hooked that engine up to an Acrobat-generation library, the Acrobat ActiveX control from Adobe Acrobat v5, all stitched together into a Winforms app built in C#. That's a lot of interop.

The toy worked, but it had some challenges. First, Adobe was apparently discouraging use of the Acrobat ActiveX control. It was available in Acrobat v5 but them removed from subsequent releases of Acrobat reader. So in order to install and use this toy, you had to go get an old code base, one which had several known security problems. That was one problem. Also Acrobat v5 did not install alongside Acrobat v6, 7, or now, 8. So anyone that already had a current or recent Acrobat Reader, couldn't use this toy. Also, the hassle of installation was a problem in general.

XBAP to the rescue! I revisited the Sudoku puzzle generator, and now I have a new version. It is an XBAP, based on WPF, and runs in the IE browser. No more Acrobat requirement. No more unsupported ActiveX controls. The use of WPF within this app is pretty mundane - I just create a table with WPF. It uses the same Dancing Links engine code, but I ported it from Java to C#, in order to avoid the use of the discontinued J# compiler. It was a very straightforward port, and there were no problems whatever. I didn't even use the JLCA, I just hand-ported it with judicious use of search-and-replace.

This is an interop blog, right? So where is the interop now? This is a C# app, using WPF, and it runs in IE. With all that, it's hard for me to call this interop. At best it is re-use of an existing Java-based asset, but I did have to convert the Java logic to C# . But it's an update to an older post, so I thought y'all wouldn't mind if I put it here.

Anyway, try it out. In order to run this, you need IE7. Also, if you don't have the .NET Framework v3.0 installed on your machine, you will get it if you run this app. That download can be a drag!! You have been warned.

Some notes

How did I build the WPF part? Well the WPF itself, as I said, is nothing to write home about. WPF can do some amazing things with dynamnic graphics and animation, but this app doesn't do those fancy things. Basically this is WPF generating a table at runtime. I built all the XAML code by hand using a text editor. I've included the code here as an attachment for those who want to check it out.

Also - just to be clear - this is a puzzle generator, not a puzzle app. I use it to generate puzzles, which I then print out, and solve. I don't like to solve Sudoku on the computer, I prefer to do it on paper (tree hater). So the app here just creates a new puzzle. If you want to click on a puzzle and try to enter numbers to solve the puzzle yourself, this app will not help you.

Also, the app only solves Sudoku puzzles that it generates. you cannot insert arbitrary sudoku puzzles in and ask for a solution. maybe that is for another day.

Given that Silverlight is out, and we have Expression Blend and so on, it seems like I ought to produce a Silverlight version of this thing. That is on my list for later! By the way, if anyone else wants to build a Sudoku App, the C# DancingLinks engine contained in this project is a good piece of re-usable infrastructure. If you do grab that part of the project, let me know, I'm interested in hearing how you are using it.

Cheers!

Re-use of existing Java code (Sudoku engine)

DotNetInterop — Wed, 15 Feb 2006 16:20:00 GMT

Re-use of existing Java code (Sudoku engine)

This isn't so much about systems interop, as it is about code re-use and language interop.

You've seen Sudoku, the "number place" puzzle. Wikipedia says that it was created by a US puzzle magazine, but popularized (and given its recognized name) by the Japanese.

Last year during the summer holiday my wife gave me a book of Sudoku puzzles to do on the beach with my kids. The first one we tried was a real challenge, but gradually we caught on to the technique. Now we do the puzzles that come in the daily paper, regularly. They started to get a little too easy for us, so our thought was, maybe we could generate puzzles ourselves?

I thought - this is a nice little programming project. The next thought was: to generate a valid Sudoku, you have to solve it, to verify there is only one solution. The simple brute force solver method I imagined would be easy to code, but wouldn't be very fast. And I hadn't thought about sudoku generation algorithms. This was getting messy. Maybe somebody has already done this for me?

In short order I found lots of Sudoku sites and an abundance of algorithms and code implementations for generators and solvers. I tried a couple and found one that looked good and fast - implemented in Java by Rolf Sandberg, based on a C implementation by Günter Stertenbrink, which was based on the Dancing Links algorithm described by Donald Knuth.

As a port from C, the Java code is not the most object-oriented or elegant, but I didn't care about that. I wanted a toy to generate Sudoku puzzles. It worked great, but there was one big drawback. The generated puzzles looked like this:

 . . 8 1 . . . . .
 . 9 1 . . . . . 7
 . . . . 5 . 3 . 2
 6 . . 3 . 2 8 . 4
 3 . 9 . . . 5 . .
 . . . . . 6 . . .
 . 1 . . . . . 2 8
 . . 6 . . . . . .
 . 5 . . 7 . . . .

It was a command line tool, and it generated string output. What I really wanted was a puzzle I could print out, easily, and hand to my sons and say "have at it!"

I had previously fiddled with itextsharp, a library for creating PDFs from within .NET. (This is a port of iText, which is a Java library with the same purpose). PDF generation would seem to be a good fit.

Here Comes the Part About Interop

The cool thing was, I didn't have to do anything to the Java code to get it to work with my C# WinForms code. I just compiled it with VJ#, and BAM! it's ready to go. So no changes were required, but I did actually make a few changes in Sandberg's Java code. I added a DTO class for the puzzle. I added a few helper methods like solve() and generate() and rate(). But I left most everything intact. (re-factoring was tempting but I didn't want to spend the time understanding the code)

So.... I built a Winform app in C#, to wrap around that generator engine. I added in the PDF generation, and added a print button. Boom, a Sudoku generation toy. Its pedigree includes Java source code, C# code, and an activeX control from 2000. All seamlessly connected.

Grab the finished binary (with a Windows Installer) if you want to use the toy. It will run on Windows XP, requires .NET 1.1 and Adobe Acrobat Reader. Grab the VS 2003 Solution if you want to examine or tweak the code.

This is just one small illustration, but it shows: if you have source code repositories in your shop, or even if you have existing Java apps, and you want to update or extend them, you may be able to re-use that code very simply in .NET.

-Dino