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Sudoku Solving Java Program

Elliot Penson

Joined: Dec 29, 2012
Posts: 1
I decided to create a small application to solve a user inputted sudoku puzzle. This class guesses numbers for cells (starting with 1) and then backtracks when a possible number cannot be found. Unfortunately, the program does not work. It seems to fail when it cannot find a correct number. Any help with this program would be greatly appreciated. Also, any tips in general would be really useful. Thanks!

Ulf Dittmer

Joined: Mar 22, 2005
Posts: 42965
There was a lengthy discussion here:
Kemal Sokolovic

Joined: Jun 19, 2010
Posts: 825

I would recommend you read Programming Sudoku by Wei-Meng Lee, if you really want to implement and understand a good solution and perhaps get an idea on how to improve it. The code is written in .NET though, but it will surely provide a good foundation on algorithms you can use to solve it.

Otherwise, if you want to use an existing solution, there are plenty of those around.

The quieter you are, the more you are able to hear.
fred rosenberger
lowercase baba

Joined: Oct 02, 2003
Posts: 11955

"It seems to fail" doesn't really tell us anything. Does it crash/core dump? Does it hang? Does it give bad results?

How do you know it seems to fail? It's not like we can run it ourselves, since we have no idea what input you used. Perhaps you are inputting something that has no solution.

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
Tony Docherty

Joined: Aug 07, 2007
Posts: 2838
Some time ago I started working on a Sudoko solver which, rather than just solving the puzzle for you, allows you to see how it solves each cell. A beta applet version can be found at
It has some fairly complex solvers built in but I got bored and so never got around to adding any more solvers or getting the whole thing beyond beta stage. If you want the code let me know and I can upload it to my website.
I agree. Here's the link:
subject: Sudoku Solving Java Program
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