Solver App for Android
Strategies for Popular Number Puzzles
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Feedback and Questions

I've received a lot of interesting comments and questions from Sudoku fans over the last few years and this page is where I try to answer them. I'm also directing Str8ts feedback here. Please feel free to drop me a note on the side of the page. Or you can email me directly at .

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Many thanks to all the people who have helped improve the solvers and strategies with their feedback!

Saturday 20-Oct-2007

... by: Harald, Bavaria

Load Sudoku:

The simple colouring step which gives "SINGLES CHAIN (Type 1): Removing 1 from F2" colours the locked pair "13" in column 6 which has nothing to do with this chain.

Andrew Stuart writes:
That's true if you are thinking just of chains - which is the alternative strategy, but with simple colouring one is colouring all cells and seeing which of them can be made into chains within that set that lead to an elimination, so its important to show and see all the cells that can be coloured. There might be two or more independent eliminations through colouring (although my solver will only pick/show the first)

Wednesday 17-Oct-2007

... by: Justin, Massachusetts

Load Sudoku:

This is from the 10/13/07 Tough puzzle at
the following eliminations have been made:
45h not 7, 23b not 8, 9c not 6
When I put it into Sudoku Solver and step, it gets down to Xwing and goes to sleep, saying Wait.
I've used this excellent program many times before without any problems, so I don't think the problem is in my system.

Andrew Stuart writes:
I Justin, I think the server had hung when you were using it. Should be ok now, but your sudoku example is not correct. May numbers the same in rows and columns

Wednesday 17-Oct-2007

... by: cbee, Malta

Can't think of a single imporovement. Its a great program I use every day. Keep up the good work.

Andrew Stuart writes:
Many thanks! appreciated

Tuesday 18-Sep-2007

... by: Jacques Bourgeois, Switzerland


Thanks a lot for your solver, it saved my life.... We tried several hours to solve some sudoku with my son which have soon a test at school. We are not experienced with sudoku and don't know all the techiques. We solved several sudokus but the last one didn't want to reveal its secrets. Looking for help about sudoku strategies we found your site explaining several of the strategies and ITS step by step solver. Using this one we could very easily understand the underlaying techniques and now everything is ok.

We congratulate you for you very well constructed site.

Best regards,
Jacques Bourgeois

Friday 20-Jul-2007

... by: RLM, Tulsa, Oklahoma, USA

Nice way to load papers daily Sudoku and solve without pencil & eraser
Nice site, very much a good place to wind down and eliminate stress,
nice to be able to check progress and not have to start over from scratch.

Saturday 9-Jun-2007

... by: Ando, Germany

Load Sudoku:

Your SDK-Solver answer for those Problem SDK: Out of strategie.
But it's really solversable with the simply prinzip in


Andrew Stuart writes:
I'm afraid you made a mistake entering the sudoku - it has two solutions and therefore the strategies are not going to work. Click on the yellow "Solution Count" to see this

Wednesday 6-Jun-2007

... by: bird, usa

How do I get the puzzle to print? When I hit "Printable Version" it comes up, but there's no place to tell it to print? Thanks!!

Andrew Stuart writes:
In Windows, press the Control (Ctrl) key (in the lower left corner of the standard keyboard) and hold it down while pressing the P key. A printer dialog window should pop up.

Tuesday 5-Jun-2007

... by: Tom, USA

Andrew- I'm a bit of an amateur programmer and want to compliment you on the solver. I've thought about writing a solver but decided it was way beyond my capabilities on both the programming and soduko end of things. So again thank you for writing it and making it so useful.

Andrew Stuart writes:
Thanks Tom, although I'd still enourage you to play with algorithms for sudoku, they are great fun and a challenge as well

Monday 4-Jun-2007

... by: Debra,

I love your solver but have a question about how to correct my errors.

Whenever I make a mistake the solver tells me and shows me where the mistake is. But when I try to put the right number in the square, it won't let me. It puts the 0 back and I still get the "oops, there are errors" message. How do I correct this. I hate starting all over.


Andrew Stuart writes:
You can click Save before you get to that point, then click Re-Load. However, if you don't have a Saved board to go back to, put the right number in the square and click on Email This Board. Then, using the Windows "Copy and Paste" feature, copy the string of 81 numbers. Then click Import a Sudoku. You may get a warning about scripted windows. If so, Temporarily allow scripted windows and click Import a Sudoku again. Paste your 81 numbers and click OK.

Monday 28-May-2007

... by: goku, Cali

Load Sudoku:

This is a sudoku that can't seem to be solved by logic but has only one solution.

Andrew Stuart writes:
You have provided one of many examples of Sudokus that have one solution but can not be solved with known strategies. There may be a, yet to be found, strategy which will solve your puzzle.
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Thank-you everyone for all your questions and contributions.