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!

Sunday 10-May-2009

... by: Rod Nash, Australia

The daily sudoko displays only partial numbers on my Iphone.

Andrew Stuart writes:

Yep, I know the problem. Its not been designed for the iPhone and the styling is poorly handled by the iPhone browser. I need to make a special version of the player for the iPhone. I do have one, so it just needs some time.

Thanks for the prompt :)

Friday 8-May-2009

... by: SGC, China

Load Sudoku:

WebSudoku.dll can work, but run out strategies from 'take step'.

hope you fine much more strategies.


Andrew Stuart writes:

Nice one. Will have to work hard on this. Where did it come from?


Wednesday 6-May-2009

... by: ECC, Oregon

Load Sudoku:

The puzzle you list as easiest sudoku has 32 clues and scores 8 on your grader. This puzzle I made has 32 clues and scores a 7 on your grader. Does that make it the new easiest sudoku?

Andrew Stuart writes:

This is great fun, and congrats for creating it. I would like to host a new competition on my site for people interested in beating the grader and creating ludicrously easy puzzles. I've opened an article here:


Its just for fun and kudos, as I say. More entries to come I hope!

Tuesday 5-May-2009

... by: Joe Read, Anaheim, CA, USA

Load Sudoku:

Hi, Andrew -
I got as far as the above situation, and asked for the "next step." I was given a Y-Wing with 8 taken off D2 and H1 using D1 G1 & H2.

I don't understand why that situations allows the 8's to be taken off D2 and H1 instead of being taken off D1 and D2, thus allowing them to remain on D2 and H1. In other words, 8's are in all four corners, so why are D1 and H2 selected as the pincers??

Thanks in advance for any insight you can provide. -Joe

Andrew Stuart writes:

Interesting Y-Wing, and I can see why it looks a puzzle in its own right.

There are two Y-Wings: D1-G1-H2 and D2-H2-G1

The first we know about takes 8 off D2 and H1
But the second one the pincers are made from candidate 6 (not 8) and these remove 6 from D1 and J2. There are no other valid or useful Y-Wings.

Both of them work and they give the same result: D1=8 and D2=6

You may have been thinking the 8s could be used in all four cells, but it’s the 'C' candidate that does the eliminations (see the theory diagram), which is 6 in the second Y-Wing.

As to why the first was highlighted that is down to the search order of the algorithm. It will only return the first successful example of each strategy. I would like to enable the solver to allow you to skip the first and look for the second but it might complicate an already complicated page to allow this.

Tricky position, I had to go through the logic very carefully as well.

Saturday 2-May-2009

... by: Roy, Australia

Really super site Andrew. I have learnt so much from it. Thank you.
Have you considered allowing visitors to input their own shapes in your Jigsaw Solver? This would expand its use considerably. Please do consider it.

Andrew Stuart writes:

Yes I would like to do that. It's not easy to think how, but I'm sure there is a way I could program the page to make that available. Thanks for the prompt.

Monday 6-Apr-2009

... by: C David Allen, England

Load Sudoku:

This was in the London Daily Telegraph of April 2 this year. I couldn't solve it: nor can your solver, claiming an error in the diagram. Yet there is one solution. Your solver seems to think there can be no 7 in H6, which the solution requires. What's afoot?

Andrew Stuart writes:

Hi David

I think you made a mistake on entry - which is odd because the sudoku you record in the feedback is fine. It grades as tough, and solves quickly. Have another go:

Best regards

Andrew Stuart

Sunday 5-Apr-2009

... by: Andy, Germany

Hello Andrew!
today i´ve got an update of my opera browser from v9.63 to v9.64
Now there is a Message in the Box under the Sudoku which shows a link to load the SudokuSapi.dll file.
I found a thread at the opera-forum ( where you kindly find a solution of this problem.
Maybe there is a problem with opera v9.64? I have v9.63 running on my second computer without problems. And i will certainly not upgrade ;o)

After that "bugreport" i have to thank you very much for your great job at this website. Me and my daughter solve Sudokus on her Nintendo DS and after many hours with your excellent stategy documentation, we can solve the puzzles much quicker now :o)

Have a good time!

Andrew Stuart writes:

Thanks for this report. I was on 9.63 and it gives the same problem. Upgraded to 9.64 and no change. I've added the mime type as suggested on the forum but it's having no effect. I'll see what else I can do.

If anyone reading this who is familiar with Windows 2000 and IIS, drop me an email. I'm not getting a result so far.

Friday 20-Mar-2009

... by: pjs, california

thanks for your site--I appreciate the occasional hint(help) needed. I am not in the "big league" but enjoy the challenge of our daily paper.

Thursday 19-Mar-2009


This is easily the best sudoku solver and website for strategy tips that I have ever come across. Your solver is invaluable as a step by step tutorial, making the seemingly impossible clear.


Tuesday 17-Mar-2009

... by: patriotkiller18, usa

is there a way to use coloring when using your solver?

Andrew Stuart writes:

I'm afraid not. Would be nice but it would greatly complicate the user interface. Something for a super-version, maybe a windows program.
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Thank-you everyone for all your questions and contributions.