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!

Thursday 2-Aug-2012

... by: Bob, Texas - USA

What happened to the print format that doesn't scatter the numbers throughout the cells?

Andrew Stuart writes:

Get the print popup page open and hit F5 a few times, to bring in the latest styles
Have tested it on Safari, Chrome, Firefox and IE (which was not working properly before)

Monday 30-Jul-2012

... by: Sonalita, England

Purchased your 5 daily puzzles app, loving it but PLEASE PLEASE could we have the ability to highlight all cells containing a certain number (solved cells and cells where the number has been entered as a candidate) like we can with the solver on the website ? This would make it easier to spot things like x-wings or singletons.

Secondly, it would be nice to be able to auto fill candidates, at least for the higher difficulty versions so we can save some time - but that is less important than the first request.

Andrew Stuart writes:

Those are good suggestions, I'll see what I can do (without confusing the interface too much). Thanks for the feedback!

Friday 27-Jul-2012

... by: Paul, Northern Ireland

Would it be possible to add a print option so that your Sudoku is printed in a smaller size similar to those found in newspapers, say 7.5 cm square?

Andrew Stuart writes:

Good idea. Just implemented it on the printable popups. Refresh the page if it doesn’t come in immediately

Saturday 21-Jul-2012

... by: Dale Kloss, Portland, Oregon, USA

I've read the article about the minimum number of clues being 17 for the original Sudoku but has anyone ever found a minimum for Jigsaw Sudoku ? I realize this may be shape dependent.

Thanks for all the work on the site ? Dale

Andrew Stuart writes:

Yes, I think there has been an attempt at a minimum Jigsaw and I published one in my book. It contains 8 clues astonishingly. You can't have a 7 clue jigsaw because that would means two numbers could be swapped creating a duplicate solution, so 8 is the minimum. Have a look at

Wednesday 18-Jul-2012

... by: Salome, Cape Town SA

Hi Andrew, Ilove our sodukos, but think there is some problem today? First time in 2 years I've visited your page!
I actually started Pinterest recently - would like to pin you there but won't today, in case something first needs to be fixed.

Andrew Stuart writes:

Nice to have you back again. Just getting over the minor bumps of a new release. Solvers should be working very well from this point. Let me know if you see anything specifically wrong (and the page) and I'll nail it. Pinterest is a fun site but I haven't signed up myself yet

Tuesday 17-Jul-2012

... by: Alain, France

thre are some bugs in the version 1.86 of the sudoku solver.
no display in the results box.
the "weekly unsolvable #64 makes the solver entering in an infinite loop when using AIC method. it looks like the value to be removed is not.

Andrew Stuart writes:

Yes, last night's release - it still had some debugging code which stopped the deleted candidates from being reported. Fixed now.
Thanks for the alert.

Friday 13-Jul-2012

... by: lamons, california

Thank you for your marvelous and mystifying web site. My wife is a serious sudoku fan and only challenges the hardest puzzles published once a week in the local paper (SJ Mercury). She got stuck back about three months ago and your solution did the trick. I cannot thank you enough, much better than psycotherapy.

Andrew Stuart writes:


Monday 2-Jul-2012

... by: Dale Kloss, Po rtland, OR,USA

Trying to run the JIGSAW Solver....Repeatable error: shape= Andrew Stuart 28 . Puzzle= Example 4. For this puzzle I get contradicting results in a row and in a column. Get cells B8 & B9 ,both 1. Cells E5 & H5 both 1.

Andrew Stuart writes:

Ok I figured this out. The fourth (extreme) example in the last list of shapes (Andrew Stuart 28) was actually a puzzle for the previous shape (27). I've swapped in a puzzle that works for the last position. Must have been a copy/paste thing

Thanks for the detailed error report, most appreciated

(might need to hit F5 a few times to pull in the latest)

Saturday 30-Jun-2012

... by: tim, usa

Can/would you explain in general the fast brute-force algorithm to check for all possible solutions when the Solution Count button is used? I am going to send you a puzzle that has a solution but, the solver could not solve. I am not sure how to do that so bear with me.

Andrew Stuart writes:

The brute force algorithm uses a super-fast method of testing every possible number in every possible position (with some tricks to make that test shorter than a year :). No one would describe this as a 'logical strategy' even if it is fundamentally deterministic. It gives solutions but without saying why.

The solver uses pattern based logical strategies and we don't know all of those yet. The problem is candidate density. If you look at my solver when it comes to 'Run out of known strategies' you will see most cells contain 3 or more candidates. Most of the advanced strategies and all the chaining ones require bi-value (2 in one cell) or bi-location (2 in one unit) to get anywhere.

Saturday 30-Jun-2012

... by: David, UK

Load Sudoku:

Hi, you expressed an interest to study valid examples that can't be solved on this page? Well, there is an example featured on the Daily Mail's website: which requires your brute force algorithm.

Andrew Stuart writes:

Hi David - and everyone else who has written about this puzzle. Thanks for the alerts. Worthy of a whole article, so you might be interested:
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Thank-you everyone for all your questions and contributions.