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 28-Dec-2014

... by: Annick, UK

I have just used your Killer Solver to get step by step help to solve a puzzle I was completely stumped on. Your website and Solver solutions are amazing and awesome!!! Huge, huge thanks for your help. There are so many of these Killer and Sudoku that drive me batty trying to puzzle them out, and sometimes the explanation of the logic of solving puzzles on other sites are more confusing than the puzzle itself. So thank you for this site, now I've found it I know I'll be back frequently. :)

Andrew Stuart writes:
Awesome, glad you enjoyed!

Saturday 27-Dec-2014

... by: Kim, Africa

Load Sudoku:

rating on this puzzles was 'diabolical' with hard to understand logic (for me). However, I solved it easily with following logic: F4, F6, & G4 contain 3,6,& 9 therefore can remove 9 from D4. It is like an xyz wing but wings are identical. Is this a labeled strategy?

Andrew Stuart writes:
Not sure that's lucky rather than true. It could also be D4=9, F4=6, G4=3 and F6=3, which fits. Its only later that it proves wrong.

Tuesday 16-Dec-2014

... by: RVtom, USA

Looks like the Jigsaw Shape List pattern numbering is "off by one". The first pattern in the Jigsaw Solver drop down list ("Andrew Stewart 1") matches the second pattern ("Andrew Stuart 2") in the Shape List page, and so on.

Andrew Stuart writes:
Doh! Fixed, thanks!

Monday 8-Dec-2014

... by: RVtom, USA - fulltimer

I enjoy the Jigsaw puzzles the most (so far). Occasionally I like to reenter an older (>30 days old) daily puzzle that is no longer listed. It is tedious to run through the drop down menu to try and find the right "shape". It would be helpful to have either a printed "shape code" associated with each daily puzzle or a separate web page depicting the "shape" associated with each shape name.

Maybe I'm overlooking something you've already provided elsewhere. Thanks for providing this set of web pages!

Andrew Stuart writes:
Good idea, something I've meant to do for a long time. Here it is:

Also links on Jigsaw Solver

All the best

Monday 8-Dec-2014

... by: John, San Bernardino, California

Enjoy playing your 'Daily Sudoku' and 'Jigsaw Sudoku'.
The last few days the 'Jigsaw Sudoku' does not display properly. The Sudoku screen appears, but without numbers or the jigsaw format.

Error message - "can't find sudo".

I updated the Java program but this did not solve the problem.


Andrew Stuart writes:
Yes, I'm working on some new puzzles now. I had my deadline alert set for the end of the month, not so soon!

Saturday 6-Dec-2014

... by: Sharp48, USA

Andrew, I got hooked on Sudoku while I was confined for few weeks few years earlier. My wife presented me with your book " Logic of Sudoku". Fantastic instructions. I understand the entire logic but it is difficult to visualize the patterns that need to be seen. I agree with you that the AIC probably is the Super Theory of Sudoku and I am trying to practice. Thanks for your good work. Best way to preserve Gray matter. Is there a specific forum to help for somewhat of an intermediate level Sudoku player?

Andrew Stuart writes:
Great to hear you are enjoying the game and the site

Longevity is a problem with websites, I'm coming up to ten years, which is unusal. There were several large forums back in the day but they ceased for one reason or another. Of the best that remain, I'd try

Monday 1-Dec-2014

... by: Mike, Florida

Good system.

Friday 28-Nov-2014

... by: Paul McIlfatrick, Northern Ireland


I have your Android App for some time now but the latest version 1.69 engine v2.01a sw360 which became available some days ago crashes each time a new puzzle is entered.

The previous version of the App never crashed on me.

A suggestion for the Android App when entering a new puzzle, please allow the entry of clues and also of solutions as is possible on your Windows PC webpage.


Paul McIlfatrick

Andrew Stuart writes:
Had a number of reports like that. Going to test again and release a new version asap. Not sure why it does yet but I'll find out

You’d like a distinction between solved and clues on the new puzzle entry? Probably do that

Thanks for the alert!

Monday 27-Oct-2014

... by: Uhm, Netherlands

Load Sudoku:

Here is an picture of Simple Sudoku were i painted the ape your solver did not find.
The blue cells are the pair from ape. combination 6,3 cannot be possible because of the purple colored cell. Combination 6,9 cannot be possible because of the triple colored in orange. So 6 can be excluded from the first blue cell.
This picture is taken right after the first found ape.

About the finned x-wing and grouped x-cycles: finned x-wing stands on place 23 where as you grouped x-cycles stand on place 21, so grouped x-cyles gets executed first so finned x-wings will never get found i think.

Outlook does not want me to send emails, so here again.

Andrew Stuart writes:
I found a rule in my code that says ignore any two cells (your blue cells/my grey cells) which are both bi-value. I have no idea why it was in there, unless I was thinking it was a short cut. But I removed it and found your example. I'm just running some long tests, now, to see what the impact is and if it creates a false positive anywhere.

OK the second APE is now showing up in the solver. I detect about 500 more APEs in my test library of 50,000 puzzles (total APE found is around 25,962) so it’s a small but decent increase but there's a 20% increase in time spent looking for APE, but not significant compared to some strats.

Good to be complete (or more complete)

I'll look at the finned x-wings next

Uhm can change your reactions

Wednesday 22-Oct-2014

... by: Uhm, Netherlands

Load Sudoku:

You solver does not find the second Aligned Pair Exclusion on J56.
This is in the examle of AIC weak link.

And am i right that there is an overlap between finned x-wing and grouped x-cycles, maybe its better to place the finned x-wing above grouped x-cycles.

Andrew Stuart writes:
Hi Uhm,
Can you provide a screen shot of the second APE? Or a scan? Like to see the full pattern.
There is an overlap, but the solver has very different algorithms for both strategies and I've not investigated the exactness of the overlap. But finned x-wing are above grouped x-cycles in the order, no?
Do leave an email address next time
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2015 2014 :1 2 3 4 5 6 7 :2013 2012 2011 2010 2009 2008 2007 2006
Thank-you everyone for all your questions and contributions.