Solver App for Android and iPhone
Strategies for Number Puzzles of all kinds
Latest Apps
Page:2014 :1 2 3 4 5 6 :2013 2012 2011 2010 2009 2008 2007 2006

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. Please feel free to drop me a note on the side of the page or try the Facebook comment box. Or you can email me directly at .

Post a Comment or Question here...
Your Name or 'Handle'

Part of the World you're from

Email Address (optional) so I can reply directly if necessary (it will not be displayed here)

Any Sudoku you want to publish here for easy loading into the solver - 81 characters, use '.' or '0' for unknowns.

public - comment/question will be added to feedback column
private - email comment/question directly to Andrew Stuart, don't display here

Comment, question or feedback:

Enter these letters
Please enter the
letters you see:
Many thanks to all the people who have helped improve the solvers and strategies with their feedback!

Wednesday 20-Aug-2014

... by: Didi, Austria

Most fascinating thing about Sudoku is the big variety of logics to solve those riddles. At the moment we all depend on some genious humans, who find these logical algorithms.
Is that true? Do you know any artificial intelligence approaches to let computers detect known and unknown solving logics?
It would be great to have an AI developed, that could at least find the most basic solving techniques! I believe that without such basic AI real Androids will never ever exist. Sudoku could be a nice starting project.

Andrew Stuart writes (23-Aug-2014):

An interesting question. Yes, all the strategies have come from discussions on forums (some now defunct) and from people suggesting improvements. Where known, I've tried to credit people. I'm not a mathematician but I know how maths minds work - the level of abstract thought that goes into working on algorithms I like to think approaches what mathematicians feel when they explore equations in their heads, but I'm not in their league. From my own study of AI systems - and I've knocked up a few models - genetic and neural network types - is that there is an "intuition barrier". Most maths people have intuition which allows them to step over a difficult problem and get insight intuitively, and then they back-fill it with logic and proof. It's actually quite hard to deduce a new or interesting proposition merely from deduction. Even choosing the direction in which to work involving a process no software can duplicate.

I do believe there will be artificial intelligences that will be equal and superior to human minds but they will be evolved, not written, and they will exhibit the intuitive trait required to solve these types of problems. But if we asked them to explain how they did it, or dumped their "software" it would be as complex and useless to us as a physical brain dump.

However, there may well be some clever people out there who do work on algorithms that create algorithms. Some of these are tricks though, like slime moulds solving the Travelling Salesman problem.

Tuesday 19-Aug-2014

... by: bruce, U.S. of A.

I love your site. It's taught me alot and I use your solver to do the daily puzzles. I like to play the game and not fill in the possibles (I always screw them up!), so I use it for that. Maybe I'm doing something wrong, but when I enter a number into the little grid, after having removed some possibilities from the large grid with say a pointed pair, the numbers removed end up back in the large grid. I'm using Chrome, showing the possibles, auto-clear is on, and allow editing is on. Any ideas? Thanks.

Andrew Stuart writes (19-Aug-2014):

Very glad you like the site. The two boards are not quite mirrors of each other. The small one is meant for easy input and it can prepare the board with auto clear. But the big board should be used for editing if you are using "take step". That is the current state of the board since it contains the candidates. Editing the big board pushes solved numbers up to the small board. I suppose I could have done it all with one board but that’s the way I initially developed and its been the structure ever since. Use the " Candidates can be () edited"

Tuesday 19-Aug-2014

... by: NiZhiyang, China

I think the Sudoku X unsolvable example is TOO EASY!Let me give you a hard unsolvable example.
See,this is harder than yours!

Andrew Stuart writes (19-Aug-2014):

That is harder, but I wasn't really trying. Here are some equivalent, I hope. Load in the Sudoku X Solver.


Do leave an email address next time!

Thursday 14-Aug-2014

... by: john, us

Why is the Sudoku board now so small and I can't zoom it?

Andrew Stuart writes (19-Aug-2014):

Did you perhaps "zoom" the browser? To reset, for example, in Firefox, it's here:
Zoom reset

Wednesday 13-Aug-2014

... by: Larry Doe, Hyde Park, NY

Load Sudoku:

Today's daily sudoku puzzle reduces to this: ..5.2.4...
Solution count says 1 solution but it actually has two solutions.

Andrew Stuart writes (19-Aug-2014):

Probably a bit late now, bit I'd love to see both solutions. I can detect if there has been a mistake, but I do promise you, in nine years, I've never made a double solution puzzle! ; )

Wednesday 13-Aug-2014

... by: Claude, Europe

I cannot find your app in the store, correct ?

Thanks for your answer

Andrew Stuart writes (23-Aug-2014):

Yes, one of our annual Apple agreements expired. I'm trying to understand the Apple process to get this sorted, not very easy.
Hopefully all apps will be back up either later today or next week if I have to wire money.

Wednesday 13-Aug-2014

... by: Mina, X

Excelent! Work, thank you !

Andrew Stuart writes (19-Aug-2014):


Sunday 10-Aug-2014

... by: Sundeep, India

Hi Andrew,
Thanks to this wonderful site, I am learning more tricks.
One small modification I would suggest (as I made that mistake) - could you make the link in (See Strategy Overview documentation) below the solver open in new tab/window by default? Or some other workaround - my issue was that manual edits (possible numbers inside unfilled squares) disappeared when I accidentally clicked the link and came back to the page.

Andrew Stuart writes (10-Aug-2014):

Hi, thanks for the idea. The right side strategies already open a new page, and the puzzle board should save itself (as a cookie) if you accidentally close or move away. Might not catch every last change, depends. I've added a new target page/tab for those other links to the strategy overview though.

Wednesday 6-Aug-2014

... by: 35436363, europe

Load Sudoku:

I want to have a Kakuro Solver. The Str8ts Solver says always: Oops - you got an error on the board (0)

Andrew Stuart writes (10-Aug-2014):

Yes, I'd like to add a Kakuro solver. I have the generator, which is half the job. All depends on getting time ; )
Kakuro won't work in any of the other solvers...

Tuesday 5-Aug-2014

... by: pat field, wisconsin

Dear Andrew,

Love your site. But recently I have been having problems when I access it on Chrome (no problems on Internet Explorer, same computer).

Problems: cannot activate Auto Clear

Delay in entering data from left screen to main screen: it takes one more keystroke for the (last) entry to show up. I am also experiencing a one keystroke delay as I type this complaint (which is disconcerting).

I'm a big fan, nevertheless.


Andrew Stuart writes (10-Aug-2014):

That's very strange behaviour. It does sound like a chrome-client side thing. No having any problems on my chrome, nor have I added anything recently that should effect it. Difficult to say. Tried clearing your cache?

Tuesday 5-Aug-2014

... by: TimCinOR, Oregon

Great site!

Especially thanks for the stepper, and the explanations of the strategies. I've got a puzzle that has some strategies for me to learn.


Page:2014 :1 2 3 4 5 6 :2013 2012 2011 2010 2009 2008 2007 2006