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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 andrew@str8ts.com.

Post a Comment or Question here...

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

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Comment, question or feedback:

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If you are writing to alert me of a problem (thank-you!) please include a url to the page in question.
Can get fixes in quicker if I know immediately where to go.

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

Thursday 26-Jun-2025

... by: hpweiss, Boston MA

I am hoping for guidance on how to build Alternating Inference Chains efficiently. A straightforward algorithm which just create chains by picking a starting point and appending strong or weak links quickly a myriad of long chains and runs forever.

I notice that the SudokuWiki finds chains very quickly.

Thank you in advance.

Andrew Stuart writes:

Big topic this one. Two ways but you are still searching a 'branching tree'. Depth-first and breadth-first. Depth-first is easiest and it is as you describe. Go through all the points. But you have to cap the depth. I think I use 20. Breadth-first I implemented using Dancing Links which and is superior in speed and better chains and has no cap. But is very memory intensive so it is not the one used on the server. Some people build up a collection of all the links (also required for dancing links) and process that rather than going over the board. However the consensus I've had from conversations is there is no short cut. Since chains are bi-directional you get twice as many as you need but the cost of detecting if a second chain is the reverse of a previous one can be greater than just processing it anyway. Lastly you have to collect and sort the chains into a list based on what rules you think one chain is better than another

My AIC work is still 90% of the cpu run time and would love to optimise. I don’t think it is particularly fast I think the server is fast.

Tuesday 24-Jun-2025

... by: Ron Winkler, California, US

Why was the auto advance option removed from the solver?

Andrew Stuart writes:

Recently some browsers have changed or reset how cookies are processed so a lot of saved settings get dropped. That leads people to think the behaviour of the solver is glitchy they just haven't realised something got unchecked. Having the same issue with auto clear. But I think auto-tab is almost always the default behaviour for number entry on the small board. Opportunity to declutter a bit more. You don't usually have it on?

Sunday 22-Jun-2025

... by: chris, United Kingdom

hi andrew great site keeps me ocupied for hours keep up the excellent good work

Small problem on the Killer solver page small grid showing the cage totals. When hovering over the cage numbers cage variable numbers no longer visible now shows "illegal cage clue and size!" the same for all cage numbers

Hope this makes Scence cheers Chris

URL https://www.sudokuwiki.org/KillerSudoku.aspx

Andrew Stuart writes:

Thanks for spotting that, silly bug from the recent update. Fixed now!

Friday 20-Jun-2025

... by: John, Canada

On the Killer solver the cage window is showing "illegal cage clue and size" for all cages.

Andrew Stuart writes:

Thanks for the alert. Fixed now

Thursday 19-Jun-2025

... by: Tom, France

I seem to be unable to delete unwanted numbers. For example, the 1 in J9 is redundant; the 8 in A5 also. Further, the puzzle appears to be solving itself, incorrectly. Or is it my finger trouble?

Andrew Stuart writes:

Try unchecking “auto clear”. I think that’s it

You’re not the first to ask me about this so there is something not quite right with the user interface. I’m releasing a new version tomorrow so I’m scrapping the auto clear effect on editing the candidates. That should really be just about editing the small board.

Thursday 19-Jun-2025

... by: Helper, CANADA

The Solve Path is not working

Andrew Stuart writes:

Left a typo 's' in the code updating last night,
Fixed now, [CTRL]+[F5]

Thanks for the alert

Thursday 19-Jun-2025

... by: Syd, USA

Hello! big fan of your website! Quick bug report, when getting the solve path on the sudoku solver (https://www.sudokuwiki.org/Sudoku.htm) I can see a console error "Uncaught ReferenceError: s is not defined
at HTMLInputElement.grade_sudoku1 (sud_common4.js?v=2.92:1028)". There appears to be an extra s in the function grade_sudoku1() function on 1028.

removing the s from the javascript in the dev tools fixed it right up for me!

Andrew Stuart writes:

Yes sorry about that. Fixed now, [CTRL]+[F5]
Thanks for the alert

Tuesday 10-Jun-2025

... by: joey, USA

When entering a board (for you to solve) I used to be able to type a number and it would automatically move to the next square, now it does not, I need to press right arrow. Can we go back to the old way?

Andrew Stuart writes:

Yes. Tick "Auto Tab". Recently some browsers have changed or reset how cookies are processed so a lot of saved settings have been dropped. However I can't think of a reason not to have "auto tab" on so the next patch will remove it and make it tab by default.

Thursday 5-Jun-2025

... by: ,

Hi Andrew,
The last update of the app is full of bugs :
Solution count is not working. Returns to the list of puzzles.
Hint button makes the app crash.
So it is unsable any more.

Andrew Stuart writes:

Yes. I pushed another update tonight fixing the remaining crashes so hopefully all stable now. Version 1.88

Friday 30-May-2025

... by: Timko259, USA

I have played with your newer version of sudoku now for about a month. I am not in favor of the change you made to cause me to move the cursor after entering a number. This is unnecessary. I prefer the previous method where the cursor automatically advanced to the next slot after entering a choice. This recent change is tedious and unnecessary. As one who has been using this site for a long time, please consider changing this back.

A very loyal user.

Dale

Andrew Stuart writes:

Referring to the small board number entry on the solver?
Is “Auto tab” ticked? For some reason the browsers have adopted a new policy on cookies and this may have been deleted. I hope it sticks if ticked again.

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Thank-you everyone for all your questions and contributions.