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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. 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 .

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

Tuesday 10-Nov-2015

... by: Dave G, Uk

I enjoy the daily sudoku puzzles which are wonderful value but I find the number of times extreme strategies are required to solve tough rated puzzles very frustrating. However keep up the good work - I would rather be frustrated than not have the puzzles.
Beat regards

Andrew Stuart writes (12-Nov-2015):

Good point. I've just been working on calibrating grades for the new Windoku puzzles, so I've taken a look at the 'tough' puzzles in the Daily Sudoku list. I can indeed see about 15% which are using extremes and about 5% which are too 'boring' in having very little strategy stuff at all. There is a warning flag for both these possibilities so I've used that again on the tough set to replace the ones with the warnings with new ones that don’t. So overall I think that grade will have less outliers it in now.

Wednesday 4-Nov-2015

... by: fbax, Canada


Killer Hard Combinations
KILLER COMBO (Hard) on cage starting on A2: cage of size 3 with clue of 13+ can only be 1/2/3/4/5/6/7/8/9
- we can remove 9 from B2

Andrew Stuart writes (5-Nov-2015):

OK this works out this way: The 1/2/3/4/5/6/7/8/9 is built up of all the combinations that make 13 with three cells. That is literally true. Hover your mouse over the cage in the small cell. But there is only one combination that includes 9 - {1,3,9}. There is only one cell with a 9 available - B2, so 1 and 3 must go in A2 and A3. But there is no 3 available in any cell, so this combination isn't available, hence 9 can be removed from B2.

I can see the virtue of expanding the result explanation to explain this, tricky to generalise

Tuesday 3-Nov-2015

... by: John, Wisconsin, USA

Hi Andrew,
I really like your website and book--well done!
My brother and I do Sudoku remotely, and often compare our solutions to yours. Recently my brother got the edge on me when he discovered W-wing, which I'm pretty fuzzy on. I didn't see it anywhere on your site--am I missing something?

Andrew Stuart writes (4-Nov-2015):

W-Wings are encoded in the solver as an experiment/investigation into a larger family of wings. But I've found they duplicate other strategies and I've decided not to release them. Their adherents claim these are all unique patterns worth looking for but I think they are formations of a more general wing-type and don’t need to be broken up into these family types. I'll try and get a page up at least of w-wings. Google might have some example on various forums in the meantime.

Did this W-Wing appear in the solver?

Thursday 22-Oct-2015

... by: Brian, US

Just want to tell you that the Sudoku Solver is a gorgeous piece of work. Thanks!

Andrew Stuart writes (25-Oct-2015):

Thanks Brian!

Saturday 29-Aug-2015

... by: Bob Lester, USA

Any plans for a kakuro solver?

Andrew Stuart writes (29-Aug-2015):

Kakuro is a nice puzzle, one do make them and have an offline solver, in that sense. But there's not many different strategies to it, it's pretty much combination elimination all the way. I've thought about it but I'd like to get more newspapers taking the puzzle before I put the time into it. Happy to be pointed at examples that are interesting though. Also, Kakuro can come in any size and shape making it very awkward to design a solver interface.

Thursday 27-Aug-2015

... by: Kasmar45, Southern Calif. USA

Hi Andrew,

I am so confused. I am a beginner at solving Sudoku puzzles. The two instructors I have been learning from are The Sudoku Professor and the Sudoku Guy. Both of these people advise against notating all the possible numbers that could go into a cell. Now, I come to your site for some extra pattern solutions and what do I see. All the numbers noted in each cell. ??? So, who is right the people I have been learning from or your method? Both of the people I have been learning from say, if you have more than 3 numbers noted in a cell, then you have too many ?

A confused Sudoku solver.
George Jorgensen

Andrew Stuart writes (29-Aug-2015):

I know what you mean. On my site I have deliberately concentrated on the logical steps that can be applied to any puzzle. The only thing we have to work with to make progress are the candidates in unsolved cells. Apart from Avoidable Rectangles strategy the solved cells provide no help whatsoever - provided you have cleared off candidates. There is a place for intuition and many people can bust through a bottleneck with an insightful guess and just a scattering of 'noted' candidates. But I was interested in the pure logic of Sudoku and that requires a full spread of all candidates. I know a lot of people use the solver to print out the board with candidates cleared off from the initial state. Then it's a process of elimination in each cell until one candidate is left. This saves you the bother of making the notes at the start, crossing them out is easy and you can use all the strategies you want, as listed on the site. Then when you feel confident about the patterns you might spot them with just notes added rather than subtracted. But everyone has a personal approach.

Note, most of the 'extreme' strategies, while logically correct, involve very complex patterns that really most people are not expected to use on a daily basis. I collect them because in some very special Sudoku puzzles they really are the only way to make process. Sudoku can be very deep.

Monday 10-Aug-2015

... by: Peter Carpenter, Monmouth UK

Dear Andrew,
I am a devotee of Killer Sudoku and your superb website. I enter puzzles each week and print them out - one for me and one for a friend. (We're both aged and need the larger size for our copious notes!)
I would love to use the "print in colour" facility but I can't make it work. My printer prints colour fine as a rule but not from your screen which nevertheless displays beautifully tinted on my monitor. Is it me - or is it it ??
With best regards and many heaps of congratulations for being such an enormous help.

Andrew Stuart writes (11-Aug-2015):

You need to tick a box in your print options to "print background colors and images". It varies from browser to browser, some advice here applies:

Very glad you like the puzzles

Saturday 8-Aug-2015

... by: john d traka, wisconsin

greetings from the land of deer flies and cheap liquor. is there any sort of strategy for solving a puzzle that involves addition? since 1+2+3+...+9=45, is there any sort of useful inference that can be drawn from that?

Andrew Stuart writes (11-Aug-2015):

Not in Sudoku since the numbers are merely placeholders, they could be letters or types of fruit. But addition is used in Killer Sudoku
a lot and also in kenKen and Kendoku, eg
(also Rule of 45 for 9x9 puzzles)

Thursday 30-Jul-2015

... by: Zack, Singapore

Hello. This is a hyper sudoku. I've spent 2 hours and I only found 2. It seems like this site doesn't solve hyper sudoku so I'm here for help.

Hyper sudoku means that there are 4 extra region of 3x3 inside the 9x9. The first 3x3 region starts from the 2nd row 2nd column. The 2nd 3x3 starts from the 2nd row 6th column. The 3rd 3x3 starts from the 6th row 2nd column. And the last 3x3 starts from the 6th row 6th column.

Andrew Stuart writes (12-Nov-2015):

On vacation at the moment. But I am working on a solver/generator for this variant of puzzle. I believe it is also call Windoku, my preferred name.
Will post on the site when it's available
And no, the normal solver wont cut it

Edit: Nov 2015 - windoku now released!

Friday 24-Jul-2015

... by: Nox, France

Dear Andrew,

Thank you for this free mine of knowledge. This website is absolutely perfect for casual sudoku players who want to learn more about it.

Salutations from France,

Andrew Stuart writes (26-Jul-2015):

Thanks. BTW, you send a private message but no email address. Can't answer those!
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