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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 .

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

Saturday 11-Nov-2006

... by: Richard Broughton, UK

Load Sudoku:


found this gem that my solver gives up on - and unfortunately so does yours (although your solver gets one further candidate reduction than mine)

Brute force will solve it - and your solution count indicates that there's only one solution.

I'd be interested to see if there is any strategy that can be applied to bring a logical conclusion to this problem

Wednesday 8-Nov-2006

... by: JC Meyrignac, France

Load Sudoku:

AI Etana ( ) cannot be solved by your solver.
Any idea how to solve it ?

Saturday 4-Nov-2006

... by: Cargill, Czech Rep.

Load Sudoku:

This is partly solved sudoku, that crashes X-Wing strategy and doesn't get solved by the solver (had to disable X-Wing to proceed further).
However it has only one solution.

Andrew Stuart writes (6-Nov-2006):

Hi Cargill. It was slow but didn't hang for me. I've restarted IIS and it seems to be a bit faster now.

Friday 3-Nov-2006

... by: Pompeo M. ACQUESTA, Italy

Load Sudoku:

Many Thanks for your beautiful sudoku solver and your explanations: It help me day by day.
I dont understand why in this sudoku

HIDDEN UNIQUE RECTANGLE removing 9 at J7 because of GJ17 and two strong links on 3

Thanks very much



Andrew Stuart writes (6-Nov-2006):

ok, well the short answer is

If any four cells contain a pair X/Y and three contain additional candidates, then one of X or Y can be eliminated from the cell diagonally opposite the bi-value cell if the other candidate in the pair forms two strong links along the row and column.

But I really need to expand and supply examples. It is in the forthcoming book, however!

Wednesday 1-Nov-2006

... by: bente, My

Hi Andrew,

Your solver is a fantastic trainer - actually! A great bulk of the hard-to-understand theories and technique are clearly demonstrated and explained by your solver. Yours is the best so far. It certainly helps me to progress tremendously. Thanks.


Andrew Stuart writes (6-Nov-2006):

Thanks Bente!

General message for posters here: sorry I've not been around to respond last two weeks. Lots of good questions here. It will happen!

Andrew Stuart

Tuesday 31-Oct-2006

... by: Randy, Portland, Oregon USA

Absolutely love the Solver. Thank you. Could you work on a Sudoko Monster Solver? I would love to do them if I could print out the candidates; otherwise, it's way too time consuming just to set up to solve.
Please consider and thank you again.

Andrew Stuart writes (6-Nov-2006):

Hi Randy, yes if by Monster you mean 16x16. I have a prototype, one with only the basic strategies. In the job queue to put on the site.

Sunday 29-Oct-2006

... by: Territan, Glen Burnie, MD

Load Sudoku:

This is a computer-generated sudoku, partially solved by your solver. I'm posting a partially solved one because shortly after this point, the solver goes up to #15 (twice; the first time is very straightforward) and performs a test that seems to go far beyond anything that's shown in the documentation. Hidden unique rectangle? Two strong links? Shto?

Could this be the example of the type 3 unique rectangle that you've been looking for? Or did the solver just do something really unaccountably weird?

Andrew Stuart writes (6-Nov-2006):

Hi Territan, I've found out what the Type 3 Unique Rectangle is and will be adding it soon. See above for the Hidden Unique Rectangle

Saturday 28-Oct-2006

... by: raleigh, USA

Love the sudoku solver. Its fast, easy to use, has great tips and explanations, and its MUCH more powerful than my previous favorite site!

Andrew Stuart writes (6-Nov-2006):


Wednesday 25-Oct-2006

... by: Ray, Rancho Cordova, CA, USA

Load Sudoku:

I derived this puzzle by entering numbers at random until I had a puzzle that tested to have only 1 solution. I then solved it and was surprized at the difficulty of it. I used nothing more sophisticated than a couple of hidden/naked pairs in my solution. Then I let Sudoku Solver do it and was surprized at the apparent difficulty level and the sophisticated tools used. It did not use any of the hidden pairs that I used in my solution.
I'm new to sudoku and I am very impressed with your solver.
I have difficulty identifying hidden pairs when I see 3 or 4 sets of the pair values I want to use. How do you know which ones are bogus??

Andrew Stuart writes (6-Nov-2006):

Hi Rancho

Well done. You made what I'd grade as a Tough sudoku. Excellent!

Sunday 22-Oct-2006

... by: Leonard Trochez, Gretna, La

Thanks for this builder. It's the best I've come across.

My question is : how do I print the Printable version?
I don't see a Print switch.


Andrew Stuart writes (6-Nov-2006):

Hi Leonard

Sorry for taking so long to reply. If you don't have a printer icon on your browser menu then [CTRL]+[p] will do the job

Thursday 19-Oct-2006

... by: Sami, Lebanon

If I do step by step for the example "Riddle of Sho" it doesn't arrive at the final solution!

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