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Strategies for Number Puzzles of all kinds
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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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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 5-Feb-2011

... by: Bill Harrison, Virginia, USA

Hello Andrew,

I want to express my appreciation for your outstanding website that makes it possible for me to analyze and modify my Sudoku solutions. I attacked (and solved) my first Sudoku puzzle in the Richmond, Virginia, newspaper at Christmas time in 2009; so you see, I am a quite recent entrant into this particular puzzle genre.

Having gotten hooked, I solved the daily Sudokus until around the middle of last year. As a programmer I began to think that creating the puzzles themselves would prove more challenging than simply solving someone elses'.

My computer printed out my first successful 81-digit Sudoku last July. However, creating a 30-or-so digits puzzle by randomly knocking out 50-or-so digits from my Sudokus has turned out to be rather frustrating. It was too easy to generate a redundant (i.e. non-unique) puzzle. But your Sudoku Solver has helped me immeasurably!

Entering my trial puzzles into your solver, I can judge their levels of difficulty by how many of your 35 strategies are needed to solve them. Also, it is relatively easy to see the puzzle combinations that cause trouble (and redundancy) by stepping through your strategies and then tweaking the puzzle distributions slightly to "fix" any difficulties.

Again, thanks so very much for your splendid site!

Best regards,
Bill Harrison

Andrew Stuart writes (18-Feb-2011):

Many thanks for writing in, appreciate your comments and compliments. Glad you're having fun making puzzles, its a very interesting area

Best of luck

Saturday 22-Jan-2011

... by: Ward, USA

Please turn off the auto-tabbing when entering numbers in the small grid. Very confusing and tough to negotiate now.

Andrew Stuart writes (23-Jan-2011):

I've had so many requests to put auto-tabbing in over the years ... :)
I've added an check box to the new version.
Don't forget the arrow keys now work and help you move around the grid

Friday 21-Jan-2011

... by: Bill Volz, USA Midwest

Key strokes for loading a new Sudoku have changed. The worst is the total loss of entries if the tab key is pressed to leave the last square empty.
Entering a number now also advances the active square making it harder to correct an error using the delete followed by the correct entry.
Please restore the old system.

Andrew Stuart writes (23-Jan-2011):

There was a bug, which I've fixed this morning. If you tabbed the last cell you went to the example picker which activated the example puzzle. Shouldn't do that now. I've also added tick box to activte/turn off auto tabbing.

You might need to refresh the pages to pick up the new version.

Thursday 6-Jan-2011

... by: Marvin Shapiro, Maryland, US

Load Sudoku:


Thanks so much for your sudoku website!

I wrote my own sudoku solving program (in Java) and, to check it out,
used the 50 hardest puzzles from a Will Shortz book.
Since my rules were sufficient to solve them all, I figured I was done.
I also figured that the chaining rules I had read about--and had NOT programmed--just
never really occurred. Wrong!

On vacation (I never do sudoku at home) I ran into an "expert" puzzle
and got as far as follows:
where I was stuck. When I got home I found that my program was stuck there, too.

So I DO have to look for chaining, which I don't think should be too difficult.

BTW, I like your way of saving the puzzle as a cookie. I hadn't thought of that.


Marvin Shapiro

Andrew Stuart writes (7-Jan-2011):

Hi Marvin

Glad you found it useful. Email me if you want a bigger stock of very hard test Sudoku puzzles
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