Solver App for Android
Strategies for Popular Number Puzzles
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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 .

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

Saturday 10-Mar-2007

... by: Wal, Switzerland

Hallo Andrew, you saved may day - once again! Thank you very much. Brgds ... Wal

Friday 2-Mar-2007

... by: lynn893, Canada

Hello! I have actually just found jigsaw sudoku puzzles and I find them absolutely fasinating!

I was working on the Daily Jigsaw sudoku competition for March 2, number 482, tough. After doing all I could by myself, I opened your solver to see if it could help me by showing me the candidates.

The next step (from where I was) showed me to place a '1' in r4c1. This does not make any sense to me at all, as there are many other 1's in row 1 and column 4. Is there any way to explain this step?

Candidates I have for 1 are:
R1 - c4, c5, c6, c9.
C4 at r1, r2, r4, r5, r6, r7, r9.

So, I don't understand how your solver came up with a 1 in R1C4.

Thanks for any light yu can shed on this for me! It really is greatly appreciated!

Andrew Stuart writes:
Lynn, the 1 is single in the upper left hand corner box.

Tuesday 27-Feb-2007

... by: aww, usa

Thanks, the solver is great. Very helpful and informative.

Saturday 24-Feb-2007

... by: Irish_guitar, Maryland USA

I find your site to be the most fabulous Sudoko site on the internet. Congratulations on a terrific site

Thursday 22-Feb-2007

... by: phil rock, new york

this is a wonderful website. what an effort!! superb learning tool for me. i've been looking a long time for a site like this. gave up sudoku for a while out of frustration and then found this. with a good puzzle book - it is a lot of fun.

thanks so much,


Wednesday 21-Feb-2007

... by: Mike Parker, Germany

Fantastic solver, but is it possible to put a breakpoint on a particular technique (i.e., ask the solver to run to the first/next instance of a particular solving technique, if any)? This would be great for those people wanting to train a specific technique, without having to painstakingly single step through the puzzle (only to find that the technique is not used in that puzzle anyway!).
If it's not possible right now, is such a feature on the "to do" list for the future?

Friday 16-Feb-2007

... by: Scott B, Salt Lake City, Utah

Just wanted to say thank you for this website, truly amazing!!

Friday 16-Feb-2007

... by: Mogulmeister, UK

Load Sudoku:


The above 23 square sudoku does have one solution but seems impervious to all attacks - including your great solver. Any other strategies possible ? This is probably the toughest one I have ever encountered.

Andrew Stuart writes:
Hi Mogulmeister, yes a very interesting sudoku. There is still a great deal to learn from these types of sudokus. The ones, such as these, that cant be solved by my solver has a certain characteristic - very few bi-value cells. Most cells in this, after all the strategies have been used, contain three or more possibles. Being able to descern a logical deduction with so many candidates left is the front line at the moment. Thanks for sharing it.

Saturday 10-Feb-2007

... by: Ruth, Gaithersburg, MD

Why are the same puzzles coming up each time I log onto your website? How can I get a different puzzle in the "Easiest", or Gentle, etc.?

Andrew Stuart writes:
These are demonstration puzzles only. Examples to show the workings of the solver. Up to you to enter a puzzle you are stuck on. If you'd like to see a daily puzzle I do then have a look at

Thursday 1-Feb-2007

... by: Richard Proctor, Utah

I've been watching for the book "Logic of Sudoku." Is there an update for it's release?

Andrew Stuart writes:
Yes, today I have completed a pre-ordering form and payment system, please have a look at AT THIS PAGE. Within two weeks we'll do a special mailing to everyone whos been so patient, submitted their address and so on, and they'll get it before it hits amazon and the book distributors. Cover looks great!
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Thank-you everyone for all your questions and contributions.