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!

Wednesday 12-Dec-2007

... by: Luis, Quezon City, Philippines

Hi Andrew,

I've undertaken my own programming project to create a sudoku solver ever since I was exposed to it this year. I recently came across your site and it's been a great resource. I have a question with regards to naked pairs/triples/quads. There is no mention of naked quid(?)s (group of 5s) and above. Does this mean that this strategy isn't valid or that there are no instances where this setup will happen? I admit I'm not much of a sudoku solver so I had to ask. Thanks for your time.


Andrew Stuart writes:
Any Naked Quin would have a compliment of a Naked Quad next to it in the same unit (assuming there were still nine unsolved cells). So there is no point searching for it as the Quad will be identified first.

Monday 10-Dec-2007

... by: Leon Heckman, United States Boston MA

Load Sudoku:


Lately, I have become interested in Sudoku because it is printed in the local paper and I try to solve the puzzles on my train ride to work. I can solve many of the puzzles but I get stumped on many as well. So, I found your excellent website to improve my skills. I also bought your book and I am wait for its arrival.

Now my question:
I found a website that generates Sudoku puzzles that can be printed. I selected a moderate puzzle since I am trying to learn the process. I printed from this site.

After working on a solution for many hours, I gave up and entered the puzzle into your application. Your application cannot find a solution either.

I don't understand. Maybe you can help me.

Leon Heckman

Andrew Stuart writes:
Hi Leon

You are the victim of an unscupulous sudoku web site. Use the link in this posting to reload the so called moderate 17 from that web site. Press the "Solution Count" button. You will see it has 51 solutions. These people don't know how to make sudoku puzzles. Logical strategies only work if there is only one solution. is probably just an advertising revenue web site. Certainly looks crowded with ads. Yuck. If you want some real puzzles go to

Wednesday 5-Dec-2007

... by: PaulWay, Canberra, Australia

Load Sudoku:

I've been using a wonderful little Java applet on my phone called M-Sudoku to do Sudokus when I've been waiting for buses, etc. I came across this one recently, and apart from the 4 in C4 I was unable to get much further with my standard techniques, especially without any way to make temporary notations. I ran this through your excellent Sudoku solver, which has been invaluable in the past for letting me see the logic behind solving some of the more tricky Sudokus I've worked on. It came up with the 9s in C8 and G9, and then got to the 'advanced strategies' section. It said "Wait" and nothing further happened, though I waited for an hour or more.

I assume you're using AJAX to send the problem to a server which can perform the more detailed analysis and send back the next step. Maybe there's some timeout there, or the process got killed because it took too long?

What I'd dearly love to know is how the M-Sudoku app came up with such a fiendish puzzle!

Have fun,


Andrew Stuart writes:
Hi. Yes the backend had some stability issues. Sorted out now I hope

Friday 30-Nov-2007

... by: vidya, indonesia

Load Sudoku:

i couldn't solve this sudoku... can u help me pleasee....
thanks before...

Andrew Stuart writes:
Solves fine now!

Thursday 29-Nov-2007

... by: David Woodard, UK

Thank you for your wonderful solver! It always works when my own simple methods fail.

Just one little question: At present the solver highlights the numbers which can be eliminated. Would it be possible to highlight also (in a different colour!) the pair or whatever it is that allows the elimination?

Andrew Stuart writes:
Good idea!

Saturday 24-Nov-2007

... by: Judy M., Alaska

The Sudoku Solver is particularly spectacular, thank you for this amazing website. I did notice that if my browser, IE, has cookies blocked, and I click "Save", the msgbox mistakenly reports that the puzzle has been saved when it has not. It would be great if your code checked for blocked cookies before reporting whether the puzzle has actually been saved or not. Overall, perfection and huge value to puzzle enthusiasts!

Andrew Stuart writes:
Good idea, I'll add that to the job list. Appreciate the feedback.

Wednesday 31-Oct-2007

... by: Carmen Martinez, Spain

Load Sudoku:

I couldn´t continue with this Sudoku, so I put it in your helper and after it wrote several numbers a legend appeared saying something like there were no more theories to resolve this sodoku. So I looked at the solution in the newspaper and the numbers that the helper wrote were wrong. All the numbers the helper wrote were based in the different types of Unique rectangles. Does this mean the unique rectangles can sometimes be used and others not ?
Thank you very much for all I´ve learned with you ,and excuse my english for I am spanish.

Andrew Stuart writes:
Carmen, please click on the yellow Solution Count button on the solver page. My solver finds 162 solutions. Unique rectangles are only a valid solving tool for sudokus guaranteed to have one solution.

Most likely, you omitted one or more of the givens when you entered this sudoku into the solver.

Tuesday 30-Oct-2007

... by: Ron M, Australia

Congrats on the best help I have found. One basic question- how can I fit your whole page of solution on my screen. Annoying to manipulate every time to fit all page in-probably a 70 yo technophobic
Regards. Ron M

Andrew Stuart writes:
Glad you like it. You need to change your screen resolution from 800x600 to at least 1024x800. Unless you are running a very old computer/monitor this should be perfectly position. Find a blank area on your deskyp and right-click with the mouse. Choose properties. Click on the settings tab. Increase your resolution.

Monday 22-Oct-2007

... by: Chuck Bruno, Virginia

First of all, I would like to thank you for this great program. It is a wonderful aid and learning tool. I have a suggestion that I think could be useful.

For the various stratagies listed on the right side, in addition to being able to turn them off by removing the check mark, how about being able to re-order them by changing the number of the stratigy, perhaps by putting another box for the number just to the right of the checkmark box. What do you think?

Thanks again for this extreemly useful program.

Chuck Bruno

Andrew Stuart writes:
You are not alone in suggesting this and its something I'd really like to add. It would significantly complicate the user interface which might put of casual users and beginners. However my ordering is subjective. It is based on my personal comparision of the complexiity of the strategies but it should be open to anyone to re order. It would help find other solve routes. In the job queue

Sunday 21-Oct-2007

... by: CES, USA

Load Sudoku:

The program came up with a "blocked" messsage a couple of days ago and now it is stuck on xwing in the solution.

Andrew Stuart writes:
The tough and higher strategies execute on a server running a program written in C++. Your computer transmits the sudoku to the server and it returns results. Your computer displays wait until results come back. Sometimes internet congestion, server overload, etc., prevent your computer from receiving results and the wait remains indefintiely. When that happens, reload the solver page and try again. This sudoku solved when I tried it.
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Thank-you everyone for all your questions and contributions.