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!

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:

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:

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:

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:

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:

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

Friday 24-Jul-2015

... by: Kevin, San Antonio, USA

Love your software!

I am currently developing a Sudoku Solver, and your site has helped me a lot...


Andrew Stuart writes:

Well done, I find the coding this stuff very satisfying

Friday 3-Jul-2015

... by: Linda, Australia

I have been using your program for many years and I love it as I have learnt so much. However, the last 2 puzzles I have been trying to solve have become stuck on " 'wait ". I don't understand whether there is a problem with the puzzles or with the program. Any suggestions ?

Andrew Stuart writes:

I'm hoping this is just the updated pages I posted to take the solver to 2.02. If you still see 2.01 on the solver then fresh a few times (F5) or clear your cache. Always happens, its just not possible to invisibly update under peoples feet with this internet stuff

Let me know is that doesn't solver it

Friday 3-Jul-2015

... by: Dave Conway, USA

Can't seem to get Jigsaw solver and Killer Solver to update to 2.02. I've tried refreshing and clearing the cache. Neither seems to work. Sudoku Solver updated.

Andrew Stuart writes:

Very sorry to confuse you, my bad. The update doesn’t effect Killer but since they share a common core engine I should have remembered to increment the version number everywhere. Done so now, working again for me. Once F5 refresh should do it – should say 2.02 now

Thursday 25-Jun-2015

... by: rec, USA

I have been trying to use your app on a Samsung S4 and have the following observations:

When I solve a particular cell by removing all but the correct value and then activate "next step" the app does not remove the candidate entries that are no longer valid. This results in my having to manually remove these candidates. This is inconsistent with your solver on the web.

Please correct this.


Andrew Stuart writes:

I've looked at the app and it does remove candidates if you press take step a few times. But I think you are talking about a "player mode" as opposed to a "solver mode". I am thinking about how to add that but it's not very easy as the candidates are incompatible, one has to be manually editing candidates as opposed to allow the solver to remove them. I agree that in "player mode" the candidates can be removed automatically. I am about to release version 1.74 today which contains some improvements, including a LONG click on the numbers - which inserts the big number instead of a candidate. This means its one "take step" to clear. On your main point I'll develop further and see if I can add "player" mode.

Sunday 7-Jun-2015

... by: Keith, Brisbane Aust

Thanks Andrew for a great web site. Gave me great peace of mind to discover the puzzle I was puzzling over was only solved by guessing.

Andrew Stuart writes:

Very happy it's been helpful, your most welcome
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2015 :1 2 3 4 5 :2014 2013 2012 2011 2010 2009 2008 2007 2006
Thank-you everyone for all your questions and contributions.