Solver App for Android and iPhone
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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Many thanks to all the people who have helped improve the solvers and strategies with their feedback!

Saturday 15-Oct-2016

... by: STSahasrabudhe, India

Load Sudoku:

All strategies (esp. the advance ones like Swordfish ) for eliminating (and thereby fixing value in cells) presuppose that candidates in all/specific cells are pencilled in.
Are there any 'rules of thumb' for zeroing on a candidate value or two, in r/o which a pattern, a chain or a strategy which will help solve Sudoku, can be looked for?
The reason for my query is that, when stuck in solving a Sudoku printed on paper, I find the job of adding candidates in each unresolved cell rather tedious and feel that there could be a shortcut.i

Andrew Stuart writes (16-Oct-2016):

Many people use my solver to get to the first step which fills in all the candidates and then removes the ones from the clues. Then the print it. It is easier to solve if you are removing candidates as you go a long, rather than re-creating the spread at every step. It is easier because no candidate will ever be added in the solving process, always removal. I'd try that.

As to the advanced strategies, well, Sudoku is very deep and most of these were once considered so theoretical that only computers could use them. But they are still the easiest logical step if you don’t want to guess. Most newspaper puzzles do not require them but on my site I am interested in the hard ones. Even now there are some puzzles which cant be solved logically.

Monday 15-Aug-2016

... by: Geomama, UK

Firstly, thank you for an outstanding teaching and learning tool for Sudoku.
I installed the Android app but had to uninstall it because the font is too tiny to see and cannot be adjusted. I did see some other comments to this effect but decided to give it a go anyway based on the photos. Alas, the numbers are nowhere near as big as the photos imply. Please can you make the font size adjustable or just make the numbers fill the boxes. I have low vision and could not even see the numbers but other users are having the same problem! The ability to make the numbers bold and high contrast would be very helpful - or just do this by default to improve everyone's experience!! Thanks for reading.

Andrew Stuart writes (16-Aug-2016):

I've been aware that for some larger devices and screens the fonts don’t seem right with the choices I've made. That’s partly because there are so many devices and resolutions (unlike Apple devices) and because I only have access to a few actual android devices. Plus the emulators are very hard to make work in a development environment. But I had an idea reading your feedback - a font size slider could be the solution. I've added one in the Preferences screen. You have back out and view a solver puzzle board to see the effect but some back and forth will get a comfortable size I think. But I'd like to hear about your experience. Give it a day or so to appear as an update on the Play Store and try again

Sunday 24-Jul-2016

... by: Andrew, England

How are you doing? Thanks for the site.
I'm looking at your solution to a Kenken that I created. The step that I can't understand is as follows:
Killer Innies/Outies
DOG LEG (3): Removing 1/3 from C3
DOG LEG (3): Removing 1/3 from E2

How do you apply the indies/outliers to Kenken with -+/ and x involved? I can only find the reference to Sudoku.

Kind regards

Andrew Stuart writes (30-Jul-2016):

Despite KenKen clues not always having + clues the rows, columns and boxes still have to add up to 21 (in the case of 6x6, 45 in 9x9) and therefore can in principle be decoded using the same technique.

Thursday 21-Jul-2016

... by: David E. Schellenberg, Winnipeg, Manitoba, Canada

Load Sudoku:

Solver makes J2 into an 8 without any good reason.

Andrew Stuart writes (30-Jul-2016):

8 really is the last remaining possible candidate. 8 and 3 are the last two in the row, but 3 is present in A2.

Sunday 17-Jul-2016

... by: Jean, UK

Hi there. your web page is brill by the way. What I want to do is put my own jigsaw suduko in to work with but I'm not sure how to do it. I don't understand the "load 81 characters" bit. Really look forward to your reply. I have a couple of jigsaw Sudoku puzzles that are really hard and are driving me crazy cos I'M STUCK lol.. Many thanks jean

Andrew Stuart writes (30-Jul-2016):

Yes it's been in my job queue for a while now to allow user defined jigsaw shapes. I will try and get it done.

Thursday 14-Jul-2016

... by: John D Traka, Mosinee WI USA

on the website, there's a puzzle for today (7/14- #3861 moderate) and it has two cages with nine cells that total to 45. the killer solver is saying those are illegal cage sizes and clues. just thought you might want to investigate; thanks!

john d traka

Andrew Stuart writes (30-Jul-2016):

Yeah...I regard that as a variant on Killer, my definition insisting on cages with less than 9 cells. Otherwise it could encompass normal Sudoku.

Wednesday 13-Jul-2016

... by: Swagman, USA

Still printing out in bold have to use smaller size still fills the page and its also bold, regular print won't print on just one page. Check everything on my end prints find in other apps.

Andrew Stuart writes (30-Jul-2016):

Do you perhaps have page zoom set to something very high in your browser? There is a reset to normal somewhere in settings. Depends on which browser. [CRTL]+mouse wheel sometimes does it.

Monday 4-Jul-2016

... by: sherie, california

This is very helpful. Can you please remove the black background and make the background white do that we can print it to study?

Andrew Stuart writes (30-Jul-2016):

You need the [print version] which is a link at the top of every documentation page. Also removes the menu, and has a flex-width so most printers can cope.

Saturday 2-Jul-2016

... by: Beekeeper, Denton County, TX

Really neat educational tool. The more I solve the easier it gets. Some are really tough. Great site.

Wednesday 29-Jun-2016

... by: Carl, Northern Ontaro

Andrew, your solver cannot solve some of your diabolical puzzles which I have brought up. Does that mean there is no solution or might they be beyond the skill of the solver?

Andrew Stuart writes (30-Jun-2016):

The solver has been updated since the stock was made. I'm aware that there is now something tiny difference that is causing previously solvable puzzles (and therefore gradable) to become 'unsolvable' and I'm trying to track that down. What was the last puzzle with that problem? Can you remember?
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