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!

Monday 11-Dec-2023

... by: Ilmārs Cīrulis, Europe, Latvia

Load Sudoku:

Greetings! What's the status of the Easiest Sudoku Competition?

As I can see, the grader has changed a bit, and now the current first place by David Filmer is graded 4, not 2. So, I offer my sudoku with 31 clues and current grade 3. :)

Andrew Stuart writes:
I had almost forgotten about that page!
That might be because I don't have a link to it from the rest of the site, or can't find it
I have added a link on the Home Page

Thinking about the scoring for these sorts of puzzles, I have a better idea, but it means computing differently
I think the first round the solved cells should score 0
The second round the cells solved should score 1
Third round either 2 or 3
I don’t think any competitors will need a fourth round, but 4 points in case

I would be fascinating to find puzzles that collapsed completely and then offer a hope that puzzles with less and less clues can also collapse that way. This new competition is more open and long term and people won't need to question the grade

What do you think?

Tuesday 14-Nov-2023

... by: Ricki, USA

I am having trouble with the 5 daily puzzles in the latest update to my iPad. It used to work perfectly, but now it shows the selected sudoku puzzle only, no menu or keypad for entering. Any suggestions?

Andrew Stuart writes:
I know that this app desperately needs and update. Unfortunately I don't have a Mac to work on or the latest skills. Hoping to hire someone though.
Other users say there is an invisible part of the page which does work as a button. Can't say for sure as I don’t have an iPad

Wednesday 1-Nov-2023

... by: Jarek, Poland

Thank you for the new version of Solver. I have one request: Can't the solver lines be wider? When entering a new solver, the most tedious and time-consuming thing is to point the mouse at the thin line to delete it, unlike the field for entering numbers. I think that the line fields and the digit fields should have a similar area. Greetings from a Polish user who is grateful for Solver.

Andrew Stuart writes:
Good idea, not a problem. Now 4px instead of 3px. Refresh the killer solver page

Thursday 26-Oct-2023

... by: Daxx, UK

Hi Andrew,
( Version 2.12 )
Unable to load Killer Sudoku from email URL
Unable to load sample KS
Unable to Enter New Killer

Andrew Stuart writes:
Just now updated the email link.
Also added the redirect
Appreciate the alert

Wednesday 25-Oct-2023

... by: Todd Lindberg, Seattle, WA, USA

Load Sudoku:

Hi Andrew,

I've been honing my algorithm for Unique Rectangles, which has been really interesting to me. One of the exemplar puzzles, linked:

has a Type 3b virtual triple in Row E. When I run it on your solver, it finds it, but doesn't eliminate 6 from E3, just the 2. Since the triple was {236}, I logically expected both 2 and 6 elimination from E3:256, just like a normal naked triple rule.

Am I missing something subtle, and only the candidates expressed by the roof cells can be eliminated in a virtual triple?

Andrew Stuart writes:
Hi Todd. I think you are right. Checking my code I don't seem to use the third candidate in the triple. I've now added it to the elimination mask and tested. Good catch, thanks for letting me know

Thursday 19-Oct-2023

... by: Alcuin, England

I just loaded the Observer killer Sudoku 15th October into the Solver and it ran out of strategies without solving a single cell. First time i had tried a killer puzzle.

Andrew Stuart writes:
Does occasionally go like that with the hardest puzzles. I'm about 60% on the hardest for killer so it lags behind normal Sudoku which I'm confident is 1/20,000. Still much more solving work to do!

Friday 13-Oct-2023

... by: ATechGuy, USA

Load Sudoku:

I finally have some time to really improve my sudoku skills and I'm looking for a great way to spot X-wing, Y-wing, and XY-wings. It's sort of the "bar" one needs to be able to clear before going for the "diabolical" logic. What I'm looking for is a way to click to "see" if there is an X, Y, or XY wing lurking on the puzzle, as I often get to the point where I *know* there is, but I can't locate it. I don't really want to SOLVE the *-wing (eliminate the values) but am looking for a way to help "find" the *-wings by first telling me IF there is an *-wing there, and then secondly, a "hint" on the pivot square. I'm just looking for as many (subtle) visual hints as possible without giving it away.

Does that make sense? I've been a loyal follower for years on your site. Also, for some reason, my Edge browser is crashing if I run the grader. It must be some cache (which I've cleared) as another browser doesn't have the issue.


Andrew Stuart writes:
Not sure if there is a half-way house. Showing the pivot cell sounds like a good hint. Computers are bad at effecting a partial pattern but you can hide some of the components, no? Or are you talking about paper and pencil solving? I agree that gets harder with pattern based logic. Much of the exotic strategies I think are for coders to test their algorithm skills but I have known people to eyeball them. How they were discovered I suppose.

Friday 13-Oct-2023

... by: Michael, Germany


this is a very smart tool!! Unfortunately I am too stupid. I have enteres a new killer sudoku, pressed validate and then send to solver.
The sudoku disappeared and I do not know were to find it.
Can you help me?


Andrew Stuart writes:
There should be a cookie which save your board. If the page is refreshed then it will restore the state. Does this happen on any solver? If not, check security settings

Tuesday 10-Oct-2023

... by: Lincoln Kinnicutt, US

I have loved your site, mostly using jigsaw sudoku. It has worked fine, including the solver. Recently, the solver stopped working, with an error message saying to clear the cache. I did so, and now solver still doesn’t work. It gets to trying naked quads, says “wait”, and then nothing happens.

How do I fix it?. Thankswqko

Andrew Stuart writes:
How does it look today? Or the normal Sudoku solver?
Were some updates and some patches to those updates. Not getting many similar reports so I hope it's local to you.
[CRTL]+[F5] is a forced reload

Monday 9-Oct-2023

... by: Graham, Engand

I keep getting the message

OKAY Solvers have been updated to version 2.10!
You will need to download the latest page and scripts, which is simple to do. Press the keys [CRTL]+[F5] together to force a reload. If this does not work, you can clear your cache.

I've done what it suggested but I'm still getting the message

Andrew Stuart writes:
Killer solver? I fixed that last night, hadn't uploaded the change for Killer.
Sorry about that!
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2015 2014 2013 2012 2011 2010 2009 2008 2007 2006
Thank-you everyone for all your questions and contributions.