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 29-Jun-2023

... by: Owen Le Blanc, England

I sometimes use the Windoku Solver to evaluate windokus. I have one (from, number J3981) which I suspect has no solution. Windoku solver says "Or it has multiple solutions (check with [Solution Count])." But there doesn't seem to be a "solution count" button on the "windoku solver". I tried "Solve Path", and I had
"Solver by Andrew Stuart, version 2.30, 23-Apr-2023
Clues: 19
Final Score: 0
Grade: Unknown"
It shows 18 steps, but I'm not sure what this means. Does "Final score: 0" mean there is no solution? Or what is the "Solution", which appears to show the numbers that the solver is able to find, plus the original clues, of couse.
-- Owen

Andrew Stuart writes:
Thanks for this feedback and nice to get something about Windoku

I have checked the puzzle with my offline solver which can perform solution counts. Does indeed have one solution and that makes it interesting

The solver when it gives up shouldn't mention the solution count as I can't figure a way to put it on the server alongside the normal Sudoku one. Next update I'll remove that message.

The 18 steps are the steps it can solve, just no final solution and therefore no score

Wednesday 26-Apr-2023

... by: str8ts, Germany

Hi Andrew,
I can´t open the German website any more - there ist alway Error 404.
So i´m missing one str8ts a day (the second one of the classical player) and nearly even worse: I can´t post any solution times or contact my "str8ts-community"
As someone (whose name should not be used) once said: very sad!
I hope the problem can be solves soon.
Greetings from Germany

Andrew Stuart writes:
Hi all. Just to let everyone know that was subject to an automated (scripted) hack through the platform software it used. Daniel is trying to put together a basic site without fancy tools as a substitute and we'll see what we should do afterwards as the best way forward. Thanks for everyone's patience.

Sunday 16-Apr-2023

... by: Harold Silander, Scotland

Many thanks for your Killer Sudoku Solver. I have been doing them for years and soon realised my limitations - can do Saturday Guardian and Observer but maybe require 2 or 3 shots at it. I was really stuck on 9/4/23 Observer puzzle - I had 4 attempts and none worked. Setting it up here was really easy - and you solved it - absolutely brilliant. I now have to work out how I went wrong - and you have given me a great start. HS.

Andrew Stuart writes:
Excellent! Glad it worked, Killer one lags behind the Sudoku

Tuesday 28-Mar-2023

... by: Djebroun, sudoku

The algorithm of the solver displays the first solution it found at a step. In my point of view, it should be interesting to know the other possible solution. Because for example, sometimes i found an AIC and when i compare with the solver, the algorithm found another AIC.
Thanks for this very good site.

Andrew Stuart writes:
Yes this is one of the top requests and I'd really like to make some kind of cycle through alternatives. Makes for a very complicated user interface though

Sunday 26-Mar-2023

... by: Charles, Somerset UK

Hi Andrew.
Have been using the Daily Sudoku iPad player for a long time, and I find it the perfect form factor. The on-screen keyboard doesn’t come up to obscure large parts of the board, and the ‘Check’ button is so incredibly handy.
So why are you threatening to retire it??? Please don’t!

Andrew Stuart writes:
I'll 99% going to keep it. Really great you have been enjoying so long

Tuesday 21-Mar-2023

... by: André, Germany

Hello, great site you have here.
I came here to get some informations about the Setti-rule of Str8ts. Your article helped me a lot to understand it, but I don't see it exactly in your example with "Extreme number 31".
You say, that you are sure, that in every column there has to be a six. But column 9 would work without a 6 right?
Maybe I don't see it but this confuses me.
Anyway, thanks for all the hints and tips on this site!!!

Andrew Stuart writes:
To be honest I barely understand Setti myself. I know I didn't finish the article and I'm hoping someone can help me write a better one. However plenty of people in the comments for the weekly do seen to know it very well, can try and ask there
Sorry for such a lame answer!

Monday 20-Mar-2023

... by: Doug Fraser, Canada

Load Sudoku:

This is an "extreme" puzzle, created by my generator, solved in 51 steps by the solver, employing tools: Alternating Inference Chains (10 times), Hidden Unique Rectangles (3 times),Aligned Pair exclusion (twice) plus Digit Forcing Chain, X-Cycle, WXYZ Wing. When I try to disable the latter two (to see if the puzzle remains solvable anyway) - the disable does not seem to take and I get the same 51 step solution path, employing those tools in the same steps.
Did I miss something?

Andrew Stuart writes:
Talking about "Solve Path"?
That uses all strategies. Ticks are for the solver only. Could be something I should make a feature

Saturday 18-Mar-2023

... by: Andy, USA

The daily of 2023-03-18, difficulty 5/6, was an entertaining puzzle. First, I made a dum mistke but was able to back out of it a dozen moves after the fact, and you know how frustrating and then satisfying that is. Second, after solving down to confetti, all little numbers, I soon recognized a potential ambiguity spanning 9 cells, and all I had to do was avoid it to solve out quickly, and you know how satisfying it is to apply an abstract meta rule. SudokuGuy on youtube refers to this concept as "Danger", and he's quite entertaining in a Mr. Rogers sorta way, so which see. Actually, the cleanest way of looking at a Sudoku puzzle is that what we're actually doing is proving, by example, that the clues specify a single populated Sudoku board. Usually, the steps are cell-wise elimination, but "Danger" is puzzle-wise elimination. Whatever ingredients went into this puzzle, it came out yummy, challenging but not tedious, looking forward to more like it. Thanks!

Andrew Stuart writes:
Glad you enjoyed and interesting breakdown, thanks!

Monday 13-Mar-2023

... by: maritza, Spain , EU

Thank you. What an enormous amount of work you have done!

Andrew Stuart writes:
Cheers! Appreciated, glad you find it useful

Monday 20-Feb-2023

... by: Chris Wray, USA

In Safari, the solve path window never appears for me. Works fine in Chrome.

Andrew Stuart writes:
I've checked on my wife's iPad and I can see the problem. Safari blocks popups but I've used and alternative. It does not open in a new tab like on Windows so you'll need to use the browser "back" button to get back to the solver.

Made some css tidyups as well
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2015 2014 2013 2012 2011 2010 2009 2008 2007 2006
Thank-you everyone for all your questions and contributions.