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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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Any Sudoku you want to publish here for easy loading into the solver - Either 81 numbers or the packed string version.

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If you are writing to alert me of a problem (thank-you!) please include a url to the page in question.
Can get fixes in quicker if I know immediately where to go.
Many thanks to all the people who have helped improve the solvers and strategies with their feedback!

Tuesday 30-Sep-2025

... by: TenPeter, USA

Continuing the discussion with Ayumu below. A Junior Exocet pattern requires no more than 2 cover houses for a candidate Base Pair digit. The subject Exocet has the digit 8 on three different rows (F,G&J) in the cover lines thus it requires 3 cover houses to cover the digit 8. This can be seen in the screen capture that you provided. This implies that this is not a valid Exocet pattern. If your were to eliminate the digit 8 from the Base Pair, then the remaining three digits (2,3,4) would form a valid Exocet.

Monday 29-Sep-2025

... by: Bellmac, Bellingham, WA USA

Solved Level 3 puzzle for today (#6481, September 29, 2025). The current scoring system release gives this a Tough Grade of 122. This seems way too high considering the puzzle solution has 19 Naked Singles, 6 Hidden Singles, and 2 Naked Pairs, none of which are Tough Strategies or above.

However, I noticed that your new beta version 4.7 scoring system gives this a Moderate score, which seems much more appropriate. So, looks like you are making good progress on revising the scoring system.

Andrew Stuart writes:
I am hoping people will notice and let me know if it is working. Will take some time to appraise the difference and I think we need a decent sample. I tested the two daily puzzles you wrote to me a few weeks ago. They seem to adjust their grade in the right direction.

From 1st of October I am replacing the daily puzzle stock. For the rest of the year I am picking puzzles which happen to have the same grade in both systems. This should remove puzzles that might have been problematic but also be a good transition. I’ll continue to post both scores for easy comparison. Will write up a page about it today to explain it.

Sunday 28-Sep-2025

... by: flix, yurp

Load Sudoku:

Hi,
when trying to grade this one, your program exits with D5 cell empty.
has one solution.
think its a bug.
best regards

Andrew Stuart writes:
I think there is a bug as well. If you press “Restart” it will work fine. Works fine from your link. Will investigate. Going to be hard one I know :)

Wednesday 24-Sep-2025

... by: Erhan, Turkiye

I have already puchased your puzzle book from Germany, and also try to solve some puzzles on front page each day but recently undo redo check line shows only half of the boxes makes difficult to press, it is my phone's android version?

Andrew Stuart writes:
Thanks for buying the book! It is tough to design a Str8ts player for all the many varieties of phone/tablet etc Can you go here
https://www.whatismyscreenresolution.org/
and screen shot the report? Might be able to duplicate your experience. I don’t have many emulators however. Also a screen shot of the player would be very helpful. Maybe I can see space I can reduce

Thursday 18-Sep-2025

... by: Bellmac, Bellingham, WA USA

Still having a lot of trouble understanding the puzzle difficulty scoring system. In today's set of puzzles (#6470), the Level 3 puzzle is given a Tough Grade (written in yellow) with a 387 score while the presumably harder Level 4 puzzle is given a Very Hard Grade (written in orange) with a 260 score. It seems inconsistent or perhaps I do not understand the grading system.

Here is a Link to the Level 3 puzzle:
https://www.sudokuwiki.org/sudoku.htm?bd=..1..5.......4..5.6...1.3...8....92.15..6..83.34........8.3...6.2..7.......8..1..

And the Level 4 puzzle:
https://www.sudokuwiki.org/sudoku.htm?bd=.4.9.....9....5..1...6..97..1.4..25...6...3...83..6.1..62..7...1..5....2.....9.3.

Andrew Stuart writes:
I’ve taken a look at these two puzzles. The “tough” one scoring 387 is inflated by the Simple Colouring getting 6 eliminations leading to 10 solved cells. The contribution to the score is too high so I’m going to spend some more time balancing the strategy weights. I also have a system to promote and demote puzzles if they under or overscore but the strategies used are either all quite low ones or some high ones. Probably confuses people as well. But the diabolical one does use several high end strategies while the tough one sticks to tough or less. So broadly they are correct. Time for some more testing.

Wednesday 17-Sep-2025

... by: Lspace, The Netherlands

In the killer solver singele numbers (solutions) are not converted to large font unless they solved by the solver. filling in a single digit will remain in small font. It is eliminated from adjacent squares just the visual is off.

Andrew Stuart writes:
Thanks for letting me know. Fixed now.

Sunday 14-Sep-2025

... by: 39_Chevy, US

The Jigsaw solver cannot be printed. The boxes are blank.

Andrew Stuart writes:
My bad with the last update. Refresh, should be okay now
Appreciate the bug report

Friday 12-Sep-2025

... by: Bellmac, Bellingham, WA, USA

Load Sudoku:

Solved this Level 3 puzzle for September 12, 2025 (#6464). When we got near the end, the puzzle had a Bug opportunity which we used, but going back I see the solver suggested a Y-Wing instead.

This brought to mind a question I have had for some time. Why is Bug the #14 in Tough Strategies, while the Y-Wing is #10. In my mind, Bug ought to be #7 as it is the easiest and most mechanical to apply of the Tough Strategies. It does not seem to occur very often, but it is easiest to recognize in a puzzle (easier than current #7 X-Wing and certainly a lot easier than finding a Y-Wing.

Andrew Stuart writes:
I think you are right. I should move it up the list. Getting more popular ;)

Friday 12-Sep-2025

... by: Louis, United States

Hi- This new solver program adds numbers back in, after they have already been removed. Please fix this glitch. Thanks! Lou

Andrew Stuart writes:
Taking about when you edit the small board? Uncheck “Auto clear”
If the big board I removed the effect of auto clear there but take step will put numbers back.
Can you describe in more details the moves you are making? Some people use the solver differently

Thursday 11-Sep-2025

... by: TenPeter, USA

Load Sudoku:

New version 2.40.2 has some sort of bug in the solver. The above puzzle is the first in the 2.2M puzzle database. The first step is an Exocet. There is an hidden Tridagon in the puzzle that has a valid pattern in Block 0. If the triplet is removed from A3 leaving 45, the "solution count" does not flag it as an incorrect value but setting cell to either 4 or 5 does get flagged as no solution. The correct solution for the cell is 1. In the case of setting cell to 45, the returned solution is the correct one.
Also it is not possible in 2.40.2 to copy the solution from the "solution count" window.

I looked at the Exocet question from Ayumu below. The pattern is not an Exocet as it violates the cover house pattern rule for digit 8. This would imply that 8 can not be a base pair nor a target digit. Removing the 8 from those cells results a proper detection by the solver of single Exocet. The second Exocet has the same cover house issue as well as invalid companion cells.

Andrew Stuart writes:
Thanks for the bug report on copying from the solution count popup. Just fixed that now.

Regards the solution count I can explain the behaviour by stating that the solution count works off clues and solved cells. Not the current candidate spread. I pass in an 81 character string so its one digit per cell. I can see the utility of checking for a solution count based on the current spread. 99.9% of the time there will be no difference as the candidates conflicting with solved/clues are flashed removed on the first step in SC. But I suppose if you are pecking way at candidates it’s a way of checking you didn’t remove a solution
I might add that to the job queue. Guess it will need some kind of checkbox.

Possible there is a problem with the very limited rule set I have for exocet. I have never had a false positive yet so I assumed I wasn’t making a mistake. But I need to go back to exocet and look at the whole thing again. Probablu after Tridagons which I need to look at first
Cheers

Ayumu writes
Reply for TenPeter in THURSDAY 11-SEP-2025 post:
Hello, I don't know why do you think 8 is not a valid number, 8 can only appear twice in CL, one is in c3, another is c7. load puzzle
Here is a img from YZF_sudoku, a sudoku program with exocet.
https://img.cdn1.vip/i/68ce272de010d_1758340909.webp
https://img.cdn1.vip/i/68ce28a4480b6_1758341284.webp
The img show the exocet with my original exocet and double exocet.
You can find yzf_sodoku from http://forum.enjoysudoku.com/yzf-sudoku-t36846.html
Welcome to furture discussion.
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2015 2014 2013 2012 2011 2010 2009 2008 2007 2006
Thank-you everyone for all your questions and contributions.