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 andrew@str8ts.com.
Post a Comment or Question here...
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
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
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
Wednesday 10-Sep-2025
... by: Handle, Water
Dead Mr. Straits,
unfortunately I'm too dumb to understand some of these great explanations of diabolical, extreme etc. strategies.
Would it be possible to make puzzles where you learn these strategies interactively and with a focussed way, e. g. you're presented with situations where the specific strategy applies and have to solve them yourself, step by step?
Thank you so much! Bridge Troll
Andrew Stuart writes:
I'm sure you're not. And yes the more complex strategies are of interest to programmers really although some people have told me they pen and paper them. But you can find “exemplars” at the bottom of most documentation pages which are trivial apart from the strategy for that page. Also, pick moderately difficult puzzles and then try the three hint modes (next to “take step”). Use Take Step until an interesting point is reached. Three hint modes: you can be presented with the pattern – find the elimination, or the elimination – find the pattern; or just the strategy name – find the pattern AND the elimination.
Monday 8-Sep-2025
... by: H, Sweden
Why does the solver auto remove numbers repeated in the two diagonals?
Andrew Stuart writes:
What solver? Should only be on Sudoku X. Drop me an email address so I can reply directly.
Monday 25-Aug-2025
... by: David, Hong Kong
I like the new format but after building the cages I cannot figure out how to enter the clues. It was easy in the old version,
Andrew Stuart writes:
Click on the blue button "Step 2". I had to split the two tasks as the operations were too complicated for so many different devices.
Wednesday 20-Aug-2025
... by: DavidC, USA
Hello Andrew, the various examples that you provide often have two links: "Load Example", and "From the Start". It seems that "Load Example" is identical to "From the Start" and thus the state of the example (solved cells vs. clue cells, and candidates) isn't reproducible. I think the links were different in the recent past where "Load Example" would have a longer string starting with "S9B".
Andrew Stuart writes:
I do have a job to go through the examples and replace the old string with the new one so the example loads directly. Been “as and when” so far. They should be distinct however.
Thursday 14-Aug-2025
... by: Tony Payne, United Kingdom
Hi neighbour Is it an intended "feature" of this website that I was asked to confirm my cookie choices twice? ;o) First on https://www.sudokuwiki.org/ Second on https://www.str8ts.com/Daily_str8ts Didn't happen when I went back into the site
Andrew Stuart writes:
I think it's necessary now. I don’t have cross-domain cookies and the browsers don't like it when I try, so that’s where we are I'm afraid. Different sites, click again
Monday 11-Aug-2025
... by: Mark, WV
Re: 6x6 KenDoku Solver- Sample 38
Grader gives "Empty cell: E6" Due to that the Solve Path ends up broken. Going step by step, when it comes to E6, it takes out all numbers in D6 resulting in a "0" for the cell solution.
Andrew Stuart writes:
Thanks for the report Mark Simplest is to delete that sample puzzle which I've now done Refresh
Sunday 14-Sep-2025
... by: 39_Chevy, US
Appreciate the bug report
Friday 12-Sep-2025
... by: Bellmac, Bellingham, WA, USA
Load Sudoku: CLICK TO LOADThis 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.
Friday 12-Sep-2025
... by: Louis, United States
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: CLICK TO LOADAlso 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.
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
Wednesday 10-Sep-2025
... by: Handle, Water
unfortunately I'm too dumb to understand some of these great explanations of diabolical, extreme etc. strategies.
Would it be possible to make puzzles where you learn these strategies interactively and with a focussed way, e. g. you're presented with situations where the specific strategy applies and have to solve them yourself, step by step?
Thank you so much!
Bridge Troll
Monday 8-Sep-2025
... by: H, Sweden
Monday 25-Aug-2025
... by: David, Hong Kong
Wednesday 20-Aug-2025
... by: DavidC, USA
Thursday 14-Aug-2025
... by: Tony Payne, United Kingdom
Is it an intended "feature" of this website that I was asked to confirm my cookie choices twice? ;o)
First on https://www.sudokuwiki.org/
Second on https://www.str8ts.com/Daily_str8ts
Didn't happen when I went back into the site
Monday 11-Aug-2025
... by: Mark, WV
Grader gives "Empty cell: E6"
Due to that the Solve Path ends up broken.
Going step by step, when it comes to E6, it takes out all numbers in D6 resulting in a "0" for the cell solution.
Simplest is to delete that sample puzzle which I've now done
Refresh