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...
Monday 14-Oct-2024
... by: Valentin, Romania
Simple Coloring is the only strategy used by the solver on the website (besides naked/hidden single) for this puzzle, but it is missing from the Strategy Overview page, why?
Andrew Stuart writes:
It is (was) documented under "Singles Chains"/ However your question does raise the further question of why I don't pick one and be consistent, so I'll do that now. Goes way way back to like 2006 or something when the Sudoku community was still naming things and different sets of people used different names. So going with "Simple Colouring"
Sunday 6-Oct-2024
... by: Alan, California, USA
Hi Andrew, 1) On the Sudoku Solver page: the "Grader" button does not work. After I have entered a Sudoku and checked that it displays correctly on the grid, I click the Grader button ...and..... nothing happens! Would be nice to have this work. Thanks. 2) On the Sudoku Solver page: when Check for solved cells step finds one or more solved cells the explanation box does not change. I suggest that it would be helpful to the user if the explanation box would, when the Check for solved cells step finds a solved cell (i.e. a "naked single"), display the coordinates of the solved cell or cells. Thanks for listening.
Andrew Stuart writes:
Hi Alan Grader working for me as of testing just now. Let me know if it stops and if there is any error message or symptom. Send the puzzle so I can check that as well. Regards the "check solved cells" these are usually a result of a naked or hidden single which are described in the text box. I highlight the number when it goes big for easy spotting.
Monday 30-Sep-2024
... by: Chris, USA
Hi there - love your site.....especially adding grading to the Daily Sudoku, but when I select a different grade and try to print (I'm old school pencil and paper), the printed version reverts to level 1 and won't print level 4......I can load level 4 into the solver, but can't print it.....any recommendations on how I can resolve? thanks in advance
Andrew Stuart writes:
Hi Chris. Just tested this and can't see a fault. send another feedback or email me so I can reply personally. See if we can sort this out. Anyone else having this problem?
Sunday 29-Sep-2024
... by: Daxx, Hull, UK
Hi Andrew,
Adding to Ryan's comment (Friday 13-Sep-2024), the combinations for 32/7 are: 32 7 12345--89 1234-67-9 123-5678-
As Ryan noted, they all have 1,2,3 and they all lie in block 9 because the only square in that cage outside block 9 is F7 which is known to be 5/6, so has no 1,2 or 3.
That's why G9/H9 (not G7/H7), also in block 9, can't be 3 The numbers 1-9 down the right side of the board might have led to confusion. Shouldn't they be A-J as on the left? :)
Cheers,
Dave
Andrew Stuart writes:
Passed your comment on.
Thursday 19-Sep-2024
... by: Tom Curd, USA - Philadelphia area
Hello Andrew,
I live in the Philadelphia area. Let me say that your site is a masterpiece. Sudoku puzzles appear to have come a long way since I found them in 2006. I am very new to the computerized aspects of working them. I hope to briefly impose on you with some thoughts and impressions. Any feedback you could provide would be very welcome.
All coloring techniques and their derivatives seem to me so far to be substantially equivalent to the judicious guessing with backtracking that I stumbled upon myself. Thanks to your fine solver, I can now detect the series potentially requiring guesswork and steer clear of them on my weaker days. To me, coloring resembles a structured form of proof by contradiction. It can pay huge dividends sometimes but I also think it's labor intensive.
There is a part of me that thinks computer assisted Sudoku is cheating and another part that thinks that it's a skill in itself. A trenchant question gets to be how well the designers of these monstrosities would fare at solving the harder puzzles from other designers but without any computer assistance that shows the candidates. I can't help wondering if the exotic techniques are needed by contestants in tournaments and competitions or if the judges keep it simpler than that while the players are on the clock. My searches about this have been inconclusive.
I aspire to small things in writing my own programs but I have probably made it to first base using compiled QB64. Any tips or notes you can share about tools, pseudocode, data structures, code sizes, or anything of the sort would be great. Once again, kudos to you and your team for this immaculate creation. Thank-you so much.
Rage on, Tom
Andrew Stuart writes:
Very eloquent and interesting feedback, many thanks. My only experience of tournament Sudoku was quite a long time ago. I was briefly involved one year with the Daily Telegraph when they ran an annual competition. I was pretty downcast by the very easy puzzle they picked and couldn’t understand why they chose it. Wasn’t my pick. The competition became a speed contest, not a thoughtful one. I’m sure other contests are better.
What’s happened with the advanced strategies like colouring wasn’t driven by contests or published puzzles really. People on forums were just interested in edge case puzzles that were found to be much more difficult than the usual fare. Often these enthusiasts would go looking for them and then advance some theory. Unlike most other pattern puzzles Sudoku happens to be unusually rich – I like to think as rich as chess. Which is why I started and continued with the site. I would not get very far or have much to say about Hitori or Kakuro for example.
Much of the site is devoted to these quite abstract and complex strategies as they are mainly of interest to other puzzle software writers but there is no clear divide where pen and paper stops. Now there are some very clever people who swear they use advanced strategies on pen and paper puzzles and they certainly enjoy doing them, whatever help they really use. So there is a market for them. But don’t publish extremes in newspapers as they would frustrate most players. The diabolical needs to be quite hard though – the spectrum is wide. I think if you avoid notes you should can validly use inspiration and still crack tough puzzles.
I agree that some patterns are so hidden you are trial and erroring in your search for them. It is an open question of whether there are more transparent replacements. We’re certainly not at the end yet of guaranteeing all puzzles have a logical solution.
Does QB64 have linked lists? I find having pointers very helpful. For example placing all cells in rows, columns and boxes into the same structure is very helpful and avoids writing code specifically for a row, or a columns or a box. Then adding other constraints in (for variants) is relatively trivial. I had to do this quite early as I was asked to make Jigsaws soon after vanilla. Use bit arrays also. Need two bytes for 9 numbers sadly but worth it for candidate spreads.
Best of luck with your solver and let me know how you get on
I thought I would bring this to your attention, I hope it helps.
Please note the 32 in 7 starting on F7. The combinations of this cage all require a 1, 2 and 3. F7 can only be a 5 or 6 which means the 3s located in G7 and H7 can be removed.
Best Regards, Ryan
Andrew Stuart writes:
Interesting puzzle! Not sure how you get the 3s removed from G7/H7. I'm sure you're right though. The solver really struggles with such large cages as the number of dog-legs gets beyond what I programmed so it might be giving up on this cage at certain points.
Monday 2-Sep-2024
... by: Graham, New Zealand
daily mini killer #33 - screen still blank today
Andrew Stuart writes:
I might have fixed it Refresh now [CRTL]+[F5], will say v 2.12 Many thanks for the reports, and I hope it works now All the best Andrew
Saturday 31-Aug-2024
... by: Phil, U S
My puzzle screen is black. And NEW button doesn't work. Phil
Andrew Stuart writes:
Possibly when I was updating the page. How is it now?
Wednesday 28-Aug-2024
... by: Bellm, USA
I have noticed what seem to be anomalies in the grading system. Below are the scores of two identical puzzles, except a clue is removed from F9. Intuitively, one would assume that removing a clue would make a puzzle harder, not easier.
I wouldn’t try and compare two close scores as anything very meaningful. They work best in aggregate and statistically but there is too much arbitrariness at that grade. So with the puzzle with the extra clue a naked single is found. This takes priority over everything else so everything takes one step more than the other puzzle (14 steps not 13). There is weighting for how long a puzzle takes to solve/collapse which modifies the scores each round. That will bias the 14 step solution and give a slightly higher score.
I'd just like to highlight that while solving the above puzzle, it uses simple coloring - twice in a unit. The rule states - "that if any unit has the same colour twice ALL those candidates which share that colour must be OFF. Step 18 - Simple Colouring
(RULE 2): Two 3s in a single unit (in Col 4) have the same color in cells E4 H4 - all yellow coloured candidates can be removed Last candidate, 9, in F7 changed to solution Last candidate, 9, in H4 changed to solution Last candidate, 9, in J9 changed to solution
The alternative colour will be ON and the solution for that cell. " the solver removes all instances of the yellow 3's , but does not take advantage of the fact that all the purple 3's are true. Wayne
Andrew Stuart writes:
Yes that’s one way to think about it. Been a long while but I’ve always approached the strategies from the pov of chipping away at candidates and hoping that will reveal a solution – and mostly that’s the way they work. This rule does go direct to solutions. The mechanism for return data back to the solver is subtractive – a list of candidates to remove. So it’s a little more mechanistic than a human. Might figure out a tweak when I go back into simple colouring gain.
Monday 14-Oct-2024
... by: Valentin, Romania
Sunday 6-Oct-2024
... by: Alan, California, USA
1) On the Sudoku Solver page: the "Grader" button does not work. After I have entered a Sudoku and checked that it displays correctly on the grid, I click the Grader button ...and..... nothing happens! Would be nice to have this work. Thanks.
2) On the Sudoku Solver page: when Check for solved cells step finds one or more solved cells the explanation box does not change. I suggest that it would be helpful to the user if the explanation box would, when the Check for solved cells step finds a solved cell (i.e. a "naked single"), display the coordinates of the solved cell or cells. Thanks for listening.
Grader working for me as of testing just now. Let me know if it stops and if there is any error message or symptom. Send the puzzle so I can check that as well.
Regards the "check solved cells" these are usually a result of a naked or hidden single which are described in the text box. I highlight the number when it goes big for easy spotting.
Monday 30-Sep-2024
... by: Chris, USA
Sunday 29-Sep-2024
... by: Daxx, Hull, UK
Adding to Ryan's comment (Friday 13-Sep-2024), the combinations for 32/7 are: 32 7
12345--89
1234-67-9
123-5678-
As Ryan noted, they all have 1,2,3 and they all lie in block 9 because the only square in that cage outside block 9 is F7 which is known to be 5/6, so has no 1,2 or 3.
That's why G9/H9 (not G7/H7), also in block 9, can't be 3
The numbers 1-9 down the right side of the board might have led to confusion. Shouldn't they be A-J as on the left? :)
Cheers,
Dave
Thursday 19-Sep-2024
... by: Tom Curd, USA - Philadelphia area
I live in the Philadelphia area. Let me say that your site is a masterpiece. Sudoku puzzles appear to have come a long way since I found them in 2006. I am very new to the computerized aspects of working them. I hope to briefly impose on you with
some thoughts and impressions. Any feedback you could provide would be very welcome.
All coloring techniques and their derivatives seem to me so far to be substantially equivalent to the judicious guessing with backtracking that I stumbled upon myself. Thanks to your fine solver, I can now detect the series potentially requiring guesswork and steer clear of them on my weaker days. To me, coloring resembles a structured form of proof by contradiction. It can pay huge dividends sometimes but I also think it's labor intensive.
There is a part of me that thinks computer assisted Sudoku is cheating and another part that thinks that it's a skill in itself. A trenchant question gets to be how well the designers of these monstrosities would fare at solving the harder puzzles from other
designers but without any computer assistance that shows the candidates. I can't help wondering if the exotic techniques are needed by contestants in tournaments and competitions or if the judges keep it simpler than that while the players are on the
clock. My searches about this have been inconclusive.
I aspire to small things in writing my own programs but I have probably made it to first base using compiled QB64. Any tips or notes you can share about tools, pseudocode, data structures,
code sizes, or anything of the sort would be great. Once again, kudos to you and your team for this immaculate creation.
Thank-you so much.
Rage on,
Tom
My only experience of tournament Sudoku was quite a long time ago. I was briefly involved one year with the Daily Telegraph when they ran an annual competition. I was pretty downcast by the very easy puzzle they picked and couldn’t understand why they chose it. Wasn’t my pick. The competition became a speed contest, not a thoughtful one. I’m sure other contests are better.
What’s happened with the advanced strategies like colouring wasn’t driven by contests or published puzzles really. People on forums were just interested in edge case puzzles that were found to be much more difficult than the usual fare. Often these enthusiasts would go looking for them and then advance some theory. Unlike most other pattern puzzles Sudoku happens to be unusually rich – I like to think as rich as chess. Which is why I started and continued with the site. I would not get very far or have much to say about Hitori or Kakuro for example.
Much of the site is devoted to these quite abstract and complex strategies as they are mainly of interest to other puzzle software writers but there is no clear divide where pen and paper stops. Now there are some very clever people who swear they use advanced strategies on pen and paper puzzles and they certainly enjoy doing them, whatever help they really use. So there is a market for them. But don’t publish extremes in newspapers as they would frustrate most players. The diabolical needs to be quite hard though – the spectrum is wide. I think if you avoid notes you should can validly use inspiration and still crack tough puzzles.
I agree that some patterns are so hidden you are trial and erroring in your search for them. It is an open question of whether there are more transparent replacements. We’re certainly not at the end yet of guaranteeing all puzzles have a logical solution.
Does QB64 have linked lists? I find having pointers very helpful. For example placing all cells in rows, columns and boxes into the same structure is very helpful and avoids writing code specifically for a row, or a columns or a box. Then adding other constraints in (for variants) is relatively trivial. I had to do this quite early as I was asked to make Jigsaws soon after vanilla. Use bit arrays also. Need two bytes for 9 numbers sadly but worth it for candidate spreads.
Best of luck with your solver and let me know how you get on
Friday 13-Sep-2024
... by: Ryan, England
Hope you are well.
Load Puzzle
I thought I would bring this to your attention, I hope it helps.
Please note the 32 in 7 starting on F7. The combinations of this cage all require a 1, 2 and 3. F7 can only be a 5 or 6 which means the 3s located in G7 and H7 can be removed.
Best Regards,
Ryan
Not sure how you get the 3s removed from G7/H7. I'm sure you're right though.
The solver really struggles with such large cages as the number of dog-legs gets beyond what I programmed so it might be giving up on this cage at certain points.
Monday 2-Sep-2024
... by: Graham, New Zealand
Refresh now [CRTL]+[F5], will say v 2.12
Many thanks for the reports, and I hope it works now
All the best
Andrew
Saturday 31-Aug-2024
... by: Phil, U S
Phil
Wednesday 28-Aug-2024
... by: Bellm, USA
Grader Scores 60:
https://www.sudokuwiki.org/sudoku.htm?bd=300000500000010968010008700900052070000090206070001009000009002130004000640000015
If clue "9" is removed from F9, it now scores 52:
https://www.sudokuwiki.org/sudoku.htm?bd=300000500000010968010008700900052070000090206070001000000009002130004000640000015
Tuesday 27-Aug-2024
... by: Wayne, Wales, UK
Load Sudoku: CLICK TO LOADI'd just like to highlight that while solving the above puzzle, it uses simple coloring - twice in a unit. The rule states - "that if any unit has the same colour twice ALL those candidates which share that colour must be OFF.
Step 18 - Simple Colouring
(RULE 2): Two 3s in a single unit (in Col 4) have the same color in cells E4 H4 - all yellow coloured candidates can be removed
Last candidate, 9, in F7 changed to solution
Last candidate, 9, in H4 changed to solution
Last candidate, 9, in J9 changed to solution
The alternative colour will be ON and the solution for that cell. " the solver removes all instances of the yellow 3's , but does not take advantage of the fact that all the purple 3's are true.
Wayne