This Sudoku puzzle has me scratching my head.

The Sudoku Analyzer solves it step by step, giving clues along the way. Which is to say, it is not one of those occasional Sudokus which can only be solved in trial-end-error guesswork manner. But at a couple points, the Sudoku Analyzer gives very complex hints where simple hints are possible. This is not according to design. Then, in at least one very complex hint, several secondary hint steps are omitted, without which the complex hint is incomplete.

What's especially baffling is that these problems seem to be unique to the grid pictured. Other Sudokus, even much more complex ones, are still solved quite methodically, logically, and correctly. What's different about this particular Sudoku?

This blog post is a heads up. If you have encountered similar symptoms in other Sudokus, or if you have any insight into what's going on with this one, I would appreciate a heads up from you in return.

**15 Feb 2020 Note:**

Have fixed (I think) the second problem mentioned above, in which secondary hint steps were omitted. Sometimes just need a good night's rest to see things with fresh eyes. Still have to address the first, less serious problem, in which simple hints are passed over in favor of more complex hints. Stay tuned.

**21 Feb 2020 Note:**

Have done little to address the aforementioned problem of giving overly complex hints. For one thing, this appears to be an oddity that occurs quite rarely, and, as noted above, is not a serious bug. Furthermore, upon studying it, it seems to be inextricably linked to the inherent complexity of Sudoku itself. I may write a longer article or web page examining this interesting phenomenon. Right now, am declaring this report closed, the bug resolved.

**22 May 2020 Note:**

Recently encountered and fixed another, unrelated bug in the Sudoku Analyzer, a very difficult bug to track down. Briefly, it involved an occasional, random failure of the server-side binary executable due to its failure to properly align the stack pointer prior to calling a C function from an assembly routine, as is required on the 64 bit BSD server. Am sure everyone reading this understands exactly what this involves. ;)

Anyway, it's worth mentioning here because the long process of troubleshooting and correcting the random binary bug exposed another much less serious anomaly, which, now corrected, results in avoiding, in at least some advanced Sudokus, the above mentioned oddity of overly complex hints. But only in some cases. As the previous note also mentions, the apparent simplicity of Sudoku masks an inherent complexity that may be impossible for human brain nor computer program to fully master.

0 comments | rev. May 22 2020 7:59pm |

The Great CyberJerry Sudoku Challenge has been answered

Wed August 1 2018 8:10pmSudoku

7-plus months ago this blog unveiled the great CyberJerry Sudoku Challenge. (See Jerry's Blog article of Dec 14 2017 for details.) In brief, the challenge is to provide a step-by-step analytical solution to a Sudoku that has CyberJerry's Sudoku Analyzer stumped. To meet the Challenge, the Sudoku must qualify thus:

- 1. The Sudoku has exactly one solution.
- 2. CyberJerry's 'Analyze' button reports that the Sudoku cannot be rated, and at some point the 'Hint' button fails to provide a Hint.
- 3. You can describe a step-by-step analytical way to solve the Sudoku. You need only do so at the point(s) where the Sudoku Analyzer fails to provide a Hint. Note that this must be deductive logic, not a trial-and-error guesswork method.

That is to say, the challenge is to find someone in SudokuLand whose brain possesses greater Sudoku skills than my Sudoku Analyzer. A tough challenge indeed, but someone has stepped forward and has met the challenge. The challenger's name is: Jerry DePyper.

Yes, that's correct. I myself have found a Sudoku for which the CyberJerry Sudoku Analyzer cannot give step-by-step hints **and** for which Jerry the human can provide the analytical solution. Not sure if I should feel proud or humbled that my brain can still out-think my brainchild, the CyberJerry software.

Whether for pride or humility, the task for me now is to improve the logic inside the Sudoku Analyzer, to provide a step-by-step software analytical solution to this Sudoku and perhaps others like it.

The original challenge remains to you, and any other Sudoku fanatics, to give an analytical solution to a Sudoku which has the Sudoku Analyzer stumped. You may start with the one I've found. Click on the Sudoku grid above and you will see the Sudoku in question, at the very step that has the Sudoku Analyzer stymied. Click the 'Hint' button; it fails to give a hint.

I will not publish my brain's analytical solution until I can incorporate my methodology into the Sudoku Analyzer's logic - until clicking 'Hint' at that point gives you a real deductive way to solve a cell. In the meantime, if you can give me your brain's solution to this Sudoku before I can 'teach' the Analyzer, that will also qualify as a successful challenge, and your name will be published as a successful CyberJerry Sudoku Challenger. The race is on.

**8 Aug 2018 Note:**

Only took me a week to 'teach' the aforementioned technique to the Sudoku Analyzer. Well, it wasn't so much that it needed to 'learn' a new technique; a little looping bug had to be corrected in its existing logic. Details upon request. The proof is that you may now click on the above Sudoku and see that, whereas the Sudoku Analyzer was formerly stumped at that step, it now gives you an analytical hint to solve one cell, and thence go on to solve the entire Sudoku.

But don't go away; there are sure to be other Sudokus that the Analyzer cannot solve. So the challenge is still on. Analytically solve a Sudoku that has my Sudoku Analyzer stumped, and you win.

3 comments | rev. Dec 4 2018 12:34pm |

After several years of development, testing, debugging, and improving the strategies, I am ready to proclaim that my Sudoku Analyzer is the best on the web, that it can analyze and give a step-by-step solution to even the toughest Sudoku.

**Please note that this does NOT entail simply giving a solution, but in providing a step-by-step analytical method to solve.**And so today I am unveiling the great CyberJerry Sudoku Challenge.

To be sure, I am still discovering some rare Sudokus for which the CyberJerry Sudoku Analyzer cannot give step-by-step analytical hints. But for those Sudokus, neither can anyone else. Or so I claim.

Therein lies the challenge: to provide a step-by-step analytical solution to a Sudoku that has CyberJerry stumped. To meet the Challenge, your Sudoku must qualify thus:

- 1. The Sudoku has exactly one solution.
- 2. CyberJerry's 'Analyze' button reports that the Sudoku cannot be rated, and at some point the 'Hint' button fails to provide a Hint.
- 3. You can describe a step-by-step analytical way to solve the Sudoku. You need only do so at the point(s) where the Sudoku Analyzer fails to provide a Hint. Note that this must be deductive logic, not a trial-and-error guesswork method.

If you think you can meet this challenge, navigate to CyberJerry's Sudoku Analyzer page. Enter the contents of your Sudoku in the grid there, and then click the 'Analyze' button to see that (most likely) CyberJerry can indeed rate the Sudoku in question and give hints for every step. In the (unlikely) event that CyberJerry is stumped (per point #2 above), you may proceed to the Challenge by clicking the hyperlink marked 'Sudoku Challenge'. There you will be able to describe your analytical method per point #3 above.

I promise to publish any successful challenge and publicly acknowledge the challenger's superior Sudoku skills. I reserve the right to likewise publish any failures.

0 comments | rev. Dec 4 2018 7:58pm |