Cave Sudoku
(Published on 10. July 2020, 12:39 by Phistomefel)
The usual sudoku rules apply. In addition, some of the cells must be colored gray so that all gray cells (the walls) are orthogonally connected to the edge and all other cells form an orthogonally connected area (the cave).
Each yellow marked cell is inside the cave and the digit inside indicates how many cells belonging to the cave can be seen in horizontal and vertical direction. The clue cell itself is counted for this number and walls obstruct the view. The digit in some of the clue cells has yet to be determined and not every possible clue cell is given.
In an orthogonally connected area of gray cells no digits may repeat. There may appear 2x2 blocks of gray cells and of non-gray cells.
Here is an example on a 6x6 grid for illustration.
Here is a small hint, which helped me a lot to understand the basic logic for cave puzzles:
In every cave puzzle it is possible to draw a slitherlink around the cave (the cells not colored gray). This helps to exclude some constellations right away.
But now for the real puzzle. It is also available online via f-puzzles and Penpa-Edit. Have fun solving!
Solution code: 1st and 7th row
Comments
on 11. October 2023, 10:53 by Piatato
Lovely puzzle! Here's a new penpa link: https://tinyurl.com/2x3red4t
on 17. September 2023, 08:48 by CrazyCrypticC
Fascinating and wonderful logic.
on 5. November 2022, 14:43 by KNT
Awesome, thanks phisto :)
on 9. November 2021, 18:08 by dissonance
Very nice puzzle, thanks for sharing.
on 21. August 2021, 18:46 by Phistomefel
Added tag "Online solving tool".
on 21. May 2021, 16:13 by Vebby
Great puzzle! I found it easier to solve upon replacing the yellow colour with one-cell cages to indicate line-of-sight restriction, so that I could shade all cave cells one colour. Link to solve on Penpa Plus with this change: https://git.io/JsM36
on 30. January 2021, 17:41 by wydadman
رائع يا فيستوميفيل!
on 5. August 2020, 16:32 by glum_hippo
Die Regeln bedürfen m.E. keiner weiteren Erläuterung... sie sind nur deswegen leicht zu missverstehen, weil da so viel los ist! Aber wer Höhlenrätsel gemacht hat, wird irgendwann den Leitfaden finden (inkl. ffricke, der sich ja sehr gut auskennt)
on 5. August 2020, 16:02 by Phistomefel
@Nylimb: Thank you for the nice feedback and the perseverance!
@ffricke: Dankeschön! Die Regeln für das Rätsel sind auch ein wenig überbordend, da kann das leicht passieren. Im Nachhinein bin ich auch nicht mehr so glücklich mit der Unterscheidung zwischen Wandzellen, Höhlenzellen mit Hinweisen und Höhlenzellen ohne Hinweise.
on 5. August 2020, 09:56 by ffricke
Wundeschönes Rätsel, ich bin zunächst nur daran gescheitert, weil ich die Regeln nicht richtig gelesen habe.
on 25. July 2020, 17:49 by Nylimb
I had to start over about 3 times, because I'd made errors that led to contradictions. It was very satisfying to finally finish it without an error. Thanks for a great puzzle!
on 13. July 2020, 15:24 by henrypijames
@MartinR: You can simply use different colors. I used blue for clues (overrode yellow becaus blue is more visible) and green for non-clue cave, as well as red for walls.
on 12. July 2020, 18:33 by Circleconstant314
I'm so glad that the English description was simply missing the rule about walls needing to contain distinct digits. I was worried that this would be the first puzzle of yours that required heavy bifurcation but that rule clarification really smoothed out the solve. What a brilliant idea for a Sudoku, thanks for sharing this one! :-)
on 12. July 2020, 17:01 by MartinR
Wonderful puzzle.
Thanks to @Narayana for that video link, that was really helpful as had not come across cave logic before.
One minor comment - when solving I found it hard to keep track of the inner clues as if I marked all the inner cells in one colour the highlights disappeared and having two colours for the same area (inner) didn't make the border between outer/inner as distinctive for me
This might be just me, but for my use I created an alternative penpa link where the inner clues were circled and unaffected by shading which I found clearer - for me at least:) - as could use one inner colour and not lose the clue locations. If interested, link is https://tinyurl.com/y44sahzv
on 12. July 2020, 09:11 by Phistomefel
Clarified rule.
on 12. July 2020, 09:05 by Phistomefel
Thank you all for the wonderful feedback and apologies for leaving you with an unsolvable puzzle by forgetting to add the no-repetition rule in the english description. I guess in the future I should leave a puzzle unpublished for a day or so and then proofread it once more before I activate it.
on 12. July 2020, 07:51 by Mody
Großartig :)
on 11. July 2020, 18:36 by Madmahogany
Another great one!
on 11. July 2020, 18:35 by glum_hippo
Nervenaufreibend, aber das ist keine Kritik! Wunderbare Idee
on 11. July 2020, 14:59 by henrypijames
Wonder how long it takes for this one to get onto CTC. My bet: within a week.
on 11. July 2020, 14:43 by anu_chakravarti
Totally missed the walls having unique numbers rule and kept staring at the puzzle for way too long. Nevertheless absolutely delightful puzzle!
on 11. July 2020, 12:43 by Jesper
I did wonder yesterday at why the small example did not seem to have a unique solution. But unfortunately, I shrugged it off, and tried to solve the puzzle, oblivious to the missing restriction. It was a lot more fun today, having found out about that restriction. Great puzzle!
on 11. July 2020, 11:57 by henrypijames
Oh wow, that is a huge additional restriction, as it dramatically limit the length of any wall right away.
Guess I should make it a habit to always read both the English and the German descriptions every time. There have been discrepancies in a number of puzzles here (most deadly, the solution code on one occasion).
on 11. July 2020, 11:18 by marcmees
got stuck in a dark cave until the additional rule gave some extra light. nice concept. thanks
on 11. July 2020, 07:10 by Phistomefel
@cdwg2000: Thanks a lot for your questions! I simply forgot to add the no-digit-repetition rule in the english description. I am very sorry for that!
on 11. July 2020, 07:09 by Phistomefel
Missing rule added in english description.
on 11. July 2020, 06:49 by r45
Tolles Rätsel!
on 11. July 2020, 03:14 by cdwg2000
The rule description should be added: in the gray area connected orthogonally, the numbers cannot be repeated.
on 10. July 2020, 21:27 by Narayana
@Big Tiger
What you describe is what Simon (CTC) calls "Checkerboard Logic." This pure cave video https://www.youtube.com/watch?v=Jjs_xA1sDCg was very helpful to understand how Cave works.
on 10. July 2020, 18:54 by Big Tiger
Can two open spaces or walls touch each other diagonally? For example, could you have Wall in R3-C3 and R4-C4, with open spaces in R3-C4 and R4-C3?
EDIT: Hmm, I THINK I just answered my own question in further experimenting, but your answer will help clarify...
@Big Tiger: This diagonal constellation is indeed impossible. And I found it easier to spot this knowing that there has to exist a path around a cave (then two pieces of the path would touch each other diagonally which is impossible).
*** Welll, that's what I thought, which is why I'm stumped. I'm creating a short video to explain my perplexity better than I could in text. I'd love to know where either I'm misunderstanding something or my logic is failing me. As soon as it's posted I'll link you to it.
on 10. July 2020, 18:17 by GuessIt
Do not click "solve" on f-puzzles once you're finished. You will regret it. I certainly do. (It messes with all the digits somehow and removes everything else, including coloring)
on 10. July 2020, 16:00 by Phistomefel
@henrypijames: Yes, that is right, an uncolored given digit can be anything. The walls can also contain 2x2 blocks. Now, I see that I could have chosen a better example. Thanks!
on 10. July 2020, 14:51 by henrypijames
An uncolored given digit can be either wall, non-clue cave, or (possible) clue cave?
And the wall doesn't have to be one cell wide, meaning it can contain 2×2 blocks?
