Normal sudoku rules apply.
Coral Variant : Shade some cells in the grid. Those cells are part of the coral. The rest of the cells are water. All coral cells are orthogonally connected. All bodies of water are orthogonally connected to the edge of the grid. No 2x2 is entirely water or entirely coral.
Digits do not repeat within cages, and the sum of the coral cells within each cage must equal the sum of the water cells within that cage.
The digit in a circle gives the number of cells within its cage which match its color (coral or water). The total includes itself.
Have fun, leave a comment if you enjoy the puzzle!
PS: I stream solving sudoku like puzzles three days a week. You can check out the channel, as well as some videos I have made about setting puzzles, at my YouTube channel here.
Solution code: The coral cells from row 7 left to right
on 19. September 2023, 00:13 by twototenth
Really excellent, if mildly brain-spraining for me.
on 10. July 2023, 04:23 by Calvinball
@henrypijames I believe it has so many solves because it was featured on CTC. There's probably a lot of people who "solve along" with Mark and Simon.
on 1. July 2023, 22:34 by henrypijames
According to the CtC counter, this puzzle has been solved 1600+ times. How is that possible?!
on 28. June 2023, 23:56 by Phynubis
Absolutely stunning! Fantastic puzzle!
on 28. June 2023, 19:38 by DaniK
Very cool puzzle with a great flow. I really had a great time solving it.
on 28. June 2023, 17:27 by Christounet
Enjoyed exploring that reef very much ! Thanks :)
on 28. June 2023, 11:37 by peacherwu2
Tersest code ever!
on 28. June 2023, 05:55 by zhall12570
A masterful puzzle as per usual. Loved every minute of it.
on 27. June 2023, 18:43 by Mennoo_
@Niverio I don't agree with that. I did find the break in tough, but not too hard and very quickly ended up with digits.
But after that it was a real challenge to find the right spot which was restrictive, be aware of all the possibilities and eliminate them so you could make more progress, which I did find harder than the actual break in.
Regardless, very nice puzzle and a joy to solve. Took me a lot of time but in the end managed it. Love those puzzles were for every small step in solving a good logical reasoning is needed.
PS: In the end colored the water as aquablue and the coral the multicolor of yellow-orange-purple to make it really look as a coral reef :P
on 27. June 2023, 02:40 by sanabas
@zetamath I have a notification that you replied as an edit on my last comment, and the timestamp is the same as when I edited it myself, so I think I've inadvertently deleted your reply 30 seconds after you made it, without ever seeing it. My apologies.
[That's funny! I was just saying I was glad at the end of all of it you thought it was worth your time! -z]
on 27. June 2023, 01:42 by wand
very cool ruleset! had to break out the post it notes for this one
on 27. June 2023, 00:53 by sanabas
@Bansalsaab thanks for the offer, I've now found my mistake and edited this post. From your comment, I think you made the same mistake as I did, eliminating a digit from the T-cage in r6c6 because I assumed (wrongly) that it must split a certain way. I even noticed in my 2nd attempt that splitting it that way walled off the water, which is what caused my problem in attempt 1, but still stuck with my assumption.
3rd attempt from scratch was much smoother. Fantastic puzzle, and it has now given me literally hours of entertainment. :D
on 26. June 2023, 22:46 by karlmortenlunna
Very nice puzzle! It took a long time for me to get my head around the coloring, but after I finally figured it out it was a smooth solve.
on 26. June 2023, 20:31 by steveire
Nice puzzle!
on 26. June 2023, 19:05 by twobear
Great puzzle! I also appreciate the relatively short solution code :)
on 26. June 2023, 18:34 by Myxo
Beautiful! The most non-zeta break-in I have seen :D
on 26. June 2023, 18:33 by Niverio
This puzzle is a 5 until you place the first digit. After that, it is consistently 3.5. Very enjoyable regardless!
on 26. June 2023, 17:24 by bansalsaab
Beautiful puzzle. I made a mistake in first try with the cage in boxes 5 and 8. Retried and found my mistake and solved it.
@sanabas if you could show me your progress somewhere, i can help.
on 26. June 2023, 15:06 by sanabas
I got 2/3 of the way through only to discover I'd broken the puzzle. Rewound a bit but couldn't find where mistake might be, so started from scratch. And then I got 2/3 through and again broke the puzzle in an identical fashion.
I've clearly done something wrong along the way, but it's very frustrating not to be able to find it. And every step has felt like it made sense, with very satisfying logic to find.
on 26. June 2023, 14:39 by Piatato
Fun puzzle, thanks!
on 26. June 2023, 08:15 by Playmaker6174
@MonsieurTRISTE: all groups of water cells connect to the 9x9 border, but it’s not necessary that all of them must connect to form a single group.
on 26. June 2023, 06:46 by MonsieurTRISTE
I must have misunderstood the rule. All water cells need not to be orthogonally connected. Instead, every connected component of water cells must be connected to the edge of the grid.
on 26. June 2023, 04:27 by MicroStudy
looking forward to anemone
on 26. June 2023, 03:50 by Calvinball
Fun fact 1: In sailing the term "reef" is used in heavy winds when you partially lower your sail to reduce the exposed surface area as a way of controlling your boat speed.
Fun fact 2: This puzzle is fantastic. Thanks Zeta!