Dr. Sudoku Prescribes #39 – Tapa
or solve online (using our beta test of Penpa-Edit tools; use tab to shift between shading mode and the composite Yajilin mode where left click marks cells, right click marks dots in cells or X’s on edges, left click+drag draws lines.)
Theme: Greek Cross
Answer String: Enter the length in cells of each of the shaded segments from left to right for the marked rows, starting at the top. Separate each row’s entry from the next with a comma.
Time Standard: Tapa Grandmaster = 1:30, Master = 4:30, Expert = 9:00
Editorial Note: The solving path on this puzzle is quite narrow to start, but it is recommended that you find it instead of randomly guessing.
Solution: PDF
4:56 just missed Master level.
Nice one, made me remember Serkan’s CTC.
Awfully slow at 4:27,after losing myself to guesswork at many points. Beautiful path, but really saw a lot of serkan style flow here,especially around the border.Really next to impossible for anyone,except maybe if you have a fruity nickname, to resist random or learned guessing,being that it has such a cunningly tough path. Thanks for a good tapa lesson.
I hope you will tell us the intended solving path later in the week. All puzzle solving boils down to making a hypothesis and testing it. More advanced solvers do this mentally, while beginners make guesses with pencil. Some guesses are more productive than others – leading to significant progress on the puzzle whether the guess is right or wrong (of course, assuming a unique solution). I found the solution within the Master time by choosing a productive place to guess, but I have no way of knowing whether that was your intended path.
Most people will explore the perimeter of this puzzle where I do not believe there are any *simple* deductions. You should start at the very center, and see if you can reason something out because of some of the surrounding clues. This is the needle in this haystack.
I started with the clues at R4,C2 and R4,C4. That seemed to unlock everything. But I did have to give in and grab a pencil!
If you have not attempted this tapa yet,you might not want to read the rest of this comment as I am showing a logical start(hopefully the intended break-in) :
Understand the interaction between the four clues at R4C2&4 and R6C2&4.(33) cannot be accomplished by shading both R5C2 and R6C3 due to the clue (113) on top of it.So you can safely shade in R5C1&3 and R7C1&3.
Now,see how (113) and (122) constrain your next move.If you shade R5C2,that block of 3 shaded cells will be isolated from the rest of the wall, as otherwise you would be violating (113) or (122).
This reveals the complete the left-most column.Continue round the top-left corner.(122) gets its ‘1’ at R3C3,so you know that R5C4 must be shaded to (122) its both 2s.
Build the rest of the wall from the remaining clues left-to-right.
I think there’s an easy enough break in at R5C5 alone, which might or might not be intended. I assume it was intended since the placement of the clues seem to point to it. I used that and it was really easy after that. Beat the Grandmaster level easily. I’ve been using these crowded configurations for difficulty level increase a lot recently myself, so maybe that played a part in recognizing it quickly.
Ah, I just saw the reply from the author that that was the intended find 🙂
I definitely did it the slow way, but yeah, I think Thomas was not at all kidding above when he suggested “the very center” — r5c5 gives a really nice break-in point.
I worked it from the limited 33 options. I wish I had recognized the center prize as I see how quickly so much of the puzzle would have flowed from identifying the R5C5 cell as blank. Good lesson for future Tapas, which I am just starting to advance on.
Thanks for a great puzzle 9and lesson).
TheSubro
Without that observation: 8:22. With that observation (and trying to act accordingly ignorant): 2:35.
I am a snail and acted innocently ignorant. But the difference is just so huge.
I didn’t use the R5C5 break in (although now that it’s pointed out, I agree that it’s very elegant), and I don’t think my approach requires (unreasonable) guess and check beyond looking at and ruling out the possibilities for one clue-square at a time.
Now, I wasn’t particularly speedy either.
Umm, yeah, didn’t use that break in (though I really like it now that I see it), I also used the 3/3 clue and worked generally left to right.
I must admit I used a quite different path starting from the 3/3 and 1/1/3 and 1/1/2 to the left.
In hindsight I see why r5c5 breaks the entire puzzle (with a little help from r1c4, r3c6 and r8c8).
The key question for me would be HOW to recognise that crucial spot.
If you know to start at that point the puzzle becomes much easier with indeed a narrow path to the end.
My hope was that either the 122 or 22 clue would draw attention to the middle since either clue has limited reach and cannot escape around the side. Once you see one and then find the other diagonally, you know how to get going. Certainly an Advanced Tapa search technique, but not one that is too unreasonable. 122 clues almost always draw my attention for some reason in human-constructed puzzles.
Fantastic puzzle, Thomas! I really enjoyed this one. I missed the super-elegant break-in, (instead found a less elegant break-in with constraints around the 3/3 clue as others mentioned above).
I really appreciated the “editorial note” encouraging solvers to look for the intended narrow-path start. Similarly, another recent puzzle (the Series of Series Outside Sudoku), included an explanation of an impressive numerical theme. I would have totally missed that theme without that explanation.
So I like that the puzzles from your introductory period often included a sentence or two of explanation, (to help the solver appreciate the theme or the solving path). More recent puzzles seem to miss that. I remember the first time I saw “Theme: Logical” I was really puzzled as to what that even meant. Now, I understand that a puzzle author wouldn’t want to give too much away about the solving path, but even just a little explanation like “Theme: Besides symmetry, an exclusively logical theme that will be revealed during the solve.” is helpful, (this was the wording from Dr. Sudoku Prescribes #5″).
While I’m on the topic, I usually work from the PDF files, and they don’t include these sentence or two of explanation. They would be nice to have there as well.
-Carl
PS. I know I have submitted puzzles without explanations, (as I was following the standard as I saw it). I’ll be happy to start add explanations like these to any future submissions.