Dr. Sudoku Prescribes #72 – Nurikabe

Nurikabe by Thomas Snyder


or solve online (using our beta test of Penpa-Edit tools)

Theme: Our 72nd prescription. But who’s counting?

Rules: Standard Nurikabe rules.

Answer String: Enter the length in cells of each of the black segments (the unnumbered, connected “ocean”) from left to right for the marked rows, starting at the top. Separate each row’s entry from the next with a comma.

Time Standards (highlight to view): Grandmaster = 7:30, Master = 10:30, Expert = 21:00

Solution: PDF

  • Jack Bross says:

    Very nice aha! moment in the middle of the puzzle when you figure out what the 27 needs to do, after which everything sort of snaps neatly into place.

  • Ravi says:

    Excellent puzzle. This time I made it to the Master level :D.
    At first the layout looked very scary to me, but once I started it I just concentrated on 27, that is it everything just fell into place.

  • Scott Handelman says:

    8:30 with a 10-month old in the room trying to kill herself, so I’m going to consider that a handicap, subtract wrangling time, and give myself an 8:00.

    Fun puzzle. I’m happy that the 27 was mostly a minimal reach island, so I didn’t have to worry about where it might twist off on a different path. Also, the two 7s at the top right ended up doing exactly what I assumed they’d do, so I didn’t have to put much work into wiggling my way into the final solve, it just fell into place.

  • Aaron Chan says:

    That was a difficult puzzle, compared to the rest of the week. Like the others said, happily nothing too weird happens to the 27, but there are still some small tricky points aside from that.

  • Projectyl says:

    I didn’t notice it as I was solving, but this thing bears an eerie resemblance to Trogdor.

  • Anuraag Sahay says:

    9:00. 27 came last in my solve,with some counting involved.I would have timed 6:00 if not for the tweaking to make 27 work.So I liked the initial part (yes, the 2s were critical),but the 27 thing became a chore.

    • James McGowan says:

      You would have been 20% faster than the best solvers in the world? Well done. 🙂

      • Anuraag Sahay says:

        This is a shading puzzle and I dont know how slow/fast I would be with pencil and paper.I struggle with marking (shading) on paper.

  • skynet says:

    ~37mins .
    Very enjoyable solve.No 2*2 rule,all black sqaures connected , only some numbers can reach some places were all equally important in the solve!!

  • chaotic_iak says:

    07:48 heh.

    Well, I won’t repeat about the 27, and I decide to comment more on the large-scale connectivity of the ocean. The puzzle definitely requires a lot of global-scale logic. After the “preliminary” work with the small numbers around the top, the puzzle has effectively a new border, and the ocean must wiggle around that border. That, and how the large islands resolve, are the major points of the puzzle.

    The layout is not symmetrical :< But I suppose that is offset by the unusual logic required, so I'd say that this puzzle is very well-made. But then this is Grandmaster Puzzles.

    • Avatar photo drsudoku says:

      No requirement for symmetry in a Nurikabe! I actually find with Nurikabe and with Masyu and a few other styles that are sometimes symmetric and sometimes not that when the puzzle is small (say 12×12 or smaller), symmetry is a good idea for puzzle balance. Once the puzzles get bigger, symmetry is actually a bad idea as it can compromise particular kinds of themes.

      • Jack Bross says:

        One of the things I like about both Nurikabe and Masyu is when the real solving theme is not obvious from the layout. Both those genres tend to a certain amount of hidden structure, and sometimes those themes are more fun to me than obvious themes. (Put another way — the connectivity/reach part of this puzzle was more interesting than the mere “2’s and 7’s” of it, and a lot of puzzle constructors would have been satisfied with just the numerical theme).

      • chaotic_iak says:

        Well yes. Perhaps I have too much of MellowMelon’s puzzles (which tried to have symmetry everywhere).

  • Arren says:

    Haven’t been keeping track of my own time, but struggled with this one on my first pass for at least half an hour. (Also while at work, so no lack of distractions) Set it down, and came back to do it from scratch a few hours later and finished it easily.

    I’m not sure what the difference was, but something on the upper right clicked that hadn’t in my earlier attempt.

  • Zotmeister says:

    My thoughts when I counted and discovered the 27 could reach the upper-left corner: “REALLY, Thomas?!” Thankfully, actual unreachables were close by and the result was a lot of fun. – ZM

  • hagriddler says:

    I don’t know why I kept thinking the ‘ocean’ cells must round the lower left corner, (so the 27 travels in col 2 for a while). That left me with two seperate ‘rivers’ instead of one ocean… So it took me forever to solve this one… After rejecting the perfect good solution (apart from my error in the lower left corner) I kept trying to connect those rivers somewhere in the middle of the grid (to no avail of course), until I finally spotted my error. So once again I have to say : silly me 🙂

  • Giovanni P. says:

    Definitely a puzzle with some “feel” involved in the solve for me. I intuited how the corner 7s could go, along with the general placement of the 27 island. I guess what I call intuiton could be called “global logic” by others, but that “this placement feels correct” vibe I get from Nurikabe (and perhaps Numberlink) is an interesting feature of the genre.

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