Dr. Sudoku Prescribes #102 – Cave

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Cave by Thomas Snyder


or solve online (using our beta test of Penpa-Edit tools; use tab to shift between shading mode and the linex mode where left click+drag draws lines and right click marks X’s)

Theme: 3456

Rules: Standard Cave rules.

Answer String: Enter the length in cells of each of the cave segments from left to right for the marked rows, starting at the top. Separate each row’s entry with a comma.

Time Standards (highlight to view): Grandmaster = 3:15, Master = 8:00, Expert = 16:00

Solution: PDF

Note: Follow this link for other classic Caves. If you are new to this puzzle type, here are our easiest Cave Puzzles to get started on.

  • chaotic_iak says:


    It was not really flavored, pretty plain overall, but the trick used takes sufficient time to discover. And I’m not sure whether trying all possibilities for a number is considered a trick. Or I miss something.

    Not really eventful, but a nice aesthetic theme. Sadly that 445 group at the left exists; it should have been a same-digit group of clues.

    • drsudoku says:

      If you would have liked more than 1 solution, I could have used a better “themed” group than 445. I originally had some version of 366 or 336 on the other side but needed to go to the three sixes to get a nice single solving puzzle.

      This uses “reach” a lot, and in one place on the left side near that 445 in a somewhat unfamiliar way. You should not need to try all possibilities for any number.

      • hagriddler says:

        I guess I understand what you mean by “reach”, but could you give a (somewhat formal) definition ?
        I used a lot that the cave segments must escape to form one region, and that the unmarked cells must escape to the edge.
        Is that what you mean by reach ?

  • Darklady says:

    Is there any particular reason you’ve switched to using dashed lines for Cave puzzles? I had been solving them by opening them in an image editor and using the fill tool to color squares for inside/outside, but with dashed lines I can’t do that anymore. If there’s another method that’s as easy I’d be happy to use that instead, but I don’t know of any.

    • I can still do that with dashed lines.I guess you didnt try,presuming like me that it wont work,or if you did, I am not sure why it didnt work for you.The reason he switched is to make it look like a workable loop puzzle.

    • drsudoku says:

      Flood fill will still work as there is a slightly gray line drawn between the dark black lines as in our Fillomino formatting.

      There were requests for a style that made drawing borders easier so I’ve switched to dashed lines.

      • Darklady says:

        Aha! On the previous Cave, I’d used printscreen to copy the image over to my editor, and I hadn’t realized that the inline image was slightly shrunk – the resizing had destroyed the slight grey line, so that’s why it wasn’t working for me. And then I didn’t actually try this one, since it looked the same as the previous one.

        It’s working fine for me now. Thanks for the help, and for the great puzzles.

        • drsudoku says:

          It’s good to know your experience with our earlier image which I had resized by html. We can definitely try to avoid this in the future which should limit problems when you don’t copy the image over directly.

  • mokrton says:


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