Kuromasu by Thomas Snyder

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Kuromasu 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: Almost Doubled

Author/Opus: This is the 190th puzzle from Thomas Snyder, aka Dr. Sudoku.

Rules: Shade some empty cells black so that each number indicates the total count of white cells connected vertically and horizontally to that number including the numbered cell itself. Black cells cannot share an edge, and all white cells must belong to a single connected group. Or see this example:

Kuromasu by Thomas Snyder

Answer String: Enter the length in cells of each of the white segments from left to right for the marked rows, starting at the top. Separate each row’s entry with a comma. This example has the key “14,221”.

Time Standards (highlight to view): Grandmaster = 2:00, Master = 2:30, Expert = 5:00

Solution: PDF

Note: Kuromasu is a new puzzle for us this week and we are curious to hear what you think of it.

  • My solve (6:42, including a reset after 3 minutes or so), saved for posterity: http://solvewith.us/replay/40-0e4ff2c9

    Spoilers, obviously. Should I avoid posting these?

    Hmm, sharing them may also violate the “-NoDerivs” clause in the CC license, so that’s another potential reason not to do so (until/unless I get permission.)


    • chaotic_iak says:

      I believe people don’t really care about things like that, although ya, the No Derivatives clause might be a little problematic here.

    • drsudoku says:

      If it is just a rare posting of a solution, that is acceptable to me. Because we have rewards including solutions and walkthroughs as a bonus to encourage patronage, anything more frequent would be a concern.

      That said, I’ve been intrigued by what you are doing with solvewith.us and do mean to think through the right policy to allow some content to be shared with online solving tools without losing the visitors that support our puzzlemakers.

      • John B says:

        IMNSHO IANAL, NoDerivs would ordinarily prohibit regular posts but a one-time post would be covered by illustrative fair use. In between you have a gray area best solved by negotiation.

        I am working tentatively on a platform for other types of puzzle to compare solutions with hashes to find out if your solution is the same as those of others without revealing solutions you haven’t received yourself. This is better for word and trivia puzzles but for logic it might be standardized to allow solvers also to compare their views on important cells and paths publicly but without spoilers.

  • Neelix says:

    That was interesting. Felt like a combination of Hitori and Cave.

    That said I think it’s almost close enough to Cave to call it a variation…

    – Neelix

    • John B says:

      Cave is a variation of Kuromasu. The variation is not that big; most of the solving techniques are the same (making Kuromasu a good site add), but Kuromasu forces more white squares and Cave forces more black.

  • chaotic_iak says:


    Nice addition to the site. Also, I apparently can’t see some rather basic deductions at the right, so keep the Kuromasu coming!

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