Puzzle 190 (Masyu) [Where is Black Cells?]

This is a Friday Masyu puzzle, with a twist. All of the black circles in this puzzle are invisible. There is exactly one black circle in each row and column. Furthermore, these ten invisible black circles are all of the black circles the puzzle could possibly have. There is nowhere else in the solution path where the path turns and goes straight at both ends. (equivalently: if you find a space in a row or column where the path turns and goes straight at both ends, the path cannot do that anywhere else in that row and column.)

Puzzle 191

Puzzle 191

Note that the variation name in the title is just poking fun at nikoli’s humorous Engrish name for Kuromasu/Kurodoko; this variation has nothing else to do with that puzzle.


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5 Responses to “Puzzle 190 (Masyu) [Where is Black Cells?]”

  1. Mark Fox Says:

    Excellent! There were so many ways to get unstuck with this one that it didn’t seem like a Friday difficulty. (i.e. knowing there was only one black circle per row/column let me switch between Maysu/sudoku strategies when I got in trouble)

    Now I have to stop and get some sleep. Thanks for posting all these.

  2. MellowMelon Says:

    I suspected this one may not have reached Friday level… I might have been better off switching it with yesterday’s. But in my test-solving I always felt like there were several steps that were far from obvious, especially when cleaning up the end. I think in general I am overestimating the difficulty of puzzles this size; probably the reason they aren’t perceived as difficult is that the search space is so small. Thanks for the comment.

  3. motris Says:

    Very nice puzzle. I don’t read too much into the difficulty ratings in general, but I also have had problems in the past with my (Tho)masyu variants where I thought a gimmick like the either/or black/white would be harder than it proved to be. This gimmick worked out rather well.

  4. MellowMelon Says:

    Glad to hear the twist worked out well from a solving perspective… it didn’t on the other side. My first attempt at constructing this was like stepping through an impenetrable minefield, and eventually I scrapped it and drew the solution path first before any clues, which proved tricky to do by itself.

    If I do this one again, there’s probably going to be a slight change to the rules somewhere so I can keep my sanity.

    Thanks for the comment.

  5. TheSubro Says:

    Its a real solid puzzle, and a good variation.

    Admittedly not a “Friday level” but it got everyone thinking and considering good solving techniques. Well done.


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