Modular Yin Yang
(Published on 17. January 2026, 03:20 by yttrio)
Rules:
Normal Sudoku rules apply.
Yin Yang: Shade some cells such that all shaded cells are orthogonally connected, all unshaded cells are orthogonally connected, and no 2x2 area is fully shaded or fully unshaded.
A digit in a cell with an arrow counts the total number of shaded cells seen in the direction of the arrow (not counting the cell itself).
For every 2x2 area in the puzzle, no two shaded cells can be from the same modulo 3 set. In other words, in any given 2x2 area, there can only be one shaded cell with a digit from [147], one from [258], and one from [369].
6x6 Example:
The image below shows a sample 6x6 puzzle and solution with the same rule set.
Play the example 6x6 in SudokuPad.
Solution code: Digits in shaded cells in row 2 (left to right) followed by digits in shaded cells in column 2 (top to bottom)
Comments
on 19. January 2026, 22:17 by dzamie
Cool! The break-in made me really glad that I've already solved a number of yin-yang puzzles, since it got me a lot of shaded/unshaded cell pretty quickly that I wouldn't have known otherwise.
on 17. January 2026, 20:05 by firespire
I didn't tune into the "key fact" until later but still very enjoyable puzzle.
on 17. January 2026, 18:48 by Fool on Hill
Lovely puzzle - yet more fresh logic. I tuned in to a key fact quite quickly, which helped a lot.
on 17. January 2026, 18:04 by Exigus
Very nice construction, had a great time solving. Thanks!
on 17. January 2026, 16:24 by Ambrose
Wonderful setting and fun interactions!
on 17. January 2026, 15:54 by mihel111
Yin Yang puzzles have something more. That more is yttrio. Thanks a lot.
on 17. January 2026, 14:21 by marcmees
Outstanding puzzle. Thanks
on 17. January 2026, 12:56 by Franjo
Thank you very much for creating and sharing another great YY-puzzle with perfect setting.
@VitP: the modular constraint is only for the shaded cells.
on 17. January 2026, 12:37 by VitP
in the 6x6 example, box 3 is broken with {14}.
more importantly, for the main puzzle, the constraints are too weak to call it even level 3
-------
The modular restriction only applies to shaded cells. The 1 and 4 in box 3 in the example are both unshaded, so the constraint doesn't apply to those cells.
~yttrio
on 17. January 2026, 11:53 by Snookerfan
Great puzzle! For me harder than 3 stars. Thanks
on 17. January 2026, 10:03 by Piatato
Lovely!
on 17. January 2026, 09:13 by Hiyou167
Amazing puzzle
on 17. January 2026, 05:32 by waffles_the_dog
Really fun puzzle, an interesting break in, the solve path was really nice though I did have a few Simon-vs-Sudoku moments :D
