Day 22: Yin-Yan
(Published on 22. December 2025, 06:00 by SharpFox)
Rules:
- Normal 4×4 Sudoku rules.
- Yin-Yan: Shade some cells such that both the shaded and the unshaded cells are orthogonally connected and no 2×2 square is either fully shaded or entirely unshaded.
- Red lines mark borders of differently shaded cells. Red crosses give the number of cells with the same shading among the (up to) 8 surrounding cells including itself.
- Orthogonally adjacent cells of the same shading have different parity i.e. one digit is odd and one even.
- Tiny tip: In this puzzle yin and yan are symmetrical i.e. it doesn't change anything if you change the shaded and unshaded cells.
Solution code: Row 1 (4 digits):
Comments
on 17. March 2026, 03:01 by Ginge
I find it interesting that if you changed the Red Crosses rule to say “Excluding itself” you still have a solvable puzzle (with a different solution, of course)
on 11. March 2026, 10:07 by EL Buderino
I really do not unterstand this one.
Even after having found the solution. ????
on 25. December 2025, 04:52 by FireTruckFuel
This puzzle seemed somewhat daunting given the rules so I read them through twice. Finished in only 1:13. I think my trepidation says more about my familiarity with Yin-Yan than it does about the puzzle itself. My favorite 4x4 of the series!
on 24. December 2025, 18:01 by tstaffor
The parity rule is very interesting for a shading puzzle.
on 22. December 2025, 19:19 by Fisherman
Happy holidays to all.
