Day 21: The longest night
(Published on 21. December 2025, 06:00 by SharpFox)
Today's Sudoku has turned out to be significantly more challenging than I had intended. I believe it exceeds the beginner level, but it is only one day.
Rules:
- Place the digits 1-7 into every row, column and region.
- Chaos Construction: Divide the grid into 7 orthogonally connected regions. No region may consist entirely of a single row or column. Digits connected by a Kropki dot must lie in the same region.
- Each circle is connected to a line of two or three cells. Either all 2-cell shapes are thermometers and all 3-cell shapes are arrows, or the other way round. Additionally lines of the same length are positionally linked, digits in corresponding cells along equal-length shapes must all be different.
- Thermometers: Digits strictly increase along a thermometer, starting from the circle.
- Arrows: Digits on an arrow sum to the digit in the attached circle.
- The two stars are swap markers: The starred cells remain part of their given region for connectivity purposes, but their digits belong to the opposite starred region.
For example, if a starred cell in region A contains a 5 and the other starred cell in region B contains a 4, then region A receives the 4 (instead of the 5) and region B receives the 5. - White Kropki dots join consecutive digits while black Kropki dots join digits, where one is double the other.
Solution code: Row 1 (7 digits):
Comments
on 13. January 2026, 16:52 by geronimo92
@CitrusGremlin : read it again more carefully, the ruleset says connected to a LINE of two or three cells !
on 24. December 2025, 17:55 by tstaffor
I think this might be the only advent sudoku that will go unsolved for me. I can't even find the break in lol
on 24. December 2025, 11:41 by wuc
Great cc 2*. Rules a bit lengthy maybe. The star rule could be clarified a bit maybe since the swap affects only the region building, not constraints.
What a great series of puzzles you provided through this month. Great work, big thx.
on 22. December 2025, 22:07 by CitrusGremlin
Rules are clear but I do have to make some assumptions. You say the shapes are two and three cells long, but the circle is part of the thermo and arrow restriction, so shouldn't it be three and four cell shapes? Not sure what the clearest way to state it would be.
