Congruity
(Published on 14. December 2025, 03:06 by Andrewsarchus)
Rules:
- Latin Square:
- Place the digits 1-9 once each into every row and column.
- Index Lines (turqoise):
- The value in the Nth cell along an Index Line (starting from the diamond) indicates the position along the line where the value N appears.
- For example, if a diamond cell contains a 3, the third cell along that line must have a 1.
- Zipper Lines (lavender):
- Pairs of values equidistant from the center of a Zipper Line have the same sum.
- Where the center lies in a cell, the sum is the value in that cell.
- The sum may be different for different lines.
- Full Rank:
- A value in an external cell represents the rank of the number formed by reading the digits in that row or column from that direction, where (1) is the lowest such row or column and (36) is the highest.
- The 36 numbers are distinct - no ties.
Play Online:
sudokupad: Congruity
Solution code: The nine digit number corresponding to rank 35.
Comments
on 29. July 2026, 20:44 by kasperd
This one felt like a six stars difficulty.
on 28. July 2026, 19:19 by Azukay
This puzzle much like an onion and an ogre had so many incredible layers to pull apart. Truly an incredible journey, my first ever 5 star.
on 24. July 2026, 20:07 by 6rank
Very good and fun puzzle. The puzzle itself didn't feel very difficult but it is so incredibly complicated, which made it a very difficult puzzle nonetheless :)
on 21. July 2026, 00:50 by Fool on Hill
I had missed this till it turned up on CTC - and stopped to solve, and the plaudits are well deserved. Not brutal, but lots of thinking required.
on 3. January 2026, 05:52 by feverlute
Proud to solve this one. Hard to keep the logic straight, but very beautiful and satisfying
on 22. December 2025, 21:35 by cyddrdrd
Learned a lot about FR in this puzzle. Thanks!
on 17. December 2025, 20:12 by War
Aptly chosen puzzle name given the continuous circling on the outer blue line. A great and rewarding challenge indeed!
on 15. December 2025, 16:10 by SenatorGronk
The sudoku equivalent of mud wrestling. Lots of inelegant flailing on this solvers part. Many times I thought I had a firm grasp, only to find things slip through my fingers.
Through determination and bullheadedness I eventually tamed the beast, but found myself exhausted at the end.
Well done, Andrew!
on 15. December 2025, 15:33 by henrypijames
This FR index line has endless potential: Rotate it by just one cell (or any number thereof), it will behave very differently.
on 15. December 2025, 14:49 by marcmees
Fantastic puzzle. Thanks
on 14. December 2025, 20:12 by bansalsaab
That was a beast
on 14. December 2025, 19:17 by Snookerfan
Incredibly clever, original and satisfying puzzle! Once you find the right way to appreciate the big index line, the puzzle unfolds nicely, still very hard. Thanks!
on 14. December 2025, 17:23 by cryptique
Superb thank you
on 14. December 2025, 06:12 by Justalilguy
Extremely enjoyable!
on 14. December 2025, 03:37 by aqjhs
behold the holy grail of index lines!
