Bits and arrows
(Published on 29. September 2025, 22:45 by Killer Joe)
Hello.
Normal sudoku rules apply.
A binary code is a sequence of bits that are either on or off.
In this puzzle, Odd digits represent bits that are 'OFF'(O) and Even digits represent bits that are 'ON'(E).
This gives us the following representation of the digits 1-9:
1 → OOOE
2 → OOEO
3 → OOEE
4 → OEOO
5 → OEOE
6 → OEEO
7 → OEEE
8 → EOOO
9 → EOOE
The digit in an arrow cell dictates the parity (odd or even) of its four orthogonal neighbours.
These four neighbours must match the binary code of the digit with the small arrow.
The arrow points to the first bit of the binary code. (read from left to right.) The full code must wrap around the central cell clockwise.
Example:
If a 6 is placed in an arrow cell, its code is OEEO.
Therefore, its four neighbours (starting from the arrow direction, moving clockwise) must be Odd, Even, Even, Odd.
Have fun.
Solution code: row 9, first 6 digits.
Comments
on 1. November 2025, 20:14 by Rollo
Toll :-)
on 29. October 2025, 11:26 by superkinkel
Very nice one, once you get the hang of it. I'm just puzzled that it should be easier for programmers? Who uses binary code in this century?
on 26. October 2025, 18:52 by Klausku
What a brilliant idea for a ruleset. And it leads to surprisingly nice logic. Loved it. If you are not familiar with binary code, it‘s probably a little harder. Thanks.
on 25. October 2025, 10:36 by bboom
Lots of fun. As a programmer, this was one I could solve pretty quickly. Only handicap as a programmer is that "the first bit" for me is automatically the least significant (rightmost) digit, so it took me a few minutes to realize that wasn't the rule, and to mentally rotate the arrows and read counterclockwise.
Very fun puzzle. I wonder if there's a more intuitive option to visualize which order the surrounding cells should be read, but this does work well enough.
on 24. October 2025, 23:26 by damo_89
20 minutes of staring blankly until I had one of those A-ha moments, then 20 minutes of delightfully smooth solving. Lovely.
on 17. October 2025, 21:28 by The Book Wyrm
Very fun puzzle! Ruleset takes some getting used to, but was pretty intuitive once I did, and has some interesting logic. Very smooth and approachable solve path, really enjoyed this.
on 13. October 2025, 12:25 by Fra314
WOW, this is probably the best parity puzzle I've ever solved... the break-in is hard if you don't find the general idea, the rest of the puzzle just flows beautifully. Please recommend this to CTC, this must be seen by everyone!
on 1. October 2025, 20:05 by dzamie
Quite challenging to break in, but surprisingly straightforward once you've gotten the parity of just one cell.
on 30. September 2025, 17:49 by StefanSch
Nice puzzle idea!
on 30. September 2025, 17:49 by StefanSch
Nice puzzle idea!
