Parity Fun 23
(Published on 4. April 2026, 10:00 by galium_odoratum)
Normal Sudoku rules apply.
Green laser: Adjacent digits on a green line must differ by at least 5.
Red laser: Draw a straight red laser beam starting at r1c2 and ending at the red dot in r1c7. Adjacent digits on the beam share the same parity (odd or even). Each time the beam crosses a box border, this parity switches. The beam may cross itself but may not reverse direction.
Prism: When the red laser beam hits a prism, it continues in one of the seven possible directions (four orthogonal or four diagonal, excluding the direction it came from). The digit in a prism indicates the number of cells the beam travels to the next prism (or the final red dot), including both prism cells. The red laser beam visits each prism exactly once.
Fog: Some green laser beams are hidden by fog. All prisms are visible!
The laser pointer handles (e.g. r1c1) are not part of the beam and only there for aesthetic reasons.
Hints for the break-in:
There is no need to start the construction at the beginning. Each prism needs a destination where it is pointing to (which is either another prism or the final red dot). This limits the possible digits for each prism. Combine this with the parity constraint and eventually you have your break in.
There are multiple break-ins for sure, but the prisms in box 6 are quite limited...
Play on SudokuPad
Try out the others of this series:
Parity Fun 10
Parity Fun 11
Parity Fun 12
Parity Fun 13
Parity Fun 14
Parity Fun 15
Parity Fun 16
Parity Fun 17
Parity Fun 18
Parity Fun 19
Parity Fun 20
Parity Fun 21
Parity Fun 22
Solution code: Row 6
Comments
today, 02:50 by marajade
Loved this! Very fun once I wrapped my brain around it; I particularly enjoyed the middle game of figuring out the rest of the red laser path once I'd initially managed to break in.
I do agree with the other commenters that the "including both prism cells" phrasing was confusing and made me think at first that the numbers should be 1 greater than they actually are.
on 12. April 2026, 07:27 by CharlesK
The (I assume) updated rules say "The digit in a prism indicates the number of cells the beam travels to the next prism (or the final red dot), *including both prism cells*." (Emphasis mine). Maybe I misunderstood but given that one of the prisms contains a 1, this seems to mean the digit in the prism doesn't count one of the prism cells.
on 5. April 2026, 16:22 by galium_odoratum
clarified prism rule
on 5. April 2026, 09:16 by VitP
hints:
1) the green lasers use gallium nitride
2) the red lasers use gallium indium phosphide.
study these points diligently
on 4. April 2026, 21:12 by Puzzlefan
Nice idea for a puzzle. For me it would be a good idea to clarify the prism rule. It wasn't clear to me if 'the cells visited before reaching another prism' included the new prism cell or not. The rule seems to indicate it doesn't, but it turned out it does. Otherwise, funny ruleset and puzzle.
-Thanks for the helpful feedback, I have rephrased the wording of the rules. ~galium
on 4. April 2026, 11:01 by zonny
Absolutely brilliant!! I loved it! :D
