RAC 'em up
(Published on 4. March 2025, 03:30 by cirne)
This is the first time I have set any sort of puzzle! I wanted to make a Sudoku experience where the board changes while you solve, like with a fog puzzle, but print-compatible. This is what I came up with, and pdyxs was gracious enough to collaborate with me to create this!
Any and all feedback is appreciated. Enjoy!
Rules
Normal Sudoku rules apply, and all clues are cosmetic unless otherwise specified.
Rule Activation Cells: A digit in an upwards-pointing triangle activates an optional rule from the list below. (If the corresponding digit appears in one or more triangles, then the rule is enforced across the whole puzzle; if a particular digit does not appear in any triangle, then its rule is not enforced, and any clues associated with it have no meaning.)
The Rules:
- German Whispers: Adjacent digits along a (solid) green line must have a difference of at least 5.
- XV (X): Digits separated by an X sum to 10. Not all possible X's are given.
- Arrows: The digit in an arrow’s circle is equal to the sum of the digits on the attached arrow. (Digits may repeat along the arrows if allowed by other rules.)
- XV (V): Digits separated by a V sum to 5. Not all possible V's are given.
- Renban: Digits on a (hollow) purple line form a set of non-repeating, consecutive digits in any order.
- White Kropki: Digits separated by a white dot are consecutive. Not all possible dots are given.
- Black Kropki: Digits separated by a black dot have a 1:2 ratio. Not all possible dots are given.
- That's Three in the Corner: There must be a 3 in one of the four corner cells of the grid.
(There is no rule #5. A 5 in a RAC has no special meaning.)
Click on the puzzle image to play in SudokuPad
Solution code: Row 9
Comments
on 15. March 2025, 15:53 by puma17
Excellent setting, with a most innovative ruleset, and a most elegant use of positive and negative constraints with the rules on and off the board !
The flow is elegant, the ending is hard but legit :)
Thank you for setting and sharing this puzzle, and kudos on the creativity
on 15. March 2025, 15:50 by RoystonDA
I've never seen RAC before and this has got to be the most fascinating way of toying with previously established rules. I loved it! Made for a fun stream.
on 13. March 2025, 20:06 by Grecolons
Very cool idea! I'd love to see more of this stuff :)
on 13. March 2025, 15:02 by Lion Crow
This is a powerful concept, and you’ve executed it brilliantly. Please make more puzzles with this ruleset.
on 12. March 2025, 18:04 by PancakePie
What a fun way to stretch my perspective! Beautiful work.
on 12. March 2025, 10:32 by TheKayOne
Very beautiful and fun puzzle
on 11. March 2025, 20:55 by cirne
dzamie, your comment made me so happy! My explicit goal here was to make something that felt sort of like a Dynamic Fog sudoku, so it's wonderful to hear that I've succeeded! As for having the clues visible even when inactive: yes, that's very important, and that definitely isn't going away! I've created a mockup of how a solve might look if and when SudokuPad does support dynamic styles, and you can find it at https://tinyurl.com/rac-solve (spoilers, obviously, for the solution here!)
mkubica, that was part of the intent, and came from some feedback I got in initial testing! Originally, the RAC legend was outside the grid entirely, like a sandwich or little killer clue, but you're absolutely right about how helpful it is to be able to mark it up! It's been fun seeing how people mark it; some people use shading, like you did, some people use the pen tool, and I've also seen people simply put a blue digit atop the grey one to mark it as active. Thank you so much for checking this out, and especially for your comment!
Snookerfan, hovestar, I'll be totally honest, *I* get stuck in that part of the puzzle, too, when I go through the solve again - and I'm the one who set it in the first place! I'll add a hidden comment with my logic for those bits, in case you're curious (and absolutely not as a way to have a record of it somewhere in case I get stuck again).
on 11. March 2025, 15:51 by Snookerfan
Great puzzle and idea! I found the last signigicant step quite hard, but maybe I missed something easier. Thank you
on 11. March 2025, 03:05 by mkubica
What a fun puzzle! You can select cells in the RAC legend, so I coloured active rules in yellow and greyed out any inactive ones. Seemed to help a bit.
on 7. March 2025, 23:52 by dzamie
This was so cool! Felt a little bit like Dynamic Fog but with more user control. It did take quite a lot of effort to NOT eliminate pencilmarks for the kropkis before I discovered whether or not they actually existed.
Honestly, I think this works well even if Sven *did* add dynamic markings - knowing where certain clues would be if they were real helped me with this puzzle, though I'm not sure how intended that was.
on 5. March 2025, 23:48 by cirne
Thank you all so much for trying out my puzzle! Big Tiger, Playmaker, I agree with you that one of the hardest parts is remembering which rules are currently active.
I dearly wish I could convince Sven to add support for dynamic style changes in SudokuPad, because then the clues could start out as faint images (so you can see where they will be if activated) and only solidify once you put the right digit in a RAC!
on 5. March 2025, 22:42 by Playmaker6174
A really fun and fascinating idea for a puzzle! (even though it can make the scanning quite messy and also certain wrong assumptions in the middle)
I especially like how the arrow in box 7 works and also how some certain triangle clues are placed x)
on 5. March 2025, 22:06 by Big Tiger
Woosh, I had to restart three times because I kept instinctively applying the constraints just because they were on the board. In the end, I had to grey out the entire grid (almost like fog) and turn the cells with constraints white again only once they applied. Lots of fun once I found a way to trick my mind into following the rules, ha ha.
on 5. March 2025, 18:44 by jwsinclair
Innovative idea, with some really nice logic. I had to ask for help with a tough early step (which turned out to be something really elegant that I was just missing), and I'm glad I stuck with it :)
on 4. March 2025, 21:58 by VitP
quite a bit harder than level 2, but still solvable by all skill levels
on 4. March 2025, 17:29 by Cantabrigiensis
Excellent puzzle, great fun; brilliant idea for an original ruleset, many thanks and well done!
