RAT RUN 31: Equivalence
(Published on 25. March 2026, 01:00 by marty_sears)
- Normal sudoku rules apply.
- AIM OF EXPERIMENT: Finkz and Phinx must both reach different cupcakes by finding a path through the maze. The paths must not visit any cell more than once, cross themselves or each other, or pass through any thick maze walls.
- As well as moving orthogonally, they may move diagonally if there's a 2x2 space in which to do so, but may never pass diagonally through a round wall-spot on the corner of a cell.
- BLACKCURRANTS: If two digits are joined by a blackcurrant, one is double the other.
- REDCURRANTS: If two cells are joined by a redcurrant, one is odd and the other is even.
- TELEPORTS: Entering a yellow teleport will cause the rat to be instantly transported to the other yellow teleport. The teleports have identical digits.
- MOTION SENSORS: The digit on a pink motion sensor indicates the number of cells that are visited (by either rat) within the (up to 9) cells immediately surrounding the sensor. The sensor itself is counted, if visited.
- TEST CONSTRAINT: In this experiment, for any row or column, the digits visited by Finkz must have the same sum as the digits visited by Phinx. This sum must be determined for each row and column.
Solution code: Digits in row 1 not visited by either rat, from left to right
Comments
on 3. April 2026, 12:40 by damo_89
How on earth did you construct this!
116 minutes but no individual deduction felt 5* just lots of possible places to look.
on 2. April 2026, 06:06 by ziratha
Pretty hard. Not sure I'd put it above 4 stars. Still very enjoyable. It's amazing how constrained the path is once you think about it for a bit.
on 31. March 2026, 20:37 by Tortugo
I think this is the first one where I am sure I made at least one faulty deduction at some point yet still arrived at the correct solution. The constraint is just so constrain-y!
on 30. March 2026, 14:48 by Klausku
Brilliant puzzle! Very hard but fair. Took me almost 3 hours of slow but steady progress. But I enjoyed every minute of it. Thanks!
on 29. March 2026, 08:57 by DonQuichopp
Took me days to solve, but what a beautiful puzzle. Really really nice! Thank you so much.
Once I broke in, it felt to flow very nicely. Slow for inexperienced solvers, but still very good.
on 27. March 2026, 03:47 by abinchen
This is the 1st 5 star puzzle I've ever solved. Cool rule set!
on 27. March 2026, 01:30 by monsen
Amazing as always. More like 4* IMHO, but very lovely. I had partial paths all over the place in this one, no simple finding the complete path (from beginning or end) but rather just giving me a rough sketch where they had to go.
Very interesting test constraint, opened up for some interesting deductions along the way.
on 26. March 2026, 22:03 by Puzzlefan
Beautiful, as always. Really enjoyed this one. Not in the least because I felt really smart I figured out the paths quite quickly. It wasn't straightforward from there, though. Another beauty of a puzzle.
on 26. March 2026, 21:06 by psams
Fantastic, my favorite of the series I have solved
on 26. March 2026, 14:14 by wuc
If every 5* was that fair. Wonderful 68 minutes. Masterpiece thx.
on 26. March 2026, 10:30 by redgecko
Wonderful fun but brutal
on 26. March 2026, 09:36 by AshBrown
Another one that seemed impossible at first. Definitely hard in the middle of the solve
on 26. March 2026, 07:03 by MissAmy254
It’s so interesting how people’s brains work so differently. When I saw the 5* rating I thought there was no chance of me solving this one, but slowly and surely I managed to make progress and made my way through. This was 4* difficulty for me, so far Productivity was the one I struggled with the most
on 26. March 2026, 04:39 by VolpeRosso
Amazing as always!!! 71 minutes. Spent the first 15 staring at it not believing it was possible for a sane person to even begin to fathom a way to commence! Then - the spark. As always, beautiful logic ensued from there <3 <3 I hope when Marty's brain has its next child, it is as beautiful as this adventure has been for the last few years... <3
on 26. March 2026, 01:01 by ufdigga
Yet another beautiful puzzle! This might have been the hardest one for me. I spent an hour stuck on the break-in, convinced I was focusing on the right set of clues. I was... not. Once I restarted and looked elsewhere, it moved much more smoothly for me.
on 26. March 2026, 00:23 by EFlatMinor
This was an odd solve for me. I worked out roughly what I thought the paths had to be. But it took quite a while to articulate why, and to actually prove it.
Brilliant as always! Thanks for this incredible series.
on 25. March 2026, 22:15 by da-hans
My first 5* puzzle. Great work.
on 25. March 2026, 22:04 by dinonugs
Whew, finally! That one took a while. I got the opening quickly, and then things slowed down and I had to resort to some extensive note taking. Thanks for the fun!
on 25. March 2026, 20:54 by Froman
Great puzzle!! I'm surprised by the five star rating, though. It had two rough spots (The break-in and a deduction around the half-point), but I never felt truly lost (And hats off to you in that regard, some puzzle magic you've done). Maybe the rats aren't the only ones learning lol
on 25. March 2026, 17:17 by scarfdoku
Wow that was amazing. I have no idea how something like this even gets made. Thanks for the great puzzle.
Marty: The key is to ask Justin Vitanza for help :)
on 25. March 2026, 16:24 by Samoth
Truly an odyssey for the rats today. A wonderful puzzle!
on 25. March 2026, 16:05 by KelleyCook
I stared at this right as it was released, but the break-in eluded me. It just didn't seem possible to get anywhere.
So I slept on it. With some lucid inspiration, in the morning I finished it in a few hours.
This series has been amazing.
on 25. March 2026, 16:04 by Franjo
Thank you very much for creating and sharing this - quite hard - episode. Took me two hours, and these were full of great pleasure! And I’m so happy the show will go on!
on 25. March 2026, 15:41 by Christounet
Definitely not a 5* for me, closer to 4*.
Excellent once again, and quite impressive that this can even exist (and solve so nicely) !
Very intrigued by the new elements of the plot, looking forward to what comes next...
Thanks :)
on 25. March 2026, 15:25 by Nairurian
I was a bit worried when I saw this sitting at 5*, but it definitely felt easier than that (I’d say it was easier than the last couple of weeks) and once I thought about what the constraint meant it was a smooth flow.
on 25. March 2026, 15:17 by mscha
Whew!
This is probably the hardest Rat Run so far. At one point I was convinced that I'd have to wait for CtC for some hints.
It took forever even finding an approximate path that might work. But then I proved a small path fragment, got a digit, used some deductions I made earlier, and I was on my way. A relatively smooth solve after that.
Wonderful puzzle, thanks Marty and Justin!
(And now I'm off to check why there is a new puzzle link, and if I need to start over. ;-) Edit: I see not a pixel difference between 37wqeifgzs and ze8ubc81ku.)
Marty: it was a small cosmetic booboonthat someone pointed out - a circle visible in r4c3 when you coloured it. its been fixed now, but the puzzle didn't change
on 25. March 2026, 14:33 by JVA
I'll be darned. I did it. Hour and a half, didn't even need to check on CtC for guidance. I can't even handle most 2*s puzzles in this site, I've almost given up on a handful 1*, yet somehow I've finished this 5* masterpiece.
Great puzzle Marty. Very cool use of topology to restrict the paths
on 25. March 2026, 14:21 by etoler
It's 8:21 in the morning, and my brain already hurts. Absolutely brutal, but brilliant as ever—and an unexpected collab! Thanks to both Marty and Justin for another incredible puzzle!
...I need another cup of coffee now. Or maybe a gallon.
on 25. March 2026, 13:58 by Atticus837
Tough, but very interesting. I enjoyed how the deductions about the path seemed to start very broad, and slowly narrow down and solidify into definitive paths. This didn't feel like finding my way along a path (as many of these puzzles do), but rather discovering a path that already existed. A difficult but very rewarding solve.
on 25. March 2026, 11:51 by lune
Yay! I feel smarter now, thanks, Marty!
on 25. March 2026, 10:59 by by81996672
This puzzle is really good. Whenever I wonder if I can only use the method of not being able to draw a specific path to delete numbers, I always find a practical way to avoid it.
on 25. March 2026, 10:54 by Rab3aron
Wow! This one was probably the hardest Rat Run for me so far, definitely 5 stars! The logic was absolutely beautiful, every time I got stuck, I found a clever new connection that opened things up. It’s hard to find a puzzle this tough yet so elegant to solve.
on 25. March 2026, 10:45 by JVA
Oh God, 5*. Even accounting for the fact these puzzles are more far more approachable than what their ratings suggest, this one might be too much for me
on 25. March 2026, 10:38 by cmusson32
I found this the hardest one yet, only just beating the 100 minute mark for my solve. I think the logic required isn't monstrous and is more akin to a 4 star puzzle, however it's often difficult to work out where you should look next along the solve path, so for me, the 5 star rating is justified.
Excellent puzzle as ever.
on 25. March 2026, 09:56 by DonQuichopp
Oh my lord. 5 stars! I'll get back with a comment in 5 weeks when I managed to solve it. Or shall I say, IF I solve it.
on 25. March 2026, 08:59 by Angara
Hardest of the series for me! Wonderful! The intrigue in the story is growing. Is the final in the beginning ofJune?)
on 25. March 2026, 04:24 by antiknight
That was a very challenging and creative puzzle, with many great deductions and a satisfying start!
on 25. March 2026, 02:34 by QuiltyAsCharged
What's left to say about this wonderful, magical series? Each week as it comes around I'm excited to realize it's Rat Run day! This chapter was one of my favorites.
on 25. March 2026, 01:43 by vitaminz
What an honor to be brought into this amazing series. I hope everyone enjoys this episode.
Marty: Couldn't have done this one without you mate. Thanks for delivering the goods once again :)
on 25. March 2026, 01:24 by blackjackfitz
Huzzah!
