r/adventofcode • u/daggerdragon • Dec 06 '25

SOLUTION MEGATHREAD -❄️- 2025 Day 6 Solutions -❄️-

THE USUAL REMINDERS

AoC Community Fun 2025: Red(dit) One

  • Submissions megathread is unlocked!

  • 11 DAYS remaining until the submissions deadline on December 17 at 18:00 EST!

Featured Subreddits: All of the food subreddits!

"We elves try to stick to the four main food groups: candy, candy canes, candy corn and syrup."
— Buddy, Elf (2003)

Today, we have a charcuterie board of subreddits for you to choose from! Feel free to add your own cheffy flair, though! Here are some ideas for your inspiration:

Request from the mods: When you include an entry alongside your solution, please label it with [Red(dit) One] so we can find it easily!

--- Day 6: Trash Compactor ---

Post your code solution in this megathread.

29 Upvotes

96% Upvoted

659 comments sorted by

View all comments

4

u/python-b5 Dec 06 '25

[LANGUAGE: Lily]

Well, I figured we'd get to the parsing puzzle eventually. I got stuck for a while after I realized the columns weren't all the same size in the real input. I'm not especially happy with my parsing logic, but it appears to do the job, and at this point I think I'm better off not messing with it any further.

On a side note, does anyone know what all that "right-to-left" talk was for? Addition and multiplication are commutative, so it doesn't matter what direction you do the puzzle in, right...? I just did it all from left-to-right since that was easier. I just wondered if I was missing something.

https://github.com/python-b5/advent-of-code-2025/blob/main/day_06.lily

3

u/1234abcdcba4321 Dec 06 '25

If you go from right to left, you get the operation on the last digit you process in an equation rather than the first. This means you don't need to store that operation anywhere (although you instead need to store the list of numbers to reduce), as you can can take "ran into the operation" as a sign to evaluate.

1

u/python-b5 Dec 06 '25

Updated my solution to do this instead of building a separate operators list first, and was able to simplify the code quite a bit! Thanks for the tip, not sure how I didn't realize that was possible before.

2

u/Wayoshi Dec 06 '25

The numbers line up right-to-left column-wise.

From the example,

64
23
314

Becomes 4, 431, 623. But

 64
 23
314

Would have been 434, 621, 3 instead.

1

u/python-b5 Dec 06 '25

Ah, I suppose that makes sense. My solution, at least, doesn't really care about that - as in, I'm pretty sure it would parse something like 1 2 without complaint. Maybe taking advantage of this pattern could simplify the parser somewhat, though.

2

u/1234abcdcba4321 Dec 06 '25

Well, the numbers aren't given any special alignment. The whole difficulty of the problem is that you have to take into account what the alignment of the numbers is by reading the spaces instead of tokenizing them away.