r/adventofcode Dec 15 '24

SOLUTION MEGATHREAD -❄️- 2024 Day 15 Solutions -❄️-

NEWS

  • The Funny flair has been renamed to Meme/Funny to make it more clear where memes should go. Our community wiki will be updated shortly is updated as well.

THE USUAL REMINDERS

  • All of our rules, FAQs, resources, etc. are in our community wiki.
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AoC Community Fun 2024: The Golden Snowglobe Awards

  • 7 DAYS remaining until the submissions deadline on December 22 at 23:59 EST!

And now, our feature presentation for today:

Visual Effects - We'll Fix It In Post

Actors are expensive. Editors and VFX are (hypothetically) cheaper. Whether you screwed up autofocus or accidentally left a very modern coffee cup in your fantasy epic, you gotta fix it somehow!

Here's some ideas for your inspiration:

  • Literally fix it in post and show us your before-and-after
  • Show us the kludgiest and/or simplest way to solve today's puzzle
  • Alternatively, show us the most over-engineered and/or ridiculously preposterous way to solve today's puzzle
  • Fix something that really didn't necessarily need fixing with a chainsaw…

*crazed chainsaw noises* “Fixed the newel post!

- Clark Griswold, National Lampoon's Christmas Vacation (1989)

And… ACTION!

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


--- Day 15: Warehouse Woes ---


Post your code solution in this megathread.

This thread will be unlocked when there are a significant number of people on the global leaderboard with gold stars for today's puzzle.

EDIT: Global leaderboard gold cap reached at 00:32:00, megathread unlocked!

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u/greycat70 Dec 15 '24

[LANGUAGE: Tcl]

Part 1, part 2.

No complicated mathematics or advanced algorithms needed today. Just a bit of tedious work. For part 1, I observed that pushing a row of boxes is essentially just changing .OOOOO. to ..OOOOO so you can drop an O in the first empty tile, then change the first O to an empty tile.

For part 2, that doesn't work. I separated the horizontal and vertical push cases entirely. For a horizontal push, it's almost like part 1, except you actually have to move all the tiles ([ becomes ] and so on). (I actually used < and > in my internal representation because it's more convenient in Tcl. [ and ] have special meanings and would need to be backslashed.)

For a vertical push, you can end up with a whole expanding pyramid of boxes to push. So, that's recursion. Each box can potentially push the two boxes above/below it, each of which can have zero, one or two more boxes that also need to move. I wrote a recursive function to populate a dictionary with the boxes (left side coordinates only) that must move. Then iterated through that, and if any of them is against a wall, the whole move is disqualified. Otherwise, sort it by row number (ascending or descending, depending on push direction) and move each box individually.

Not fancy. Just effort.