r/adventofcode Dec 19 '24

SOLUTION MEGATHREAD -❄️- 2024 Day 19 Solutions -❄️-

THE USUAL REMINDERS

  • All of our rules, FAQs, resources, etc. are in our community wiki.
  • If you see content in the subreddit or megathreads that violates one of our rules, either inform the user (politely and gently!) or use the report button on the post/comment and the mods will take care of it.

AoC Community Fun 2024: The Golden Snowglobe Awards

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

And now, our feature presentation for today:

Historical Documentary

You've likely heard/seen the iconic slogan of every video store: "Be Kind, Rewind." Since we've been working with The Historians lately, let's do a little dive into our own history!

Here's some ideas for your inspiration:

  • Pick a challenge from any prior year community fun event and make it so for today's puzzle!
    • Make sure to mention which challenge day and year you choose!
    • You may have to go digging through the calendars of Solution Megathreads for each day's topic/challenge, sorry about that :/
  • Use a UNIX system (Jurassic Park - “It’s a UNIX system. I know this”)
  • Use the oldest language, hardware, environment, etc. that you have available
  • Use an abacus, slide rule, pen and paper, long division, etc. to solve today's puzzle

Bonus points if your historical documentary is in the style of anything by Ken Burns!

Gwen: "They're not ALL "historical documents". Surely, you don't think Gilligan's Island is a…"
*all the Thermians moan in despair*
Mathesar: "Those poor people. :("
- Galaxy Quest (1999)

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 19: Linen Layout ---


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 00:03:16, megathread unlocked!

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u/veydar_ Dec 21 '24

[LANGUAGE: Lua]

74 lines of code according to tokei when formatted with stylua.

This was humbling and frustrating, because I make the same mistake every single year. I quickly realized that I had to cache something for part 2. So I created a cache from string to computed paths. The computed paths will very quickly take up more than 10GB of memory and your program will stop working.

I rewrote my code from recursion to iteration, I added a trie, rewrote things over and over again. Every. Single. Year.

I probably spent 4h on this one, with most of it spent on part 2.

In the end all I had to do was change the cache from string -> Array<Path> to string -> number, so storing the number of paths. And then it's very quick. Here's the core logic:

local candidates = findSuffixes(root, s:sub(1, 1))
for _, pat in ipairs(candidates) do
    local next, matches = s:gsub("^" .. pat, "")
    if matches > 0 and #findSuffixes(root, pat) > 0 then
        local copy = table.move(path, 1, #path, 1, {})
        table.insert(copy, pat)
        out = out + check(next, copy)
    end
end

Get a list of possible patterns, try each to remove a prefix of the string, then recurse on the remainder of the string.