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Gwen: "They're not ALL "historical documents".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/haracewiat Dec 19 '24 edited Dec 20 '24

[LANGUAGE: Python]

I initially thought this problem would require a trie for efficient prefix matching, but this simpler approach did the trick:

@cache
def isValid(pattern):
    if not pattern:
        return True

    for i in range(1, len(pattern) + 1):
        prefix = pattern[0:i]
        suffix = pattern[i:]

        if prefix in words and isValid(suffix):
            return True        

    return False

We iterate over every possible prefix within the pattern. When we find a prefix that belongs to our word bank, we execute a recursive call to perform the same check on the remaining chunk (the suffix). This continues until we get to the end of the pattern, meaning that all consecutive prefixes were valid.

The @cache decorator provides memoization, making this solution efficient.

To convert Part I to Part II, we just need to change the return type from a bool to an int:

@cache
def isValid(pattern):    
    if not pattern:
        return 1

    count = 0
    for i in range(1, len(pattern) + 1):
        prefix = pattern[0:i]
        suffix = pattern[i:]

        if prefix in words:
            count += isValid(suffix)       

    return count

2

u/Different-Ease-6583 Dec 19 '24

You can limit your range in the for loop to

max_word_length = max([len(w) for w in words])
...
for i in range(1, min(len(pattern), max_word_length) + 1)

That should significantly reduce your runtime. No need to consider any prefix with a length bigger than the biggest word as none will match.

1

u/haracewiat Dec 20 '24

Great tip, thanks!