Advent Of Code

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An unofficial home for the advent of code community on programming.dev!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

AoC 2024

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CameronDev@programming.dev

👻 - 2024 DAY 19 SOLUTIONS -👻 (programming.dev)

submitted 1 week ago by CameronDev@programming.dev to c/advent_of_code@programming.dev

34 comments fedilink hide all child comments

Day 19 - Linen Layout

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[–] sjmulder@lemmy.sdf.org 2 points 1 week ago (1 children)

I don't know much about Rust but I assume the HashMap<String, i64> requires hashing on insertion and lookup, right? I realized that, for every design, all the strings you'll see are substrings of that design from different starting positions, so I made my lookup table int pos -> int count. The table is reset after every design.

[–] CameronDev@programming.dev 2 points 1 week ago* (last edited 1 week ago) (1 children)

That does mean that if two or more strings end with the same substring, you'd recalculate those substrings? Would be a faster lookup cost though, clever.

My code ran in 120ms, so its pretty damn fast as is, especially compared to the non-memoised version

edit: Tried the array of lengths method, shaved about 20ms off. Not bad, but probably not my main issue either

[–] sjmulder@lemmy.sdf.org 3 points 1 week ago (1 children)

That does mean that if two or more strings end with the same substring, you’d recalculate those substrings?

I hadn't really considered that, but yes. I'm inclined to think that replacing hash table lookups with plain array indexing (which this allows) outweighs that downside but I'm not sure. Indeed 120ms is pretty damn fast!

[–] CameronDev@programming.dev 1 points 1 week ago (1 children)

It saved me 20ms, and given your using C, saved you dealing with uthash or similar, so probably worth it.

The hashmap is probably a more generic solution though

[–] sjmulder@lemmy.sdf.org 2 points 1 week ago

Certainly more generic and less prone to user error too. Indeed dealing with hash maps or any advanced data structure is a pain with C, this is where generics or templates really shine, especially if you have control over lifetime aspects as you do with C++ or Rust (e.g. moves, lvalue references, constness, etc).