this post was submitted on 19 Dec 2024
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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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Day 19 - Linen Layout

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[โ€“] gentooer 2 points 2 weeks ago

Haskell

Runs in 115 ms. Today's pretty straight forward. Memoization feels like magic sometimes!

Code

import Control.Monad.Memo
import Data.List

splitX :: Eq a => [a] -> [a] -> [[a]]
splitX xs = go
    where
        go [] = [[]]
        go ys@(y : ys') = case stripPrefix xs ys of
            Just ys'' -> [] : go ys''
            Nothing   -> let (zs : zss) = go ys' in (y : zs) : zss

parse :: String -> ([String], [String])
parse s =
    let (patterns : _ : designs) = lines s
    in  (splitX ", " patterns, takeWhile (not . null) designs)

countPatterns :: (Eq a, Ord a) => [[a]] -> [a] -> Memo [a] Int Int
countPatterns yss = go
    where
        go [] = return 1
        go xs = sum <$> sequence
            [memo go xs' | Just xs' <- map (\ys -> stripPrefix ys xs) yss]

main :: IO ()
main = do
    (patterns, designs) <- parse <$> getContents
    let ns = startEvalMemo $ mapM (countPatterns patterns) designs
    print $ length $ filter (> 0) ns
    print $ sum ns