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Day 19 - Linen Layout
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Haskell
solution
{-# LANGUAGE LambdaCase #-} module Main where import Control.Arrow import Control.Monad.State import Data.Char import Data.List import Data.Map qualified as M import Data.Monoid import Text.ParserCombinators.ReadP parse = fst . last . readP_to_S ((,) <$> (patterns <* eol <* eol) <*> designs) where eol = char '\n' patterns = sepBy word (string ", ") designs = endBy word eol word = munch1 isLetter part1 patterns = length . filter (valid patterns) part2 patterns = getSum . combinations patterns dropPrefix = drop . length valid :: [String] -> String -> Bool valid patterns design = go design where go "" = True go design = case filter (`isPrefixOf` design) patterns of [] -> False l -> any (go . (`dropPrefix` design)) l combinations :: [String] -> [String] -> Sum Int combinations patterns designs = evalState (fmap mconcat . mapM go $ designs) mempty where go "" = return $ Sum 1 go design = gets (M.lookup design) >>= \case Just c -> return c Nothing -> case filter (`isPrefixOf` design) patterns of [] -> return $ Sum 0 l -> do res <- mconcat <$> mapM (go . (`dropPrefix` design)) l modify (M.insert design res) return res main = getContents >>= print . (uncurry part1 &&& uncurry part2) . parse
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