42 lines
1023 B
Haskell
42 lines
1023 B
Haskell
{-# LANGUAGE LambdaCase #-}
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import Control.Arrow
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import Data.Char
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import Data.List.Split
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import qualified Data.Map as M
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type LR a = (a, a) -> a
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type Tunnels = M.Map String (String, String)
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main :: IO ()
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main = interact $ show . day08 . parse . lines
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parse :: [String] -> ([LR String], Tunnels)
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parse =
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cycle .
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map
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(\case
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'L' -> fst
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'R' -> snd
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_ -> error "Malformed directions input") .
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head &&&
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M.fromList . map parseLine . tail . tail
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parseLine :: String -> (String, (String, String))
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parseLine s = (a, (b, c))
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where
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[a, b, c] = wordsBy (not . isAlphaNum) s
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day08 :: ([LR String], Tunnels) -> (Int, Int)
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day08 (lrs, m) = day08a lrs m *** day08b lrs m $ ("AAA", starts)
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where
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starts = filter ((== 'A') . last) (M.keys m)
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day08a :: [LR String] -> Tunnels -> String -> Int
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day08a _ _ [_, _, 'Z'] = 0
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day08a (lr:lrs) m pos = 1 + day08a lrs m (lr (m M.! pos))
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day08b :: [LR String] -> Tunnels -> [String] -> Int
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day08b lrs m starts = foldr1 lcm $ map (day08a lrs m) starts
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