44 lines
1.2 KiB
Haskell
44 lines
1.2 KiB
Haskell
import Control.Arrow
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import Data.Function
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import Data.List
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import Data.List.Split
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import Data.Maybe
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import Text.Read
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type HASH = (String, Maybe Int)
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main :: IO ()
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main = interact $ show . genBuckets . parse . init
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parse :: String -> [HASH]
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parse = map (second (readMaybe . tail) . break (`elem` "=-")) . splitOn ","
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day15a :: String -> Int
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day15a = sum . map (foldl' hashAlg 0) . splitOn ","
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hashAlg :: Int -> Char -> Int
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hashAlg x y = (17 * (fromEnum y + x)) `mod` 256
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removeHashes :: [String] -> [HASH] -> [HASH]
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removeHashes _ [] = []
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removeHashes rs ((label, Nothing):xs) = removeHashes (label : rs) xs
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removeHashes rs ((label, Just x):xs)
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| label `elem` rs = removeHashes (delete label rs) xs
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| otherwise = (label, Just x) : removeHashes rs xs
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genBuckets :: [HASH] -> Int
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genBuckets input =
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sum
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[ sum $ zipWith (*) [1 ..] $ map ((* (succ x)) . fromJust . snd) (sorted x)
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| x <- [0 .. 255]
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]
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where
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filterBucket x f =
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nubBy ((==) `on` fst) $
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f $ removeHashes [] (reverse $ filter (f1 x) input)
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sorted x =
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sortOn
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(\y -> fst y `elemIndex` (map fst (filterBucket x reverse)))
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(filterBucket x id)
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f1 n (x, _) = foldl hashAlg 0 x == n
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