64 lines
1.6 KiB
Haskell
64 lines
1.6 KiB
Haskell
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data Password = Password Int Int Char String
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deriving Show
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main :: IO ()
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main = do
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raw <- readFile "day2.txt"
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let ls = map parse $ lines raw
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fs = case (sequence ls) of
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Nothing -> error "invalid input"
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(Just ps) -> ps
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ansA = length $ filter (== True) $ map validA fs
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ansB = length $ filter (== True) $ map validB fs
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in do
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putStrLn $ "day2a: " ++ (show ansA)
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putStrLn $ "day2b: " ++ (show ansB)
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validA :: Password -> Bool
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validA (Password l u t p) =
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let len = length $ filter (== t) p
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in (len >= l)
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&& (len <= u)
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validB :: Password -> Bool
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validB (Password a' b' t p) =
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case (inBounds a b p) of
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(False,False) -> False
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(True,False) -> (p !! a) == t
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(False,True) -> (p !! b) == t
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_ -> xor ((p !! a) == t) ((p !! b) == t)
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where
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a = (pred a')
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b = (pred b')
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parse :: String -> Maybe Password
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parse [] = error "empty password"
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parse s =
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do (l,s') <- parseInt s
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(u,s'') <- parseInt $ dropChar s'
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(t,s''') <- parseChar $ dropChar s''
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let p = (dropChar . dropChar) s'''
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in (Just $ Password l u t p)
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parseInt :: String -> Maybe (Int,String)
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parseInt s = case (reads s) of
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[] -> Nothing
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[a] -> Just a
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parseChar :: String -> Maybe (Char,String)
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parseChar [] = Nothing
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parseChar (t:s) = Just (t,s)
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dropChar :: String -> String
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dropChar [] = []
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dropChar (_:ls) = ls
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xor :: Bool -> Bool -> Bool
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xor True False = True
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xor False True = True
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xor _ _ = False
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inBounds :: Int -> Int -> String -> (Bool, Bool)
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inBounds a b s = ( len >= a, len >= b )
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where len = length s
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