56 lines
1.5 KiB
Haskell
56 lines
1.5 KiB
Haskell
-- requires cabal install --lib megaparsec
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module Main (main) where
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import Control.Monad (void, when)
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import Data.Void
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import Text.Megaparsec
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import Text.Megaparsec.Char
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import System.Exit (die)
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exampleExpectedOutput = 2
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data Rule = Rule { lower :: Int
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, higher :: Int
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, elt :: Char
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, pass :: String
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} deriving (Show)
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type Parser = Parsec Void String
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parseRule :: Parser Rule
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parseRule = do
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l <- try (some digitChar)
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void (char '-')
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h <- try (some digitChar)
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void (char ' ')
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e <- anySingle
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void (string ": ")
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pass <- (some letterChar)
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void (char '\n')
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return Rule { lower = read l, higher = read h, elt = e, pass = pass }
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parseRules :: Parser [Rule]
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parseRules = some parseRule <* eof
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parseInput :: String -> IO [Rule]
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parseInput filename = do
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input <- readFile filename
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case runParser parseRules filename input of
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Left bundle -> die $ errorBundlePretty bundle
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Right rules -> return rules
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validateRule :: Rule -> Int
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validateRule Rule{lower=l, higher=h, elt=e, pass=pass} = if (n >= l && n <= h) then 1 else 0
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where
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n = length $ filter (== e) pass
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compute :: [Rule] -> Int
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compute = sum . map validateRule
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main :: IO ()
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main = do
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example <- parseInput "example"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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