86 lines
2.3 KiB
Haskell
86 lines
2.3 KiB
Haskell
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-- requires cabal install --lib megaparsec parser-combinators
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module Main (main) where
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import Control.Monad (void, when)
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import Data.List (foldl')
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import Data.Map qualified as M
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import Data.Void (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 = 71
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data Range = Range { field :: String
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, ll :: Int
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, lh :: Int
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, hl :: Int
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, hh :: Int
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} deriving (Show)
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type Ticket = [Int]
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data Input = Input { ranges :: [Range]
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, myTicket :: Ticket
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, nearbyTickets :: [Ticket]
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} deriving (Show)
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type Parser = Parsec Void String
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parseInt :: Parser Int
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parseInt = do
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n <- some digitChar
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void $ optional (char ',')
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return $ read n
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parseRange :: Parser Range
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parseRange = do
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f <- some (letterChar <|> char ' ')
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void $ string ": "
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ll <- parseInt
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void $ char '-'
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lh <- parseInt
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void $ string " or "
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hl <- parseInt
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void $ char '-'
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hh <- parseInt
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void $ char '\n'
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return $ Range f ll lh hl hh
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parseTicket :: Parser Ticket
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parseTicket = some parseInt <* char '\n'
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parseInput' :: Parser Input
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parseInput' = do
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r <- some parseRange
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void $ string "\nyour ticket:\n"
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t <- parseTicket
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void $ string "\nnearby tickets:\n"
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nts <- some parseTicket
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void eof
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return $ Input r t nts
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> die $ errorBundlePretty bundle
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Right ops -> return ops
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compute :: Input -> Int
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compute (Input ranges ticket nearbyTickets) = foldl' compute' 0 nearbyTickets
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where
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compute' :: Int -> Ticket -> Int
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compute' acc nt = acc + (sum $ map isValid nt)
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isValid :: Int -> Int
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isValid n = minimum $ map (isValid' n) ranges
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isValid' :: Int -> Range -> Int
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isValid' n (Range{ll, lh, hl, hh})
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| (n >= ll && n <= lh) || (n >= hl && n <= hh) = 0
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| otherwise = n
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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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