58 lines
1.9 KiB
Haskell
58 lines
1.9 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Monad (void, when)
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import qualified Data.List as L
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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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exampleExpectedOutput = 12
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type Pair = (Int, Int)
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type Robot = (Pair, Pair)
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type Input = [Robot]
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type Parser = Parsec Void String
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parseNumber :: Parser Int
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parseNumber = read <$> some (digitChar <|> char '-')
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parsePair :: Parser Pair
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parsePair = (,) <$> parseNumber <* char ','
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<*> parseNumber
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parseRobot :: Parser Robot
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parseRobot = (,) <$> (string "p=" *> parsePair)
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<*> (string " v=" *> parsePair)
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parseInput' :: Parser Input
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parseInput' = some (parseRobot <* eol) <* eof
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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 -> error $ errorBundlePretty bundle
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Right input' -> return input'
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compute :: Int -> Int -> Input -> Int
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compute width height input = product $ L.foldl' safety [0, 0, 0, 0] input'
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where
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mx = width `div` 2
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my = height `div` 2
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input' = map step input
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step ((x, y), (v, w)) = (((x + v * 100) `mod` width), ((y + w * 100) `mod` height))
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safety acc@[a, b, c, d] (x, y) | x < mx && y < my = [a+1, b, c, d]
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| x > mx && y < my = [a, b+1, c, d]
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| x < mx && y > my = [a, b, c+1, d]
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| x > mx && y > my = [a, b, c, d+1]
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| otherwise = acc
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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 11 7 example
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when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute 101 103 input
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