109 lines
3.8 KiB
Haskell
109 lines
3.8 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 Data.Functor
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import qualified Data.List as L
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import qualified Data.Vector as V
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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 = 2028
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example2ExpectedOutput = 10092
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data Tile = Wall | Box | Floor | Robot deriving (Eq, Show)
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type Line = V.Vector Tile
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type Warehouse = V.Vector Line
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data Op = N | S | E | W deriving Show
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data Input = Input Warehouse [Op] deriving Show
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type Parser = Parsec Void String
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parseTile :: Parser Tile
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parseTile = char '#' $> Wall
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<|> char 'O' $> Box
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<|> char '.' $> Floor
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<|> char '@' $> Robot
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parseLine :: Parser Line
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parseLine = do
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line <- some parseTile <* eol
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return $ V.generate (length line) (line !!)
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parseOp :: Parser Op
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parseOp = char '^' $> N
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<|> char 'v' $> S
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<|> char '>' $> E
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<|> char '<' $> W
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parseInput' :: Parser Input
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parseInput' = do
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line <- some parseLine <* eol
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ops <- some (parseOp <* optional eol) <* eof
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return $ Input (V.generate (length line) (line !!)) ops
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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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type Coord = (Int, Int)
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next :: Coord -> Op -> Coord
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next (x, y) N = (x, y-1)
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next (x, y) S = (x, y+1)
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next (x, y) E = (x+1, y)
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next (x, y) W = (x-1, y)
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compute :: Input -> Int
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compute (Input warehouse ops) = V.ifoldl' scoreBoxes 0 warehouse'
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where
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scoreBoxes :: Int -> Int -> Line -> Int
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scoreBoxes acc y line = V.ifoldl' (scoreBox y) acc line
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scoreBox :: Int -> Int -> Int -> Tile -> Int
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scoreBox y acc x Box = acc + 100 * y + x
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scoreBox _ acc _ _ = acc
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warehouse' = fst $ L.foldl' step (warehouse, start) ops
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step :: (Warehouse, Coord) -> Op -> (Warehouse, Coord)
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step a@(w, r@(x, y)) op | t == Wall = a
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| t == Box = case push w r' op of
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Just w' -> let line = w' V.! y'
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line' = line V.// [(x', Floor)]
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w'' = w' V.// [(y', line')]
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in (w'', r')
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Nothing -> a
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| otherwise = (w, (x', y'))
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where
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r'@(x', y') = next r op
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t = w V.! y' V.! x'
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push :: Warehouse -> Coord -> Op -> Maybe Warehouse
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push w r@(x, y) op | t == Wall = Nothing
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| t == Box = push w (x', y') op
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| otherwise = Just w'
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where
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(x', y') = next r op
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t = w V.! y' V.! x'
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line = w V.! y'
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line' = line V.// [(x', Box)]
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w' = w V.// [(y', line')]
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start = V.ifoldl' findRobot (0, 0) warehouse
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findRobot :: (Int, Int) -> Int -> Line -> (Int, Int)
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findRobot (0, _) y line = (V.ifoldl' findRobotInLine 0 line, y)
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findRobot a _ _ = a
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findRobotInLine :: Int -> Int -> Tile -> Int
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findRobotInLine 0 x Robot = x
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findRobotInLine a _ _ = a
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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) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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example2 <- parseInput "example2"
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let example2Output = compute example2
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when (example2Output /= example2ExpectedOutput) (error $ "example2 failed: got " ++ show example2Output ++ " instead of " ++ show example2ExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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