2024-15 in haskell
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2024/15-Warehouse_Woes/second.hs
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164
2024/15-Warehouse_Woes/second.hs
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-- 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 = 9021
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data Tile = Wall | Box | Lbox | Rbox | 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 (Eq, 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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showWarehouse :: Warehouse -> String
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showWarehouse w = V.foldl' showOne [] w
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showOne acc line = acc ++ (V.foldl' showTile [] line) ++ "\n"
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showTile acc Wall = acc ++ "#"
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showTile acc Lbox = acc ++ "["
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showTile acc Rbox = acc ++ "]"
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showTile acc Floor = acc ++ "."
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showTile acc Robot = acc ++ "@"
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showTile acc Box = acc ++ "O"
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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 Lbox = 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 == Lbox = case push w r' op of
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Just w' -> (w', r')
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Nothing -> a
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| (op == N || op == S) && t == Rbox = case push w (x'-1, y') op of -- we want to always push boxes from their left side to reduce push cases
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Just w' ->(w', r')
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Nothing -> a
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| t == Rbox = case push w (x', y') op of
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Just w' -> (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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| (op == N || op == S) && tr == Wall = Nothing
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| (op == N || op == S) && t == Lbox = case push w (x, y') op of -- pushing a boxes that matches ours
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Just w' -> let l1 = w' V.! y
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l1' = l1 V.// [(x, Floor), (x+1, Floor)]
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l2 = w' V.! y'
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l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
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in Just (w' V.// [(y, l1'), (y', l2')])
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Nothing -> Nothing
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| (op == N || op == S) && t == Rbox = case push w (x-1, y') op of
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Just w' -> if tr == Lbox then case push w' (x+1, y') op of -- are we pushing two boxes?
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Just w'' -> let l1 = w'' V.! y
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l1' = l1 V.// [(x, Floor), (x+1, Floor)]
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l2 = w'' V.! y'
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l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
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in Just (w'' V.// [(y, l1'), (y', l2')])
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Nothing -> Nothing
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else let l1 = w' V.! y -- or just one on our left
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l1' = l1 V.// [(x, Floor), (x+1, Floor)]
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l2 = w' V.! y'
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l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
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in Just (w' V.// [(y, l1'), (y', l2')])
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Nothing -> Nothing
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| (op == N || op == S) && tr == Lbox = case push w (x+1, y') op of -- or just one on our right
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Just w' -> let l1 = w' V.! y
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l1' = l1 V.// [(x, Floor), (x+1, Floor)]
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l2 = w' V.! y'
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l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
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in Just (w' V.// [(y, l1'), (y', l2')])
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Nothing -> Nothing
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| (op == N || op == S) = let l1 = w V.! y -- free space
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l1' = l1 V.// [(x, Floor), (x+1, Floor)]
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l2 = w V.! y'
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l2' = l2 V.// [(x, Lbox), (x+1, Rbox)]
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in Just (w V.// [(y, l1'), (y', l2')])
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| t == Lbox || t == Rbox = case push w (x', y) op of -- East-West movements are simpler
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Just w' -> let l = w' V.! y
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l' = l V.// [(x, Floor), (x', to)]
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in Just (w' V.// [(y, l')])
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Nothing -> Nothing
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| otherwise = let l = w V.! y -- free space
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l' = l V.// [(x, Floor), (x', to)]
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in Just (w V.// [(y, l')])
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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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tr = w V.! y' V.! (x'+1)
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to = w V.! y V.! x
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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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wideWidth = 2 * V.length (warehouse V.! 0)
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warehouse' = V.map widen warehouse
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widen line = V.ifoldl' widenOne (V.replicate wideWidth Floor) line
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widenOne acc x Wall = acc V.// [(2*x, Wall), (2*x+1, Wall)]
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widenOne acc x Box = acc V.// [(2*x, Lbox), (2*x+1, Rbox)]
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widenOne acc x Robot = acc V.// [(2*x, Robot)]
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widenOne acc _ _ = acc
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main :: IO ()
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main = do
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example <- parseInput "example2"
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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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input <- parseInput "input"
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print $ compute input
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