Day 15: Warehouse Woes

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FAQ

  • gentooer@programming.devEnglish
    2·
    8 days ago

    Haskell

    Runs in 12 ms. I was very happy with my code for part 1, but will sadly have to rewrite it completely for part 2.

    Code 
    import Control.Monad.State.Lazy
import qualified Data.Map.Strict as M

type Coord = (Int, Int)
data Block = Box | Wall
type Grid = M.Map Coord Block

parse :: String -> ((Coord, Grid), [Coord])
parse s =
    let robot = head
            [ (r, c)
            | (r, row) <- zip [0 ..] $ lines s
            , (c, '@') <- zip [0 ..] row
            ]
        grid = M.fromAscList
            [ ((r, c), val)
            | (r, row) <- zip [0 ..] $ lines s
            , (c, Just val) <- zip [0 ..] $ map f row
            ]
    in  ((robot, grid), go s)
    where
        f 'O' = Just Box
        f '#' = Just Wall
        f _ = Nothing
        go ('^' : rest) = (-1,  0) : go rest
        go ('v' : rest) = ( 1,  0) : go rest
        go ('<' : rest) = ( 0, -1) : go rest
        go ('>' : rest) = ( 0,  1) : go rest
        go (_   : rest) =            go rest
        go [] = []

add :: Coord -> Coord -> Coord
add (r0, c0) (r1, c1) = (r0 + r1, c0 + c1)

moveBoxes :: Coord -> Coord -> Grid -> Maybe Grid
moveBoxes dr r grid = case grid M.!? r of
    Nothing   -> Just grid
    Just Wall -> Nothing
    Just Box  ->
        M.insert (add r dr) Box . M.delete r <$> moveBoxes dr (add r dr) grid

move :: Coord -> State (Coord, Grid) Bool
move dr = state $ \(r, g) -> case moveBoxes dr (add r dr) g of
    Just g' -> (True, (add r dr, g'))
    Nothing -> (False, (r, g))

moves :: [Coord] -> State (Coord, Grid) ()
moves = mapM_ move

main :: IO ()
main = do
    ((robot, grid), movements) <- parse <$> getContents
    let (_, grid') = execState (moves movements) (robot, grid)
    print $ sum [100 * r + c | ((r, c), Box) <- M.toList grid']