91 lines
3.3 KiB
Haskell
91 lines
3.3 KiB
Haskell
|
-- requires cabal install --lib megaparsec parser-combinators heap vector
|
||
|
|
module Main (main) where
|
||
|
|
|
||
|
|
import Control.Monad (void, when)
|
||
|
|
import Data.Functor
|
||
|
|
import qualified Data.Heap as H
|
||
|
|
import qualified Data.List as L
|
||
|
|
import qualified Data.Map as M
|
||
|
|
import qualified Data.Vector as V
|
||
|
|
import Data.Void (Void)
|
||
|
|
import Text.Megaparsec
|
||
|
|
import Text.Megaparsec.Char
|
||
|
|
|
||
|
|
exampleExpectedOutput = 11048
|
||
|
|
|
||
|
|
data Tile = Wall | Floor | Start | End deriving (Eq, Show)
|
||
|
|
type Line = V.Vector Tile
|
||
|
|
type Input = V.Vector Line
|
||
|
|
|
||
|
|
type Parser = Parsec Void String
|
||
|
|
|
||
|
|
parseTile :: Parser Tile
|
||
|
|
parseTile = char '#' $> Wall
|
||
|
|
<|> char '.' $> Floor
|
||
|
|
<|> char 'E' $> End
|
||
|
|
<|> char 'S' $> Start
|
||
|
|
|
||
|
|
parseLine :: Parser Line
|
||
|
|
parseLine = do
|
||
|
|
line <- some parseTile <* eol
|
||
|
|
return $ V.generate (length line) (line !!)
|
||
|
|
|
||
|
|
parseInput' :: Parser Input
|
||
|
|
parseInput' = do
|
||
|
|
line <- some parseLine <* eof
|
||
|
|
return $ V.generate (length line) (line !!)
|
||
|
|
|
||
|
|
parseInput :: String -> IO Input
|
||
|
|
parseInput filename = do
|
||
|
|
input <- readFile filename
|
||
|
|
case runParser parseInput' filename input of
|
||
|
|
Left bundle -> error $ errorBundlePretty bundle
|
||
|
|
Right input' -> return input'
|
||
|
|
|
||
|
|
type Cost = Int
|
||
|
|
data Heading = N | S | E | W deriving (Eq, Show)
|
||
|
|
type Coord = (Int, Int)
|
||
|
|
data Position = Position Coord Heading Cost deriving Show
|
||
|
|
instance Ord Position where
|
||
|
|
compare (Position _ _ c1) (Position _ _ c2) = c1 `compare` c2
|
||
|
|
instance Eq Position where
|
||
|
|
(Position _ _ c1) == (Position _ _ c2) = c1 == c2
|
||
|
|
type Visited = M.Map Coord Int
|
||
|
|
|
||
|
|
type Candidates = H.MinHeap Position
|
||
|
|
|
||
|
|
compute :: Input -> Int
|
||
|
|
compute input = walk M.empty $ H.singleton (Position start E 0)
|
||
|
|
where
|
||
|
|
walk :: Visited -> Candidates -> Int
|
||
|
|
walk v h | t == End = c
|
||
|
|
| otherwise = walk v' $ H.union h' $ H.fromList $ nexts v' $ Position p d c
|
||
|
|
where
|
||
|
|
([(Position p@(x, y) d c)], h') = H.splitAt 1 h
|
||
|
|
t = input V.! y V.! x
|
||
|
|
v' = case M.lookup p v of
|
||
|
|
Just c' -> if c < c' then M.insert p c v else v
|
||
|
|
Nothing -> M.insert p c v
|
||
|
|
nexts :: Visited -> Position -> [Position]
|
||
|
|
nexts v p = L.filter (valid v) $ candidates p
|
||
|
|
valid :: Visited -> Position -> Bool
|
||
|
|
valid v (Position p@(x, y) _ c) = input V.! y V.! x /= Wall && case M.lookup p v of
|
||
|
|
Just c' -> c < c'
|
||
|
|
Nothing -> True
|
||
|
|
candidates :: Position -> [Position]
|
||
|
|
candidates (Position (x, y) N c) = [ Position (x-1, y) W (c+1001), Position (x+1, y) E (c+1001), Position (x, y-1) N (c+1) ]
|
||
|
|
candidates (Position (x, y) S c) = [ Position (x-1, y) W (c+1001), Position (x+1, y) E (c+1001), Position (x, y+1) S (c+1) ]
|
||
|
|
candidates (Position (x, y) E c) = [ Position (x, y-1) N (c+1001), Position (x, y+1) S (c+1001), Position (x+1, y) E (c+1) ]
|
||
|
|
candidates (Position (x, y) W c) = [ Position (x, y-1) N (c+1001), Position (x, y+1) S (c+1001), Position (x-1, y) W (c+1) ]
|
||
|
|
height = V.length input
|
||
|
|
width = V.length (input V.! 0)
|
||
|
|
start = (1, height - 2)
|
||
|
|
|
||
|
|
main :: IO ()
|
||
|
|
main = do
|
||
|
|
example <- parseInput "example"
|
||
|
|
let exampleOutput = compute example
|
||
|
|
when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
|
||
|
|
input <- parseInput "input"
|
||
|
|
print $ compute input
|