124 lines
3.9 KiB
Haskell
124 lines
3.9 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators
|
|
module Main (main) where
|
|
|
|
import Control.Applicative.Permutations
|
|
import Control.Monad (void, when)
|
|
import Data.Char qualified as C
|
|
import Data.Either
|
|
import Data.Functor
|
|
import Data.List qualified as L
|
|
import Data.Map qualified as M
|
|
import Data.Maybe
|
|
import Data.Set qualified as S
|
|
import Data.Vector qualified as V
|
|
import Data.Void (Void)
|
|
import Text.Megaparsec
|
|
import Text.Megaparsec.Char
|
|
|
|
import Debug.Trace
|
|
|
|
exampleExpectedOutput = 4
|
|
|
|
data Direction = N | S | E | W deriving (Eq, Show)
|
|
data Tile = NS | NE | NW | EW | ES | WS | Floor | Start deriving (Eq, Show)
|
|
type Line = V.Vector Tile
|
|
type Input = V.Vector Line
|
|
|
|
type Parser = Parsec Void String
|
|
|
|
parseTile :: Parser Tile
|
|
parseTile = char '|' $> NS
|
|
<|> char 'L' $> NE
|
|
<|> char 'J' $> NW
|
|
<|> char '-' $> EW
|
|
<|> char 'F' $> ES
|
|
<|> char '7' $> WS
|
|
<|> char '.' $> Floor
|
|
<|> 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'
|
|
|
|
compatible :: Tile -> Direction -> Bool
|
|
compatible NS N = True
|
|
compatible NS S = True
|
|
compatible NE N = True
|
|
compatible NE E = True
|
|
compatible NW N = True
|
|
compatible NW W = True
|
|
compatible EW E = True
|
|
compatible EW W = True
|
|
compatible ES E = True
|
|
compatible ES S = True
|
|
compatible WS W = True
|
|
compatible WS S = True
|
|
compatible _ _ = False
|
|
|
|
type Position = (Int, Int)
|
|
type Heading = (Position, Direction)
|
|
|
|
compute :: Input -> Int
|
|
compute input = walk start 0 `div` 2
|
|
where
|
|
walk :: Heading -> Int -> Int
|
|
walk h i | tile (fst h) == Just Start = i+1
|
|
| otherwise = walk h' (i+1)
|
|
where
|
|
h' = step h
|
|
step :: Heading -> Heading
|
|
step (p@(x, y), N) | tile p == Just NS = ((x, y-1), N)
|
|
| tile p == Just ES = ((x+1, y), E)
|
|
| tile p == Just WS = ((x-1, y), W)
|
|
step (p@(x, y), S) | tile p == Just NS = ((x, y+1), S)
|
|
| tile p == Just NE = ((x+1, y), E)
|
|
| tile p == Just NW = ((x-1, y), W)
|
|
step (p@(x, y), E) | tile p == Just NW = ((x, y-1), N)
|
|
| tile p == Just EW = ((x+1, y), E)
|
|
| tile p == Just WS = ((x, y+1), S)
|
|
step (p@(x, y), W) | tile p == Just NE = ((x, y-1), N)
|
|
| tile p == Just EW = ((x-1, y), W)
|
|
| tile p == Just ES = ((x, y+1), S)
|
|
start = head $ catMaybes [startn, starte, starts, startw]
|
|
startn = nearStart (sx, sy-1) N
|
|
starts = nearStart (sx, sy+1) S
|
|
starte = nearStart (sx+1, sy) E
|
|
startw = nearStart (sx-1, sy) W
|
|
nearStart :: Position -> Direction -> Maybe Heading
|
|
nearStart p d = case tile p of
|
|
Just t -> if compatible t d then Just (p, d) else Nothing
|
|
Nothing -> Nothing
|
|
(sx, sy) = (x, y) -- start
|
|
where
|
|
hasNoStart :: Line -> Bool
|
|
hasNoStart = V.all (/= Start)
|
|
y = length $ V.takeWhile hasNoStart input
|
|
x = length $ V.takeWhile (/= Start) (input V.! y)
|
|
tile :: Position -> Maybe Tile
|
|
tile (x, y) = case input V.!? y of
|
|
Just line -> line V.!? x
|
|
Nothing -> Nothing
|
|
|
|
main :: IO ()
|
|
main = do
|
|
example <- parseInput "example"
|
|
let exampleOutput = compute example
|
|
when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
|
|
example2 <- parseInput "example2"
|
|
let exampleOutput2 = compute example2
|
|
when (exampleOutput2 /= 8) (error $ "example failed: got " ++ show exampleOutput2 ++ " instead of " ++ show 8)
|
|
input <- parseInput "input"
|
|
print $ compute input
|