86 lines
2.7 KiB
Haskell
86 lines
2.7 KiB
Haskell
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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.Applicative.Permutations
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import Control.Monad (void, when)
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import qualified Data.Char as C
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import Data.Either
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import Data.Functor
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import qualified Data.Heap as H
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import qualified Data.List as L
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import qualified Data.Map as M
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import Data.Maybe
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import qualified Data.Set as S
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import qualified Data.Vector as V
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import qualified Data.Vector.Unboxed as VU
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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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import Debug.Trace
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exampleExpectedOutput = 16
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data Tile = Start | Plot | Rock deriving Eq
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instance Show Tile where
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show Start = "S"
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show Plot = "."
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show Rock = "#"
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type Line = V.Vector Tile
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type Input = V.Vector Line
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type Parser = Parsec Void String
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parseTile :: Parser Tile
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parseTile = char 'S' $> Start
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<|> char '.' $> Plot
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<|> char '#' $> Rock
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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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parseInput' :: Parser Input
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parseInput' = do
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line <- some parseLine <* eof
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return $ V.generate (length line) (line !!)
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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 Steps = M.Map (Int, Int) ()
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compute :: Input -> Int -> Int
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compute input s = M.size $ compute' s start
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where
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compute' :: Int -> Steps -> Steps
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compute' 0 steps = steps
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compute' i steps = compute' (i-1) next
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where
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next :: Steps
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next = M.foldrWithKey nextSteps M.empty steps
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nextSteps :: (Int, Int) -> () -> Steps -> Steps
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nextSteps (x, y) _ = nextOne (x-1, y) . nextOne (x+1, y) . nextOne (x, y-1) . nextOne (x, y+1)
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nextOne :: (Int, Int) -> Steps -> Steps
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nextOne (x, y) acc = case input V.!? y of
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Just line -> case line V.!? x of
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Just Rock -> acc
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Just _ -> M.insert (x, y) () acc
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_ -> acc
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Nothing -> acc
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start = M.singleton (mid, mid) ()
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mid = V.length input `div` 2
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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 6
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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 64
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