66 lines
2.1 KiB
Haskell
66 lines
2.1 KiB
Haskell
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-- requires cabal install --lib megaparsec parser-combinators
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module Main (main) where
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import Control.Monad (void, when)
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import Data.List qualified as L
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import Data.Map qualified as M
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import Data.Maybe (fromJust)
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import Data.Set qualified as S
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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 System.Exit (die)
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exampleExpectedOutput = 10
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data Direction = E | W | NE | NW | SE | SW
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type Directions = [Direction]
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type Coordinates = (Int, Int, Int)
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type Floor = M.Map Coordinates Bool
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type Input = [Directions]
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type Parser = Parsec Void String
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parseDirection :: Parser Direction
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parseDirection = (string "se" *> return SE)
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<|> (string "sw" *> return SW)
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<|> (string "ne" *> return NE)
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<|> (string "nw" *> return NW)
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<|> (char 'e' *> return E)
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<|> (char 'w' *> return W)
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parseInput' :: Parser Input
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parseInput' = some (some parseDirection <* optional (char '\n')) <* eof
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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 -> die $ errorBundlePretty bundle
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Right input' -> return input'
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compute :: Input -> Int
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compute input = M.size . M.filter id $ L.foldl' compute' M.empty input
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where
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compute' :: Floor -> Directions -> Floor
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compute' floor directions = case M.lookup destination floor of
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Just f -> M.insert destination (not f) floor
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Nothing -> M.insert destination True floor
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where
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destination :: Coordinates
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destination = L.foldl' run (0, 0, 0) directions
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run :: Coordinates -> Direction -> Coordinates
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run (x, y, z) E = (x+1,y-1,z)
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run (x, y, z) W = (x-1,y+1,z)
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run (x, y, z) NE = (x+1,y,z-1)
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run (x, y, z) SW = (x-1,y,z+1)
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run (x, y, z) NW = (x,y+1,z-1)
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run (x, y, z) SE = (x,y-1,z+1)
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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
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when (exampleOutput /= exampleExpectedOutput) (die $ "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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