50 lines
1.6 KiB
Haskell
50 lines
1.6 KiB
Haskell
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{-# LANGUAGE BangPatterns #-}
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import Data.HashMap.Strict (HashMap, lookupDefault, insert, empty)
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data Direction = North | East | South | West deriving Enum
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type Grid = HashMap (Int, Int) Char
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type State = (Grid, (Int, Int), Direction, Int)
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(%) = mod
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changeDirection :: Char -> Direction -> Direction
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changeDirection c = case c of
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'#' -> toEnum . (%4) . (+1) . fromEnum
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'F' -> toEnum . (%4) . (+2) . fromEnum
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'.' -> toEnum . (%4) . (+3) . fromEnum
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'W' -> id
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changeNode :: Char -> Char
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changeNode c = case c of
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'.' -> 'W'
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'W' -> '#'
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'#' -> 'F'
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'F' -> '.'
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incrementPosition :: Direction -> (Int, Int) -> (Int, Int)
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incrementPosition dir (x, y) = case dir of
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North -> (x, y - 1)
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East -> (x + 1, y)
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South -> (x, y + 1)
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West -> (x - 1, y)
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nextState :: State -> State
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nextState (grid, pos, dir, count) =
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let currNode = lookupDefault '.' pos grid
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newDir = changeDirection currNode dir
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newGrid = insert pos (changeNode currNode) grid
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newPos = incrementPosition newDir pos
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!newCount = count + if currNode == 'W' then 1 else 0
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in (newGrid, newPos, newDir, newCount)
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stricterate :: Int -> State -> Int
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stricterate 0 (_, _, _, count) = count
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stricterate n state = let !next = nextState state in stricterate (n-1) next
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parseRow :: (Int, [(Int, Char)]) -> Grid -> Grid
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parseRow (y, xs) grid = foldr (\(x, c) currGrid -> insert (x, y) c currGrid) grid xs
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main :: IO ()
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main = do
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input <- readFile "22.txt"
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let grid = foldr parseRow empty $ zip [-12..12] . map (zip [-12..12]) . lines $ input
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print $ stricterate 10000000 (grid, (0, 0), North, 0)
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