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import Prelude hiding (Right, Left, flip)
import Control.Monad
import Data.Array.Unboxed
import Data.Char
type Idx = (Int, Int)
type Chart = UArray Idx Char
data Dir = Up | Right | Down | Left
deriving (Show, Eq)
add :: Idx -> Dir -> Idx
add (y, x) dir = case dir of
Up -> (y - 1, x)
Right -> (y, x + 1)
Down -> (y + 1, x)
Left -> (y, x - 1)
flip :: Dir -> Dir
flip Down = Up
flip Up = Down
flip Right = Left
flip Left = Right
corresponds :: Char -> Dir -> Bool
corresponds '|' dir = dir `elem` [Down, Up]
corresponds '-' dir = dir `elem` [Right, Left]
corresponds '+' _ = True
corresponds c _ | isAlpha c = True
corresponds ' ' _ = False
corresponds c d = error ("corresponds: " ++ show c ++ " " ++ show d)
steer :: Chart -> Idx -> Char -> Dir -> Dir
steer _ _ '|' Down = Down
steer _ _ '|' Up = Up
steer _ _ '|' dir = dir
steer _ _ '-' Right = Right
steer _ _ '-' Left = Left
steer _ _ '-' dir = dir
steer chart idx '+' dir =
let [newdir] = [dir' | dir' <- [Up, Right, Down, Left],
dir' /= flip dir,
corresponds (chart ! add idx dir') dir']
in newdir
steer _ idx ' ' dir = error ("Went into spaces with direction " ++ show dir ++ " at " ++ show idx)
follow :: Chart -> Idx -> Dir -> ([Char], Int)
follow chart idx dir =
if isAlpha (chart ! idx)
then if chart ! add idx dir == ' '
then ([chart ! idx], 1)
else let (str, count) = follow chart (add idx dir) dir
in (chart ! idx : str, count + 1)
else let newdir = steer chart idx (chart ! idx) dir
in fmap succ $ follow chart (add idx newdir) newdir
findStart :: Chart -> Idx
findStart chart =
let ((0, 0), (_, w')) = bounds chart
[x] = [i | i <- [0..w'], chart ! (0, i) /= ' ']
in (0, x)
main :: IO ()
main = do
input <- (readFile "19.in")
let w = length (head (lines input))
h = length (lines input)
chart = listArray ((0, 0), (h-1, w-1)) (filter (/= '\n') input)
let start = findStart chart
(str, count) = follow chart start Down
putStrLn str
print count
|
