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+module Main where
+
+import Data.List (intercalate)
+import Data.Maybe (fromMaybe)
+import Data.Set (Set)
+import qualified Data.Set as S
+
+data Direction = East | South deriving (Show, Eq, Ord)
+
+type Coord = (Int, Int)
+
+type Board = Set (Coord, Direction)
+
+spaceFilled :: Board -> Coord -> Bool
+spaceFilled b c = S.member (c, East) b || S.member (c, South) b
+
+getDirection :: Board -> Coord -> Direction
+getDirection b c
+  | (c, East) `S.member` b = East
+  | (c, South) `S.member` b = South
+  | otherwise = undefined
+
+wrapAround :: Board -> Coord -> Coord
+wrapAround b (x, y) = (x', y')
+  where
+    x' = if x > mx then 0 else x
+    y' = if y > my then 0 else y
+    mx = 138
+    my = 136
+
+stepOne :: Board -> (Coord, Direction) -> (Coord, Direction)
+stepOne b (c@(x, y), d) = (if canMove then newCoord else c, d)
+  where
+    newCoord = case d of
+      East -> wrapAround b (x + 1, y)
+      South -> wrapAround b (x, y + 1)
+    canMove = not $ spaceFilled b newCoord
+
+stepAll :: Board -> Board
+stepAll ib = S.map (stepSouth eastStepped) eastStepped
+  where
+    eastStepped = S.map (stepEast ib) ib
+    stepEast b x@(_, East) = stepOne b x
+    stepEast b x = x
+    stepSouth b x@(_, South) = stepOne b x
+    stepSouth b x = x
+
+stepTillStationary :: Board -> (Board, Int)
+stepTillStationary ib = keepStepping ib 0
+  where
+    keepStepping b n
+      | b == b' = (b, n + 1)
+      | otherwise = keepStepping b' (n + 1)
+      where
+        b' = stepAll b
+
+parseFile :: String -> Board
+parseFile str = S.fromList $ getFilled str 0 0
+  where
+    getFilled [] x y = []
+    getFilled ('.' : cs) x y = getFilled cs (x + 1) y
+    getFilled ('\n' : cs) x y = getFilled cs 0 (y + 1)
+    getFilled ('>' : cs) x y = ((x, y), East) : getFilled cs (x + 1) y
+    getFilled ('v' : cs) x y = ((x, y), South) : getFilled cs (x + 1) y
+    getFilled (_ : cs) x y = undefined
+
+printBoard :: Board -> String
+printBoard b = intercalate "\n" $ map printLine [0 .. 10]
+  where
+    printLine y = map (printCell y) [0 .. 10]
+    printCell y x
+      | spaceFilled b (x, y) = case getDirection b (x, y) of
+        East -> '>'
+        South -> 'v'
+      | otherwise = '.'
+
+main :: IO ()
+main = do
+  input <- readFile "./input"
+  let parsed = parseFile input
+  print $ fromMaybe 0 $ S.lookupMax $ S.map (fst . fst) parsed
+  print $ fromMaybe 0 $ S.lookupMax $ S.map (snd . fst) parsed
+  -- putStrLn $ printBoard parsed
+  -- putStrLn "---"
+  -- putStrLn $ printBoard $ foldr (\x b -> stepAll b) parsed [0 .. 0]
+
+  print $ snd $ stepTillStationary parsed
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