Day 14, part 2 - partial progress

14.hs

@@ -2,6 +2,8 @@ import Data.List.Split (chunksOf)
 import Data.Char (ord)
 import Data.Bits (xor)
 import Text.Printf (printf)
+import Data.Matrix (Matrix, fromLists, safeGet)
+import Data.HashSet (Set, member, insert)
 
 type Length = Int
 type State = ([Int], Int, Int)
@@ -23,9 +25,19 @@ sparseHash lengths =
     let (hashed, _, _) = iterate (hash lengths) ([0..255], 0, 0) !! 64
     in  concat . map (printf "%08b" . foldr xor 0) . chunksOf 16 $ hashed
 
+visit :: Matrix Int -> (Int, Int) -> Set (Int, Int) -> Set (Int, Int)
+visit matrix (row, col) seen = if member (row, col) seen then seen else 
+    let newSeen = insert (row, col) seen
+    in
+    case safeGet row col matrix of 
+        Nothing -> seen
+        Just 0  -> newSeen
+        Just 1  -> foldr (visit matrix) newSeen [(row + 1, col), (row - 1, col), (row, col + 1), (row, col - 1)]
+
 main :: IO ()
 main = do
     let hashes = map (sparseHash . (++ [17, 31, 73, 47, 23]) . map ord . ("ffayrhll-" ++) . show) [0..127]
         used   = length . filter (== '1') . concat $ hashes
+        matrix = fromLists hashes
     print $ used
     mapM_ print hashes