1 files changed, 6 insertions, 5 deletions
diff --git a/12-1.hs b/12-1.hs
index 78ea186..11b793f 100644
--- a/12-1.hs
+++ b/12-1.hs
@@ -1,4 +1,5 @@
 import Data.Array
+import Data.HashSet as HS (HashSet, fromList, member, singleton, toList)
 import Data.List (nub)
 
 type Map = Array (Int,Int) (Maybe Char)
@@ -25,18 +26,18 @@ findNext = go
                  | otherwise = Nothing
 
 getRegion :: Map -> (Int,Int) -> [(Int,Int)]
-getRegion m p = go [p] [p]
+getRegion m p = go (HS.singleton p) [p]
   where
-    go :: [(Int,Int)]  -> [(Int,Int)] -> [(Int,Int)]
+    go :: HS.HashSet (Int,Int) -> [(Int,Int)] -> [(Int,Int)]
     go visited points =
       let v = filter f
-            . filter (not . (`elem` visited))
+            . filter (not . (`HS.member` visited))
             . nub
             . concatMap neighbours
             $ points
       in case v of
-           [] -> visited
-           _  -> go (visited ++ v) v
+           [] -> HS.toList visited
+           _  -> go (visited <> HS.fromList v) v
     
     f :: (Int,Int) -> Bool
     f p' = inRange (bounds m) p' && m ! p == m ! p'