Commit before potential Door refactor

src/IntMapHelp.hs

@@ -18,6 +18,7 @@ module IntMapHelp
     cycleGT,
     cycleLT,
     invertIntMap,
+    invertIntMapUnique,
 ) where
 
 import Control.Applicative
@@ -97,7 +98,7 @@ cycleLT :: Int -> IntMap a -> Maybe (Int, a)
 cycleLT i m = lookupLT i m <|> lookupMax m
 
 invertIntMap :: Ord a => IntMap a -> M.Map a [Int]
-invertIntMap =
-    foldrWithKey
-        (\k xs -> M.insertWith (++) xs [k])
-        mempty
+invertIntMap = foldrWithKey (\k x -> M.insertWith (++) x [k]) mempty
+
+invertIntMapUnique :: Ord a => IntMap a -> M.Map a Int
+invertIntMapUnique = foldlWithKey' (\m k x -> M.insert x k m) mempty