Cleanup

src/IntMapHelp.hs

@@ -18,11 +18,14 @@ module IntMapHelp
 
     cycleGT,
     cycleLT,
+
+    invertIntMap,
 ) where
 
 import Control.Applicative
 import Data.Aeson
 import Data.IntMap.Strict
+import qualified Data.Map.Strict as M
 import GHC.Generics
 import LensHelp
 
@@ -94,3 +97,9 @@ cycleGT i m = lookupGT i m <|> lookupMin m
 
 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
+