1 files changed, 21 insertions, 0 deletions
diff --git a/Util.hs b/Util.hs
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+++ b/Util.hs
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+module Util where
+
+import qualified Data.Map.Strict as Map
+
+
+uniq :: Eq a => [a] -> [a]
+uniq (x:y:zs) | x == y = uniq (y:zs)
+              | otherwise = x : uniq (y:zs)
+uniq l = l
+
+sortUniq :: Ord a => [a] -> [a]
+sortUniq = uniq . sort
+
+oppositeGraph :: (Show a, Ord a) => Map.Map a [a] -> Map.Map a [a]
+oppositeGraph graph =
+    let nodes = concat [k : vs | (k, vs) <- Map.assocs graph]
+        edges = map ((,) <$> fst . head <*> map snd)
+                . groupBy ((==) `on` fst)
+                . sortOn fst
+                $ [(to, from) | (from, tos) <- Map.assocs graph, to <- tos]
+    in Map.fromList (map (,[]) nodes ++ edges)