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{-# LANGUAGE TupleSections #-}
module Util where
import Data.Function (on)
import Data.List
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)
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