Write a priority queue module to handle dependencies efficiently

This commit is contained in:
Tissevert 2020-01-01 17:16:19 +01:00
parent e751a60f47
commit 6b254dcdeb
2 changed files with 51 additions and 0 deletions

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@ -23,6 +23,7 @@ executable sjw
, Context
, Module
, Paths_SJW
, Priority
-- other-extensions:
build-depends: attoparsec
, base >=4.12 && <4.13

50
src/Priority.hs Normal file
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@ -0,0 +1,50 @@
{-# LANGUAGE NamedFieldPuns #-}
module Priority (
Queue(..)
, empty
, set
, toList
) where
import Data.Map (Map)
import qualified Data.Map as Map (
adjust, alter, delete, empty, insert, lookup, lookupMax
)
data Queue a = Queue {
byElement :: Map a Int
, byRank :: Map Int [a]
}
empty :: Queue a
empty = Queue {byElement = Map.empty, byRank = Map.empty}
set :: Ord a => a -> Int -> Queue a -> Queue a
set x priority queue@(Queue {byElement, byRank}) =
case Map.lookup x byElement of
Nothing -> Queue {
byElement = Map.insert x priority byElement
, byRank = Map.alter (push x) priority byRank
}
Just formerPriority
| formerPriority >= priority -> queue
| otherwise -> queue {
byElement = Map.insert x priority byElement
, byRank = move x formerPriority priority byRank
}
push :: a -> Maybe [a] -> Maybe [a]
push a Nothing = Just [a]
push a (Just as) = Just (a:as)
move :: Eq a => a -> Int -> Int -> Map Int [a] -> Map Int [a]
move a from to =
Map.alter (push a) to . Map.adjust (filter (/= a)) from
toList :: Queue a -> [(Int, a)]
toList = extract . byRank
where
extract tmpMap =
case Map.lookupMax tmpMap of
Nothing -> []
Just (k, elems) -> ((,) k <$> elems) ++ extract (Map.delete k tmpMap)