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Problem 83: Almost there...

This commit is contained in:
Jonathan Chan 2017-10-23 22:47:05 -07:00
parent d09a6587ff
commit c0292d1a34
1 changed files with 23 additions and 13 deletions
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83_alt.hs
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@ -5,11 +5,11 @@ import Data.Foldable
import Data.PQueue.Min import Data.PQueue.Min
type Value = Integer type Value = Integer
type Distance = Maybe Integer -- Nothing represents infinity type Distance = Integer
type Position = (Int, Int) type Position = (Int, Int)
data Element = Element { data Element = Element {
value :: Value, value :: Value,
distance :: Distance, distance :: Maybe Distance, -- Nothing represents infinity
position :: Position position :: Position
} deriving (Eq, Show) } deriving (Eq, Show)
data PQE = PQE Element Distance deriving (Eq, Show) data PQE = PQE Element Distance deriving (Eq, Show)
@ -19,29 +19,39 @@ instance Ord PQE where
_ <= PQE _ Nothing = True _ <= PQE _ Nothing = True
PQE _ (Just d1) <= PQE _ (Just d2) = d1 <= d2 PQE _ (Just d1) <= PQE _ (Just d2) = d1 <= d2
dijkstra :: Matrix Element -> MinQueue PQE -> Position -> Distance getNeighbours :: Matrix Element -> Element -> [Element]
dijkstra m q p = getNeighbours m e =
let (i, j) = position e
in catMaybes [safeGet (i - 1) j m,
safeGet (i + 1) j m,
safeGet i (j - 1) m,
safeGet i (j + 1) m]
dijkstra :: Position -> Matrix Element -> MinQueue PQE -> Distance
dijkstra p m q =
let PQE minElement minDistance = findMin q let PQE minElement minDistance = findMin q
in if position minElement == p in if position minElement == p
then distance minElement then minDistance
else undefined --TODO else let (newM, newQ) = foldr update (m, q) $ getNeighbours m minElement
in dijkstra p newM newQ
where update neighbour (prevM, prevQ) =
let newDistance = minDistance + value neighbour
in case distance neighbour of
Nothing -> undefined
Just d -> undefined
findShortestPathLength :: Matrix Element -> Distance findShortestPathLength :: Matrix Element -> Distance
findShortestPathLength m = findShortestPathLength m =
let initialElement = m ! (1, 1) let initialElement = m ! (1, 1)
initialMinQ = singleton $ PQE initialElement $ distance initialElement initialMinQ = singleton $ PQE initialElement $ value initialElement
lastPos = (nrows m, ncols m) lastPos = (nrows m, ncols m)
in dijkstra m initialMinQ lastPos in dijkstra lastPos m initialMinQ
setInitial :: Matrix Element -> Matrix Element setInitial :: Matrix Element -> Matrix Element
setInitial m = setInitial m =
let v = value $ m ! (1, 1) let v = value $ m ! (1, 1)
maybeMatrix = safeSet (Element v (Just v) (1, 1)) (1, 1) m in unsafeSet (Element v (Just v) (1, 1)) (1, 1) m
in case maybeMatrix of
Just mm -> mm
Nothing -> m
initElement :: Matrix Integer -> Position -> Element initElement :: Matrix Integer -> Position -> Element
initElement m p = initElement m p =