WIP on Prim algorithm.

A total mess at the moment.

src/Grasph/Algorithm/MWST.hs

@@ -19,14 +19,42 @@ kruskal' (e:es) mwt = if acyclic mwtWithEdge
           acyclic g = length (vertices g) == length (edges g) + 1
 
 prim :: (Ord w) => Graph v w d -> Graph v w d
-prim g = g {edges = prim' g g [] (lengthmap g)}
+prim g = g {edges = prim' g [tail $ vertices g] [head $ vertices g] [] (lengthmap g)}
 
-prim' :: (Ord w) => [v] -> [Edge v w d] -> Int -> M.Map v (Infinitable w)
-prim' v v' t lv
-    | length v' == n = t
-    |
+prim' :: (Ord w) => Graph v w d
+                 -> [v]                     -- the set (V-V')
+                 -> [v]                     -- V'
+                 -> [Edge v w d]            -- T
+                 -> M.Map v (Infinitable w) -- L(v)
+                 -> [Edge v w d]
+prim' g unvisited v'@(u:us) t lv
+    | length v' == (length $ vertices g) = t
+    | otherwise = prim' g unvisited' v'' e:t lv'
+    where w = minWeightV [(v, fromJust (M.lookup lv v)) | v <- unvisited]
+          e = findEdge (u, w)
 
-lengthmap :: (Ord w) => Graph v w d -> v -> M.Map v (Infinitable w)
-lengthmap g v = fromList . map f $ edges g
-    where f edge =
-          adj = adjacencyList g v
+lengthmap :: (Ord w) => Graph v w d
+                     -> [v]
+                     -> v
+                     -> M.Map v (Edge v w d, Infinitable w)
+lengthmap g vs u = fromList . map f $ vertices g
+    where f v= (v, dist g vs v)
+          adj = adjacencyList g u
+
+dist :: Graph v w d -> v -> v -> Infinitable w
+dist g u v = dist' (allEdges g) u v
+
+-- Find the distance from a set of vertices to a given vertex
+dist :: Graph v w d -> [v] -> v -> (v, Infinitable w)
+dist g vset v' = dist' (allEdges g) vset v
+
+dist' [] _ _ = PositiveInfinity
+dist' es vset v' = tupleSndMin $ map (\v -> dist'' es v v')
+
+dist'' :: [Edge v w d] -> v -> v -> (v, Infinitable w)
+dist'' [] _ _ = PositiveInfinity
+dist'' (e:es) u v
+    | endpoints e == (u,v) = Regular $ weight e
+    | otherwise = dist' es u v
+
+tupleSndMin = foldl1 (\t1 t2 -> if (snd t1) < (snd t2) then t1 else t2)

src/Grasph/Graph.hs

@@ -183,10 +183,12 @@ reverseEdge e@(Edge (v1,v2) _ _) = e { endpoints=(v2,v1) }
 reverseEdges :: Graph v w c -> [Edge v w c]
 reverseEdges g = map reverseEdge $ edges g
 
-
 allEdges :: Graph v w c -> [Edge v w c]
 allEdges g = if directed g then edges g else edges g ++ reverseEdges g
 
+findEdge :: Graph v w d -> (v,v) -> Edge v w d
+findEdge g pair = head $ filter (\e -> endpoints e == pair) (edges g)
+
 incidentEdges :: (Eq v) => Graph v w c -> v -> [Edge v w c]
 incidentEdges g v = incidentEdges' (edges g) v []