Prims

Author: soumyadip007

Graph/prims.py

@@ -0,0 +1,123 @@
+import heapq
+
+class Vertex():
+
+	def __init__(self, name):
+		self.name = name
+		self.visited = False
+		self.predecessor = None
+		self.adjacencyList = []
+		
+	def __str__(self):
+		return self.name
+		
+class Edge():
+
+	def __init__(self, weight, startVertex, targetVertex):
+		self.weight = weight
+		self.startVertex = startVertex
+		self.targetVertex = targetVertex	
+		
+	def __lt__(self, other):
+		selfPriority = self.weight;
+		otherPriority = other.weight;
+		return selfPriority < otherPriority;
+	
+class PrimsJarnik():
+
+	def __init__(self, unvisitedList):
+		self.unvisitedList = unvisitedList
+		self.spanningTree = []
+		self.edgeHeap = []
+		self.fullCost = 0
+		
+	def calculateSpanningTree(self, vertex):
+		self.unvisitedList.remove(vertex);
+		while self.unvisitedList:
+		
+			for edge in vertex.adjacencyList:
+				if edge.targetVertex in self.unvisitedList:
+					heapq.heappush(self.edgeHeap, edge);
+
+			minEdge  = heapq.heappop(self.edgeHeap);
+
+			if minEdge.targetVertex in self.unvisitedList:
+				self.spanningTree.append(minEdge)      
+				print("Edge added to spanning tree: %s - %s" % (minEdge.startVertex.name,minEdge.targetVertex.name))
+				self.fullCost += minEdge.weight
+				vertex = minEdge.targetVertex
+				self.unvisitedList.remove(vertex)
+
+	def getSpanningTree(self):
+		return self.spanningTree
+		
+	def getCost(self):
+		return self.fullCost
+
+
+vertexA = Vertex("A")
+vertexB = Vertex("B")
+vertexC = Vertex("C")
+vertexD = Vertex("D")
+vertexE = Vertex("E")
+vertexF = Vertex("F")
+vertexG = Vertex("G")
+ 
+edgeAB = Edge(2, vertexA, vertexB)
+edgeBA = Edge(2, vertexB, vertexA)
+edgeAE = Edge(5, vertexA, vertexE)
+edgeEA = Edge(5, vertexE, vertexA)
+edgeAC = Edge(6, vertexA, vertexC)
+edgeCA = Edge(6, vertexC, vertexA)
+edgeAF = Edge(10, vertexA, vertexF)
+edgeFA = Edge(10, vertexF, vertexA)
+edgeBE = Edge(3, vertexB, vertexE)
+edgeEB = Edge(3, vertexE, vertexB)
+edgeBD = Edge(3, vertexB, vertexD)
+edgeDB = Edge(3, vertexD, vertexB)
+edgeCD = Edge(1, vertexC, vertexD)
+edgeDC = Edge(1, vertexD, vertexC)
+edgeCF = Edge(2, vertexC, vertexF)
+edgeFC = Edge(2, vertexF, vertexC)
+edgeDE = Edge(4, vertexD, vertexE)
+edgeED = Edge(4, vertexE, vertexD)
+edgeDG = Edge(5, vertexD, vertexG)
+edgeGD = Edge(5, vertexG, vertexD)
+edgeFG = Edge(3, vertexF, vertexG)
+edgeGF = Edge(3, vertexG, vertexF)
+ 
+unvisitedList = []
+unvisitedList.append(vertexA)
+unvisitedList.append(vertexB)
+unvisitedList.append(vertexC)
+unvisitedList.append(vertexD)
+unvisitedList.append(vertexE)
+unvisitedList.append(vertexF)
+unvisitedList.append(vertexG)
+ 
+vertexA.adjacencyList.append(edgeAB)
+vertexA.adjacencyList.append(edgeAC)
+vertexA.adjacencyList.append(edgeAE)
+vertexA.adjacencyList.append(edgeAF)
+vertexB.adjacencyList.append(edgeBA)
+vertexB.adjacencyList.append(edgeBD)
+vertexB.adjacencyList.append(edgeBE)
+vertexC.adjacencyList.append(edgeCA)
+vertexC.adjacencyList.append(edgeCD)
+vertexC.adjacencyList.append(edgeCF)
+vertexD.adjacencyList.append(edgeDB)
+vertexD.adjacencyList.append(edgeDC)
+vertexD.adjacencyList.append(edgeDE)
+vertexD.adjacencyList.append(edgeDG)
+vertexE.adjacencyList.append(edgeEA)
+vertexE.adjacencyList.append(edgeEB)
+vertexE.adjacencyList.append(edgeED)
+vertexF.adjacencyList.append(edgeFA)
+vertexF.adjacencyList.append(edgeFC)
+vertexF.adjacencyList.append(edgeFG)
+vertexG.adjacencyList.append(edgeGD)
+vertexG.adjacencyList.append(edgeGF)
+ 
+algorithm = PrimsJarnik(unvisitedList)
+algorithm.calculateSpanningTree(vertexD)
+print(algorithm.getCost())