Bellmanford

Author: soumyadip007

Graph/bellmanford.py

@@ -0,0 +1,119 @@
+import sys;
+
+class Node(object):
+
+	def __init__(self, name):
+		self.name = name;
+		self.visited = False;
+		self.predecessor = None;
+		self.adjacenciesList = [];
+		self.minDistance = sys.maxsize;
+		
+class Edge(object):
+
+	def __init__(self, weight, startVertex, targetVertex):
+		self.weight = weight;
+		self.startVertex = startVertex;
+		self.targetVertex = targetVertex;
+		
+class BellmanFord(object):
+
+	HAS_CYCLE = False;
+	
+	def calculateShortestPath(self, vertexList, edgeList, startVertex):
+	
+		startVertex.minDistance = 0;
+		
+		for i in range(0,len(vertexList)-1):
+			for edge in edgeList:
+			
+				u = edge.startVertex;
+				v = edge.targetVertex;
+				
+				newDistance = u.minDistance + edge.weight;
+				
+				if newDistance < v.minDistance:
+					v.minDistance = newDistance;
+					v.predecessor = u;
+					
+		for edge in edgeList:
+			if self.hasCycle(edge):
+				print("Negative cycle detected...");
+				BellmanFord.HAS_CYCLE = True;
+				return;
+				
+	def hasCycle(self, edge):
+		if (edge.startVertex.minDistance + edge.weight) < edge.targetVertex.minDistance:
+			return True;
+		else:
+			return False;
+			
+	def getShortestPathTo(self, targetVertex):
+
+		if not BellmanFord.HAS_CYCLE:
+			print("Shortest path exists with value: ", targetVertex.minDistance);
+			
+			node = targetVertex;
+			
+			while node is not None:
+				print("%s " % node.name);
+				node = node.predecessor;
+		else:
+			print("Negative cycle detected...");
+			
+			
+node1 = Node("A");
+node2 = Node("B");
+node3 = Node("C");
+node4 = Node("D");
+node5 = Node("E");
+node6 = Node("F");
+node7 = Node("G");
+node8 = Node("H");
+
+edge1 = Edge(5,node1,node2);
+edge2 = Edge(8,node1,node8);
+edge3 = Edge(9,node1,node5);
+edge4 = Edge(15,node2,node4);
+edge5 = Edge(12,node2,node3);
+edge6 = Edge(4,node2,node8);
+edge7 = Edge(7,node8,node3);
+edge8 = Edge(6,node8,node6);
+edge9 = Edge(5,node5,node8);
+edge10 = Edge(4,node5,node6);
+edge11 = Edge(20,node5,node7);
+edge12 = Edge(1,node6,node3);
+edge13 = Edge(13,node6,node7);
+edge14 = Edge(3,node3,node4);
+edge15 = Edge(11,node3,node7);
+edge16 = Edge(9,node4,node7);
+
+edge17 = Edge(1,node1,node2);
+edge18 = Edge(1,node2,node3);
+edge19 = Edge(-3,node3,node1);
+
+node1.adjacenciesList.append(edge1);
+node1.adjacenciesList.append(edge2);
+node1.adjacenciesList.append(edge3);
+node2.adjacenciesList.append(edge4);
+node2.adjacenciesList.append(edge5);
+node2.adjacenciesList.append(edge6);
+node8.adjacenciesList.append(edge7);
+node8.adjacenciesList.append(edge8);
+node5.adjacenciesList.append(edge9);
+node5.adjacenciesList.append(edge10);
+node5.adjacenciesList.append(edge11);
+node6.adjacenciesList.append(edge12);
+node6.adjacenciesList.append(edge13);
+node3.adjacenciesList.append(edge14);
+node3.adjacenciesList.append(edge15);
+node4.adjacenciesList.append(edge16);
+
+
+vertexList = (node1,node2,node3, node4, node5, node6, node7, node8);
+#edgeList = (edge1,edge2,edge3,edge4,edge5,edge6,edge7,edge8,edge9,edge10,edge11,edge12,edge13,edge14,edge15,edge16);
+edgeList = (edge17, edge18, edge19);
+
+algorithm = BellmanFord();
+algorithm.calculateShortestPath(vertexList, edgeList, node1);
+algorithm.getShortestPathTo(node7);