Krushkal

Author: soumyadip007

Graph/kruskal.py

@@ -0,0 +1,154 @@
+
+class Vertex(object):
+
+	def __init__(self, name):
+		self.name = name;
+		self.node = None; # !!!!
+		
+class Node(object):
+
+	def __init__(self, height, nodeId, parentNode):
+		self.height = height;
+		self.nodeId = nodeId;
+		self.parentNode = parentNode;
+		
+class Edge(object):
+	
+	def __init__(self, weight, startVertex, targetVertex):
+		self.weight = weight;
+		self.startVertex = startVertex;
+		self.targetVertex = targetVertex;
+		
+	def __cmp__(self, otherEdge):
+		return self.cmp(self.weight, otherEdge.weight);
+		
+	def __lt__(self, other):
+		selfPriority = self.weight;
+		otherPriority = other.weight;
+		return selfPriority < otherPriority;
+		
+class DisjointSet(object):
+
+	def __init__(self, vertexList):
+		self.vertexList = vertexList;
+		self.rootNodes = [];
+		self.nodeCount = 0;
+		self.setCount = 0;
+		self.makeSets(vertexList);
+		
+	def find(self, node):
+	
+		currentNode = node;
+		
+		while currentNode.parentNode is not None:
+			currentNode = currentNode.parentNode;
+			
+		root = currentNode;
+		currentNode = node;
+		
+		while currentNode is not root:
+			temp = currentNode.parentNode;
+			currentNode.parentNode = root;
+			currentNode = temp;
+			
+		return root.nodeId;
+	
+	def merge(self, node1, node2):
+	
+		index1 = self.find(node1);
+		index2 = self.find(node2);
+		
+		if index1 == index2:
+			return;  # they are in the same set !!!!
+			
+		root1 = self.rootNodes[index1];
+		root2 = self.rootNodes[index2];
+		
+		if root1.height < root2.height:
+			root1.parentNode = root2;
+		elif root1.height > root2.height:
+			root2.parentNode = root1;
+		else:
+			root2.parentNode = root1;
+			root1.height = root1.height + 1;
+		
+	def makeSets(self, vertexList):
+		for v in vertexList:
+			self.makeSet(v);
+			
+	def makeSet(self, vertex):
+		node = Node(0, len(self.rootNodes),None);
+		vertex.node = node;
+		self.rootNodes.append(node);
+		self.setCount = self.setCount + 1;
+		self.nodeCount = self.nodeCount + 1;
+		
+class KruskalAlgorithm(object):
+
+	def spanningTree(self, vertexList, edgeList):
+	
+		disjointSet = DisjointSet(vertexList);
+		spanningTree = [];
+		
+		edgeList.sort();
+		
+		for edge in edgeList:
+		
+			u = edge.startVertex;
+			v = edge.targetVertex;
+			
+			if disjointSet.find(u.node) is not disjointSet.find(v.node):
+				spanningTree.append(edge);
+				disjointSet.merge(u.node, v.node);  # !!!! dot
+				
+		for edge in spanningTree:
+			print(edge.startVertex.name," - ", edge.targetVertex.name);
+			
+vertex1 = Vertex("a");
+vertex2 = Vertex("b");
+vertex3 = Vertex("c");
+vertex4 = Vertex("d");
+vertex5 = Vertex("e");
+vertex6 = Vertex("f");
+vertex7 = Vertex("g");
+
+edge1 = Edge(2,vertex1,vertex2);
+edge2 = Edge(6,vertex1,vertex3);
+edge3 = Edge(5,vertex1,vertex5);
+edge4 = Edge(10,vertex1,vertex6);
+edge5 = Edge(3,vertex2,vertex4);
+edge6 = Edge(3,vertex2,vertex5);
+edge7 = Edge(1,vertex3,vertex4);
+edge8 = Edge(2,vertex3,vertex6);
+edge9 = Edge(4,vertex4,vertex5);
+edge10 = Edge(5,vertex4,vertex7);
+edge11 = Edge(5,vertex6,vertex7);
+
+
+vertexList = [];
+vertexList.append(vertex1);
+vertexList.append(vertex2);
+vertexList.append(vertex3);
+vertexList.append(vertex4);
+vertexList.append(vertex5);
+vertexList.append(vertex6);
+vertexList.append(vertex7);
+
+edgeList = [];
+edgeList.append(edge1);
+edgeList.append(edge2);
+edgeList.append(edge3);
+edgeList.append(edge4);
+edgeList.append(edge5);
+edgeList.append(edge6);
+edgeList.append(edge7);
+edgeList.append(edge8);
+edgeList.append(edge9);
+edgeList.append(edge10);
+edgeList.append(edge11);
+
+algorithm = KruskalAlgorithm();
+algorithm.spanningTree(vertexList, edgeList);			
+	
+
+