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Deepali-SrivastavaDeepali-Srivastava
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Adjacency list in Java
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‎Graph/adjacencyListRepresentation/Demo.java

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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package adjacencyListRepresentation;
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import java.util.Scanner;
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public class Demo
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{
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public static void main(String [] args)
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{
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Scanner scan = new Scanner(System.in);
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LinkedDigraph g = new LinkedDigraph();
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int choice;
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String u,v;
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while(true)
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{
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System.out.println("1.Display ");
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System.out.println("2.Insert a vertex");
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System.out.println("3.Delete a vertex");
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System.out.println("4.Insert an edge");
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System.out.println("5.Delete an edge");
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System.out.println("6.Display Indegree and outdegree of a vertex");
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System.out.println("7.Check if there is an edge between two vertices");
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System.out.println("8.Exit");
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System.out.print("Enter your choice : ");
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choice = scan.nextInt();
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if(choice==8)
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break;
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switch(choice)
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{
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case 1:
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System.out.println();
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g.display();
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System.out.println("\n Vertices = " + g.vertices()+ ", Edges = " + g.edges() + "\n");
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break;
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case 2:
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System.out.print("Enter a vertex to be inserted : ");
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u=scan.next();
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g.insertVertex(u);
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break;
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case 3:
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System.out.print("Enter a vertex to be deleted : ");
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u=scan.next();
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g.deleteVertex(u);
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break;
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case 4:
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System.out.print("Enter an edge to be inserted : ");
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u=scan.next();
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v=scan.next();
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g.insertEdge(u,v);
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break;
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case 5:
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System.out.print("Enter an edge to be deleted : ");
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u=scan.next();
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v=scan.next();
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g.deleteEdge(u,v);
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break;
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case 6:
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System.out.print("Enter a vertex : ");
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u=scan.next();
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System.out.println("Indegree is : " + g.inDegree(u));
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System.out.println("Outdegree is : " + g.outDegree(u));
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break;
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case 7:
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System.out.print("Enter two vertices : ");
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u=scan.next();
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v=scan.next();
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if(g.edgeExists(u,v))
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System.out.println("Vertex " + v + " is adjacent to vertex " + u);
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else
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System.out.println("Vertex " + v + " is not adjacent to vertex " + u);
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if(g.edgeExists(v,u))
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System.out.println("Vertex " + u + " is adjacent to vertex " + v);
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else
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System.out.println("Vertex " + u + " is not adjacent to vertex " + v);
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default:
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System.out.println("Wrong choice");
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break;
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}
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}
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}
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}

‎Graph/adjacencyListRepresentation/EdgeNode.java

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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package adjacencyListRepresentation;
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public class EdgeNode
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{
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VertexNode endVertex;
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EdgeNode nextEdge;
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public EdgeNode(VertexNode v)
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{
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endVertex = v;
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}
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}

‎Graph/adjacencyListRepresentation/LinkedDigraph.java

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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package adjacencyListRepresentation;
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public class LinkedDigraph
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{
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VertexNode start;
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int n;
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int e;
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public int vertices()
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{
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return n;
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}
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public int edges()
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{
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return e;
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}
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public void insertVertex(String s)
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{
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VertexNode temp = new VertexNode(s);
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if(start==null)
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start=temp;
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else
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{
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VertexNode p=start;
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while(p.nextVertex!=null)
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{
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if(p.name.equals(s))
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{
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System.out.println("Vertex already present");
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return;
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}
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p=p.nextVertex;
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}
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if(p.name.equals(s))
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{
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System.out.println("Vertex already present");
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return;
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}
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p.nextVertex=temp;
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}
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n++;
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}
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public void deleteVertex(String s)
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{
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deletefromEdgeLists(s);
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deletefromVertexList(s);
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}
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/*Delete incoming edges*/
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private void deletefromEdgeLists(String s)
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{
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for(VertexNode p=start; p!=null; p=p.nextVertex)
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{
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if(p.firstEdge==null)
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continue;
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if(p.firstEdge.endVertex.name.equals(s))
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{
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p.firstEdge = p.firstEdge.nextEdge;
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e--;
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}
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else
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{
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EdgeNode q=p.firstEdge;
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while(q.nextEdge!=null)
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{
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if(q.nextEdge.endVertex.name.equals(s))
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{
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q.nextEdge = q.nextEdge.nextEdge;
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e--;
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break;
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}
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q=q.nextEdge;
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}
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}
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}
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}
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private void deletefromVertexList(String s)
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{
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if(start==null)
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{
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System.out.println("No vertices to be deleted");
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return;
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}
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if(start.name.equals(s)) /* Vertex to be deleted is first vertex of list*/
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{
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for(EdgeNode q=start.firstEdge; q!=null; q=q.nextEdge)
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e--;
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start=start.nextVertex;
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n--;
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}
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else
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{
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VertexNode p=start;
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while(p.nextVertex!=null)
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{
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if(p.nextVertex.name.equals(s))
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break;
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p=p.nextVertex;
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}
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if(p.nextVertex==null)
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{
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System.out.println("Vertex not found");
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return;
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}
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else
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{
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for(EdgeNode q=p.nextVertex.firstEdge; q!=null; q=q.nextEdge)
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e--;
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p.nextVertex = p.nextVertex.nextVertex;
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n--;
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}
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}
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}
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private VertexNode findVertex(String s)
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{
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VertexNode p=start;
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while(p!=null)
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{
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if(p.name.equals(s))
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return p;
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p=p.nextVertex;
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}
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return null;
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}/*End of findVertex()*/
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/*Insert an edge (s1,s2) */
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public void insertEdge(String s1, String s2)
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{
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if(s1.equals(s2))
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{
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System.out.println("Inavlid Edge : Start and end vertices are same");
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return;
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}
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VertexNode u = findVertex(s1);
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VertexNode v = findVertex(s2);
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if(u==null)
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{
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System.out.println("Start vertex not present, first insert vertex " + s1);
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return;
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}
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if(v==null)
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{
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System.out.println("End vertex not present, first insert vertex " + s2);
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return;
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}
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EdgeNode temp = new EdgeNode(v);
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if(u.firstEdge==null)
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{
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u.firstEdge=temp;
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e++;
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}
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else
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{
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EdgeNode p=u.firstEdge;
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while(p.nextEdge!=null)
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{
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if(p.endVertex.name.equals(s2))
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{
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System.out.println("Edge present");
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return;
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}
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p=p.nextEdge;
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}
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if(p.endVertex.name.equals(s2))
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{
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System.out.println("Edge present");
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return;
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}
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p.nextEdge=temp;
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e++;
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}
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}
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/* Delete the edge (s1,s2) */
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public void deleteEdge(String s1, String s2)
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{
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VertexNode u = findVertex(s1);
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if(u==null)
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{
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System.out.println("Start vertex not present");
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return;
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}
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if(u.firstEdge == null)
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{
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System.out.println("Edge not present");
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return;
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}
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if(u.firstEdge.endVertex.name.equals(s2))
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{
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u.firstEdge = u.firstEdge.nextEdge;
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e--;
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return;
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}
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EdgeNode q = u.firstEdge;
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while(q.nextEdge != null)
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{
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if(q.nextEdge.endVertex.name.equals(s2))
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{
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q.nextEdge = q.nextEdge.nextEdge;
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e--;
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return;
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}
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q=q.nextEdge;
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}
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System.out.println("Edge not present");
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}
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public void display()
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{
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EdgeNode q;
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for(VertexNode p=start; p!=null; p=p.nextVertex)
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{
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System.out.print(p + "->");
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for(q=p.firstEdge; q!=null; q=q.nextEdge)
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System.out.print(" " + q.endVertex);
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System.out.println();
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}
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}
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/* Returns true if s2 is adjacent to s1, i.e. if edge (s1,s2) exists */
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public boolean edgeExists(String s1, String s2)
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{
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VertexNode u = findVertex(s1);
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EdgeNode q=u.firstEdge;
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while(q!=null)
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{
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if(q.endVertex.name.equals(s2))
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return true;
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q=q.nextEdge;
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}
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return false;
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}
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/*Returns number of edges going out from vertex s*/
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public int outDegree(String s)
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{
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VertexNode u = findVertex(s);
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if(u==null)
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throw new IllegalArgumentException("Vertex not present");
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int out=0;
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EdgeNode q = u.firstEdge;
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while(q!=null)
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{
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q=q.nextEdge;
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out++;
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}
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return out;
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}
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/*Returns number of edges coming to vertex s*/
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public int inDegree(String s)
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{
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VertexNode u = findVertex(s);
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if(u==null)
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throw new IllegalArgumentException("Vertex not present");
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int in=0;
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for(VertexNode p=start; p!=null; p=p.nextVertex)
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{
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for(EdgeNode q=p.firstEdge; q!=null; q=q.nextEdge)
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if(q.endVertex.name.equals(s))
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in++;
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}
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return in;
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}
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}

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