Chapter 29 Exercise 16, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

29.16 (Display a dynamic MST) Write a program that lets the user create a weighted graph dynamically. The user can create a vertex by entering its name and location, as shown in Figure 29.28. The user can also create an edge to connect two vertices. To simplify the program, assume that vertex names are the same as those of vertex indices. You have to add the vertex indices 0, 1, . . ., and n, in this order. The edges in the MST are displayed in red. As new edges are added, the MST is redisplayed.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;

import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.border.EmptyBorder;
import javax.swing.border.TitledBorder;

public class Exercise16 extends JApplet{
 private static final long serialVersionUID = 1L;
 private DynamicGrpah dynamicGrpah = new DynamicGrpah();
 private ArrayList<Vertex> vertexes = new ArrayList<>();
 private ArrayList<WeightedEdge> edges = new ArrayList<>();
 private JTextField jTextField1 = new JTextField();
 private JTextField jTextField2 = new JTextField();
 private JTextField jTextField3 = new JTextField();
 private JTextField jTextField4 = new JTextField();
 private JTextField jTextField5 = new JTextField();
 private JTextField jTextField8 = new JTextField();
 private AbstractGraph<String>.Tree path = null;
 
 public Exercise16() {
  setLayout(new BorderLayout());
  JPanel jPanel6 = new JPanel(new BorderLayout(5, 5));
  jPanel6.setBorder(new EmptyBorder(5, 5, 5, 5));
  jPanel6.add(dynamicGrpah, BorderLayout.CENTER);
  
  JPanel jPanel1 = new JPanel(new GridLayout(1, 2, 5, 5));
  JPanel jPanel2 = new JPanel(new GridLayout(4, 2, 5, 5));
  JPanel jPanel3 = new JPanel(new GridLayout(4, 2, 5, 5));
  jPanel2.setBorder(new TitledBorder("Add a new vertex"));
  jPanel3.setBorder(new TitledBorder("Add a new ebge"));
  
  jPanel2.add(new JLabel("Vertex name: "));
  jPanel2.add(jTextField1);
  jPanel2.add(new JLabel("x-coordinate: "));
  jPanel2.add(jTextField2);
  jPanel2.add(new JLabel("y-coordinate: "));
  jPanel2.add(jTextField3);
  jPanel2.add(new JLabel(" "));
  JButton jButton2 = new JButton("Add Vertex");
  jPanel2.add(jButton2);
  
  jButton2.addActionListener(new ActionListener() {   
   @Override
   public void actionPerformed(ActionEvent e) {
    try {
     String name = jTextField1.getText();
     int x = Integer.parseInt(jTextField2.getText());
     int y = Integer.parseInt(jTextField3.getText());
     vertexes.add(new Vertex(name, x, y));
     jTextField1.setText("");
     jTextField2.setText("");
     jTextField3.setText("");
     updateMST();
     dynamicGrpah.repaint();
    } catch (NumberFormatException e2) {
     JOptionPane.showMessageDialog(null, "Wrong Number Format", "Error", JOptionPane.ERROR_MESSAGE);
    }    
   }
  });
  
  jPanel3.add(new JLabel("Vertex u (index): "));
  jPanel3.add(jTextField4);
  jPanel3.add(new JLabel("Vertex v (index): "));
  jPanel3.add(jTextField5);
  jPanel3.add(new JLabel("Weight (int): "));
  jPanel3.add(jTextField8);
  jPanel3.add(new JLabel(" "));
  JButton jButton3 = new JButton("Add Edge");
  jPanel3.add(jButton3);
  
  jButton3.addActionListener(new ActionListener() {   
   @Override
   public void actionPerformed(ActionEvent e) {
    try {
     int u = Integer.parseInt(jTextField4.getText());
     int v = Integer.parseInt(jTextField5.getText());
     int weight = Integer.parseInt(jTextField8.getText());
     edges.add(new WeightedEdge(u, v, weight));
     jTextField4.setText("");
     jTextField5.setText("");
     jTextField8.setText("");
     updateMST();
     dynamicGrpah.repaint();
    } catch (NumberFormatException e2) {
     JOptionPane.showMessageDialog(null, "Wrong Number Format", "Error", JOptionPane.ERROR_MESSAGE);
    } catch (IndexOutOfBoundsException e2) {
     JOptionPane.showMessageDialog(null, "Wrong Index", "Error", JOptionPane.ERROR_MESSAGE);
    }
   }
  });
  
 
  jPanel1.add(jPanel2);
  jPanel1.add(jPanel3);
  JPanel jPanel5 = new JPanel(new BorderLayout(5, 5));
  jPanel5.add(jPanel1, BorderLayout.CENTER);
  JButton jButton1 = new JButton("Start Over (Clear Graph)");
  jPanel5.add(jButton1, BorderLayout.SOUTH);
  jPanel6.add(jPanel5, BorderLayout.SOUTH);
  add(jPanel6);
  
  jButton1.addActionListener(new ActionListener() {   
   @Override
   public void actionPerformed(ActionEvent e) {
    vertexes.clear();
    edges.clear();
    jTextField1.setText("");
    jTextField2.setText("");
    jTextField3.setText("");
    jTextField4.setText("");
    jTextField5.setText("");
    jTextField8.setText("");
    updateMST();
    dynamicGrpah.repaint();
   }
  });
 }

 private void updateMST() {
  ArrayList<String> newVertices = new ArrayList<>();
  for (int i = 0; i < vertexes.size(); i++) {
   newVertices.add(vertexes.get(i).name);
  }
  
  ArrayList<WeightedEdge> newEdges = new ArrayList<>();
  for (int i = 0; i < edges.size(); i++) {
   WeightedEdge tmp = edges.get(i);
   newEdges.add(tmp);
   newEdges.add(new WeightedEdge(tmp.v, tmp.u, tmp.weight));
  }

  WeightedGraph<String> graph = new WeightedGraph<>(newEdges, newVertices);   
  path = graph.getMinimumSpanningTree();
 }
 
 static class Vertex {
  String name;
  int x;
  int y;
  
  public Vertex(String name, int x, int y) {
   this.name = name;
   this.x = x;
   this.y = y;
  }  
 }
 
 public static void main(String[] args) {
  JFrame jFrame = new JFrame("Exercise16");
  JApplet jApplet = new Exercise16();
  jFrame.add(jApplet);
  jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  jFrame.pack();
  jFrame.setMinimumSize(new Dimension(jFrame.getWidth(), jFrame.getHeight()));
  jFrame.setLocationRelativeTo(null);
  jFrame.setVisible(true);
 }
 
 class DynamicGrpah extends JPanel {
  private static final long serialVersionUID = 1L;
  
  @Override
  public Dimension getPreferredSize() {
   return new Dimension(800, 300);
  }

  @Override
  protected void paintComponent(Graphics g) {
   super.paintComponent(g);
   int radius = 10;
   g.setFont(new Font("SansSerif", Font.BOLD, 16));
   for (int i = 0; i < vertexes.size(); i++) {
    g.drawString(vertexes.get(i).name + "(" + i + ")", vertexes.get(i).x - radius, vertexes.get(i).y - radius);
    g.fillOval(vertexes.get(i).x - radius, vertexes.get(i).y - radius, radius * 2, radius * 2);
   }
   for (int i = 0; i < edges.size(); i++) {
    Vertex u = vertexes.get(edges.get(i).u);
    Vertex v = vertexes.get(edges.get(i).v);
    double weight = edges.get(i).weight;
    g.drawLine(u.x, u.y, v.x, v.y);
    g.drawString(weight + "", (u.x + v.x) / 2, (u.y + v.y) / 2);
   }
   if(path != null) {
    g.setColor(Color.RED);
    for (int i = 0; i < path.parent.length; i++) {
     if (path.parent[i] != -1) {
      int length = 20;
      int x0 = vertexes.get(i).x;
      int y0 = vertexes.get(i).y;
      int x1 = vertexes.get(path.parent[i]).x;
      int y1 = vertexes.get(path.parent[i]).y;
      double angle1 = Math.atan2(y1 - y0, x1 - x0);
      g.drawLine(x1, y1, x0, y0);
      
      double angle2 = Math.toRadians(Math.toDegrees(angle1) + 30);
      int x2 = (int)(x0 + Math.cos(angle2) * length);
      int y2 = (int)(y0 + Math.sin(angle2) * length);      
      g.drawLine(x0, y0, x2, y2);
      
      double angle3 = Math.toRadians(Math.toDegrees(angle1) - 30);
      int x3 = (int)(x0 + Math.cos(angle3) * length);
      int y3 = (int)(y0 + Math.sin(angle3) * length);      
      g.drawLine(x0, y0, x3, y3);
      
     }
    }
   }
  }
 }
 
 static class WeightedGraph<V> extends AbstractGraph<V> {
  // Priority adjacency lists
  private List<PriorityQueue<WeightedEdge>> queues = new ArrayList<PriorityQueue<WeightedEdge>>();

  /** Construct a WeightedGraph from edges and vertices in arrays */
  public WeightedGraph() {
  }

  /** Construct a WeightedGraph from edges and vertices in arrays */
  public WeightedGraph(int[][] edges, V[] vertices) {
   super(edges, vertices);
   createQueues(edges, vertices.length);
  }

  /** Construct a WeightedGraph from edges and vertices in List */
  public WeightedGraph(int[][] edges, int numberOfVertices) {
   super(edges, numberOfVertices);
   createQueues(edges, numberOfVertices);
  }

  /** Construct a WeightedGraph for vertices 0, 1, 2 and edge list */
  @SuppressWarnings({ "rawtypes", "unchecked" })
  public WeightedGraph(List<WeightedEdge> edges, List<V> vertices) {
   super((List) edges, vertices);
   createQueues(edges, vertices.size());
  }

  /** Construct a WeightedGraph from vertices 0, 1, and edge array */
  @SuppressWarnings({ "rawtypes", "unchecked" })
  public WeightedGraph(List<WeightedEdge> edges, int numberOfVertices) {
   super((List) edges, numberOfVertices);
   createQueues(edges, numberOfVertices);
  }

  /** Create priority adjacency lists from edge arrays */
  private void createQueues(int[][] edges, int numberOfVertices) {
   for (int i = 0; i < numberOfVertices; i++) {
    queues.add(new PriorityQueue<WeightedEdge>()); // Create a queue
   }

   for (int i = 0; i < edges.length; i++) {
    int u = edges[i][0];
    int v = edges[i][1];
    int weight = edges[i][2];
    // Insert an edge into the queue
    queues.get(u).offer(new WeightedEdge(u, v, weight));
   }
  }

  /** Create priority adjacency lists from edge lists */
  private void createQueues(List<WeightedEdge> edges, int numberOfVertices) {
   for (int i = 0; i < numberOfVertices; i++) {
    queues.add(new PriorityQueue<WeightedEdge>()); // Create a queue
   }

   for (WeightedEdge edge : edges) {
    queues.get(edge.u).offer(edge); // Insert an edge into the queue
   }
  }

  /** Display edges with weights */
  public void printWeightedEdges() {
   for (int i = 0; i < queues.size(); i++) {
    System.out.print(getVertex(i) + " (" + i + "): ");
    for (WeightedEdge edge : queues.get(i)) {
     System.out.print("(" + edge.u + ", " + edge.v + ", "
       + edge.weight + ") ");
    }
    System.out.println();
   }
  }

  /** Get the edges from the weighted graph */
  public List<PriorityQueue<WeightedEdge>> getWeightedEdges() {
   return queues;
  }

  /** Clears the weighted graph */
  public void clear() {
   vertices.clear();
   neighbors.clear();
   queues.clear();
  }

  /** Add vertices to the weighted graph */
  public void addVertex(V vertex) {
   super.addVertex(vertex);
   queues.add(new PriorityQueue<WeightedEdge>());
  }

  /** Add edges to the weighted graph */
  public void addEdge(int u, int v, double weight) {
   super.addEdge(u, v);
   queues.get(u).add(new WeightedEdge(u, v, weight));
   queues.get(v).add(new WeightedEdge(v, u, weight));
  }

  /** Get a minimum spanning tree rooted at vertex 0 */
  public MST getMinimumSpanningTree() {
   return getMinimumSpanningTree(0);
  }

  /** Get a minimum spanning tree rooted at a specified vertex */
  public MST getMinimumSpanningTree(int startingVertex) {
   List<Integer> T = new ArrayList<Integer>();
   // T initially contains the startingVertex;
   T.add(startingVertex);

   int numberOfVertices = vertices.size(); // Number of vertices
   int[] parent = new int[numberOfVertices]; // Parent of a vertex
   // Initially set the parent of all vertices to -1
   for (int i = 0; i < parent.length; i++)
    parent[i] = -1;
   double totalWeight = 0; // Total weight of the tree thus far

   // Clone the priority queue, so to keep the original queue intact
   List<PriorityQueue<WeightedEdge>> queues = deepClone(this.queues);

   // All vertices are found?
   while (T.size() < numberOfVertices) {
    // Search for the vertex with the smallest edge adjacent to
    // a vertex in T
    int v = -1;
    double smallestWeight = Double.MAX_VALUE;
    for (int u : T) {
     while (!queues.get(u).isEmpty()
       && T.contains(queues.get(u).peek().v)) {
      // Remove the edge from queues[u] if the adjacent
      // vertex of u is already in T
      queues.get(u).remove();
     }

     if (queues.get(u).isEmpty()) {
      continue; // Consider the next vertex in T
     }

     // Current smallest weight on an edge adjacent to u
     WeightedEdge edge = queues.get(u).peek();
     if (edge.weight < smallestWeight) {
      v = edge.v;
      smallestWeight = edge.weight;
      // If v is added to the tree, u will be its parent
      parent[v] = u;
     }
    } // End of for

    if (v != -1)
     T.add(v); // Add a new vertex to the tree
    else
     break; // The tree is not connected, a partial MST is found

    totalWeight += smallestWeight;
   } // End of while

   return new MST(startingVertex, parent, T, totalWeight);
  }

  /** Clone an array of queues */
  private List<PriorityQueue<WeightedEdge>> deepClone(
    List<PriorityQueue<WeightedEdge>> queues) {
   List<PriorityQueue<WeightedEdge>> copiedQueues = new ArrayList<PriorityQueue<WeightedEdge>>();

   for (int i = 0; i < queues.size(); i++) {
    copiedQueues.add(new PriorityQueue<WeightedEdge>());
    for (WeightedEdge e : queues.get(i)) {
     copiedQueues.get(i).add(e);
    }
   }

   return copiedQueues;
  }

  /** MST is an inner class in WeightedGraph */
  public class MST extends Tree {
   private double totalWeight; // Total weight of all edges in the tree

   public MST(int root, int[] parent, List<Integer> searchOrder,
     double totalWeight) {
    super(root, parent, searchOrder);
    this.totalWeight = totalWeight;
   }

   public double getTotalWeight() {
    return totalWeight;
   }
  }

  /** Find single source shortest paths */
  public ShortestPathTree getShortestPath(int sourceVertex) {
   // T stores the vertices whose path found so far
   List<Integer> T = new ArrayList<Integer>();
   // T initially contains the sourceVertex;
   T.add(sourceVertex);

   // vertices is defined in AbstractGraph
   int numberOfVertices = vertices.size();

   // parent[v] stores the previous vertex of v in the path
   int[] parent = new int[numberOfVertices];
   parent[sourceVertex] = -1; // The parent of source is set to -1

   // cost[v] stores the cost of the path from v to the source
   double[] cost = new double[numberOfVertices];
   for (int i = 0; i < cost.length; i++) {
    cost[i] = Double.MAX_VALUE; // Initial cost set to infinity
   }
   cost[sourceVertex] = 0; // Cost of source is 0

   // Get a copy of queues
   List<PriorityQueue<WeightedEdge>> queues = deepClone(this.queues);

   // Expand T
   while (T.size() < numberOfVertices) {
    int v = -1; // Vertex to be determined
    double smallestCost = Double.MAX_VALUE; // Set to infinity
    for (int u : T) {
     while (!queues.get(u).isEmpty()
       && T.contains(queues.get(u).peek().v)) {
      queues.get(u).remove(); // Remove the vertex in queue
            // for u
     }

     if (queues.get(u).isEmpty()) {
      // All vertices adjacent to u are in T
      continue;
     }

     WeightedEdge e = queues.get(u).peek();
     if (cost[u] + e.weight < smallestCost) {
      v = e.v;
      smallestCost = cost[u] + e.weight;
      // If v is added to the tree, u will be its parent
      parent[v] = u;
     }
    } // End of for

    T.add(v); // Add a new vertex to T
    cost[v] = smallestCost;
   } // End of while

   // Create a ShortestPathTree
   return new ShortestPathTree(sourceVertex, parent, T, cost);
  }

  /** ShortestPathTree is an inner class in WeightedGraph */
  public class ShortestPathTree extends Tree {
   private double[] cost; // cost[v] is the cost from v to source

   /** Construct a path */
   public ShortestPathTree(int source, int[] parent,
     List<Integer> searchOrder, double[] cost) {
    super(source, parent, searchOrder);
    this.cost = cost;
   }

   /** Return the cost for a path from the root to vertex v */
   public double getCost(int v) {
    return cost[v];
   }

   /** Print paths from all vertices to the source */
   public void printAllPaths() {
    System.out.println("All shortest paths from "
      + vertices.get(getRoot()) + " are:");
    for (int i = 0; i < cost.length; i++) {
     printPath(i); // Print a path from i to the source
     System.out.println("(cost: " + cost[i] + ")"); // Path cost
    }
   }
  }
 }

 static class WeightedEdge extends AbstractGraph.Edge implements Comparable<WeightedEdge> {
  public double weight; // The weight on edge (u, v)

  /** Create a weighted edge on (u, v) */
  public WeightedEdge(int u, int v, double weight) {
   super(u, v);
   this.weight = weight;
  }

  /** Compare two edges on weights */
  public int compareTo(WeightedEdge edge) {
   if (weight > edge.weight) {
    return 1;
   } else if (weight == edge.weight) {
    return 0;
   } else {
    return -1;
   }
  }
  
  @Override
  public boolean equals(Object obj) {
   if (obj instanceof WeightedEdge) {
    WeightedEdge that = (WeightedEdge)obj;
    return (u == that.u) && (v == that.v) && (weight == that.weight);   
   } else {
    return false;
   }
  }
  
  @Override
  public String toString() {
   return "(" + u + ", " + v + ", " + weight + ")";
  }
 }

 static abstract class AbstractGraph<V> implements Graph<V> {
  protected List<V> vertices = new ArrayList<V>(); // Store vertices
  protected List<List<Integer>> neighbors = new ArrayList<List<Integer>>(); // Adjacency
                     // lists

  /** Construct an empty graph */
  protected AbstractGraph() {
  }

  /** Construct a graph from edges and vertices stored in arrays */
  protected AbstractGraph(int[][] edges, V[] vertices) {
   for (int i = 0; i < vertices.length; i++)
    this.vertices.add(vertices[i]);

   createAdjacencyLists(edges, vertices.length);
  }

  /** Construct a graph from edges and vertices stored in List */
  protected AbstractGraph(List<Edge> edges, List<V> vertices) {
   for (int i = 0; i < vertices.size(); i++)
    this.vertices.add(vertices.get(i));

   createAdjacencyLists(edges, vertices.size());
  }

  /** Construct a graph for integer vertices 0, 1, 2 and edge list */
  @SuppressWarnings("unchecked")
  protected AbstractGraph(List<Edge> edges, int numberOfVertices) {
   for (int i = 0; i < numberOfVertices; i++)
    vertices.add((V) (new Integer(i))); // vertices is {0, 1, ...}

   createAdjacencyLists(edges, numberOfVertices);
  }

  /** Construct a graph from integer vertices 0, 1, and edge array */
  @SuppressWarnings("unchecked")
  protected AbstractGraph(int[][] edges, int numberOfVertices) {
   for (int i = 0; i < numberOfVertices; i++)
    vertices.add((V) (new Integer(i))); // vertices is {0, 1, ...}

   createAdjacencyLists(edges, numberOfVertices);
  }

  /** Create adjacency lists for each vertex */
  private void createAdjacencyLists(int[][] edges, int numberOfVertices) {
   // Create a linked list
   for (int i = 0; i < numberOfVertices; i++) {
    neighbors.add(new ArrayList<Integer>());
   }

   for (int i = 0; i < edges.length; i++) {
    int u = edges[i][0];
    int v = edges[i][1];
    neighbors.get(u).add(v);
   }
  }

  /** Create adjacency lists for each vertex */
  private void createAdjacencyLists(List<Edge> edges, int numberOfVertices) {
   // Create a linked list for each vertex
   for (int i = 0; i < numberOfVertices; i++) {
    neighbors.add(new ArrayList<Integer>());
   }

   for (Edge edge : edges) {
    neighbors.get(edge.u).add(edge.v);
   }
  }
  
  public boolean isCyclic() {
   for (int i = 0; i < vertices.size(); i++) {
    if(isCyclic(i)) {
     return true;
    }
   }
   return false;
  }
  
  private boolean isCyclic(int v) {
   List<Integer> searchOrder = new ArrayList<Integer>();
   int[] parent = new int[vertices.size()];
   for (int i = 0; i < parent.length; i++) {
    parent[i] = -1;
   }

   boolean[] isVisited = new boolean[vertices.size()];

   return isCyclic(v, v, parent, searchOrder, isVisited);

  }

  private boolean isCyclic(int first, int v, int[] parent, List<Integer> searchOrder, boolean[] isVisited) {
   searchOrder.add(v);
   isVisited[v] = true;

   for (int i : neighbors.get(v)) {
    if (!isVisited[i]) {
     parent[i] = v;
     int[] newParent = java.util.Arrays.copyOf(parent, parent.length);
     boolean[] newIsVisited = java.util.Arrays.copyOf(isVisited, parent.length);
     @SuppressWarnings("unchecked")
     List<Integer> newSearchOrder = (List<Integer>) ((ArrayList<Integer>)searchOrder).clone();
     if(isCyclic(first, i, newParent, newSearchOrder, newIsVisited)) {
      return true;
     }
    } else if(first == i) {
     if(searchOrder.size() > 2) {
      return true;
     }
    }
   }
   return false;
  }


  @Override
  /** Return the number of vertices in the graph */
  public int getSize() {
   return vertices.size();
  }

  @Override
  /** Return the vertices in the graph */
  public List<V> getVertices() {
   return vertices;
  }

  @Override
  /** Return the object for the specified vertex */
  public V getVertex(int index) {
   return vertices.get(index);
  }

  @Override
  /** Return the index for the specified vertex object */
  public int getIndex(V v) {
   return vertices.indexOf(v);
  }

  @Override
  /** Return the neighbors of the specified vertex */
  public List<Integer> getNeighbors(int index) {
   return neighbors.get(index);
  }

  @Override
  /** Return the degree for a specified vertex */
  public int getDegree(int v) {
   return neighbors.get(v).size();
  }

  @Override
  /** Print the edges */
  public void printEdges() {
   for (int u = 0; u < neighbors.size(); u++) {
    System.out.print(getVertex(u) + " (" + u + "): ");
    for (int j = 0; j < neighbors.get(u).size(); j++) {
     System.out.print("(" + u + ", " + neighbors.get(u).get(j)
       + ") ");
    }
    System.out.println();
   }
  }

  @Override
  /** Clear graph */
  public void clear() {
   vertices.clear();
   neighbors.clear();
  }

  @Override
  /** Add a vertex to the graph */
  public void addVertex(V vertex) {
   vertices.add(vertex);
   neighbors.add(new ArrayList<Integer>());
  }

  @Override
  /** Add an edge to the graph */
  public void addEdge(int u, int v) {
   neighbors.get(u).add(v);
   neighbors.get(v).add(u);
  }

  /** Edge inner class inside the AbstractGraph class */
  public static class Edge {
   public int u; // Starting vertex of the edge
   public int v; // Ending vertex of the edge

   /** Construct an edge for (u, v) */
   public Edge(int u, int v) {
    this.u = u;
    this.v = v;
   }
  }

  @Override
  /** Obtain a DFS tree starting from vertex v */
  /** To be discussed in Section 27.6 */
  public Tree dfs(int v) {
   List<Integer> searchOrder = new ArrayList<Integer>();
   int[] parent = new int[vertices.size()];
   for (int i = 0; i < parent.length; i++)
    parent[i] = -1; // Initialize parent[i] to -1

   // Mark visited vertices
   boolean[] isVisited = new boolean[vertices.size()];

   // Recursively search
   dfs(v, parent, searchOrder, isVisited);

   // Return a search tree
   return new Tree(v, parent, searchOrder);
  }

  /** Recursive method for DFS search */
  private void dfs(int v, int[] parent, List<Integer> searchOrder,
    boolean[] isVisited) {
   // Store the visited vertex
   searchOrder.add(v);
   isVisited[v] = true; // Vertex v visited

   for (int i : neighbors.get(v)) {
    if (!isVisited[i]) {
     parent[i] = v; // The parent of vertex i is v
     dfs(i, parent, searchOrder, isVisited); // Recursive search
    }
   }
  }

  @Override
  /** Starting bfs search from vertex v */
  /** To be discussed in Section 27.7 */
  public Tree bfs(int v) {
   List<Integer> searchOrder = new ArrayList<Integer>();
   int[] parent = new int[vertices.size()];
   for (int i = 0; i < parent.length; i++)
    parent[i] = -1; // Initialize parent[i] to -1

   java.util.LinkedList<Integer> queue = new java.util.LinkedList<Integer>(); // list
                      // used
                      // as
                      // a
                      // queue
   boolean[] isVisited = new boolean[vertices.size()];
   queue.offer(v); // Enqueue v
   isVisited[v] = true; // Mark it visited

   while (!queue.isEmpty()) {
    int u = queue.poll(); // Dequeue to u
    searchOrder.add(u); // u searched
    for (int w : neighbors.get(u)) {
     if (!isVisited[w]) {
      queue.offer(w); // Enqueue w
      parent[w] = u; // The parent of w is u
      isVisited[w] = true; // Mark it visited
     }
    }
   }

   return new Tree(v, parent, searchOrder);
  }

  /** Tree inner class inside the AbstractGraph class */
  /** To be discussed in Section 27.5 */
  public class Tree {
   private int root; // The root of the tree
   private int[] parent; // Store the parent of each vertex
   private List<Integer> searchOrder; // Store the search order

   /** Construct a tree with root, parent, and searchOrder */
   public Tree(int root, int[] parent, List<Integer> searchOrder) {
    this.root = root;
    this.parent = parent;
    this.searchOrder = searchOrder;
   }

   /** Return the root of the tree */
   public int getRoot() {
    return root;
   }

   /** Return the parent of vertex v */
   public int getParent(int v) {
    return parent[v];
   }

   /** Return an array representing search order */
   public List<Integer> getSearchOrder() {
    return searchOrder;
   }

   /** Return number of vertices found */
   public int getNumberOfVerticesFound() {
    return searchOrder.size();
   }

   /** Return the path of vertices from a vertex to the root */
   public List<V> getPath(int index) {
    ArrayList<V> path = new ArrayList<V>();

    do {
     path.add(vertices.get(index));
     index = parent[index];
    } while (index != -1);

    return path;
   }
   
   public List<Integer> getIntPath(int index) {
    ArrayList<Integer> path = new ArrayList<Integer>();

    do {
     path.add(index);
     index = parent[index];
    } while (index != -1);

    return path;
   }

   /** Print a path from the root to vertex v */
   public void printPath(int index) {
    List<V> path = getPath(index);
    System.out.print("A path from " + vertices.get(root) + " to "
      + vertices.get(index) + ": ");
    for (int i = path.size() - 1; i >= 0; i--)
     System.out.print(path.get(i) + " ");
   }

   /** Print the whole tree */
   public void printTree() {
    System.out.println("Root is: " + vertices.get(root));
    System.out.print("Edges: ");
    for (int i = 0; i < parent.length; i++) {
     if (parent[i] != -1) {
      // Display an edge
      System.out.print("(" + vertices.get(parent[i]) + ", "
        + vertices.get(i) + ") ");
     }
    }
    System.out.println();
   }
  }
 }

 interface Graph<V> {
  /** Return the number of vertices in the graph */
  public int getSize();

  /** Return the vertices in the graph */
  public java.util.List<V> getVertices();

  /** Return the object for the specified vertex index */
  public V getVertex(int index);

  /** Return the index for the specified vertex object */
  public int getIndex(V v);

  /** Return the neighbors of vertex with the specified index */
  public java.util.List<Integer> getNeighbors(int index);

  /** Return the degree for a specified vertex */
  public int getDegree(int v);

  /** Print the edges */
  public void printEdges();

  /** Clear graph */
  public void clear();

  /** Add a vertex to the graph */
  public void addVertex(V vertex);

  /** Add an edge to the graph */
  public void addEdge(int u, int v);

  /** Obtain a depth-first search tree */
  public AbstractGraph<V>.Tree dfs(int v);

  /** Obtain a breadth-first search tree */
  public AbstractGraph<V>.Tree bfs(int v);
 }

}