Chapter 29 Exercise 5, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

29.5 (Prove or disprove) The conjecture is that both NineTailModel and
WeightedNineTailModel result in the same shortest path. Write a program to
prove or disprove it. (Hint: Let tree1 and tree2 denote the trees rooted at node
511 obtained from NineTailModel and WeightedNineTailModel , respec-
tively. If the depth of a node u is the same in tree1 and in tree2 , the length of
the path from u to the target is the same.)

import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.PriorityQueue;

public class Exercise05 {

 public static void main(String[] args) {

  AbstractGraph<Integer>.Tree tree1 = new NineTailModel().tree;
  AbstractGraph<Integer>.Tree tree2 = new WeightedNineTailModel().tree;
  tree1.printTree();
  tree2.printTree();
  
  for (int i = 0; i <= 511; i++) {
   int depth1 = tree1.getDepth(i);
   int depth2 = tree2.getDepth(i);
   System.out.println(i + "\t" + depth1 + "\t" +  + depth2);
   if (depth1 != depth2) {
    System.out.println("Disproved");
   }
  }
 }

 static class WeightedNineTailModel extends NineTailModel {
  /** Construct a model */
  public WeightedNineTailModel() {
   List<WeightedEdge> edges = getEdges();
   WeightedGraph<Integer> graph = new WeightedGraph<Integer>(edges,NUMBER_OF_NODES);
   tree = graph.getShortestPath(511);
  }

  /** Create all edges for the graph */
  private List<WeightedEdge> getEdges() {
   // Store edges
   List<WeightedEdge> edges = new ArrayList<WeightedEdge>();

   for (int u = 0; u < NUMBER_OF_NODES; u++) {
    for (int k = 0; k < 9; k++) {
     char[] node = getNode(u); // Get the node for vertex u
     if (node[k] == 'H') {
      int v = getFlippedNode(node, k);
      int numberOfFlips = getNumberOfFlips(u, v);

      // Add edge (v, u) for a legal move from node u to node
      // v
      edges.add(new WeightedEdge(v, u, numberOfFlips));
     }
    }
   }

   return edges;
  }

  private static int getNumberOfFlips(int u, int v) {
   char[] node1 = getNode(u);
   char[] node2 = getNode(v);

   int count = 0; // Count the number of different cells
   for (int i = 0; i < node1.length; i++){
    if (node1[i] != node2[i]) {
     count++;
    }
   }

   return count;
  }

  @SuppressWarnings("unchecked")
  public int getNumberOfFlips(int u) {
   return (int) ((WeightedGraph<Integer>.ShortestPathTree) tree).getCost(u);
  }
 }

 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));
  }

  public MST getMinimumKruskalSpanningTree() {
   return getMinimumKruskalSpanningTree(0);
  }

  public MST getMinimumKruskalSpanningTree(int startingVertex) {
   ArrayList<WeightedEdge> all = new ArrayList<>();
   for (int i = 0; i < queues.size(); i++) {
    PriorityQueue<WeightedEdge> tmpQueue = queues.get(i);
    for (WeightedEdge weightedEdge : tmpQueue) {
     all.add(weightedEdge);
    }
   }
   Collections.sort(all);

   List<V> newVertices = getVertices();
   List<WeightedEdge> newEdges = new LinkedList<>();

   while (true) {
    WeightedEdge newEdge1 = all.remove(0);
    WeightedEdge newEdge2 = new WeightedEdge(newEdge1.v,
      newEdge1.u, newEdge1.weight);
    for (int i = 0; i < all.size(); i++) {
     if (newEdge2.equals(all.get(i))) {
      all.remove(i);
      break;
     }
    }
    newEdges.add(newEdge1);
    newEdges.add(newEdge2);

    WeightedGraph<V> tmpGraph = new WeightedGraph<V>(newEdges,
      newVertices);
    if (tmpGraph.isCyclic()) {
     newEdges.remove(newEdges.size() - 1);
     newEdges.remove(newEdges.size() - 1);
    }

    Tree tree = tmpGraph.dfs(startingVertex);
    if (tree.getNumberOfVerticesFound() == newVertices.size()) {
     double totalWeight = 0;
     for (int i = 0; i < newEdges.size(); i++) {
      totalWeight += newEdges.get(i).weight;
     }
     totalWeight = totalWeight / 2;
     return new MST(startingVertex, tree.parent,
       tree.searchOrder, totalWeight);
    }
   }
  }

  /** 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 class NineTailModel {
  public final static int NUMBER_OF_NODES = 512;
  protected AbstractGraph<Integer>.Tree tree; // Define a tree

  public NineTailModel() {
   List<AbstractGraph.Edge> edges = getEdges();
   UnweightedGraph<Integer> graph = new UnweightedGraph<Integer>(edges, NUMBER_OF_NODES);
   tree = graph.bfs(511);
  }

  /** Create all edges for the graph */
  private List<AbstractGraph.Edge> getEdges() {
   List<AbstractGraph.Edge> edges = new ArrayList<AbstractGraph.Edge>();

   for (int u = 0; u < NUMBER_OF_NODES; u++) {
    for (int k = 0; k < 9; k++) {
     char[] node = getNode(u);
     if (node[k] == 'H') {
      int v = getFlippedNode(node, k);
      // Add edge (v, u) for a legal move from node u to node
      // v
      edges.add(new AbstractGraph.Edge(v, u));
     }
    }
   }

   return edges;
  }

  public static int getFlippedNode(char[] node, int position) {
   int row = position / 3;
   int column = position % 3;

   flipACell(node, row, column);
   flipACell(node, row - 1, column);
   flipACell(node, row + 1, column);
   flipACell(node, row, column - 1);
   flipACell(node, row, column + 1);

   return getIndex(node);
  }

  public static void flipACell(char[] node, int row, int column) {
   if (row >= 0 && row <= 2 && column >= 0 && column <= 2) {
    // Within the boundary
    if (node[row * 3 + column] == 'H')
     node[row * 3 + column] = 'T'; // Flip from H to T
    else
     node[row * 3 + column] = 'H'; // Flip from T to H
   }
  }

  public static int getIndex(char[] node) {
   int result = 0;

   for (int i = 0; i < 9; i++)
    if (node[i] == 'T')
     result = result * 2 + 1;
    else
     result = result * 2 + 0;

   return result;
  }

  public static char[] getNode(int index) {
   char[] result = new char[9];

   for (int i = 0; i < 9; i++) {
    int digit = index % 2;
    if (digit == 0)
     result[8 - i] = 'H';
    else
     result[8 - i] = 'T';
    index = index / 2;
   }

   return result;
  }

  public List<Integer> getShortestPath(int nodeIndex) {
   return tree.getPath(nodeIndex);
  }

  public static void printNode(char[] node) {
   for (int i = 0; i < 9; i++)
    if (i % 3 != 2)
     System.out.print(node[i]);
    else
     System.out.println(node[i]);

   System.out.println();
  }
 }

 static class UnweightedGraph<V> extends AbstractGraph<V> {
  /** Construct an empty graph */
  public UnweightedGraph() {
  }

  /** Construct a graph from edges and vertices stored in arrays */
  public UnweightedGraph(int[][] edges, V[] vertices) {
   super(edges, vertices);
  }

  /** Construct a graph from edges and vertices stored in List */
  public UnweightedGraph(List<Edge> edges, List<V> vertices) {
   super(edges, vertices);
  }

  /** Construct a graph for integer vertices 0, 1, 2 and edge list */
  public UnweightedGraph(List<Edge> edges, int numberOfVertices) {
   super(edges, numberOfVertices);
  }

  /** Construct a graph from integer vertices 0, 1, and edge array */
  public UnweightedGraph(int[][] edges, int numberOfVertices) {
   super(edges, numberOfVertices);
  }
 }

 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;
   }

   /** 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) + " ");
   }

   public int getDepth(int index) {
    return getPath(index).size();
   }
   
   /** 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);
 }
}