Chapter 25 Exercise 6, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

25.6 (Find the leaves) Add a method in the BST class to return the number of the
leaves as follows:
/** Returns the number of leaf nodes */
public int getNumberOfLeaves()

import java.util.ArrayList;


public class Exercise06 {

 public static void main(String[] args) {
  BST<Integer> tree = new BST<>(new Integer[] {60, 55, 100, 45, 57, 67, 107, 101, 59});
  System.out.println("Number Of Leaves: " + tree.getNumberOfLeaves());
  
 }

 static class BST<E extends Comparable<E>> extends AbstractTree<E> {
  protected TreeNode<E> root;
  protected int size = 0;
  
  public int getNumberOfLeaves() {
   return getNumberOfLeaves(root);
  }
  
  public int getNumberOfLeaves(TreeNode<E> node) {
   if(node == null) {
    return 0;
   } else if((node.left == null) && (node.right == null)) {
    return 1;
   } else {
    return getNumberOfLeaves(node.left) + getNumberOfLeaves(node.right);
   }
  }
  
  /** Displays the nodes in a breadth-first traversal */
  public void breadthFirstTraversal() {
   if(root == null) {
    return;
   }   
   ArrayList<TreeNode<E>> list = new ArrayList<>();
   list.add(root);   
   while(!list.isEmpty()) {
    ArrayList<TreeNode<E>> tmpList = new ArrayList<>();
    for (TreeNode<E> treeNode : list) {
     if(treeNode!= null) {
      System.out.print(treeNode.element + " ");
      tmpList.add(treeNode.left);
      tmpList.add(treeNode.right);
     }
     list = tmpList;     
    }
   }
  }
  
  
  public boolean isFullBST() {
    return size == Math.round(Math.pow(2, height()) - 1);
  }
  
  /** Returns the height of this binary tree, i.e., the
  * number of the nodes in the longest path of the root to a leaf */
  public int height() {
   return height(root);
  }
  
  public int height(TreeNode<E> node) {
   if(node == null) {
    return 0;
   } else {
    return 1 + Math.max(height(node.left), height(node.right));
   }
  }

  /** Create a default binary tree */
  public BST() {
  }

  /** Create a binary tree from an array of objects */
  public BST(E[] objects) {
   for (int i = 0; i < objects.length; i++)
    insert(objects[i]);
  }

  @Override
  /** Returns true if the element is in the tree */
  public boolean search(E e) {
   TreeNode<E> current = root; // Start from the root

   while (current != null) {
    if (e.compareTo(current.element) < 0) {
     current = current.left;
    } else if (e.compareTo(current.element) > 0) {
     current = current.right;
    } else
     // element matches current.element
     return true; // Element is found
   }

   return false;
  }

  @Override
  /** Insert element o into the binary tree
   * Return true if the element is inserted successfully */
  public boolean insert(E e) {
   if (root == null)
    root = createNewNode(e); // Create a new root
   else {
    // Locate the parent node
    TreeNode<E> parent = null;
    TreeNode<E> current = root;
    while (current != null)
     if (e.compareTo(current.element) < 0) {
      parent = current;
      current = current.left;
     } else if (e.compareTo(current.element) > 0) {
      parent = current;
      current = current.right;
     } else
      return false; // Duplicate node not inserted

    // Create the new node and attach it to the parent node
    if (e.compareTo(parent.element) < 0)
     parent.left = createNewNode(e);
    else
     parent.right = createNewNode(e);
   }

   size++;
   return true; // Element inserted
  }

  protected TreeNode<E> createNewNode(E e) {
   return new TreeNode<E>(e);
  }

  @Override
  /** Inorder traversal from the root*/
  public void inorder() {
   inorder(root);
  }

  /** Inorder traversal from a subtree */
  protected void inorder(TreeNode<E> root) {
   if (root == null)
    return;
   inorder(root.left);
   System.out.print(root.element + " ");
   inorder(root.right);
  }

  @Override
  /** Postorder traversal from the root */
  public void postorder() {
   postorder(root);
  }

  /** Postorder traversal from a subtree */
  protected void postorder(TreeNode<E> root) {
   if (root == null)
    return;
   postorder(root.left);
   postorder(root.right);
   System.out.print(root.element + " ");
  }

  @Override
  /** Preorder traversal from the root */
  public void preorder() {
   preorder(root);
  }

  /** Preorder traversal from a subtree */
  protected void preorder(TreeNode<E> root) {
   if (root == null)
    return;
   System.out.print(root.element + " ");
   preorder(root.left);
   preorder(root.right);
  }

  /**
   * This inner class is static, because it does not access any instance
   * members defined in its outer class
   */
  public static class TreeNode<E extends Comparable<E>> {
   protected E element;
   protected TreeNode<E> left;
   protected TreeNode<E> right;

   public TreeNode(E e) {
    element = e;
   }
  }

  @Override
  /** Get the number of nodes in the tree */
  public int getSize() {
   return size;
  }

  /** Returns the root of the tree */
  public TreeNode<E> getRoot() {
   return root;
  }

  /** Returns a path from the root leading to the specified element */
  public java.util.ArrayList<TreeNode<E>> path(E e) {
   java.util.ArrayList<TreeNode<E>> list = new java.util.ArrayList<TreeNode<E>>();
   TreeNode<E> current = root; // Start from the root

   while (current != null) {
    list.add(current); // Add the node to the list
    if (e.compareTo(current.element) < 0) {
     current = current.left;
    } else if (e.compareTo(current.element) > 0) {
     current = current.right;
    } else
     break;
   }

   return list; // Return an array of nodes
  }

  @Override
  /** Delete an element from the binary tree.
   * Return true if the element is deleted successfully
   * Return false if the element is not in the tree */
  public boolean delete(E e) {
   // Locate the node to be deleted and also locate its parent node
   TreeNode<E> parent = null;
   TreeNode<E> current = root;
   while (current != null) {
    if (e.compareTo(current.element) < 0) {
     parent = current;
     current = current.left;
    } else if (e.compareTo(current.element) > 0) {
     parent = current;
     current = current.right;
    } else
     break; // Element is in the tree pointed at by current
   }

   if (current == null)
    return false; // Element is not in the tree

   // Case 1: current has no left children
   if (current.left == null) {
    // Connect the parent with the right child of the current node
    if (parent == null) {
     root = current.right;
    } else {
     if (e.compareTo(parent.element) < 0)
      parent.left = current.right;
     else
      parent.right = current.right;
    }
   } else {
    // Case 2: The current node has a left child
    // Locate the rightmost node in the left subtree of
    // the current node and also its parent
    TreeNode<E> parentOfRightMost = current;
    TreeNode<E> rightMost = current.left;

    while (rightMost.right != null) {
     parentOfRightMost = rightMost;
     rightMost = rightMost.right; // Keep going to the right
    }

    // Replace the element in current by the element in rightMost
    current.element = rightMost.element;

    // Eliminate rightmost node
    if (parentOfRightMost.right == rightMost)
     parentOfRightMost.right = rightMost.left;
    else
     // Special case: parentOfRightMost == current
     parentOfRightMost.left = rightMost.left;
   }

   size--;
   return true; // Element inserted
  }

  @Override
  /** Obtain an iterator. Use inorder. */
  public java.util.Iterator<E> iterator() {
   return new InorderIterator();
  }

  // Inner class InorderIterator
  private class InorderIterator implements java.util.Iterator<E> {
   // Store the elements in a list
   private java.util.ArrayList<E> list = new java.util.ArrayList<E>();
   private int current = 0; // Point to the current element in list

   public InorderIterator() {
    inorder(); // Traverse binary tree and store elements in list
   }

   /** Inorder traversal from the root */
   private void inorder() {
    inorder(root);
   }

   /** Inorder traversal from a subtree */
   private void inorder(TreeNode<E> root) {
    if (root == null)
     return;
    inorder(root.left);
    list.add(root.element);
    inorder(root.right);
   }

   @Override
   /** More elements for traversing? */
   public boolean hasNext() {
    if (current < list.size())
     return true;

    return false;
   }

   @Override
   /** Get the current element and move to the next */
   public E next() {
    return list.get(current++);
   }

   @Override
   /** Remove the current element */
   public void remove() {
    delete(list.get(current)); // Delete the current element
    list.clear(); // Clear the list
    inorder(); // Rebuild the list
   }
  }

  /** Remove all elements from the tree */
  public void clear() {
   root = null;
   size = 0;
  }
 }

 static abstract class AbstractTree<E> implements Tree<E> {
  @Override
  /** Inorder traversal from the root*/
  public void inorder() {
  }

  @Override
  /** Postorder traversal from the root */
  public void postorder() {
  }

  @Override
  /** Preorder traversal from the root */
  public void preorder() {
  }

  @Override
  /** Return true if the tree is empty */
  public boolean isEmpty() {
   return getSize() == 0;
  }

  @Override
  /** Return an iterator for the tree */
  public java.util.Iterator<E> iterator() {
   return null;
  }
 }

 interface Tree<E> extends Iterable<E> {
  /** Return true if the element is in the tree */
  public boolean search(E e);

  /**
   * Insert element o into the binary tree Return true if the element is
   * inserted successfully
   */
  public boolean insert(E e);

  /**
   * Delete the specified element from the tree Return true if the element
   * is deleted successfully
   */
  public boolean delete(E e);

  /** Inorder traversal from the root */
  public void inorder();

  /** Postorder traversal from the root */
  public void postorder();

  /** Preorder traversal from the root */
  public void preorder();

  /** Get the number of nodes in the tree */
  public int getSize();

  /** Return true if the tree is empty */
  public boolean isEmpty();

  public java.util.Iterator<E> iterator();
 }
}