数据结构与算法-第12章二叉树和其他树-004求二叉树的最多结点数及对应的层数

1.

package chapter12Tree;

import dataStructures.ArrayQueue;

//We perform a level-order traversal. To differentiate among nodes at different levels,
//we use a unique pointer which serves as an end of level marker. 
//This pointer is added to the level order queue following the last node at each level. 
//As nodes are removed from the queue, a counter is incremented until the end of level 
//marker is removed. This strategy enables us to determine the number of nodes 
//in a level. The code is given below.
public class BinaryTreeMaxLevel
{
   /** @return level with max umber of nodes */
   public static int maxLevel(BinaryTreeNode t)
   {
      if (t == null)
         // tree is empty
         return 0;

      // maxLevel is current level with max nodes
      // maxNodes is number of nodes on level maxLevel
      int maxLevel = 0;
      int maxNodes = 0;
      
      // create a unique pointer to use an end of level marker in queue
      BinaryTreeNode endOfLevel = new BinaryTreeNode();
   
      // put t and endOfLevel marker on queue q
      ArrayQueue q = new ArrayQueue();
      q.put(t);
      q.put(endOfLevel);

      // do a level order traversal
      int currentLevel = 1;    // level of nodes being examined
      int numOfNodes = 0;      // number of nodes seen of currentLevel
      while (true) 
      {
         BinaryTreeNode p = (BinaryTreeNode) q.remove();
         if (p == endOfLevel)
         {
            // see if currentLevel has more nodes than MaxLevel
            if (numOfNodes > maxNodes)
            {// found a level with more nodes
               maxNodes = numOfNodes;
                maxLevel = currentLevel;
            }
            else
               if (numOfNodes == 0)
                  // empty level, no more nodes
                  return maxLevel;

            // set currentLevel and numOfNodes to start new level
            currentLevel++;
            numOfNodes = 0;

            q.put(endOfLevel);
         }
         else
         {// continuation of current level
            numOfNodes++;

            // put p's children on queue
            if (p.leftChild != null) 
               q.put(p.leftChild);
            if (p.rightChild != null)
               q.put(p.rightChild);
         }
      }
    }
}

2.

/** a queue class that uses a one-dimensional array */

package dataStructures;

public class ArrayQueue implements Queue
{
   // data members
   int front;          // one counterclockwise from first element
   int rear;           // position of rear element of queue
   Object [] queue;    // element array

   // constructors
   /** create a queue with the given initial capacity */
   public ArrayQueue(int initialCapacity)
   {
      if (initialCapacity < 1)
         throw new IllegalArgumentException
               ("initialCapacity must be >= 1");
      queue = new Object [initialCapacity + 1];
      // default front = rear = 0
   }

   /** create a queue with initial capacity 10 */
   public ArrayQueue()
   {// use default capacity of 10
      this(10);
   }

   // methods
   /** @return true iff queue is empty */
   public boolean isEmpty()
      {return front == rear;}


   /** @return front element of queue
     * @return null if queue is empty */
   public Object getFrontElement()
   {
      if (isEmpty())
         return null;
      else
         return queue[(front + 1) % queue.length];
   }

   /** @return rear element of queue
     * @return null if the queue is empty */
   public Object getRearElement()
   {
      if (isEmpty())
         return null;
      else
         return queue[rear];
   }

   /** insert theElement at the rear of the queue */
   public void put(Object theElement)
   {
      // increase array length if necessary
      if ((rear + 1) % queue.length == front)
      {// double array size
         // allocate a new array
         Object [] newQueue = new Object [2 * queue.length];

         // copy elements into new array
         int start = (front + 1) % queue.length;
         if (start < 2)
            // no wrap around
            System.arraycopy(queue, start, newQueue, 0,
                             queue.length - 1);
         else
         {  // queue wraps around
            System.arraycopy(queue, start, newQueue, 0,
                             queue.length - start);
            System.arraycopy(queue, 0, newQueue,
                             queue.length - start, rear + 1);
         }

         // switch to newQueue and set front and rear
         front = newQueue.length - 1;
         rear = queue.length - 2;   // queue size is queue.length - 1
         queue = newQueue;
      }

      // put theElement at the rear of the queue
      rear = (rear + 1) % queue.length;
      queue[rear] = theElement;
   }

   /** remove an element from the front of the queue
     * @return removed element
     * @return null if the queue is empty */
   public Object remove()
   {
      if (isEmpty())
         return null;
      front = (front + 1) % queue.length;
      Object frontElement = queue[front];
      queue[front] = null;   // enable garbage collection
      return frontElement;
   }
   
   /** test program */
   public static void main(String [] args)
   {  
      int x;
      ArrayQueue q = new ArrayQueue(3);
      // add a few elements
      q.put(new Integer(1));
      q.put(new Integer(2));
      q.put(new Integer(3));
      q.put(new Integer(4));

      // remove and add to test wraparound array doubling
      q.remove();
      q.remove();
      q.put(new Integer(5));
      q.put(new Integer(6));
      q.put(new Integer(7));
      q.put(new Integer(8));
      q.put(new Integer(9));
      q.put(new Integer(10));
      q.put(new Integer(11));
      q.put(new Integer(12));

      // delete all elements
      while (!q.isEmpty())
      {
         System.out.println("Rear element is " + q.getRearElement());
         System.out.println("Front element is " + q.getFrontElement());
         System.out.println("Removed the element " + q.remove());
      }
   }  
}