(九)链式队列以及优先级队列应用

链式队列

链式存储结构的队列称作链式队列。

链式队列的存储结构如下图所示

链式队列的实现

//结点类
public class Node {
  
	Object element; //数据域
	Node next;  //指针域
	
	//头结点的构造方法
	public Node(Node nextval)
	{
		this.next = nextval;
	}
	
	//非头结点的构造方法
	public Node(Object obj,Node nextval)
	{
	   this.element = obj;
	   this.next = nextval;
	}
	
	//获得当前结点的后继结点
	public Node getNext()
	{
		return this.next;
	}
	
	//获得当前的数据域的值
	public Object getElement()
	{
		return this.element;
	}
	
	//设置当前结点的指针域
	public void setNext(Node nextval)
	{
		this.next = nextval;
	}
	
	//设置当前结点的数据域
	public void setElement(Object obj)
	{
		this.element = obj;
	}
	
	public String toString()
	{
	   return this.element.toString();	
	}
}

//队列接口
public interface Queue {

   //入队
   public void append(Object obj) throws Exception;
   //出队
   public Object delete() throws Exception;
   //获得队头元素
   public Object getFront() throws Exception;
   //判断对列是否为空
   public boolean isEmpty();
}

//链式队列

public class LinkQueue implements Queue {
    
	Node front; //队头
	Node rear;  //队尾
	int count; //计数器
	
	public LinkQueue()
	{
		init();
	}
	
    public void init()
    {
    	front=rear=null;
    	count=0;
    }
	
	@Override
	public void append(Object obj) throws Exception {
		// TODO Auto-generated method stub
		Node node = new Node(obj,null);
		
		//如果当前队列不为空。
		if(rear!=null)
		{
			rear.next = node; //队尾结点指向新结点
		}
		
		rear = node; //设置队尾结点为新结点
		
		//说明要插入的结点是队列的第一个结点
		if(front==null)
		{
		  front = node;	
		}
		count++;
	}

	@Override
	public Object delete() throws Exception {
		// TODO Auto-generated method stub
		if(isEmpty())
		{
			new Exception("队列已空！");
		}
		Node node = front;
		front = front.next;
		count--;
		return node.getElement();
	}

	@Override
	public Object getFront() throws Exception {
		// TODO Auto-generated method stub
		if(!isEmpty())
		{
			return front.getElement();
		}
		else
		{
			return null;	
		}
	}

	@Override
	public boolean isEmpty() {
		// TODO Auto-generated method stub
		return count==0;
	}

}

链式队列的应用

思路：设字符数组str中存放了要判断的字符串。把字符数组中的字符逐个分别存入一个队列和栈中，然后逐个出队和出栈比较出队的字符与出栈的字符是否相同，若全部相等则该字符串为回文。

//栈接口
public interface Stack {
    
	//入栈
	public void push(Object obj) throws Exception;
    //出栈
	public Object pop() throws Exception;
	//获得栈顶元素
	public Object getTop() throws Exception;
	//判断栈是否为空
	public boolean isEmpty();
}

public class LinkStack implements Stack {
    
	Node head;  //栈顶指针
	int size;  //结点的个数
	
	public LinkStack()
	{
		head = null;
		size = 0;
	}
	
	@Override
	public Object getTop() throws Exception {
		// TODO Auto-generated method stub
		return head.getElement();
	}

	@Override
	public boolean isEmpty() {
		// TODO Auto-generated method stub
		return head==null;
	}

	@Override
	public Object pop() throws Exception {
		// TODO Auto-generated method stub
		if(isEmpty())
		{
			throw new Exception("栈为空！");
		}
		Object obj = head.getElement();
		head = head.getNext();
		size--;
		return obj;
		
	}

	@Override
	public void push(Object obj) throws Exception {
		// TODO Auto-generated method stub
		head = new Node(obj,head);
		size++;
	}

}

public class Test {

	/**
	 * @param args
	 */
	
	public static boolean isHuiWen(String str)throws Exception
	{
		int n = str.length();
		LinkStack stack = new LinkStack();//创建堆栈
		LinkQueue queue = new LinkQueue();//创建队列
		for(int i=0;i

优先级队列

优先级队列是带有优先级的队列。

用顺序存储结构实现的优先级队列称作顺序优先级队列。

用链式存储结构存储的优先级队列称作链式优先级队列。

顺序优先级队列

顺序优先级队列和顺序循环队列相比主要有两点不同：

（1）对于顺序优先级队列来说，出队列操作不是把队头数据元素出队列，而是把队列中优先级最高的数据元素出队列。

（2）对于顺序优先级队列来说，数据元素由两部分组成，一部分是原先意义上的数据元素，另一部分是优先级。通常设计优先级为int类型的数值，并规定数值越小优先级越高。

设计顺序优先级队列（分为两个类）

数据元素类

优先级队列类

//优先级队列元素类
public class Element {

	private Object element; // 数据
	private int priority; // 优先级
    
	public Element(Object obj,int priority)
	{
		this.element = obj;
		this.priority = priority;
	}
	
	public Object getElement() {
		return element;
	}

	public void setElement(Object element) {
		this.element = element;
	}

	public int getPriority() {
		return priority;
	}

	public void setPriority(int priority) {
		this.priority = priority;
	}

}

//队列接口
public interface Queue {

   //入队
   public void append(Object obj) throws Exception;
   //出队
   public Object delete() throws Exception;
   //获得队头元素
   public Object getFront() throws Exception;
   //判断对列是否为空
   public boolean isEmpty();
}

//优先级队列
public class PrioritySequenceQueue implements Queue {
    
	static final int defaultSize = 10; //默认队列长度
	int front ; //队头
	int rear;  //队尾
	int count;  //计数器
	int maxSize; //队列最大长度
	Element[] queue; //队列
	
	public PrioritySequenceQueue()
	{
		init(defaultSize);
	}
	
	public PrioritySequenceQueue(int size)
	{
		init(size);
	}
	
	public void init(int size)
	{
		maxSize = size;
		front= rear = 0;
		count=0;
		queue = new Element[size];
	}
	
	@Override
	public void append(Object obj) throws Exception {
		// TODO Auto-generated method stub
		//如果队列已满
		if(count>=maxSize)
		{
			throw new Exception("队列已满！");
		}
		queue[rear]=(Element)obj;
		rear++;
		count++;
	}

	@Override
	public Object delete() throws Exception {
		// TODO Auto-generated method stub
		if(isEmpty())
		{
			throw new Exception("队列为空！");
		}
		//默认第一个元素为优先级最高的。
		Element min = queue[0];
		int minIndex = 0;
		for(int i=0;i

public class Test {

	/**
	 * @param args
	 */
	public static void main(String[] args) throws Exception {
		// TODO Auto-generated method stub
       PrioritySequenceQueue queue = new PrioritySequenceQueue();
       Element temp;
       
       //五个进程入队
       queue.append(new Element(1,30));
       queue.append(new Element(2,20));
       queue.append(new Element(3,40));
       queue.append(new Element(4,20));
       queue.append(new Element(5,0));
       
       //按照优先级出队。
       System.out.println("编号  优先级");
       while(!queue.isEmpty())
       {
    	   temp =(Element)queue.delete();
    	   System.out.println(temp.getElement()+" "+temp.getPriority());
       }
       
       
	}

}