队列的创建Java实现

关键词：结点类、队列类、队头队尾指针

1.结点类的设计

class QueueNode {
	int data;
	QueueNode next;
	
	QueueNode(){
		data = 0;
		next = null;
	}
	QueueNode(int d, QueueNode n){
		data = 0;
		next = n;
	}
}

2.链式队列类的设计（基于链表实现）

class LinQueue {
	private QueueNode front;//队头指针
	private QueueNode rear;//队尾指针
	
	public LinQueue(){
		front = rear = null;
	}
	public boolean isEmpty(){
		return front == null;
	}
	public int getHead(){
		if(isEmpty()){
			System.out.println("当前队列为空");
			return -1;
		}
		return front.data;
	}
	public void enQueue(QueueNode node){
		if(front == null){//如果队列为空
			front = rear = node；
		}
		else{
			rear = rear.next = node;
		}
	}
	public int deQueue(){
		if(isEmpty){
			System.out.println("当前队列为空");
			return -1;
		}
		int data = front.data;
		front = front.next;
		return data;
	}
}

3.顺序队列类的设计（基于数组实现）

class SeqQueue {
	private QueueNode[] array;
	private int front;
	private int rear;
	
	public SeqQueue(){
		array = new QueueNode[10];//默认队列大小为10
		front = rear = 0;
	}
	public SeqQueue(int size){
		array = new QueueNode[size];
		front = rear = 0;
	}
	public boolean isEmpty(){
		return front == rear;
	}
	public boolean isFull(){
		return rear == array.length;
	}
	public int getHead(){
		if(isEmpty()){
			System.out.println("当前队列为空");
			return -1;//负数表示空
		}
		return array[front].data;
	}
	public void enQueue(QueueNode node){
		if(isEmpty()){//如果队列为空
			array[front]=array[rear]=node；
		}
		else{
			if(isFull())
				System.out.println("队满，无法入队");
			else
				array[++rear]=node;
		}
	}
	public int deQueue(){
		if(isEmpty())
			System.out.println("当前队列是空的");
		else{
			int data = array[front];//队头front=0
			for(int i=0; i<rear; i++){
				array[i] = array[i+1];
			}
			rear--;
			return data;
		}
	}
}

基于数组的顺序队列会产生假溢出的问题，解决解决假溢出问题通常有两种方法：

（1）每次出队时，剩余元素都往前移（时间复杂度大，上面代码就是此种方法）

（2）使用循环队列（请看下面的代码）

4.循环队列类的设计（基于数组实现）

循环队列要点：

1.队列空条件：front == rear

2.队列满条件：(rear+1)%MaxSize == front

3.元素进队：data[rear] = e; rear = (rear+1)%MaxSize

4.元素出队：e = data[front]; front = (front+1)%MaxSize

class CirQueue {
	private static final int maxSize = 10;
	private int front;
	private int rear;
	private QueueNode[] array;
	
	public CirQueue(){
		array = new QueueNode[maxSize];
		rear = front = 0;
	}
	public void clear(){
		front = rear = 0;
	}
	public boolean isEmpty(){
		return front==rear;
	}
	public boolean isFull(){
		return (rear+1) % array.length == front;
	}
	public int getSize(){
		return (rear - front + array.length) % array.length;
	}
	public Type getFront( ){
		if(isEmpty())
			throw new NoSuchElementException();
		return array[(front+1)%element.length];    
	}
	public void enQueue(Type item){
		if(isFull())
			throw new OutOfQueueException();
		rear = (rear+1) % array.length;
		array[rear] = item;    
	}
	public Type deQueue( ){
		if(isEmpty())
			throw new NoSuchElementException();
		front = (front+1) % array.length;
		return array[front];    
	}
}

队列的创建Java实现

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