day18--栈队列

1.队列

队列是一种特殊的线性表，特殊之处在于它只允许在表的前端（front）进行删除操作，而在表的后端（rear）进行插入操作，和栈一样，队列是一种操作受限制的线性表。进行插入操作的端称为队尾，进行删除操作的端称为队头。

2.入队

• 创建一个新的节点
• 将新节点接在队尾
• 然后队尾指针指向新节点

public void enqueue(int paraValue) {
    
		Node tempNode = new Node(paraValue);
		tail.next = tempNode;
		tail = tempNode;
	}// of enqueue

3.出栈

• 首先判断队列是否为空
• 然后队列从队头开始出队
• 出队后，判断header的next是否为空，如果为空，这该队列为空，将tail=header

public int dequeue() {
    
		if (header == tail) {
    
			System.out.println("No element in the queue");
			return -1;
		} 

		int resultValue = header.next.data;
		header.next = header.next.next;

		if (header.next == null) {
    
			tail = header;
		}

		return resultValue;
	}// of dequeue

4.代码实现

package com.datastructure;

public class LinkedQueue {
    

	class Node {
    
		int data;
		Node next;

		public Node(int paraValue) {
    
			data = paraValue;
			next = null;
		}// Of the constructor
	}// of class Node

	Node header;

	Node tail;

	public LinkedQueue() {
    
		header = new Node(-1);
		tail = header;
	}// of the first constructor

	//入队，入队操作再队尾进行
	//1.创建一个新节点，再将新节点接在队尾，将队尾指针指向新节点
	public void enqueue(int paraValue) {
    
		Node tempNode = new Node(paraValue);
		tail.next = tempNode;
		tail = tempNode;
	}// of enqueue

	//出队，出队操作再对头进行
	//1.判断队列是否为空
	public int dequeue() {
    
		if (header == tail) {
    
			System.out.println("No element in the queue");
			return -1;
		} 

		int resultValue = header.next.data;
		header.next = header.next.next;

		// 出队后，判断header的next是否为空，如果为空，这该队列为空，将tail=header
		if (header.next == null) {
    
			tail = header;
		}

		return resultValue;
	}// of dequeue

	public String toString() {
    
		String resultString = "";

		if (header.next == null) {
    
			return "empty";
		} // Of if

		Node tempNode = header.next;
		resultString += tempNode.data;
		tempNode = tempNode.next;
		while (tempNode != null) {
    
			resultString += ", " + tempNode.data;
			tempNode = tempNode.next;
		} //of while

		return resultString;
	}//of toString

	public static void main(String args[]) {
    
		LinkedQueue tempQueue = new LinkedQueue();
		System.out.println("Initialized, the list is: " + tempQueue.toString());

		for (int i = 0; i < 5; i++) {
    
			tempQueue.enqueue(i + 1);
		} // of for i
		System.out.println("Enqueue, the queue is: " + tempQueue.toString());

		tempQueue.dequeue();
		System.out.println("Dequeue, the queue is: " + tempQueue.toString());

		int tempValue;
		for (int i = 0; i < 5; i++) {
    
			tempValue = tempQueue.dequeue();
			System.out.println("Looped delete " + tempValue + ", the new queue is: " + tempQueue.toString());
		} // of for i

		for (int i = 0; i < 3; i++) {
    
			tempQueue.enqueue(i + 10);
		} // of for i
		System.out.println("Enqueue, the queue is: " + tempQueue.toString());
	}//of main
}// of class LinkedQueue

运行结果