day17 链队列

1. 链队列特点

队列相比于栈，它是两端都可以操作，但队头只能进行出队列，队尾只能进行入队列（就像生活中的排队买东西一样）在删除队列时，需要判断队列是否为空（如下代码：header.next == null）。当对头(header)和队尾(tail)指向同一个节点时，则队列为空，所以空队列也需要一个节点

2. 图示

创建一个队列
结合图去理解代码的入队和出队就很好理解。 ## 代码
队列判空头指针和尾指针指向相等 header == tail

package datastructure.queue;
public class LinkedQueue {
    class Node{
        /**
         * The data
         */
        int data;
        /**
         * The reference to the next node
         */
        Node next;

        /**
         * The constructor
         * @param paraValue The data
         */
        public Node(int paraValue){
            data = paraValue;
            next = null;
        }
    }

    /**
     * The header of the queue
     */
    Node header;

    /**
     * The tail of the queue
     */
    Node tail;

    /**
     * Construct an empty sequential list.
     */
    public LinkedQueue(){
        header = new Node(-1);

        tail = header;
    }

    /**
     * Enqueue
     * @param paraValue The value of the new node.
     */
    public void enqueue(int paraValue){
        Node tempNode = new Node(paraValue);
        tail.next = tempNode;
        tail = tempNode;
    }

    /**
     * Dequeue
     * @return The value at the 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;

        // The queue becomes empty.
        if (header.next == null){
            tail = header;
        }
        return resultValue;
    }

    /**
     * Overrides the method claimed in Object, the superclass of any class.
     * @return
     */
    @Override
    public String toString(){
        String resultString = "";

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

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

        return resultString;
    }

    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);
        }
        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());
        }

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


    }
}

在这里插入图片描述

java学习day17

day17 链队列

1. 链队列特点

2. 图示