Java队列的实现数组和链表

一、队列

队列是一种线性数据结构，也是一种操作受限的数据结构，先进先出，后进后出，只能从head出队，从tail入队。

 

二、队列的实现

 

1. 顺序队列「数组实现」

import java.util.Arrays;

public class ArrayQueue {
    private String[] queue;
    //队列元素个数
    private int n;
    //头位置
    int head;
    //尾位置
    int tail;

    public ArrayQueue(int n) {
        queue = new String[n];
        this.n = n;
        this.head = 0;
        this.tail = 0;
    }

    @Override
    public String toString() {
        return "ArrayQueue{" +
                "queue=" + Arrays.toString(queue) +
                ", n=" + n +
                ", head=" + head +
                ", tail=" + tail +
                '}';
    }

    /**
     * 数据入队
     *
     * @return
     */
    public boolean enqueue(String item) {

        if (tail == n) {
            //队列已满
            if (head == 0) {
                return false;
            } else {
                //队列满了，但是可以移动数据继续插入数据
                for (int i = 0; i < tail - head; i++) {
                    queue[i] = queue[head+i];
                }
                tail = tail - head;
                head = 0;
            }
        }

        queue[tail] = item;
        tail++;
        return true;

    }

    /**
     * 数据出队
     *
     * @return
     */
    public String dequeue() {
        //如果头尾节点相同，证明队列没数据
        if (head == tail) {
            return null;
        }

        String tmp = queue[head];
        head++;
        return tmp;
    }

    public static void main(String[] args) {
        ArrayQueue arrayQueue = new ArrayQueue(3);

        arrayQueue.enqueue("a");
        System.out.println(arrayQueue);

        arrayQueue.enqueue("b");
        System.out.println(arrayQueue);


        arrayQueue.enqueue("c");
        System.out.println(arrayQueue);

        arrayQueue.dequeue();
        System.out.println(arrayQueue);

        arrayQueue.enqueue("d");
        System.out.println(arrayQueue);

    }
}

 

2. 链式队列「链表实现」

定义节点

public class Node {
    public String data;
    public Node next;

    public Node() {
    }

    public Node(String data) {
        this.data = data;
    }

    public Node(String data, Node next) {
        this.data = data;
        this.next = next;
    }

    @Override
    public String toString() {
        return "Node{" +
                "data='" + data + '\'' +
                '}';
    }
}

 

实现

public class LinkedQueue {
    Node head;
    Node tail;

    public LinkedQueue() {
        this.head = null;
        this.tail = null;
    }

    @Override
    public String toString() {
        Node tmp = head;
        StringBuffer sb = new StringBuffer();
        while (tmp != null) {
            sb.append(tmp.data).append(",");
            tmp = tmp.next;
        }
        sb.append("\t");
        sb.append("head:").append(head.data).append("\t");
        sb.append("tail:").append(tail.data);
        return sb.toString();
    }

    public boolean enqueue(String item) {
        tail = new Node(item, null);
        if (head == null) {
            head = tail;
        } else {
           Node tmp = head;
            while (tmp.next != null) {
                tmp = tmp.next;
            }
            tmp.next = tail;
        }

        return true;
    }

    public String dequeue() {
        if (head==tail) {
            return null;
        }
        String tmp = head.data;
        head = head.next;
        return tmp;
    }

    public static void main(String[] args) {
        LinkedQueue linkedQueue = new LinkedQueue();
        linkedQueue.enqueue("a");
        System.out.println(linkedQueue);

        linkedQueue.enqueue("b");
        System.out.println(linkedQueue);

        linkedQueue.enqueue("c");
        System.out.println(linkedQueue);

        linkedQueue.enqueue("d");
        System.out.println(linkedQueue);

        linkedQueue.dequeue();
        System.out.println(linkedQueue);

        linkedQueue.dequeue();
        System.out.println(linkedQueue);
    }

}

 

3. 环形队列「数组实现」

import java.util.Arrays;

//环形队列
public class CircleQueue {
    String[] queue;
    int head;
    int tail;
    //队列的长度
    int n;

    public CircleQueue(int n) {
        this.queue = new String[n];
        this.n = n;
        this.head = 0;
        this.tail = 0;
    }


    @Override
    public String toString() {
        return "CircleQueue{" +
                "queue=" + Arrays.toString(queue) +
                ", head=" + head +
                ", tail=" + tail +
                ", n=" + n +
                '}';
    }

    public boolean enqueue(String item) {
        if ((tail + 1) % n == head) {
            return false;
        }

        queue[tail] = item;
        tail = (tail + 1) % n;
        return true;
    }

    public String dequeue() {
        if (head == tail) {
            return null;
        }
        String tmp = queue[head];
        head = (head + 1) % n;
        return tmp;
    }

    public static void main(String[] args) {
        CircleQueue circleQueue = new CircleQueue(3);

        circleQueue.enqueue("a");
        System.out.println(circleQueue);

        circleQueue.enqueue("b");
        System.out.println(circleQueue);

        circleQueue.enqueue("c");
        System.out.println(circleQueue);

        circleQueue.dequeue();
        System.out.println(circleQueue);

        circleQueue.dequeue();
        System.out.println(circleQueue);

        circleQueue.enqueue("d");
        System.out.println(circleQueue);

        circleQueue.dequeue();
        System.out.println(circleQueue);

        circleQueue.dequeue();
        System.out.println(circleQueue);


        circleQueue.enqueue("e");
        System.out.println(circleQueue);
    }
}