【Java】数据结构-链表实现队列(完整代码)

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孤桜懶契：http://gylq.github.io

链表实现队列的接口

Queue.java

public interface Queue<E> {

    int getSize();
    boolean isEmpty();
    void enqueue(E e);
    E dequeue();
    E getFront();
}

链表实现队列操作执行结果

链表实现队列操作（完整代码）

LinkedListQueue.java（实现队列的操作）

public class LinkedListQueue<E> implements Queue<E> {

    private class Node{
        public E e;
        public Node next;

        public Node(E e, Node next){
            this.e = e;
            this.next = next;
        }

        public Node(E e) { this(e, null);}

        public Node() {this(null, null);}

        @Override
        public String toString(){ return e.toString(); }
    }

    private Node head, tail;
    private int size;

    public LinkedListQueue(){
        head = null;
        tail = null;
        size = 0;
    }

    @Override
    public int getSize(){
        return size;
    }

    @Override
    public boolean isEmpty(){
        return size == 0;
    }

    //入队
    @Override
    public void enqueue(E e){
        if(tail == null){
            tail = new Node(e);
            head = tail;
        }
        else{
            tail.next = new Node(e);
            tail = tail.next;
        }
        size ++;
    }

    //出队
    @Override
    public E dequeue(){
        if(isEmpty())
            throw new IllegalArgumentException("Cannot dequeue from an empty queue.");

        Node retNode = head;
        head = head.next;
        retNode.next = null;
        if(head == null)
            tail = null;
        size --;
        return retNode.e;
    }

    @Override
    public E getFront(){
        if(isEmpty())
            throw new IllegalArgumentException("Queue is empty");
        return head.e;
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append("Queue: front ");

        Node cur = head;
        while(cur != null){
            res.append((cur + "->"));
            cur = cur.next;
        }
        res.append("NULL tail");
        return res.toString();
    }
    public static void main(String[] args){

        LinkedListQueue<Integer> queue = new LinkedListQueue<>();
        for(int i = 0 ; i < 10 ; i ++){
            queue.enqueue(i);
            System.out.println(queue);

            if(i % 3 == 2){
                queue.dequeue();
                System.out.println(queue);
            }
        }
    }
}

我对比了一下数组队列、循环数组队列、链表实现队列的时间输出结果截图

• 明显循环数组队列和列表实现队列的时间相当，数组队列最差。相差100倍左右

测试时间代码

import java.util.Random;

public class Main {

    // 测试使用q运行opCount个enqueue和dequeue操作所需要的时间，单位：秒
    private static double testQueue(Queue<Integer> q, int opCount){

        long startTime = System.nanoTime();

        Random random = new Random();
        for(int i = 0 ; i < opCount; i ++)
            q.enqueue(random.nextInt(Integer.MAX_VALUE));
        for(int i = 0 ; i < opCount ; i ++)
            q.dequeue();

        long endTime = System.nanoTime();

        return (endTime - startTime) / 100000000.0;

    }
    public static void main(String[] args){

        int opCount = 100000;

        LoopQueue<Integer> loopQueue = new LoopQueue<>();
        double time1 = testQueue(loopQueue, opCount);
        System.out.println("LoopQueue , time: " + time1 + "s");
        ArrayQueue<Integer> arrayQueue = new ArrayQueue<>();
        double time2 = testQueue(arrayQueue, opCount);
        System.out.println("arrayQueue , time: " + time2 + "s");
        LinkedListQueue<Integer> linkedListQueue = new LinkedListQueue<>();
        double time3 = testQueue(linkedListQueue, opCount);
        System.out.println("LinkedListQueue , time: " + time3 + "s");


    }
}