Question

所以我被要求在数组中执行队列，直到我看到我在出列并尝试将其他值排入后得到一个有趣的输出时，我没有遇到任何麻烦......
例如（输出）：

Queue: [1]     //Enqueue 1  
Queue: [1, 2]  //Enqueue 2
Queue: [2]      //Dequeue
Queue: [2, 2]   //Enqueue 3
Queue: [2, 2, 3] //Enqueue 4
Queue: [5, 2, 3, 4]  //Now is a total mess...

我的代码包含队列，dequeque和resize方法，一切正常，我真的不知道如何修复它... 如果您想尝试，我的代码是主要的。感谢。

public class MainQueue {
    public static void main(String[] args) {

        int capacity=5;
        Queue<Integer> queue = new Queue<Integer>(capacity);

        queue.enqueue(1);
        System.out.println("Queue: "+ queue);
        queue.enqueue(2);
        System.out.println("Queue: "+ queue);
        queue.dequeue();
        queue.enqueue(3);
        System.out.println("Queue: "+ queue);
        queue.enqueue(4);
        System.out.println("Queue: "+ queue);
        queue.enqueue(5);
        System.out.println("Queue: "+ queue);

    }
}

类

import java.util.NoSuchElementException;


public class Queue<E> {
    private E[] elements;//array in generic
    private int front;//first element or front of the queue
    private int back;//last element or back of the queue
    private int capacity; //capacity of the queue
    private int count; //indicates number of elements currently stored in the queue

    public Queue(int size)
    {
        capacity = size;
        count = 0;
        back = size-1;
        front = 0;
        elements =(E []) new Object[size];  //queue array empty
    }

    //Returns true if the queue is empty or false
    public boolean isEmpty()
    {
        return count==0;//means its true
    }

    //Add elements to the queue
    public void enqueue(E item)
    {
        if(count == capacity)
        {
            resize(capacity*2);
            // System.out.println("Queue is full");

        }

        back =(back+1) % capacity;    //example back=(0+1)%10=1
        elements[back]=item;
        //elements[0]=0
        //item=elements[count];
        count++;
    }


    //Public resize
    public void resize(int reSize){
        E[] tmp = (E[]) new Object[reSize];

        int current = front;
        for (int i = 0; i &lt; count; i++)
        {
            tmp[i] = elements[current];
            current = (current + 1) % count;
        }

        elements = tmp;
        front = 0;
        back = count-1;
        capacity=reSize;

    }


    //Dequeue method to remove head
    public E dequeue()
    {
        if(isEmpty())
        throw new NoSuchElementException("Dequeue: Queue is empty");
        else
        {
            count--;
            for(int x = 1; x <= count; x++)
            {
                elements[x-1] = elements[x];
            }
            capacity--;
            return (E) elements;
        }
    }

    //peek the first element
    public E peek()
    {
        if(isEmpty())
        throw new NoSuchElementException("Peek: Queue is empty");

        else
        return elements[front];
    }


    //Print queue as string
    public String toString()
    {

        if(isEmpty()) {
            throw new NoSuchElementException("Queue is empty");
        }

        String s = "[";
        for(int i = 0; i < count; i++)
        {
            if(i != 0)
            s += ", ";
            s = s + elements[i];// [value1,value2,....]
        }

        s +="]";
        return s;
    }

    public void delete() {   //Delete everything
        count = 0;
    }
}

Answer 1

您正在使用back的当前值更新enqueue()方法中的back，但您根本不会使用dequeu()方法更新它。这不会正常工作。实际上，您应该根据back计算count。

只需改变：

back = (back + 1) % capacity;

为：

back = count % capacity;

Answer 2

在dequeue中，您没有更新back变量，该变量决定了您使用enqueue添加新值的位置。此外，在dequque中，当0只有1时，您可以从索引count复制索引1上不存在的值。这是一个特殊情况，如果您创建了一个容量（大小）为1的队列，将某些内容排队然后将其出列，那么将超出边界错误。

队列实现为Array

2 个答案: