【Java】数据结构-循环队列

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队列 Queue

• 队列是一种先进先出的数据结果

循环队列实现输出截图

循环队列实现代码（完整）

Queue.java（队列接口）

public interface Queue<E> {

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

LoopQueue.java

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

    private E[] data;
    private int front, tail;
    private int size;

    public LoopQueue(int capacity){
        data =(E[]) new Object[capacity + 1];
        front = 0;
        tail = 0 ;
        size = 0 ;
    }

    public LoopQueue(){
        this(10);
    }

    public int getCapacity(){
        return data.length - 1;
    }

    @Override
    public boolean isEmpty(){
        return front == tail;
    }

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

    @Override
    public void enqueue(E e){

        if((tail + 1) % data.length == front)
            resize(getCapacity() * 2);

        data[tail] = e ;
        tail = (tail + 1) % data.length;
        size ++;
    }

    @Override
    public E dequeue(){

        if(isEmpty()){
            throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
        }
        E ret = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        size --;
        if(size == getCapacity() / 4 && getCapacity() / 2 != 0)
            resize(getCapacity() / 2);
        return ret;
    }

    @Override
    public E getFront(){
        if(isEmpty())
            throw new IllegalArgumentException("Queue is empty.");
        return data[front];
    }


    private void resize(int newCapacity){

        E[] newData =(E[]) new Object[newCapacity + 1];
        for(int i = 0 ; i < size ; i ++)
            newData[i] = data[(i + front) % data.length];
        data = newData;
        front = 0;
        tail = size;
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append(String.format("LoopQueue: size = %d, capacity = %d \n", size, getCapacity()));
        res.append("front [");
        for(int i = front ; i != tail; i = (i + 1) % data.length) {
            res.append(data[i]);
            if ((i + 1) % data.length != tail)
                res.append(", ");
        }
        res.append("] tail");
        return res.toString();
    }

    public static void main(String[] args) {

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

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