数据结构循环队列

Posted 2022-12-11 写Bug的渣渣高

/**
 * 队列的改良，使得删除元素的时间复杂度为o1
 * @param <E>
 */
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;
    


    private void resize(int newCapacity) 
//      要浪费一个空间
        E[] newData = (E[]) new Object[newCapacity+1];
//      将 data 要按照顺序放入
        for (int i = 0; i < size; i++) 
            newData[i] = data[(i+front) % data.length];
        
        data = newData;
        front = 0;
        tail = size;
    


    public LoopQueue()
        this(10);
    

    @Override
    public int getSize() 
        return size;
    


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


    @Override
    public void enqueue(E e) 
//        看看队列是否是满的
        if ((tail+1) % data.length == front)
//        为什么不直接使用data.length,因为
            resize(getCapacity()*2);
        
        data[tail] = e;
        tail = (tail + 1) % data.length;
        size ++;
    


    @Override
    public E dequeue() 
        if (isEmpty())
            throw new IllegalArgumentException("队列为空,无法出队");
        
        E ret = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        if (size == getCapacity() /4 && getCapacity() / 2 !=0)
            resize(getCapacity() / 2);
        
        return ret;
    


    @Override
    public E getFront() 
//      判断队列不能为空
        if (isEmpty())
            throw new IllegalArgumentException("队列为空");
        
        return data[front];
    


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


    @Override
    public String toString() 
        StringBuffer res = new StringBuffer();
        res.append(String.format("Queue:size = %d,capacity = %d\\n",size,getCapacity()));
        res.append("front [");
//      注意这里的界限
        for (int i = front; i != tail; i++) 
            res.append(data[i]);
            res.append(",");
        
        res.append("] tail");
        return res.toString();