数据结构之循环队列[Java]-蒲公英云

数据结构之循环队列[Java]

/** * @ClassName: LoopQueue * @Author: Leo * @Description: 循环队列 * @Date: 4/4/2020 4:35 PM */
public class LoopQueue<E> implements Queue<E> { 
    //存放元素的数组
    private E[] data;
    //队首引用 队尾引用
    private int front, tail;
    //队列元素数量
    private int size;
    public LoopQueue(int capacity) { 
        data = (E[]) new Object[capacity + 1];
        front = 0;
        tail = 0;
        size = 0;
    }
    public LoopQueue() { 
        this(10);
    }
    /** * 获取队列容积 * * @return */
    public int getCapacity() { 
        return data.length - 1;
    }
    /** * 获取队列元素数量 * * @return */
    @Override
    public int getSize() { 
        return size;
    }
    /** * 判断队列是否为空 * * @return */
    @Override
    public boolean isEmpty() { 
        //首尾引用相等 证明队列为空 如果(tail + 1) % data.length == front 则队列满
        return front == tail;
    }
    /** * 入队 * * @param e */
    @Override
    public void enqueue(E e) { 
        //如果队列满 则扩容两倍
        if ((tail + 1) % data.length == front) { 
            resize(getCapacity() * 2);
        }
        //把元素添加到队尾
        data[tail] = e;
        //队尾指针后移一位
        tail = (tail + 1) % data.length;
        size++;
    }
    /** * 扩容 * * @param newCapacity */
    private void resize(int newCapacity) { 
        //新建一个指定容量的数组
        E[] newData = (E[]) new Object[newCapacity + 1];
        //把之前数组的元素复制到新数组
        for (int i = 0; i < size; i++) { 
            //偏移量为front
            newData[i] = data[(i + front) % data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }
    /** * 出队 * * @return */
    @Override
    public E dequeue() { 
        if (isEmpty()) { 
            throw new IllegalArgumentException("Cannot dequeue from an empty queue.");
        }
        //暂存出队元素
        E e = data[front];
        data[front] = null;
        //头引用+1
        front = (front + 1) % data.length;
        size--;
        //如果元素数量为容积的1/4 则缩容为原来的1/2
        if (size == getCapacity() / 4 && getCapacity() / 2 != 0) { 
            resize(getCapacity() / 2);
        }
        return e;
    }
    /** * 获取队首元素 * * @return */
    @Override
    public E getFront() { 
        if (isEmpty()) { 
            throw new IllegalArgumentException("Queue is empty.");
        }
        return data[front];
    }
    @Override
    public String toString() { 
        StringBuilder res = new StringBuilder();
        res.append(String.format("Queue: 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();
    }
}