基于动态数组实现的循环队列

循环队列的添加和删除操作都是O(1),比普通数组实现的队列要快很多倍。

代码实现

//接口类
public interface Queue<E> {
	int getSize();
	boolean isEmpty();
	void enqueue(E e);
	E dequeue();
	E getFront();
}

/实现类

public class LoopQueue<E> implements Queue<E> {
	
	private E[] data;
	private int tail,front;
	private int size;
	
	
	
	public LoopQueue(int capacity) {
		data = (E[])new Object[capacity + 1];
		tail = 0;
		front = 0;
		size = 0;
	}
	
	public LoopQueue() {
		this(10);
	}

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

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

	@Override
	public void enqueue(E e) {
		if(front == (tail+1) % data.length){
			resize(getCapacity() * 2);
		}
		
		data[tail] = e;
		tail = (tail + 1) % data.length;
		size ++;
	}
	
	public int getCapacity(){
		return data.length - 1;
	}

	@Override
	public E dequeue() {
		if(isEmpty())
			throw new IllegalArgumentException("Queue is empty.");
		
		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("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();
    }
}

来源：CSDN

作者：FeiPeng_

链接：https://blog.csdn.net/FeiPeng_/article/details/104822080