Java数据结构之队列（二）

动态数组实现循环队列

/**
 * 循环队列避免空间浪费 循环队列不使用动态数组，底层的动态数组自己维护
 * 
 * @author zyw
 *
 * @param <E>
 */
public class LoopQueue<E> implements MyQueue<E> {

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

	@SuppressWarnings("unchecked")
	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 void enqueue(E e) {
		if ((tail + 1) % data.length == front) {
			resize(getCapacity() * 2);
		}
		data[tail] = e;
		tail = (tail + 1) % data.length;
		size++;
	}

	private void resize(int capacity) {
		@SuppressWarnings("unchecked")
		E[] newData = (E[]) new Object[capacity];
		for (int i = 0; i < size; i++) {
			newData[i] = data[(i + front) % data.length];
		}
		data = newData;
		front = 0;
		tail = size;
	}

	@Override
	public E dequeue() {
		if (isEmpty()) {
			throw new RuntimeException("队列为空，无法出队");
		}

		E res = data[front];
		data[front] = null;
		front = (front + 1) % data.length;
		size--;
		if (size == getCapacity() / 4 && getCapacity() / 2 != 0) {
			resize(getCapacity() / 2);
		}
		return res;
	}

	@Override
	public E getFront() {
		if (isEmpty()) {
			throw new RuntimeException("队列为空");
		}
		return data[front];
	}

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

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

	/**
	 * toSting方法与扩容方法的遍历方式不一样，两种不同的遍历方式
	 */
	@Override
	public String toString() {
		StringBuilder res = new StringBuilder();
		res.append(String.format("Queue:size = %d,capacity = %d\n", size, data.length - 1));
		res.append("front [");
		for (int i = front; i != tail; i = (i + 1) % data.length) {
			if ((i + 1) % data.length != tail) {
				res.append(data[i]);
				res.append(",");
			} else {
				res.append(data[i]);
				res.append("] tail");
			}
		}
		return res.toString();
	}

}