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();
}
}