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Copy pathLoopQueue.java
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108 lines (93 loc) · 2.39 KB
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package queue.impl;
/**
* 循环队列
* <p>
* front == tail 队列为空
* <p>
* front == (tail+1)/c c为长度 队列为满
* <p>
* 复杂度分析
* 算法优化：
*
*/
public class LoopQueue<E> implements Queue<E> {
private E[] data;
private int front, tail;
private int size;
public LoopQueue(int capacity) {
this.data = (E[]) new Object[capacity + 1];
this.front = 0;
this.tail = 0;
this.size = 0;
}
public LoopQueue() {
this(10);
}
////O(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++;
}
//O(1)
@Override
public E dequeue() {
if (isEmpty()) {
throw new IllegalArgumentException("Can not dequeue from an empty Queue");
}
E ret = data[front];
data[front] = null;
front = (front + 1) % data.length;
size--;
//缩容
if (size == getCapacity() / 4 && getCapacity() / 2 != 0) {
resize(getCapacity() / 2);
}
return null;
}
@Override
public E getFront() {
if (isEmpty()) {
throw new IllegalArgumentException("Can not dequeue from an empty Queue");
}
return data[front];
}
@Override
public int getSize() {
return size;
}
@Override
public boolean isEmpty() {
return front == tail;
}
public int getCapacity() {
return data.length - 1;
}
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 builder = new StringBuilder();
builder.append(String.format("Queue:Size = %d , capacity = %d \n", getSize(), getCapacity()));
builder.append("front [");
for (int i = front; i != tail; i = (i + 1) % data.length) {
builder.append(data[i]);
if ((i + 1) % data.length != tail) {
builder.append(", ");
}
}
builder.append("] tail");
return builder.toString();
}
}