基于java的数据结构学习——数组实现的队列和循环队列及性能对比

队列 Queue

队列也是一种线性结构
相比数组，队列对应的操作是数组的子集
只能从一端（队尾）添加元素，只能从另一端（队首）取出元素
队列是一种先进先出的数据结构

队列的实现及复杂度分析

Queue<E>

void enqueu(E)
E dequeue()
E getFront()
int getSize()
boolean isEmpty()

数组队列的复杂度分析

ArrayQueue<E>

void enqueue(E) O(1) 均摊
E dequeue() O(n)
E getFront() O(1)
int getSize() O(1)
boolean isEmpty() O(1)

代码实现：

public class ArrayQueue<E> implements Queue<E> {private Array<E> data;public ArrayQueue(int Capacity){data = new Array<>(Capacity);}public ArrayQueue(){this(10);}@Overridepublic int getSize(){return data.getSize();}public int getCapacity(){return data.getCapacity();}@Overridepublic boolean isEmpty(){return data.isEmpty();}@Overridepublic void enqueue(E e){data.addLast(e);}@Overridepublic E dequeue(){return data.removeFirst();}@Overridepublic E getFront(){return data.getFirst();}@Overridepublic String toString(){StringBuilder res = new StringBuilder();res.append("Queue : front [");for (int i = 0; i < data.getSize(); i++) {res.append(data.get(i));if (i != data.getSize() - 1)res.append(", ");}res.append("] tail");return res.toString();}public static void main(String[] args){ArrayQueue<Integer> queue = new ArrayQueue<>();for(int i = 0 ; i < 10 ; i ++){queue.enqueue(i);System.out.println(queue);if(i % 3 == 2){queue.dequeue();System.out.println(queue);}}}
}

循环队列的复杂度分析

LoopQueue<E>

void enqueue(E) O(1) 均摊
E dequeue() O(1) 均摊
E getFront() O(1)
int getSize() O(1)
boolean isEmpty() O(1)

front == tail 队列为空

(tail + 1) % c = front 队列已满

tail不用于存储元素，capacity中浪费一个空间

代码实现：


public class LoopQueue<E> implements Queue<E> {private E[] data;private int front, tail;private int size;public LoopQueue(int capacity){data  = (E[])new Object[capacity + 1];front = 0;tail  = 0;size  = 0;}public LoopQueue(){this(10);}@Overridepublic boolean isEmpty(){return size == 0;}public boolean isFull(){return front == (tail + 1) % data.length;}public int getCapacity(){return data.length - 1;}@Overridepublic int getSize(){return size;}@Overridepublic void enqueue(E e){if (isFull())resize(getCapacity() * 2 + 1);data[tail] = e;tail = (tail + 1) % data.length;size++;}@Overridepublic E dequeue(){if (isEmpty())throw new IllegalArgumentException("Dequeue Failed.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 + 1);return ret;}@Overridepublic E getFront(){if (isEmpty())throw new IllegalArgumentException("Queue is empty.");return data[front];}public void resize(int newCapacity){if (newCapacity <= 0)throw new IllegalArgumentException("newCapacity is Illegal.");E[] newData = (E[])new Object[newCapacity];for (int i = 0; i < size; ++i)newData[i] = data[(i + front) % data.length];data = newData;front = 0;tail = size;}@Overridepublic String toString(){StringBuilder res = new StringBuilder();res.append(String.format("LoopQueue Capacity = %d, Size = %d\n", getCapacity(), getSize()));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();}public static void main(String[] args) {LoopQueue<Integer> queue = new LoopQueue<>();for (int i = 0; i < 10; i++) {queue.enqueue(i);System.out.println(queue);if (i % 3 == 2) {queue.dequeue();System.out.println(queue);}}}
}

性能比较：

测试函数：

// 测试使用q运行opCount个enqueueu和dequeue操作所需要的时间，单位：秒private static double testQueue(Queue<Integer> q, int opCount){long startTime = System.nanoTime();for (int i = 0; i < opCount; ++i)q.enqueue(i);for (int i = 0; i < opCount; ++i)q.dequeue();long endTime = System.nanoTime();return (endTime - startTime) / 1000000000.0;}

测试：

    public static void main(String[] args){int opCount = 100000;ArrayQueue<Integer> arrayQueue = new ArrayQueue<>();double timeArray = testQueue(arrayQueue, opCount);System.out.println("ArrayQueue time :" + timeArray + " s");LoopQueue<Integer> loopQueue = new LoopQueue<>();double timeQueue = testQueue(loopQueue, opCount);System.out.println("LoopQueue time :" + timeQueue + " s");}

运行结果：