Android数据结构-队列与循环队列的实现

引用的前面设计的数组类

Array.java

/**
 * Array
 *
 * @author : lao
 * @date : 2019/11/2  13:17
 */
public class Array<E> {
    private E[] data;
    private int size;

    /**
     * 构造函数
     *
     * @param capacity 传入数值初始值大小
     */
    public Array(int capacity) {
        //Java不支持直接构造函数中new 泛型数据类型，使用强制装换
//        data = new E[capacity];
        data = (E[])new Object[capacity];
        size = 0;
    }

    /**
     * 无参构造函数，默认容量capacity=10
     */
    public Array() {
        this(10);
    }

    /**
     * @return 返回数组元素的个数
     */
    public int getSize() {
        return size;
    }

    /**
     * @return 返回数组的容量
     */
    public int getCapacity() {
        return data.length;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    /**
     * 向数组中添加一个元素
     *
     * @param e
     */
    public void addLast(E e) {
        add(size, e);
    }

    /**
     * 向数组添加一个 元素
     *
     * @param e
     */
    public void addFirst(E e) {
        add(0, e);
    }

    /**
     * 在index位置插入一个元素
     *
     * @param index 位置
     * @param e     参数值
     */
    public void add(int index, E e) {

        if (index < 0 || index > size) {
            throw new IllegalArgumentException("AddList failed.Require index>=0 and index <= size");
        }
        if (size == data.length) {
            resize(2 * data.length);
        }
        for (int i = size - 1; i >= index; i--) {
            data[i + 1] = data[i];
        }
        data[index] = e;
        size++;
    }

    /**
     *  获取数组中某一元素
     * @param index
     * @return
     */
    public E get(int index) {
        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Get failed.Index is illegal.");
        }
        return data[index];
    }

    public E getLast() {
        return get(size - 1);
    }

    public E getFirst() {
        return get(0);
    }

    /**
     * 设置某一位置的元素值
     * @param index
     * @param e
     */
    public void set(int index, E e) {
        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Get failed.Index is illegal.");
        }
        data[index] = e;
    }

    /**
     * 查找数组中是否包含某一元素e
     * @return
     */
    public boolean contains(E e) {
        for (int i = 0; i < size; i++) {
            if (data[i].equals(e)) {
                return true;
            }
        }
        return false;
    }

    /**
     * 查找数组中元素e的位置
     * @param e 查找元素
     * @return 成功返回元素下标，不成功返回-1
     */
    public int find(E e) {
        for (int i = 0; i < size; i++) {
            //比较是否为同一对象
            if (data[i].equals(e)) {
                return i;
            }
        }
        return -1;
    }

    /**
     * 删除index位置的元素，返回index中的元素
     * @param index
     * @return
     */
    public E remove(int index) {
        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Get failed.Index is illegal.");
        }
        E res = data[index];
        for (int i = index + 1; i < size; i++) {
            data[i - 1] = data[i];
        }
        size--;
        data[size] = null;  //loitering object != memory leak
        //减少容量，不能创建数组大小为0
        if (size == data.length / 4 && data.length / 2 != 0) {
            resize(data.length / 2);
        }
        return res;
    }

    /**
     * 删除数组首元素
     * @return
     */
    public E removeFirst() {
        return remove(0);
    }

    /**
     * 删除数组末尾元素
     */
    public E removeLast() {
        return remove(size - 1);
    }

    /**
     * 删除数组中指定元素
     * @param e
     * @return
     */
    public boolean removeElement(E e) {
        int index = find(e);
        if (index != -1) {
            remove(index);
            return true;
        }
        return false;
    }

    /**
     * @return 返回数组大小、容量
     */
    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append(String.format("Array: size = %d , capacity = %d\n", size, data.length));
        res.append('[');
        for (int i = 0; i < size; i++) {
            res.append(data[i]);
            if (i != size - 1) {
                res.append(", ");
            }
        }
        res.append(']');
        return res.toString();
    }

    /**
     * 数组扩容
     * @param newCapacity
     */
    private void resize(int newCapacity) {
        E[] newData = (E[])new Object[newCapacity];
        for (int i = 0; i < size; i++) {
            newData[i] = data[i];
        }
        data = newData;
    }
}

定义队列的接口

Queue.java

/**
 * Queue
 *
 * @author : lao
 * @date : 2019/11/3  12:45
 */
public interface Queue<E> {
    int getSize();
    boolean isEmpty();
    void enqueue(E e);
    E dequeue();
    E getFront();
}

普通队列

ArrayQueue.java

/**
 * ArrayQueue
 *
 * @author : lao
 * @date : 2019/11/3  12:46
 */
public class ArrayQueue<E> implements Queue<E> {
    private Array<E> array;

    public ArrayQueue(int capacity) {
        array = new Array<>(capacity);
    }

    public ArrayQueue() {
        array = new Array<>();
    }

    @Override
    public int getSize() {
        return array.getSize();
    }

    @Override
    public boolean isEmpty() {
        return array.isEmpty();
    }

    public int getCapacity() {
        return array.getCapacity();
    }

    /**
     * 添加元素
     */
    @Override
    public void enqueue(E e) {
        array.addLast(e);
    }

    /**
     * 取出元素
     * @return
     */
    @Override
    public E dequeue() {
        return array.removeFirst();
    }

    /**
     * 查看队首元素
     * @return
     */
    @Override
    public E getFront() {
        return array.getFirst();
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append("Queue: ");
        res.append("front [");
        for (int i = 0; i < array.getSize(); i++) {
            res.append(array.get(i));
            if (i != array.getSize() - 1) {
                res.append(", ");
            }
        }
        res.append("] tail");
        return res.toString();
    }
}

循环队列

LoopQueue.java

/**
 * LoopQueue
 *
 * @author : lao
 * @date : 2019/11/3  13:00
 */
public class LoopQueue<E> implements Queue<E> {
    private E[] data;  //数组
    private int front;  //队头
    private int tail;   //队尾
    private int size;   //容量

    public LoopQueue(int capacity) {
        data = (E[])new Object[capacity + 1];
        front = 0;
        tail = 0;
        size = 0;
    }

    public LoopQueue() {
        this(10);
    }

    /**
     * 容量
     * @return
     */
    public int getCapacity() {
        return data.length - 1;
    }

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

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

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

    /**
     * 出队
     * @return
     */
    @Override
    public E dequeue() {
        if (isEmpty()) {
            throw new IllegalArgumentException("Cannot dequeue from an queue.");
        }
        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;
    }

    /**
     * 获取队头元素
     * @return
     */
    @Override
    public E getFront() {
        if (isEmpty()) {
            throw new IllegalArgumentException("Queue is empty.");
        }
        return data[front];
    }

    /***
     * 队列扩容或缩减
     * @param newCapacity 扩容或缩减大小
     */
    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();
    }

    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);
            }
            System.out.println("---");
        }
    }
}

队列的运行比较

Main.java

import java.util.Random;

public class Main {

    private static double testQueue(Queue<Integer> q, int opCount) {
        long startTime = System.nanoTime();

        Random random = new Random();
        for (int i = 0; i < opCount; i++) {
            q.enqueue(random.nextInt(Integer.MAX_VALUE));
        }
        for (int i = 0; i < opCount; i++) {
            q.dequeue();
        }

        long endTime = System.nanoTime();
        return (endTime - startTime) / 1000000000.0;
    }
    public static void main(String[] args) {

        int opCount  = 100000;

        ArrayQueue<Integer> arrayQueue = new ArrayQueue<>();
        double time1 = testQueue(arrayQueue, opCount);
        System.out.println("ArrayQueue, time: " + time1 + "s");

        LoopQueue<Integer> loopQueue = new LoopQueue<>();
        double time2 = testQueue(loopQueue, opCount);
        System.out.println("LoopQueue, time: " + time2 + "s");

    }
}

执行比较的结果：