队列

基于数组的循环队列

• Java实现

/**
 * 基于数组的循环队列实现
 *
 * @param  泛型
 * @author ZhuZongxing
 */
public class LoopQueue implements Queue {
    private E[] data;
    private int front;
    private int tail;
    private int size;

    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 int getSize() {
        return size;
    }

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

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

    private void resize(int newCapacity) {
        E[] newData = (E[]) new Object[newCapacity];
        for (int i = 0; i < getSize(); i++) {
            newData[i] = data[(i + front) % data.length];
        }
        data = newData;
        front = 0;
        tail = getSize();
    }

    @Override
    public E deQueue() {
        if (isEmpty()) {
            throw new IllegalArgumentException("队列中没有数据了！");
        }
        E ret = data[front];
        front = (front + 1) % data.length;
        size--;
        if (size == getCapacity() / 4 && getCapacity() / 2 != 0) {
            resize(getCapacity() / 2);
        }
        return ret;
    }

    @Override
    public E getFront() {
        return data[front];
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(String.format("LoopQueue: Capacity: %d , Size: %d \nfront [", getCapacity(), getSize()));
        for (int i = front; i != tail; i = (i + 1) % data.length) {
            sb.append(data[i]);
            if (tail != (i + 1) % data.length) {
                sb.append(", ");
            }
        }
        sb.append("] tail");
        return sb.toString();
    }
}

基于链表的队列实现

• Java实现

package queue;

/**
 * 基于链表的队列实现
 *
 * @param  泛型
 * @author ZhuZongxing
 */
public class LinkedListQueue implements Queue {
    private class Node {
        public E e;
        public Node next;

        public Node(E e) {
            this(e, null);
        }

        public Node(E e, Node next) {
            this.e = e;
            this.next = next;
        }

        @Override
        public String toString() {
            return e.toString();
        }
    }

    private Node head, tail;
    private int size;

    public LinkedListQueue() {
        head = null;
        tail = null;
        size = 0;
    }

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

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

    @Override
    public void enQueue(E e) {
        if (tail == null) {
            tail = new Node(e);
            head = tail;
        } else {
            tail.next = new Node(e);
            tail = tail.next;
        }
        size++;
    }

    @Override
    public E deQueue() {
        if (isEmpty()) {
            throw new IllegalArgumentException("队列中已经没有元素了！！！");
        }
        Node retNode = head;
        head = head.next;
        retNode.next = null;
        if (head == null) {
            tail = null;
        }
        size--;
        return retNode.e;
    }

    @Override
    public E getFront() {
        if (isEmpty()) {
            throw new IllegalArgumentException("队列中已经没有元素了！！！");
        }
        return head.e;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("LinkedListQueue: Front [");
        Node curNode = this.head;
        while (curNode != null) {
            sb.append(curNode.e + "-->");
            curNode = curNode.next;
        }
        sb.append("Null] Tail");
        return sb.toString();
    }

    public static void main(String[] args) {
        LinkedListQueue linkedListQueue = new LinkedListQueue<>();
        for (int i = 0; i < 10; i++) {
            linkedListQueue.enQueue(i);
        }
        System.out.println(linkedListQueue);
        linkedListQueue.deQueue();
        System.out.println(linkedListQueue);
        System.out.println(linkedListQueue.getFront());
    }
}