QueueWithTwoStacks.java

package org.xukai.coderising.queue;

import java.util.Stack;

/**
 * 用两个栈来实现一个队列
 * @author liuxin
 *
 * @param <E>
 */
public class QueueWithTwoStacks<E> {
	private Stack<E> stack1;    
    private Stack<E> stack2;    

    
    public QueueWithTwoStacks() {
        stack1 = new Stack<E>();
        stack2 = new Stack<E>();
    }

   
    

    public boolean isEmpty() {
        return stack1.isEmpty();
    }


    
    public int size() {
        return stack1.size();
    }



    public void enQueue(E item) {
        stack1.push(item);
    }

    public E deQueue() {
        if (stack1.isEmpty()) {
            return null;
        }
        while (!stack1.isEmpty()) {
            stack2.push(stack1.pop());
        }
        E e = stack2.pop();
        while (!stack2.isEmpty()) {
            stack1.push(stack2.pop());
        }
        return e;
    }

    public static void main(String[] args) {
        QueueWithTwoStacks queue = new QueueWithTwoStacks();
        queue.enQueue(1);
        queue.enQueue(2);
        queue.enQueue(3);
        queue.enQueue(4);
        queue.enQueue(5);
        queue.enQueue(6);
        System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());System.out.println(queue.deQueue());System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());
        queue.enQueue(7);
        queue.enQueue(8);
        queue.enQueue(9);
        queue.enQueue(0);
        queue.enQueue(1);
        System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());
        System.out.println(queue.deQueue());


    }

 }