算法－第四版－练习1.3.6解答

下面这段代码对队列q进行了什么操作？

Stack<String> stack = new Stack<String>();
while (!q.isEmpty())
    stack.push(q.dequeue());
while (!stack.isEmpty())
    q.enqueue(stack.pop());

显然，将队列中的元素进行了逆序。

/**
 * Description : 
 * Author      : mn@furzoom.com
 * Date        : Sep 28, 2016 10:21:54 AM
 * Copyright (c) 2013-2016, http://furzoom.com All Rights Reserved.
 */
package com.furzoom.lab.algs.ch103;

import java.util.Iterator;

import edu.princeton.cs.algs4.StdIn;

/**
 * ClassName    : Queue <br>
 * Function     : TODO ADD FUNCTION. <br>
 * date         : Sep 28, 2016 10:21:54 AM <br>
 * 
 * @version 
 */
public class Queue<Item> implements Iterable<Item>
{
    private Node first;
    private Node last;
    private int n;
    
    private class Node
    {
        Item item;
        Node next;
    }
    
    public boolean isEmpty()
    {
        return first == null;
    }
    
    public int size()
    {
        return n;
    }
    
    public void enqueue(Item item)
    {
        Node oldlast = last;
        last = new Node();
        last.item = item;
        last.next = null;
        if (isEmpty())
        {
            first = last;
        }
        else 
        {
            oldlast.next = last;
        }
        n++;
    }
    
    public Item dequeue()
    {
        Item item = first.item;
        first = first.next;
        if (isEmpty())
        {
            last = null;
        }
        n--;
        return item;
    }
    
    @Override
    public Iterator<Item> iterator()
    {
        return new QueueIterator();
    }
    
    private class QueueIterator implements Iterator<Item>
    {
        private Node current = first;
        @Override
        public boolean hasNext()
        {
            return current != null;
        }
        
        @Override
        public Item next()
        {
            Item item = current.item;
            current = current.next;
            return item;
        }
    }
}

测试代码：

/**
 * Description : 
 * Author      : mn@furzoom.com
 * Date        : Sep 28, 2016 4:20:38 PM
 * Copyright (c) 2013-2016, http://furzoom.com All Rights Reserved.
 */
package com.furzoom.lab.algs.ch103;

/**
 * ClassName    : E10306 <br>
 * Function     : TODO ADD FUNCTION. <br>
 * date         : Sep 28, 2016 4:20:38 PM <br>
 * 
 * @version 
 */
public class E10306
{
    public static void test(Queue<String> q)
    {
        Stack<String> stack = new Stack<String>();
        while (!q.isEmpty())
            stack.push(q.dequeue());
        while (!stack.isEmpty())
            q.enqueue(stack.pop());
    }
    
    public static void main(String[] args)
    {
        Queue<String> q = new Queue<String>();
        q.enqueue("a");
        q.enqueue("b");
        q.enqueue("c");
        q.enqueue("d");
        
        for (String s : q)
            System.out.print(s + " ");
        System.out.println();
        
        test(q);
        
        for (String s : q)
            System.out.print(s + " ");
        System.out.println();
        
    }

}

结果如下：

a b c d 
d c b a

算法－第四版－1.3 背包、队列和栈－习题索引汇总

算法－第四版习题索引汇总