算法－第四版－练习1.3.29解答

问题

用环形链表实现Queue。环形链表也是一条链表，只是没有任何结点链接为空，且只要链表非空则last.next的值就为first。只能使用一个Node类型的实例变量（last）。

解决思路

出列时将last.next指向last.next.next。入列时需要修改两条链接才能真正的让一个结点加入到一个环中。最后在移到last的位置。

待优化，出列后的结点应该修改其next为null。

代码

/**
* Description :
* Author      : mn@furzoom.com
* Date        : Oct 25, 2016 11:39:46 AM
* Copyright (c) 2013-2016, http://furzoom.com All Rights Reserved.
*/
package com.furzoom.lab.algs.ch103;

import java.util.Iterator;

/**
* ClassName    : CircleQueue <br>
* Function     : TODO ADD FUNCTION. <br>
* date         : Oct 25, 2016 11:39:46 AM <br>
*
* @version
*/
public class CircleQueue<Item> implements Iterable<Item>
{
private Node last;

private class Node
{
public Item item;
public Node next;
}

public CircleQueue()
{
last = null;
}

public boolean isEmpty()
{
return last == null;
}

public Item dequeue()
{
if (isEmpty())
return null;

Item item = last.next.item;
if (last.next == last)
{
last = null;
}
else
{
last.next = last.next.next;
}
return item;
}

public void enqueue(Item item)
{
Node node = new Node();
node.item = item;
if (last == null)
{
last = node;
node.next = node;
}
else {
node.next = last.next;
last.next = node;
last = node;
}
}

@Override
public Iterator<Item> iterator()
{
return new Iter();
}

private class Iter implements Iterator<Item>
{
private Node first;
private boolean one;

public Iter()
{
if (last == null)
{
first = null;
}
else
{
first = last.next;
one = (last == last.next);
}
}
@Override
public boolean hasNext()
{
// if
if (last == last.next)
{
if (one)
{
one = false;
return true;
}
else
{
return false;
}
}
else
{
return first != null;
}
}
@Override
public Item next()
{
Item item;
if (last == last.next)
{
first = null;
item = last.item;
}
else
{
item = first.item;
first = first.next;
if (first == last.next)
{
first = null;
}
}
return item;
}
}
}

测试代码：

/**
* Description :
* Author      : mn@furzoom.com
* Date        : Oct 25, 2016 11:38:20 AM
* Copyright (c) 2013-2016, http://furzoom.com All Rights Reserved.
*/
package com.furzoom.lab.algs.ch103;

import java.util.Iterator;

/**
* ClassName    : E10329 <br>
* Function     : TODO ADD FUNCTION. <br>
* date         : Oct 25, 2016 11:38:20 AM <br>
*
* @version
*/
public class E10329
{
public static void main(String[] args)
{
CircleQueue<String> queue = new CircleQueue<String>();
queue.enqueue("a");
queue.enqueue("b");
queue.enqueue("c");
queue.enqueue("d");
queue.enqueue("e");

Iterator<?> it = queue.iterator();
while (it.hasNext())
{
System.out.println(it.next());
}
System.out.println("dequeue: ");
String s;
while ((s = queue.dequeue()) != null)
{
System.out.println(s);
}
}

}

结果：

a
b
c
d
e
dequeue:
a
b
c
d
e

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