leetcode 【 Copy List with Random Pointer 】 python 实现

题目：

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

代码：Runtime: 215 ms

 # Definition for singly-linked list with a random pointer.
 # class RandomListNode:
 #     def __init__(self, x):
 #         self.label = x
 #         self.next = None
 #         self.random = None
 
 class Solution:
     # @param head, a RandomListNode
     # @return a RandomListNode
     def copyRandomList(self, head):
         if head is None:
             return head
 
         # insert newnode between every two nodes between oldlist
         p = head
         while p is not None:
             newnode = RandomListNode(p.label)
             tmp = p.next
             p.next = newnode
             newnode.next = tmp
             p = tmp
 
         # copy random point
         p = head
         while p is not None:
             if p.random is not None:
                 p.next.random = p.random.next
             p = p.next.next
 
         # extract the new list from mixed list
         newhead = head.next
         p = head
         while p is not None:
             tmp = p.next
             p.next = p.next.next
             p = p.next
             if tmp.next:
                 tmp.next = tmp.next.next
             tmp = tmp.next
 
         return newhead

思路：

自己想不出来巧的方法 网上找个靠谱的帖子：

http://mp.weixin.qq.com/mp/appmsg/show?__biz=MjM5ODIzNDQ3Mw==&appmsgid=10000291&itemidx=1&sign=ccde63918a24dee181f1fd1a4e3e6781

参照上述帖子的思路写的python代码。

遇到的一个问题是，一开始判断极端case的时候有“if head.next is None: return head”

结果一直报错，后来去掉后AC了。注意一个点的时候也要复制。

还有就是，一直对python里面变量间的赋值不太清楚，google了一篇如下的日志，讲的比较靠谱一些。

http://www.cnblogs.com/evening/archive/2012/04/11/2442788.html