剑指offer-链表中倒数第k个结点

正确代码

class Solution:
     def FindKthToTail(self, head, k):
        l = []
        while head!=None:
            l.append(head)
            head = head.next
        if k > len(l) or k < 1:
            return
        return l[-k]
或者
class Solution:
     def FindKthToTail(self, head, k):
        l = []
        while head is not None:
            l.append(head)
            head = head.next
        if k > len(l) or k < 1:
            return
        return l[-k]

错误代码

class Solution:
     def FindKthToTail(self, head, k):
        l = []
        while head!=None:
            l.append(head)
            head = head.next
        if k > len(l) or k < 1:
            return
        return l[-k]

这就是not head 与head!=None(head is not None)的区别了。这个在博客http://blog.youkuaiyun.com/sasoritattoo/article/details/12451359中讲的很清楚，在这我就不细说。
贴一个该博客中的很好的例子

>>> x = []
>>> y = None
>>> 
>>> x is None
False
>>> y is None
True
>>> 
>>> 
>>> not x
True
>>> not y
True
>>> 
>>> 
>>> not x is None
>>> True
>>> not y is None
False
>>>