LeetCode 19. Remove Nth Node From End of List （Python）

题目描述：

Given a linked list, remove the nth node from the end of list and return its head.

For Example:

Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.

注意点：

加一个if判断看是否是头结点被删除，或者在开始时就加一个节点指向头结点

AC代码：

class Solution(object):
def removeNthFromEnd(self, head, n):
"""
:type head: ListNode
:type n: int
:rtype: ListNode
"""
length = 1
copy1, copy2 = head, head
while copy1.next:
copy1 = copy1.next
length += 1
for i in range(length - n - 1):
copy2 = copy2.next
if length == n:
head = head.next
return head
if copy2.next.next is None:
copy2.next = None
else:
copy2.next = copy2.next.next
return head