难度：容易
1. Description
174. 删除链表中倒数第n个节点
2. Solution
- python
pre_n指向的位置在cur指向位置的前面第n个。
当cur是链表尾部时，pre_n正好是倒数第n个。
"""
Definition of ListNode
class ListNode(object):
def __init__(self, val, next=None):
self.val = val
self.next = next
"""
class Solution:
"""
@param head: The first node of linked list.
@param n: An integer
@return: The head of linked list.
"""
def removeNthFromEnd(self, head, n):
# write your code here
if n==1:
if head.next is None:
return None
pre_n = head
cur = head
for i in range(n):
cur = cur.next
while cur.next is not None:
pre_n = pre_n.next
cur = cur.next
pre_n.next = pre_n.next.next
return head
pre_n = head
cur = head
for i in range(n-1):
cur = cur.next
while cur.next is not None:
pre_n = pre_n.next
cur = cur.next
pre_n.val = pre_n.next.val
pre_n.next = pre_n.next.next
return head
