# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
def removeNthFromEnd(self, head: ListNode, n: int) -> ListNode:
firs=head
while(n>0):
firs=firs.next
n-=1
if not firs:
return head.next //当第一个指针为空时,删除首节点,返回none
sec=head
while(firs.next):
sec=sec.next
firs=firs.next
sec.next=sec.next.next //删除节点,可以利用前节点直接指向后节点,这样就方便操作
return head