题解 | #反转链表#

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param head ListNode类 
# @return ListNode类
#
class Solution:
    def ReverseList(self , head: ListNode) -> ListNode:
        pre = None
        current = head
        while current is not None:
            temp = current.next
            current.next = pre
            pre = current
            current = temp
        return pre

关键：反转一个节点的指针时，会丢失这个节点的next信息，所以需要增加一个temp变量来临时存储。