题解 | #反转链表#

思路：翻转链表一般直接处理比较绕，采用头插法比较好

# 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:
        # write code here
        
        if not head:
            return
        if not head.next:
            return head
        
        
        h = ListNode(-1)
        pre = h
        p = head
        
        while p:
            nxt = p.next
            p.next = pre.next
            pre.next = p
            p = nxt
        return h.next