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:
        if not head:	# 如果非空
            return head
        a, a.next, b =head, None, head.next		# 初始化
        while b:
            b, a, a.next = b.next, b, a			# 遍历
        return a