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:
        # write code here
        if not head or not  head.next:
            return  head 
        cur=head 
        pre=None
        while cur:
            next=cur.next
            cur.next=pre
            pre=cur
            cur=next
        return pre