剑指Offer25-反转链表

快慢指针法，但是只需要慢指针即可。

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    # 返回ListNode
    def ReverseList(self, pHead):
        # write code here
        slow = pHead
        prev = None
        
        while slow is not None:
            Next = slow.next
            slow.next = prev
            prev = slow
            slow = Next
        
        return prev