剑指offer-反转链表

输入一个链表，反转链表后，输出链表的所有元素。

#-*- 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
        if not pHead:
            return None
        pre = None
        while pHead:
            current = pHead
            pHead = pHead.next
            current.next = pre
            pre = current
        return current

思路，三个指针，current表示当前指针，pre前指针，后指针。通过各自复制，将current.next = pre后，各自向后移动直到链表为空，返回current即倒序后的头指针。