剑指offer：反转链表

问题描述

输入一个链表，反转链表后，输出新链表的表头。

c++代码

 /*

 struct ListNode {

     int val;

     struct ListNode *next;

     ListNode(int x) :

             val(x), next(NULL) {

     }

 };*/

 class Solution {

 public:

     ListNode* ReverseList(ListNode* pHead) {

         if(pHead == NULL)  return pHead;

         ListNode *cur = pHead, *nxt, *pre = NULL;

         while(cur != NULL){

             nxt = cur->next;

             cur->next = pre;

             pre = cur;

             cur = nxt;

         }

         return pre;

     }

 };

python代码

 # -*- 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 pHead

         cur, pre = pHead, None

         while cur:

             nxt = cur.next

             cur.next = pre

             pre = cur

             cur = nxt

         return pre