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