LeetCode OJ：Reverse Linked List （反转链表）

Reverse a singly linked list.

做II之前应该先来做1的，这个导师很简单，基本上不用考虑什么，简单的链表反转而已：

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* reverseList(ListNode* head) {
12         if(head == NULL) return NULL;
13         ListNode * prev = NULL;
14         ListNode * p = head;
15         ListNode * next;
16         while(p != NULL){
17             next = p->next;
18             p->next = prev;
19             prev = p;
20             p = next;
21         }
22         return prev;
23     }
24 };