面试题24. 反转链表

 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     {
13         if (NULL == head || NULL == head->next)
14         {
15             return head;
16         }
17 
18         ListNode *p1;
19         ListNode *p2;
20         ListNode *p3;
21 
22         p1 = head;
23         p2 = head->next;
24         while (p2 != NULL)
25         {
26             p3 = p2->next;
27             p2->next = p1;
28             p1 = p2;
29             p2 = p3;
30         }
31 
32         head->next = NULL;
33         head = p1;
34 
35         return head;
36     }
37 };