反转链表

 1 /*
 2 struct ListNode {
 3     int val;
 4     struct ListNode *next;
 5     ListNode(int x) :
 6             val(x), next(NULL) {
 7     }
 8 };*/
 9 class Solution {
10 public:
11     ListNode* ReverseList(ListNode* pHead) {
12         if(pHead==NULL||pHead->next==NULL)
13                return pHead;
14         ListNode* p=pHead;
15         ListNode* q=p->next ;
16          ListNode* s;
17       
18        while(q!=NULL)
19             {
20             s=q->next;
21              q->next=p;
22             p=q;
23             q=s;
24         }
25        pHead->next=NULL;
26        return p;
27 
28     }
29 };