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         ListNode* p = pHead;
13         ListNode* q = NULL;
14         ListNode* r = NULL;
15         while(p != NULL){
16             r = p->next;
17             p->next = q;
18             q = p;
19             p = r;
20         }
21         return q;
22     }
23 };