/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* reverseList(ListNode* head) {
if(!head||!(head->next)) return head;
ListNode* p=head;
ListNode* q=head->next;
while(q){
ListNode* o=q->next;
q->next=p;
p=q;
q=o;
}
head->next=NULL;
return p;
}
};