/
* 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;
auto p = head, q = p->next;
while(q)
{
auto o = q ->next;
q ->next = p;
p = q, q = o;
}
head->next = NULL;
return p;
}
};