/
* 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* tail=reverseList(head->next);
head->next->next=head;
head->next=nullptr;
return tail;
}

};