/**
* 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) {
ListNode *a=nullptr,*b=head;
while(b){
ListNode *c=b->next;
b->next=a;
a=b;
b=c;
}
return a;
}
};