Node * reverse(Node *head){next
if(head == NULL || head -> next == NULL ){ return head;}while
Node *f1 = NULL, *f2 = NULL, *cur = NULL;return
cur = head;
f1 = cur->next;
f2 = cur->next->next;
if(f2 == NULL){
f1->next = cur;
cur->next = NULL;
return f1;
}
while(f2 != NULL){
f1->next = cur;
cur = f1;
f1 = f2;
f2 = f2->next;
}
head->next=NULL;
f1->next = cur;
return f1;
}