class Solution {public:    ListNode *rotateRight(ListNode *head, int k) {        if(head == NULL || head->next == NULL) return head;                int len = 0;        for(ListNode * p = head; p; p = p->next, len++);                if(len == k) return head;                k = k%len;                if(k == 0) return head;                ListNode * first = head, *second = head;        for(int i = 0; i < k-1; i++,second = second->next);                ListNode *dummy = new ListNode(-1);        dummy->next = head;                ListNode * pre_first = dummy;        while(second->next){            pre_first = first;            first = first->next;            second = second->next;        }                second->next = dummy->next;        pre_first->next = NULL;        dummy->next = first;                return dummy->next;            }};