Rotate List

Given a list, rotate the list to the right by k places, where k is non-negative.

For example:
Given 1->2->3->4->5->NULL and k = 2,
return 4->5->1->2->3->NULL.

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* rotateRight(ListNode* head, int k) {        if(head==NULL) return NULL;        ListNode* dummy=new ListNode(-1);        dummy->next=head;        ListNode *tail=getRightk(dummy,k);        if(tail==dummy) return head;        dummy->next=tail->next;        ListNode *tmp=tail;        while(tmp->next){            tmp=tmp->next;        }        tmp->next=head;        tail->next=NULL;        return dummy->next;    }    ListNode* getRightk(ListNode* dummy,int k){        ListNode* right=dummy->next;        ListNode* left=dummy->next;        ListNode* leftpre=dummy;                int length=0;        ListNode* tmp=dummy->next;        while(tmp){            length++;            tmp=tmp->next;        }                if(k%length==0) return dummy;        for(int i=0;i<k%length;i++){            right=right->next;        }        while(right!=NULL){            right=right->next;            leftpre=leftpre->next;        }        return leftpre;    }};