Rotate List

struct ListNode
{
    int m_nKey;
    ListNode* next; 
}

class Solution{
    public:
        ListNode* rotateRight(ListNode *head, int k){
            if(!head) return NULL;
            int n = 0;
            ListNode *cur = head;
            while(cur){
                ++n;
                cur = cur->next;
            }
            
            k %= n;
            ListNode *fast = head, *slow = head;
            for(int i = 0; i < k; ++i)
            {
                if(fast)
                    fast = fast->next;
            }
            
            if(!fast) return head;
            while(fast->next){
                fast = fast->next;
                slow = slow->next;
            }
            
            fast->next = head;
            fast = slow->next;
            slow->next = NULL;
            return fast;
        }
};