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) return NULL;
        ListNode *cur = head;
        int n = 0;
        while(cur) {
            cur = cur->next;
            ++n;
        }
                
        ListNode *slow = head;
        ListNode 
 
*fast = head;
        
        k %= n;
        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;
    }
};

LeetCode 61. Rotate List