LeetCode - Refresh - Rotate List

/**
* 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 || !head->next) return head;
int len = 1;
ListNode *runner = head;
while (runner->next) {
runner = runner->next;
len++;
}
k %= len;
runner->next = head;
for (int i = 0; i < len-k; i++) {
runner = runner->next;
}
head = runner->next;
runner->next = NULL;
return head;
}
};