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;
    }
};