[LeetCode] Rotate List

 1 class Solution {
 2 public:
 3     ListNode* rotateRight(ListNode* head, int k) {
 4         if (!head) return NULL;
 5         int len = listLength(head);
 6         k %= len;
 7         ListNode* fast = head;
 8         for (int i = 0; i < k; i++)
 9             fast = fast -> next;
10         ListNode* slow = head;
11         while (fast -> next) {
12             slow = slow -> next;
13             fast = fast -> next;
14         }
15         fast -> next = head;
16         head = slow -> next;
17         slow -> next = NULL;
18         return head;
19     }
20 private:
21     int listLength(ListNode* head) {
22         int len = 0;
23         while (head) {
24             len++;
25             head = head -> next;
26         }
27         return len;
28     }
29 };