060. Rotate List

                        |
1->2->3->4->5->NULL     | ListNode *slow = head, *fast = head;
^     ^                 | while (k--) {
slow  fast --->         |      if (fast == NULL) fast = head; // [1]
 |_____|                |      fast = fast->next;
    k                   | }
                        | if (fast == NULL) return head;
1->2->3->4->5->NULL     | while (fast->next) {
^     ^     ^           |      fast = fast->next;
head  slow  fast        |      slow = slow->next;
       |_____|          | }
          k             | List *new_head = slow->next;
                        | slow->next = NULL;
                        | fast->next = head;
                        | return new_head;

唯一要注意的在于:

[1]: 如果 k > linklist.size(n) 怎么办？

用示例来表示到底什么叫 rotate the list to the right by k places.

k	origin	after
1	0->1->2	2->0->1
2	0->1->2	1->2->0
3	0->1->2	0->1->2
4	0->1->2	2->0->1

可以观察的出来，当 k > n 的时候，k = k % n.

参考资料：what to do when k is greater than size of list ?