61. rotate list

 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class  {
    public ListNode rotateRight(ListNode head, int k) {
        if (head == null) {
            return null;
        }
        // get length, k = k%len, len - k -> null, final node->n0
        int len = 1;
        ListNode curt = head;
        while (curt.next != null) {
            len++;
            curt = curt.next;
        }
        curt.next = head;

        k = k % len;
       // 断开tail, return head
        ListNode tail = head;
        int count = len - k;
        for (int i = 1; i < count; i++) {
            tail = tail.next;
        }
        head = tail.next;
        tail.next = null;

        return head;

    }

}