61. Rotate List.java

class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if (head == null) {
            return head;
        }
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode fast = dummy;
        ListNode slow = dummy;
        int length = 0;
        while (fast.next != null) {
            length++;
            fast = fast.next;
        }
        for (int i = 0; i < length - k % length; i++) {
            slow = slow.next;
        }
        fast.next = head;
        head = slow.next;
        slow.next = null;
        return head;
    }
}