/**

* Definition for singly-linked list.

* public class ListNode {

* int val;

* ListNode next;

* ListNode(int x) { val = x; }

* }

*/

public class Solution {

public ListNode rotateRight(ListNode head, int k) {

if (head == null || k < 0)

return null;

k %= getLength(head);

ListNode newHead = head;

ListNode fast = head;

ListNode slow = head;

int currIndex = 0;

while (fast != null && currIndex < k) {

fast = fast.next;

currIndex++;

}

if (fast == null || currIndex < k) {

return head;

}

ListNode prevSlow = slow;

ListNode prevFast = fast;

while (slow != null && fast != null) {

prevFast = fast;

fast = fast.next;

prevSlow = slow;

slow = slow.next;

}

if (slow == null) {

newHead = head;

} else {

newHead = slow;

prevFast.next = head;

prevSlow.next = null;

}

return newHead;

}

private int getLength(ListNode head) {

int length = 0;

while (head != null) {

length++;

head = head.next;

}

return length;

}

}