/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode rotateRight(ListNode head, int k) {
// base cases
if (head == null) return null;
if (head.next == null) return head;
// close the linked list into the ring
ListNode old_tail = head;
int n;
for(n = 1; old_tail.next != null; n++)
old_tail = old_tail.next;
old_tail.next = head;
// find new tail : (n - k % n - 1)th node
// and new head : (n - k % n)th node
ListNode new_tail = head;
for (int i = 0; i < n - k % n - 1; i++)
new_tail = new_tail.next;
ListNode new_head = new_tail.next;
// break the ring
new_tail.next = null;
return new_head;
}
}
