LeetCode 61

/**
 * 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) {
        if(head == null || head.next == null || k == 0){
            return head;
        }
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode fast = head;
        ListNode slow = head;
        int i = 0;
        while(fast.next != null){
            if(i < k){
                fast = fast.next;
                i++;
                continue;
            }
            fast = fast.next;
            slow = slow.next;
        }
        if(i != k){
            if(k % (i+1) == 0){
                return dummy.next;
            }else{
                return rotateRight(dummy.next, k%(i+1));
            }
        }else{
            ListNode newHead = slow.next;
            slow.next = null;
            fast.next = dummy.next;
            return newHead;
        }
    }
}