LinkedList - 61. Rotate List

/**

 * 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) return head;
        
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        
        ListNode fast = dummy, slow = dummy;
        int len; // get list len;
        for (len = 0; fast.next != null; len++) fast = fast.next;
    
        // find rotate node
        for (int i = len - k % len; i > 0; i--) slow = slow.next;
        
        // rotate
        fast.next = dummy.next;
        dummy.next = slow.next;
        slow.next = null;
        
        return dummy.next;
    }
}