Rotate List

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) {
 7  *         val = x;
 8  *         next = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     /**
14      * @param head: the List
15      * @param k: rotate to the right k places
16      * @return: the list after rotation
17      */
18     public ListNode rotateRight(ListNode head, int k) {
19         if (head == null || head.next == null) return head; 
20         // write your code here
21         int size = size(head);
22         k = k % size;
23         
24         if (k == 0) return head;
25         ListNode pointer = head;
26         for (int i = 1; i <= size - k - 1; i++) {
27             pointer = pointer.next;
28         }
29         
30         ListNode newHead = pointer.next;
31         pointer.next = null;
32         
33         // link the tail to the head
34         ListNode current = newHead;
35         while (current.next != null) {
36             current = current.next;
37         }
38         current.next = head;
39         return newHead;
40     }
41     
42     public int size(ListNode head) {
43         int count = 0;
44         while (head != null) {
45             count++;
46             head = head.next;
47         }
48         return count;
49     }
50 }