61. Rotate List

https://leetcode.com/problems/rotate-list/

观察到：倒数第k%length个节点就是新头节点，新头节点的前一个点就是新尾节点

corner case：当k % length = 0的时候，rotate之后还是和原链表一样，故无需变换

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; }
 7  * }
 8  */
 9 class Solution {
10     public ListNode rotateRight(ListNode head, int k) {
11         if(head == null || k == 0){
12             return head;
13         }
14         int length = 1;
15         ListNode tail = head;
16         while(tail.next != null){
17             length += 1;
18             tail = tail.next;
19         }
20         if(k % length == 0){
21             return head;
22         }
23         int newHeadIndex = length - k % length;
24         
25         ListNode newTail = head;
26         ListNode newHead = head.next;
27         while(newHeadIndex != 1){
28             newTail = newTail.next;
29             newHead = newHead.next;
30             newHeadIndex -= 1;
31         }
32         tail.next = head;
33         newTail.next = null;
34         return newHead;
35     }
36 }