LeetCode -- Rotate List

Question:

Given a list, rotate the list to the right by k places, where k is non-negative.

For example:
Given 1->2->3->4->5->NULL and k = 2,
return 4->5->1->2->3->NULL.

Analysis:

给出一个单链表，旋转链表的从右边数k个位置，将他们按顺序放到左边。k是个非负的整数。

注意一些特殊情况：

如当给出的k值比链表长度还大怎么办？当k=0怎么办？

Answer：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if(head == null || head.next == null) 
            return head;
        int len = 0;
        ListNode p = head;
        ListNode end = null;
        while(p != null) {
            if(p.next == null) 
                end = p;
            p = p.next;
            len++;
        }
        k %= len;
        if(k == 0)
            return head;
        int pre = len - k;
        len = 0;
        p = head;
        while(len +1 < pre) {
            p = p.next;
            len++;
        }
        ListNode q = p.next;
        end.next = head;
        p.next = null;
        return q;
    }
}