Rotate List

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.

题目大意：给定一个链表，右移k个位置

题目难度：Medium

import java.util.*;
/**
 * Created by gzdaijie on 16/5/26
 */
public class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        ListNode p = head, pre = null, last= null;
        int len = 0;
        while (p != null) {
            len++;
            last = p;
            p = p.next;
        }
        if (len == 0) return head;
        // 将链表分为 len - k，和k 2个部分
        k = len - k % len;
        p = head;
        while (k-- > 0) {
            pre = p;
            p = p.next;
        }

        if (p != null && last != null) {
            last.next = head;
            pre.next = null;

        }
        return p == null ? head : p;
    }
}