leetcode -- 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.

[解题思路]

初始的想法是类似于求倒数第k个数，结果发现k可能会比len大，到网上搜索了下：

从head节点开始跑，一直跑到尾节点，得到len，将尾节点的next指针指向head，接着跑(len -n) % len步，断开

这里需注意(len -n) % len可能为负数，需+len

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode rotateRight(ListNode head, int n) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(head == null || n == 0){
            return head;
        }
        int len = 1;
        ListNode p = head;
        while(p.next != null){
            len ++;
            p = p.next;
        }
        p.next = head;
        /*
        int count = (len - n - 1) % len;
        while(count < 0){
            count += len;
            count %= len;
        }
        p = head;
        */
        int count = (len - n) % len;
        while(count < 0){
            count += len;
            count %= len;
        }
        int step = 0;
        while(step < count){
            p = p.next;
            step ++;
        }
        head = p.next;
        p.next = null;
        return head;
    }
}