LeetCode -- 61. Rotate List

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if(head==null) return head;
        ListNode p = head,q,top = new ListNode(-1);
        top.next = head;
        int len = 0;
        while(p!=null) {len++; p=p.next;}
        k %= len;
        while(k-->0){
            p = top;
            //找到尾节点前面一个位置
            while(p.next.next!=null) {p=p.next;}
            q = p.next;
            p.next = q.next;
            q.next = top.next;
            top.next = q;
        }
        return top.next;
    }
}