面试题27：单链表向右旋转k个节点

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

For example:
Given1->2->3->4->5->NULLand k =2,
return4->5->1->2->3->NULL.

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     ListNode *next;
  *     ListNode(int x) : val(x), next(NULL) {}
  * };
  */
 class Solution {
 public:
     ListNode *rotateRight(ListNode *head, int k) {
         if(head == nullptr || head->next == nullptr) return head;

         int length = ;
         ListNode* p = head;
         while(p){
             length++;
             p = p->next;
         }
         k = k % length;
         if(k == ) return head;
         int m = length - k;
         p = head;
         while(m > ){
             p = p->next;
             m--;
         }
         ListNode* right = p->next;
         p->next = nullptr;
         p = right;
         while(p->next){
             p = p->next;
         }
         p->next = head;
         head = right;
         return head;
     }
 };