LeetCode-Rotate List

 1  * Definition for singly-linked list.
 2  * struct ListNode {
 3  *     int val;
 4  *     ListNode *next;
 5  *     ListNode(int x) : val(x), next(NULL) {}
 6  * };
 7  */
 8 class Solution {
 9 public:
10     ListNode *rotateRight(ListNode *head, int k) {
11         
12         if(k == 0 || !head)
13             return head;
14         ListNode *p=head, *q=head;
15         ListNode *l=head;
16         //模长度，求旋转步长
17         int len = 0;
18         while(l!=NULL){
19             l = l->next;
20             len++;
21         }
22         k = k>len ? k%len : k;
23         //p先走K步，q再开始走
24         while(--k >= 0 && p != NULL){
25             p = p->next;
26         }
27         
28         if( p == NULL  )
29             return head;
30         
31         while(p->next!=NULL){
32             q = q->next;
33             p = p->next;
34         }
35         
36         p->next = head;
37         head = q->next;
38         q->next = NULL;
39         
40         return head;
41     }
42 };