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leetcode - Rotate List

2013-11-25 22:07  张汉生  阅读(159)  评论(0)  编辑  收藏  举报

 

 1 class Solution {
 2 public:
 3   ListNode *rotateRight(ListNode *head, int k) {
 4     // Note: The Solution object is instantiated only once and is reused by each test case.
 5     if (head == NULL ||  head->next ==NULL)
 6       return head;
 7     int size = 0;
 8     ListNode * tmp = head;
 9     while (tmp!=NULL){
10       size++;
11       tmp = tmp->next;
12     }
13     k = k%size;
14     if (k<=0)
15       return head;
16     ListNode * rhead = NULL, * ltail = NULL, * rtail = NULL;
17     ListNode * itr = head;
18     int i = 0;
19     while (itr !=NULL){
20       i++;
21       if (i==k){
22         ltail = NULL;
23         rhead = head;
24       }
25       else if (i>k){
26         ltail = rhead;
27         rhead = rhead->next;
28       }
29       rtail = itr;
30       itr = itr->next;
31     }
32     if (ltail!=NULL &&ltail !=rtail)
33       ltail->next = NULL;
34     if (rhead!=NULL && rhead!=head){
35       rtail->next = head;
36       return rhead;
37     }
38     return head;
39   }
40 };