25. K 个一组翻转链表

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution 
10 {
11 public:
12     ListNode* reverseKGroup(ListNode* head, int k) 
13     {
14         int len = 0;
15         for(ListNode* i = head;i != NULL;i = i->next) len ++;
16 
17         ListNode* dummy = new ListNode(-1);
18         dummy->next = head;
19         ListNode* pre = dummy;
20         ListNode* cur = head;
21 
22         for(int i = 0;i < len/k;i ++)
23         {
24             ListNode* new_head = NULL;
25             ListNode* first = cur;
26             int m = k;
27             while(m-- && cur)
28             {
29                 ListNode* temp = cur->next;
30                 cur->next = new_head;
31                 new_head = cur;
32                 cur = temp;    
33             }
34             pre->next = new_head;
35             first->next = cur;
36             pre = first;
37         }
38         return dummy->next;
39     }
40 };