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leetcode - Reverse Nodes in k-Group

2013-11-25 21:30  张汉生  阅读(180)  评论(0)    收藏  举报

 

 1 class Solution {
 2 public:
 3   ListNode *reverseKGroup(ListNode *head, int k) {
 4     // IMPORTANT: Please reset any member data you declared, as
 5     // the same Solution instance will be reused for each test case.
 6     if (k<=1 || head == NULL)
 7       return head;
 8     ListNode * itr =head;
 9     ListNode * lastTail = NULL;
10     while (itr != NULL){
11       ListNode * nextItr = NULL;
12       ListNode * curHead = NULL, *curTail =NULL;
13       for (int i=0; i<k && itr!=NULL; i++){
14         nextItr = itr->next;
15         if (i==0)
16           curHead = itr;
17         if (i==k-1)
18           curTail = itr;
19         itr = nextItr;
20       }
21       if (curTail != NULL){
22         ListNode * tmp = curHead->next, *last=curHead;
23         for (int j=0; j<k-1; j++){
24           ListNode * nextTmp = tmp->next;
25           tmp->next = last;
26           last = tmp;
27           tmp = nextTmp;
28         }
29         if (curHead == head)
30           head = curTail;
31         if (lastTail != NULL)
32           lastTail->next = curTail;
33         lastTail = curHead;
34         lastTail->next = NULL;
35       }
36       else {
37         if (lastTail!=NULL)
38           lastTail->next = curHead;
39         break;
40       }
41     }
42     return head;
43   }
44 };