leetcode

0 class Solution {

1 public:

2 ListNode *reverseEvenLengthGroups(ListNode *head) {

3 ListNode *prev = head, *crnt = head->next;

4

5 for (int lvl = 2; crnt; lvl++) {

6 ListNode *bg = prev;

7

8 int size = 0;

9 while (crnt && size < lvl) {

10 prev = crnt;

11 crnt = crnt->next;

12 size++;

13 }

14

15 if (size % 2) continue;

16

17 crnt = bg->next;

18 ListNode *last = crnt, *first = crnt, *tmp;

19 while (size--) {

20 tmp = crnt;

21 crnt = crnt->next;

22 tmp->next = last;

23 last = tmp;

24 }

25 bg->next = last;

26 first->next = crnt;

27 prev = first;

28 }

29

30 return head;

31 }

32 };