leetcode

0 class Solution {

1 ListNode *pre_mid(ListNode *head) {

2 ListNode *slow = head, *fast = head;

3 while (fast->next && fast->next->next) {

4 slow = slow->next;

5 fast = fast->next->next;

6 }

7 return slow;

8 }

9

10 ListNode *reverse(ListNode *head) {

11 ListNode *p = head, *q = nullptr, *r = nullptr;

12 while (p) {

13 r = q;

14 q = p;

15 p = p->next;

16 q->next = r;

17 }

18 return q;

19 }

20

21 public:

22 int pairSum(ListNode *head) {

23 ListNode *pre = pre_mid(head);

24 ListNode *head2 = reverse(pre->next);

25

26 int maxi = INT_MIN;

27 for (ListNode *p = head, *q = head2; q; p = p->next, q = q->next)

28 maxi = max(p->val + q->val, maxi);

29

30 pre->next = reverse(head2);

31 return maxi;

32 }

33 };