2130. Maximum Twin Sum of a Linked List.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    int pairSum(ListNode* head) {
        vector<int> arr;
        while(head){
            arr.push_back(head->val);
            head=head->next;
        }

        int i=0,j=arr.size()-1,sum = 0;
        while(i<j){
            sum = max(sum,arr[i]+arr[j]);
            i++;
            j--;
        }
        return sum;
    }
};