/**
 * 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:
    ListNode* middleNode(ListNode* head) {
        auto ptr1 = head;
        auto ptr2 = head;
        while (ptr2 && ptr2->next){
            ptr1=ptr1->next;
            ptr2=ptr2->next->next;
        }
        return ptr1;
    }
};