876

/**
 * 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) {
        ListNode *slow, *fast;
        slow = fast = head;
        while(!(fast->next == nullptr || fast->next->next == nullptr)){
            slow = slow->next;
            fast = fast->next->next;
        }
        if(fast->next && !fast->next->next) slow = slow->next;
        return slow;
    }
};