2095.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:
        ListNode* deleteMiddle(ListNode* head) {
            if (!head->next) {
                return nullptr;
            }
            ListNode* prev = nullptr;
            ListNode* slow = head;
            ListNode* fast = head;
            while (fast && fast->next) {
                prev = slow;
                slow = slow->next;
                fast = fast->next->next;
            }
            // remove slow
            prev->next = slow->next;
            return head;
        }
};