2095. Delete the Middle Node of a Linked List 

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class Solution {
    public ListNode deleteMiddle(ListNode head) {
        // d -> 1 -> 3 -> 4 -> 7 -> 1 -> 2 -> 6
        //      f         f         f         f
        // s    s    s    s

        // d -> 1 -> 2 -> 3 -> 4
        //      f         f         f
        // s    s    s

        // d -> 2 -> 1
        // f         f
        // s    s

        ListNode dummyHead = new ListNode(-1, head);
        ListNode slow = dummyHead, fast = head;
        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            slow = slow.next;
        }

        slow.next = slow.next.next;
        return dummyHead.next;
    }
}

References

2095. Delete the Middle Node of a Linked List