876. Middle of The Linked List - https://leetcode.com/problems/middle-of-the-linked-list/

middleNode1.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode middleNode(ListNode head) {
        ListNode middle = head;
        ListNode end = head;
        
        while(end != null && end.next != null) {
            middle = middle.next;
            end = end.next.next;
        }

        return middle;
    }
}