876.java

/**
 * 876. Middle of the Linked List
 * 
 * Given the head of a singly linked list, return the middle node of the linked list.
 * If there are two middle nodes, return the second middle node.
 */
class Solution {
    public ListNode middleNode(ListNode head) {
        ListNode slow = head;
        ListNode fast = head;
        while (fast.next != null) {
            slow = slow.next;
            fast = fast.next;
            if (fast.next != null) fast = fast.next;
        }
        return slow;
    }
}


class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) { this.val = val; }
    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
}