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import { ListNode } from "../reverse-linked-list/ListNode.ts";
export default function middleNode(head: ListNode | null): ListNode | null {    if (!head) return head;    if (!head.next) return head;    let slow: null | ListNode = head;    let fast: null | ListNode = head;    while (fast && fast.next && slow) {        slow = slow.next;        fast = fast.next.next;    }    return slow;}