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import { Node } from "./Node.ts";
export default function levelOrder(root: Node | null): number[][] {    if (!root) return [];    const current: Node[] = [root];    const result: number[][] = [];
    level(current, (r) => result.push(r));    return result;}function level(nodes: Node[], output: (r: number[]) => void) {    if (nodes.length === 0) return;
    output(nodes.map((n) => n.val));
    level(nodes.map((n) => n.children).flat(), output);}