1234567891011121314151617181920212223
import { Node } from "../n-ary-tree-level-order-traversal/Node.ts";
export default function preorder(root: Node | null): number[] {    if (!root) {        return [];    }    const res: number[] = [];    prehelper(root, (a) => res.push(a));    return res;}function prehelper(root: Node | null, output: (a: number) => void) {    if (!root) {        return;    }    output(root.val);    for (const n of root.children) {        prehelper(n, output);    }    //     root.children.forEach(n=>{    //   prehelper(n, output);    //     })}