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