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import { TreeNode } from "../binary-tree-inorder-traversal/TreeNode.ts";
/** * Definition for a binary tree node. * class TreeNode { *     val: number *     left: TreeNode | null *     right: TreeNode | null *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) { *         this.val = (val===undefined ? 0 : val) *         this.left = (left===undefined ? null : left) *         this.right = (right===undefined ? null : right) *     } * } */
export default function levelOrder(root: TreeNode | null): number[][] {    if (!root) return [];    const current: TreeNode[] = [root];    const result: number[][] = [];
    level(current, (r) => result.push(r));    return result;}function level(nodes: TreeNode[], output: (r: number[]) => void) {    if (nodes.length === 0) return;
    output(nodes.map((n) => n.val));
    level(        nodes            .map((n) => [n.left, n.right].filter(Boolean) as TreeNode[])            .flat() as TreeNode[],        output,    );}