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import { TreeNode } from "../binary-tree-inorder-traversal/TreeNode.ts";import { inorder } from "./inorder.ts";
export default function isValidBST(root: TreeNode | null): boolean {    const signal: Signal = { aborted: false };    if (!root) return false;    let result = true;    let last: number | undefined;    inorder(        root,        (a) => {            if (signal.aborted) throw Error("aborted");
            if (typeof last === "undefined") {                last = a;            } else {                if (a > last) {                    last = a;                } else {                    signal.aborted = true;                    result = false;                }            }        },        signal,    );    return result;}export interface Signal {    aborted: boolean;}