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export { TreeBuilder as default };class TreeBuilder {    buildTree(postfix: string[]): Node {        const stack: Node[] = [];
        for (const char of postfix) {            if (isNumber(char)) {                stack.push(new Node(char));            } else {                const num2 = stack.pop();                const num1 = stack.pop();                if (typeof num2 == "undefined") {                    throw Error("number expected");                }                if (typeof num1 == "undefined") {                    throw Error("number expected");                }                if (char === "+") {                    stack.push(new Node(char, num1, num2));                } else if (char === "-") {                    stack.push(new Node(char, num1, num2));                } else if (char === "*") {                    stack.push(new Node(char, num1, num2));                } else if (char === "/") {                    stack.push(new Node(char, num1, num2));                } else throw Error("unknown operator:" + char);            }        }        return stack[0];    }}export class Node {    constructor(        public val: string = "",        public left: Node | null = null,        public right: Node | null = null,    ) {}    evaluate(): number {        if (this.left == null && this.right == null) return Number(this.val);        if (!(this.left && this.right)) {            throw Error("accident");        }        const l = this.left.evaluate();        const r = this.right.evaluate();
        switch (this.val) {            case "+":                return l + r;            case "-":                return l - r;            case "*":                return l * r;            case "/":                return Math.trunc(l / r);        }        throw Error("unknown operator:" + this.val);    }}export function isNumber(token: string) {    return /\d+/g.test(token);}