题解 | #表达式求值#

const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;

void (async function () {
    // Write your code here
    while ((line = await readline())) {
        let str = line.replaceAll(" ", "");
        console.log(eval(str));
        // console.log(Function(`return ${str}`)());
        return;

        let strA, strB, strC;
        let indexLeft, indexRight;
        let match1;
		// 1、括号内的优先级最高，先计算括号里的内容
        while (str.match(/\(/)) {
            match1 = str.match(/(\([\+\-\*\/0-9]+\))/);
            indexLeft = match1["index"];
            indexRight = indexLeft + match1[1].length - 1;
            strA = str.substring(0, indexLeft);
            strB = str.substring(indexLeft + 1, indexRight);
            strC = str.substring(indexRight + 1);
			// 2、括号里的内容在这里运算
            strB = String(execVal(strB));

            //判断strB是否为负，如果是，则需要把负数提前
            if (strB.indexOf("-") >= 0) {
                strB = strB.substring(1);
                let isDone = false;
                let arrA = strA.split("");
                for (let i = arrA.length; i >= 0; i--) {
                    if (/[\+|\-]/.test(arrA[i])) {
                        arrA[i] = arrA[i] == "+" ? "-" : "+";
                        isDone = true;
                        break;
                    }
                }
                strA = arrA.join("");
                if (!isDone) {
                    strA = "-" + strA;
                }
            }
            str = `${strA}${strB}${strC}`;
        }
		// 3、最后不包含括号的内容在这里运算
        console.log(Number(execVal(str)));
    }
})();

// 计算不包含括号的内容
var execVal = function (str) {
    // let matchArr = str.match(/(\w+)([\*\/\+\-])(\w+)/);
    let a, b, val, sign, strNew;
    let left, right;
    let matchArr = str.match(/([\-]?\w+)([\*\/])([\-]?\w+)/);
    if (!matchArr) {
        matchArr = str.match(/([\-]?\w+)([\+\-])([\-]?\w+)/);
    }
    if (matchArr) {
        //a,b...,strNew...
        a = Number(matchArr[1]);
        b = Number(matchArr[3]);
        sign = matchArr[2];

        switch (sign) {
            case "*":
                val = a * b;
                break;
            case "/":
                val = a / b;
                break;
            case "+":
                val = a + b;
                break;
            case "-":
                val = a - b;
                break;
        }
        left = str.substring(0, matchArr["index"]);
        if (left && !/[\+\-\*\/]/.test(left[left.length - 1])) {
            //left 如果是个减号，可能会在匹配 matchArr 被 a 拿走
            if (val >= 0) {
                //此时需要根据 val 正负判断需要补充什么，如果为负数自身转换成 String 以后不需要补充符号
                // "15+8" + "+" + "0" + right
                // "15+8" + "-2" + right
                left += "+";
            }
        }
        right = str.substring(matchArr["index"] + matchArr[0].length);
        strNew = `${left}${String(val)}${right}`;
        // strNew = `${str.substring(0, matchArr['index'])}${String(val)}${str.substring(matchArr['index']+ matchArr['input'])}`;
        return execVal(strNew);
    } else {
        //此时为不带运算符的数字
        return str;
    }
};