import Big from "big.js";
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/**
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* 安全计算器（支持 + - * / 和括号）
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* @param {string} expr 数学表达式，如 "(0.1 + 0.2) * 3"
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* @returns {string} 计算结果字符串
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*/
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export function bigEval(expr) {
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console.log(expr)
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// 步骤1：词法分析
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const tokens = tokenize(expr);
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// 步骤2：转换为逆波兰表达式（后缀表达式）
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const rpn = shuntingYard(tokens);
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// 步骤3：执行计算
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return evaluateRPN(rpn);
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}
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// 词法分析器
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function tokenize(expr) {
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const tokens = [];
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let numBuffer = "";
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let prevToken = null;
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const flushNumber = () => {
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if (numBuffer) {
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// 新增：验证数字格式（支持负数、小数）
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if (!/^-?(\d+(\.\d*)?|\.\d+)$/.test(numBuffer)) {
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throw new Error(`无效数字格式: ${numBuffer}`);
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}
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if (numBuffer.startsWith(".")) numBuffer = "0" + numBuffer;
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tokens.push({ type: "number", value: numBuffer });
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numBuffer = "";
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}
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};
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for (let i = 0; i < expr.length; i++) {
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const c = expr[i];
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if (/\d|\./.test(c)) {
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numBuffer += c;
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} else if ("+-*/()".includes(c)) {
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// 修改：增加 numBuffer 为空的判断，确保负号只能作为数字前缀（关键修复）
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if (c === "-" && numBuffer === "" && (
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!prevToken ||
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(prevToken.type === "operator" && prevToken.value !== ")")
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)) {
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numBuffer += c;
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} else {
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flushNumber();
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tokens.push({ type: "operator", value: c });
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}
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prevToken = tokens[tokens.length - 1];
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} else if (c !== " ") {
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throw new Error(`非法字符: ${c}`);
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}
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}
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flushNumber();
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return tokens;
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}
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// 调度场算法生成逆波兰表达式
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function shuntingYard(tokens) {
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const output = [];
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const stack = [];
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const precedence = { "+": 1, "-": 1, "*": 2, "/": 2 };
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for (const token of tokens) {
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if (token.type === "number") {
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output.push(token.value);
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} else if (token.value === "(") {
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stack.push(token.value);
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} else if (token.value === ")") {
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while (stack.length && stack[stack.length - 1] !== "(") {
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output.push(stack.pop());
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}
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stack.pop(); // 弹出左括号
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} else {
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while (
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stack.length &&
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stack[stack.length - 1] !== "(" &&
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precedence[stack[stack.length - 1]] >= precedence[token.value]
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) {
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output.push(stack.pop());
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}
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stack.push(token.value);
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}
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}
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while (stack.length) output.push(stack.pop());
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return output;
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}
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// 执行逆波兰表达式计算
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function evaluateRPN(rpn) {
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const stack = [];
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for (const token of rpn) {
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if (/[-]?\d|\./.test(token)) {
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stack.push(new Big(token));
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} else {
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const b = stack.pop();
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const a = stack.pop();
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switch (token) {
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case "+": stack.push(a.plus(b)); break;
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case "-": stack.push(a.minus(b)); break;
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case "*": stack.push(a.times(b)); break;
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case "/":
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if (b.eq(0)) throw new Error("除数不能为零");
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stack.push(a.div(b));
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break;
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default: throw new Error(`未知运算符: ${token}`);
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}
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}
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}
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return stack.pop().toString();
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}
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