#include <iostream>
#include <stack>
#include <sstream>
#include <stdexcept>
<p>double evaluateRPN(const std::string& expression) {
std::stack<double> operands;
std::istringstream iss(expression);
std::string token;</p><pre class='brush:php;toolbar:false;'>while (iss >> token) {
    if (token == "+" || token == "-" || token == "*" || token == "/") {
        if (operands.size() < 2) {
            throw std::runtime_error("invalid RPN expression: not enough operands");
        }
        double b = operands.top(); operands.pop();
        double a = operands.top(); operands.pop();
        double result = 0;

        if (token == "+") result = a + b;
        else if (token == "-") result = a - b;
        else if (token == "*") result = a * b;
        else if (token == "/") {
            if (b == 0) throw std::runtime_error("division by zero");
            result = a / b;
        }
        operands.push(result);
    } else {
        try {
            double num = std::stod(token);
            operands.push(num);
        } catch (...) {
            throw std::runtime_error("invalid token: " + token);
        }
    }
}

if (operands.size() != 1) {
    throw std::runtime_error("invalid RPN expression");
}

return operands.top();

}

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int main() {
    std::string expr = "3 4 + 5 *";
    try {
        double result = evaluateRPN(expr);
        std::cout << "Result: " << result << std::endl; // 输出 35
    } catch (const std::exception& e) {
        std::cerr << "Error: " << e.what() << std::endl;
    }
    return 0;
}