C++实现Reverse Polish Notation计算器测试不通过问题排查

问题核心错误排查 #

你代码中存在三个核心错误导致测试失败：

• 运算符处理逻辑完全错误：遇到运算符时没有从栈中取已压入的操作数，反而错误读取原始token数组中当前位置前两位的token计算，仅第一个长度为3的测试用例刚好命中正确取值，后续测试全部取值错误。
• 二元运算符的操作数顺序需要适配栈的后进先出特性：先弹出的是右操作数，后弹出的是左操作数，要保证运算顺序正确。
• 类成员默认是私有访问权限，main函数无法直接调用evaluateCountdown方法，需要修改为public权限。

修复后的完整代码 #

#include <string>
#include <vector>
#include <stack>
 
class CountdownSolution {
public:
    std::vector<std::string> stringToVector(const std::string newString,const char token)
    {
        std::vector<std::string> stringVector;
        
        size_t posLast = 0, pos = 0;
        while((pos = newString.find(token, pos)) != std::string::npos)
        {
            if(newString[pos] != newString[posLast])
                stringVector.push_back(newString.substr(posLast, pos - posLast));
            posLast = ++pos;
        }
        if(newString[posLast] != 0)
            stringVector.push_back(newString.substr(posLast));
        
        return stringVector;
    }
    
    double evaluateCountdown(const std::string& rpnString) {
        std::vector<std::string> rpnStringVector = stringToVector(rpnString,' ');
        std::stack<double> rpnStack;
        for (auto& token : rpnStringVector)
        {
            if(token == "+" ){
                double right = rpnStack.top(); rpnStack.pop();
                double left = rpnStack.top(); rpnStack.pop();
                rpnStack.push(left + right);
            } else if(token == "-"){
                double right = rpnStack.top(); rpnStack.pop();
                double left = rpnStack.top(); rpnStack.pop();
                rpnStack.push(left - right);
            } else if(token == "*"){
                double right = rpnStack.top(); rpnStack.pop();
                double left = rpnStack.top(); rpnStack.pop();
                rpnStack.push(left * right);
            } else if(token == "/"){
                double right = rpnStack.top(); rpnStack.pop();
                double left = rpnStack.top(); rpnStack.pop();
                rpnStack.push(left / right);
            } else {
                rpnStack.push(std::stod(token));
            }
        }
        return rpnStack.top();
    }
};

测试代码适配修改 #

因为evaluateCountdown是类成员方法，需要创建类实例调用：

#include <iostream>
using std::cout;
using std::endl;
#include <string>
 
int main() {
    CountdownSolution sol;
    int retval = 0;
    
    {
        double answer = sol.evaluateCountdown(std::string("3.0 4.0 +"));
        if (answer == 7.0) {
            cout << "1) Pass: evaluated '3.0 4.0 +', got 7.0\n";
        } else {
            cout << "1) Fail: evaluated '3.0 4.0 +' expecting 7.0, but got " << answer << std::endl;
            ++retval;
        }
    }
    
    {
        double answer = sol.evaluateCountdown(std::string("3.0 4.0 - 4.0 +"));
        if (answer == 3.0) {
            cout << "2) Pass: evaluated '3.0 4.0 - 4.0 +', got 3.0\n";
        } else {
            cout << "2) Fail: evaluated '3.0 4.0 - 4.0 +' expecting 3.0, but got " << answer << std::endl;
            ++retval;
        }
    }
    
    {
        double answer = sol.evaluateCountdown(std::string("3.0 4.0 - 2.0 *"));
        if (answer == -2.0) {
            cout << "3) Pass: evaluated '3.0 4.0 - 2.0 *', got -2.0\n";
        } else {
            cout << "3) Fail: evaluated '3.0 4.0 - 2.0 *' expecting -2.0, but got " << answer << std::endl;
            ++retval;
        }
    }
    
 
    {
        double answer = sol.evaluateCountdown(std::string("100 20 / 4 +"));
        if (answer == 9) {
            cout << "4) Pass: evaluated '100 20 / 4 +', got 9\n";
        } else {
            cout << "4) Fail: evaluated '100 20 / 4 +' expecting 9, but got " << answer << std::endl;
            ++retval;
        }
    }
 
    return retval;
}

修复后运行测试所有用例均可通过。

内容的提问来源于stack exchange，提问作者Anna Lenkovska