leetcode 150. 逆波兰表达式求值

我的解题

class Solution
{
public:
    int evalRPN(vector<string> &tokens)
    {
        stack<int> st;
        for (auto &&token : tokens)
        {
            if (isOperator(token))
            {
                int operand2 = st.top();
                st.pop();
                int operand1 = st.top();
                st.pop();
                st.push(cal(operand1, operand2, token));
            }
            else
            {
                st.push(stoi(token));
            }
        }
        return st.top();
    }
    bool isOperator(string &s)
    {
        return s == "+" || s == "-" || s == "*" || s == "/";
    }
    int cal(int operand1, int operand2, string &Operator)
    {
        if (Operator == "+")
        {
            return operand1 + operand2;
        }
        else if (Operator == "-")
        {
            return operand1 - operand2;
        }
        else if (Operator == "*")
        {
            return operand1 * operand2;
        }
        else if (Operator == "/")
        {
            return operand1 / operand2;
        }
        else
        {
            return 0;
        }
    }
};