题目：

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代码(首刷看解析 2024年1月21日）：

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<long long> st; 
        for (int i = 0; i < tokens.size(); i++) {
            if (tokens[i] == "+" || tokens[i] == "-" || 
                tokens[i] == "*" || tokens[i] == "/") {
                long long num1 = st.top();
                st.pop();
                long long num2 = st.top(); 
                st.pop();
                if (tokens[i] == "+") st.push(num2 + num1);
                if (tokens[i] == "-") st.push(num2 - num1);
                if (tokens[i] == "*") st.push(num2 * num1);
                if (tokens[i] == "/") st.push(num2 / num1);
            } else {
                st.push(stoll(tokens[i]));
            }
        }

        int result = st.top();
        return result;
    }
};