Evaluate Reverse Polish Notation

// 4 ms (Beats 90%)
// 15.49 MB (Beats 62%)
#include <stack>
#include <string>

class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<int> s;
        for (const string& token : tokens) {
            if (token.compare("-") == 0) {
                const int op1 = s.top(); s.pop();
                const int op2 = s.top(); s.pop();
                s.push(op2 - op1);
            }
            else if (token.compare("*") == 0) {
                const int op1 = s.top(); s.pop();
                const int op2 = s.top(); s.pop();
                s.push(op1 * op2);
            } else if (token.compare("+") == 0) {
                const int op1 = s.top(); s.pop();
                const int op2 = s.top(); s.pop();
                s.push(op1 + op2);
            } else if (token.compare("/") == 0) {
                const int op1 = s.top(); s.pop();
                const int op2 = s.top(); s.pop();
                s.push(op2 / op1);
            } else {
                s.push(stoi(token));
            }
        }
        return s.top();
    }
};