Evaluate Reverse Polish Notation

 1 class Solution {
 2 public:
 3     int evalRPN(vector<string> &tokens) {
 4         stack<int> s;
 5         for (int i = 0; i < tokens.size(); ++i) {
 6             if (tokens[i] != "+" && tokens[i] != "-" && tokens[i] != "*" && tokens[i] != "/")
 7                 s.push(stoi(tokens[i]));
 8             else {
 9                 int op2 = s.top();s.pop();
10                 int op1 = s.top();s.pop();
11                 int result = 0;
12                 if(tokens[i] == "+")
13                     result = op1 + op2;
14                 else if(tokens[i] == "-")
15                     result = op1 - op2;
16                 else if(tokens[i] == "*")
17                     result = op1 * op2;
18                 else if(tokens[i] == "/")
19                     result = op1 / op2;
20                 s.push(result);
21             }
22         }
23         return s.top();
24     }
25 };