Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Some examples:

  ["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
  ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

class Solution {
public:
    int evalRPN(vector<string> &tokens) {
        stack<int> data;
        int i,len=tokens.size();
        int op_data1,op_data2;
        for(i=0;i<len;i++){
            if(tokens[i]!="+" && tokens[i]!="-" && tokens[i]!="*" && tokens[i]!="/") 
                data.push(atoi(tokens[i].c_str()));
            else{
                op_data2=data.top();
                data.pop();
                op_data1=data.top();
                data.pop();
                if(tokens[i]=="+") data.push(op_data1+op_data2);
                if(tokens[i]=="-") data.push(op_data1-op_data2);
                if(tokens[i]=="*") data.push(op_data1*op_data2);
                if(tokens[i]=="/") data.push(op_data1/op_data2);
            }
        }
        return data.top();
    }
};

Evaluate Reverse Polish Notation