Evaluate Reverse Polish Notation

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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();    }};

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