Evaluate Reverse Polish Notation

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) {
int sum;
string operators="+-*/";
stack<int>sta;
for(int i=0;i<tokens.size();i++){
if(operators.find(tokens[i])==string::npos){
sta.push(atoi(tokens[i].c_str()));
}

else{
int a=sta.top();
sta.pop();
int b=sta.top();
sta.pop();
if(tokens[i]=="+"){
sta.push(a+b);
}
if(tokens[i]=="-"){
sta.push(b-a);
}
if(tokens[i]=="*"){
sta.push(a*b);
}
if(tokens[i]=="/"){
sta.push(b/a);
}
}

}

sum=sta.top();
return sum;
}
};