150. Evaluate Reverse Polish Notation (Stack)

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 > operandStack;
int operand1;
int operand2;
for(int i = 0; i < tokens.size(); i++){
if(tokens[i]=="+"){
operand1 = operandStack.top();
operandStack.pop();
operand2 = operandStack.top();
operandStack.pop();
operand2 += operand1;
operandStack.push(operand2);
}
else if(tokens[i]=="-"){
operand1 = operandStack.top();
operandStack.pop();
operand2 = operandStack.top();
operandStack.pop();
operand2 -= operand1;
operandStack.push(operand2);
}
else if(tokens[i]=="*"){
operand1 = operandStack.top();
operandStack.pop();
operand2 = operandStack.top();
operandStack.pop();
operand2 *= operand1;
operandStack.push(operand2);
}
else if(tokens[i]=="/"){
operand1 = operandStack.top();
operandStack.pop();
operand2 = operandStack.top();
operandStack.pop();
operand2 /= operand1;
operandStack.push(operand2);
}
else{
operand1 = atoi(tokens[i].c_str());
operandStack.push(operand1);
}
}
return operandStack.top();
}
};