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(String[] tokens) {
        Stack<Integer> stack =new Stack<>();
        for(String s:tokens){
            if(s.equals("+")){
                int a=stack.pop();
                int b=stack.pop();
                stack.push(a+b);
            }else if(s.equals("-")){
                int a=stack.pop();
                int b=stack.pop();
                stack.push(b-a);
            }else if(s.equals("*")){
                int a=stack.pop();
                int b=stack.pop();
                stack.push(a*b);
            }else if(s.equals("/")){
                int a=stack.pop();
                int b=stack.pop();
                stack.push(b/a);
            }else{
                stack.push(Integer.parseInt(s));
            }
        }
        return stack.pop();
    }
}