Stack: Evaluate Reverse Polish Notation

• https://leetcode.com/problems/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

public int evalRPN(String[] tokens) {
    Stack<String> stack = new Stack();
    String operators = "+-/*";

    for (String s : tokens) {
        if (!operators.contains(s)) {
            stack.push(s);
        } else {
            int a = Integer.valueOf(stack.pop());
            int b = Integer.valueOf(stack.pop());

            switch (s) {
                case "+" : stack.push(String.valueOf(a+b));
                    break;
                case "-" : stack.push(String.valueOf(b-a)); 
                    break;
                case "*" : stack.push(String.valueOf(a*b));
                    break;
                case "/" : stack.push(String.valueOf(b/a));   
                    break;
            }
        }
    }

    return Integer.valueOf(stack.pop());
}