public static void main(String[] args) {
        System.out.println(evalRPN(new String[]{"2"}));
    }
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
src/problems/medium/EvaluateReversePolishNotation.java