Solution.java

import java.util.*;

public class Solution
{
    public int evalRPN(String[] tokens)
    {
        List<String> operators = Arrays.asList("+", "-", "*", "/");
        Stack<Integer> stack = new Stack<>();
        for (int i = 0; i < tokens.length; i++)
        {
            stack.push(operators.contains(tokens[i]) ? value(stack, tokens[i]) : Integer.parseInt(tokens[i]));
        }
        return stack.pop();
    }

    private int value(Stack<Integer> stack, String operator)
    {
        int y = stack.pop(), x = stack.pop();
        switch (operator)
        {
            case "+":
                return x + y;
            case "-":
                return x - y;
            case "*":
                return x * y;
            default:
                return x / y;
        }
    }
}