Evaluate Reverse Polish Notation

Solution.java

package com.interviewbytes.rpn;

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.HashSet;
import java.util.Set;

public class Solution {

    private static final Set<String> OPERATORS = new HashSet<>();

    static {
        OPERATORS.add("+");
        OPERATORS.add("-");
        OPERATORS.add("*");
        OPERATORS.add("/");
    }

    public int evalRPN(String[] tokens) {

        Deque<Integer> stack = new ArrayDeque<>();

        for (String token : tokens) {
            if (OPERATORS.contains(token)) {
                int a = stack.pop();
                int b = stack.pop();
                switch (token) {
                    case "+":
                        stack.push(a + b);
                        break;
                    case "-":
                        stack.push(b - a);
                        break;
                    case "*":
                        stack.push(a * b);
                        break;
                    case "/":
                        stack.push(b / a);
                        break;
                    default:
                        break;
                }
            } else {
                stack.push(Integer.valueOf(token));
            }
        }

        return stack.pop();
    }
}