Will the Guru

Problem

https://leetcode.com/problems/evaluate-reverse-polish-notation/

Solution

class Solution {
    Set<String> operator = new HashSet<>();
    Stack<String> stack = new Stack<>();

    public int evalRPN(String[] tokens) {
        operator.add("+");
        operator.add("-");
        operator.add("*");
        operator.add("/");

        int result = 0;
        for (int i=0;i<tokens.length;i++) {
            String token = tokens[i];
            if (operator.contains(token)) {
                int a = Integer.parseInt(stack.pop());
                int b = Integer.parseInt(stack.pop());

                if ("+".equals(token)) {
                    stack.push(String.valueOf(a + b));
                } else if ("-".equals(token)) {
                    stack.push(String.valueOf(b - a));
                } else if ("*".equals(token)) {
                    stack.push(String.valueOf(a * b));
                } else if ("/".equals(token)) {
                    stack.push(String.valueOf(b / a));
                }
            } else {
                stack.push(token);
            }
        }
        result = Integer.parseInt(stack.pop());
        return result;
    }

}