150. Evaluate Reverse Polish Notation

import operator

class Solution:
    def evalRPN(self, tokens: List[str]) -> int:
        opt = {
            "+": operator.add,
            "-": operator.sub,
            "*": operator.mul,
            "/": operator.truediv
        }
        s = []
        for token in tokens:
            if token in opt:
                s.append(int(opt[token](s.pop(-2), s.pop(-1))))
            else:
                s.append(int(token))
        return s[0]

class Solution {
    public int evalRPN(String[] tokens) {
        Deque<Integer> s = new ArrayDeque<>();
        int left, right;
        for (String token : tokens) {
            switch(token) {
            case "+":
                right = s.pop();
                left = s.pop();
                s.push(left + right);
                break;
            case "-":
                right = s.pop();
                left = s.pop();
                s.push(left - right);
                break;
            case "*":
                right = s.pop();
                left = s.pop();
                s.push(left * right);
                break;
            case "/":
                right = s.pop();
                left = s.pop();
                s.push(left / right);
                break;
            default:
                s.push(Integer.valueOf(token));
            }
        }
        return s.pop();
    }
}