150. Evaluate Reverse Polish Notation

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

class Solution {    public int evalRPN(String[] tokens) {        Stack<Integer> s = new Stack<Integer>();        String operators = "+-*/";        for(String token : tokens){            if(!operators.contains(token)){                s.push(Integer.valueOf(token));                continue;            }            int a = s.pop();            int b = s.pop();            if(token.equals("+")) {                s.push(b + a);            } else if(token.equals("-")) {                s.push(b - a);            } else if(token.equals("*")) {                s.push(b * a);            } else {                s.push(b / a);            }        }        return s.pop();    }}