【LeetCode】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

public class Solution {
    public int evalRPN(String[] tokens) {
        Stack<String> stack = new Stack<String>();
        if(tokens.length==0)
            return 0;
        
        int[] op = new int[2];
        Arrays.fill(op, 0);
        
        for(int i=0;i<tokens.length;i++){
            if(!tokens[i].equals("+")&&!tokens[i].equals("-")&&!tokens[i].equals("*")&&!tokens[i].equals("/")){
                stack.push(tokens[i]);
                continue;
            }else{
                String operator = tokens[i];
                op[1]=Integer.parseInt(stack.peek());
                stack.pop();
                op[0]=Integer.parseInt(stack.peek());
                stack.pop();
                int t=0;
                switch(operator){
                    case "+":t=op[0]+op[1];break;
                    case "-":t=op[0]-op[1];break;
                    case "*":t=op[0]*op[1];break;
                    case "/":t=op[0]/op[1];break;
                    default:t=0;break;
                }
                stack.push(String.valueOf(t));               
            }
        
        }
        if(stack.isEmpty()||stack.peek().equals("+")||stack.peek().equals("-")||stack.peek().equals("*")||stack.peek().equals("/"))
            return 0;
        return Integer.parseInt(stack.peek());
    }
}