150. 逆波兰表达式求值

class Solution {
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack=new Stack();
        for(String s:tokens){
            if(s.equals("+")){
                int a=stack.pop();
                int b=stack.pop();
                stack.push(b+a);
            }else if(s.equals("*")){
                int a=stack.pop();
                int b=stack.pop();
                stack.push(b*a);
            }else if(s.equals("-")){
                int a=stack.pop();
                int b=stack.pop();
                stack.push(b-a);
            }else if(s.equals("/")){
                int a=stack.pop();
                int b=stack.pop();
                stack.push(b/a);
            }else {
                stack.push(Integer.parseInt(s));
            }
        }
        if(!stack.isEmpty()){
            return stack.peek();
        }
        return 0;

    }
}