leetcode-简单-栈-逆波兰表达式

class Solution {
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack = new Stack<>();
        int len = tokens.length;
        int ans = 0;
        Integer op1, op2;
        ArrayList<String> list =new ArrayList<>(Arrays.asList("+","-","*","/"));
        for(int i = 0; i < len; i++){
            if(list.contains(tokens[i])){
                if(!stack.empty()){
                    op1 = stack.pop();
                    if(!stack.empty()){
                        op2 = stack.pop();
                        switch (tokens[i]){
                            case "+":
                                stack.push(op1+op2);
                                break;
                            case "-":
                                stack.push(op2-op1);
                                break;
                            case "*":
                                stack.push(op2*op1);
                                break;
                            case "/":
                                try{
                                    stack.push(op2/op1);
                                }catch (Exception e){
                                    e.printStackTrace();
                                }
                        }
                    }
                }
            }else{
                stack.push(Integer.valueOf(tokens[i]));
            }
        }
        return stack.pop();
    }
}