华为机试LISP加减乘除语句解析

[ss98791616]

第一题
简单的 LISP 加减乘除语句解析并计算结果，四种运算符号为 add、sub、mul、div，分别为加减乘除。其中数字部分皆为整数。除法取整，除数为零输出 error。
例子：
(add 3 5 7) 结果为 15

(sub 1 9) 结果为 -8

(mul 0 9) 结果为 0

(div 8 3) 结果为 2

(div 8 0) 结果为 error

(add (sub (div 8 2) (mul 1 9)) 20) 结果为 15

public static void main(String[] args) throws IOException {
        String s="(add (sub (div 8 2) (mul 1 9)) 20)";
//        for (String s1 : s.split("\\(")) {
//            System.out.println(s1);
//        }
        System.out.println(operation(s));


    }
    public static String operation(String str){
        if (str.indexOf("(",1)==-1){
            String[] split = str.split("\\s+");
            String ope = split[0].replace("(","");
            int c1 = Integer.parseInt(split[1].replace(")",""));
            int c2 = Integer.parseInt(split[2].replace(")",""));
            int result=-1;
            if ("div".equals(ope)&&c2==0){
                return "error";
            }
            switch (ope){
                case  "div":
                    result=c1/c2;
                    break;
                case  "add":
                    result=c1+c2;
                    break;
                case  "mul":
                    result=c1*c2;
                    break;
                case  "sub":
                    result=c1-c2;
                    break;
            }
            return String.valueOf(result);
        }
        int left=str.lastIndexOf("("),right=str.indexOf(")",left);
        String substring = str.substring(left, right+1);
        String result = " "+operation(substring);
        StringBuilder sb = new StringBuilder(str);
        sb.replace(left,right+1,result.replace(")",""));
        return operation(sb.toString());
    }