题解 | 数列求和 字符串解法

public class Main {
    public static void main(String[] args) {

        
        //write your code here........
        long sum = 0;
        StringBuilder s=new StringBuilder();
        while(s.length()<10){
            s.append("9");
            long i=Long.valueOf(s.toString());
            sum+=i;
        }
        System.out.println(sum);
    

    }
}