题解 | 数列求和

public class Main {   
     public static void main(String[] args) {
        long sum = 0;
        long tirm = 0;
        for(int i = 1;i<=10;i++){
            tirm = tirm*10 + 9;
            sum  = sum + tirm;
        }
        System.out.println(sum);

    }
}

循环构造每一项的值