题解 | #数列求和#

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

    //write your code here........
    
    
    long sum = 0;
    long a = 9;
    for(int i = 0; i < 10; i++){
        sum += a;
        a = a * 10 + 9;
    }
    System.out.println(sum);
}

}