题解 | #数列求和#

import static java.lang.Math.pow;
public class Main {
    public static void main(String[] args) {

        //write your code here........
        long arr[] = new long[10];
        long sum = 0;
        arr[0] = 9;
        for (int i = 1; i < 10 ; i++) {
            arr[i] = (long) (arr[i - 1] + 9 * (pow(10, i)));
            sum += arr[i];
        }
        System.out.println(arr[0] + sum);

    }
}