题解 | #数列求和#

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

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