题解 | 数列求和

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

        //write your code here........
        
        long max = 9999999999L;
        long result = 0L;
        for(long temp = 9; temp <= max; ){
            result += temp;
            temp = temp * 10 + 9;   
        }
        System.out.println(result);
    }
}