题解 | 数列求和

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        long index = 9L;
        List<Long> numbers = new ArrayList<>();
        for (int i = 1; i <= 10; i++) {
            if (i != 1) index = index * 10L + 9;
            numbers.add(index);
        }
        long all = 0L;
        for (Long number : numbers) {
            all += number;
        }
        System.out.println(all);
    }
}