题解 | #数列求和#

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

        //write your code here........

        //1.数学函数Math。pow 用来算多次方
        // 2.应该用长整形

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

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

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

数学公式忘记，长整型忘记