Question

java语言计算9,99,999,9999,.......9999999999的和

Answer 1

我们观察这组数字的规律，它是等比数列

10,100,1000...里面每个元素减一的出来的，初始数long num = 10

数列里面最大的数是9999999999，所以要有一个最大限制long max = 9999999999L;

再用一个变量存储总和long sum = 0;

所以代码为

public class Test {
public static void main(String[] args) {
long max = 9999999999L;
long sum = 0;
long num = 10;
while (num-1 <= max) {
sum += (num - 1);
num*=10;
}
System.out.println(sum);
}
}

结果11111111100