题解 | #规律数列求和#

#include <iostream>
using namespace std;

int main() {
    long num=0;
    long sum=0;
    // write your code here......
    for(int i=0;i<10;i++){
        num=num*10;
        num+=9;
        sum+=num;
    }
    cout<<sum;

    return 0;
}