题解 | #规律数列求和#

#include <cmath>
#include <iostream>
#include <string>
#include <vector>
using namespace std;

int main() {

    // write your code here......
    long sum;
    for (int i=1; i<=10; i++) {
        sum += pow(10, i)-1;
    }

    cout << sum << endl;

    return 0;
}