题解 | 规律数列求和

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

int main() {
 long long sum = 0;
 long long num = 0;
    // write your code here......
    for(int i=1; i<=10; i++)
    {
       long long num = pow(10,i)-1;
       sum += num;

    }
    cout<< sum <<endl;
    return 0;
}