题解 | #规律数列求和#

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

int main() {

    // write your code here......
    //+= 9*= (10*i)
    long long sum;
    for(int i = 0; i <= 10; i++)
    {
        sum += pow(10,i)-1;
    }
    cout<<sum<<endl;

    return 0;
}

pow(10,i)-1 就是9,99,999...了