题解 | #规律数列求和#

#include <iostream>
using namespace std;

int main() {

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

        
    }
    cout << sum << endl;
        
    

    return 0;
}