Sum of digits from 1 to N

[benni515]

http://www.geeksforgeeks.org/count-sum-of-digits-in-numbers-from-1-to-n/

This is a good algorithm so use for calculating the sum of digits from 1 to N
I tried implementing it but it did not work for a problem on Kattis.
https://open.kattis.com/problems/digitsum This is the Problem
I got TLE, so i added an unordered_map to know what has been calculated before, but that gave me WA

If anybody can implement this algorithm so it works, then please add the implementation to the Math folder

[benni515]

This algorithm above is not valid