Find number of pairs of x, y such that
1 <= x < y <= N and sumOfDigits(x) > sumOfDigits(y)
N <= 10^100 and is given as a string.
I don't remember the sign of inequality properly, it might sumOfDigits(x) < sumOfDigits(y). I read about digit DP to solve this but I cannot find any approach.
How to solve this?