
Given two positive integers low and high represented as strings, find the count of stepping numbers in the inclusive range [low, high].
A stepping number is an integer such that all of its adjacent digits have an absolute difference of exactly 1.
Return an integer denoting the count of stepping numbers in the inclusive range [low, high].
Since the answer may be very large, return it modulo 10^9 + 7.
Hard, Acceptance Level 14.5%.
Dynamic Programming (DP).
Efficiently handles large inputs (10^9 + 7).
Latest and Most Hardest Problem.