Leetcode 2801. Count Stepping Numbers in Range

Count how many integers in the inclusive range [low, high] (given as decimal strings up to 100 digits) have every pair of adjacent digits differ by exactly 1 and no leading zeros, returning the result modulo 1e9+7. The core challenge is handling enormous bounds efficiently (typically via digit-DP or equivalent) to count valid numbers up to high and subtract those below low.