Count Stepping Numbers - Problem Statement

A stepping number has adjacent digits differing by exactly 1. Count stepping numbers in $[L, R]$. State: $(pos, tight, lastDigit, started)$.

Transition: if $|newDigit - lastDigit| = 1$, valid. Handle leading zeros: before placing the first non-zero digit, any digit is valid. Track $started$ flag. Examples: 123, 321, 12321 are stepping. $135$, $100$, $122$ are not. The stepping constraint only involves adjacent digits. Track the last digit placed to check the constraint.