LeetCode 2376 Count Special Integers - Problem Statement

Given a positive integer $n$, return the number of positive integers in $[1, n]$ that have all distinct digits. For $n = 20$: integers $1$-$10$ are all special (single digit or "10"). Integers $11$-$20$: only $11$ has repeated digits.

Answer: $19$. For $n = 135$: you need to count all numbers up to $135$ where no digit repeats. This requires tracking which digits you've used. Before reading the solution, try to identify the base case and recursive relationship yourself.