Count Numbers with Unique Digits

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Description

Given an integer n, return the count of all numbers with unique digits, x, where 0 <= x < 10ⁿ.

Example 1:

Input: n = 2

Output: 91

Explanation: The answer should be the total numbers in the range of 0 ≤ x < 100, excluding 11,22,33,44,55,66,77,88,99

Example 2:

Input: n = 0

Output: 1

Solution