357\. Count Numbers with Unique Digits

Medium

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

**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

**Constraints:**

*   `0 <= n <= 8`