<p>Given an integer <code>n</code>, return the count of all numbers with unique digits, <code>x</code>, where <code>0 <= x < 10<sup>n</sup></code>.</p> <p> </p> <p><strong>Example 1:</strong></p> <pre> <strong>Input:</strong> n = 2 <strong>Output:</strong> 91 <strong>Explanation:</strong> The answer should be the total numbers in the range of 0 ≤ x < 100, excluding 11,22,33,44,55,66,77,88,99 </pre> <p><strong>Example 2:</strong></p> <pre> <strong>Input:</strong> n = 0 <strong>Output:</strong> 1 </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li><code>0 <= n <= 8</code></li> </ul>