440\. K-th Smallest in Lexicographical Order

Hard

Given two integers `n` and `k`, return _the_ <code>k<sup>th</sup></code> _lexicographically smallest integer in the range_ `[1, n]`.

**Example 1:**

**Input:** n = 13, k = 2

**Output:** 10

**Explanation:** The lexicographical order is [1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9], so the second smallest number is 10. 

**Example 2:**

**Input:** n = 1, k = 1

**Output:** 1 

**Constraints:**

*   <code>1 <= k <= n <= 10<sup>9</sup></code>