Given the `root`

of a binary search tree, and an integer `k`

, return *the* `k`

(^{th}**1-indexed**) *smallest element in the tree*.

**Example 1:**

Input:root = [3,1,4,null,2], k = 1Output:1

**Example 2:**

Input:root = [5,3,6,2,4,null,null,1], k = 3Output:3

**Constraints:**

- The number of nodes in the tree is
`n`

. `1 <= k <= n <= 10`

^{4}`0 <= Node.val <= 10`

^{4}