Kth Smallest Element in a BST
Difficulty: Medium
Category: DSA
Topics: Tree, Depth-First Search, Binary Search Tree, Binary Tree
Asked at: Amazon, Facebook, Adobe, Microsoft, Oracle
Given the `root` of a binary search tree, and an integer `k`, return _the_ `kth` _smallest value (**1-indexed**) of all the values of the nodes in the tree_.
**Example 1:**
**Input:** root = [3,1,4,null,2], k = 1
**Output:** 1
```
**Example 2:**
**Input:** root = [5,3,6,2,4,null,null,1], k = 3
**Output:** 3
```
**Constraints:**
- The number of nodes in the tree is `n`.
- `1 <= k <= n <= 104`
- `0 <= Node.val <= 104`
**Follow up:** If the BST is modified often (i.e., we can do insert and delete operations) and you need to find the kth smallest frequently, how would you optimize?