Kth Smallest Element in a BST

Medium

Given the root of a binary search tree and an integer k, return the k-th smallest value (1-indexed).

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

• 1 <= k <= number of nodes <= 10^4
• 0 <= Node.val <= 10^4