You are given the root of a binary search tree and an integer `k`. Return the value of the node that would appear in the `k`th position if all node values were listed in ascending order. A binary search tree has the property that for every node: - all values in the left subtree are smaller than the node value, and - all values in the right subtree are larger than the node value. You may assume `1 <= k <= number of nodes in the tree`. Example: - Input: root = [5,3,6,2,4,null,null,1], k = 3 - In-order traversal gives: [1,2,3,4,5,6] - Output: 3 Discuss an efficient approach and analyze its time and space complexity.