K-th Smallest Element in BST

Your task is to find the ‘K-th’ smallest element in a given Binary Search Tree (BST).

Explanation:

A Binary Search Tree is a binary tree in which for each node, all elements in the left subtree of a node are smaller, and all elements in the right subtree are larger.

Input:

The input begins with an integer ‘T’ representing the number of test cases.
Each test case consists of two parts:
1. An integer ‘K’.
2. A single line containing the elements of the tree in level order format, with node values separated by spaces. '-1' represents a null node.

Output:

For each test case, output the K-th smallest element in the BST. If the K-th smallest element does not exist, return -1.

Example:

Input:

1
3
4 2 7 -1 -1 5 8 -1 -1 -1 -1

Output:

5

Constraints:

• 1 <= T <= 100
• 1 <= N, K <= 3000
• -10^9 <= data <= 10^9

Note:

1. Implement the function to determine the K-th smallest element. No need to print outputs explicitly.
2. Focus is on returning the value of the K-th smallest node, not the node itself.
3. Inputs may include '-1' to denote the absence of a node in certain positions.