Boundary Traversal of a Binary Tree

Given a binary tree of integers, your task is to return the boundary nodes of the tree in Anti-Clockwise direction starting from the root node.

Input:

The first line contains an integer 'T' which denotes the number of test cases or queries.
Each test case consists of a single line containing elements in level order, with node values separated by spaces. Use -1 to denote a null node.

Output:

For each test case, return the boundary nodes of the given binary tree, separated by spaces.
Provide the output for each test case in a separate line.

Example:

Input:
1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1

Output:
1 2 4 7 6 3

Explanation:

• The boundary nodes for the binary tree are: root node, left boundary, leaf nodes, and right boundary nodes.
• If there are duplicates in node values from the boundaries, include them only once.

Constraints:

• 1 <= T <= 10^2
• 1 <= N <= 2^12 where 'N' is the total number of nodes in the binary tree.
• Time Limit: 1 sec

Note:

The format of input is for clarity on forming a binary tree. Every tree is listed in a single line, separated by spaces.
Implement the function without printing as printing is already managed.