Preorder Traversal Problem Statement

You are provided with the root node of a binary tree comprising N nodes. Your objective is to output its preorder traversal. Preorder traversal of a binary tree is performed by visiting nodes in the following sequence:

1- Visit the root node.
2- Traverse all nodes in the left subtree of the root node.
3- Traverse all nodes in the right subtree of the root node.

Example:

Input:

The elements are provided in level order format. Input consists of space-separated values of nodes in a single line, substituting -1 for null nodes.

For example, the input for the depicted tree is:
1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1

Output:

[1, 2, 4, 7, 3, 5, 6]

Explanation:

For the given binary tree, the preorder traversal results in [1, 2, 4, 7, 3, 5, 6].

Constraints:

• 1 ≤ T ≤ 10
• 1 ≤ N ≤ 10^4
• 1 ≤ nodeVal ≤ 10^9

Time limit: 1 sec

Note:

You are not required to print anything; the printing is handled separately. Focus on implementing the function only.