Second Largest in Tree Level

You are given a binary tree where each node contains an integer value. Your task is to find the second largest unique value at each level of the tree.

You must return a list of these second-largest values, ordered from the root level to the deepest level.

Rules for determining the second largest value:

If a level has two or more unique node values (e.g., [5, 5, 3]), the second largest is the second highest distinct value (in this case, 3).

If a level has fewer than two unique node values (e.g., [10] or [20, 20, 20]), there is no second largest value. In such cases, you should use -1 as a placeholder for that level's result.

Input Format:

The first line contains a single integer N, the number of nodes in the level-order representation of the tree.

The second line contains N space-separated integers, representing the tree in level-order format. A value of -1 indicates a null node.

Output Format:

Print a single line containing the second-largest values for each level, separated by spaces.

Note:

This problem is best solved by traversing the tree level by level, which is a classic application of Breadth-First Search (BFS). For each level, you will need to collect all node values and then apply a method to find the largest and second-largest unique values among them.