Given the root of a binary tree, invert the tree, and return its root.

Example 1:

Input:  4 2 7 1 3 6 9
Output: 4 7 2 9 6 3 1

Example 2:

Input:  2 1 3
Output: 2 3 1

Constraints:

• The number of nodes in the tree is in the range [0, 100]
• -100 ≤ Node.val ≤ 100

Input format: A single line of space-separated integers in BFS level-order. Use null for missing nodes.

Output format: BFS level-order of the inverted tree (no trailing nulls).