Given the root of a binary tree, invert the tree and return its root.
Inverting means every node swaps its left and right children.
For the Cheetcode runner, trees are represented as level-order arrays with null placeholders for missing children.
Reason about the value returned from each subtree and the state passed down from ancestors. Empty children and single-node trees should be handled naturally.
Examples
Input: root = [4,2,7,1,3,6,9] Output: [4,7,2,9,6,3,1]
Input: root = [2,1,3] Output: [2,3,1]
Constraints
- The number of nodes is in the range [0, 100].
- -100 <= Node.val <= 100