Invert Binary Tree
Given a binary tree, invert it and return the new value. You may invert it in-place.
To "invert" a binary tree, switch the left subtree and the right subtree, and invert them both. Inverting an empty tree does nothing.
Input
tree: a binary tree that needs to be inverted.
Output
The inverted binary tree.
Examples
Example 1:
Input:
tree = <See explanation>
Output: <See explanation>
Explanation:
Original tree:
Inverted tree:
