# 226. Invert Binary Tree

Invert a binary tree.

## Example:

### Input:

```
     4
   /   \
  2     7
 / \   / \
1   3 6   9
```

### Output:

```
     4
   /   \
  7     2
 / \   / \
9   6 3   1
```

## Trivia:

This problem was inspired by this original tweet by Max Howell:

> Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.