## Invert binary tree

A problem that Homebrew's author complained.

Invert a binary tree. Problem from leetcode.

Here's the input:

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

and the out put looks like:

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

This problem was inspired by this tweet:

https://twitter.com/mxcl/status/608682016205344768

Here's the solution implemented in Java.

```
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode invertTree(TreeNode root) {
if(null != root){
TreeNode leftChild = root.left;
root.left = root.right;
root.right = leftChild;
root.left = invertTree(root.left);
root.right = invertTree(root.right);
}
return root;
}
}
```

There's much different logic behind software engineering with computer science. Max replied this question about it on quora.com after 2 years.