**Solution**

**Invert Binary Tree** https://leetcode.com/problems/invert-binary-tree/?tab=Description

- Postorder - invert left and right sub-trees. Then swap left and right sub-trees.

```
class Solution(object):
def invertTree(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""
self.invert(root)
return root
def invert(self, root):
if root == None:
return
self.invert(root.left)
self.invert(root.right)
root.left, root.right = root.right, root.left
return
```