# LeetCode 226. Invert Binary Tree

## Description

https://leetcode.com/problems/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 canâ€™t invert a binary tree on a whiteboard so f*** off.

## Explanation

Invert left and right subtrees.

## Python Solution

``````# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def invertTree(self, root: TreeNode) -> TreeNode:
return self.helper(root)

def helper(self, root):
if not root:
return root

if not root.left and not root.right:
return root

left = self.helper(root.left)
right = self.helper(root.right)

root.left = right
root.right = left

return root``````
• Time Complexity: O(N)
• Space Complexity: O(1)