226. Invert Binary Tree.py

'''
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.
'''

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):if 
#         self.val = val
#         self.left = left
#         self.right = right

class Solution:
    def invertTree(self, root: TreeNode) -> TreeNode:
        inverter(root)
        return root
        
def inverter(root):
    if root==None:
        return
    
    root.right, root.left = root.left, root.right
    inverter(root.left)
    inverter(root.right)