Invert_Binary_Tree_226.py

from typing import Optional

# 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: Optional[TreeNode]) -> Optional[TreeNode]:
        if root is None: 
            return None

        root.left, root.right = root.right, root.left # swap the left and right children without using a temporary variable 

        self.invertTree(root.left)
        self.invertTree(root.right)

        return root