invert_binary_tree.py

# 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):
        if root is None:
            return root

        root.left, root.right = root.right, root.left

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

        return root

        # Time Complexity: O(n) where n is the number of nodes
        # Space Complexity: O(h) where h is the height of tree

    def invertTree(self, root):
        if not root:
            return None

        stack = [root]

        while stack:
            node = stack.pop()

            node.left, node.right = node.right, node.left

            stack.append(node.right) if node.right else None
            stack.append(node.left) if node.left else None

        return root