Maximum Depth of Binary Tree Solutions in Python

#!python3

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution:
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if root is None:
            return 0
        return max(self.maxDepth(root.left), self.maxDepth(root.right)) + 1


if __name__ == "__main__":
    root = TreeNode(1)
    root.left = TreeNode(2)
    root.right = TreeNode(3)
    root.left.left = TreeNode(4)
    root.left.right = TreeNode(5)
    root.right.left = TreeNode(6)
    root.left.left.left = TreeNode(7)
    root.left.left.right = TreeNode(8)
    root.left.left.right.left = TreeNode(9)

    print(Solution().maxDepth(root))