answer.py

#!/usr/bin/env python

#-------------------------------------------------------------------------------
# Definition for a binary tree node.
# 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 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))
#-------------------------------------------------------------------------------
# Testing