104. Maximum Depth of Binary Tree.py

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

class Solution(object):
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        
        def depth(root):
            if not root:
                return 0
            
            return max(depth(root.left),depth(root.right)) + 1
        
        return depth(root)