Easy

求一棵二叉树的最大深度。

递归。

# 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
        """
        
        if root == None:
            return 0
        else:
            depth = 1
            if root.left == None and root.right == None:
                return 1
            else:
                depth += max(self.maxDepth(root.left), self.maxDepth(root.right))
                return depth