递归
# Definition for a binary tree node
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
# @param root, a tree node
# @return an integer
def maxDepth(self, root):
if root is None:
return 0
return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))