leetcode:Maximum Depth of Binary Tree

# 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 == None:
            return 0
        l,r = 1,1
        if root.left != None:
            l = l+self.maxDepth(root.left)
        if root.right != None:
            r = r+self.maxDepth(root.right)
        if l>r:
            return l
        else:
            return r