二叉树的最大深度

递归不解释

class Solution:
    """
    @param root: The root of binary tree.
    @return: An integer
    """ 
    def maxDepth(self, root):
        # write your code here
        if root == None:
            return 0
        lh = self.maxDepth(root.left)
        rh = self.maxDepth(root.right)
       return max(lh,rh)+1