01_二叉树的最大深度

# 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
        解题思路：递归
        """
        if not root:
            return 0
        l = 1 + self.maxDepth(root.left)
        r = 1 + self.maxDepth(root.right)
        return max(l, r)