链接：104. 二叉树的最大深度 - 力扣（LeetCode）

深搜dfs

注意这里递归前要加self.

 1 # Definition for a binary tree node.
 2 # class TreeNode(object):
 3 #     def __init__(self, val=0, left=None, right=None):
 4 #         self.val = val
 5 #         self.left = left
 6 #         self.right = right
 7 class Solution(object):
 8     def maxDepth(self, root):
 9         """
10         :type root: Optional[TreeNode]
11         :rtype: int
12         """
13         if not root:
14             return 0
15         leftDepth = self.maxDepth(root.left)
16         rightDepth = self.maxDepth(root.right) 
17         return max(leftDepth, rightDepth) + 1
18             
19