[leetcode: Python]104. Maximum Depth of Binary Tree

题目：

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

方法一：性能65ms

# 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
"""
if root == None:
return 0
left_depth = self.maxDepth(root.left)
right_depth = self.maxDepth(root.right)
return max(left_depth, right_depth) + 1

方法二：性能52ms

# 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
"""
if not root:
return 0

return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))

两种方法有本质区别吗？为什么有性能差异的。。。