[LeetCode] 104. Maximum Depth of Binary Tree

题：https://leetcode.com/problems/maximum-depth-of-binary-tree/description/

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.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

3

/ \
9 20
/ \
15 7
return its depth = 3.

思路

dfs 返回 当前层然后比较

code

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

def dfstry(p,layer):
    if p!= None:
        layer+=1
        return max(dfstry(p.left,layer),dfstry(p.right,layer))
    return layer

class Solution:
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        return dfstry(root,0)