1. 题目

2. 思想

简单的递归实现即可。

3. 代码

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        depth = self.dfs(root) # 根的节点高度为0
        return depth

    def dfs(self,root):
        if root is None:
            return 0
        left_depth = self.dfs(root.left)
        right_depth = self.dfs(root.right)
        return max(left_depth,right_depth) + 1
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