104-Maximum_Depth_of_Binary_Tree.py

# 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:
        
        def dfs(node):
            
            if node is None:
                return 0
            return max( dfs(node.left), dfs(node.right)) + 1
        
        return dfs(root)