LC104. Maximum Depth of a Binary Tree

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

Complexity

Time: $O(n)$
Space: $O(n)$ for function stack