104. Maximum Depth of Binary Tree

Given the root of a binary tree, return its maximum depth.

A binary tree's maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: 3

Example 2:

Input: root = [1,null,2]
Output: 2

def maxDepth(self, root: Optional[TreeNode]) -> int:
	if not root:
		return 0
	
	return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))