"""
104. Maximum Depth of Binary Tree
Difficulty: Easy
https://leetcode.com/problems/maximum-depth-of-binary-tree/

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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



Constraints:

        • The number of nodes in the tree is in the range [0, 10^4].

        • -100 <= Node.val <= 100
"""


# 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:
        if not root:
            return 0

        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))