104.py

# 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.
# Input: root = [3,9,20,null,null,15,7], Output: 3
# Input: root = [1,null,2], Output: 2

# Definition for a binary tree node.
from typing import List, Optional
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
        left_depth = self.maxDepth(root.left)
        right_depth = self.maxDepth(root.right)

        return 1 + max(left_depth, right_depth)

root = TreeNode(3)
root.left = TreeNode(9)
root.right = TreeNode(20, TreeNode(15), TreeNode(7))
sol = Solution()
print(sol.maxDepth(root))