maximum-depth-of-binary-tree.py

"""
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 root is None:
            return 0
        elif root.left is None and root.right is None:
            return 1
        left = self.maxDepth(root.left)
        right = self.maxDepth(root.right)
        return max(left, right) + 1