Easy

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

Example 3:

Input: root = []

Output: 0

Example 4:

Input: root = [0]

Output: 1

Constraints:

• The number of nodes in the tree is in the range [0, 104].
• -100 <= Node.val <= 100

To solve the "Maximum Depth of Binary Tree" problem in Python with a Solution class, we'll perform a depth-first search (DFS) traversal of the binary tree. Below are the steps:

1. Create a Solution class: Define a class named Solution to encapsulate our solution methods.

2. Create a maxDepth method: This method takes the root node of the binary tree as input and returns its maximum depth.

3. Check for null root: Check if the root is null. If it is, return 0 as the depth.

4. Perform DFS traversal: Recursively compute the depth of the left and right subtrees. The maximum depth of the binary tree is the maximum depth of its left and right subtrees, plus 1 for the current node.

5. Return the result: After the DFS traversal is complete, return the maximum depth of the binary tree.

Here's the Python implementation:

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

This implementation follows the steps outlined above and efficiently computes the maximum depth of the binary tree in Python using DFS traversal.