Binary Tree

Table of Contents

• 104. Maximum Depth of Binary Tree

104. Maximum Depth of Binary Tree

• LeetCode Link: Maximum Depth of Binary Tree
• Difficulty: Easy
• Topic(s): Binary Tree, Depth-First Search, Breadth-First Search

🧠 Problem Statement

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

🧩 Approach

• DFS (Depth-First Search):
  • Recursively calculate the depth of the left and right subtrees.
  • The maximum depth is 1 + max(depth of left subtree, depth of right subtree).

💡 Solution

def maxDepth(self, root: Optional[TreeNode]) -> int:
    """
    Calculate the maximum depth of a binary tree.

    Args:
        root (Optional[TreeNode]): The root node of the binary tree.

    Returns:
        int: The maximum depth of the binary tree.
    """
    if not root:
        return 0

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

🧮 Complexity Analysis

• Time Complexity: O(n)
• Space Complexity: O(h)