Maximum Depth of Binary Tree
Given the root of a binary tree, return its maximum depth.
The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.
For an empty tree, the depth is 0.
Example 1
Input
root = [3,9,20,null,null,15,7]
Output
3
Explanation
The longest path is:
3 → 20 → 15
or
3 → 20 → 7
So the maximum depth is 3.
Example 2
Input
root = [1,null,2]
Output
2
Explanation
The longest path is:
1 → 2
Therefore, the maximum depth is 2.
Constraints
Hints:
Hint 1
The depth of a node is:
1 + maximum depth of its left and right subtrees
Hint 2
Use recursion:
maxDepth(root) = 1 + max(maxDepth(root.left), maxDepth(root.right))
Author & Technical Reviewer
Technically reviewed by: ExamAdda Technical Review Team
Technical Reviewers, ExamAdda
Software engineers at ExamAdda who check every article's definitions, complexity claims and code examples before and after publishing.
Published
Aug 11, 2026
Last updated
Aug 12, 2026
Content Verification Methodology
Definitions and complexity claims were checked against authoritative computer-science references. Code examples were compiled and tested with standard, boundary and edge-case inputs.
Expected Output