Maximum Depth of Binary Tree

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.

Leetcode Link

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, 10⁴].
• -100 <= Node.val <= 100

Code

Python

class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        def dfs(root, depth):
            if not root: return depth
            return max(dfs(root.left, depth + 1), dfs(root.right, depth + 1))

        return dfs(root, 0)