Maximum Depth of Binary Tree

Easy

Given the root of a binary tree, return its maximum depth — the number of nodes along the longest path from the root down to the farthest leaf. Trees are given in level order with null for missing children.

Example 1

Input:  root = [3,9,20,null,null,15,7]
Output: 3

Example 2

Input:  root = [1,null,2]
Output: 2

Constraints

• 0 <= number of nodes <= 10^4
• -100 <= Node.val <= 100