Maximum Depth of Binary Tree

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.

Class TreeNode:
    val (int)
    left (TreeNode)
    right (TreeNode)

Input Format

First Parameter - TreeNode root

Output Format

Return the number

Example 1:

Input: 
    3 9 20 null null 15 7
Output: 3

Example 2:

Input:
    1 null 2
Output: 2

Constraints:

• The number of nodes in the tree is in the range [0, 10⁴].
• -100 <= Node.val <= 100
• Expected Time Complexity: O(n)
• Expected Space Complexity: O(n)