Description
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.
Examples
Input:
root = [3,9,20,null,null,15,7]Output:
3Explanation:
The tree has depth 3.
Input:
root = [1,null,2]Output:
2Explanation:
The tree has depth 2.
Input:
root = []Output:
0Explanation:
An empty tree has depth 0.
Constraints
- •
The number of nodes in the tree is in the range [0, 10⁴] - •
-100 ≤ Node.val ≤ 100