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 longest path is root(3) -> right(20) -> left(15) or right(7), counting 3 nodes. The left subtree with just node 9 has depth 2, so the maximum is 3.
Input:
root = [1,null,2]Output:
2Explanation:
The tree has root node 1 with only a right child 2. The longest path is root(1) -> right(2), which is 2 nodes deep.
Input:
root = []Output:
0Explanation:
With no nodes in the tree (null root), there is no path to any leaf. By definition, the maximum depth of an empty tree is 0.
Constraints
- •
The number of nodes in the tree is in the range [0, 10⁴] - •
-100 ≤ Node.val ≤ 100