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# 104. Maximum Depth of Binary Tree

## Easy

***

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.

 

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/11/26/tmp-tree.jpg)

```
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`