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# Maximum Depth of Binary Tree

## [Maximum Depth of Binary Tree](https://leetcode.com/problems/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.

**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
```

**Example 3:**

```

Input: root = []
Output: 0
```

**Example 4:**

```

Input: root = [0]
Output: 1
```

**Constraints:**

* The number of nodes in the tree is in the range `[0, 104]`.
* `-100 <= Node.val <= 100`

## Solutions

### 🧠 Cpp

```cpp
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root)
    {        
        if(!root)
            return 0;
        return 1 + max(maxDepth(root->left), maxDepth(root->right));
    }
};
```