# LC 104. Maximum Depth of Binary Tree

### [Problem link](https://leetcode.com/problems/maximum-depth-of-binary-tree/)

###### tags: `leedcode` `easy` `python` `c++` `Binary Tree`

Given the <code>root</code> 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:**
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/26/tmp-tree.jpg" style="width: 400px; height: 277px;" />

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 <code>[0, 10⁴]</code>.
- <code>-100 <= Node.val <= 100</code>

## Solution 1
#### Python

class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        if not root:
            return 0
        return 1 + max(self.maxDepth(root.left), self.maxDepth(root.right))

#### C++

/**
 * 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 == nullptr) {
            return 0;
        }
        int leftLevel = maxDepth(root->left);
        int rightLevel = maxDepth(root->right);
        return max(leftLevel, rightLevel) + 1;
    }
};

>### Complexity
>n = The number of nodes in the tree
>| | Time Complexity | Space Complexity |
>| ----------- | --------------- | ---------------- |
>| Solution 1 | O(n) | O(n) |

## Note
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