# 104. 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.

### Thoughts

* As with a lot of tree algorithms I think the best solution here is to use a recursive algorithm to count while traversing down the tree
    

### Solution

```java
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) return 0;
        
        return Math.max(maxDepth(root.left) + 1, maxDepth(root.right) + 1);
    }
}
```

**Time Complexity:** O(n)  
**Space Complexity:** O(1)

### Conclusion

Wow. This was much easier than I was thinking it would be lmao. I forgot just how easy this was. Still good review and gets me in a tree-thinking mindset.