# 104. Maximum Depth of Binary Tree

# Submission

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:**

**Input:** root = [3,9,20,null,null,15,7] **Output:** 3

**Example 2:**

**Input:** root = [1,null,2] **Output:** 2

# Solution

```
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def maxDepth(self, root: Optional[TreeNode]) -> int:
# It's easier to use our own function so we can avoid self.
# cleaner too
def calculate(root):
# Basecase always first in recursive algos
if root == None:
return 0
# calculate left then right, order doesn't matter but this is a DFS search which is something we can say in an interview to sound smarter
left = calculate(root.left)
right = calculate(root.right)
# add + 1 to the depth as we've gone down a level
# we only care about the max, so calculate the max of both subtrees
return 1 + max(left, right)
return calculate(root)
```