(Easy) 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:

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

Output: 3

 

Example 2:

Input: root = [1,null,2]

Output: 2

 

풀이

if not root:

return 0

 

left = self.maxDepth(root.left)

right = self.maxDepth(root.right)

 

return max(left, right) + 1