104 - Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

class Solution:
    def maxDepth(self, root):
        return 1 + max(self.maxDepth(root.right), self.maxDepth(root.left)) if root else 0