104.maximum-depth-of-binary-tree.python3.py

#
# [104] Maximum Depth of Binary Tree
#
# https://leetcode.com/problems/maximum-depth-of-binary-tree/description/
#
# algorithms
# Easy (56.70%)
# Total Accepted:    403.3K
# Total Submissions: 700.7K
# Testcase Example:  '[3,9,20,null,null,15,7]'
#
# 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
# 
# return its depth = 3.
# 
#
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def maxDepth(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        def dfs(node):
            if not node:
                return 0
            l = dfs(node.left) + 1
            r = dfs(node.right) + 1

            return max(l, r)
        
        return dfs(root)