[Leet Code] Maximum Depth Of Binary Tree

Input: root = [3,9,20,null,null,15,7]
Output: 3
Input: root = [1,null,2]
Output: 2
Input: root = []
Output: 0
Input: root = [0]
Output: 1
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution(object):
def maxDepth(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if root:
stack = [root]
elements = [[root.val]]
self.helper(root, stack, elements)
return len(elements)
else:
return 0

def helper(self, root, stack, elements):
while(len(stack) > 0):
length = len(stack)
values = []
for i in range(length):
node = stack.pop(0)
if node.left:
values.append(node.left.val)
stack.append(node.left)
if node.right:
values.append(node.right.val)
stack.append(node.right)
if values != []:
elements.append(values)

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