104_Maximum_Depth_of_Binary_Tree.py

"""
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
 

Constraints:

The number of nodes in the tree is in the range [0, 104].
-100 <= Node.val <= 100

"""

# 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:
        if root is None:
            return 0
            
        elementQueue = deque()
        elementQueue.append(root)
        numberOfLevels = 0

        while True:
            nodeCountAtLevel = len(elementQueue)

            if nodeCountAtLevel == 0:
                return numberOfLevels
            
            while nodeCountAtLevel > 0:
                element = elementQueue.popleft()
                if element.left is not None:
                    elementQueue.append(element.left)
                if element.right is not None:
                    elementQueue.append(element.right)
                nodeCountAtLevel -= 1
            numberOfLevels += 1