0104-maximum-depth-of-binary-tree.py

# 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
from collections import deque
class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        if root is None:
            return 0
        
        queue = deque([root])
        depth = 0
        
        while queue:
            depth += 1
            for _ in range(len(queue)):
                cur = queue.popleft()
                if cur.left is not None:
                    queue.append(cur.left)
                if cur.right is not None:
                    queue.append(cur.right)
        
        return depth