Maximum Depth of Binary Tree

def maxDepth(root):
    if not root:
        return 0
    return 1 + max(maxDepth(root.left), maxDepth(root.right))
    
# BFS approach
from collections import deque
def maxDepthBFS(root):
    if not root:
        return 0
    queue = deque([(root, 1)])
    while queue:
        node, depth = queue.popleft()
        if not node:
            continue
        if not node.left and not node.right:
            return depth
        if node.left:
            queue.append((node.left, depth + 1))
        if node.right:
            queue.append((node.right, depth + 1))
    return 0