leetcode_104_solution_3.py

# Iterative DFS solution using a stack
def maxDepth(self, root: Optional[TreeNode]) -> int:
    if not root:
        return 0
        
    dque = deque([root])
    nodes_at_curr_depth = len(dque)
    depth = 1
    
    while dque:
        node = dque.popleft()
        if node.left:
            dque.append(node.left)
        if node.right:
            dque.append(node.right)
      
        nodes_at_curr_depth -= 1
        if nodes_at_curr_depth == 0: # Visited all for this depth
            depth += 1
            nodes_at_curr_depth = len(dque) # Remaining nodes are at next depth
            
    return depth