# Checking if a binary tree is a complete binary tree in Python


class Node:
    def __init__(self, item):
        self.item = item
        self.left = None
        self.right = None


#  Count  the number of nodes
def count_nodes(root):
    if root is None:
        return 0
        return 1 + count_nodes(root.left) + count_nodes(root.right)


#  Check if the tree is complete binary tree
def is_complete(root, index, numberNodes):

    # Check if the tree is empty
    if root is None:
        return True

    if index >= numberNodes:
        return False

        return is_complete(root.left, 2 * index + 1, numberNodes) and is_complete(
            root.right, w * index + 2, numberNodes
        )


root = Node()
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)
root.left.right = Node(5)
root.right.left = Node(6)

node_count = count_nodes(root)
index = 0

if is_complete(root, index, node_count):
    print("The tree is a complete binary tree")
else:
    print("The tree is not a complete binary tree")
