Write a function numempty returns returns the number of empty branches in a tree. Function should count the total number of empty branches among the nodes of the tree. A leaf node has two empty branches. In the case, if root is None, it considered as a 1 empty branch For example: the following tree has 10 empty branch  is empty branch 9         6            12                3     8       10      15                           7                18                                                 emptybranch  10 The tree is created for testing: 9        6         12             3     8   10      15                7                18 numempty  10
import unittest
from bst import Node
from bst import bst

def num_empty(root):
    if root is None:
        return 1
    elif root.left is None and root.right:
        return 1 + num_empty(root.right)
    elif root.right is None and root.left:
        return 1 + num_empty(root.left)
    else:
        return num_empty(root.left) + num_empty(root.right)

"""
    The tree is created for testing:

                    9
                 /      \
               6         12
              / \       /   \
            3     8   10      15
                 /              \
                7                18

    num_empty = 10

"""

class TestSuite(unittest.TestCase):
    def setUp(self):
        self.tree = bst()
        self.tree.insert(9)
        self.tree.insert(6)
        self.tree.insert(12)
        self.tree.insert(3)
        self.tree.insert(8)
        self.tree.insert(10)
        self.tree.insert(15)
        self.tree.insert(7)
        self.tree.insert(18)

    def test_num_empty(self):
        self.assertEqual(10, num_empty(self.tree.root))

if __name__ == '__main__':
    unittest.main()
