adding count complete nodes

src/my_project/interviews/top_150_questions_round_11/count_complete_three_nodes.py

@@ -0,0 +1,17 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+
+class Solution:
+    def countNodes(self, root: Optional[TreeNode]) -> int:
+
+        if not root:
+            return 0
+        else: 
+            return self.countNodes(root.left) + self.countNodes(root.right) + 1

tests/test_150_questions_round_11/test_count_complete_three_nodes_round_11.py

@@ -0,0 +1,20 @@
+import unittest
+from src.my_project.interviews.top_150_questions_round_11\
+.count_complete_three_nodes import TreeNode, Solution
+
+class CountNodesTestCase(unittest.TestCase):
+
+    def test_count_none(self):
+        solution = Solution()
+        tree = None 
+        output = solution.countNodes(root=tree)
+        self.assertEqual(0, output)
+
+
+    def test_count_non_empty_tree(self):
+        solution = Solution()
+        tree = TreeNode(1, TreeNode(2), TreeNode(3))
+        output = solution.countNodes(root=tree)
+        self.assertEqual(3, output)
+
+