This is a Python program to find the number of nodes in a binary tree.

The program creates a binary tree and counts the number of nodes in the tree.

1. Create a class BinaryTree with instance variables key, left and right.

2. Define methods set_root, insert_left, insert_right, inorder and search.

3. The method set_root takes a key as argument and sets the variable key equal to it.

4. The methods insert_left and insert_right insert a node as the left and right child respectively.

5. The method inorder displays the inorder traversal.

6. The method search returns a node with a specified key.

7. Define the function count_nodes which takes a binary tree as argument.

8. The recursive function count_nodes returns the number of nodes in the binary tree.

Here is the source code of a Python program to count the number of nodes in a binary tree. The program output is shown below.

class BinaryTree: def __init__(self, key=None): self.key = key self.left = None self.right = None def set_root(self, key): self.key = key def inorder(self): if self.left is not None: self.left.inorder() print(self.key, end=' ') if self.right is not None: self.right.inorder() def insert_left(self, new_node): self.left = new_node def insert_right(self, new_node): self.right = new_node def search(self, key): if self.key == key: return self if self.left is not None: temp = self.left.search(key) if temp is not None: return temp if self.right is not None: temp = self.right.search(key) return temp return None def count_nodes(node): if node is None: return 0 return 1 + count_nodes(node.left) + count_nodes(node.right) btree = None print('Menu (this assumes no duplicate keys)') print('insert <data> at root') print('insert <data> left of <data>') print('insert <data> right of <data>') print('count') print('quit') while True: print('inorder traversal of binary tree: ', end='') if btree is not None: btree.inorder() print() do = input('What would you like to do? ').split() operation = do[0].strip().lower() if operation == 'insert': data = int(do[1]) new_node = BinaryTree(data) suboperation = do[2].strip().lower() if suboperation == 'at': btree = new_node else: position = do[4].strip().lower() key = int(position) ref_node = None if btree is not None: ref_node = btree.search(key) if ref_node is None: print('No such key.') continue if suboperation == 'left': ref_node.insert_left(new_node) elif suboperation == 'right': ref_node.insert_right(new_node) elif operation == 'count': print('Number of nodes in tree: {}'.format(count_nodes(btree))) elif operation == 'quit': break

1. A variable is created to store the binary tree.

2. The user is presented with a menu to perform operations on the tree.

3. The corresponding methods are called to perform each operation.

4. The function count_nodes is called to count the number of nodes in the binary tree.

Case 1: Menu (this assumes no duplicate keys) insert <data> at root insert <data> left of <data> insert <data> right of <data> count quit inorder traversal of binary tree: What would you like to do? insert 1 at root inorder traversal of binary tree: 1 What would you like to do? insert 2 left of 1 inorder traversal of binary tree: 2 1 What would you like to do? insert 3 right of 1 inorder traversal of binary tree: 2 1 3 What would you like to do? insert 4 right of 2 inorder traversal of binary tree: 2 4 1 3 What would you like to do? count Number of nodes in tree: 4 inorder traversal of binary tree: 2 4 1 3 What would you like to do? quit Case 2: Menu (this assumes no duplicate keys) insert <data> at root insert <data> left of <data> insert <data> right of <data> count quit inorder traversal of binary tree: What would you like to do? count Number of nodes in tree: 0 inorder traversal of binary tree: What would you like to do? insert 1 at root inorder traversal of binary tree: 1 What would you like to do? count Number of nodes in tree: 1 inorder traversal of binary tree: 1 What would you like to do? insert 2 right of 1 inorder traversal of binary tree: 1 2 What would you like to do? count Number of nodes in tree: 2 inorder traversal of binary tree: 1 2 What would you like to do? quit

**Sanfoundry Global Education & Learning Series – Python Programs.**

To practice all Python programs, __here is complete set of 150+ Python Problems and Solutions__.

**Next Steps:**

- Get Free Certificate of Merit in Python Programming
- Participate in Python Programming Certification Contest
- Become a Top Ranker in Python Programming
- Take Python Programming Tests
- Chapterwise Practice Tests: Chapter 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
- Chapterwise Mock Tests: Chapter 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

**Related Posts:**

- Apply for Python Internship
- Buy Information Technology Books
- Practice Programming MCQs
- Buy Python Books
- Apply for Programming Internship