Python Program to Sort using a Binary Search Tree

This is a Python program to sort using a binary search tree.

Problem Description

The program sorts a list using a binary search tree.

Problem Solution

1. Create a class BSTNode with instance variables key, left, right and parent.
2. Define methods insert and inorder in BSTNode.
3. The method insert takes a node as argument and inserts that node in the BST with the BSTNode object as root.
4. The method inorder displays the inorder traversal of the BST with the BSTNode object as root.
5. Create a class BSTree with instance variable root.
6. Define methods inorder and add in BSTree.
7. The method inorder calls the inorder method of the root node.
8. The method add takes a key as argument and adds a node with that key by calling the insert method of the root node.

Program/Source Code

Here is the source code of a Python program to sort a list using a binary search tree. The program output is shown below.

class BSTNode:
    def __init__(self, key):
        self.key = key
        self.left = None
        self.right = None
        self.parent = None
 
    def insert(self, node):
        if self.key > node.key:
            if self.left is None:
                self.left = node
                node.parent = self
            else:
                self.left.insert(node)
        elif self.key <= node.key:
            if self.right is None:
                self.right = node
                node.parent = self
            else:
                self.right.insert(node)
 
    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()
 
 
class BSTree:
    def __init__(self):
        self.root = None
 
    def inorder(self):
        if self.root is not None:
            self.root.inorder()
 
    def add(self, key):
        new_node = BSTNode(key)
        if self.root is None:
            self.root = new_node
        else:
            self.root.insert(new_node)
 
 
bstree = BSTree()
 
alist = input('Enter the list of numbers: ').split()
alist = [int(x) for x in alist]
for x in alist:
    bstree.add(x)
print('Sorted list: ', end='')
bstree.inorder()
Program Explanation

1. The user is prompted to enter a list of numbers.
2. Each element in the list is added to the binary search tree.
3. The inorder traversal of the binary search tree is displayed.

advertisement
Runtime Test Cases
Case 1:
Enter the list of numbers: 4 2 3 4 5 6 1 7 9 10 3
Sorted list: 1 2 3 3 4 4 5 6 7 9 10 
 
Case 2:
Enter the list of numbers: 6 5 4 3 2 1
Sorted list: 1 2 3 4 5 6 
 
Case 3:
Enter the list of numbers: 5
Sorted list: 5

Sanfoundry Global Education & Learning Series – 1000 Python Programs.

If you wish to look at all Python Programming examples, go to 1000 Python Programs.

🔥 Enroll Now for Free Python Certification - December 2025

advertisement
Subscribe to our Newsletters (Subject-wise). Participate in the Sanfoundry Certification to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

Youtube | Telegram | LinkedIn | Instagram | Facebook | Twitter | Pinterest
Manish Bhojasia - Founder & CTO at Sanfoundry
I’m Manish - Founder and CTO at Sanfoundry. I’ve been working in tech for over 25 years, with deep focus on Linux kernel, SAN technologies, Advanced C, Full Stack and Scalable website designs.

You can connect with me on LinkedIn, watch my Youtube Masterclasses, or join my Telegram tech discussions.

If you’re in your 20s–40s and exploring new directions in your career, I also offer mentoring. Learn more here.