Add Binary Search Tree implementation in Python

Python/data_structures/trees/binary_search_tree.py

@@ -0,0 +1,224 @@
+"""
+Binary Search Tree Implementation
+Time Complexity:
+    - Insert: O(log n) average, O(n) worst case
+    - Search: O(log n) average, O(n) worst case
+    - Delete: O(log n) average, O(n) worst case
+Space Complexity: O(n)
+Author: Karanjot Singh
+Date: October 2025
+Hacktoberfest 2025
+"""
+
+class TreeNode:
+    """Node class for Binary Search Tree"""
+    def __init__(self, value):
+        self.value = value
+        self.left = None
+        self.right = None
+
+
+class BinarySearchTree:
+    """Binary Search Tree implementation with common operations"""
+
+    def __init__(self):
+        self.root = None
+
+    def insert(self, value):
+        """
+        Insert a value into the BST
+
+        Args:
+            value: Value to insert
+        """
+        if self.root is None:
+            self.root = TreeNode(value)
+        else:
+            self._insert_recursive(self.root, value)
+
+    def _insert_recursive(self, node, value):
+        """Helper method for recursive insertion"""
+        if value < node.value:
+            if node.left is None:
+                node.left = TreeNode(value)
+            else:
+                self._insert_recursive(node.left, value)
+        else:
+            if node.right is None:
+                node.right = TreeNode(value)
+            else:
+                self._insert_recursive(node.right, value)
+
+    def search(self, value):
+        """
+        Search for a value in the BST
+
+        Args:
+            value: Value to search for
+
+        Returns:
+            True if value exists, False otherwise
+        """
+        return self._search_recursive(self.root, value)
+
+    def _search_recursive(self, node, value):
+        """Helper method for recursive search"""
+        if node is None:
+            return False
+
+        if value == node.value:
+            return True
+        elif value < node.value:
+            return self._search_recursive(node.left, value)
+        else:
+            return self._search_recursive(node.right, value)
+
+    def inorder_traversal(self):
+        """
+        Perform inorder traversal (Left -> Root -> Right)
+        Returns sorted order for BST
+
+        Returns:
+            List of values in inorder
+        """
+        result = []
+        self._inorder_recursive(self.root, result)
+        return result
+
+    def _inorder_recursive(self, node, result):
+        """Helper method for inorder traversal"""
+        if node:
+            self._inorder_recursive(node.left, result)
+            result.append(node.value)
+            self._inorder_recursive(node.right, result)
+
+    def preorder_traversal(self):
+        """
+        Perform preorder traversal (Root -> Left -> Right)
+
+        Returns:
+            List of values in preorder
+        """
+        result = []
+        self._preorder_recursive(self.root, result)
+        return result
+
+    def _preorder_recursive(self, node, result):
+        """Helper method for preorder traversal"""
+        if node:
+            result.append(node.value)
+            self._preorder_recursive(node.left, result)
+            self._preorder_recursive(node.right, result)
+
+    def postorder_traversal(self):
+        """
+        Perform postorder traversal (Left -> Right -> Root)
+
+        Returns:
+            List of values in postorder
+        """
+        result = []
+        self._postorder_recursive(self.root, result)
+        return result
+
+    def _postorder_recursive(self, node, result):
+        """Helper method for postorder traversal"""
+        if node:
+            self._postorder_recursive(node.left, result)
+            self._postorder_recursive(node.right, result)
+            result.append(node.value)
+
+    def find_min(self):
+        """
+        Find minimum value in BST
+
+        Returns:
+            Minimum value or None if tree is empty
+        """
+        if self.root is None:
+            return None
+
+        current = self.root
+        while current.left:
+            current = current.left
+        return current.value
+
+    def find_max(self):
+        """
+        Find maximum value in BST
+
+        Returns:
+            Maximum value or None if tree is empty
+        """
+        if self.root is None:
+            return None
+
+        current = self.root
+        while current.right:
+            current = current.right
+        return current.value
+
+    def height(self):
+        """
+        Calculate height of the tree
+
+        Returns:
+            Height of tree (0 for single node, -1 for empty tree)
+        """
+        return self._height_recursive(self.root)
+
+    def _height_recursive(self, node):
+        """Helper method to calculate height"""
+        if node is None:
+            return -1
+
+        left_height = self._height_recursive(node.left)
+        right_height = self._height_recursive(node.right)
+
+        return 1 + max(left_height, right_height)
+
+
+# Test cases
+if __name__ == "__main__":
+    print("=== Binary Search Tree Implementation ===\n")
+
+    # Create BST and insert values
+    bst = BinarySearchTree()
+    values = [50, 30, 70, 20, 40, 60, 80]
+
+    print(f"Inserting values: {values}")
+    for val in values:
+        bst.insert(val)
+
+    # Test traversals
+    print(f"\nInorder traversal (sorted): {bst.inorder_traversal()}")
+    print(f"Preorder traversal: {bst.preorder_traversal()}")
+    print(f"Postorder traversal: {bst.postorder_traversal()}")
+
+    # Test search
+    print("\n--- Search Operations ---")
+    search_values = [40, 25, 80, 100]
+    for val in search_values:
+        found = bst.search(val)
+        print(f"Search for {val}: {'Found' if found else 'Not found'}")
+
+    # Test min/max
+    print("\n--- Min/Max Operations ---")
+    print(f"Minimum value: {bst.find_min()}")
+    print(f"Maximum value: {bst.find_max()}")
+
+    # Test height
+    print(f"\nTree height: {bst.height()}")
+
+    # Test with another tree
+    print("\n--- Another BST Example ---")
+    bst2 = BinarySearchTree()
+    values2 = [15, 10, 20, 8, 12, 17, 25]
+    print(f"Inserting values: {values2}")
+    for val in values2:
+        bst2.insert(val)
+
+    print(f"Inorder traversal: {bst2.inorder_traversal()}")
+    print(f"Tree height: {bst2.height()}")
+
+    print("\n✅ All test cases completed!")