(1)_avl-tree.py

# AVL Tree
#
# AVL tree is a self-balancing binary search tree in which each node maintains extra information called a balance factor
# whose value is either -1, 0 or +1. AVL tree got its name after its inventor Georgy Adelson-Velsky and Landis.
#
# Balance Factor:
# Balance factor of a node in an AVL tree is the difference between the height of the left subtree and that of the right subtree of that node.
# Balance Factor = (Height of Left Subtree - Height of Right Subtree) or (Height of Right Subtree - Height of Left Subtree)
# The self-balancing property of an avl tree is maintained by the balance factor. The value of balance factor should always be -1, 0 or +1.
#
# Operations of an AVL tree:
# Left Rotate: In left-rotation, the arrangement of the nodes on the right is transformed into the arrangements on the left node.
# Right Rotate: In left-rotation, the arrangement of the nodes on the left is transformed into the arrangements on the right node.
# Left-Right Rotate: In left-right rotation, the arrangements are first shifted to the left and then to the right.
# Right-Left Rotate: In right-left rotation, the arrangements are first shifted to the right and then to the left.
#
# AVL Tree implementation in Python
# Source:
# AVL Tree
# Programiz.com
# URL: https://www.programiz.com/dsa/avl-tree

import sys

# Create a tree node
class TreeNode(object):
    def __init__(self, key):
        self.key = key
        self.left = None
        self.right = None
        self.height = 1

class AVLTree(object):
    # Function to insert a node
    def insert_node(self, root, key):

        # Find the correct location and insert the node
        if not root:
            return TreeNode(key)
        elif key < root.key:
            root.left = self.insert_node(root.left, key)
        else:
            root.right = self.insert_node(root.right, key)

        root.height = 1 + max(self.getHeight(root.left),
                              self.getHeight(root.right))
        # Update the balance factor and balance the tree
        balanceFactor = self.getBalance(root)
        if balanceFactor > 1:
            if key < root.left.key:
                return self.rightRotate(root)
            else:
                root.left = self.leftRotate(root.left)
                return self.rightRotate(root)

        if balanceFactor < -1:
            if key > root.right.key:
                return self.leftRotate(root)
            else:
                root.right = self.rightRotate(root.right)
                return self.leftRotate(root)

        return root

    # Function to delete a node
    def delete_node(self, root, key):

        # Find the node to be deleted and remove it
        if not root:
            return root
        elif key < root.key:
            root.left = self.delete_node(root.left, key)
        elif key > root.key:
            root.right = self.delete_node(root.right, key)
        else:
            if root.left is None:
                temp = root.right
                root = None
                return temp
            elif root.right is None:
                temp = root.left
                root = None
                return temp
            temp = self.getMinValueNode(root.right)
            root.key = temp.key
            root.right = self.delete_node(root.right,
                                          temp.key)
        if root is None:
            return root

        # Update the balance factor of nodes
        root.height = 1 + max(self.getHeight(root.left),
                              self.getHeight(root.right))

        balanceFactor = self.getBalance(root)

        # Balance the tree
        if balanceFactor > 1:
            if self.getBalance(root.left) >= 0:
                return self.rightRotate(root)
            else:
                root.left = self.leftRotate(root.left)
                return self.rightRotate(root)
        if balanceFactor < -1:
            if self.getBalance(root.right) <= 0:
                return self.leftRotate(root)
            else:
                root.right = self.rightRotate(root.right)
                return self.leftRotate(root)
        return root

    # Function to perform left rotation
    def leftRotate(self, z):
        y = z.right
        T2 = y.left
        y.left = z
        z.right = T2
        z.height = 1 + max(self.getHeight(z.left),
                           self.getHeight(z.right))
        y.height = 1 + max(self.getHeight(y.left),
                           self.getHeight(y.right))
        return y

    # Function to perform right rotation
    def rightRotate(self, z):
        y = z.left
        T3 = y.right
        y.right = z
        z.left = T3
        z.height = 1 + max(self.getHeight(z.left),
                           self.getHeight(z.right))
        y.height = 1 + max(self.getHeight(y.left),
                           self.getHeight(y.right))
        return y

    # Get the height of the node
    def getHeight(self, root):
        if not root:
            return 0
        return root.height

    # Get balance factor of the node
    def getBalance(self, root):
        if not root:
            return 0
        return self.getHeight(root.left) - self.getHeight(root.right)

    def getMinValueNode(self, root):
        if root is None or root.left is None:
            return root
        return self.getMinValueNode(root.left)

    def preOrder(self, root):
        if not root:
            return
        print("{0} ".format(root.key), end="")
        self.preOrder(root.left)
        self.preOrder(root.right)

        # Print the tree

    def printHelper(self, currPtr, indent, last):
        if currPtr != None:
            sys.stdout.write(indent)
            if last:
                sys.stdout.write("R----")
                indent += "     "
            else:
                sys.stdout.write("L----")
                indent += "|    "
            print(currPtr.key)
            self.printHelper(currPtr.left, indent, False)
            self.printHelper(currPtr.right, indent, True)

myTree = AVLTree()
root = None
nums = [33, 13, 52, 9, 21, 61, 8, 11]
for num in nums:
    root = myTree.insert_node(root, num)
myTree.printHelper(root, "", True)
key = 13
root = myTree.delete_node(root, key)
print("After Deletion: ")
myTree.printHelper(root, "", True)