# AVL Trees in Machine Learning

An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, the tree is rebalanced. The AVL tree is named after its two Soviet inventors, Georgy Adelson-Velsky and Evgenii Landis, who published it in their 1962 paper "An algorithm for the organization of information". AVL trees provide O(log n) time complexity for basic operations such as insertion, deletion, and search, making them efficient for use in many types of data structures and algorithms.

## How AVL Tree Works?

AVL trees work by maintaining a balance property between the left and right subtrees of each node. The balance property states that the difference in height between the left and right subtrees of any node should not be more than 1. This is achieved by checking for imbalances when a new node is added to the tree, and then using rotations to rebalance the tree if an imbalance is found.

When a new node is inserted into the AVL tree, it is first added to the tree like in a normal binary search tree. However, after the insertion, the tree is checked for any imbalances. If an imbalance is found, the tree is rebalanced using rotations.

There are two types of rotations used in AVL trees: left rotations and right rotations. A left rotation is performed when the right subtree of a node is heavier than its left subtree. A right rotation is performed when the left subtree of a node is heavier than its right subtree.

A left rotation is performed by making the right child of the imbalanced node the new root of the subtree, and then making the former root the left child of the new root. A right rotation is performed by making the left child of the imbalanced node the new root of the subtree, and then making the former root the right child of the new root.

After the rotation, the tree is still checked for imbalances, if it founds then again it will perform the rotations accordingly.

When a node is deleted, the tree is first searched for the node to be deleted, and then it is removed like in a normal binary search tree. After the removal, the tree is checked for any imbalances and rebalanced using rotations if needed.

By maintaining the balance property, AVL trees ensure that the height of the tree is always logarithmic in the number of nodes, which guarantees an efficient performance for operations such as insertion, deletion, and search.

## AVL Tree Examples

``````class Node:
def __init__(self, key):
self.key = key
self.left = None
self.right = None
self.height = 1

class AVLTree:
def insert(self, root, key):
if not root:
return Node(key)
elif key < root.key:
root.left = self.insert(root.left, key)
else:
root.right = self.insert(root.right, key)

root.height = 1 + max(self.getHeight(root.left), self.getHeight(root.right))
balance = self.getBalance(root)

# Left Left Case
if balance > 1 and key < root.left.key:
return self.rightRotate(root)
# Right Right Case
if balance < -1 and key > root.right.key:
return self.leftRotate(root)
# Left Right Case
if balance > 1 and key > root.left.key:
root.left = self.leftRotate(root.left)
return self.rightRotate(root)
# Right Left Case
if balance < -1 and key < root.right.key:
root.right = self.rightRotate(root.right)
return self.leftRotate(root)

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

if __name__ == '__main__':
avl = AVLTree()
root = None
root = avl.insert(root, 10)
root = avl.insert(root,20)
root = avl.insert(root, 30)
root = avl.insert(root, 40)
root = avl.insert(root, 50)
root = avl.insert(root, 25)

print("Preorder traversal of the constructed AVL tree is")
avl.preOrder(root)``````

## Types of AVL Tree

AVL trees are a type of self-balancing binary search tree. In a self-balancing binary search tree, the height of the tree is guaranteed to be logarithmic in the number of nodes, which ensures efficient performance for operations such as insertion, deletion, and search. The AVL tree is one of the most common types of self-balancing binary search tree, named after its two Soviet inventors, Georgy Adelson-Velsky and Evgenii Landis, who published it in their 1962 paper "An algorithm for the organization of information".

Other types of self-balancing binary search trees include:

• Red-Black Tree: a type of self-balancing binary search tree in which each node has a color attribute, either red or black, to ensure that the tree remains balanced.
• Splay Tree: a type of self-balancing binary search tree in which the most recently accessed element is moved to the root of the tree, ensuring that frequently accessed elements are quick to access.
• B-Tree: a type of self-balancing tree that is often used in file systems and databases to store large amounts of data.

Each type of self-balancing tree has its own unique characteristics and trade-offs, and the choice of which type to use will depend on the specific requirements of the application.

## Application of AVL Tree

AVL trees have a number of applications in computer science and engineering, due to their efficient performance for operations such as insertion, deletion, and search. Some of the common applications of AVL trees include:

1. Data Storage: AVL trees are often used to store large amounts of data in a sorted manner. They are particularly useful when the data is constantly changing, as the self-balancing feature ensures that the tree remains balanced, even with frequent insertions and deletions.

2. Database Indexing: AVL trees are commonly used as indexing structures in databases to quickly search for specific data. The self-balancing feature ensures that the height of the tree remains logarithmic in the number of nodes, which makes searching for data more efficient.

3. File Systems: AVL trees are also used in file systems to store the file hierarchy and metadata. The self-balancing feature ensures that the file system remains efficient even as the number of files and directories changes.

4. Graph Algorithms: AVL trees are also used in graph algorithms such as Dijkstra's shortest path algorithm and Prim's minimum spanning tree algorithm.

5. Network Routing: AVL trees are also used in network routing algorithms, such as distance-vector routing and link-state routing.

6. Scheduling and Resource Allocation: AVL trees are also used in scheduling and resource allocation algorithms to efficiently manage and allocate resources.

## Time and Space Complexity

The time and space complexity of AVL trees depends on the specific operations being performed. Here are the time complexities of the common operations on AVL trees:

1. Insertion: The worst-case time complexity of inserting a new element into an AVL tree is O(log n), where n is the number of nodes in the tree. This is because in the worst case, the height of the tree may become logarithmic in the number of nodes, and each insertion may require up to one rotation.

2. Deletion: The worst-case time complexity of deleting an element from an AVL tree is also O(log n), for the same reasons as insertion.

3. Search: The worst-case time complexity of searching for an element in an AVL tree is also O(log n), as the height of the tree is guaranteed to be logarithmic in the number of nodes.

4. Traversal: The time complexity of traversing an AVL tree is O(n), where n is the number of nodes in the tree, as all nodes must be visited during a traversal.

In terms of space complexity, AVL trees typically use O(n) space to store the nodes in the tree, where n is the number of nodes in the tree.

It's worth noting that AVL trees provide O(log n) time complexity for searching and insertion and deletion in the average case. But in the worst case, the complexity will be O(n).

AVL trees have a number of advantages and disadvantages, depending on the specific use case. Here are some of the main advantages and disadvantages of AVL trees:

1. Self-balancing: One of the main advantages of AVL trees is that they are self-balancing, which ensures that the height of the tree remains logarithmic in the number of nodes. This makes operations such as insertion, deletion, and search more efficient.

2. Efficient Performance: AVL trees provide efficient performance for operations such as insertion, deletion, and search, with time complexities of O(log n) in the average case.

3. Stable: AVL trees are stable data structures, meaning that the order of elements in the tree is maintained even after insertions and deletions.

4. Flexible: AVL trees can be used in a wide range of applications, including data storage, database indexing, file systems, graph algorithms, and more.