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# What is an AVL tree? How is it different from a binary search tree?

Ravi

Apr 25, 2023

Data structures are an essential aspect of computer science, and one such structure is a tree. A tree is a hierarchical structure that is widely used in computer science and programming. One type of tree is the binary search tree (BST), which is commonly used to store and retrieve data in a sorted manner. However, there are limitations to the BST, such as inefficient retrieval and insertion of data when the tree is unbalanced. This is where the AVL tree comes into play.

## Binary Search Tree (BST)

### Limitations of BST

The binary search tree has a few limitations. When the tree is unbalanced, the retrieval and insertion of data become inefficient. Unbalanced trees can occur when the tree is skewed to the left or right, causing one side of the tree to have more nodes than the other side. The unbalanced tree can lead to a significant reduction in the performance of the search algorithm. Hence, there is a need for a self-balancing tree data structure, which is where the AVL tree comes in.

## AVL Tree

An AVL tree is a self-balancing binary search tree that maintains the height balance of the tree. The tree is named after its inventors Adelson-Velsky and Landis, who created the tree in 1962. The AVL tree is designed to keep the height difference between the left and right subtrees to a minimum of one. The height of a node is defined as the length of the longest path from the node to the leaf node.

### Balancing the AVL Tree

Whenever an insertion or deletion is performed in the AVL tree, the tree is rebalanced to maintain the height balance. The balancing of the tree is performed by checking the balance factor of each node. The balance factor is the difference between the height of the left subtree and the height of the right subtree. If the balance factor is greater than one or less than negative one, the tree is unbalanced, and a rotation operation is performed to rebalance the tree.

### Types of Rotations

There are two types of rotation operations in AVL trees: left rotation and right rotation. In a left rotation, the right child of the unbalanced node becomes the new root, and the original root becomes the left child of the new root. In a right rotation, the left child of the unbalanced node becomes the new root, and the original root becomes the right child of the new root. The rotation operation ensures that the height balance of the tree is maintained.

## Differences between AVL Tree and Binary Search Tree

### Self-Balancing

The AVL tree is a self-balancing tree that automatically balances itself whenever a new node is inserted or deleted. In contrast, the binary search tree is not self-balancing and can become unbalanced when nodes are inserted or deleted.

### Height-Balanced

The AVL tree is height-balanced, which means that the height of the tree is kept at a minimum. In contrast, the binary search tree is not height-balanced, and the height can become arbitrarily large.

The AVL tree has a few advantages over the binary search tree. The AVL tree's self-balancing mechanism ensures that the tree is always balanced, which results in faster search, insertion, and deletion operations. The height-balanced nature of the AVL tree ensures that the height of the tree is kept to a minimum, which results in a reduction of memory usage. The AVL tree is widely used in databases, file systems, and computer graphics.

## Conclusion

In conclusion, the AVL tree is a self-balancing binary search tree that maintains the height balance of the tree. The tree's self-balancing mechanism ensures that the tree is always balanced, resulting in faster search, insertion, and deletion operations. The height-balanced nature of the AVL tree ensures that the height of the tree is kept to a minimum, which results in a reduction of memory usage. The AVL tree is widely used in databases, file systems, and computer graphics.

Q: What is the difference between AVL tree and red-black tree?

A: Both AVL tree and red-black tree are self-balancing binary search trees, but the AVL tree maintains the height balance of the tree by ensuring that the height difference between the left and right subtrees is at most one, while the red-black tree ensures that the tree is balanced by maintaining a balance of black nodes on each path from the root node to the leaf nodes.

Q: What is the worst-case time complexity of AVL tree?

A: The worst-case time complexity of AVL tree for search, insertion, and deletion operations is O(log n), where n is the number of nodes in the tree.

Q: Can an AVL tree be unbalanced?

A: No, an AVL tree cannot be unbalanced because the tree's self-balancing mechanism ensures that the tree is always balanced.

Q: What is the difference between AVL tree and B-tree?

A: AVL tree is a self-balancing binary search tree, while B-tree is a self-balancing tree data structure that is designed to reduce the number of disk accesses required to search for a key in a database or file system. B-tree is used in databases and file systems to store large amounts of data efficiently.

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