What Is a AVL Tree in Data Structure?

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Heather Bennett

An AVL tree is a self-balancing binary search tree in data structure. It was named after its inventors, Adelson-Velsky and Landis. AVL trees are designed to maintain their balance by automatically adjusting the heights of their subtrees.

What is a Binary Search Tree?

A binary search tree (BST) is a type of data structure that organizes elements in a hierarchical manner. Each node in a BST has at most two children, referred to as the left child and the right child. The key value of each node in a BST is greater than all the key values in its left subtree and less than all the key values in its right subtree.

Why Use AVL Trees?

While binary search trees provide efficient operations like insertion, deletion, and searching with an average time complexity of O(log n), they may become unbalanced over time. An unbalanced BST can lead to inefficient operations with a worst-case time complexity of O(n).

This is where AVL trees come into play.

They ensure that the height difference between the left and right subtrees of any node is at most 1, making them self-balancing. As a result, AVL trees guarantee efficient operations with a worst-case time complexity of O(log n).

How AVL Trees Maintain Balance

To maintain balance, AVL trees use rotation operations. A rotation operation shifts nodes around within the tree without changing their relative order or violating any BST properties.

There are four rotations commonly used in AVL trees:

• Left-Left (LL) Rotation: This rotation occurs when there is an imbalance in the left subtree of the left child of a node.
• Right-Right (RR) Rotation: This rotation occurs when there is an imbalance in the right subtree of the right child of a node.
• Left-Right (LR) Rotation: This rotation occurs when there is an imbalance in the left subtree of the right child of a node.
• Right-Left (RL) Rotation: This rotation occurs when there is an imbalance in the right subtree of the left child of a node.

By performing these rotations whenever necessary, AVL trees ensure that the height difference between the left and right subtrees does not exceed 1. This guarantees balanced trees and efficient operations.

The advantages of AVL trees include:

• Efficient Operations: AVL trees provide efficient insertion, deletion, and searching operations with a worst-case time complexity of O(log n).
• Balanced Structure: The self-balancing property ensures that the tree remains balanced, preventing worst-case scenarios.

The disadvantages of AVL trees include:

• Overhead: Maintaining balance requires additional overhead in terms of memory and computational cost compared to regular binary search trees.
• Complexity: The rotation operations can be complex to implement correctly, making AVL trees more challenging to code than regular binary search trees.

In Conclusion

An AVL tree is a self-balancing binary search tree that ensures efficiency by maintaining balance through rotation operations. It provides efficient insertion, deletion, and searching operations with a worst-case time complexity of O(log n). While it has some disadvantages in terms of overhead and complexity, AVL trees are a powerful data structure for applications that require guaranteed balance and efficient operations.