What Is AB Tree in Data Structure?


Scott Campbell

Data structures are an essential aspect of computer science and programming. One commonly used data structure is the AB tree. In this article, we will explore what an AB tree is, its properties, and how it is used in practice.

What is an AB Tree?

An AB tree is a self-balancing variant of a binary search tree (BST). It is named after its two main properties: the A property and the B property.

The A property states that every node in the tree must have at most A children. The B property states that all non-leaf nodes (except for the root) must have at least B/2 children.

The AB tree maintains these properties to ensure that the height of the tree remains balanced, which provides efficient search, insertion, and deletion operations. By balancing the tree, we can achieve a logarithmic time complexity for these operations.

Properties of an AB Tree

  • Root Property: The root node can have between 1 and A children.
  • Internal Node Property: Any internal node can have between B/2 and A children.
  • Leaf Node Property: All leaf nodes are at the same level.

These properties ensure that an AB tree remains balanced even after performing various operations on it.

Insertion in AB Tree

When inserting a new element into an AB tree, we follow these steps:

  1. If the root is full (A children), create a new root with a single child (the original root).
  2. If the current node is full, split it into two nodes and promote the median element to its parent.
  3. Recursively insert the new element into the appropriate child of the current node.

By splitting nodes and promoting elements, the AB tree ensures that it remains balanced.

Deletion in AB Tree

Deleting an element from an AB tree is a bit more complex than insertion. Here are the steps to follow:

  1. If the element is found in a leaf node, simply remove it.
  2. If the element is found in an internal node, replace it with its predecessor or successor (based on our preference).
  3. If removing the predecessor or successor causes a violation of the B property, perform rotation or merging operations to rebalance the tree.

These steps guarantee that after deletion, the AB tree retains its balanced structure.


AB trees are a self-balancing variant of binary search trees. By maintaining specific properties, they ensure that search, insertion, and deletion operations have logarithmic time complexity. Understanding AB trees and their properties is essential for creating efficient and optimized data structures in computer science.

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