A binary search tree that remains balanced to some extent when insertion and deletion is carried out is called a self-balancing binary search tree. To create a balanced version of an unbalanced tree, we use a peculiar operation called rotation. We will discuss rotation in the following section:

Rotation of a binary search tree

This figure shows the rotation operation on nodes A and B. Left rotation on A creates the right image, and right rotation on B creates the left image. To visualize a rotation, first think about pulling out the subtree D. This subtree is somewhere in the middle. Now the nodes are rotated in either the left or right direction. In the case of the left rotation, the right child becomes the parent and the parent becomes the left child of the original child. Once this rotation is done, the D subtree is added to the right child's position of the original parent. The right rotation is exactly the same but in the opposite direction.

How does it...