AVL Tree Building Example

If the balance factor of each node in the tree is 0 then it is called a perfectly balanced tree.
As we keep inserting nodes, we eventually reach a point like this.

We need to perform a rotation.

Cases for Rotation

There are 4 cases of violation: 1. An assertion into the left subtree of the left child of alpha. 2. An assertion into the right subtree of the right child of alpha. 3. An assertion into the left subtree of the right child of alpha. 4. An assertion into the left subtree of the right child of alpha.

For case 1 and 2, the single rotation is enough to balance the tree but for other cases, it is not.