In the previous article we’ve reviewed Randomized Binary Search Trees. Today we are going to review the implementation of AVL Trees. They must be the first type of Balanced Binary Search Trees. They were invented by two Soviet inventors, G. M. Adelson-Velskii and E. M. Landis in 1962. There are plenty of AVL trees implementations, but, to my mind, none of them is good enough when you try to make sense of it all from scratch.