Implementation of tree types - Week 7

Last week, I have been working on the implementation of HollowBallBound. This class represents the area included between two concentric ball bounds. The radius of the inner ball may be equal to 0.

The HollowBallBound class is intended to replace the original piece-wise ball bound of the vantage point tree. This bound allows to calculate the minimum distance to a point much faster than the original bound. One of the disadvantages is the loss the crucial property of the binary space tree: the use of HollowBallBound may lead to overlapping children.

Since the vantage point tree is slightly different from the binary space tree, namely each intermediate node contains a point, I had to move the vantage point tree to a separate class. Unfortunately, that led to the duplication of the code.

Moreover, I added some tests for the vantage point tree.