DPO-simple-strategy

This is a one of tasks at course MI-DPO at Faculty of Information Technology Czech Technical University:
Strategy pattern
Null Object pattern

Strategy pattern is shown on search and printing strategy in the simple binary tree
Context: BinaryTree Strategy: ITreeStrategy Concrete strategy: BFSStrategy, DFSStrategy

Null Object pattern is shown on the class NullNode as a node that represents that there in node
is no other subtree.