The strategy design pattern (behavioral design pattern) allows you to change the behavior
of an application that does not violate the open/closed principle (OCP)
By defining a family of algorithms, encapsulate each one, and make them
interchangeable, it makes the algorithm vary independently
from the application that use it.
Example: Build a soccer game that allow a user play with a computer
Steps:
1. Create an IComputerPlayer interface
2. Create 3 classes: EasyComputerPlayer, MediumComputerPlayer and HardComputerPlayer that implement the IComputerPlayer interface
3. Create a SoccerGame class that allow user to play soccer with one of 3 ComputerPlayer level above
4. Create a demo program that uses the SoccerGame class
