Write a method called countUnique that accepts a list of integers as a parameter and returns the number of unique integer values in the list. Use a set as auxiliary storage to help you solve this problem. For example, if a list contains the values {3, 7, 3, -1, 2, 3, 7, 2, 15, 15}, your method should return 5. The empty list contains 0 unique values.

java