* add CombinationSum and test
* Format array and list literals in CombinationSumTest
* Fix sorting comparator in CombinationSumTest
* Refactor CombinationSum for better handling and clarity
Updated combinationSum method to handle null or empty candidates and improved variable naming for clarity.
* Fix sorting comparator in CombinationSumTest
* Update CombinationSumTest.java
* Fix sorting comparator for list of integers
* Fix formatting issues in CombinationSum class
* Change CombinationSum class to final
* Refactor norm method to accept Iterable instead of List
* Remove unnecessary whitespace in CombinationSumTest
