armandino: minimise hash collisions + other improvements

[armandino]

Check List:

• [x] Tests pass (./test.sh <username> shows no differences between expected and actual outputs)

• [x] All formatting changes by the build are committed

• [x] Your launch script is named calculate_average_<username>.sh (make sure to match casing of your GH user name) and is executable

• [x] Output matches that of calculate_average_baseline.sh

• [x] For new entries, or after substantial changes: When implementing custom hash structures, please point to where you deal with hash collisions (line number: 243)

• Execution time: 3.4 sec

• Execution time of reference implementation: 2m40s

[gunnarmorling]

00:05.709 now.

[armandino]

@gunnarmorling many thanks :)