Hackerrank exercise answers - my examples/practise for maximising a TDD workflow effectively

###Exercises:

#####python-default-dict - using default dict to efficiently find where words from a list appear in another list, output exact indices of occurrence, one line of indices per word, output -1 if no occurrence for that word

#####python-lists uses a generator and tracks unimplemented cases in test output. Generators: https://www.programiz.com/python-programming/generator#create

#####sock-merchant uses a Counter

Check commit history on this file for showing how I started with this exercise and gradually made it more effient, stepping up to default dict and then counters. Also added pep 8 formatting. A good example of TDD workflow for testing/efficiency.

###WIP python-named-tuples python-numpy