Word Count Engine sorting not stable

[domfarolino]

I believe your implementation of Word Count Engine may have some errors. With an input string like "z y x o n m d c b a", your solution does not always maintain the relative order in which words with the same occurrence. While Collections.sort does guarantee a stable sort, iterating over the keys in a HashMap is not guaranteed to give you keys in insertion order, and in fact no guarantee is made on the order of key retrieval here.