Implemented partial solution for CodeEval's Play With DNA challenge
https://www.codeeval.com/open_challenges/126/

Went with a Dictionary first because I taught duplicates where not needed.
Then refactored by adding a custom struct to keep track of how often we have seen this substring.

Next iteration I will replace the Dictionary + custom Struct with a regular list.
Replaced Dictionary + custom struct with a List<KeyValuePair<string, int>>
Still only partial success.