Retrieved from https://en.wikibooks.org/wiki/Algorithm_Implementation/Strings/Dice's_coefficient#Java
Here's an optimized version of the dice coefficient calculation.
Based on pseudocode at https://en.wikipedia.org/wiki/Most_frequent_k_characters and http://rosettacode.org/wiki/Most_frequent_k_chars_distance
Does not handle digits [0-9] for obvious reasons.