radix sort, like counting sort and bucket sort, is an integer based
* algorithm (i.e. the values of the input array are assumed to be
* integers). Hence radix sort is among the fastest sorting algorithms
* around, in theory. The particular distinction for radix sort is that it
* creates a bucket for each cipher (i.e. digit); as such, similar to
* bucket sort, each bucket in radix sort must be a growable list that may
* admit different keys.