In this exercise you will take a very simple data structure and make it generic.
It uses a
std::collections::HashMap
to keep track of which values have been seen and how many times each one has
appeared.
The initial version of Counter is hard coded to only work for u32 values.
Make the struct and its methods generic over the type of value being tracked,
that way Counter can track any type of value.
If you finish early, try using the
entry
method to halve the number of hash lookups required to implement the count
method.