## Implementation

You should define a custom type 'DNA' with a function 'Counts' that outputs two values: 

- a frequency count for the given DNA strand
- an error (if there are invalid nucleotides)

Which is a good type for a DNA strand ? 

Which is the best Go types to represent the output values ?

Take a look at the test cases to get a hint about what could be the possible inputs.


## note about the tests
You may be wondering about the `cases_test.go` file. We explain it in the
[leap exercise][leap-exercise-readme].

[leap-exercise-readme]: https://github.com/exercism/go/blob/master/exercises/leap/README.md