```
"""
count_nucleotides(s::AbstractString)
Given: A DNA string s
of length at most 1000 nt.
Return: Four integers (separated by spaces) counting the respective number of times that the symbols 'A', 'C', 'G', and 'T' occur in s
"""
function count_nucleotides(s::AbstractString)
return join(map(y -> count(x -> x == y, s), ['A', 'C', 'G', 'T']), " ")
end
```