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# Nucleotide Count
Each of us inherits from our biological parents a set of chemical
instructions known as DNA that influence how our bodies are constructed.
All known life depends on DNA!
> Note: You do not need to understand anything about nucleotides or DNA
> to complete this exercise.
DNA is a long chain of other chemicals and the most important are the
four nucleotides, adenine, cytosine, guanine and thymine. A single DNA
chain can contain billions of these four nucleotides and the order in
which they occur is important! We call the order of these nucleotides in
a bit of DNA a "DNA sequence".
We represent a DNA sequence as an ordered collection of these four
nucleotides and a common way to do that is with a string of characters
such as "ATTACG" for a DNA sequence of 6 nucleotides. 'A' for adenine,
'C' for cytosine, 'G' for guanine, and 'T' for thymine.
Given a string representing a DNA sequence, count how many of each
nucleotide is present. If the string contains characters that aren't A,
C, G, or T then it is invalid and you should signal an error.
For example:
```
"GATTACA" -> 'A': 3, 'C': 1, 'G': 1, 'T': 2
"INVALID" -> error
```
## Rust Installation
Refer to the [exercism help page][help-page] for Rust installation and learning
resources.
## Writing the Code
Execute the tests with:
```bash
$ cargo test
```
All but the first test have been ignored. After you get the first test to
pass, open the tests source file which is located in the `tests` directory
and remove the `#[ignore]` flag from the next test and get the tests to pass
again. Each separate test is a function with `#[test]` flag above it.
Continue, until you pass every test.
If you wish to run all ignored tests without editing the tests source file, use:
```bash
$ cargo test -- --ignored
```
To run a specific test, for example `some_test`, you can use:
```bash
$ cargo test some_test
```
If the specific test is ignored use:
```bash
$ cargo test some_test -- --ignored
```
To learn more about Rust tests refer to the [online test documentation][rust-tests]
Make sure to read the [Modules][modules] chapter if you
haven't already, it will help you with organizing your files.
## Further improvements
After you have solved the exercise, please consider using the additional utilities, described in the [installation guide](https://exercism.io/tracks/rust/installation), to further refine your final solution.
To format your solution, inside the solution directory use
```bash
cargo fmt
```
To see, if your solution contains some common ineffective use cases, inside the solution directory use
```bash
cargo clippy --all-targets
```
## Submitting the solution
Generally you should submit all files in which you implemented your solution (`src/lib.rs` in most cases). If you are using any external crates, please consider submitting the `Cargo.toml` file. This will make the review process faster and clearer.
## Feedback, Issues, Pull Requests
The [exercism/rust](https://github.com/exercism/rust) repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!
If you want to know more about Exercism, take a look at the [contribution guide](https://github.com/exercism/docs/blob/master/contributing-to-language-tracks/README.md).
[help-page]: https://exercism.io/tracks/rust/learning
[modules]: https://doc.rust-lang.org/book/ch07-02-defining-modules-to-control-scope-and-privacy.html
[cargo]: https://doc.rust-lang.org/book/ch14-00-more-about-cargo.html
[rust-tests]: https://doc.rust-lang.org/book/ch11-02-running-tests.html
## Source
The Calculating DNA Nucleotides_problem at Rosalind [http://rosalind.info/problems/dna/](http://rosalind.info/problems/dna/)
## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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