# Circular Buffer

A circular buffer, cyclic buffer or ring buffer is a data structure that
uses a single, fixed-size buffer as if it were connected end-to-end.

A circular buffer first starts empty and of some predefined length. For
example, this is a 7-element buffer:

    [ ][ ][ ][ ][ ][ ][ ]

Assume that a 1 is written into the middle of the buffer (exact starting
location does not matter in a circular buffer):

    [ ][ ][ ][1][ ][ ][ ]

Then assume that two more elements are added — 2 & 3 — which get
appended after the 1:

    [ ][ ][ ][1][2][3][ ]

If two elements are then removed from the buffer, the oldest values
inside the buffer are removed. The two elements removed, in this case,
are 1 & 2, leaving the buffer with just a 3:

    [ ][ ][ ][ ][ ][3][ ]

If the buffer has 7 elements then it is completely full:

    [6][7][8][9][3][4][5]

When the buffer is full an error will be raised, alerting the client
that further writes are blocked until a slot becomes free.

When the buffer is full, the client can opt to overwrite the oldest
data with a forced write. In this case, two more elements — A & B —
are added and they overwrite the 3 & 4:

    [6][7][8][9][A][B][5]

3 & 4 have been replaced by A & B making 5 now the oldest data in the
buffer. Finally, if two elements are removed then what would be
returned is 5 & 6 yielding the buffer:

    [ ][7][8][9][A][B][ ]

Because there is space available, if the client again uses overwrite
to store C & D then the space where 5 & 6 were stored previously will
be used not the location of 7 & 8. 7 is still the oldest element and
the buffer is once again full.

    [D][7][8][9][A][B][C]

## 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, remove the ignore flag (`#[ignore]`) from the next test and get the tests
to pass again.  The test file is located in the `tests` directory.   You can
also remove the ignore flag from all the tests to get them to run all at once
if you wish.

Make sure to read the [Modules](https://doc.rust-lang.org/book/second-edition/ch07-00-modules.html) chapter if you
haven't already, it will help you with organizing your files.

## 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](https://github.com/orgs/exercism/teams/rust) 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]: http://exercism.io/languages/rust
[modules]: https://doc.rust-lang.org/book/second-edition/ch07-00-modules.html
[cargo]: https://doc.rust-lang.org/book/second-edition/ch14-00-more-about-cargo.html

## Source

Wikipedia [http://en.wikipedia.org/wiki/Circular_buffer](http://en.wikipedia.org/wiki/Circular_buffer)

## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.