82 lines
2.5 KiB
Markdown
82 lines
2.5 KiB
Markdown
# 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3 & 4 have been replaced by A & B making 5 now the oldest data in the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]
|
|
|
|
* * * *
|
|
|
|
For installation and learning resources, refer to the
|
|
[Ruby resources page](http://exercism.io/languages/ruby/resources).
|
|
|
|
For running the tests provided, you will need the Minitest gem. Open a
|
|
terminal window and run the following command to install minitest:
|
|
|
|
gem install minitest
|
|
|
|
If you would like color output, you can `require 'minitest/pride'` in
|
|
the test file, or note the alternative instruction, below, for running
|
|
the test file.
|
|
|
|
Run the tests from the exercise directory using the following command:
|
|
|
|
ruby circular_buffer_test.rb
|
|
|
|
To include color from the command line:
|
|
|
|
ruby -r minitest/pride circular_buffer_test.rb
|
|
|
|
|
|
## 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.
|