82 lines
2.5 KiB
Markdown
82 lines
2.5 KiB
Markdown
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# Circular Buffer
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A circular buffer, cyclic buffer or ring buffer is a data structure that
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uses a single, fixed-size buffer as if it were connected end-to-end.
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A circular buffer first starts empty and of some predefined length. For
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example, this is a 7-element buffer:
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[ ][ ][ ][ ][ ][ ][ ]
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Assume that a 1 is written into the middle of the buffer (exact starting
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location does not matter in a circular buffer):
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[ ][ ][ ][1][ ][ ][ ]
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Then assume that two more elements are added — 2 & 3 — which get
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appended after the 1:
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[ ][ ][ ][1][2][3][ ]
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If two elements are then removed from the buffer, the oldest values
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inside the buffer are removed. The two elements removed, in this case,
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are 1 & 2, leaving the buffer with just a 3:
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[ ][ ][ ][ ][ ][3][ ]
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If the buffer has 7 elements then it is completely full:
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[6][7][8][9][3][4][5]
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When the buffer is full an error will be raised, alerting the client
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that further writes are blocked until a slot becomes free.
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When the buffer is full, the client can opt to overwrite the oldest
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data with a forced write. In this case, two more elements — A & B —
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are added and they overwrite the 3 & 4:
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[6][7][8][9][A][B][5]
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3 & 4 have been replaced by A & B making 5 now the oldest data in the
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buffer. Finally, if two elements are removed then what would be
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returned is 5 & 6 yielding the buffer:
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[ ][7][8][9][A][B][ ]
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Because there is space available, if the client again uses overwrite
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to store C & D then the space where 5 & 6 were stored previously will
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be used not the location of 7 & 8. 7 is still the oldest element and
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the buffer is once again full.
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[D][7][8][9][A][B][C]
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* * * *
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For installation and learning resources, refer to the
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[Ruby resources page](http://exercism.io/languages/ruby/resources).
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For running the tests provided, you will need the Minitest gem. Open a
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terminal window and run the following command to install minitest:
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gem install minitest
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If you would like color output, you can `require 'minitest/pride'` in
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the test file, or note the alternative instruction, below, for running
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the test file.
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Run the tests from the exercise directory using the following command:
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ruby circular_buffer_test.rb
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To include color from the command line:
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ruby -r minitest/pride circular_buffer_test.rb
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## Source
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Wikipedia [http://en.wikipedia.org/wiki/Circular_buffer](http://en.wikipedia.org/wiki/Circular_buffer)
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## Submitting Incomplete Solutions
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It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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