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):
[ ][ ][ ][ ][ ][ ]
Then assume that two more elements are added — 2 & 3 — which get appended after the 1:
[ ][ ][ ][ ]
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:
[ ][ ][ ][ ][ ][ ]
If the buffer has 7 elements then it is completely full:
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:
3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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:
[ ][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.
To ensure the correctness of your implementation, see test.sh with usage:
sh test.sh /path/to/program
It is expected that your program takes as its first argument the size of the buffer, followed by arguments to be written into the buffer in order. Certain arguments are special and should not be written to the buffer but interpreted as commands instead:
READ: Read the next item from the buffer and print to a line on STDOUT
CLEAR: Make the buffer empty
OVERWRITE: The next write should overwrite the first element if the buffer is full, instead of erroring as below
Your program must either print all requested items to STDOUT. It must then exit success, or else exit with one of the following codes:
1: Tried to read an empty buffer
2: Tried to write to full buffer
All submissions must contain a statement that the code is your own work (groups are ok!) and placing the code under either CC0, CC-BY, or CC-BY-SA. Submissions are by email to email@example.com. Attaching each source file is preferred, but tarballs or git URLs will also be accepted (especially when directory structure matters). Submissions may be in any programming language that can be compiled or interpreted on a Debian Stable system.
If relevant, please make it clear what name, pseudonym, or group name you would like your submission attributed to. This name (and the code content of your submission) will be made public.
Submissions are due by and the winning teardown post will be published the following month.
This excercise and its tests based on https://github.com/exercism/rust/tree/master/exercises/circular-buffer, original license:
Copyright (c) 2017 Exercism, Inc
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