# Instructions

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:
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    [ ][ ][ ][ ][ ][ ][ ]

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

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

If the buffer has 7 elements then it is completely full:
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    [5][6][7][8][9][3][4]

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

3 & 4 have been replaced by A & B making 5 now the oldest data in the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:
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    [ ][ ][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.
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    [C][D][7][8][9][A][B]
