Add circular buffer exercise

circular-buffer.md

@@ -0,0 +1,22 @@
+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]
+
+A consequence of the circular buffer is that when it is full and a subsequent write is performed, then it starts overwriting the oldest data. In this case, two more elements — A & B — are added and they overwrite the 3 & 4:
+[6][7][8][9][A][B][5]
+
+Finally, if two elements are now removed then what would be returned is not 3 & 4 but 5 & 6 because A & B overwrote the 3 & the 4 yielding the buffer with:
+[ ][7][8][9][A][B][ ]

circular-buffer.yml

@@ -0,0 +1,4 @@
+---
+blurb: "A data structure that uses a single, fixed-size buffer as if it were connected end-to-end."
+source: "Wikipedia"
+source_url: "http://en.wikipedia.org/wiki/Circular_buffer"