Add circular-buffer

config.json

@@ -530,6 +530,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 2
+      },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "85672148-01f2-4c88-b859-5d9ecc5c1ada",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

exercises/practice/circular-buffer/.docs/instructions.md

@@ -0,0 +1,58 @@
+# 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:
+
+```text
+[ ][ ][ ][ ][ ][ ][ ]
+```
+
+Assume that a 1 is written into the middle of the buffer (exact starting location does not matter in a circular buffer):
+
+```text
+[ ][ ][ ][1][ ][ ][ ]
+```
+
+Then assume that two more elements are added — 2 & 3 — which get appended after the 1:
+
+```text
+[ ][ ][ ][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:
+
+```text
+[ ][ ][ ][ ][ ][3][ ]
+```
+
+If the buffer has 7 elements then it is completely full:
+
+```text
+[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:
+
+```text
+[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+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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:
+
+```text
+[ ][ ][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.
+
+```text
+[C][D][7][8][9][A][B]
+```

exercises/practice/circular-buffer/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "circular-buffer.coffee"
+    ],
+    "test": [
+      "circular-buffer.spec.coffee"
+    ],
+    "example": [
+      ".meta/example.coffee"
+    ]
+  },
+  "blurb": "A data structure that uses a single, fixed-size buffer as if it were connected end-to-end.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Circular_buffer"
+}

exercises/practice/circular-buffer/.meta/example.coffee

@@ -0,0 +1,24 @@
+class CircularBuffer
+  constructor: (@capacity) ->
+    @data = []
+
+  write: (value) ->
+    if @data.length == @capacity
+      throw new Error "full buffer"
+    @data.push value
+
+  read: () ->
+    if !@data.length
+      throw new Error "empty buffer"
+    [head, @data...] = @data
+    head
+
+  overwrite: (value) ->
+    if @data.length == @capacity
+      @read()
+    @write value
+
+  clear: () ->
+    @data = []
+
+module.exports = CircularBuffer

exercises/practice/circular-buffer/.meta/tests.toml

@@ -0,0 +1,52 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[28268ed4-4ff3-45f3-820e-895b44d53dfa]
+description = "reading empty buffer should fail"
+
+[2e6db04a-58a1-425d-ade8-ac30b5f318f3]
+description = "can read an item just written"
+
+[90741fe8-a448-45ce-be2b-de009a24c144]
+description = "each item may only be read once"
+
+[be0e62d5-da9c-47a8-b037-5db21827baa7]
+description = "items are read in the order they are written"
+
+[2af22046-3e44-4235-bfe6-05ba60439d38]
+description = "full buffer can't be written to"
+
+[547d192c-bbf0-4369-b8fa-fc37e71f2393]
+description = "a read frees up capacity for another write"
+
+[04a56659-3a81-4113-816b-6ecb659b4471]
+description = "read position is maintained even across multiple writes"
+
+[60c3a19a-81a7-43d7-bb0a-f07242b1111f]
+description = "items cleared out of buffer can't be read"
+
+[45f3ae89-3470-49f3-b50e-362e4b330a59]
+description = "clear frees up capacity for another write"
+
+[e1ac5170-a026-4725-bfbe-0cf332eddecd]
+description = "clear does nothing on empty buffer"
+
+[9c2d4f26-3ec7-453f-a895-7e7ff8ae7b5b]
+description = "overwrite acts like write on non-full buffer"
+
+[880f916b-5039-475c-bd5c-83463c36a147]
+description = "overwrite replaces the oldest item on full buffer"
+
+[bfecab5b-aca1-4fab-a2b0-cd4af2b053c3]
+description = "overwrite replaces the oldest item remaining in buffer following a read"
+
+[9cebe63a-c405-437b-8b62-e3fdc1ecec5a]
+description = "initial clear does not affect wrapping around"

exercises/practice/circular-buffer/circular-buffer.coffee

@@ -0,0 +1,12 @@
+class CircularBuffer
+  constructor: (capacity) ->
+
+  write: (value) ->
+
+  read: () ->
+
+  overwrite: (value) ->
+
+  clear: () ->
+
+module.exports = CircularBuffer

exercises/practice/circular-buffer/circular-buffer.spec.coffee

@@ -0,0 +1,112 @@
+CircularBuffer = require './circular-buffer'
+
+describe "Circular Buffer", ->
+  it "reading empty buffer should fail", ->
+    buff = new CircularBuffer 1
+    expect ->
+      buff.read()
+    .toThrow new Error "empty buffer"
+
+  xit "can read an item just written", ->
+    buff = new CircularBuffer 1
+    buff.write 1
+    expect(buff.read()).toEqual 1
+
+  xit "each item may only be read once", ->
+    buff = new CircularBuffer 1
+    buff.write 1
+    expect(buff.read()).toEqual 1
+    expect ->
+      buff.read()
+    .toThrow new Error "empty buffer"
+
+  xit "items are read in the order they are written", ->
+    buff = new CircularBuffer 2
+    buff.write 1
+    buff.write 2
+    expect(buff.read()).toEqual 1
+    expect(buff.read()).toEqual 2
+
+  xit "full buffer can't be written to", ->
+    buff = new CircularBuffer 1
+    buff.write 1
+    expect ->
+      buff.write 2
+    .toThrow new Error "full buffer"
+
+  xit "a read frees up capacity for another write", ->
+    buff = new CircularBuffer 1
+    buff.write 1
+    expect(buff.read()).toEqual 1
+    buff.write 2
+    expect(buff.read()).toEqual 2
+
+  xit "read position is maintained even across multiple writes", ->
+    buff = new CircularBuffer 3
+    buff.write 1
+    buff.write 2
+    expect(buff.read()).toEqual 1
+    buff.write 3
+    expect(buff.read()).toEqual 2
+    expect(buff.read()).toEqual 3
+
+  xit "items cleared out of buffer can't be read", ->
+    buff = new CircularBuffer 1
+    buff.write 1
+    buff.clear()
+    expect ->
+      buff.read()
+    .toThrow new Error "empty buffer"
+
+  xit "clear frees up capacity for another write", ->
+    buff = new CircularBuffer 1
+    buff.write 1
+    buff.clear()
+    buff.write 2
+    expect(buff.read()).toEqual 2
+
+  xit "clear does nothing on empty buffer", ->
+    buff = new CircularBuffer 1
+    buff.clear()
+    buff.write 1
+    expect(buff.read()).toEqual 1
+
+  xit "overwrite acts like write on non-full buffer", ->
+    buff = new CircularBuffer 2
+    buff.write 1
+    buff.overwrite 2
+    expect(buff.read()).toEqual 1
+    expect(buff.read()).toEqual 2
+
+  xit "overwrite replaces the oldest item on full buffer", ->
+    buff = new CircularBuffer 2
+    buff.write 1
+    buff.write 2
+    buff.overwrite 3
+    expect(buff.read()).toEqual 2
+    expect(buff.read()).toEqual 3
+
+  xit "overwrite replaces the oldest item remaining in buffer following a read", ->
+    buff = new CircularBuffer 3
+    buff.write 1
+    buff.write 2
+    buff.write 3
+    expect(buff.read()).toEqual 1
+    buff.write 4
+    buff.overwrite 5
+    expect(buff.read()).toEqual 3
+    expect(buff.read()).toEqual 4
+    expect(buff.read()).toEqual 5
+
+  xit "initial clear does not affect wrapping around", ->
+    buff = new CircularBuffer 2
+    buff.clear()
+    buff.write 1
+    buff.write 2
+    buff.overwrite 3
+    buff.overwrite 4
+    expect(buff.read()).toEqual 3
+    expect(buff.read()).toEqual 4
+    expect ->
+      buff.read()
+    .toThrow new Error "empty buffer"