Add circular buffer (#246)

config.json

@@ -437,6 +437,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 2
+      },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "0b6ade33-0ca0-4bfe-8b7b-d4370cb6e7f1",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
       }
     ]
   },
@@ -482,4 +490,4 @@
     "used_for/frontends",
     "used_for/web_development"
   ]
-}
+}

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+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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/Example.cfc

@@ -0,0 +1,51 @@
+/**
+* Here is an example solution for the CircularBuffer exercise
+*/
+component {
+
+	/**
+	* @returns 
+	*/
+	CircularBuffer function init( required numeric capacity ) {
+		variables.capacity = arguments.capacity;
+		clear();
+
+		return this;
+	}
+
+	numeric function read() {
+		if (variables.size == 0) {
+			throw( message="Empty buffer" );
+		}
+		var value = variables.data[variables.readIndex]
+		variables.readIndex = ( variables.readIndex + 1)  % variables.capacity
+		variables.size -= 1;
+		return value;
+	}
+
+	void function write( required numeric value ) {
+		if (variables.size >= variables.capacity) {
+			throw( message="Full buffer" );
+		}
+
+		variables.data.set( variables.writeIndex, 1, arguments.value);
+		variables.writeIndex = ( variables.writeIndex + 1 ) % variables.capacity;
+		variables.size += 1;
+	}
+
+	void function overwrite( required numeric value ) {
+		if (variables.size == variables.capacity) {
+			read();
+		}
+
+		write( arguments.value );
+	}
+
+	void function clear() {
+		variables.size = 0;
+		variables.data = arraySet( [], 1, variables.capacity, nullValue() );
+		variables.readIndex = 1;
+		variables.writeIndex = 1;
+	}
+
+}

exercises/practice/circular-buffer/.meta/ExampleTest.cfc

@@ -0,0 +1,7 @@
+component extends="CircularBufferTest" {
+
+	function beforeAll(){
+	  SUT = createObject( 'Solution' );
+	}
+
+}

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "CircularBuffer.cfc"
+    ],
+    "test": [
+      "CircularBufferTest.cfc"
+    ],
+    "example": [
+      ".meta/Example.cfc"
+    ]
+  },
+  "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/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/CircularBuffer.cfc

@@ -0,0 +1,40 @@
+/**
+* Your implementation of the CircularBuffer exercise
+*/
+component {
+
+	/**
+	* @returns
+	*/
+	function init( capacity ) {
+		// Implement me here
+	}
+
+	/**
+	* @returns
+	*/
+	function read() {
+		// Implement me here
+	}
+
+	/**
+	* @returns
+	*/
+	function write( value ) {
+		// Implement me here
+	}
+
+	/**
+	* @returns
+	*/
+	function overwrite( value ) {
+		// Implement me here
+	}
+
+	/**
+	* @returns
+	*/
+	function clear() {
+		// Implement me here
+	}
+}

exercises/practice/circular-buffer/CircularBufferTest.cfc

@@ -0,0 +1,126 @@
+component extends="testbox.system.BaseSpec" {
+
+
+	function run(){
+
+		describe( "My CircularBuffer class", function(){
+
+			it( "reading empty buffer should fail", function(){
+				SUT = new CircularBuffer( capacity = 1 );
+				expect( function(){ SUT.read(); } ).toThrow( message="Empty buffer" );
+			});
+
+			it( "can read an item just written", function(){
+				SUT = new CircularBuffer( capacity = 1 );
+				SUT.write( 1 );
+				expect( SUT.read() ).toBe( 1 );
+			});
+
+			it( "each item may only be read once", function(){
+				SUT = new CircularBuffer( capacity = 1 );
+				SUT.write( 1 );
+				expect( SUT.read() ).toBe( 1 );
+				expect( function(){ SUT.read(); } ).toThrow( message="Empty buffer" );
+			});
+
+			it( "items are read in the order they are written", function(){
+				SUT = new CircularBuffer( capacity = 2 );
+				SUT.write( 1 );
+				SUT.write( 2 );
+				expect( SUT.read() ).toBe( 1 );
+				expect( SUT.read() ).toBe( 2 );
+			});
+
+			it( "full buffer can't be written to", function(){
+				SUT = new CircularBuffer( capacity = 1 );
+				SUT.write( 1 );
+				expect( function(){ SUT.write( 2 ); } ).toThrow( message="Full buffer" );
+			});
+
+			it( "a read frees up capacity for another write", function(){
+				SUT = new CircularBuffer( capacity = 1 );
+				SUT.write( 1 );
+				expect( SUT.read() ).toBe( 1 );
+				SUT.write( 2 );
+				expect( SUT.read() ).toBe( 2 );
+			});
+
+			it( "read position is maintained even across multiple writes", function(){
+				SUT = new CircularBuffer( capacity = 3 );
+				SUT.write( 1 );
+				SUT.write( 2 );
+				expect( SUT.read() ).toBe( 1 );
+				SUT.write( 3 );
+				expect( SUT.read() ).toBe( 2 );
+				expect( SUT.read() ).toBe( 3 );
+			});
+
+			it( "items cleared out of buffer can't be read", function(){
+				SUT = new CircularBuffer( capacity = 1 );
+				SUT.write( 1 );
+				SUT.clear();
+				expect( function(){ SUT.read(); } ).toThrow( message="Empty buffer" );
+			});
+
+			it( "clear frees up capacity for another write", function(){
+				SUT = new CircularBuffer( capacity = 1 );
+				SUT.write( 1 );
+				SUT.clear();
+				SUT.write( 2 );
+				expect( SUT.read() ).toBe( 2 );
+			});
+
+			it( "clear does nothing on empty buffer", function(){
+				SUT = new CircularBuffer( capacity = 1 );
+				SUT.clear();
+				SUT.write( 1 );
+				expect( SUT.read() ).toBe( 1 );
+			});
+
+			it( "overwrite acts like write on non-full buffer", function(){
+				SUT = new CircularBuffer( capacity = 2 );
+				SUT.write( 1 );
+				SUT.overwrite( 2 );
+				expect( SUT.read() ).toBe( 1 );
+				expect( SUT.read() ).toBe( 2 );
+			});
+
+			it( "overwrite replaces the oldest item on full buffer", function(){
+				SUT = new CircularBuffer( capacity = 2 );
+				SUT.write( 1 );
+				SUT.write( 2 );
+				SUT.overwrite( 3 );
+				expect( SUT.read() ).toBe( 2 );
+				expect( SUT.read() ).toBe( 3 );
+			});
+
+			it( "overwrite replaces the oldest item remaining in buffer following a read", function(){
+				SUT = new CircularBuffer( capacity = 3 );
+				SUT.write( 1 );
+				SUT.write( 2 );
+				SUT.write( 3 );
+				expect( SUT.read() ).toBe( 1 );
+				SUT.write( 4 );
+				SUT.overwrite( 5 );
+				expect( SUT.read() ).toBe( 3 );
+				expect( SUT.read() ).toBe( 4 );
+				expect( SUT.read() ).toBe( 5 );
+			});
+
+			it( "initial clear does not affect wrapping around", function(){
+				SUT = new CircularBuffer( capacity = 2 );
+				SUT.clear();
+				SUT.write( 1 );
+				SUT.write( 2 );
+				SUT.overwrite( 3 );
+				SUT.overwrite( 4 );
+				expect( SUT.read() ).toBe( 3 );
+				expect( SUT.read() ).toBe( 4 );
+				expect( function(){ SUT.read(); } ).toThrow( message="Empty buffer" );
+			});
+
+		});
+
+	}
+
+}