Add grains exercise (#246)

* Add grains exercise

* Format stub

* Add pending status

* Update exercises/practice/grains/grains.coffee

Co-authored-by: Erik Schierboom <erik_schierboom@hotmail.com>

---------

Co-authored-by: Erik Schierboom <erik_schierboom@hotmail.com>

config.json

@@ -113,6 +113,14 @@
           "transforming"
         ]
       },
+      {
+        "slug": "grains",
+        "name": "Grains",
+        "uuid": "1244927f-9ff6-422e-a8bc-5e476dc46a90",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "darts",
         "name": "Darts",

exercises/practice/grains/.docs/instructions.md

@@ -0,0 +1,15 @@
+# Instructions
+
+Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.
+
+There once was a wise servant who saved the life of a prince.
+The king promised to pay whatever the servant could dream up.
+Knowing that the king loved chess, the servant told the king he would like to have grains of wheat.
+One grain on the first square of a chess board, with the number of grains doubling on each successive square.
+
+There are 64 squares on a chessboard (where square 1 has one grain, square 2 has two grains, and so on).
+
+Write code that shows:
+
+- how many grains were on a given square, and
+- the total number of grains on the chessboard

exercises/practice/grains/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "grains.coffee"
+    ],
+    "test": [
+      "grains.spec.coffee"
+    ],
+    "example": [
+      ".meta/example.coffee"
+    ]
+  },
+  "blurb": "Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.",
+  "source": "The CodeRanch Cattle Drive, Assignment 6",
+  "source_url": "https://coderanch.com/wiki/718824/Grains"
+}

exercises/practice/grains/.meta/example.coffee

@@ -0,0 +1,10 @@
+class Grains
+  square: (number) ->
+    if number not in [1..64]
+        throw 'square must be between 1 and 64'
+
+    Math.pow(2, number - 1)
+
+  total: () ->
+    Math.pow(2, 64) - 1
+module.exports = Grains

exercises/practice/grains/.meta/tests.toml

@@ -0,0 +1,43 @@
+# 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.
+
+[9fbde8de-36b2-49de-baf2-cd42d6f28405]
+description = "returns the number of grains on the square -> grains on square 1"
+
+[ee1f30c2-01d8-4298-b25d-c677331b5e6d]
+description = "returns the number of grains on the square -> grains on square 2"
+
+[10f45584-2fc3-4875-8ec6-666065d1163b]
+description = "returns the number of grains on the square -> grains on square 3"
+
+[a7cbe01b-36f4-4601-b053-c5f6ae055170]
+description = "returns the number of grains on the square -> grains on square 4"
+
+[c50acc89-8535-44e4-918f-b848ad2817d4]
+description = "returns the number of grains on the square -> grains on square 16"
+
+[acd81b46-c2ad-4951-b848-80d15ed5a04f]
+description = "returns the number of grains on the square -> grains on square 32"
+
+[c73b470a-5efb-4d53-9ac6-c5f6487f227b]
+description = "returns the number of grains on the square -> grains on square 64"
+
+[1d47d832-3e85-4974-9466-5bd35af484e3]
+description = "returns the number of grains on the square -> square 0 is invalid"
+
+[61974483-eeb2-465e-be54-ca5dde366453]
+description = "returns the number of grains on the square -> negative square is invalid"
+
+[a95e4374-f32c-45a7-a10d-ffec475c012f]
+description = "returns the number of grains on the square -> square greater than 64 is invalid"
+
+[6eb07385-3659-4b45-a6be-9dc474222750]
+description = "returns the total number of grains on the board"

exercises/practice/grains/grains.coffee

@@ -0,0 +1,6 @@
+class Grains
+  @square: (number) ->
+
+  @total: () ->
+
+module.exports = Grains

exercises/practice/grains/grains.spec.coffee

@@ -0,0 +1,58 @@
+Grains = require './grains'
+
+describe 'Grains', ->
+  grains = new Grains()
+  it 'grains on square 1', ->
+    results = grains.square(1)
+    expected = 1
+    expect(results).toEqual expected
+
+  xit 'grains on square 2', ->
+    results = grains.square(2)
+    expected = 2
+    expect(results).toEqual expected
+
+  xit 'grains on square 3', ->
+    results = grains.square(3)
+    expected = 4
+    expect(results).toEqual expected
+
+  xit 'grains on square 4', ->
+    results = grains.square(4)
+    expected = 8
+    expect(results).toEqual expected
+
+  xit 'grains on square 16', ->
+    results = grains.square(16)
+    expected = 32768
+    expect(results).toEqual expected
+
+  xit 'grains on square 32', ->
+    results = grains.square(32)
+    expected = 2147483648
+    expect(results).toEqual expected
+
+  xit 'grains on square 64', ->
+    results = grains.square(64)
+    expected = 9223372036854775808
+    expect(results).toEqual expected
+
+  xit 'square 0 is invalid', ->
+    expect ->
+      grains.square(0)
+    .toThrow new Error 'square must be between 1 and 64'
+
+  xit 'negative square is invalid', ->
+    expect ->
+      grains.square(-1)
+    .toThrow new Error 'square must be between 1 and 64'
+
+  xit 'square greater than 64 is invalid', ->
+    expect ->
+      grains.square(65)
+    .toThrow new Error 'square must be between 1 and 64'
+
+  xit 'returns the total number of grains on the board', ->
+    results = grains.total(65)
+    expected = 18446744073709551615 
+    expect(results).toEqual expected