Add grains exercise

Author: pfertyk

config.json

@@ -139,6 +139,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "grains",
+        "name": "Grains",
+        "uuid": "e163b0a9-b9fe-4303-b047-11e588d684da",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "luhn",
         "name": "Luhn",

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": [
+    "pfertyk"
+  ],
+  "files": {
+    "solution": [
+      "grains.gd"
+    ],
+    "test": [
+      "grains_test.gd"
+    ],
+    "example": [
+      ".meta/example.gd"
+    ]
+  },
+  "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.gd

@@ -0,0 +1,8 @@
+func square(number):
+	if number < 1 or number > 64:
+		return null
+	return pow(2, number - 1)
+
+
+func total():
+	return pow(2, 64) - 1

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.gd

@@ -0,0 +1,6 @@
+func square(number):
+	pass
+
+
+func total():
+	pass

exercises/practice/grains/grains_test.gd

@@ -0,0 +1,44 @@
+func test_grains_on_square_1(solution_script):
+	return [solution_script.square(1), 1]
+
+
+func test_grains_on_square_2(solution_script):
+	return [solution_script.square(2), 2]
+
+
+func test_grains_on_square_3(solution_script):
+	return [solution_script.square(3), 4]
+
+
+func test_grains_on_square_4(solution_script):
+	return [solution_script.square(4), 8]
+
+
+func test_grains_on_square_16(solution_script):
+	return [solution_script.square(16), 32768]
+
+
+func test_grains_on_square_32(solution_script):
+	return [solution_script.square(32), 2147483648]
+
+
+func test_grains_on_square_64(solution_script):
+	return [solution_script.square(64), 9223372036854775808]
+
+
+func test_square_0_is_invalid(solution_script):
+	return [solution_script.square(0), null]
+
+
+func test_negative_square_is_invalid(solution_script):
+	return [solution_script.square(-1), null]
+
+
+func test_square_greater_than_64_is_invalid(solution_script):
+	return [solution_script.square(65), null]
+
+
+func test_returns_the_total_number_of_grains_on_the_board(solution_script):
+	return [solution_script.total(), 18446744073709551615]
+
+