New practice exercise

Author: jiegillet

config.json

@@ -2661,7 +2661,22 @@
           "bitstrings"
         ],
         "difficulty": 6
-      }
+       },
+       {
+        "slug": "resistor-color-duo",
+        "name": "Resistor Color Duo",
+        "uuid": "92387ac7-4c6d-4568-819e-e037b1d86a72",
+        "prerequisites": [
+          "atoms",
+          "lists",
+          "pattern-matching",
+          "maps"
+        ],
+        "practices": [
+          "maps"
+        ],
+        "difficulty": 2
+       }
     ],
     "foregone": [
       "linked-list",

exercises/practice/resistor-color-duo/.docs/instructions.md

@@ -0,0 +1,34 @@
+# Description
+
+If you want to build something using a Raspberry Pi, you'll probably use _resistors_.
+For this exercise, you need to know two things about them:
+
+* Each resistor has a resistance value.
+* Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read.
+
+To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values.
+Each band has a position and a numeric value.
+
+The first 2 bands of a resistor have a simple encoding scheme: each color maps to a single number.
+For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.
+
+In this exercise you are going to create a helpful program so that you don't have to remember the values of the bands.
+The program will take color names as input and output a two digit number, even if the input is more than two colors!
+
+The band colors are encoded as follows:
+
+- Black: 0
+- Brown: 1
+- Red: 2
+- Orange: 3
+- Yellow: 4
+- Green: 5
+- Blue: 6
+- Violet: 7
+- Grey: 8
+- White: 9
+
+From the example above:
+brown-green should return 15
+brown-green-violet should return 15 too, ignoring the third color.
+

exercises/practice/resistor-color-duo/.formatter.exs

@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

exercises/practice/resistor-color-duo/.meta/config.json

@@ -0,0 +1,18 @@
+{
+  "authors": ["jiegillet"],
+  "contributors": [],
+  "files": {
+    "example": [
+      ".meta/example.ex"
+    ],
+    "solution": [
+      "lib/resistor_color_duo.ex"
+    ],
+    "test": [
+      "test/resistor_color_duo_test.exs"
+    ]
+  },
+  "blurb": "Convert color codes, as used on resistors, to a numeric value.",
+  "source": "Maud de Vries, Erik Schierboom",
+  "source_url": "https://github.com/exercism/problem-specifications/issues/1464"
+}

exercises/practice/resistor-color-duo/.meta/example.ex

@@ -0,0 +1,22 @@
+defmodule ResistorColorDuo do
+  @colors %{
+    black: 0,
+    brown: 1,
+    red: 2,
+    orange: 3,
+    yellow: 4,
+    green: 5,
+    blue: 6,
+    violet: 7,
+    grey: 8,
+    white: 9
+  }
+
+  @doc """
+  Calculate a resistance value from two colors
+  """
+  @spec value(colors :: [atom]) :: integer
+  def value([a, b | _]) do
+    10 * @colors[a] + @colors[b]
+  end
+end

exercises/practice/resistor-color-duo/.meta/tests.toml

@@ -0,0 +1,24 @@
+# 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.
+[ce11995a-5b93-4950-a5e9-93423693b2fc]
+description = "Brown and black"
+
+[7bf82f7a-af23-48ba-a97d-38d59406a920]
+description = "Blue and grey"
+
+[f1886361-fdfd-4693-acf8-46726fe24e0c]
+description = "Yellow and violet"
+
+[77a8293d-2a83-4016-b1af-991acc12b9fe]
+description = "Orange and orange"
+
+[0c4fb44f-db7c-4d03-afa8-054350f156a8]
+description = "Ignore additional colors"

exercises/practice/resistor-color-duo/lib/resistor_color_duo.ex

@@ -0,0 +1,8 @@
+defmodule ResistorColorDuo do
+  @doc """
+  Calculate a resistance value from two colors
+  """
+  @spec value(colors :: [atom]) :: integer
+  def value(colors) do
+  end
+end

exercises/practice/resistor-color-duo/mix.exs

@@ -0,0 +1,28 @@
+defmodule ResistorColorDuo.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :resistor_color_duo,
+      version: "0.1.0",
+      # elixir: "~> 1.8",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

exercises/practice/resistor-color-duo/test/resistor_color_duo_test.exs

@@ -0,0 +1,48 @@
+defmodule ResistorColorDuoTest do
+  use ExUnit.Case
+
+  # @tag :pending
+  test "Brown and black" do
+    colors = [:brown, :black]
+    output = ResistorColorDuo.value(colors)
+    expected = 10
+
+    assert output == expected
+  end
+
+  @tag :pending
+  test "Blue and grey" do
+    colors = [:blue, :grey]
+    output = ResistorColorDuo.value(colors)
+    expected = 68
+
+    assert output == expected
+  end
+
+  @tag :pending
+  test "Yellow and violet" do
+    colors = [:yellow, :violet]
+    output = ResistorColorDuo.value(colors)
+    expected = 47
+
+    assert output == expected
+  end
+
+  @tag :pending
+  test "Orange and orange" do
+    colors = [:orange, :orange]
+    output = ResistorColorDuo.value(colors)
+    expected = 33
+
+    assert output == expected
+  end
+
+  @tag :pending
+  test "Ignore additional colors" do
+    colors = [:green, :brown, :orange]
+    output = ResistorColorDuo.value(colors)
+    expected = 51
+
+    assert output == expected
+  end
+end

exercises/practice/resistor-color-duo/test/test_helper.exs

@@ -0,0 +1,2 @@
+ExUnit.start()
+ExUnit.configure(exclude: :pending, trace: true)