[#767] New practice exercise darts (#777)

Co-authored-by: Angelika Tyborska <[email protected]>

Author: jiegillet

config.json

@@ -2464,6 +2464,20 @@
         ],
         "difficulty": 5
       },
+      {
+        "slug": "darts",
+        "name": "Darts",
+        "uuid": "a68113f8-92be-40e0-a97f-eb4239303ef5",
+        "prerequisites": [
+          "cond",
+          "integers",
+          "floating-point-numbers"
+        ],
+        "practices": [
+          "cond"
+        ],
+        "difficulty": 2
+      },
       {
         "slug": "affine-cipher",
         "name": "Affine Cipher",

exercises/practice/darts/.docs/hints.md

@@ -0,0 +1,5 @@
+## General
+
+- The distance of a point `(x, y)` from the center of the target `(0, 0)` can be calculated with `sqrt(x*x + y *y)`
+
+- You can calculate the square root of `x` by raising it to the power of `1/2`. In other words, `sqrt(x) == pow(x, 0.5)`

exercises/practice/darts/.docs/instructions.md

@@ -0,0 +1,17 @@
+# Description
+
+Write a function that returns the earned points in a single toss of a Darts game.
+
+[Darts](https://en.wikipedia.org/wiki/Darts) is a game where players
+throw darts to a [target](https://en.wikipedia.org/wiki/Darts#/media/File:Darts_in_a_dartboard.jpg).
+
+In our particular instance of the game, the target rewards with 4 different amounts of points, depending on where the dart lands:
+
+* If the dart lands outside the target, player earns no points (0 points).
+* If the dart lands in the outer circle of the target, player earns 1 point.
+* If the dart lands in the middle circle of the target, player earns 5 points.
+* If the dart lands in the inner circle of the target, player earns 10 points.
+
+The outer circle has a radius of 10 units (This is equivalent to the total radius for the entire target), the middle circle a radius of 5 units, and the inner circle a radius of 1. Of course, they are all centered to the same point (That is, the circles are [concentric](http://mathworld.wolfram.com/ConcentricCircles.html)) defined by the coordinates (0, 0).
+
+Write a function that given a point in the target (defined by its `real` cartesian coordinates `x` and `y`), returns the correct amount earned by a dart landing in that point.

exercises/practice/darts/.formatter.exs

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

exercises/practice/darts/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": ["jiegillet"],
+  "contributors": [
+    "angelikatyborska"
+  ],
+  "files": {
+    "example": [
+      ".meta/example.ex"
+    ],
+    "solution": [
+      "lib/darts.ex"
+    ],
+    "test": [
+      "test/darts_test.exs"
+    ]
+  },
+  "blurb": "Write a function that returns the earned points in a single toss of a Darts game.",
+  "source": "Inspired by an exercise created by a professor Della Paolera in Argentina"
+}

exercises/practice/darts/.meta/example.ex

@@ -0,0 +1,18 @@
+defmodule Darts do
+  @type position :: {number, number}
+
+  @doc """
+  Calculate the score of a single dart hitting a target
+  """
+  @spec score(position :: position) :: integer
+  def score({x, y}) do
+    radius = :math.sqrt(x * x + y * y)
+
+    cond do
+      radius > 10 -> 0
+      radius > 5 -> 1
+      radius > 1 -> 5
+      true -> 10
+    end
+  end
+end

exercises/practice/darts/.meta/tests.toml

@@ -0,0 +1,48 @@
+# 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.
+[9033f731-0a3a-4d9c-b1c0-34a1c8362afb]
+description = "Missed target"
+
+[4c9f6ff4-c489-45fd-be8a-1fcb08b4d0ba]
+description = "On the outer circle"
+
+[14378687-ee58-4c9b-a323-b089d5274be8]
+description = "On the middle circle"
+
+[849e2e63-85bd-4fed-bc3b-781ae962e2c9]
+description = "On the inner circle"
+
+[1c5ffd9f-ea66-462f-9f06-a1303de5a226]
+description = "Exactly on centre"
+
+[b65abce3-a679-4550-8115-4b74bda06088]
+description = "Near the centre"
+
+[66c29c1d-44f5-40cf-9927-e09a1305b399]
+description = "Just within the inner circle"
+
+[d1012f63-c97c-4394-b944-7beb3d0b141a]
+description = "Just outside the inner circle"
+
+[ab2b5666-b0b4-49c3-9b27-205e790ed945]
+description = "Just within the middle circle"
+
+[70f1424e-d690-4860-8caf-9740a52c0161]
+description = "Just outside the middle circle"
+
+[a7dbf8db-419c-4712-8a7f-67602b69b293]
+description = "Just within the outer circle"
+
+[e0f39315-9f9a-4546-96e4-a9475b885aa7]
+description = "Just outside the outer circle"
+
+[045d7d18-d863-4229-818e-b50828c75d19]
+description = "Asymmetric position between the inner and middle circles"

exercises/practice/darts/lib/darts.ex

@@ -0,0 +1,10 @@
+defmodule Darts do
+  @type position :: {number, number}
+
+  @doc """
+  Calculate the score of a single dart hitting a target
+  """
+  @spec score(position :: position) :: integer
+  def score({x, y}) do
+  end
+end

exercises/practice/darts/mix.exs

@@ -0,0 +1,28 @@
+defmodule Darts.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :darts,
+      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/darts/test/darts_test.exs

@@ -0,0 +1,68 @@
+defmodule DartsTest do
+  use ExUnit.Case
+
+  # @tag :pending
+  test "Missed target" do
+    assert Darts.score({-9, 9}) == 0
+  end
+
+  @tag :pending
+  test "On the outer circle" do
+    assert Darts.score({0, 10}) == 1
+  end
+
+  @tag :pending
+  test "On the middle circle" do
+    assert Darts.score({-5, 0}) == 5
+  end
+
+  @tag :pending
+  test "On the inner circle" do
+    assert Darts.score({0, -1}) == 10
+  end
+
+  @tag :pending
+  test "Exactly on centre" do
+    assert Darts.score({0, 0}) == 10
+  end
+
+  @tag :pending
+  test "Near the centre" do
+    assert Darts.score({-0.1, -0.1}) == 10
+  end
+
+  @tag :pending
+  test "Just within the inner circle" do
+    assert Darts.score({0.7, 0.7}) == 10
+  end
+
+  @tag :pending
+  test "Just outside the inner circle" do
+    assert Darts.score({0.8, -0.8}) == 5
+  end
+
+  @tag :pending
+  test "Just within the middle circle" do
+    assert Darts.score({-3.5, 3.5}) == 5
+  end
+
+  @tag :pending
+  test "Just outside the middle circle" do
+    assert Darts.score({-3.6, -3.6}) == 1
+  end
+
+  @tag :pending
+  test "Just within the outer circle" do
+    assert Darts.score({-7.0, 7.0}) == 1
+  end
+
+  @tag :pending
+  test "Just outside the outer circle" do
+    assert Darts.score({7.1, -7.1}) == 0
+  end
+
+  @tag :pending
+  test "Asymmetric position between the inner and middle circles" do
+    assert Darts.score({0.5, -4}) == 5
+  end
+end