difference-of-squares

elixir/difference-of-squares/.exercism/config.json

@@ -0,0 +1,36 @@
+{
+  "authors": [
+    "petehuang"
+  ],
+  "contributors": [
+    "andrewsardone",
+    "angelikatyborska",
+    "Cohen-Carlisle",
+    "dalexj",
+    "devonestes",
+    "jinyeow",
+    "kytrinyx",
+    "lpil",
+    "neenjaw",
+    "parkerl",
+    "rubysolo",
+    "Scientifica96",
+    "sotojuan",
+    "Teapane",
+    "waiting-for-dev"
+  ],
+  "files": {
+    "solution": [
+      "lib/squares.ex"
+    ],
+    "test": [
+      "test/squares_test.exs"
+    ],
+    "example": [
+      ".meta/example.ex"
+    ]
+  },
+  "blurb": "Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.",
+  "source": "Problem 6 at Project Euler",
+  "source_url": "https://projecteuler.net/problem=6"
+}

elixir/difference-of-squares/.exercism/metadata.json

@@ -0,0 +1 @@
+{"track":"elixir","exercise":"difference-of-squares","id":"71804265a0684ed3ba15a88ed184ef81","url":"https://exercism.org/tracks/elixir/exercises/difference-of-squares","handle":"negrienko","is_requester":true,"auto_approve":false}

elixir/difference-of-squares/.formatter.exs

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

elixir/difference-of-squares/.gitignore

@@ -0,0 +1,24 @@
+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where third-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+difference_of_squares-*.tar
+

elixir/difference-of-squares/HELP.md

@@ -0,0 +1,75 @@
+# Help
+
+## Running the tests
+
+From the terminal, change to the base directory of the exercise then execute the tests with:
+
+```bash
+$ mix test
+```
+
+This will execute the test file found in the `test` subfolder -- a file ending in `_test.exs`
+
+Documentation:
+
+* [`mix test` - Elixir's test execution tool](https://hexdocs.pm/mix/Mix.Tasks.Test.html)
+* [`ExUnit` - Elixir's unit test library](https://hexdocs.pm/ex_unit/ExUnit.html)
+
+## Pending tests
+
+In test suites of practice exercises, all but the first test have been tagged to be skipped.
+
+Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.
+
+For example:
+
+```elixir
+# @tag :pending
+test "shouting" do
+  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
+end
+```
+
+If you wish to run all tests at once, you can include all skipped test by using the `--include` flag on the `mix test` command:
+
+```bash
+$ mix test --include pending
+```
+
+Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the file `test/test_helper.exs`.
+
+```elixir
+# ExUnit.configure(exclude: :pending, trace: true)
+```
+
+## Useful `mix test` options
+
+* `test/<FILE>.exs:LINENUM` - runs only a single test, the test from `<FILE>.exs` whose definition is on line `LINENUM`
+* `--failed` - runs only tests that failed the last time they ran
+* `--max-failures` - the suite stops evaluating tests when this number of test failures
+is reached
+* `--seed 0` - disables randomization so the tests in a single file will always be ran
+in the same order they were defined in
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit lib/squares.ex` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Elixir track's documentation](https://exercism.org/docs/tracks/elixir)
+- The [Elixir track's programming category on the forum](https://forum.exercism.org/c/programming/elixir)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+If you're stuck on something, it may help to look at some of the [available resources](https://exercism.org/docs/tracks/elixir/resources) out there where answers might be found.

elixir/difference-of-squares/README.md

@@ -0,0 +1,47 @@
+# Difference of Squares
+
+Welcome to Difference of Squares on Exercism's Elixir Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
+
+The square of the sum of the first ten natural numbers is
+(1 + 2 + ... + 10)² = 55² = 3025.
+
+The sum of the squares of the first ten natural numbers is
+1² + 2² + ... + 10² = 385.
+
+Hence the difference between the square of the sum of the first ten natural numbers and the sum of the squares of the first ten natural numbers is 3025 - 385 = 2640.
+
+You are not expected to discover an efficient solution to this yourself from first principles; research is allowed, indeed, encouraged.
+Finding the best algorithm for the problem is a key skill in software engineering.
+
+## Source
+
+### Created by
+
+- @petehuang
+
+### Contributed to by
+
+- @andrewsardone
+- @angelikatyborska
+- @Cohen-Carlisle
+- @dalexj
+- @devonestes
+- @jinyeow
+- @kytrinyx
+- @lpil
+- @neenjaw
+- @parkerl
+- @rubysolo
+- @Scientifica96
+- @sotojuan
+- @Teapane
+- @waiting-for-dev
+
+### Based on
+
+Problem 6 at Project Euler - https://projecteuler.net/problem=6

elixir/difference-of-squares/lib/squares.ex

@@ -0,0 +1,29 @@
+defmodule Squares do
+  @moduledoc """
+  Calculate sum of squares, square of sum, difference between two sums from 1 to a given end number.
+  """
+
+  @doc """
+  Calculate sum of squares from 1 to a given end number.
+  """
+  @spec sum_of_squares(pos_integer) :: pos_integer
+  def sum_of_squares(number) do
+    div(number * (number + 1) * (2 * number + 1), 6)
+  end
+
+  @doc """
+  Calculate square of sum from 1 to a given end number.
+  """
+  @spec square_of_sum(pos_integer) :: pos_integer
+  def square_of_sum(number) do
+    div(number * (number + 1), 2) ** 2
+  end
+
+  @doc """
+  Calculate difference between sum of squares and square of sum from 1 to a given end number.
+  """
+  @spec difference(pos_integer) :: pos_integer
+  def difference(number) do
+    abs(square_of_sum(number) - sum_of_squares(number))
+  end
+end

elixir/difference-of-squares/mix.exs

@@ -0,0 +1,29 @@
+defmodule Squares.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :squares,
+      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
+    [
+      {:lettuce, "~> 0.3.0", only: ~w(dev)a}
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end

elixir/difference-of-squares/mix.lock

@@ -0,0 +1,3 @@
+%{
+  "lettuce": {:hex, :lettuce, "0.3.0", "823198f053714282f980acc68c7157b9c78c740910cb4f572a642e020417a850", [:mix], [], "hexpm", "a47479d94ac37460481133213f08c8283dabbe762f4f8f8028456500d1fca9c4"},
+}

elixir/difference-of-squares/test/squares_test.exs

@@ -0,0 +1,45 @@
+defmodule SquaresTest do
+  use ExUnit.Case
+
+  describe "square_of_sum" do
+    test "square of sum to 1" do
+      assert Squares.square_of_sum(1) == 1
+    end
+
+    test "square of sum to 5" do
+      assert Squares.square_of_sum(5) == 225
+    end
+
+    test "square of sum to 100" do
+      assert Squares.square_of_sum(100) == 25_502_500
+    end
+  end
+
+  describe "sum_of_squares" do
+    test "sum of squares to 1" do
+      assert Squares.sum_of_squares(1) == 1
+    end
+
+    test "sum of squares to 5" do
+      assert Squares.sum_of_squares(5) == 55
+    end
+
+    test "sum of squares to 100" do
+      assert Squares.sum_of_squares(100) == 338_350
+    end
+  end
+
+  describe "difference" do
+    test "difference of sum to 1" do
+      assert Squares.difference(1) == 0
+    end
+
+    test "difference of sum to 5" do
+      assert Squares.difference(5) == 170
+    end
+
+    test "difference of sum to 100" do
+      assert Squares.difference(100) == 25_164_150
+    end
+  end
+end

elixir/difference-of-squares/test/test_helper.exs

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