binary_search

elixir/binary-search/.exercism/config.json

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+{
+  "authors": [
+    "bernardoamc"
+  ],
+  "contributors": [
+    "angelikatyborska",
+    "Cohen-Carlisle",
+    "devonestes",
+    "lpil",
+    "martinsvalin",
+    "neenjaw",
+    "parkerl",
+    "screamingjungle",
+    "sotojuan",
+    "waiting-for-dev"
+  ],
+  "files": {
+    "solution": [
+      "lib/binary_search.ex"
+    ],
+    "test": [
+      "test/binary_search_test.exs"
+    ],
+    "example": [
+      ".meta/example.ex"
+    ]
+  },
+  "blurb": "Implement a binary search algorithm.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Binary_search_algorithm"
+}

elixir/binary-search/.exercism/metadata.json

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+{"track":"elixir","exercise":"binary-search","id":"46907374d6fd43e0815717c10201d2e0","url":"https://exercism.org/tracks/elixir/exercises/binary-search","handle":"negrienko","is_requester":true,"auto_approve":false}

elixir/binary-search/.formatter.exs

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

elixir/binary-search/.gitignore

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+# 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").
+binary_search-*.tar
+

elixir/binary-search/HELP.md

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+# 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/binary_search.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/binary-search/README.md

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+# Binary Search
+
+Welcome to Binary Search on Exercism's Elixir Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Introduction
+
+You have stumbled upon a group of mathematicians who are also singer-songwriters.
+They have written a song for each of their favorite numbers, and, as you can imagine, they have a lot of favorite numbers (like [0][zero] or [73][seventy-three] or [6174][kaprekars-constant]).
+
+You are curious to hear the song for your favorite number, but with so many songs to wade through, finding the right song could take a while.
+Fortunately, they have organized their songs in a playlist sorted by the title — which is simply the number that the song is about.
+
+You realize that you can use a binary search algorithm to quickly find a song given the title.
+
+[zero]: https://en.wikipedia.org/wiki/0
+[seventy-three]: https://en.wikipedia.org/wiki/73_(number)
+[kaprekars-constant]: https://en.wikipedia.org/wiki/6174_(number)
+
+## Instructions
+
+Your task is to implement a binary search algorithm.
+
+A binary search algorithm finds an item in a list by repeatedly splitting it in half, only keeping the half which contains the item we're looking for.
+It allows us to quickly narrow down the possible locations of our item until we find it, or until we've eliminated all possible locations.
+
+~~~~exercism/caution
+Binary search only works when a list has been sorted.
+~~~~
+
+The algorithm looks like this:
+
+- Find the middle element of a _sorted_ list and compare it with the item we're looking for.
+- If the middle element is our item, then we're done!
+- If the middle element is greater than our item, we can eliminate that element and all the elements **after** it.
+- If the middle element is less than our item, we can eliminate that element and all the elements **before** it.
+- If every element of the list has been eliminated then the item is not in the list.
+- Otherwise, repeat the process on the part of the list that has not been eliminated.
+
+Here's an example:
+
+Let's say we're looking for the number 23 in the following sorted list: `[4, 8, 12, 16, 23, 28, 32]`.
+
+- We start by comparing 23 with the middle element, 16.
+- Since 23 is greater than 16, we can eliminate the left half of the list, leaving us with `[23, 28, 32]`.
+- We then compare 23 with the new middle element, 28.
+- Since 23 is less than 28, we can eliminate the right half of the list: `[23]`.
+- We've found our item.
+
+## Source
+
+### Created by
+
+- @bernardoamc
+
+### Contributed to by
+
+- @angelikatyborska
+- @Cohen-Carlisle
+- @devonestes
+- @lpil
+- @martinsvalin
+- @neenjaw
+- @parkerl
+- @screamingjungle
+- @sotojuan
+- @waiting-for-dev
+
+### Based on
+
+Wikipedia - https://en.wikipedia.org/wiki/Binary_search_algorithm

elixir/binary-search/lib/binary_search.ex

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+defmodule BinarySearch do
+  @doc """
+    Searches for a key in the tuple using the binary search algorithm.
+    It returns :not_found if the key is not in the tuple.
+    Otherwise returns {:ok, index}.
+
+    ## Examples
+
+      iex> BinarySearch.search({}, 2)
+      :not_found
+
+      iex> BinarySearch.search({1, 3, 5}, 2)
+      :not_found
+
+      iex> BinarySearch.search({1, 3, 5}, 5)
+      {:ok, 2}
+
+  """
+
+  @spec search(tuple, integer) :: {:ok, integer} | :not_found
+  def search({}, _value), do: :not_found
+  def search(numbers, value), do: do_search(numbers, value, 0, tuple_size(numbers) - 1)
+
+  defp do_search(_numbers, _value, from, to) when from > to, do: :not_found
+  defp do_search(numbers, value, from, to) do
+    middle = div(from + to, 2)
+    element = elem(numbers, middle)
+    cond do
+      value == element -> {:ok, middle}
+      value < element -> do_search(numbers, value, from, middle - 1)
+      value > element -> do_search(numbers, value, middle + 1, to)
+    end
+  end
+end

elixir/binary-search/mix.exs

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+defmodule BinarySearch.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :binary_search,
+      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

elixir/binary-search/test/binary_search_test.exs

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+defmodule BinarySearchTest do
+  use ExUnit.Case
+
+  test "finds a value in a tuple with one element" do
+    assert BinarySearch.search({6}, 6) == {:ok, 0}
+    assert BinarySearch.search({3}, 3) == {:ok, 0}
+  end
+
+  test "finds a value in the middle of a tuple" do
+    assert BinarySearch.search({1, 2, 4, 5, 6}, 4) == {:ok, 2}
+    assert BinarySearch.search({1, 3, 4, 6, 8, 9, 11}, 6) == {:ok, 3}
+  end
+
+  test "finds a value at the beginning of a tuple" do
+    assert BinarySearch.search({1, 2, 4, 5, 6}, 1) == {:ok, 0}
+    assert BinarySearch.search({1, 3, 4, 5, 8, 9, 11}, 1) == {:ok, 0}
+  end
+
+  test "finds a value at the end of a tuple" do
+    assert BinarySearch.search({1, 2, 4, 5, 6}, 6) == {:ok, 4}
+    assert BinarySearch.search({1, 3, 4, 5, 8, 9, 11}, 11) == {:ok, 6}
+  end
+
+  test "finds a value in a tuple of odd length" do
+    tuple = {1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 634}
+    assert BinarySearch.search(tuple, 144) == {:ok, 9}
+  end
+
+  test "finds a value in a tuple of even length" do
+    tuple = {1, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377}
+    assert BinarySearch.search(tuple, 21) == {:ok, 5}
+    assert BinarySearch.search(tuple, 34) == {:ok, 6}
+  end
+
+  test "identifies that a value is not included in the tuple" do
+    assert BinarySearch.search({2, 4, 6}, 3) == :not_found
+    assert BinarySearch.search({1, 3, 4, 6, 8, 9, 11}, 7) == :not_found
+  end
+
+  test "a value smaller than the tuple's smallest value is not found" do
+    assert BinarySearch.search({2, 4, 6}, 1) == :not_found
+    assert BinarySearch.search({1, 3, 4, 6, 8, 9, 11}, 0) == :not_found
+  end
+
+  test "a value larger than the tuple's largest value is not found" do
+    assert BinarySearch.search({2, 4, 6}, 9) == :not_found
+    assert BinarySearch.search({1, 3, 4, 6, 8, 9, 11}, 13) == :not_found
+  end
+
+  test "nothing is found in an empty tuple" do
+    assert BinarySearch.search({}, 1) == :not_found
+  end
+
+  test "nothing is found when the left and right bounds cross" do
+    assert BinarySearch.search({1, 2}, 0) == :not_found
+  end
+end

elixir/binary-search/test/test_helper.exs

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+ExUnit.start()
+ExUnit.configure(exclude: :pending, trace: true)