angelikatyborska's solution to Series on the Elixir track

Instructions

Test suite

Solution

Given a string of digits, output all the contiguous substrings of length n in that string in the order that they appear.

For example, the string "49142" has the following 3-digit series:

"491"
"914"
"142"

And the following 4-digit series:

"4914"
"9142"

And if you ask for a 6-digit series from a 5-digit string, you deserve whatever you get.

Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.

Running tests

Execute the tests with:

$ mix test

Pending tests

In the test suites, all but the first test have been 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:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.

Source

A subset of the Problem 8 at Project Euler http://projecteuler.net/problem=8

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

series_test.exs

defmodule StringSeriesTest do
  use ExUnit.Case

  # @tag :pending
  test "slices of size 1" do
    assert StringSeries.slices("01234", 1) == ["0", "1", "2", "3", "4"]
  end

  @tag :pending
  test "slices of size 2" do
    assert StringSeries.slices("01234", 2) == ["01", "12", "23", "34"]
  end

  @tag :pending
  test "slices of size 3" do
    assert StringSeries.slices("01234", 3) == ["012", "123", "234"]
  end

  @tag :pending
  test "slices of size 4" do
    assert StringSeries.slices("01234", 4) == ["0123", "1234"]
  end

  @tag :pending
  test "slices same size as string" do
    assert StringSeries.slices("01234", 5) == ["01234"]
  end

  @tag :pending
  test "Unicode characters count as a single character" do
    assert StringSeries.slices("José", 1) == ["J", "o", "s", "é"]
    assert StringSeries.slices("José", 2) == ["Jo", "os", "sé"]
  end

  @tag :pending
  test "slices with size longer than string return empty list" do
    assert StringSeries.slices("01234", 6) == []
  end

  @tag :pending
  test "slices with size zero or negative return empty list" do
    assert StringSeries.slices("01234", -1) == []
    assert StringSeries.slices("01234", 0) == []
  end
end

test_helper.exs

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

defmodule StringSeries do
  @doc """
  Given a string `s` and a positive integer `size`, return all substrings
  of that size. If `size` is greater than the length of `s`, or less than 1,
  return an empty list.
  """
  @spec slices(s :: String.t(), size :: integer) :: list(String.t())
  def slices(_s, size) when size <= 0, do: []

  def slices(s, size) do
    s
    |> String.split("", trim: true)
    |> Enum.chunk_every(size, 1, :discard)
    |> Enum.map(&Enum.join/1)
  end
end

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angelikatyborska's solution

to Series in the Elixir Track