Exercism v3 launches on Sept 1st 2021. Learn more! 🚀🚀🚀
Avatar of thekeele

thekeele's solution

to Series in the Elixir Track

Published at May 21 2019 · 0 comments
Test suite


This exercise has changed since this solution was written.

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:

$ elixir series_test.exs

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!"

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.


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.


if !System.get_env("EXERCISM_TEST_EXAMPLES") do
  Code.load_file("series.exs", __DIR__)

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

defmodule StringSeriesTest do
  use ExUnit.Case

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

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

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

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

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

  @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"]

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

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

  @spec slices(s :: String.t(), size :: integer) :: list(String.t())
  def slices(_, size) when size < 1, do: []
  def slices(s, size) when size == 1, do: String.codepoints(s)
  def slices("", _), do: []
  def slices(<<_::binary-size(1), rest::binary>> = s, size) do
    {slice, _} = String.split_at(s, size)

    if String.length(slice) == size, do: [slice | slices(rest, size)], else: []

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?