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giusdp's solution

to Series in the Elixir Track

Published at Jun 22 2020 · 0 comments
Test suite

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!"

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.


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) == []


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("", _), do: []
  def slices(_, size) when size <= 0, do: []
  def slices(<<l>>, 1), do: [<<l>>]
  def slices(<<h>> <> rest, size) do
    if (size > String.length(<<h>> <> rest)) do
      sliced = String.slice(<<h>> <> rest, 0..(size-1))
      [sliced | slices(rest, size)]

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