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lujanfernaud's solution

to Series in the Ruby Track

Published at Mar 07 2019 · 0 comments
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.

In this exercise you're practicing iterating over an array, meaning: executing an operation on each element of an array. Ruby has many useful built-in methods for iterations. Take a look at this article.

Most of the methods listed in the article are not methods specifically for Array, but come from Enumerable. The article doesn't list iterating over consecutive elements. The first challenge is to find a method that does.

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby series_test.rb

To include color from the command line:

ruby -r minitest/pride series_test.rb

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.rb

require 'minitest/autorun'
require_relative 'series'

class SeriesTest < Minitest::Test
  def test_simple_slices_of_one
    series = Series.new('01234')
    assert_equal ['0', '1', '2', '3', '4'], series.slices(1)
  end

  def test_simple_slices_of_one_again
    skip
    series = Series.new('92834')
    assert_equal ['9', '2', '8', '3', '4'], series.slices(1)
  end

  def test_simple_slices_of_two
    skip
    series = Series.new('01234')
    assert_equal ['01', '12', '23', '34'], series.slices(2)
  end

  def test_other_slices_of_two
    skip
    series = Series.new('98273463')
    expected = ['98', '82', '27', '73', '34', '46', '63']
    assert_equal expected, series.slices(2)
  end

  def test_simple_slices_of_two_again
    skip
    series = Series.new('37103')
    assert_equal ['37', '71', '10', '03'], series.slices(2)
  end

  def test_simple_slices_of_three
    skip
    series = Series.new('01234')
    assert_equal ['012', '123', '234'], series.slices(3)
  end

  def test_simple_slices_of_three_again
    skip
    series = Series.new('31001')
    assert_equal ['310', '100', '001'], series.slices(3)
  end

  def test_other_slices_of_three
    skip
    series = Series.new('982347')
    assert_equal ['982', '823', '234', '347'], series.slices(3)
  end

  def test_simple_slices_of_four
    skip
    series = Series.new('01234')
    assert_equal ['0123', '1234'], series.slices(4)
  end

  def test_simple_slices_of_four_again
    skip
    series = Series.new('91274')
    assert_equal ['9127', '1274'], series.slices(4)
  end

  def test_simple_slices_of_five
    skip
    series = Series.new('01234')
    assert_equal ['01234'], series.slices(5)
  end

  def test_simple_slices_of_five_again
    skip
    series = Series.new('81228')
    assert_equal ['81228'], series.slices(5)
  end

  def test_simple_slice_that_blows_up
    skip
    series = Series.new('01234')
    assert_raises ArgumentError do
      series.slices(6)
    end
  end

  def test_more_complicated_slice_that_blows_up
    skip
    slice_string = '01032987583'

    series = Series.new(slice_string)
    assert_raises ArgumentError do
      series.slices(slice_string.length + 1)
    end
  end

  def test_sequential_slices
    skip
    series = Series.new('1234')
    assert_equal ['12', '23', '34'], series.slices(2)
    assert_equal ['123', '234'], series.slices(3)
  end
end
class Series
  def initialize(digits)
    @digits = digits.chars
  end

  def slices(slice_length)
    raise ArgumentError, "Slice length can't be bigger than string length." if
      slice_length > @digits.length

    @digits.each_cons(slice_length).map(&:join)
  end
end

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