Given a string of digits, output all the contiguous substrings of length
that string in the order that they appear.
For example, the string "49142" has the following 3-digit series:
And the following 4-digit series:
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:
To include color from the command line:
ruby -r minitest/pride series_test.rb
A subset of the Problem 8 at Project Euler http://projecteuler.net/problem=8
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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(string) @digits = string end def slices(length) raise ArgumentError if length > digits.length digits.chars.each_cons(length).map(&:join) end private attr_reader :digits end
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.