Published at Jul 13 2018
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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
```

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.

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

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