Published at Jul 13 2018
·
2 comments

Instructions

Test suite

Solution

Given a string of digits, output all the contiguous substrings of length `n`

in
that string.

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*.

For installation and learning resources, refer to the exercism help 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')
expected = ['982', '823', '234', '347']
assert_equal expected, 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_of_digits)
@digits = string_of_digits
end
def slices(n)
fail ArgumentError if n < 0
fail ArgumentError if n > digits.length
digits.each_cons(n).to_a
end
private
def digits
@digits.chars.map(&:to_i)
end
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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## Community comments

I moved some work from the constructor. Not sure that I am happy with that. It seems very expensive to compute digits many times.

The first argument error could be removed. It is handled by each_cons, but I like it for making the pre-conditions explicit. I could have used a range I suppose.

This solution returns an array of arrays. To return an array of strings, the line 10 should be updated this way: digits.each_cons(n).to_a.map(&:join)