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# tagliala's solution

## to Largest Series Product in the Ruby Track

Published at Feb 26 2020 · 0 comments
Instructions
Test suite
Solution

Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.

For example, for the input `'1027839564'`, the largest product for a series of 3 digits is 270 (9 * 5 * 6), and the largest product for a series of 5 digits is 7560 (7 * 8 * 3 * 9 * 5).

Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.

For the input `'73167176531330624919225119674426574742355349194934'`, the largest product for a series of 6 digits is 23520.

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 largest_series_product_test.rb
``````

To include color from the command line:

``````ruby -r minitest/pride largest_series_product_test.rb
``````

## Source

A variation on 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.

### largest_series_product_test.rb

``````require 'minitest/autorun'
require_relative 'largest_series_product'

# Common test data version: 1.2.0 85da7a5
class LargestSeriesProductTest < Minitest::Test
def test_finds_the_largest_product_if_span_equals_length
# skip
assert_equal 18, Series.new('29').largest_product(2)
end

def test_can_find_the_largest_product_of_2_with_numbers_in_order
skip
assert_equal 72, Series.new('0123456789').largest_product(2)
end

def test_can_find_the_largest_product_of_2
skip
assert_equal 48, Series.new('576802143').largest_product(2)
end

def test_can_find_the_largest_product_of_3_with_numbers_in_order
skip
assert_equal 504, Series.new('0123456789').largest_product(3)
end

def test_can_find_the_largest_product_of_3
skip
assert_equal 270, Series.new('1027839564').largest_product(3)
end

def test_can_find_the_largest_product_of_5_with_numbers_in_order
skip
assert_equal 15120, Series.new('0123456789').largest_product(5)
end

def test_can_get_the_largest_product_of_a_big_number
skip
assert_equal 23520, Series.new('73167176531330624919225119674426574742355349194934').largest_product(6)
end

def test_reports_zero_if_the_only_digits_are_zero
skip
assert_equal 0, Series.new('0000').largest_product(2)
end

def test_reports_zero_if_all_spans_include_zero
skip
assert_equal 0, Series.new('99099').largest_product(3)
end

def test_rejects_span_longer_than_string_length
skip
assert_raises(ArgumentError) do
Series.new('123').largest_product(4)
end
end

def test_reports_1_for_empty_string_and_empty_product_0_span
skip
assert_equal 1, Series.new('').largest_product(0)
end

def test_reports_1_for_nonempty_string_and_empty_product_0_span
skip
assert_equal 1, Series.new('123').largest_product(0)
end

def test_rejects_empty_string_and_nonzero_span
skip
assert_raises(ArgumentError) do
Series.new('').largest_product(1)
end
end

def test_rejects_invalid_character_in_digits
skip
assert_raises(ArgumentError) do
Series.new('1234a5').largest_product(2)
end
end

def test_rejects_negative_span
skip
assert_raises(ArgumentError) do
Series.new('12345').largest_product(-1)
end
end
end``````
``````# frozen_string_literal: true

class Series
FORMAT = /\A[0-9]*\z/.freeze

def initialize(number)
raise ArgumentError unless number.match?(FORMAT)

@number = number.chars.map(&:to_i)
end

def largest_product(digits)
raise ArgumentError if digits > number.length
return 1 if digits.zero?

number
.each_cons(digits)
.map { |chunk| chunk.reduce(:*) }
.max
end

private

end``````

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