angelikatyborska's solution to Sum Of Multiples on the Ruby track

Instructions

Test suite

Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Given a number, find the sum of all the unique multiples of particular numbers up to but not including that number.

If we list all the natural numbers below 20 that are multiples of 3 or 5, we get 3, 5, 6, 9, 10, 12, 15, and 18.

The sum of these multiples is 78.

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 sum_of_multiples_test.rb

To include color from the command line:

ruby -r minitest/pride sum_of_multiples_test.rb

Source

A variation on Problem 1 at Project Euler http://projecteuler.net/problem=1

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

sum_of_multiples_test.rb

require 'minitest/autorun'
require_relative 'sum_of_multiples'

# Common test data version: 1.1.0 df076b2
class SumOfMultiplesTest < Minitest::Test
  def test_multiples_of_3_or_5_up_to_1
    # skip
    assert_equal 0, SumOfMultiples.new(3, 5).to(1)
  end

  def test_multiples_of_3_or_5_up_to_4
    skip
    assert_equal 3, SumOfMultiples.new(3, 5).to(4)
  end

  def test_multiples_of_3_up_to_7
    skip
    assert_equal 9, SumOfMultiples.new(3).to(7)
  end

  def test_multiples_of_3_or_5_up_to_10
    skip
    assert_equal 23, SumOfMultiples.new(3, 5).to(10)
  end

  def test_multiples_of_3_or_5_up_to_100
    skip
    assert_equal 2_318, SumOfMultiples.new(3, 5).to(100)
  end

  def test_multiples_of_3_or_5_up_to_1000
    skip
    assert_equal 233_168, SumOfMultiples.new(3, 5).to(1000)
  end

  def test_multiples_of_7_13_or_17_up_to_20
    skip
    assert_equal 51, SumOfMultiples.new(7, 13, 17).to(20)
  end

  def test_multiples_of_4_or_6_up_to_15
    skip
    assert_equal 30, SumOfMultiples.new(4, 6).to(15)
  end

  def test_multiples_of_5_6_or_8_up_to_150
    skip
    assert_equal 4_419, SumOfMultiples.new(5, 6, 8).to(150)
  end

  def test_multiples_of_5_or_25_up_to_51
    skip
    assert_equal 275, SumOfMultiples.new(5, 25).to(51)
  end

  def test_multiples_of_43_or_47_up_to_10000
    skip
    assert_equal 2_203_160, SumOfMultiples.new(43, 47).to(10000)
  end

  def test_multiples_of_1_up_to_100
    skip
    assert_equal 4_950, SumOfMultiples.new(1).to(100)
  end

  def test_multiples_of_an_empty_list_up_to_10000
    skip
    assert_equal 0, SumOfMultiples.new().to(10000)
  end

  # Problems in exercism evolve over time, as we find better ways to ask
  # questions.
  # The version number refers to the version of the problem you solved,
  # not your solution.
  #
  # Define a constant named VERSION inside of the top level BookKeeping
  # module, which may be placed near the end of your file.
  #
  # In your file, it will look like this:
  #
  # module BookKeeping
  #   VERSION = 1 # Where the version number matches the one in the test.
  # end
  #
  # If you are curious, read more about constants on RubyDoc:
  # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html

  def test_bookkeeping
    skip
    assert_equal 2, BookKeeping::VERSION
  end
end

class SumOfMultiples
  DEFAULT_FACTORS = [3, 5]

  def initialize(*factors)
    @factors = factors
  end

  def to(boundary)
    multiples = @factors.each_with_object([]) do |factor, multiples|
      multiples << (factor...boundary).step(factor).to_a
    end

    multiples.flatten.uniq.inject(0, :+)
  end

  def self.to(boundary)
    new(*DEFAULT_FACTORS).to(boundary)
  end
end

Community comments

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angelikatyborska

Solution Author

commented over 5 years ago

I moved 3 and 5 to a constant to signify their meaning. I don't like the way the tests for this exercise were written. Why even assume that the default behavior should be to sum multiples of 3 and 5? Why those numbers? The existence of the class to method doesn't make any sense to me.

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angelikatyborska's solution

to Sum Of Multiples in the Ruby Track