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:
To include color from the command line:
ruby -r minitest/pride sum_of_multiples_test.rb
A variation on Problem 1 at Project Euler http://projecteuler.net/problem=1
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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
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.