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to Sum Of Multiples in the Elixir Track

Published at Jul 13 2018 · 0 comments
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.

Running tests

Execute the tests with:

$ elixir sum_of_multiples_test.exs

Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant @tag :pending with a # symbol.

For example:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

For more detailed information about the Elixir track, please see the help page.

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.exs

if !System.get_env("EXERCISM_TEST_EXAMPLES") do
  Code.load_file("sum_of_multiples.exs", __DIR__)
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule SumOfMultiplesTest do
  use ExUnit.Case

  # @tag :pending
  test "sum to 1" do
    assert SumOfMultiples.to(1, [3, 5]) == 0
  end

  @tag :pending
  test "sum to 3" do
    assert SumOfMultiples.to(4, [3, 5]) == 3
  end

  @tag :pending
  test "sum to 10" do
    assert SumOfMultiples.to(10, [3, 5]) == 23
  end

  @tag :pending
  test "sum to 20" do
    assert SumOfMultiples.to(20, [3, 5]) == 78
  end

  @tag :pending
  test "sum to 100" do
    assert SumOfMultiples.to(100, [3, 5]) == 2318
  end

  @tag :pending
  test "sum to 1000" do
    assert SumOfMultiples.to(1000, [3, 5]) == 233_168
  end

  @tag :pending
  test "configurable 7, 13, 17 to 20" do
    multiples = [7, 13, 17]
    assert SumOfMultiples.to(20, multiples) == 51
  end

  @tag :pending
  test "configurable 4, 6 to 15" do
    multiples = [4, 6]
    assert SumOfMultiples.to(15, multiples) == 30
  end

  @tag :pending
  test "configurable 5, 6, 8 to 150" do
    multiples = [5, 6, 8]
    assert SumOfMultiples.to(150, multiples) == 4419
  end

  @tag :pending
  test "configurable 43, 47 to 10000" do
    multiples = [43, 47]
    assert SumOfMultiples.to(10000, multiples) == 2_203_160
  end
end
defmodule SumOfMultiples do
  @doc """
  Adds up all numbers from 1 to a given end number that are multiples of the factors provided.
  """
  @spec to(non_neg_integer, [non_neg_integer]) :: non_neg_integer
  def to(limit, _) when limit <= 1, do: 0
  def to(limit, factors) do
    1..(limit - 1)
    |> Stream.filter( &(is_multiple? &1, factors) )
    |> Enum.sum
  end

  defp is_multiple?(num, factors), do: Enum.any? factors, &(rem(num, &1) == 0)

end

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