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to Sum Of Multiples in the Elm Track

Published at Apr 16 2019 · 0 comments
Instructions
Test suite
Solution

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.

Elm Installation

Refer to the Installing Elm page for information about installing elm.

Writing the Code

The first time you start an exercise, you'll need to ensure you have the appropriate dependencies installed. Thankfully, Elm makes that easy for you and will install dependencies when you try to run tests or build the code.

Execute the tests with:

$ elm-test

Automatically run tests again when you save changes:

$ elm-test --watch

As you work your way through the test suite, be sure to remove the skip <| calls from each test until you get them all passing!

Source

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

Submitting Incomplete Solutions

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

Tests.elm

module Tests exposing (tests)

import Expect
import SumOfMultiples exposing (sumOfMultiples)
import Test exposing (..)


tests : Test
tests =
    describe "Sum Of Multiples"
        [ test "[3, 5] 15" <|
            \() -> Expect.equal 45 (sumOfMultiples [ 3, 5 ] 15)
        , skip <|
            test "[7, 13, 17] 20" <|
                \() -> Expect.equal 51 (sumOfMultiples [ 7, 13, 17 ] 20)
        , skip <|
            test "[4, 6] 15" <|
                \() -> Expect.equal 30 (sumOfMultiples [ 4, 6 ] 15)
        , skip <|
            test "[5, 6, 8] 150" <|
                \() -> Expect.equal 4419 (sumOfMultiples [ 5, 6, 8 ] 150)
        , skip <|
            test "[43, 47] 10000" <|
                \() -> Expect.equal 2203160 (sumOfMultiples [ 43, 47 ] 10000)
        , skip <|
            test "[5, 25] 51" <|
                \() -> Expect.equal 275 (sumOfMultiples [ 5, 25 ] 51)
        ]
module SumOfMultiples exposing (sumOfMultiples)


sumOfMultiples : List Int -> Int -> Int
sumOfMultiples multiples limit =
    let
        numsUntilLimit =
            List.range 1 (limit - 1)

        isInMultiples num =
            List.any (\x -> modBy x num == 0) multiples
    in
    numsUntilLimit
        |> List.filter isInMultiples
        |> List.sum

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