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.
Refer to the Installing Elm page for information about installing elm.
The code you have to write is located inside the
src/ directory of the exercise.
Elm automatically installs packages dependencies the first time you run the tests
so we can start by running the tests from the exercise directory with:
To automatically run tests again when you save changes:
$ elm-test --watch
As you work your way through the tests suite in the file
be sure to remove the
calls from each test until you get them all passing!
A variation on Problem 1 at Project Euler http://projecteuler.net/problem=1
It is possible to submit an incomplete solution so you can see how others have completed the exercise.
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) import Set sumOfMultiples : List Int -> Int -> Int sumOfMultiples divisors limit = let multiples = List.map (\n -> multiplesFor n limit ) divisors |> List.concat |> deduplicate in List.sum multiples multiplesFor : Int -> Int -> List Int -> List Int multiplesFor n limit soFar = let -- As per the instructions, we don't -- include `n` as a multiple of itself. numberOfMultiples = if modBy n limit == 0 then limit // n - 1 else limit // n in if List.length soFar == numberOfMultiples then soFar else multiplesFor n limit (n + n * List.length soFar :: soFar) deduplicate : List Int -> List Int deduplicate = Set.fromList >> Set.toList
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.