Exercism v3 launches on Sept 1st 2021. Learn more! ๐๐๐

Published at Apr 28 2021
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Instructions

Test suite

Solution

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

If we list all the natural numbers up to but not including 20 that are multiples of either 3 or 5, we get 3, 5, 6 and 9, 10, 12, 15, and 18.

The sum of these multiples is 78.

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.

```
module Test.Main where
import Prelude
import Effect (Effect)
import SumOfMultiples (sumOfMultiples)
import Test.Unit (TestSuite, suite, test)
import Test.Unit.Assert as Assert
import Test.Unit.Main (runTest)
main :: Effect Unit
main = runTest suites
suites :: TestSuite
suites = do
suite "SumOfMultiples.sumOfMultiples" do
test "multiples of 3 or 5 up to 1" do
Assert.equal 0 (sumOfMultiples [3, 5] 1)
test "multiples of 3 or 5 up to 4" do
Assert.equal 3 (sumOfMultiples [3, 5] 4)
test "multiples of 3 up to 7" do
Assert.equal 9 (sumOfMultiples [3] 7)
test "multiples of 3 or 5 up to 10" do
Assert.equal 23 (sumOfMultiples [3, 5] 10)
test "multiples of 3 or 5 up to 100" do
Assert.equal 2318 (sumOfMultiples [3, 5] 100)
test "multiples of 3 or 5 up to 1000" do
Assert.equal 233168 (sumOfMultiples [3, 5] 1000)
test "multiples of 7, 13 or 17 up to 20" do
Assert.equal 51 (sumOfMultiples [7, 13, 17] 20)
test "multiples of 4 or 6 up to 15" do
Assert.equal 30 (sumOfMultiples [4, 6] 15)
test "multiples of 5, 6 or 8 up to 150" do
Assert.equal 4419 (sumOfMultiples [5, 6, 8] 150)
test "multiples of 5 or 25 up to 51" do
Assert.equal 275 (sumOfMultiples [5, 25] 51)
test "multiples of 43 or 47 up to 10000" do
Assert.equal 2203160 (sumOfMultiples [43, 47] 10000)
test "multiples of 1 up to 100" do
Assert.equal 4950 (sumOfMultiples [1] 100)
test "multiples of an empty list up to 10000" do
Assert.equal 0 (sumOfMultiples [] 10000)
```

```
module SumOfMultiples
( sumOfMultiples
) where
import Prelude (otherwise, ($), (*), (+), (<=))
import Data.Array
sumOfMultiples :: Array Int -> Int -> Int
sumOfMultiples xs n = foldl (+) 0 $ nub $ concatMap (findMultiples 1 n) xs
findMultiples :: Int -> Int -> Int -> Array Int
findMultiples i n y
| n <= (y * i) = [0]
| otherwise = (y * i) : (findMultiples (i + 1) n y)
```

A huge amount can be learned from reading other peopleโs 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.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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