# yarik3571's solution

## to Change in the Scala Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Correctly determine the fewest number of coins to be given to a customer such that the sum of the coins' value would equal the correct amount of change.

## For example

• An input of 15 with [1, 5, 10, 25, 100] should return one nickel (5) and one dime (10) or [0, 1, 1, 0, 0]
• An input of 40 with [1, 5, 10, 25, 100] should return one nickel (5) and one dime (10) and one quarter (25) or [0, 1, 1, 1, 0]

## Edge cases

• Does your algorithm work for any given set of coins?
• Can you ask for negative change?
• Can you ask for a change value smaller than the smallest coin value?

The Scala exercises assume an SBT project scheme. The exercise solution source should be placed within the exercise directory/src/main/scala. The exercise unit tests can be found within the exercise directory/src/test/scala.

To run the tests simply run the command `sbt test` in the exercise directory.

For more detailed info about the Scala track see the help page.

## Source

Software Craftsmanship - Coin Change Kata https://web.archive.org/web/20130115115225/http://craftsmanship.sv.cmu.edu:80/exercises/coin-change-kata

## Submitting Incomplete Solutions

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

### ChangeTest.scala

``````import org.scalatest.{Matchers, FunSuite}

/** @version 1.2.0 */
class ChangeTest extends FunSuite with Matchers {

test("single coin change") {
Change.findFewestCoins(25, List(1, 5, 10, 25, 100)) should be (Some(List(25)))
}

test("multiple coin change") {
pending
Change.findFewestCoins(15, List(1, 5, 10, 25, 100)) should be (Some(List(5, 10)))
}

test("change with Lilliputian Coins") {
pending
Change.findFewestCoins(23, List(1, 4, 15, 20, 50)) should be (Some(List(4, 4, 15)))
}

test("change with Lower Elbonia Coins") {
pending
Change.findFewestCoins(63, List(1, 5, 10, 21, 25)) should be (Some(List(21, 21, 21)))
}

test("large target values") {
pending
Change.findFewestCoins(999, List(1, 2, 5, 10, 20, 50, 100)) should be (Some(List(2, 2, 5, 20, 20, 50, 100, 100, 100, 100, 100, 100, 100, 100, 100)))
}

test("possible change without unit coins available") {
pending
Change.findFewestCoins(21, List(2, 5, 10, 20, 50)) should be (Some(List(2, 2, 2, 5, 10)))
}

test("another possible change without unit coins available") {
pending
Change.findFewestCoins(27, List(4, 5)) should be (Some(List(4, 4, 4, 5, 5, 5)))
}

test("no coins make 0 change") {
pending
Change.findFewestCoins(0, List(1, 5, 10, 21, 25)) should be (Some(List()))
}

test("error testing for change smaller than the smallest of coins") {
pending
Change.findFewestCoins(3, List(5, 10)) should be (None)
}

test("error if no combination can add up to target") {
pending
Change.findFewestCoins(94, List(5, 10)) should be (None)
}

test("cannot find negative change values") {
pending
Change.findFewestCoins(-5, List(1, 2, 5)) should be (None)
}
}``````
``````import scala.util.Try

object Change {
type Coins = List[Int]

def findFewestCoins(sum: Int, coins: Coins): Option[Coins] = (sum, coins) match {
case (s, c) if s == 0 => Some(List())
case (s, c) if c.forall(s - _ < 0) => None
case (s, c) /*if c.exists(s - _ >= 0)*/ =>
val pathesOpt = findShortest(sum, coins, List())
pathesOpt
}

private def findShortest(sum: Int,
coins: Coins,
path: Coins): Option[Coins] = {
sum match {
case 0 => Some(path.reverse)
case s =>
def a = coins
.filter(s - _ >= 0)
.flatMap { c => findShortest(s - c, coins, c :: path) }
.minBy(_.length)

Try(a).toOption
}
}

//  private def findShortest(sum: Int,
//                           coins: Coins): Coins =
//    sum match {
//      case 0 => List()
//      case s =>
//        val a = coins
//          .filter(s - _ >= 0)
//          .map { c => c :: findShortest(s - c, coins) }
//          .minBy(_.length)
//        a
//    }

}``````