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SergiiVlasiuk's solution

to Change in the Scala Track

Published at Aug 26 2019 · 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)
}
}``````
``````// solution is borrowed form Wows's
object Change {
type Change = Option[List[Int]]

def findFewestCoins(totalPay: Int, coins: List[Int]): Change = {
@annotation.tailrec
def loop(pay: Int, resM: Map[Int, Change]): Map[Int, Change] = {
if (pay > totalPay) resM else {
loop(pay + 1, resultFor(pay, resM))
}
}

def resultFor(pay: Int, resM: Map[Int, Change]): Map[Int, Change] = {
val results = coins.filter(_ <= pay)
.foldLeft(List[Change]())((cs, coin) => resM(pay - coin).map(coin :: _) :: cs)

val result = if (results.flatten.isEmpty) None else Some(results.flatten.minBy(_.length).sorted)
resM + (pay -> result)
}

if (totalPay < 0) None else
loop(1, Map(0 -> Some(List())))(totalPay)
}
}``````