Give change with the least amount of coins

changes_with_least_amount_of_coins.scala

object CoinMachine {

  def changeWithBigCoin(accum: Change, changeOwing: Double, avaliableChange: Change): (Change, Double, Change) = {
    if (changeOwing < 0) throw new Error("Cannot give change with existing coins")
    else if (changeOwing == 0) return (accum, 0, avaliableChange)
    else if (changeOwing >= 5 && avaliableChange.fiveDollarsLeft > 0) changeWithBigCoin(accum.changeFiveDollar(1), changeOwing - 5, avaliableChange.changeFiveDollar(-1))
    else if (changeOwing >= 2 && avaliableChange.twoDollarsLeft > 0) changeWithBigCoin(accum.changeTwoDollar(1), changeOwing - 2, avaliableChange.changeTwoDollar(-1))
    else if (changeOwing >= 1 && avaliableChange.dollarsLeft > 0) changeWithBigCoin(accum.changeDollar(1), changeOwing - 1, avaliableChange.changeDollar(-1))
    else if (changeOwing >= 0.5 && avaliableChange.fiftycentsLeft > 0) changeWithBigCoin(accum.changeFiftyCent(1), changeOwing - 0.5, avaliableChange.changeFiftyCent(-1))
    else throw new Error("Cannot give change on remainder: " + changeOwing)
  }

  def pay(paidAmount: Double, cost: Double, availableChange: Change): Change = {
    val requiredChange: Double = paidAmount - cost

    if (requiredChange < 0) throw new Error("Pay me more")
    else if (requiredChange == 0) return new Change(0, 0, 0, 0)
    else {
      val result = changeWithBigCoin(new Change(0, 0, 0, 0), requiredChange, availableChange)
      result._1
    }
  }
  
  pay(10, 7, new Change(2, 2, 0, 5))

  class Change(fiftycents: Int, dollars: Int, twoDollars: Int, fiveDollars: Int) {
    def changeFiveDollar(amt: Int) = new Change(fiftycents, dollars, twoDollars, fiveDollars + amt)
    def changeTwoDollar(amt: Int) = new Change(fiftycents, dollars, twoDollars + amt, fiveDollars)
    def changeDollar(amt: Int) = new Change(fiftycents, dollars + amt, twoDollars, fiveDollars)
    def changeFiftyCent(amt: Int) = new Change(fiftycents + amt, dollars, twoDollars, fiveDollars)

    override def toString() = "(" + fiftycents + ", " + dollars + ", " + twoDollars + ", " + fiveDollars + ")"

    def fiftycentsLeft = fiftycents;
    def dollarsLeft = dollars;
    def twoDollarsLeft = twoDollars;
    def fiveDollarsLeft = fiveDollars
  }
}