Learning Scala / Scala snippets

Coins.scala

package com.davidlukac.learn.scala

/**
  * Created by davidlukac on 30/04/16.
  */
class Coins {

  def countChange(money: Int, coins: List[Int]): Int = {

    // Just for the sake of algorithm logic, sort the coins from highest value, to smallest value.
    val sortedCoins = coins.sorted.reverse

    /**
      * Recursive function that counts number of ways to split given amount of money with given coins.
      * E.g.:
      * 10GBP can by split using coins 1, 2 and 5 in following ways:
      * - 01: 5 + 5
      * - 02: 5 + 2 + 2 + 1
      * - 03: 5 + 2 + 1 + 1 + 1
      * - ...
      * - Nm:   2 + 2 + 2 + 2 + 2
      * - Nm+1: 2 + 2 + 2 + 2 + 1 + 1
      * - ...
      * - 10: 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
      * @param money Sum to split.
      * @param coins List of coins.
      * @return Number of way we can split the sum.
      */
    def countChangeRec(money: Int, coins: List[Int]): Int = {
      // We have successfully subtracted the sum of money using given coins to zero - count as positive result.
      if (money == 0) 1
      // If the subtraction got us below zero, we can't use this combination of coins,
      // also if there are no coin combinations left and we still didn't reach zero, this can't be counted as
      // successful coin change.
      else if (money < 0 || coins.isEmpty) 0
      // Recursively try to find out number of ways to get the change, with remainder of sum and remainder of coins.
      else countChangeRec(money - coins.head, coins) + countChangeRec(money, coins.tail)
    }

    countChangeRec(money, sortedCoins)
  }

}

object Coins {
  def main(args: Array[String]) {
    val c = new Coins
    // Expected result - 293.
    println(c.countChange(100, List(1, 5, 10 , 25, 50, 100)))
  }
}