Functional Programming in Scala, Course 1, Exercises

recfun_Main.scala

package recfun

object Main {
  def main(args: Array[String]) {
    println("Pascal's Triangle")
    for (row <- 0 to 10) {
      for (col <- 0 to row)
        print(pascal(col, row) + " ")
      println()
    }

    println("Parentheses Balancing")
    val lista = (
        "(if (zero? x) max (/ 1 x))",
        "I told him (that it’s not (yet) done). (But he wasn’t listening)",
        ":-)", 
        "())("
    )
    lista.productIterator.foreach(arg => {print(arg);print(balance((arg+"").toList));println()})

    println("Counting Change")
    println(countChange(4, List(1, 2)))
  }

  /**
   * Exercise 1
   */
    def pascal(c: Int, r: Int): Int = {
        if (c == 0 || r ==c) {
            1;
        } else {
            pascal(c, r-1) + pascal(c-1, r-1);
        }
    }

  
  /**
   * Exercise 2
   */
    def balance(chars: List[Char]): Boolean = {
        def balIter(cs: List[Char], c: Int):Boolean = {
            if (cs.isEmpty) {
                if (c == 0) true else false
            } else {
                cs.head.toString match {
                    case ")" => if (c < 1) false else balIter(cs.tail, c - 1);
                    case "(" => balIter(cs.tail, c + 1);
                    case   _ => balIter(cs.tail, c);
                }
               /**
                * if (cs.head.toString == ")") {
                *     if (c < 1) false else balIter(cs.tail, c - 1);
                * } else if (cs.head.toString == "(") {
                *     balIter(cs.tail, c + 1);
                * } else {
                *     balIter(cs.tail, c);
                * }
                */
            }
        }
        balIter(chars, 0)
    }
        
  
  /**
   * Exercise 3
   */
    def countChange(money: Int, coins: List[Int]): Int = {
    if (money == 0) 1 else if (money <= 0 || coins.isEmpty) 0 else {countChange(money - coins.head, coins) + countChange(money, coins.tail)}
    }
  }