gistfile1.scala

package recfun
import common._

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()
    }
  }

  /**
   * Exercise 1
   */
  def pascal(c: Int, r: Int): Int = (c,r) match {
    case (0,0) => 1
    case (0,_) => 1
    case (a,b) if a == b => 1
    case (a,b) => pascal(a-1,b-1) + pascal(a,b-1)
  }

  /**
   * Exercise 2
   */
  def balance(chars: List[Char]): Boolean = balance_inner(chars,false,0);
  
  def balance_inner(chars: List[Char],isOpen : Boolean,depth : Int) : Boolean = chars match {
    case head :: tail => {
      head match {
        case '(' => balance_inner(tail,true,depth+1)
        case ')' => balance_inner(tail,(depth-1) != 0,depth-1)
        case _ => balance_inner(tail,isOpen,depth)
      }
    }
    case Nil => {
      !isOpen && depth == 0
    }
  }

  /**
   * Exercise 3
   */
  def countChange(money: Int, coins: List[Int]): Int = {
      (money,coins) match {
        case (0,Nil) => 1
        case (a,_) if a < 0 => 0
        case (_,Nil) => 0
        case (_,head :: tail) => {
          countChange(money - head,coins) + countChange(money,tail)
        }
      }
  }
}