simple recursion examples

simple_recursion_examples.scala

def sumInts(a: Int, b: Int): Int =
  if (a > b) 0 else a + sumInts(a + 1, b)
  
def countChange(money: Int, couns: List[Int]): Int = {
  if (money == 0) 1
  else if (money < 0) 0
  else if (coins.isEmpty && money >= 1) 0
  else { 
    countChange(money, coins.tail) + countChange(money - coins.head, coins)
  }
}

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


/**
 * tail recursion
 */

def sum(f: Int => Int, a: Int, b: Int): Int = {
  def loop(a: Int, acc: Int): Int = {
    if (a > b) acc
    else loop(a + 1, acc + f(a))
  }
  loop(a, 0)
}