is_sort.scala

/**Below are 2 implementations of the same function for checking whether a binary tree is sorted. isSortedA was made by myself as an answer to an exercise in FP in Scala. isSortedB was found on github as an answer to the same exercise. I assume isSortedB is better, but can anyone tell me why (other than the fact that I left out @annotation.tailrec).*/
def isSortedA[A](as: Array[A], gt: (A, A) => Boolean): Boolean = {
  def go(n: Int): Boolean = {
    if (n <= 0) true
    else if (!gt(as(n), as(n-1)))false
    else go(n-1)
  }
  go(as.length-1)
}

def isSortedB[A](as: Array[A], gt: (A,A) => Boolean): Boolean = {
  @annotation.tailrec
  def go(i: Int, prev: A): Boolean = 
    if (i == as.length) true
    else if (gt(as(i), prev)) go(i + 1, as(i))
    else false
  if (as.length == 0) true
  else go(1, as(0))
}