zip strings with tail recursion

stringzip.scala

impprt scala.annotation.tailrec

def f(a: String, b: String): String = {
  @tailrec
  def loop(a: String, b: String, acc: String): String = {
    if (a.length == 0 && b.length ==0 ) acc
    else {
      val (al, ar) = a.splitAt(1)
      val (bl, br) = b.splitAt(1)
      val x = al + bl
      loop(ar, br, x + acc)}
  }
  loop(a.reverse,b.reverse,"")
}
f("hacker","ranker")