Generate Permutations of String in Scala

permutations.scala

/**
 * A question I normally ask in Scala interviews, this is not a tail-recursive implementation
 */
 
object Permutations {
  def permutations(s: String): List[String] = {
    def merge(ins: String, c: Char): Seq[String] =
      for (i <- 0 to ins.length) yield
        ins.substring(0, i) + c + ins.substring(i, ins.length)

    if (s.length() == 1)
      List(s)
    else
      permutations(s.substring(0, s.length - 1)).flatMap { p =>
        merge(p, s.charAt(s.length - 1))
      }
  }
}