Compression for HackerRank

Compression.scala

 def pack(s:String):List[String]=
   if (s.isEmpty()) Nil
   else{
    val (packed, rest) = s span { _ == s.head }
    packed::pack(rest)  
   }    
   
   def rle(s:String)= pack(s).map(e=>(e.head,e.length))
   
   def compress(s:String):String=
    rle(s).map{case (ch,len)=>if (len==1) ch else s"$ch$len"}.mkString 
   
   compress("aaaaabbbbbbbbbccccpqrstuv")
   
   // a5b9c4pqrstuv

Compression2.scala

// Another implementation

def compress(s: String): String = {
    @scala.annotation.tailrec
    def recurse(l: List[(Char, Int)], acc: List[(Char, Int)] = Nil): List[(Char, Int)] = {
      val (head@(ch, n)) :: tail = l
      tail match {
        case Nil => head :: acc
        case (`ch`, tailn) :: subtail => recurse((ch, n + tailn) :: subtail, acc)
        case _ => recurse(tail, head :: acc)
      }
    }
    val listCharInt=recurse(s.toList.map(_->1))
    listCharInt.reverse.map{ case (ch, n) => if (n == 1) ch else s"$ch$n" }.mkString
  }