S-99 P11-P20

p11-p20.scala

// P11
def encodeModified[A](ls: Seq[A]): Seq[Any] = encode(ls) map {t => if(t._1 == 1) t._2 else t}

// P12
def decode[A](ls: Seq[(Int, A)]): Seq[A] = ls flatMap(n => List.fill(n._1)(n._2))

// P13
def encodeDirect[A](ls: Seq[A]): Seq[(Int, A)] = {
  if (ls.isEmpty) Nil
  else{
    val (packed, next) = ls span (_ == ls.head)
    (packed.length, packed.head) +: encodeDirect(next)
  }
}

// P14
def duplicate[A](ls: Seq[A]): Seq[A] = ls flatMap(n => List(n, n))

// P15
def duplicateN[A](n: Int, ls: Seq[A]): Seq[A] = ls.flatMap(e => List.fill(n)(e))
// Curry
def duplicateNC[A](n: Int)(ls: Seq[A]): Seq[A] = ls.flatMap(e => List.fill(n)(e))

// P16
def drop[A](n: Int, ls: Seq[A]): Seq[A] = ls.zipWithIndex filter {_._2%n != (n-1)} map {_._1}

// P17
def split[A](n: Int, ls: Seq[A]): (Seq[A], Seq[A]) = (ls.take(n), ls.drop(n))

// P18
def slice[A](i: Int, k: Int, ls: Seq[A]): Seq[A] = ls.take(k).drop(i)

// P19
def rotate[A](i: Int, ls: Seq[A]): Seq[A] = if (i > 0) ls.drop(i) ++ ls.take(i) else ls.drop(ls.length+i) ++ ls.take(ls.length+i)

// P20
def removeAt[A](i: Int, ls: Seq[A]): (Seq[A], A) = (ls.slice(0, i) ++ ls.slice(i+1, ls.length), ls(i))