gistfile1.scala

  /* render a tweet using entities: for example
   * val e = Entity(10, 21, """<a href="https://twitter.com/search/?q=%23ScalaIntro">#ScalaIntro</a>""")
   * val entities = Seq(e)
   * render("I love my #ScalaIntro exercises!", entities)
   * should result in
   * """I love my <a href="https://twitter.com/search/?q=%23ScalaIntro">#ScalaIntro</a> exercises!"""
   * The "start" and "end" fields of an Entity refer to the indices in the
   * original string to be substituted with the html field; you may assume
   * that these indices are all non-overlapping.
  */
  case class Entity(start: Int, end: Int, html: String)
  // note: the entities are not guaranteed to be in any particular order
  def render(text: String, entities: Seq[Entity]): CharSequence = {
    val sortedEntities = entities.sortWith((x: Entity, y: Entity) => x.start < y.start)

    def renderIter(buffer: StringBuilder, start: Int, end: Int, sortedEntities: Seq[Entity]): StringBuilder = sortedEntities match {
      case Seq() => buffer.append(text.slice(start, end))
      case e +: es => {
        buffer.append(text.slice(start, e.start)).append(e.html)
        renderIter(buffer, e.end, end, es)
      }
    }
    
    renderIter(new StringBuilder, 0, text.length, sortedEntities).toString
  }

qsort_like.scala

  // Oppa Functional Style
  def render(text: String, entities: Seq[Entity]): CharSequence = {

    def renderIter(start: Int, end: Int, entities: Seq[Entity]): String = entities match {
      case Seq() => text.slice(start, end)
      case e +: es => {
        val (lesser, greater) = es.partition(_.start < e.start)
        renderIter(start, e.start, lesser) + e.html + renderIter(e.end, end, greater)
      }
    }
    
    renderIter(0, text.length, entities)
  }