Coalesce a list of overlapping start/end tuples

gistfile1.scala

val ranges = List((2,3), (1,2), (5,11), (4,10), (3,3), (6,7), (15,16))

ranges.sorted.foldLeft(List[(Int, Int)]()) { (acc, t) =>
  acc match {
    case x :: xs if x._2 >= t._1 => (x._1, math.max(x._2, t._2)) :: xs
    case x :: xs => t +: acc
    case _ => List(t)
  }
}.reverse

// List((1,3), (4,11), (15,16))


// variation for Scala 2.10, which allows case init :+ last =>
// not sure if that operation is optimized, though
ranges.sorted.foldLeft(List[(Int, Int)]()) { (acc, t) =>
  acc match {
    case init :+ last if last._2 >= t._1 => init :+ (last._1, math.max(last._2, t._2))
    case init :+ last => acc :+ t
    case _ => List(t)
  }
}

Thanks mate! I had the same intuition, but bumbled the execution.