Ensuring contiguity among pairs

gistfile1.scala

def ensureContiguity(xs: List[(Int, Int)], acc: List[(Int, Int)] = List.empty): List[(Int, Int)] =
  (xs, acc) match {
    case (Nil, l) => l
    case (l, Nil) => ensureContiguity(l dropRight 1, List(l.last))
    case _ => {
      val t = xs.last
      val h = acc.head

      if (t._2 == h._1)
        ensureContiguity(xs dropRight 1, t +: acc)
      else
        ensureContiguity(xs dropRight 1, t +: (t._2, h._1) +: acc)
    }
  }

/*
scala> ensureContiguity(List((1, 2), (2, 3), (6, 9), (10, 11)))
res3: List[(Int, Int)] = List((1,2), (2,3), (3,6), (6,9), (9,10), (10,11))

scala> ensureContiguity(List((4, 9), (40, 200)))
res4: List[(Int, Int)] = List((4,9), (9,40), (40,200))

scala> ensureContiguity(List.empty)
res5: List[(Int, Int)] = List()

scala> ensureContiguity(List((1, 2), (2, 3)))
res6: List[(Int, Int)] = List((1,2), (2,3))
*/