Function to check if a list has no gaps

I just want a function that returns true if all the elements of a List[Integer] follow each other, i.e.

noGaps(List(3,4,5)) // true
noGaps(List(4,3,5)) // false
noGaps(List(3,4,6)) // false

I have something t开发者_JAVA百科hat works but it's a bit verbose - what's the most elegant solution?

How about this?

def noGaps(xs: Seq[Int]) =
  xs.size < 2 || xs.sliding(2).forall { case Seq(x, y) => y == x + 1 }

def noGaps(xs: Seq[Int]) = xs.isEmpty||xs.tail == xs.map(_+1).init

You can make it explicit that you compare the List to a Range:

def noGaps(l: Seq[Int]): Boolean =
  l.isEmpty || l.sameElements(l.head to l.last)

Note that, although elegant, this is slightly less efficient than the sliding solution, due to l.last which is O(n). If n is the size of the list and i the first element for which there is a gap (or n if no gap), then the sliding solution would be performed in i steps whereas this one is performed in n + i steps.