Interval representation of an integer set c#

Question

This is an assignment that I've been given, it says that if an hash-set contains the values {12, 13, 14, 23, 88, 89, 90, 91} then they would be represented as the set of intervals { [12..14], [23..23], [88..91]}.

Now to the question, should I use for-each for this? I'm kind of confused since I'm not sure if you could group several intervals into 1 set, or should there be different hash-sets?

I did look into some methods like group-by but i don't know if its the right one to use.

Advice or hints are appreciated!

possibly relevant http://stackoverflow.com/questions/7469828/linq-query-to-split-an-ordered-list-into-sublists-of-contiguous-points-by-some-c/7470048#7470048 — sehe, Feb 19 '12 at 13:25
possible duplicate of [Use LINQ to group a sequence of numbers with no gaps](http://stackoverflow.com/questions/4681949/use-linq-to-group-a-sequence-of-numbers-with-no-gaps) — dtb, Feb 19 '12 at 13:27

CodesInChaos · Accepted Answer · 2012-02-19T13:31:17.523

2

I'd first sort them, and then iterate that ordered set, and combine elements, as long as the difference is only one.

IEnumerable<Tuple<int,int>> GetIntervals(IEnumerable<int> seq)
{
    var orderedSet=seq.OrderBy(i=>i);
    bool first=true;
    int startOfInterval=0,endOfInterval=0;
    foreach(var element in orderedSet)
    {
      if(first)
      {
        startOfInterval=element;
        endOfInterval=element;
        first=false;
      }
      else
      {
        if(element==endOfInterval+1)
          endOfInterval=element;
        else
        {            
          yield return Tuple.Create(startOfInterval, endOfInterval);
          startOfInterval=element;
          endOfInterval=element;
        } 
      }
    }
    yield return Tuple.Create(startOfInterval, endOfInterval);
}

void Main()
{
  var input=new int[]{12, 13, 14, 23, 88, 89, 90, 91};
  GetIntervals(input).Dump();
}

Note that this requires distinct elements in the input. If the input is a hashset, that's guaranteed. Else throw in a Distict() call before calling OrderBy.

edited Feb 19 '12 at 13:31

answered Feb 19 '12 at 13:17

CodesInChaos

106,488
23
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1

Don’t forget to add a final `yield` _after_ your loop; otherwise, you’d miss the last interval. (However, check that the sequence is not empty first; you can `yield break` if it is.) – Douglas Feb 19 '12 at 13:22
Now it's tested, and it works at least for the given example. – CodesInChaos Feb 19 '12 at 13:27
.Dump(), doesn't exist. At least for me. – saturn Feb 19 '12 at 13:49
@saturn That's just the LinqPad test code. You don't need my `Main` function to use the code. – CodesInChaos Feb 19 '12 at 14:01

Interval representation of an integer set c#

1 Answers1