Question

I need to test if some objects inside a database fill a specific range, i.e 0-999.

I’m using C# and I’ve created a generic class using IComparable to test for the intersection. This works fine but I need to invert and find all the gaps that I have in this interval.

My database objects have start and end properties, that are integers. I can find where are the gaps, but I need to cluster them to create the missing pieces.

foreach (var interval in intervals)
{
    for (int i = 0; i <= 999; i++)
    {
        if (Range<int>.Intersects(interval,new Range<int>(i,i)))
            continue;
        else
            doesNotIntersect.Add(i);
    }
}

With this code I have a pretty list of “holes”. What I’m trying to do now is to group these values, but I find that my solution is not optimal and certainly not elegant.

I’ve read about BitArrays, but how can they help me? I wish that from a list of ranges I can find the gaps in a fixed range. If we are talking about a line, I need basically the result of fixed – intervals.

I can only use .NET to solve this. I have a large piece of middleware and this process of validation will occur several times a day, so I prefer not having to go through middleware and then databasr to solve.

Let me try to create a picture

Fixed range that needs to be filled

111111111

Ranges that objects provided

101100001

Ranges that need to be filled

010011110

This is my range object:

public class Range<T> where T : IComparable
{
    public T Start { get; set; }
    public T End { get; set; }

    public Range(T start, T end)
    {
        Start = start;
        End = end;
    }

    public static bool Intersects(Range<T> left,Range<T> right)
    {
        if (left.Start.CompareTo(right.Start) == 0)
            return true;

        if (left.Start.CompareTo(right.Start) > 0)
        {
            return left.Start.CompareTo(right.End) <= 0;
        }

        return right.Start.CompareTo(left.End) <= 0;
    }
}

I need to find gaps in start end points, instead of continous intervals.

Help?

Answer 1

00000000000000000000000000000
|              |
8:00           9:00                       

Suppose every ‘0’ in the bitarray represents a time unit(second, hour etc.)
Start looping the intervals and set bits according to start & end values.
Now you will have something like this

11110001111110001111000111000

The ‘0’ are your grouped gaps