Implementation of extremely sparse arrays

arrays, c#, sparse-matrix

Solution

First, I would argue that plain arrays are quite clearly the wrong kind of data structure for your problem.

How about using a dictionary where you use a 4-tuple as index?

var lookup = new Dictionary<Tuple<int,int,int,int>, int>();

I've never done that myself, but it should work fine. If you don't have `Tuple` ready because you're working with a version of the .NET Framework preceding .NET 4, you could provide your own index type:

struct LookupKey
{
    public readonly int First;
    public readonly int Second;
    public readonly int Third;
    public readonly int Fourth;
    …
}

var lookup = new Dictionary<LookupKey, int>();

Problem

Original source