How to calculate combinations of n elements with no repetitions

Question

Hi I need to calculate all the possible combinations of n-elements without repetition, I am using the following code but Unfortunately when I have a lot of elements it takes too much to get all the combinations...

private void calculateCombinationThread(int index, 
                                        int n, 
                                        List<Ricerca> elements, 
                                        List<Ricerca> rsr, 
                                        ref List<List<Ricerca>> Combinations)
{
    if (n == 0)
    {
        if (rsr.Count != 0)
        {
            List<Ricerca> rrr = new List<Ricerca>() { };
            rrr.AddRange(rsr);
            Combinations.Add(rrr);
        }

        return;
    }

    for (int i = index; i <= elements.Count - n && !outOfMemory; ++i)
    {
        rsr.Add(elements[i]);
        calculateCombinationThread(i + 1, n - 1, elements, rsr, ref Combinations);
        rsr.RemoveAt(rsr.Count - 1);
    }
}

am I doing something wrong!?! is there a faster way to get all the combinations !?!

you use recursive inside a for loop? , something is not right — Jacky, Jun 22 '18 at 10:23
@Jacky yeas... to be honest I have found that solution on the web, it works fine but it is too slow unfortunately — Ale61268967, Jun 22 '18 at 10:27

How to calculate combinations of n elements with no repetitions

0 Answers0