Different combinations of an array (C#)

Question

how can we find out different combination of the elements of an array using c# code. are there any inbuilt library function for this.?

for eg: suppose an array has e

Answer 1

static void Main()
{
    var cnk = comb(new [] {1,2,3},2);
    foreach ( var c in cnk)
    {
    }
}

public static IEnumerable<int[]> comb(int[] a, int k)
{
    if (a == null || a.Length == 0 || k < 1 || k > a.Length)
        yield break;

    int n = a.Length;   
    // 1
    if ( k == 1)
        for ( int i = 0; i < n; i++)
        {   
            yield return new int[] {a[i]};
        }
    else
        {
            // k
            for ( int i = 0; i < n - k + 1; i++)
            {
                var res = new int[k];
                    for (int t = i, c = 0; t < i + k - 1; t++, c++)                 
                        res[c] = a[t];              
                for (int j = i + k - 1; j < n; j++)
                {                                                               
                    res[k-1] = a[j];                    
                    yield return res;
                }
            }
        }
}

You should take the algorithm from here, my answer doesn't solve your problem Algorithm to return all combinations of k elements from n

Answer 2

Seemed logic is not absolutely correct as:

var cnk = comb(new[] { 1, 2, 3, 4 }, 3);

This gives 3 variants, but as a matter of fact it is 4:

1 2 3
1 2 4
1 3 4
2 3 4

I guess comb is better to be implemented in recursive way.