Merge multiple lists with variable length “popping” elements from each

Question

I\'d like to sort multiple lists (variable number of them) into single list, but keeping the specific order. For example:

List A: { 1,2,3,4,5 }
List B: { 6,7         


        

Answer 1

I'd go with:

static void Main(string[] args)
{
    var a = new List() { 1, 2, 3, 4, 5 };
    var b = new List() { 6, 7, 8 };
    var c = new List() { 9, 10, 11, 12 };

    var abc = XYZ(new[] { a, b, c }).ToList();
}

static IEnumerable XYZ(IEnumerable> lists)
{
    if (lists == null)
        throw new ArgumentNullException();
    var finished = false;
    for (int index = 0; !finished; index++)
    {
        finished = true;
        foreach (var list in lists)
            if (list.Count > index) // list != null (prior checking for count)
            {
                finished = false;
                yield return list[index];
            }
    }
}

I had to use use IList to have indexer and Count. It doesn't creates anything (no enumerators, no lists, etc.), purely yield return.