Solution pour "Les billets du Curiolande" http://enigme.blog.lemonde.fr/2016/01/27/les-billets-du-curiolande/

Curiolande.cs

// Run in LINQPad

void Main()
{
    var noteValues = new[] { 501, 251, 126, 64, 33 };
    var notes = MakeAmount(1000, noteValues);
    notes.GroupBy(v => v).Select(g => new { Value = g.Key, Count = g.Count() }).Dump();
}

IEnumerable<int> MakeAmount(int remaining, IEnumerable<int> noteValues)
{
    var validNotes = noteValues.Where(v => v <= remaining).ToList();
    foreach (var value in validNotes)
    {
        var list = new List<int> { value };
        if (value == remaining)
            return list;
        var rest = MakeAmount(remaining - value, validNotes);
        if (rest != null)
        {
            list.AddRange(rest);
            return list;
        }
    }
    return null;
}