private List<Combination> GeneratePermutations(Combination numbers)
{
List<Combination> permutations = new List<Combination>();
if (1 == numbers.Length) {
permutations.Add (numbers);
return permutations;
}
for (var i=0; i<numbers.Length; i++) {
List<Combination> subPerm = GeneratePermutations (numbers.GetSubCombination(i, numbers.Step+1));
foreach (var sub in subPerm) {
var newNumbers = new int[numbers.Length];
newNumbers [0] = numbers [i];
var length = sub.Length;
Array.Copy (sub.Numbers, 0, newNumbers, 1, length);
permutations.Add (new Combination(newNumbers, sub.Step));
}
}
return permutations;
}