/// <summary>
/// Initialize the combinations by settings a copy of the values from the
/// </summary>
/// <param name="values">List of values to select combinations from.</param>
/// <param name="lowerIndex">The size of each combination set to return.</param>
/// <param name="type">The type of Combinations set to generate.</param>
/// <remarks>
/// Copies the array and parameters and then creates a map of booleans that will
/// be used by a permutations object to refence the subset. This map is slightly
/// different based on whether the type is with or without repetition.
///
/// When the type is WithoutRepetition, then a map of upper index elements is
/// created with lower index false's.
/// E.g. 8 choose 3 generates:
/// Map: {1 1 1 1 1 0 0 0}
/// Note: For sorting reasons, false denotes inclusion in output.
///
/// When the type is WithRepetition, then a map of upper index - 1 + lower index
/// elements is created with the falses indicating that the 'current' element should
/// be included and the trues meaning to advance the 'current' element by one.
/// E.g. 8 choose 3 generates:
/// Map: {1 1 1 1 1 1 1 1 0 0 0} (7 trues, 3 falses).
/// </remarks>
private void Initialize(ICollection <T> values, Int32 lowerIndex, GenerateOption type)
{
Type = type;
LowerIndex = lowerIndex;
_values = new List <T>();
_values.AddRange(values);
List <Boolean> map = new List <Boolean>();
if (type == GenerateOption.WithoutRepetition)
{
map.AddRange(_values.Select((t, i) => i < _values.Count - LowerIndex));
}
else
{
for (Int32 i = 0; i < values.Count - 1; ++i)
{
map.Add(true);
}
for (Int32 i = 0; i < LowerIndex; ++i)
{
map.Add(false);
}
}
_permutations = new Permutations <Boolean>(map);
}
/// <summary>
/// Construct a enumerator with the parent object.
/// </summary>
/// <param name="source">The source Permutations object.</param>
public Enumerator(Permutations <T> source)
{
_parent = source;
_lexicographicalOrders = new Int32[source._lexicographicOrders.Length];
source._lexicographicOrders.CopyTo(_lexicographicalOrders, 0);
Reset();
}