/// <summary>
/// Construct a enumerator with the parent object.
/// </summary>
/// <param name="source">The source Permutations object.</param>
public Enumerator(Permutations <T> source)
{
_ = source ?? throw new ArgumentNullException(nameof(source));
_myParent = source;
_myLexicographicalOrders = new int[source._myLexicographicOrders.Length];
_myValues = new List <T>(source._myValues.Count);
source._myLexicographicOrders.CopyTo(_myLexicographicalOrders, 0);
_myPosition = Position.BeforeFirst;
}
/// <summary>
/// Create a combination set from the provided list of values.
/// The upper index is calculated as values.Count, the lower index is specified.
/// </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>
public Combinations(IEnumerable <T> values, int lowerIndex, GenerateOption type)
{
_ = values ?? throw new ArgumentNullException(nameof(values));
// Copy the array and parameters and then create a map of booleans that will
// be used by a permutations object to reference 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).
Type = type;
LowerIndex = lowerIndex;
_myValues = values.ToList();
List <bool> myMap;
if (type == GenerateOption.WithoutRepetition)
{
myMap = new List <bool>(_myValues.Count);
myMap.AddRange(_myValues.Select((t, i) => i < _myValues.Count - LowerIndex));
}
else
{
myMap = new List <bool>(_myValues.Count + LowerIndex - 1);
for (var i = 0; i < _myValues.Count - 1; ++i)
{
myMap.Add(true);
}
for (var i = 0; i < LowerIndex; ++i)
{
myMap.Add(false);
}
}
_myPermutations = new Permutations <bool>(myMap);
}
/// <summary>
/// Create a variation set from the indicated list of values.
/// The upper index is calculated as values.Count, the lower index is specified.
/// </summary>
/// <param name="values">List of values to select variations from.</param>
/// <param name="lowerIndex">The size of each variation set to return.</param>
/// <param name="type">Type indicates whether to use repetition in set generation.</param>
public Variations(IEnumerable <T> values, int lowerIndex, GenerateOption type)
{
Type = type;
LowerIndex = lowerIndex;
_myValues = values.ToList();
if (type != GenerateOption.WithoutRepetition)
{
return;
}
var myMap = new List <int>(_myValues.Count);
var index = 0;
for (var i = 0; i < _myValues.Count; ++i)
{
myMap.Add(i >= _myValues.Count - LowerIndex ? index++ : int.MaxValue);
}
_myPermutations = new Permutations <int>(myMap);
}
