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Address Subsets to-do about clearer members names #1048

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Nov 18, 2023
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Address Subsets to-do about clearer members names #1048

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43 changes: 21 additions & 22 deletions MoreLinq/Subsets.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -136,14 +136,12 @@ sealed class SubsetEnumerator : IEnumerator<IList<T>>
readonly T[] _subset; // the current subset to return
readonly int[] _indices; // indices into the original set

// TODO: It would be desirable to give these index members clearer names
bool _continue; // termination indicator, set when all subsets have been produced

int _m; // previous swap index (upper index)
int _m2; // current swap index (lower index)
int _k; // size of the subset being produced
int _n; // size of the original set (sequence)
int _z; // count of items excluded from the subset
int _prevSwapIndex; // previous swap index (upper index)
int _currSwapIndex; // current swap index (lower index)
int _subsetSize; // size of the subset being produced
int _setSize; // size of the original set (sequence)

public SubsetEnumerator(IList<T> set, int subsetSize)
{
Expand All @@ -161,11 +159,10 @@ public SubsetEnumerator(IList<T> set, int subsetSize)

public void Reset()
{
_m = _subset.Length;
_m2 = -1;
_k = _subset.Length;
_n = _set.Count;
_z = _n - _k + 1;
_prevSwapIndex = _subset.Length;
_currSwapIndex = -1;
_subsetSize = _subset.Length;
_setSize = _set.Count;
_continue = true;
}

Expand All @@ -178,35 +175,37 @@ public bool MoveNext()
if (!_continue)
return false;

if (_m2 == -1)
if (_currSwapIndex == -1)
{
_m2 = 0;
_m = _k;
_currSwapIndex = 0;
_prevSwapIndex = _subsetSize;
}
else
{
if (_m2 < _n - _m)
if (_currSwapIndex < _setSize - _prevSwapIndex)
{
_m = 0;
_prevSwapIndex = 0;
}
_m++;
_m2 = _indices[_k - _m];
_prevSwapIndex++;
_currSwapIndex = _indices[_subsetSize - _prevSwapIndex];
}

for (var j = 1; j <= _m; j++)
_indices[_k + j - _m - 1] = _m2 + j;
for (var j = 1; j <= _prevSwapIndex; j++)
_indices[_subsetSize + j - _prevSwapIndex - 1] = _currSwapIndex + j;

ExtractSubset();

_continue = _indices.Length > 0 && _indices[0] != _z;
// ........................................ count of items excluded from the subset
_continue = _indices is [var i, ..] && i != _setSize - _subsetSize + 1;

return true;
}

void IDisposable.Dispose() { }

void ExtractSubset()
{
for (var i = 0; i < _k; i++)
for (var i = 0; i < _subsetSize; i++)
_subset[i] = _set[_indices[i] - 1];
}
}
Expand Down