internal MtxOne(Link <MtxOne> prvRow, Link <MtxOne> prvCol, ColHeader header, object rowInfo = null)
{
RowLink = new Link <MtxOne>(this, prvRow);
ColLink = new Link <MtxOne>(this, prvCol);
Header = header;
RowInfo = rowInfo;
}
public IEnumerable <IEnumerable <MtxOne> > Solve()
{
// If R[h] == h
if (_mtx.Solved)
{
// print the current solution and return
yield return(_slnRows);
yield break;
}
// Otherwise choose a column object c
var sizeMin = int.MaxValue;
ColHeader colSelect = null;
foreach (var col in _mtx.Columns)
{
if (col.Size < sizeMin)
{
if (col.Size == 0)
{
// Slight shortcut
yield break;
}
colSelect = col;
sizeMin = col.Size;
}
}
// Cover column c
Debug.Assert(colSelect != null, nameof(colSelect) + " != null");
colSelect.Cover();
// For each r <- D[c], D[D[c]],..., while r != c
foreach (var one in colSelect.Ones)
{
// Set O[k] <- r
_slnRows.Push(one);
// For each j <- R[r], R[R[r]],..., while j != r
foreach (var colCovered in one.RowLink.Elements().Skip(1).Select(o => o.Header))
{
// cover column j
colCovered.Cover();
}
// search(k + 1)
// NOTE: We don't use k because we put solutions into a stack whose
// length is kept internal to the stack - effectively, k == _solns.Count.
foreach (var soln in Solve())
{
yield return(soln);
}
// r <- O[k], c <- C[r]
// NOTE: We haven't altered r (one) or c (colSelect) so no need to reset them here but since we
// keep our solutions in a stack, we have to pop the current one off
_slnRows.Pop();
// For each j <- L[r], L[L[r]],..., while j != r
foreach (var colUncover in one.RowLink.Elements(false).Skip(1).Select(o => o.Header))
{
colUncover.Uncover();
}
}
// Uncover column c and return
colSelect.Uncover();
}
