private void SearchRec(DomainStore dstore, Sudoku sudoku)
{
// Select the sudoku cell with the smallest domain and try to fill it first
Field f = dstore.GetFieldWithSmallestDomain();
if (f == null)
{
// There's no cell with a domain size > 1 left, the sudoku is filled completely
dstore.UpdateSudoku(sudoku);
return;
}
// Try to solve the sudoku with every possible value of the cell's domain
HashSet <int> domain = dstore.GetDomain(f);
foreach (int digit in domain)
{
DomainStore dstoreClone = new(dstore);
dstoreClone.SetDomain(f, new HashSet <int>()
{
digit
});
Search(dstoreClone, sudoku);
if (sudoku.IsSolved())
{
return;
}
else
{
// Prune this try and take a step back
dstore.UpdateSudoku(sudoku);
}
}
}
public DomainStore(DomainStore dstore)
{
InitFieldsByDomainSize();
for (int x = 0; x < Sudoku.Size; x++)
{
for (int y = 0; y < Sudoku.Size; y++)
{
SetDomain(x, y, dstore.GetDomain(x, y));
}
}
}
private bool Propagate(DomainStore dstore)
{
if (_cts.IsCancellationRequested)
{
return(false);
}
bool domainsHaveChanged = EliminateRowValues(dstore);
domainsHaveChanged |= EliminateColumnValues(dstore);
domainsHaveChanged |= EliminateRegionValues(dstore);
return(domainsHaveChanged);
}
private bool EliminateColumnValues(DomainStore dstore)
{
bool domainsHaveChanged = false;
for (int y = 0; y < Sudoku.Size; y++)
{
List <Field> column = new();
for (int x = 0; x < Sudoku.Size; x++)
{
Field f = new(x, y);
column.Add(f);
}
domainsHaveChanged |= Eliminate(dstore, column);
}
return(domainsHaveChanged);
}
private void Search(DomainStore dstore, Sudoku sudoku)
{
if (_cts.IsCancellationRequested)
{
return;
}
// Try to solve sudoku via constraint propagation only
while (Propagate(dstore))
{
}
dstore.UpdateSudoku(sudoku);
if (sudoku.IsSolved())
{
return;
}
// If that didn't work, perform a recursive search
SearchRec(dstore, sudoku);
}
private bool EliminateRegionValues(DomainStore dstore)
{
bool domainsHaveChanged = false;
for (int i = 0; i < Sudoku.Size; i++)
{
List <Field> region = new();
for (int j = 0; j < Sudoku.Size; j++)
{
int x = (i / Sudoku.RegionSize) * Sudoku.RegionSize + j / Sudoku.RegionSize;
int y = (i % Sudoku.RegionSize) * Sudoku.RegionSize + j % Sudoku.RegionSize;
Field f = new(x, y);
region.Add(f);
}
domainsHaveChanged |= Eliminate(dstore, region);
}
return(domainsHaveChanged);
}
private bool Eliminate(DomainStore dstore, IEnumerable <Field> fields)
{
bool domainsHaveChanged = false;
// Go through the cells and remeber the digits you see
HashSet <int> seenDigits = new();
foreach (Field f in fields)
{
if (dstore.GetDomainSize(f) == 1)
{
HashSet <int> domain = dstore.GetDomain(f);
foreach (int digit in domain) // Workaround to access first HashSet value quickly
{
seenDigits.Add(digit);
break;
}
}
}
// Now, go through the cells again and update each cell's domain considering the digits you saw in the other cells
foreach (Field f in fields)
{
// If a cells's domain has just a single digit left, it does not have to be changed anymore
if (dstore.GetDomainSize(f) == 1)
{
continue;
}
HashSet <int> domain = dstore.GetDomain(f);
HashSet <int> impossibleDigits = new(seenDigits);
HashSet <int> subtraction = Util.Subtract(domain, impossibleDigits);
// Prune this try if no digit can't be assigned to the cell
if (subtraction.Count == 0)
{
return(false);
}
// If a cell's domain has to be updated based on the seen digits, do it and note that there was a change
if (!domain.SetEquals(subtraction))
{
domainsHaveChanged = true;
dstore.SetDomain(f, subtraction);
}
}
return(domainsHaveChanged);
}
