protected SudokuBoard SolvePuzzleRecursion(ref SudokuBoard board)
{
bool foundKnow = false;
bool deadSpace = false;
SudokuSpace spaceWithPossbile = null;
int rowOfLeast = -1;
int colOfLeast = -1;
if (board is null)
{
return(board);
}
if (!board.GetSpaces().All(i => i.KnownValue))
{
for (int i = 0; i < board.SquareSize; i++)
{
IEnumerable <int> rowSpaces = SpacesValuesKnown(board.GetRowValues(i));
for (int j = 0; j < board.SquareSize; j++)
{
SudokuSpace space = board.GetSudokuSpace(i, j);
if (!space.KnownValue)
{
IEnumerable <int> colSpaces = SpacesValuesKnown(board.GetColumnValues(j));
int uppperRow = i / 3;
int upperColumn = j / 3;
IEnumerable <int> block = SpacesValuesKnown(board.GetBlockValues(uppperRow * 3, upperColumn * 3, 3));
space.PosibleValues = (from pos in board.NumberRange.AsEnumerable()
where !rowSpaces.Contains(pos) &&
!colSpaces.Contains(pos) &&
!block.Contains(pos)
select pos).ToList();
if (space.PosibleValues.Count == 0)
{
deadSpace = true;
}
else if (space.PosibleValues.Count == 1)
{
foundKnow = true;
space.KnownValue = true;
space.SpaceValue = space.PosibleValues.First();
space.SpaceCharter = space.PosibleValues.First().ToString();
}
else
{
if (spaceWithPossbile == null ||
spaceWithPossbile.PosibleValues.Count > space.PosibleValues.Count)
{
rowOfLeast = i;
colOfLeast = j;
spaceWithPossbile = space;
}
}
}
}
}
if (deadSpace)
{
board = null;
}
else if (foundKnow)
{
SolvePuzzleRecursion(ref board);
}
else if (rowOfLeast != -1)
{
SudokuSpace space = board.GetSudokuSpace(rowOfLeast, colOfLeast);
foreach (int posibleValue in space.PosibleValues)
{
if (!(Solved is null))
{
break;
}
SudokuBoard clone = board.Copy();
SudokuSpace cloneSpace = clone.GetSudokuSpace(rowOfLeast, colOfLeast);
cloneSpace.PosibleValues = null;
cloneSpace.KnownValue = true;
cloneSpace.SpaceValue = posibleValue;
cloneSpace.SpaceCharter = posibleValue.ToString();
SolvePuzzleRecursion(ref clone);
if (Solved is null &&
!(clone is null) &&
clone.GetSpaces().All(i => i.KnownValue))
{
Solved = clone;
break;
}
}
}
}
return(Solved is null? board:Solved);
}
