// Method establishes which values can fill an empty square by eliminating any values already occurring in row/column/box.
public List<int> DetermineValidOptionsForSquare(SquareCoordinate squareCoordinate, IImmutableSudokuGrid grid)
{
HashSet<int> validSquareOptions = new HashSet<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
for (int offset = 1; offset < 9; offset++)
{
validSquareOptions.Remove(grid.Elements[(squareCoordinate.Row + offset) % 9, squareCoordinate.Column]);
validSquareOptions.Remove(grid.Elements[(squareCoordinate.Row), (squareCoordinate.Column + offset) % 9]);
validSquareOptions.Remove(grid.Elements[(3 * (squareCoordinate.Row / 3)) + offset % 3, (3 * (squareCoordinate.Column / 3)) + (offset - offset % 3) / 3]);
}
return validSquareOptions.ToList<int>();
}
// Method establishes which values can fill an empty square by eliminating any values already occurring in row/column/box.
public List <int> DetermineValidOptionsForSquare(SquareCoordinate squareCoordinate, IImmutableSudokuGrid grid)
{
HashSet <int> validSquareOptions = new HashSet <int> {
1, 2, 3, 4, 5, 6, 7, 8, 9
};
for (int offset = 1; offset < 9; offset++)
{
validSquareOptions.Remove(grid.Elements[(squareCoordinate.Row + offset) % 9, squareCoordinate.Column]);
validSquareOptions.Remove(grid.Elements[(squareCoordinate.Row), (squareCoordinate.Column + offset) % 9]);
validSquareOptions.Remove(grid.Elements[(3 * (squareCoordinate.Row / 3)) + offset % 3, (3 * (squareCoordinate.Column / 3)) + (offset - offset % 3) / 3]);
}
return(validSquareOptions.ToList <int>());
}
private ImmutableSudokuGrid Solve(ImmutableSudokuGrid grid, SudokuSolver simpleSolver, bool isRandomSolve, int disallowedValue, int disallowedRow, int disallowedColumn)
{
SudokuGrid mutableGrid = grid.MakeMutableCopy();
bool isGridValid = simpleSolver.TryAndSolveOnce(mutableGrid);
grid = new ImmutableSudokuGrid(mutableGrid.Elements);
if (!isGridValid)
{
return(null);
}
var emptySquareList = grid.FindAllEmptySquares();
if (emptySquareList.Count == 0)
{
return(grid);
}
SquareCoordinate emptySquareToFill = emptySquareList[0];
if (isRandomSolve)
{
var randomEmptySquare = new Random().Next(emptySquareList.Count - 1);
emptySquareToFill = emptySquareList[randomEmptySquare];
}
var validOptions = simpleSolver.DetermineValidOptionsForSquare(emptySquareToFill, grid);
if (emptySquareToFill.Row == disallowedRow && emptySquareToFill.Column == disallowedColumn && disallowedValue != 0)
{
validOptions.Remove(disallowedValue);
}
for (int i = 0; i < validOptions.Count; i++)
{
ImmutableSudokuGrid solvedGrid = Solve(grid.WithExtraSquare(emptySquareToFill, validOptions[i]), isRandomSolve);
if (solvedGrid != null)
{
return(solvedGrid);
}
}
return(null);
}
private ImmutableSudokuGrid FillInSquareWithValue(int value)
{
SquareCoordinate newSquare = new SquareCoordinate(0, 0);
ImmutableSudokuGrid newGrid = sudokuGrid.WithExtraSquare(newSquare, value);
return newGrid;
}
public ImmutableSudokuGrid WithoutSquare(SquareCoordinate squareCoordinate)
{
int[,] arrayForNewGrid = (int[,])Elements.Clone();
arrayForNewGrid[squareCoordinate.Row, squareCoordinate.Column] = -1;
return new ImmutableSudokuGrid(arrayForNewGrid);
}
public ImmutableSudokuGrid WithoutSquare(SquareCoordinate squareCoordinate)
{
int[,] arrayForNewGrid = (int[, ])Elements.Clone();
arrayForNewGrid[squareCoordinate.Row, squareCoordinate.Column] = -1;
return(new ImmutableSudokuGrid(arrayForNewGrid));
}
public void FillInSquare(SquareCoordinate squareCoordinate, int value)
{
Elements[squareCoordinate.Row, squareCoordinate.Column] = value;
}
public bool CanBeSolvedWithDifferentValueInSquare(ImmutableSudokuGrid grid, SquareCoordinate square, int disallowedValue)
{
ImmutableSudokuGrid differentValuedGrid = Solve(grid, disallowedValue: disallowedValue, disallowedRow: square.Row, disallowedColumn : square.Column);
return differentValuedGrid == null ? false : true;
}
public void FillInSquare(SquareCoordinate squareCoordinate, int value)
{
Elements[squareCoordinate.Row, squareCoordinate.Column] = value;
}
public bool CanBeSolvedWithDifferentValueInSquare(ImmutableSudokuGrid grid, SquareCoordinate square, int disallowedValue)
{
ImmutableSudokuGrid differentValuedGrid = Solve(grid, disallowedValue: disallowedValue, disallowedRow: square.Row, disallowedColumn: square.Column);
return(differentValuedGrid == null ? false : true);
}