private ImmutableSudokuGrid EmptyGridForSimpleSolve(ImmutableSudokuGrid inputGrid, SudokuSolver solver)
{
ImmutableSudokuGrid grid = inputGrid;
while (true)
{
bool hasSquareBeenRemoved = false;
List <SquareCoordinate> filledSquareList = grid.FindAllFilledSquares();
foreach (SquareCoordinate square in filledSquareList)
{
ImmutableSudokuGrid gridWithoutSquare = grid.WithoutSquare(square);
int numberOfOptions = solver.DetermineValidOptionsForSquare(square, gridWithoutSquare).Count;
if (numberOfOptions == 1)
{
grid = gridWithoutSquare;
hasSquareBeenRemoved = true;
}
}
if (!hasSquareBeenRemoved)
{
return(grid);
}
}
}
private ImmutableSudokuGrid EmptyGridForHardSolve(ImmutableSudokuGrid inputGrid, HarderSudokuSolver solver)
{
ImmutableSudokuGrid grid = EmptyGridForSimpleSolve(inputGrid);
var listOfFilledSquares = grid.FindAllFilledSquares();
for (int i = 0; i < listOfFilledSquares.Count; i++)
{
var square = listOfFilledSquares[i];
bool isNotUniqueValue = solver.CanBeSolvedWithDifferentValueInSquare(grid, square, grid.Elements[square.Row, square.Column]);
if (!isNotUniqueValue)
{
grid = grid.WithoutSquare(square);
return(EmptyGridForHardSolve(grid));
}
}
return(grid);
}