public SudokuPuzzle GenerateSudoku(SudokuDifficuty difficulty, int length = 9)
{
// get randomly filled out sudoku
SudokuPuzzle solution = SolveSudoku(new SudokuPuzzle());
SudokuPuzzle sudoku = (SudokuPuzzle)solution.Clone();
// check how many fields need to be removed (depending on desired difficulty)
int fieldsToRemove = ((length * length) - (int)difficulty);
while (fieldsToRemove > 0)
{
int freeFieldsCount = sudoku.GetFreeFields().Count;
foreach (var field in sudoku.GetSetFields().Shuffle())
{
if (fieldsToRemove > 0 && isFieldDetermined(sudoku, solution, field.RowIndex, field.ColumnIndex))
{
field.SetValue(0);
fieldsToRemove--;
}
}
// check if progress was made (if not => try with another sudoku puzzle)
if ((freeFieldsCount - sudoku.GetFreeFields().Count) == 0)
{
sudoku = GenerateSudoku(difficulty, length);
break;
}
}
// check if the generated sudoku is unique. if not create a new one.
return((HasSudokuUniqueSolution(sudoku)) ? sudoku : GenerateSudoku(difficulty, length));
}