private void SolveByRow(SudokuBoard board, int number)
{
foreach (var sudokuRow in board.Rows.Where(r => !r.HasNumberBeenUsed(number)))
{
var possibleColumns = new List <int>();
foreach (var sudokuRowCell in sudokuRow.Cells.Where(c => !c.IsFilled))
{
//Check if the number can be used in this cell
var column = board.Columns.FirstOrDefault(c => c.ColumnNumber == sudokuRowCell.ColumnNumber);
if (column.HasNumberBeenUsed(number))
{
continue;
}
var squareNumber = SudokuBoard.CalculateSquareNumber(sudokuRowCell.RowNumber, sudokuRowCell.ColumnNumber);
var square = board.Squares.FirstOrDefault(s => s.SquareNumber == squareNumber);
if (square.HasNumberBeenUsed(number))
{
continue;
}
//The number has not been used in either the present row, column or square
//Check if the number is the only one that can be used by adding all
//possible numbers except the number being checked to the possible numbers list
var possibleNumbers = new List <int>();
for (int i = 1; i <= board.NumbersPerUnit; i++)
{
if (i == number)
{
continue;
}
if (!sudokuRow.HasNumberBeenUsed(i) && !column.HasNumberBeenUsed(i) && !square.HasNumberBeenUsed(i))
{
possibleNumbers.Add(i);
}
}
//If the possible numbers list contains any numbers, then the number being checked is not the only option in this cell
if (possibleNumbers.Any())
{
//But the number could possibly be used in the column of the present cell - otherwise the code would have skipped previously
possibleColumns.Add(sudokuRowCell.ColumnNumber);
continue;
}
//But if the possible numbers list does NOT contain any numbers
//Then Number IS the only one that is allowed
sudokuRowCell.Number = number;
return;
}
//And if the list of possible columns contains ONLY one record, then this cell is the only place where the number can be used
if (possibleColumns.Count == 1)
{
sudokuRow.Cells.FirstOrDefault(c => c.ColumnNumber == possibleColumns.First()).Number = number;
}
}
}
private void SolveByBruteForce(SudokuBoard board)
{
var listOfAttempts = new List <Attempt>();
foreach (var sudokuRow in board.Rows)
{
foreach (var sudokuRowCell in sudokuRow.Cells.Where(c => !c.IsFilled))
{
var column = board.Columns.FirstOrDefault(c => c.ColumnNumber == sudokuRowCell.ColumnNumber);
var squareNumber = SudokuBoard.CalculateSquareNumber(sudokuRowCell.RowNumber, sudokuRowCell.ColumnNumber);
var square = board.Squares.FirstOrDefault(s => s.SquareNumber == squareNumber);
var unusedNumber = 0;
for (int i = 1; i <= board.NumbersPerUnit; i++)
{
if (!sudokuRow.HasNumberBeenUsed(i) && !column.HasNumberBeenUsed(i) && !square.HasNumberBeenUsed(i) && !DoesAttemptExist(sudokuRowCell, i, listOfAttempts))
{
unusedNumber = i;
}
}
if (unusedNumber == 0)
{
continue;
}
//Try setting the number of the cell to the first unused number
listOfAttempts.Add(new Attempt(sudokuRowCell, unusedNumber));
var attemptBoard = board.Clone();
var attemptCell = attemptBoard.GetCell(sudokuRowCell.ColumnNumber, sudokuRowCell.RowNumber);
attemptCell.Number = unusedNumber;
SolveBoard(attemptBoard);
if (attemptBoard.IsSolved)
{
sudokuRowCell.Number = unusedNumber;
SolveBoard(board);
return;
}
}
}
}