public static IEnumerable <Cell[, ]> Solve(Cell[,] board)
{
board = board.Copy();
var i = 0;
var unknowns = board.Points()
.Where(s => board[s.x, s.y] == Cell.Unknown)
.ToArray();
while (i >= 0)
{
var(x, y) = unknowns[i];
var cell = board[x, y];
int nextGuessIndex = cell == Cell.Unknown ? 0 : Array.IndexOf(FillOptions, cell) + 1;
if (nextGuessIndex >= FillOptions.Length)
{
board[x, y] = Cell.Unknown;
i--;
continue;
}
board[x, y] = FillOptions[nextGuessIndex];
if (board.LegalSquare(x, y) && board.LegalNumbers(x, y))
{
if (i < unknowns.Length - 1)
{
i++;
}
else if (board[x, y] == Cell.Full && board.LegalPath(x, y) || board[x, y] != Cell.Full && board.LegalPath())
{
yield return(board.Copy());
}
}
}
}
public static bool LegalPath(this Cell[,] board, int x, int y)
{
if (!board.Contains(x, y) || board[x, y] != Cell.Full)
{
return(true);
}
var copy = board.Copy();
FloodFill(copy, x, y, Cell.Full + 1);
return(!copy.Points().Any(s => copy[s.x, s.y] == Cell.Full));
}
