bool TryPlaceQueenOnSquare(Board board, int rank, int file)
{
if (board.CanIPlaceQueen(rank, file))
{
board.OccupySquare(rank, file);
board.MarkThreatenedSquares(rank, file);
return true;
}
return false;
}
bool TryPlaceQueenOnFile(Board board, int rank, int startingFile)
{
var queenIsPlaced = false;
for (int file = startingFile; file < boardSize; file++)
{
queenIsPlaced = TryPlaceQueenOnSquare(board, rank, file);
if (queenIsPlaced)
{
break;
}
}
return queenIsPlaced;
}
void TryPlaceQueenOnRank(Board board, ref int rank, ref int startingFile)
{
var queenIsPlaced = TryPlaceQueenOnFile(board, rank, startingFile);
if (queenIsPlaced)
{
startingFile = 0;
}
else
{
startingFile = RevertLastQueenPlacement(board, ref rank);
}
}
int RevertLastQueenPlacement(Board board, ref int rank)
{
rank = MoveToPreviousRank(rank);
var startingFile = RemoveQueenOnRank(board, rank);
rank = MoveToPreviousRank(rank);
board.ClearAllThreatenings();
board.CalculateAllThreatenings();
return startingFile;
}
int RemoveQueenOnRank(Board board, int rank)
{
var occupiedFile = board.FindOccupiedFileOnRank(rank);
board.ClearSquare(rank, occupiedFile);
return MoveToNextFile(occupiedFile);
}
void FindSolution(Board board)
{
var startingfile = 0;
for (int rank = 0; rank < 8; rank++)
{
TryPlaceQueenOnRank(board, ref rank, ref startingfile);
}
}
List<Tuple<int, int>> ExtractSolution(Board board)
{
List<Tuple<int, int>> result = new List<Tuple<int, int>>();
board.GetAllSquares().ToList().ForEach(square => AddQueenToResult(square, result));
return result;
}
public List<Tuple<int, int>> Solve()
{
var board = new Board(boardSize);
FindSolution(board);
return ExtractSolution(board);
}