/// <summary>
/// Returns the best move score
/// </summary>
/// <param name="col_to_move_in">The best move index for this level of move</param>
/// <param name="remaining_depth"></param>
/// <param name="white_min"></param>
/// <param name="black_max"></param>
/// <param name="board"></param>
/// <returns></returns>
int findBestBlackMove(AbstractBoard.CommonMove col_to_move_in, int remaining_depth, int white_min, int black_max, C4Board board)
{
int best_score = BIG_SCORE;
var best_move = new AbstractBoard.CommonMove();
var move_status = new AbstractBoard.MoveResult();
List <AbstractBoard.CommonMove> valid_moves = board.validMoves();
for (int black_move_idx = 0; black_move_idx < valid_moves.Count; ++black_move_idx)
{
// Make each move in turn and see if it would be a winning move
var curr_move = valid_moves[black_move_idx];
var new_board = new C4Board(board);
move_status = new_board.makeMove(curr_move);
if (move_status.was_winning_move)
{
col_to_move_in.move_idx = curr_move.move_idx;
return(BLACK_WIN);
}
int score = 0;
if (remaining_depth == 0)
{
score = new_board.rateBoard();
}
else
{
score = findBestWhiteMove(col_to_move_in: curr_move,
remaining_depth: remaining_depth - 1,
white_min: white_min,
black_max: black_max,
board: new_board);
}
if (score < best_score)
{
// Best move yet
best_score = score;
best_move.move_idx = curr_move.move_idx;
if (black_max > best_score)
{
black_max = best_score;
}
}
if (black_max <= white_min)
{
// Pruning - short-circuit rest of processing
col_to_move_in.move_idx = best_move.move_idx;
return(best_score);
}
}
col_to_move_in.move_idx = best_move.move_idx;
return(best_score);
}
public C4Board(AbstractBoard board)
{
if (board is C4Board)
{
C4Board c4_board = board as C4Board;
// Call C4Board ctor
setupBoard(c4_board);
}
}
private void setupBoard(C4Board board)
{
// Copy squares
for (int row_idx = 0; row_idx < NUM_ROWS; ++row_idx)
{
for (int col_idx = 0; col_idx < NUM_COLS; ++col_idx)
{
squares[row_idx, col_idx] = board.squares[row_idx, col_idx];
}
}
blackToMove = board.blackToMove;
// Copy numPieceInCol
for (int col_idx = 0; col_idx < NUM_COLS; ++col_idx)
{
numPiecesInCol[col_idx] = board.numPiecesInCol[col_idx];
}
}
/*
* Work out how much credit to give the given colour in the
* current position
*/
public int rateBoard(PieceType colour)
{
const int THREE_IN_LINE_WITH_GAP_SCORE = 100;
int result = 0;
// Try moving in each of the empty squares and see if this
// gives a win:
// TO DO: Look for a move that gives us 3+ a gap in a block of 4.
// Copy squares
for (int row_idx = 0; row_idx < NUM_ROWS; ++row_idx)
{
for (int col_idx = 0; col_idx < NUM_COLS; ++col_idx)
{
if (squares[row_idx, col_idx] == PieceType.EMPTY)
{
//System.Console.WriteLine($"Considering row {row_idx} col {col_idx}");
var new_board = new C4Board(this);
if (colour == PieceType.WHITE)
{
new_board.blackToMove = true;
}
else
{
new_board.blackToMove = false;
}
MoveResult res = new_board.placePiece(row_idx, col_idx);
if (res.was_winning_move)
{
// Give more credit to a lower winning move than a higher up one
result += THREE_IN_LINE_WITH_GAP_SCORE;
result += NUM_COLS - col_idx;
//System.Console.WriteLine("3 in line with gap found");
}
}
} // end for col
} // end for row
return(result);
}
// TO DO: Use abstract board throughout
public BestMoveFinder(C4Board board)
{
this.board = board;
}
public C4Board(C4Board board)
{
setupBoard(board);
}