// Make an automatic move
private void DoAutoPlay()
{
// Player to play
IPlayer player = Turn == CellState.X ? PlayerX : PlayerO;
// Log, to be optionally filled by the AI players
string log = "";
// Keep start time
DateTime startTime = DateTime.Now;
// Ask player for a move
Pos pos = player.Play(gameBoard, ref log);
// Print log, including how much time it took
Debug.LogFormat("{0} took {1} ms\n{2}",
player.GetType().Name,
(DateTime.Now - startTime).TotalMilliseconds,
log);
// Is this an invalid move?
if (gameBoard.GetStateAt(pos) != CellState.Undecided)
{
overrideWinner = Turn.Other();
return;
}
// Perform the actual move
Move(pos);
}
// Get board score for the specified player, ignoring the other player
private float ScoreFor(Board board, CellState player)
{
// Current score
float score = 0;
// Search all corridors in the board
foreach (Pos[] corridor in Board.winCorridors)
{
// By default we assume a line is available
bool lineAvailable = true;
// Cycle through all the positions in the current corridor
foreach (Pos position in corridor)
{
// Check if there's an opponent piece at this position
if (board.GetStateAt(position) == player.Other())
{
// If so, it means there's no line available here, so
// let's take a note of that and skip the rest of the line
lineAvailable = false;
break;
}
}
// Was the previous line available for our player?
if (lineAvailable)
{
// If so, increment score
score++;
}
}
// Return the score
return(score);
}
public Pos Play(Board gameBoard, ref string log)
{
// Populate a list with available board positions
IList <Pos> emptyPositions = new List <Pos>();
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 3; j++)
{
Pos pos = new Pos(i, j);
if (gameBoard.GetStateAt(pos) == CellState.Undecided)
{
emptyPositions.Add(pos);
}
}
}
// Return a random empty board position
return(emptyPositions[random.Next(emptyPositions.Count)]);
}
// Helper method which obtains valid moves for the given board
private static IList <Pos> ValidMovesFromBoard(Board board)
{
// List of valid moves
List <Pos> validMoves = new List <Pos>();
// Search for valid moves
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 3; j++)
{
// Is current position a valid move?
Pos move = new Pos(i, j);
if (board.GetStateAt(move) == CellState.Undecided)
{
// If so, add it to list of valid moves
validMoves.Add(move);
}
}
}
return(validMoves);
}
// Process given board with ABNegamax
private (float score, Pos move) Negamax(Board board, int depth)
{
// Increment number of evaluations (recursive ABNegamax calls)
numEvals++;
// Check what's the status of this board
if (board.Status().HasValue)
{
// GAME OVER! Who won?
if (board.Status().Value == CellState.Undecided)
{
// It's a tie, return 0
return(0, Board.NoMove);
}
else if (board.Status().Value == board.Turn)
{
// Current player wins, return max heuristic value
return(heuristic.WinScore, Board.NoMove);
}
else
{
// The other player won, return min heuristic value
return(-heuristic.WinScore, Board.NoMove);
}
}
else if (depth == maxDepth)
{
// We reached the max depth, return the heuristic value for this
// board
return(heuristic.Evaluate(board, board.Turn), Board.NoMove);
}
else
{
// Game is not over and we haven't reached maximum depth, so let's
// recursively call Negamax on all possible moves
// Declare best move, which for now is no move at all
(float score, Pos move)bestMove =
(float.NegativeInfinity, Board.NoMove);
// Try to play on all board positions
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 3; j++)
{
// Get the current board position
Pos pos = new Pos(i, j);
// Only consider making a move at this position if it's
// not already occupied
if (board.GetStateAt(pos) == CellState.Undecided)
{
// Score for current move
float score;
// Make a virtual move at this position
board.DoMove(pos);
// Get score for this move
score = -Negamax(board, depth + 1).score;
// Undo the move we just evaluated
board.UndoMove();
// Is this the best move so far?
if (score > bestMove.score)
{
// If so, keep it
bestMove = (score, pos);
}
}
}
}
// Return the best move found among all the tested moves
return(bestMove);
}
}