//gets the number of available rows, columns and diagonals for specified State.
private int heuristics(Board.State player)
{
Board.State opponent = (player == Board.State.X) ? Board.State.O : Board.State.X;
int heuristic = 0;
for (int x = 0; x < 3; x++)
{
//for each row
for (int i = 0; i < 3; i++)
{
if (board[x][i] == opponent)
{
break;
}
if (i == 2)
{
heuristic++;
}
}
//for each column
for (int i = 0; i < 3; i++)
{
if (board[i][x] == opponent)
{
break;
}
if (i == 2)
{
heuristic++;
}
}
}
//diagonal
for (int i = 0; i < 3; i++)
{
if (board[i][i] == opponent)
{
break;
}
if (i == 2)
{
heuristic++;
}
}
//diagonal
for (int i = 0; i < 3; i++)
{
if (board[2 - i][i] == opponent)
{
break;
}
if (i == 2)
{
heuristic++;
}
}
return(heuristic);
}
public int score(Board board, Board.State player)
{
Board.State opponent = (player == Board.State.X) ? Board.State.O : Board.State.X;
if (board.isGameOver() && board.getWinner() == player)
{
return(10);
}
else if (board.isGameOver() && board.getWinner() == opponent)
{
return(-10);
}
else
{
return(board.heuristic());
}
}
int _Rollout(Board board)
{
Board.State player = board.turn;
while (!board.IsEnd())
{
Random rand = new Random((int)DateTime.Now.Ticks);
var moves = _GetValidMove(board);
List <Point> pt = new List <Point>();
double prior = double.MinValue;
foreach (var m in moves)
{
if (Prior[m.X, m.Y] > prior)
{
pt.Clear();
prior = Prior[m.X, m.Y];
pt.Add(m);
}
else if (Prior[m.X, m.Y] == prior)
{
pt.Add(m);
}
}
var move = pt[rand.Next(0, pt.Count)];
board.Play(move.X, move.Y);
}
if (board.GetWinner() == Board.State.SAME)
{
return(0);
}
else if (board.GetWinner() == player)
{
return(-1);
}
else
{
return(1);
}
}
public int alphaBetaPruning(Board board, Board.State player, int depth, double alpha, double beta)
{
Board.State opponent = (player == Board.State.X) ? Board.State.O : Board.State.X;
if (board.isGameOver() || depth++ == maxDepth)
{
return(score(board, player));
}
if (board.getTurn() == player)
{
int indexOfBestMove = -1;
List <int> moves = board.getAvailableStates();
for (int i = 0; i < moves.Count; i++)
{
int theMove = moves[i];
Board modifiedBoard = board.getDeepCopy();
modifiedBoard.move(theMove);
int score = alphaBetaPruning(modifiedBoard, player, depth, alpha, beta);
if (score > alpha)
{
alpha = score;
indexOfBestMove = theMove;
}
if (alpha >= beta)
{
break;
}
}
if (indexOfBestMove != -1)
{
board.move(indexOfBestMove);
}
return((int)alpha);
}
else
{
int indexOfBestMove = -1;
List <int> moves = board.getAvailableStates();
for (int i = 0; i < moves.Count; i++)
{
int theMove = moves[i];
Board modifiedBoard = board.getDeepCopy();
modifiedBoard.move(theMove);
int score = alphaBetaPruning(modifiedBoard, player, depth, alpha, beta);
if (score < beta)
{
beta = score;
indexOfBestMove = theMove;
}
if (alpha >= beta)
{
break;
}
}
if (indexOfBestMove != -1)
{
board.move(indexOfBestMove);
}
return((int)beta);
}
}
public StateEnumerator(Board.State state)
{
_state = state;
}
//heuristic value calculated according to:
//(number of available rows,columns and diagonals for player)-(number of available rows,columns and diagonals for computer)
public int heuristic()
{
Board.State player = Board.State.X;
Board.State opponent = Board.State.O;
return((heuristics(player)) - (heuristics(opponent)));
}
