override public int CalcuateMove(Position gameBoard)
{
winningmovefound = false;
//if first play in the middle
if (gameBoard.GetMoves() == 0)
{
print("AI plays first");
//AI should always play the middle col if playing first
return(3);
}
///create a copy of the boardstate to expand tree from
Position boardState = new Position(gameBoard);
print("before minmax");
boardState.DebugBoard();
ScoreCol calcuate = MinMaxStart(boardState);
print("after minmax");
boardState.DebugBoard();
print("original board");
gameBoard.DebugBoard();
print("Our best answer here is col" + calcuate.GetCol());
print("Best answer is of score" + calcuate.GetScore());
return(calcuate.GetCol());
}
//MinMax algorithmn without alpha-beta pruning. Modifies the boardState to find the
ScoreCol MinMax(ref Position boardState)
{
nodeCount++;
if (winningmovefound == true)
{
ScoreCol winner = new ScoreCol(0, winningSlot);
return(winner);
}
//
//make sure game is not a tie
if (boardState.GetMoves() == GameController.numColumns * GameController.numRows)
{
print("we hit a tie");
ScoreCol tie = new ScoreCol(0, 0);
return(tie);
}
///check to prevent winning move from player
int winningcol = CheckWinningMove(boardState);
if (winningcol != -1)
{
ScoreCol winner = new ScoreCol(GameController.numColumns * GameController.numRows + 1 - boardState.GetMoves() / 2
, winningcol);
print("the other player will win");
print(winningSlot);
winningmovefound = true;
winningSlot = winningcol;
return(winner);
}
if (nodeCount > 50)
{
ScoreCol earlyexit = new ScoreCol(-(GameController.numColumns * GameController.numRows), -1);
return(earlyexit);
}
int bestScore = -(GameController.numColumns * GameController.numRows); // best possible score with a lower bound of score.
int bestCol = -1;
// compute the score of all possible moves and keep the best one
for (int x = 0; x < GameController.numColumns; x++)
{
if (boardState.CanPlay(x))
{
Position deeperState = new Position(boardState);
// It's opponent turn in deeper position after current player plays x column.
deeperState.SimPlay(x);
// If current player plays col x, his score will be the opposite of opponent's score after playing col
ScoreCol check = MinMax(ref deeperState);
int score = check.GetScore();
// keep track of best possible score so far.
if (score > bestScore)
{
bestScore = score;
bestCol = x;
if (bestScore >= (GameController.numColumns * GameController.numRows) / 10)
{
ScoreCol earlyexit = new ScoreCol(bestScore, bestCol);
return(earlyexit);
}
}
}
}
ScoreCol exit = new ScoreCol(bestScore, bestCol);
return(exit);
}
