// returns the score for the current position from the point of view of the given player.
public Move evaluate(moveBoard board, Move evalMove)
{
int boardScore = evalBoardForAI();
evalMove.Score = boardScore;
return(evalMove);
}
static Move getBestMove(GameBoard.PLAYERS_ID player)
{
//make a moveBoard of the current state of the board
moveBoard currentMoveBoard = new moveBoard();
//this move board is used as a scratch pad to examine possible next moves
currentMoveBoard.setCurrentGameBoardToMoveBoard(player);
//using the moveboard the minimax function finds the next BEST move
Move bestMove = miniMax(currentMoveBoard, currentMoveBoard.Root, player, MAX_DEPTH, 0);
return(bestMove);
}
//
//This function implements the Minimax algorithm
//
//moveboard board --represents the current game board as a scratch pad to make moves on (before actually making the move)
// --board also holds the actual player's turn for the game (first player in the tree)
//Move nextMove --represents the next move to be made on the game board
// --nexMove also holds a score value for the move
//evaluatePlayer --represents the players turn on the tree ( it will change as we traverse each level of the tree )
//
//maxDepth --represents the number of levels to use in the minimax algorithm (how far down the tree do we want to go?)
//
//currentDepth --represents the current level we are evaluating
//
//return --this function returns the best move to make on the board
static public Move miniMax(moveBoard board, Move nextMove, GameBoard.PLAYERS_ID evaluatePlayer, int maxDepth, int currentDepth)
{
//
//create a bestmove to return
//
Move bestMove = new Move();
//
//if game is over ( no more moves left/win/loss ) || we have reached our max depth to search || there are no children for this move and it isnt the very first move
//
if (board.isGameOver() || currentDepth == maxDepth || ((currentDepth != 0) && nextMove.PossibleMoves.Count == 0))
{
//
//evaluate the board and return the best move for this board, the move data structure also holds a score value for the board
//
Move eMove = board.evaluate(board, nextMove);
eMove.Depth = currentDepth;
//
//copy the evaluated move into bestMove
//
eMove.Copy(bestMove);
}
else
{
//
//if we haven't reached a terminal node traverse the children and call minimax
//
Move currentBubbledUpScore = null;
//
//Initialize the bestmove object
//
nextMove.Copy(bestMove);
bestMove.Score = INFINITY;
//
//Ask: whose turn is it on the tree? Keep track of the max or min score for all the possible moves (children)
//
if (board.CurrentPlayer == evaluatePlayer)
{
bestMove.Score = -INFINITY;
}
//
//Loop through all the possible moves from nextMove
//
foreach (Move move in nextMove.PossibleMoves)
{
//
//make the move ( take the turn ) and then call minimax for the next move
//makeMove also adds the move to our move game board scratch pad
//
board.makeMove(move, evaluatePlayer);
currentBubbledUpScore = miniMax(board, move, GetNextPlayerID(evaluatePlayer), maxDepth, currentDepth + 1);
//
//remove move from our game board (game board scratch pad)
//
board.RemoveMoveFromGameMoveBoard(move);
//
//if we are the current player, then take the highest score found of all the moves
//
if (board.CurrentPlayer == evaluatePlayer)
{
if (currentBubbledUpScore.Score > bestMove.Score)
{
bestMove.Row = move.Row;
bestMove.Column = move.Column;
bestMove.Score = currentBubbledUpScore.Score;
bestMove.Depth = currentBubbledUpScore.Depth;
}
else if (currentBubbledUpScore.Score == bestMove.Score)
{
if (currentBubbledUpScore.Depth < bestMove.Depth)
{
bestMove.Row = move.Row;
bestMove.Column = move.Column;
bestMove.Score = currentBubbledUpScore.Score;
bestMove.Depth = currentBubbledUpScore.Depth;
}
}
}
else
{
if (currentBubbledUpScore.Score < bestMove.Score)
{
bestMove.Row = move.Row;
bestMove.Column = move.Column;
bestMove.Score = currentBubbledUpScore.Score;
bestMove.Depth = currentBubbledUpScore.Depth;
}
}
//
// the opponent is the current player then take the lowest score of all the moves
//
}
}
return(bestMove);
}
