public OthelloMove getMove(OthelloState state) {
if (state.generateMoves().isEmpty()) return null;
OthelloMove bestMove = MonteCarloTreeSearch(state, iterations);
return bestMove;
}
public OthelloMove getMove(OthelloState state) {
List<OthelloMove> moves = state.generateMoves();
// If there are no possible moves, just return "pass":
if (moves.isEmpty()) return null;
int best_move_index = 0;
int best_score;
boolean player1_turn;
// Set player and set best_score according to player
if (state.nextPlayerToMove == 0) {
player1_turn = true;
best_score = (int) Double.NEGATIVE_INFINITY;
} else {
player1_turn = false;
best_score = (int) Double.POSITIVE_INFINITY;
}
// Calculate the score for each move
for (int i = 0; i < moves.size(); i++) {
OthelloState new_state = state.applyMoveCloning(moves.get(i));
int score =
Minimax(new_state, 0, (int) Double.NEGATIVE_INFINITY, (int) Double.POSITIVE_INFINITY);
// Maximizing player
if (player1_turn) {
if (score > best_score) {
best_score = score;
best_move_index = i;
}
} // Minimizing player
else {
if (score < best_score) {
best_score = score;
best_move_index = i;
}
}
}
// Return best move
return moves.get(best_move_index);
}
private int Minimax(OthelloState state, int depth, int alpha, int beta) {
// Reached max search depth or game is over
if (depth == max_depth) return state.score();
else {
// Generate all moves
List<OthelloMove> moves = state.generateMoves();
// No possible moves or end of game
if (moves == null) return state.score();
// Maximizing (player 1)
else if (state.nextPlayerToMove == 0) {
int best_score = (int) Double.NEGATIVE_INFINITY;
for (int i = 0; i < moves.size(); i++) {
OthelloState new_state = state.applyMoveCloning(moves.get(i));
int score = Minimax(new_state, depth + 1, alpha, beta);
if (score > best_score) best_score = score;
// alpha-beta pruning
alpha = Math.max(alpha, best_score);
if (alpha >= beta) return alpha;
}
return best_score;
}
// Minimizing (player 2)
else {
int best_score = (int) Double.POSITIVE_INFINITY;
for (int i = 0; i < moves.size(); i++) {
OthelloState new_state = state.applyMoveCloning(moves.get(i));
int score = Minimax(new_state, depth + 1, alpha, beta);
if (score < best_score) best_score = score;
// alpha-beta pruning
beta = Math.min(beta, best_score);
if (beta <= alpha) return beta;
}
return best_score;
}
}
}