public Move getComputerMove(BoardSymbol symbol) {
BoardSymbol oppositeSymbol = symbol.getOppositeSymbol();
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[i].length; j++) {
if (board[i][j] == BoardSymbol.Empty) {
Move move = new Move(i, j);
if (isWinningMove(symbol, move)) {
return move;
}
}
}
}
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[i].length; j++) {
if (board[i][j] == BoardSymbol.Empty) {
Move move = new Move(i, j);
if (isWinningMove(oppositeSymbol, move)) {
return move;
}
}
}
}
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[i].length; j++) {
if (board[i][j] == BoardSymbol.Empty) {
return new Move(i, j);
}
}
}
throw new BoardFullException();
}
private boolean isWinningMove(BoardSymbol symbol, Move move) {
boolean isWinner = makeMove(symbol.name(), move);
// undo the move
board[move.getX()][move.getY()] = BoardSymbol.Empty;
numberOfMoves--;
return isWinner;
}
/** @see Board#makeMove(String, Move) */
@Override
public boolean makeMove(String symbolString, Move move) {
BoardSymbol symbol = BoardSymbol.valueOf(symbolString);
int x = move.getX();
int y = move.getY();
// put the player's symbol at this move on the board
board[x][y] = symbol;
numberOfMoves++;
int horizontalCount = 0;
int verticalCount = 0;
int forwardDiagonalCount = 0;
int backwardDiagonalCount = 0;
for (int i = 0; i < BOARD_SIZE; i++) {
if (board[i][y] == symbol) {
horizontalCount++;
}
if (board[x][i] == symbol) {
verticalCount++;
}
if (board[i][i] == symbol) {
forwardDiagonalCount++;
}
if (board[i][BOARD_SIZE - 1 - i] == symbol) {
backwardDiagonalCount++;
}
}
// if there are 3 of the same symbols in any of the possible winning directions, then we have a
// winner
if (horizontalCount == BOARD_SIZE
|| verticalCount == BOARD_SIZE
|| forwardDiagonalCount == BOARD_SIZE
|| backwardDiagonalCount == BOARD_SIZE) {
return true;
} else {
return false;
}
}
