bfs-region-x-o

  private void bfs(char[][] board, int row, int col) {
    Deque<int[]> q = new ArrayDeque<>();
    q.offer(new int[] { row, col });
    board[row][col] = '*';
    while (!q.isEmpty()) {
      int[] cell = q.poll();
      int r = cell[0], c = cell[1];

      for (int[] dir : dirs) {
        if (r + dir[0] >= 0 && r + dir[0] < rows && c + dir[1] >= 0 && c + dir[1] < cols
            && board[r + dir[0]][c + dir[1]] == 'O') {
          q.offer(new int[] { r + dir[0], c + dir[1] });
          board[r + dir[0]][c + dir[1]] = '*';
        }
      }
    }
  }