@Override
	public String toString() {
		StringBuilder sb = new StringBuilder("");
		for (int x=size-1; x >= 0; x--) {
			for (int y=0; y < size; y++) {
				switch (grid[x][y]) {
				case UNSAFE:
					sb.append(" X ");
					break;
				case OCCUPIED:
					sb.append(" Q ");
					break;
				case EMPTY:
					sb.append(" _ ");
					break;
				default:
					break;
				} 
			}
			sb.append('\n');
		}
		return sb.toString();
	}