public Config(String s, int w, int h) throws ParseException
{
    tiles = char[w][h];
    char[] cs = s.toCharArray();
    boolean blank = false;
    if(s.length() == w*h)
    for(int i = 0; i < h; i++)
        for(int j = 0; j < w; j++) {
            char c = cs[i+j];
            if(blank && c == '_') throw new ParseException("Configuration has too many blank tiles");
            else if(c == '_') blank = true;
            else char[i][j] = c;
            }
    else throw new ParseException("Configuration wrong", x * y);
}