规则Rules：
标准数独基础上：
① 摩天楼规则：外圈的提示数为摩天楼数。摩天楼数：从这一方向上看过去，当大数字遮住小数字时，可以看见的数字的个数。
② 箭头规则：圆圈内数字等于线条上数字之和。
Classic rules applied. Additionally:
① Rule of Skyscrapers: The outside number is skyscraper numbers. The skyscraper number means how many numbers can be seen, when you look from this direction, with large numbers hiding the lower ones.
② Rule of Arrow: Arrow circle is the sum of numbers on arrow line.
