规则Rules：
标准数独基础上，提示数字表示从这一方向上观察，大数字能遮住小数字时，可以看见的数字的个数。
Classic rules applied. Additionally, clue shows how many numbers can be seen in this direction, when larger number will hide lower ones.
◆例题 Example
◆在线涂鸦 Draw it Online
◆在线做 Do it by CTC
◆在线做 Do it by Penpa
