规则Rules：
填入1~4（黑格不填数），使得每行、列、宫内数字不重复。
Fill in the squares (without black squares) with digits from 1 to 4 so that no digit is repeated in a row, column or outlined box.
◆例题 Example
◆在线涂鸦 Draw it Online
◆在线做 Do it by CTC
◆在线做 Do it by Penpa
