规则Rules：
标准数独基础上，如果某行/列的第一格是X，则该行/列的第X格是外提示里的数字。
Classic rules applied. Additionally, if the first cell is X in a Row or Column, the Xth cell is the outside clue.
◆例题 Example
◆在线做 Do it by CTC
◆在线做 Do it by Penpa
