规则Rules：
标准数独基础上，提示数是其所指方向上前X个数字之和，X是其方向上第一个数字。如果斜向上只有Y格，那么X≤Y。
Classic rules applied. Additionally, the clue is the first X numbers' sum, with X is the first number in this direction. If there are Y cells on the direction, X≤Y.
作者Author：LYun
◆X和规则 Rules of X-Sum
◆在线做Do it by CTC
◆在线做 Do it by Penpa
