距离 Distance

标准数独基础上，外提示有两种，单数字提示表示的是另外两个数字之间的距离（这两个数字有方向，从左到右、从上到下）。

Classic rules applied. Additionally, there're 2 kinds of outside clues, the 1-digit number is the distance of the other clue ( the 2-digit clue with order left→right, up→down).

例如，68-8意味着6在9前方，9是6后方第八个单元格。

For example, 69-8 means 6 before 9, and 9 is the 8th number after 6.