七数雪花 Snowflake with 7
三个方向上数字不重复，但是每个区域里的6格填入1~7，意味着每行列宫里会缺失一些数字。
Numbers cannot repeat in each direction (3 kinds) and each hexagon, but 1~7 will be filled in 6 cells in each region, so there must be one missing number in each Row, Column or Box.
本题作者：Sudoku52
