The language of all mahjong hands is regular by virtue of being finite. However, there are 3.70534329521 * 10^29 mahjong hands. There isn't enough storage space on Earth to store the corresponding regular expression.
If you can come up with a regex/NFA/whatever for a mahjong hand that isn't just a union of all strings, let me know, because it seems impossible. The limitation of no more than 4 copies of each tile makes something like
([1-9](m|p|s))|([1-7]z)
repeated 14 times not work, because it can't keep track of how many of each tile there are.
([1-9](m|p|s))|([1-7]z)
repeated 14 times not work, because it can't keep track of how many of each tile there are.
@applejack That still cannot count, and modern "regular" expressions are not regular since they can recognize non-regular languages.
