RegEx / computer theory - construct a regEx in alphabetical order

问题

In my grammars - Computer theory class I am trying to create a regular expression in alphabetical order(a-z)

l = {a, b, x, y, z, i, o, u, e, c}

This is what i have come up with using the kleene closure

aeiou(x*, y*, z*, i*, o*, u* e*) 

With the kleene close * thats zero or more so that should force abceioxyz?

We have not been learning this type of form

[^abc]

am i on the right track?

回答1:

As far as I understand, you want to capture strings with the following format:

• The string contains any number of a's, afterwards any number of b's, then any number of c's, and so on...

Let's consider a derived example: We want all strings consisting of 0 and 1 and that has all 0's before 1's: Therefore, we can simply write 0*1*. Now try to adapt the pattern for more complex alphabets.

回答2:

the word must be in alphabetical order, so if it contains any a's, they surely must be at the front. likewise, if it contains any b's , they must come after the a's, and nothing can come in between the a's and b's

so we have: a*b*...

and so a pattern emerges.

来源：https://stackoverflow.com/questions/7667838/regex-computer-theory-construct-a-regex-in-alphabetical-order