CODEWITHSUNDEEP
regexkleene-star
user1988365
user1988365

Reputation:

Regular expression: does Kleene star have a distributive property?

Would there be a difference between (aa)* and (a*a*)?

Is there a distributive property?

Upvotes: 5

Views: 4003

Answers (3)

nneonneo
nneonneo

Reputation: 179402

Kleene star does not distribute. (ab)* is very different from (a*b*).

In your specific example, (aa)* would match groups of two as (thus, it only matches even numbers of as), while (a*a*) is equivalent to (a*) and matches any sequence of as. (In that case, L((aa)*) is a proper subset of L((a*a*)), but this is not necessarily true for a general regex).

Upvotes: 6

Denys Séguret
Denys Séguret

Reputation: 382132

The (aa)* group does not match the whole aaa so yes, there's a difference, it only return you a group of 2 a.

But (a*a*) is just the same as (a*).

Upvotes: 1

Evan Knowles
Evan Knowles

Reputation: 7501

Yes, there is a difference. (aa)* would be groups of aa, whereas (a*a*) would be a's.

Basically, the first phrasing would only be even numbers of a, whereas the second would not in this case.

Upvotes: 0

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