what is regular expression not generated over {a,b}?

Posted by Loop on Stack Overflow See other posts from Stack Overflow or by Loop
Published on 2010-04-20T22:20:05Z Indexed on 2010/04/20 22:23 UTC
Read the original article Hit count: 147

Filed under:

regex

|

regex-negation

|

homework

|

string

Hello all,

I am really stuck with these 2 question for over 2 days now. trying to figure out what the question means.... my tutor is out of town too....

write a regular expression for the only strings that are not generated over {a,b} by the expression: (a+b)*a(a+b)*. explain your reasoning.

and i tried the second question, do you think is there any better answer than this one?

what is regular expression of set of string that contain an odd number of a's or exactly two b's................(a((a|b)(a|b))*|bb).... coz i know to represent any odd length of a's, the RE is a((a|b)(a|b))*

© Stack Overflow or respective owner

Related posts about regex

Find multiple regex in each line and skip result if one of the regex doesn't match

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a list of variables: variables = ['VariableA', 'VariableB','VariableC'] which I'm going to search for, line by line ifile = open("temp.txt",'r') d = {} match = zeros(len(variables)) for line in ifile: emptyCells=0 for i in range(len(variables)): regex = r'('+variables[i]+r')[:|=|\(](-… >>> More
OWASP Regex Repository: Is this regex correct?

as seen on Stack Overflow - Search for 'Stack Overflow'
I was looking at the regular expression for validating various data types from the (OWASP Regex Repository). One of the regular expressions in there is called safetext and looks like: ^[a-zA-Z0-9\s.\-]+$ My first question is: Is this regular expression correct? complementary question If this… >>> More
Make a Perl-style regex interpreter behave like a basic or extended regex interpreter

as seen on Stack Overflow - Search for 'Stack Overflow'
I am writing a tool to help students learn regular expressions. I will probably be writing it in Java. The idea is this: the student types in a regular expression and the tool shows which parts of a text will get matched by the regex. Simple enough. But I want to support several different regex… >>> More
JS regex isn't matching, even thought it works with a regex tester

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm writing a piece of client-side javascript code that takes a function and finds the derivative of it, however, the regex that's supposed to match with the power rule fails to work in the context of the javascript program, even though it sucessfully matches when it's used with an independent regex… >>> More
c# RegEx with "|"

as seen on Stack Overflow - Search for 'Stack Overflow'
I need to be able to check for a pattern with | in them. For example an expression like d*|*t should return true for a string like "dtest|test". I'm no regex hero so I just tried a couple of things, like: Regex Pattern = new Regex("s*\|*d"); //unable to build because of single backslash Regex Pattern… >>> More

Related posts about regex-negation

Why is negation of a regex needed?

as seen on Stack Overflow - Search for 'Stack Overflow'
There are so many questions on regex-negation here on SO. I am not sure I understand why people feel the need to negate a regex. Why not use something like grep -v that shows only the results that do not match the regex? $ ls april august december february january july june march may… >>> More
Regex to match a whole string only if it lacks a given substring/suffix

as seen on Stack Overflow - Search for 'Stack Overflow'
I've searched for questions like this, but all the cases I found were solved in a problem-specific manner, like using !g in vi to negate the regex matches, or matching other things, without a regex negation. Thus, I'm interested in a “pure” solution to this: Having a set of strings I need to filter… >>> More
How to negate the whole regex?

as seen on Stack Overflow - Search for 'Stack Overflow'
I have a regex, for example ([m]{2}|(t){1}). It matches ma and t and doesn't match bla. I want to negate the regex, thus it must match bla and not ma and t, by adding something to this regex. I know I can write bla, the actual regex is however more complex. >>> More
how to negate whole regex ??

as seen on Stack Overflow - Search for 'Stack Overflow'
I have regex (for example) ([m]{2}|(t){1}) and it matches ma and t and doesnt match bla I want it to match bla and doesnt match ma and t by adding something to this regex, i know i can write bla, my real-life regex is more complex. >>> More
Negating a set of words via java regex!

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi folks, I would like to negate a set of words using java regex. Say, I want to negate cvs, svn, nvs, mvc. I wrote a regex which is ^[(svn|cvs|nvs|mvc)]. Some how that seems not to be working. Could you please help? Thanks. .\J >>> More