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Regular expressions - odd amounts, as opposed to even

The_B_Man · 2011-10-30 15:14:26

Can someone answer this for me: Give a regular expression for "The set of all strings of 0's and 1's having an odd number of 0's". The input alphabet is obviously {0,1}. I understand the question, but I just don't know how to represent an odd amount of 0's in regular expression form. I could even draw a Finite State…

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30-10-2011 4:14pm

#1

The_B_Man

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Can someone answer this for me:

Give a regular expression for "The set of all strings of 0's and 1's having an odd number of 0's".

The input alphabet is obviously {0,1}. I understand the question, but I just don't know how to represent an odd amount of 0's in regular expression form. I could even draw a Finite State Machine to represent it!

Any help appreciated.
Thanks.

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#2 01-11-2011 12:00am
humbert

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Posts: 5108

This looks like a sufficiently similar example. Although I only took a cursory glance at it.

I think the approach would be to create an expression to find pairs of 0s that may or may not be consecutive, then find 0 to infinitely many of them, and finally check to make sure that sequence is followed by a 0.

I'm sure there are other approaches.

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