Question

The regular expression denotes a language comprising all possible strings of even length over the alphabet (0, 1).

(a) 1 + 0(1+0)*

(b) (0+1) (1+0)*

(c) (1+0)

(d) (00+0111+10)*

I have been asked this question at a job interview.

Origin of the question is Regular Expression in chapter Compiler Introduction of Compiler

Answer 1

The correct answer is (d) (00+0111+10)*

To elaborate: Option 1 + 0(1+0)* → It does not consider even length criteria for the question.

Option (0+1) (1+0)* → It can so happen here that from the former bracket it takes 0 or 1 and takes null from the latter then it forms a string of odd length

Option (1+0) → It gives either 1 or 0.

Hence Option (00+0111+10)* is the answer.