APDCL 2017 Which one of the following regular expressions....

Question

Which one of the following regular expressions....

Comments

Option A cannot have bab

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Oh..Yeah. What should be our approach to solve such questions?

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Try to insert set of a or b ie (a+b)* inbetween the given conditions for getting set of all strings

Eg for atleast two b's we write the string as (a+b)*b(a+b)*b(a+b)*

For exactly two b's   a*ba*ba* so that we get strings in which a can either be in front or/and end or/and in the middle

For all strings with every a followed by exactly two b's    b*(abb)* string can either comprise of only b's or/and a followed by exactly two b's

You can think of many other examples

Answer 1

Answer should be D -(a+b)*b(a+b)*b(a+b)*