The length of the shortest string NOT in the language (over Σ = {a, b}) of the following regular
expression is ______________.
a*b*(ba)*a*
(A) 2
(B) 3
(C) 4
(D) 5
Answer: (B)
Explanation: All the strings that can be generated till length-2 are definitely present in this language.
Now, let’s look at the strings of length-3; {aaa, aab, aba, abb, baa, bab, bba, bbb} . String “bab” cannot be generated from given language. so, the string “bab” is the shortest string not acceptable by given regular expression.