GATE | GATE-CS-2014-(Set-3) | Question 65

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.

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