Consider the following two statements:

(A) Only S1 is correct
(B) Only S2 is correct
(C) Both S1 and S2 are correct
(D) None of S1 and S2 is correct


Answer: (A)

Explanation: We can easily build a DFA for S1. All we need to check is whether input string has even number of 0’s. Therefore S1 is regular.

We can’t make a DFA for S2. For S2, we need a stack. Therefore S2 is not regular.

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