Aptitude | GATE CS 1998 | Question 12

The string 1101 does not belong to the set represented by
(A) 110* (0+1)
(B) 1(0+1)* 101
(C) (10)* (01)* (00+11)*
(D) (00+(11)*0)*

Answer: (C) (D)

Explanation: R.E of option C won’t generate 1101 as you can see the language will contain L(C) = {epsilon,10,1010,1001,0101,00,11,0011,1100,………..}
Also, R.E of option D has ‘1’ but here two ’11’ are together hence its impossible to generate 1101.L(D) = {Epsilon,0,00,110,11110,11000,…………….}
Here Option (C) and (D) both are correct.

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