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GATE 2013 CS (CS1) – Question 43

Theory of Computation · Regular Expressions and Finite Automata · 2 marks · Multiple choice

For the shown DFA A, which are false? 1: Its language complement is context-free. 2: L(A)=L((11*0+0)(0+1)*0*1*). 3: A is minimal. 4: A accepts all binary strings of length at least two.

Diagram for GATE 2013 CS (CS1) question 43
  1. 1 and 3 only
  2. 2 and 4 only
  3. 2 and 3 only
  4. 3 and 4 only

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Show answer and explanation

Correct answer: (D) 3 and 4 only

Explanation

The DFA accepts strings containing at least one zero. Its two nonaccepting states have identical future behaviour and can merge, so 3 is false. Strings such as 11 are rejected despite length two, so 4 is false. A regular complement is context-free, and the given expression denotes a zero after an optional run of ones followed by any suffix. Thus 1,2 are true and D is correct.

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