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Question

Consider a language A defined over the alphabet \(\Sigma = \{0, 1\}\) as \(A = \left\{0^{\lfloor n/2 \rfloor} 1^{n} : n \gt = 0\right\}\).

The expression \(\lfloor n/2 \rfloor\) means the floor of n/2, or what you get by rounding n/2 down to the nearest integer.

Which of the following is not an example of a string in A ?

This question was previously asked in
UGC NET 2015 Paper 1 Question Paper (27-Dec-2015)
The correct answer is

0011

A string in A has n ones preceded by exactly \(\lfloor n/2 \rfloor\) zeros.

011: n = 2, \(\lfloor 2/2 \rfloor = 1\) zero, valid. 0111: n = 3, \(\lfloor 3/2 \rfloor = 1\) zero, valid. 001111: n = 4, \(\lfloor 4/2 \rfloor = 2\) zeros, valid.

0011: n = 2 ones but 2 zeros, while \(\lfloor 2/2 \rfloor = 1\), so it is not in A.

Hence, 0011.

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Similar Questions

  1. According to pumping lemma for context free languages :

    Let L be an infinite context free language, then there exists some positive integer m such that any \(w \in L\) with \(|w| \ge m\) can be decomposed as \(w = uvxyz\)

  2. Given the following two languages :

    \(L_{1} = \{a^{n}\, b\, a^{n} \mid n \gt 0\}\)

    \(L_{2} = \{a^{n}\, b\, a^{n}\, b^{n+1} \mid n \gt 0\}\)

    Which of the following is correct ?

  3. Which of the following are context free language ?

    (A) {wi xj yk zl | i + k = j + l, where i, j, k, l ≥ 0}

    (B) {wi xj yk zl | i = j and k = l, where i, j, k, l ≥ 0}

    (C) {wi xj yk zl | i = j = k and k ≠ l, where i, j, k, l ≥ 0}

    (D) {wi xj yk zl | i = j = k + l, where i, j, k, l ≥ 0}

    (E) {wi xj yk zl | i = j = l and k ≠ l, where i, j, k, l ≥ 0}

    Choose the correct answer from the options given below :

  4. If L1 and L2 are context free languages, which of the following is True about L1∩L2 ?

  5. In Pumping Lemma for context free languages, to say a language is satisfying pumping lemma, what is the minimum length of ‘vx’ together, if you consider the string as ‘uvwxy’?

  6. Let L = {0n1n|n ≥ 0} be a context free language.

    Which of the following is correct ?

  7. Given the following two statements :

    A. L = {w|na(w) = nb(w)} is deterministic context free language, but not linear.

    B. L = {an bn} ∪ {an b2n} is linear, but not deterministic context free language.

    Which of the following options is correct ?

  8. Given the following two languages :

    L1 = {an bn | n ≥ 0, n ≠ 100}

    L2 = {w ∈ {a, b, c}*| na(w) = nb(w) = nc(w)}

    Which of the following options is correct ?


Important Questions from Context Free Languages

  1. Let $\Sigma = \{a, b, c, d\}$ and let $L = \{a^ib^jc^kd^\ell \mid i, j, k, \ell \ge 0\}$.

    Which of the following constraints ensure(s) that the language $L$ is context-free?
  2. According to pumping lemma for context free languages :

    Let L be an infinite context free language, then there exists some positive integer m such that any \(w \in L\) with \(|w| \ge m\) can be decomposed as \(w = uvxyz\)

  3. Given the following two languages :

    \(L_{1} = \{a^{n}\, b\, a^{n} \mid n \gt 0\}\)

    \(L_{2} = \{a^{n}\, b\, a^{n}\, b^{n+1} \mid n \gt 0\}\)

    Which of the following is correct ?

  4. Which of the following are context free language ?

    (A) {wi xj yk zl | i + k = j + l, where i, j, k, l ≥ 0}

    (B) {wi xj yk zl | i = j and k = l, where i, j, k, l ≥ 0}

    (C) {wi xj yk zl | i = j = k and k ≠ l, where i, j, k, l ≥ 0}

    (D) {wi xj yk zl | i = j = k + l, where i, j, k, l ≥ 0}

    (E) {wi xj yk zl | i = j = l and k ≠ l, where i, j, k, l ≥ 0}

    Choose the correct answer from the options given below :

  5. If L1 and L2 are context free languages, which of the following is True about L1∩L2 ?

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