GATE CS Theory of Computation questions

Let $L \subseteq \{0,1\}^*$ be an arbitrary regular language accepted by a minimal $\text{DFA}$ with $k$ states. Which one of the following languages must necessarily be accepted by a minimal $\text{DFA}$ with $k$ states?

Let $L_1$ be a regular language and $L_2$ be a context-free language. Which of the following languages is/are context-free?

Consider the following deterministic finite automaton $\text{(DFA)}$ The number of strings of length $8$ accepted by the above automaton is ___________

Suppose we want to design a synchronous circuit that processes a string of $0$’s and $1$’s. Given a string, it produces another string by replacing the first $1$ in any subsequence of consecutive $1$’s by a $0$. Consider the following example. …

​​​​​​Consider the following two statements about regular languages: $S_1$: Every infinite regular language contains an undecidable language as a subset. $S_2$: Every finite language is regular. Which one of the following choices is correct?

For a string $w$, we define $w^R$ to be the reverse of $w$. For example, if $w=01101$ then $w^R=10110$. Which of the following languages is/are context-free?

Which of the following regular expressions represent(s) the set of all binary numbers that are divisible by three? Assume that the string $\epsilon$ is divisible by three.

Which one of the following regular expressions represents the set of all binary strings with an odd number of $1’$s?

Consider the following statements. If $L_1 \cup L_2$ is regular, then both $L_1$ and $L_2$ must be regular. The class of regular languages is closed under infinite union. Which of the above statements is/are TRUE?

Consider the language $L = \{a^{n}\mid n \geq 0\} \cup \{a^{n}b^{n}\mid n \geq 0\}$ and the following statements. $L$ is deterministic context-free. $L$ is context-free but not deterministic context-free. $L$ is not $LL(k)$ for any $k$. Which of the above statements is/are TRUE?

Consider the following languages. $$\begin{array}{ll} L_1= \{ wxyx \mid w,x,y \in (0+1)^{+} \} \\ L_2= \{xy \mid x,y \in (a+b)^{*}, \mid x \mid=\mid y \mid, x \neq y \} \end{array}$$ Which one of the following is TRUE?

Consider the following language. $L = \{{ x\in \{a,b\}^*\mid}$number of $a$’s in $x$ divisible by $2$ but not divisible by $3\}$ The minimum number of states in DFA that accepts $L$ is _________

If $L$ is a regular language over $\Sigma = \{a,b\}$, which one of the following languages is NOT regular?

For $\Sigma = \{a ,b \}$, let us consider the regular language $L=\{x \mid x = a^{2+3k} \text{ or } x=b^{10+12k}, k \geq 0\}$. Which one of the following can be a pumping length (the constant guaranteed by the pumping lemma) for $L$ ?

Which one of the following languages over $\Sigma=\{a, b\}$ is NOT context-free?

Consider the following sets: S1: Set of all recursively enumerable languages over the alphabet $\{0, 1\}$ S2: Set of all syntactically valid C programs S3: Set of all languages over the alphabet $\{0,1\}$ S4: Set of all non-regular languages over the alphabet $\{ 0,1 \}$ Which of the above sets are uncountable?

Let $\Sigma$ be the set of all bijections from $\{1, \dots , 5\}$ to $\{1, \dots , 5 \}$, where $id$ denotes the identity function, i.e. $id(j)=j, \forall j$. Let $\circ$ denote composition on functions. For a string $x=x_1 x_2 \dots x_n \in \Sigma^n, n \geq 0$, let $\pi(x)=x_1 \circ x_2 \circ \dots \circ x_n$. Consider the language …

Given a language $L$, define $L^i$ as follows:$$L^0 = \{ \varepsilon \}$$$$L^i = L^{i-1} \bullet L \text{ for all } I >0$$The order of a language $L$ is defined as the smallest $k$ such that $L^k = L^{k+1}$. Consider the language $L_1 ($over alphabet $0)$ accepted by the following automaton. The order of $L_1$ is ________.

Consider the following problems. $L(G)$ denotes the language generated by a grammar $G$. L(M) denotes the language accepted by a machine $M$. For an unrestricted grammar $G$ and a string $w$, whether $w \in L(G)$ Given a Turing machine $M$, whether $L(M)$ is regular Given two grammar$G_1$ and $G_2$, whether $L(G_1) = L(G_2)$ Given an …

Consider the following languages: $\{a^mb^nc^pd^q \mid m+p=n+q, \text{ where } m, n, p, q \geq 0 \}$ $\{a^mb^nc^pd^q \mid m=n \text{ and }p=q, \text{ where } m, n, p, q \geq 0 \}$ $\{a^mb^nc^pd^q \mid m=n =p \text{ and } p \neq q, \text{ where } m, n, p, q \geq 0 \}$ $\{a^mb^nc^pd^q \mid mn =p+q, \text{ where } m, n, p, q \geq 0 \}$ Which of the …