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GATE CSE

Finite Automata and Regular Language

Theory of Computation

Previous Years Questions

Marks 1

More
Which one of the following regular expressions correctly represents the language of the finite automation given below? ...
GATE CSE 2022
Which one of the following regular expressions represents the set of all binary strings with an odd number of 1’s?
GATE CSE 2020
Consider the following statements. I. If L1 $$ \cup $$ L2 is regular, then both L1 and L2 must be regular. II. The class...
GATE CSE 2020
For Σ = {a, b}, let us consider the regular language L = {x | x = a2+3k or x = b10+12k, k ≥ 0}. Which one of the followi...
GATE CSE 2019
If L is a regular language over Σ = {a,b}, which one of the following languages is NOT regular?
GATE CSE 2019
Language $${L_1}$$ is defined by the grammar: $$S{}_1 \to a{S_1}b|\varepsilon $$ Language $${L_2}$$ is defined by the gr...
GATE CSE 2016 Set 2
The number of states in the minimum sized $$DFA$$ that accepts the language defined by the regular expression $$${\left...
GATE CSE 2016 Set 2
Which one of the following regular expressions represents the language: the set of all binary strings having two consecu...
GATE CSE 2016 Set 1
Let $$L$$ be the language represented by the regular expression $$\sum {^ * 0011\sum {^ * } } $$ where $$\sum { = \left\...
GATE CSE 2015 Set 3
The length of the shortest string NOT in the language (over $$\sum { = \left\{ {a,\,\,b} \right\}} $$) of the following ...
GATE CSE 2014 Set 3
Consider the finite automation in the following figure. What is the set of reachable states for the input string $$001...
GATE CSE 2014 Set 1
If $${L_1} = \left\{ {{a^n}\left| {n \ge \left. 0 \right\}} \right.} \right.$$ and $${L_2} = \left\{ {{b^n}\left| {n \ge...
GATE CSE 2014 Set 2
Which one of the following is TRUE?
GATE CSE 2014 Set 1
Consider the languages $${L_1} = \phi $$ and $${L_2} = \left\{ a \right\}.$$ Which one of the following represents $${L_...
GATE CSE 2013
What is the complement of the language accepted by the $$NFA$$ shown below? Assume $$\sum { = \left\{ a \right\}\,\,} $...
GATE CSE 2012
Let $${L_1}$$ recursive language. Let $${L_2}$$ and $${L_3}$$ be languages that are recursively enumerable but not recur...
GATE CSE 2010
Which one of the following languages over the alphabet $$\left\{ {0,\left. 1 \right)} \right.$$ is described by the regu...
GATE CSE 2009
Consider the set $$\sum {^ * } $$ of all strings over the alphabet $$\,\sum { = \,\,\,\left\{ {0,\,\,\,1} \right\}.\sum ...
GATE CSE 2003
The regular expression $${0^ * }\left( {{{10}^ * }} \right){}^ * $$denotes the same set as
GATE CSE 2003
Given an arbitrary non-deterministic finite automaton $$(NFA)$$ with $$N$$ states, the maximum number of states in an eq...
GATE CSE 2001
Consider the following two statements; $${S_1}\,\,:\,\,\left\{ {{0^{2n}}\left| {n \ge 1} \right.} \right\}$$ is a regula...
GATE CSE 2001
Let $$L$$ denote the language generated by the grammar $$S \to 0S\left. 0 \right|00.$$ Which one of the following is tru...
GATE CSE 2000
Let $$S$$ and $$T$$ be languages over $$\sum { = \left\{ {a,b} \right\}} $$ represented by the regular expressions $${\l...
GATE CSE 2000
Consider the regular expression $$(0+1)(0+1).......n$$ times. The minimum state finite automation that recognizes the la...
GATE CSE 1999
How many substrings of different lengths (non-zero) can be formed from a character string of length $$n$$ ?
GATE CSE 1998
Which of the following sets can be recognized by a Deterministic Finite-state Automation?
GATE CSE 1998
The string $$1101$$ does not belong to the set represented by
GATE CSE 1998
If the regular set $$A$$ is represented by $$A = {\left( {01 + 1} \right)^ * }$$ and the regular set $$'B'$$ is represen...
GATE CSE 1998
$$\sum { = \left\{ {a,b} \right\},\,\,} $$ which one of the following sets is not countable.
GATE CSE 1997
Let $$L \subseteq \sum {^{^ * }\,} $$ where $$\,\sum { = \,\,\left\{ {a,b} \right\}\,\,} $$ which of the following is tr...
GATE CSE 1996
Which two of the following four regular expressions are equivalent? (i) $${\left( {00} \right)^ * }\left( {\varepsilon ...
GATE CSE 1996
State True or False with one line explanation: A FSM (Finite State Machine) can be designed to add two integers of any a...
GATE CSE 1994

Marks 2

More
Consider the following language. L = { w ∈ {0, 1}* | w ends with the substring 011} Which one of the following de...
GATE CSE 2021 Set 1
Consider the following language. L = {x $$ \in $$ {a, b}* | number of a’s in x is divisible by 2 but not divisible by 3}...
GATE CSE 2020
Given a language $$𝐿,$$ define $${L^i}$$ as follows: $${L^0} = \left\{ \varepsilon \right\}$$ $${L^i} = {L^{i - 1}}.\...
GATE CSE 2018
Let $$N$$ be an $$NFA$$ with $$n$$ states. Let $$k$$ be the number of states of a minimal $$DFA$$ which is equivalent to...
GATE CSE 2018
Consider the following languages: $$$\eqalign{ & {L_1} = \left\{ {{a^n}{b^m}{c^{n + m}}:m,n \ge 1} \right\} \cr ...
GATE CSE 2016 Set 2
Consider the following two statements: $$\,\,\,\,\,\,\,{\rm I}.\,\,\,\,\,$$ If all states of an $$NFA$$ are accepting st...
GATE CSE 2016 Set 2
Consider the transition diagram of a $$PDA$$ given below with input alphabet $$\sum {\, = \left\{ {a,b} \right\}} $$ and...
GATE CSE 2016 Set 1
Consider the alphabet $$\sum { = \left\{ {0,1} \right\},} $$ the null/empty string $$\lambda $$ and the sets of strings ...
GATE CSE 2015 Set 2
Which of the following languages is/are regular? $${L_1}:\left\{ {wx{w^R}|w,x\, \in \left\{ {a,b} \right\}{}^ * } \right...
GATE CSE 2015 Set 2
The number of states in the minimal deterministic finite automaton corresponding to the regular expression $${\left( {0 ...
GATE CSE 2015 Set 2
Consider the DFAs M and N given above. The number of states in a minimal DFA that accepts the language L(M) ∩ L(N) is__...
GATE CSE 2015 Set 1
Consider the NPDA $$\left\langle {Q = \left\{ {{q_0},{q_1},{q_2}} \right\}} \right.,$$ $$\Sigma = \left \{ 0, 1 \right \...
GATE CSE 2015 Set 1
Let $${L_1} = \left\{ {w \in \left\{ {0,1} \right\}{}^ * \left| w \right.} \right.$$ has at least as many occurrences o...
GATE CSE 2014 Set 2
Let $${L_1} = \left\{ {w \in \left\{ {0,1} \right\}{}^ * \left| w \right.} \right.$$ has at least as many occurrences o...
GATE CSE 2014 Set 2
Which of the regular expression given below represent the following $$DFA?$$ ...
GATE CSE 2014 Set 1
Consider the following languages $${L_1} = \left\{ {{0^p}{1^q}{0^r}\left| {p,q,r \ge 0} \right.} \right\}$$ $${L_2} = \...
GATE CSE 2013
Consider the set of strings on $$\left\{ {0,1} \right\}$$ in which, every substring of $$3$$ symbols has at most two zer...
GATE CSE 2012
Definition of the language $$L$$ with alphabet $$\left\{ a \right\}$$ is given as following. $$L = \left\{ {{a^{nk}}} \r...
GATE CSE 2011
Let $$w$$ be any string of length $$n$$ in $${\left\{ {0,1} \right\}^ * }$$. Let $$L$$ be the set of all substrings of $...
GATE CSE 2010
Let $$L = \left\{ {w \in {{\left( {0 + 1} \right)}^ * }\left| {\,w} \right.} \right.$$ has even number of $$\,\left. {1'...
GATE CSE 2010
The above $$DFA$$ accepts the set of all strings over $$\left\{ {0,\,\,1} \right\}$$ that...
GATE CSE 2009
$$L = {L_1} \cap {L_2}$$ where $${L_1}$$ and $${L_2}$$ are languages defined as follows. $${L_1} = \left\{ {{a^m}{b^m}...
GATE CSE 2009
Match the following $$NFAs$$ with the regular expressions they correspond to ...
GATE CSE 2008
Which of the following are regular sets? ...
GATE CSE 2008
Given below are two finite state automata ($$ \to $$ indicates the start state and $$F$$ indicates a final state) W...
GATE CSE 2008
Consider the following finite state automation The minimum state automation equivalent to the above $$FSA$$ has the fo...
GATE CSE 2007
Consider the following finite state automation The language accepted by this automation is given by the regular expres...
GATE CSE 2007
Which of the following languages is regular?
GATE CSE 2007
A minimum state deterministic finite automation accepting the language $$L = \left\{ {w\left| {w \in } \right.\,\,{{\lef...
GATE CSE 2007
Consider the regular language $$L = {\left( {111 + 11111} \right)^ * }.$$ The minimum number of states in any $$DFA$$ ac...
GATE CSE 2006
If $$s$$ is a string over $${\left( {0 + 1} \right)^ * }$$ then let $${n_0}\left( s \right)$$ denote the number of $$0'$...
GATE CSE 2006
Consider the machine $$M:$$ The language recognized by $$M$$ is: ...
GATE CSE 2005
The following finite state machine accepts all those binary strings in which the number of $$1's$$ and $$0's$$ are respe...
GATE CSE 2004
Consider the following deterministic finite state automation $$M.$$ Let $$S$$ denote the set of seven bit binary stri...
GATE CSE 2003
Consider the $$NFA$$ $$M$$ shown below. Let the language accepted by $$M$$ be $$L.$$ Let $${L_1}$$ be the language acc...
GATE CSE 2003
The Finite state machine described by the following state diagram with $$A$$ as starting state, where an arc label is $$...
GATE CSE 2002
The smallest finite automaton which accepts the language $$L = \left. {\left\{ x \right.} \right|$$ length of $$x$$ is...
GATE CSE 2002
Consider the following languages: $${L_1} = \left\{ {w\,w\left| {w \in {{\left\{ {a,\,b} \right\}}^ * }} \right.} \right...
GATE CSE 2001
Consider a $$DFA$$ over $$\sum { = \left\{ {a,\,\,b} \right\}} $$ accepting all strings which have number of $$a'$$s div...
GATE CSE 2001
What can be said about a regular language $$L$$ over $$\left\{ a \right\}$$ whose minimal finite state automation has t...
GATE CSE 2000
Let $$L$$ be the set of all binary strings whose last two symbols are the same. The number of states in the minimum stat...
GATE CSE 1998
Which one of the following regular expressions over $$\left\{ {0,\,\,1} \right\}$$ denotes the set of all strings not co...
GATE CSE 1997
Which of the following definitions below generates the same language as $$L$$ Where $$L = {\left\{ x \right.^n}{y^n}\le...
GATE CSE 1995
A finite state machine with the following state table has a single input $$X$$ and a single out $$Z$$. If the initial...
GATE CSE 1995
The number of sub-strings (of all lengths inclusive) that can be formed from a character string of length $$n$$ is
GATE CSE 1994
The regular expression for the language recognized by the finite state automation of is _________. ...
GATE CSE 1994
If $$G$$ is a context-free grammar and $$w$$ is a string of length $$n$$ in $$L(G),$$ how long is a derivation of $$w$$ ...
GATE CSE 1992
Which of the following regular expression identities are true?
GATE CSE 1992
Let $$r = 1\,{\left( {1 + 0} \right)^ * },s = {11^ * }\,0$$ and $$\,t = {1^ * }\,0$$ be three regular expressions. Which...
GATE CSE 1991
Let $${R_1}$$ and $${R_2}$$ be regular sets defined over the alphabet $$\sum \, $$ then:
GATE CSE 1990
How many substrings (of all lengths inclusive ) can be formed from a character string of length $$n$$? Assume all charac...
GATE CSE 1989

Marks 5

More
Given that language $${L_1}$$ is regular and that the language $${L_1} \cap {L_2}$$ is regular is the language $${L_2}$$...
GATE CSE 1994
Is the class of regular sets closed under infinite union? Explain.
GATE CSE 1989
Give the regular expression over $${\left\{ {0,\,\,1} \right\}}$$ to denote the set of proper non-null substrings of the...
GATE CSE 1987
Give minimal $$DFA$$ that performs as a Mod-$$3$$ $$1's$$ counter, i.e., outputs a $$1$$ each time the number of $$1's$$...
GATE CSE 1987

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