# Technical Interview Questions and Answers :: Finite Automata

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what is finite automata?

A finite automaton (FA) is a simple idealized machine used to recognize patterns within input taken from some character set (or alphabet) C. The job of an FA is to accept or reject an input depending on whether the pattern defined by the FA occurs in the input.

A finite automaton consists of:

• a finite set S of N states

• a special start state

• a set of final (or accepting) states

• a set of transitions T from one state to another, labeled with chars in C

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What are the types of finite automata?

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What is the difference between the strings and the words of a language?

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What is the difference between an Alphabet and an element of a set. Whether Alphabet is an element of a set or it is a set itself?

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What is the difference between FA , TG , GTG. ?

• n Finite Automata transitions are marked with single letter of alphabet. In Transition Graph, they can be marked with letters or strings (combination of letters).

• In Finite Automata states transition are shown for all letters of given alphabet. In Transition Graph, it does not necessarily shows transition for all letters.

• Strings transitions can be showed with TGs but impossible with FAs.

• In GTG transition edges are labelled about RE but in TG edges are labeled with strings.