GATE Computer Science (CS) 2018 Shift 1 Solved Paper

Question : 51 of 65

Marks: +1, -0

A lexical analyzer uses the following patterns to recognize three tokens

T_{1}, T_{2}

and

T_{3}

over the alphabet

\{a, b, c\}

T_{1}: a ?(b ∣ c)* a
T_{2}: b ?(a ∣ c)* b
T_{3}: c ?(b ∣ a)* c
Note that 'X?' means 0 or 1 occurrence of the symbol

x

. Note also that the analyzer outputs the token that matches the longest possible prefix.
If the string bbaacabc is processed by the analyzer, which one of the following is the sequence of tokens it outputs?

$T_{1} T_{2} T_{3}$
$T_{1} T_{1} T_{3}$
$T_{2} T_{1} T_{3}$
$T_{3} T_{3}$

Validate

Solution:

Ans is

T_{3} T_{3}

because from first

T_{3}

bbaac is taken from second

T_{3} a b c

is taken longest possible prefix.
Hence

T_{3} T_{3}

token output.

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