LEXICAL ANALYSIS
REGULAR EXPRESSIONS AND FINITE AUTOMATA
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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aba*b*bba
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ab(ab)*bba
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ab(a+b)*bba
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All of the above
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Detailed explanation-1: -Regular expression for all strings starts with ab and ends with bba is. Explanation: Starts with ab then any number of a or b and ends with bba. 12. How many DFA’s exits with two states over input alphabet 0, 1 ?
Detailed explanation-2: -*’ will match all strings starting with ‘aa’. #6 The dollar($): It implies the last character of a string. ‘. *b$’ will match all strings ending with a ‘b’.
Detailed explanation-3: -Example strings = aaba, aaaba, aabba, aaabba, aababa, ………and all other strings that can start with aa and end with ba.
Detailed explanation-4: -The Regular Expression b*ab*ab*, over a, b correspond to: The set of all strings containing exactly 2a’s.
Detailed explanation-5: -A regular expression describes a set of strings. The simplest case is one that describes a particular string; for example, the string ‘ foo ‘ when regarded as a regular expression matches ‘ foo ‘ and nothing else. Nontrivial regular expressions use certain special constructs so that they can match more than one string.