Question
Download Solution PDFA lexical analyzer uses the following patterns to recognize three tokens T1, T2, and T3 over the alphabet {a,b,c}.
π1: π? (π|π)∗π
π2: π? (π|π)∗π
π3: π? (π|π)∗π
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 ππππππππ is processed by the analyzer, which one of the following is the sequence of tokens it outputs?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
Take relational algebra which generates the longest subsequence.
With T3 we get a subsequence of 5, and T1 we get a subsequence of only 4, T2 we get a subsequence of only 3.
Hence, T3 preferred over T2 and T1
Explanation
String = ππππππππ
(π|π)∗ = (a + b)*
π? = (Ο΅ + c)
π3: π? (π|π)∗π
T3 = bbaac (longest prefix match)
T3= abc
π3π3 = πππππ πππ
Therefore option 4 is correct
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