to Answers Questions from Topics Presentations Finite Automata (Cht 2) Questions and Answers (1) Can a DFA be used to parse a compuer language like C? Yes (2) What would the DFA look like for (abab)*c(bb)*?
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Regular Languages (Cht 14) Questions and Answers
Q: Given a DFA D with two accept states, can you create a DFA D' which accepts exactly the same language as D, but with only one accept state? A: Not necessarily--If you are willing for D' to end up an NFA-lambda, then yes, it would be possible--however, by restricting the result as a DFA most likely D' will be unable to have only one accept state. The reason that this is the case is hinged on a property of DFA's that no lookahead "guessing" is allowed--each state must unequivocally list the path taken for a given input. Consider the DFA D with three states, S, Q1, and Q2, and paths f(S, a) = Q1, and f(Q1, b) = Q2, where states Q1 and Q2 are both final/accepting states. The RL described by this DFA is (a U ab). There are two nodes we can remove from the accepting set, so let's look at both possibilities. The problem with the following D' is that by accepting the string "ab" we ignore the fact that "a" is too short to make it to the end. Remove Q1 from the accepting set: This will end up with Q2 being the only final state. * In order for the machine to accept "ab", we need an arc for "a" going from S->Q1, and "b" from Q1->Q2 * However, w...
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