问题
There are three different solutions to implement regular expression matching: DFA, NFA and Backtracking. I am looking for examples:
- a regexp, which can be solved with a DFA and the reason, why a DFA is sufficient.
- a regexp, which requires a NFA and the reason why a NFA is necessary.
- a regexp, which requires backtracking and the reason why backtracking is necessary.
A recommendation for some good literature about this topic would be nice, too.
回答1:
i guess there is more than 1 meaning to the word backtracking - even '.*a' has to backtrack to match the string "lalaiiiiiii" (because .* will first match the whole string - so then a won't match anything - and only then it will give up one character at a time, so the final match would be "lala")
i highly recommend http://www.regular-expressions.info/
回答2:
What I found out so far is:
Every regular expression, which can be implemented with a NFA, can also be implemented with a DFA. Every NFA can be transformed into a DFA.
Regular expressions, which require backtracking, are regular expressions, which contain back references like
/(a)\1/.
来源：https://stackoverflow.com/questions/8132412/which-regular-expression-requires-backtracking