No, I meant solved by an NFA.

Today NFAs can solve all problems that DFAs can solve, but it is possible to by accident write an NFA that will take several years to finish. My suggestion allows you to convert an NFA into an equivalent NFA which backtracks at fewer points. However it remains an NFA, and where an NFA would find a different match than a DFA, it will find the match that an NFA would find, and not the one that a DFA would. (Thereby allowing it to be used in an NFA engine without changing the behaviour.)

Now if the RE is one that you could use a DFA to solve, then you can convert the NFA into an NFA with no backtracking anywhere. However it still retains NFA characteristics. For instance with alternation it will prefer to match the first alternative in the sequence, and won't match the second if that allows a longer overall match.

Unfortunately optimizing the NFA that far may result in a combinatorial explosion from n states to n!, but since the optimization goes in steps, you can just optimize until you hit some threshold, and then stop. (Or you could run, profile, incrementally optimize, wash, rinse, and repeat.)

In reply to Re (tilly) 3: Research ideas by tilly
in thread Research ideas by Wodin

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.