Constructing NFA s by Optimal Use of Positions in Regular Expressions

  • Authors:
  • Lucian Ilie;Sheng Yu

  • Affiliations:
  • -;-

  • Venue:
  • CPM '02 Proceedings of the 13th Annual Symposium on Combinatorial Pattern Matching
  • Year:
  • 2002

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Abstract

We give two new algorithms for constructing small nondeterministic finite automata (NFA) from regular expressions. The first constructs NFAs with 驴-moves (驴NFA) which are smaller than all the other 驴NFAs obtained by similar constructions. Their size is at most 3/2 |驴|+ 5/2, where 驴 is the regular expression. The second constructs NFAs. It uses 驴-elimination in the 驴NFAs we just introduced and builds a quotient of the well-known position automaton. Our NFA is always smaller and faster to compute than the position automaton. It uses optimally the information from the positions of a regular expression.