Dfa

A DFA is a deterministic finite automaton, a simple model of computation

Nfa

An NFA is a nondeterministic finite automaton, a mathematical model of computation that decides membership in regular languages.



Easier representation equivalent

Example

"Because representation of a given problem with a nfa is far easier than the equivalent dfa"

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Non-deterministic finite state machines in software development?

"Stephen string search or a compiled dfa you can construct stephen string search or a compiled dfa from an nfa which is easier to make"

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Faster way of searching a string in text files

Slower powerful engine

Example

"Perl uses nfa which is slower yet more powerful than the dfa engine sed has"

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Is it faster to use alternation than subsequent replacements in regular expressions

"Regex is a nfa and is as such in most cases slower than a dfa or hand-written parser"

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Rewrite IsHexString method with RegEx

Simple transitions smaller

Example

"The dfa is much more complex in terms of the nodes the nfa contains but has really simple rules since there is exactly one output state for any given input"

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A succinct description of NFA to DFA conversion?

"In fact because you are eliminating the redundancy of epsilon transitions many simple dfa s actually get smaller than the nfa they represent but there is simply no way to guarantee that"

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DFA based regular expression matching - how to get all matches?

Others

Example

The net effect is that the backtracking implementations i like that name better than traditional nfa are slightly more expressive than dfa implementations because traditional nfa can match regexes like which matches three or more word characters repeated twice something that can t be matched by a dfa

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If NFA and DFA were equivalent, why would we have two engines for regex?

At the same time the compilation phase for a dfa is typically more complex than for an nfa and dfas don t have all the capabilities of nfas

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How much faster are regular expressions processed in C/Java than in Python?

If we express combinations of states in an nfa as states themselves we ve got a dfa with a lot more states than the nfa but which does the same thing

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DFA vs NFA engines: What is the difference in their capabilities and limitations?

If it finds a match then it goes back and matches the full regex using an nfa engine i think traditional non-posix but starting at the location where the simplified match occurred;this is much faster for both non-matches and matches than a straight nfa engine but still lets you use all the things in an nfa that a dfa does not support

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Which regular expression engine type does R use as a standard?

If it can be practically determinized this give you a dfa that can be exponentially larger than the nfa then by all means do that

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Match Regular expression from a dictionary in C#

If you have a regular expression without any optional such as ab the nfa graph doesn t have to contain any epsilon edges;an important concept in nfa simulation and nfa to dfa translation is the epsilon closure a set of states reachable from a state by following epsilon transitions

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Converting NFA to DFA without epsilon

Generally speaking dfa is faster but nfa is more compact

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Parallel regex matching with NFA vs DFA? Which one is faster?

As a result a posix nfa engine is slower than a traditional nfa engine and when using a posix nfa you cannot favor a shorter match over a longer one by changing the order of the backtracking search;traditional nfa engines are favored by programmers because programmers are more expressive than either dfa or posix nfa engines

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DFA vs NFA engines: What is the difference in their capabilities and limitations?

Dfa is a better choice over nfa because it has only one transition for an input while nfa can have many

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Parallel regex matching with NFA vs DFA? Which one is faster?

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