# How to approach NFA design questions intuitively? [closed]

I did see a lot of nice and informative questions, articles on inter-net and on StackOverflow itself, of-course. But I found all the questions or articles following a specific rule or a pattern to explain the topic. I mean, when a question was asked on NFA, DFA or Regular Expression, a solution was presented to the question abiding by the theorems / rules of these topics (Theory of Computation).

But what I feel is that, as most of the questions on DFA/NFA are of the type "Design an NFA...." or "design a DFA..." , I feel that developing/Designing DFA/NFA must be an ART.

And where there is ART I feel there is an intuition. If these problems involve "DESIGNING" something ,then everyone must have their own way (of-course not going out-of-the-way of theorems or rules as such) of solving or attacking these problems. One should have developed a thinking process (over the years of practise) to solve these problems.

So I would like all the experts over this Site to share their knowledge (preferably in simple words) how they think over the problems (simple ones) of these topics.

I would like to elaborate the question with a simple example.

Let F be the language of all strings over {0,1} that do not contain a pair of 1s that are separated by an odd number of symbols. Give the state diagram of a DFA with five states that recognizes F .

Or maybe this:

Design an NFA to find a 4-state NFA for the complement of F.

These questions are from the Sipser's book and I have also found the solutions for them myself.

I just want to know , how one can develop an intuition for solving the problems?

## closed as too broad by J.-E. Pin, D.W.♦, Juho, Guy Coder, Luke MathiesonDec 13 '13 at 8:23

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• This topic has already been covered on this site: cs.stackexchange.com/q/1331/755 You will find many techniques and methods for designing a NFA (or DFA) there. – D.W. Dec 12 '13 at 8:59
• My answer here contains advice on how to design automata. Excutive summary: each state has a "meaning", e.g., "The automaton is in this state whenever the number of zeroes it has seen is even." – David Richerby Dec 12 '13 at 9:26