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Homework Help: Find a DFA that accepts words with "aa" twice

  1. Nov 23, 2014 #1
    Hi everyone,

    I have just started learning about DFA's and I have to solve the problem from the thread title with
    Σ = {a,b}.

    My attempts so far are in the attachments.

    I am struggling as to what to do with the words in state 2 that have a b*a*b* substring before getting their second "aa". Can anyone help me with this?

    NB: It was noted in the exercise that "aaa" is accepted by the DFA because it contains the substring "aa" twice as well.


    Attached Files:

    • DFA.jpg
      File size:
      25.2 KB
  2. jcsd
  3. Nov 23, 2014 #2


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    2017 Award

    Staff: Mentor

    Why do you have 4 and 0 and where is the difference between those states? What do they mean?
    "abaaa" does not get accepted like that.

    2b will need a new state I think.
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