Construct a Turing Machine for language L = {wwr | w ∈ {0, 1}}



Prerequisite – Turing Machine
The language L = {wwr | w ∈ {0, 1}} represents a kind of language where you use only 2 character, i.e., 0 and 1. The first part of language can be any string of 0 and 1. The second part is the reverse of the first part. Combining both these parts out string will be formed. Any such string which falls in this category will be accepted by this language. The beginning and end of string is marked by $ sign.

For example, if first part w = 1 1 0 0 1 then second part wr = 1 0 0 1 1. It is clearly visible that wr is the reverse of w, so the string 1 1 0 0 1 1 0 0 1 1 is a part of given language.

Examples –

Input : 0 0 1 1 1 1 0 0
Output : Accepted
Input : 1 0 1 0 0 1 0 1 
Output : Accepted

Basic Representation –



Assumption: We will replace 0 by Y and 1 by X.

Approach Used –
First check the first symbol, if it’s 0 then replace it by Y and by X if it’s 1. Then go to the end of string. So last symbol is same as first. We replace it also by X or Y depending on it.
Now again come back to the position next to the symbol replace from the starting and repeat the same process as told above.

One important thing to note is that since wr is reverse of w of both of them will have equal number of symbols. Every time replace a nth symbol from beginning of string, replace a corresponding nth symbol from the end.

  • Step-1:
    If symbol is 0 replace it by Y and move right, Go to state Q2
    If symbol is 1 replace it by X and move right, Go to state Q1

  • Step-2:
    If symbol is 0 replace it by 0 and move right, remain on same state
    If symbol is 1 replace it by 1 and move right, remain on same state
    ——————————————————————-
    If symbol is X replace it by X and move right, Go to state Q3
    If symbol is Y replace it by Y and move right, Go to state Q3
    If symbol is $ replace it by $ and move right, Go to state Q3

  • Step-3:
    If symbol is 1 replace it by X and move left, Go to state Q4
    If symbol is 0 replace it by Y and move left, Go to state Q5

  • Step-4:
    If symbol is 1 replace it by 1 and move left
    If symbol is 0 replace it by 0 and move left
    Remain on same state

  • Step-5:
    If symbol is X replace it by X and move right
    If symbol is Y replace it by Y and move right
    Go to state Q0

  • Step-6:
    If symbol is X replace it by X and move right
    If symbol is Y replace it by Y and move right
    Go to state Q6
    ELSE
    Go to step 1

  • Step-7:
    If symbol is X replace it by X and move right, Remain on same state
    If symbol is Y replace it by Y and move right, Remain on same state
    If symbol is $ replace it by $ and move left, STRING IS ACCEPTED, GO TO FINAL STATE Q7



My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.




Article Tags :

Be the First to upvote.


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.