I'm having an exam on Friday and i need to know if the following exercise its correct, because our dear professor won't put solutions to our exercises, like everybody else does so we can test if it is correct or not. I need to know if the algorithm that i used it is correct.
Below is an IMG of an NFA diagram and the second image is where i convert it to DFA (it is hand written).
Here are the exercise: Exercise
Here is how i solved it: Solved exercise
Yes, it's correct. Good job! You have followed the text book way to convert to DFA. And to answer the further question, "C" is a state that is not accessible in the DFA when you start at the start-state.
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Draw the diagram of a two tape Non deterministic Turing Machine M that decides the language
L={w∈Σ* | w=uuu ∈Σ* }
if i could get help explaining the steps how to construct the NDTM (linguistically), I believe I could draw the diagram but I couldnt come out with an answer..
thank you
By u*u*u (viewed in the edit history), I presume what you intend is the language of all words of the form u^3 (u repeated three times) where u is any string over the alphabet.
Our NDTM needs to accept strings in the language in at least one way, and it must never accept anything not in the language. In particular, the key is that an NDTM can reject strings in the language, as long as some path through the NDTM does accept every string in the language.
Given that, our first step can be do guess about the length of u. The NDTM can mark three tape symbols (say, by writing versions of the symbols that are underlined) by nondeterministically transitioning from state q0 to q1 then q2 at arbitrary points while scanning right. Then, we can reset the tape head and use a deterministic TM to answer the question: did the split we guessed in the first step result in a string of the form u^3?
This is deterministic since we know the delineation of parts. We can check the first two parts (say, by bouncing back ad forth and marking symbols we've already processed), and then the second two parts (using the same technique, but applied to the 2nd and 3rd parts).
We have reduced the problem to that of checking whether a string is of the form w|w where we know the split. This deterministic TM is easier to come up with. When we put it after the NDTM that guesses about how to split up the initial input, we get a NDTM that can (and for exactly one guess, does) accept any string of the form u^3, but cannot possibly accept anything else. This is what we were after and we are done.
I'm having trouble proving a particular language is non-regular. The language is defined as
La = { wz: w,z ∈ {0,1}* and |w| > |z|}
I don't know how to approach this one. No matter what string I choose, I always run into the issue where w and z are moving targets for me; I haven't been able to create a string which couldn't be pumped or otherwise contradicted. Any thoughts on the right direction for this one?
This problem was part of a homework set, and apparently this question wasn't worded properly and is in fact regular.
I'm just learning C language, so I apologize in advanced if my question is not clear or if I'm asking the wrong question (or a dummy question).
I wrote a code in C that produces the fractal fern points and then plots them using openGL.
My code is similar to the one found here (http://www.cs.csubak.edu/~marc/code/opengl/fern.c).
Now I want to save the image that I obtained to a file. I've been searching about this and most of the answers suggest to use a library for this, but I'd like to write my own function. I understand that the first step is to use glreadpixels to read the pixel, but I'm not sure what should be the next step.
Thanks for your time and help
libbmp is a very good choice.
http://code.google.com/p/libbmp/
I am going to be making a program that reads in a line and gets up to 6 numbers. The program will eventually solve a a square matrix between 2x2 and 6x6. My question is what errors do I need to look for on the get_numb() function?
I am thinking that the function will have to check character by character to make sure that the individual characters are actual numbers and not a EOF or \n. I will have to also check that there is not more than 6 numbers on a line. I am about a week into programing, so is there anything I need to know to tackle this?
I absolutely recommend you start by taking into use a good unit testing framework, and write unit tests as you go. This way you can cover all the cases you mention above, and make sure that your program really works the way you think it should work.
There are loads of questions on SO about C unit testing frameworks; pick your favourite.
Apart from the cases you mention, I can think of the following:
less than 6 numbers on a line
empty line
(if the numbers are floating point, various number formats)
If your teacher gave you sample input / output, you may of course incorporate that into your unit tests as well.
The potential errors you described are reasonable ones to check for.
I recommend you give it a shot. If they're not sufficient and you get stuck, then post your code and explain what you're seeing.
Most ascii to integer converters will help you out with the error checking. Here's hoping your teacher gave you some example input code and perhaps, depending on the input methods, some example conversion code. As this is homework, I don't want to get too specific.
I am trying to do something in C with the MD5 (and latter trying to do something with the SHA1 algorithm). My main problem is that I never really did anything complex in C, just simple stuff (nothing like pointers to pointers or structs).
I got the md5 algorithm here.
I included the files md5.c and md5.h in my C project (using codeblocks) but the only problem is that I don't really understand how to use it. I have read and re-read the code and I don't understand how I use those functions to turn 'example' into a MD5 hash.
I haven't done C programming in a while (mostly php) so I am a bit lost here.
Basically what I am asking is for some examples of usage. They are provided via the md5main.c file but I don't understand them.
Am I aiming high here? Should I stop all this and start reading the C book again or can anyone give me some pointers and see if I can figure this out.
Thanks.
While I agree with Bill, you should go back to the C book if you want to really understand what you're doing. But, in an effort to help, I've modified and commented some of the code from md5main.c...
const char* testData = "12345"; // this is the data you want to hash
md5_state_t state; // this is a state object used by the MD5 lib to do "stuff"
// just treat it as a black box
md5_byte_t digest[16]; // this is where the MD5 hash will go
// initialize the state structure
md5_init(&state);
// add data to the hasher
md5_append(&state, (const md5_byte_t *)testData, strlen(testData));
// now compute the hash
md5_finish(&state, digest);
// digest will now contain a MD5 hash of the testData input
Hope this helps!
You should stop all this and start reading the C book again.
My experience is that when I am trying to learn a new programming language, it's not practical to try implementing a complex project at the same time. You should do simple exercises in C until you are comfortable with the language, and then tackle something like implementing MD5 or integrating an existing implementation.
By the way, reading code is a skill different from writing code. There are differences between these two skills, but both require that you understand the language well.
I think you picked about the worst thing to look at (by no fault of your own). Encryption and hash type algorithms are going to make the strangest use of the language possible to do the type of math they need to do quickly. They are almost guaranteed to be obfuscated and difficult to understand. Plus, you will need to get bogged down in math in order to really understand them.
If you just want a hashing algorithm, get a well-known implementation and use it as a black box. Don't try and implement it yourself, you will almost certainly introduce some cryptographic weakness into the implementation.
Edit: To be fully responsive if you want great books (or resources) on encryption, look to Bruce Schneier. Applied Cryptography is a classic.