The title says it all... I can't seem to get the idea... I know it uses the index of coincidence but I'm not sure with whom or what am I supposed to compare it with... How is the formula used?... It would help me a lot if it were exposed in an algorithmic representation...
This link should probably light up your mind...
http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-vigenere-cipher/
I'm using the book Cryptography Theory and Practice Third Edition, and it's horrible. It states the formula but never a concrete example.
Can someone please help me understanding which one is more efficient strstr() or KMP as recently I was doing a question on SPOJ and found that strstr() was in one way or other faster than KMP..
someone please explain the mystery behind this..
You are comparing apples with pears, strstr() is a function to find substrings, KMP is an algorithm to do it, so strstr() could theoretically be implemented using KMP. You need to find out which algorithm is the strstr() in question implementing to give a statement.
Take a look at this answer and the comments on it.
This was asked in an interview.
I think the answer can be done by constructing a trie of all valid words and then suggestions can be made based on a possible valid path which was otherwise given as incorrect.
Say if user types apfle, and system would detect that after ap a possible valid path was app, which would then satisfy apple.
Is there any better solution than this? Perhaps the one implemented by spell checkers.
See:
How does the Google "Did you mean?" Algorithm work?
How do I approximate "Did you mean?" without using Google?
How to write a spelling corrector
Youtube Video: Search 101
Within typical search engines you will find a lot of Analyzer stuff, which directs to the same underlying problem. A very popular Analyzer would be the n-gram Analyzer.
Perhaps this helps.
I have an assignment to correct an ambiguous BNF, but I am completely lost. I know this not a true programming question, and I will gladly delete it if it is not an appropriate question for these boards. Are there any good sites where I could learn more about BNF's? The one I am dealing with seems rather simple, but I can't find any examples or good explanations regarding BNF's. I have had some experience spotting ambiguous parse trees and other sorts of grammars, but I am completely lost on this one.
Since it is a school assignment, I am not sure I should post the BNF in question, but if anyone knows of a good site that I could look over to perhaps gain a better understanding of how to attack my question. I really just don't know where to start.
Some BNF describing a context-free grammar is also describing a state machine (in this case a Pushdown automata). The best way to do this is probably by inspection of the state machine.
As a starting point, you could look into what a conflict is within parsers that make use of such automata.
If there are two or more of the same nonterminals at the right side of a sentence it's ambiguous. For example: < expr > -> < expr > + < expr > | < facto >. The right side expr's can be exported in different ways in the tree, so different trees can be drawn and it's ambiguous.
He is good programmer (won some competitions) but he absolutely ignores formatting.
He consider i, j, k beautiful... I hope he won't find out about existence of goto keyword.
Write some code in his "style" and then ask him to read it and explain to you what it is doing.
What's good for the goose and all...
I told my students (post-secondary) that they had the choice of writing code well or of me writing their assignments in the same sort of way that they wrote their code. I told them I would write the following program:
take the text of the assignment
lookup a number of the words in a thesaurus and replace them with obscure versions
remove all punctuation
remove all whitespace
convert everything to lower case
insert random whitespace
capitalize random letters
They could then have the assignment... hey its "right" (all of the words are there) good luck understanding what the assignment is though.
Oddly the complaints stopped at that point :-)
I also compared it to English. We use paragraph breaks, capitalizations, etc... as a convention. When someone chooses not to follow the conventions it makes reading much harder.
tell him about python :)
Make him maintain somebody else's code that's written the way he writes. Then make him maintain somebody else's code that was written with good style.
A combination of FORTRAN77 and Python should sort him out.
Code maintainability
Stuff I didn't care in high school neither :)
Write a bunch of "his" code and ask him to find a particular piece of code.
Give him some badly written code with a bug in it and ask him to find the bug.
Well, if he plans to do this for a living just explain that he will have a very rough life on a real team if he doesn't at least make some effort to follow the team standards. If he doesn't plan to do it for a living, don't worry about it.
You also might determine if there is anyone(s) that he admires. If there is then there is a pretty good chance that they follow standards.
I would point out that having clean code is a sign of a organized and intelligent mind. However, the real killer will be when he writes a large amount of code. I doubt you will be able to convince him because more than likely he is getting excited about the logic of the app and not the process. It will take experience to teach him a harsh lesson. So here are my suggestions.
Give him a project full of messy unformatted poorly named code and let him suffer.
Encourage him to work on a project with a large code base and let him see how well he remembers his own variable names after the 1,000th source file.
You probably can't.
Some people just don't get it.
I use self-describing variable names both at work and in private where noone tells me to. I also got some appreciation at work for using long and understandable names.
If a guy does not do it neither for himself or for your project then you've got that kind of guy. Show him some docs on the source code style policy. Explain why this is important.
You begin to use the right naming convention after you've got some experience and you see how and why this was useful. Without experience it's just an abstract talk.
P.S. Sometimes I get stuck with variable names because I'm not sure if this particular name does conform to the common linguistic style I use in the current project or how would the name scale on the high litterature language. The problem of using bool b1 vs. bool IsSomePropertyAvailable has never come up since the first university years.
I'm pretty sure you can misconfigure a code beautifier to present such horrible output. Obfuscaters are common, and do essentially the same thing (short useless variable names, no indenting, poor use of whitespace).
Give him the assignment of taking an existing program with his style and adding a trivial feature.
Also, take code he wrote 6 months or more ago and give the same assignment.
-Adam
Maybe he's not ignorant, maybe he's just inspired by Kernighan & Pike.
i,j,k is fine for loops.
I personally prefer using 1 letter vars in iterations...
foreach ($test as $t)
{
}
beautiful :D