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In a recent question I was encouraged to try using some basic data structures such as binary trees, red-black trees, et cetera, before tackling other things like quadtrees.
My experience in C is fairly limited and I am fearful of using pointers for anything but simple data (like 2D grids, image storage and strings), although I am familiar with referencing, malloc, realloc and other trivial actions, I am not used to the "hard" parts of C, which makes such structures hard to tackle from theory, and I don't want to just copy working code into this.
What I'd like to know, in order to tackle basic trees, is a practical application for them. Sort of an exercise with some guidelines (sort of "don't do this or you will kill performance" or "don't do that or this will leak memory"), just to be able to know the practical purpose. Even if I memorize the theory, I still don't know what sort of experiment to conduct in order to understand their application.
I am mostly attempting to use plain C, I don't really understand C++/# code when reading it, although I have certain mastery of the Lua language in case that helps.
So far I've been coding combining Lua for dictionary searches and designing data (and some logic parts) and left all video and audio storage, heavy math and "world" storage in C (using grid structures and a not-too-bruteforced collision detection approach (using a linear array to place objects in 1/24 of the map, nothing complex in code terms)). Because I could always rely on Lua's solid code for some functions, I neglected learning more of C and now I am paying for it with lack of knowledge.
So, to formulate a question: "What is the basic use case for data trees?" The only idea I have so far is using a splay tree to match strings (filenames?) to textures. Is that a valid use? Should I begin with that?
One of the uses for data trees was when writing a parser / compiler. After breaking up the source (Lexical analysis) and running the parsing (verifying grammar), we would build a tree structure of the source code (Syntactic tree), which was then repeatedly visited by the next parts of the compiler.
Another use of trees is when having to match if strings belong to a set of words very quickly, using very little memory, you can use a DAWG (Directed acyclic word graph).
Finally, a classic use is writing a solver for a Travelling Salesman problem using a data tree to store your cities in memory.
The classic Sedgewick Algorithms in C, Part 5: Graph Algorithms is full of examples, also if you have access to it.
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I want to fundamentally learn algorithm efficiency by self study (hopefully both in how a program can make best use of hardware and in designing an algorithm). I wanted to know about some good books on this topic. I write my programs in c.
I'll recommend the book Algorithms in C, Parts 1-4: Fundamentals, Data Structures, Sorting, Searching, the author Robert Sedgewick has a magic power to explain hard things easily understood. The book though not well edited, is the best reference on data structure and algorithms in C I've read.
Quoting from editorial reviews:
Highlights
Expanded coverage of arrays, linked lists, strings, trees, and other
basic data structures Greater emphasis on abstract data types (ADTs)
than in previous editions
Over 100 algorithms for sorting, selection, priority queue ADT
implementations, and symbol table ADT (searching) implementations
New implementations of binomial queues, multiway radix sorting,
Batcher's sorting networks, randomized BSTs, splay trees, skip lists,
multiway tries, and much more
Increased quantitative information about the algorithms, including
extensive empirical studies and basic analytic studies, giving you a
basis for comparing them
Over 1000 new exercises to help you learn the properties of
algorithms
Whether you are a student learning the algorithms for the first time or a professional interested in having up-to-date reference material, you will find a wealth of useful information in this book.
As a reader, I'll say it deserves this accomplishment.
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In C I have noted that pointers result in faster program execution. How is it possible, as it must fetch the pointer variable before going to the actual variable?
Pointers don't result in faster program execution. Smart algorithms result in faster program execution. Sometimes algorithms can be made smarter by using pointers in the right way. Pointers are never a magic wand to throw at problems to make the solutions faster.
Pointers are just a design paradigm though, using functional programming you do not use any pointers at all.
This is not true. The reason for faster program execution is not the availablility of pointers. It's a question of what you do with the pointers. The (possibly) faster program execution yields from the fact that no hidden functionality is introduced with C.
Take a string for example. Common implementations in other languages introduce a length field along with the string in order to keep track of the length of the string. This "bookkeeping" (although hidden from the programmer) causes extra cycles to be executed.
Another example is the fact that C does not check if the pointer you are dereferencing is valid or not. This evaluation would also cost extra cycles.
The C standard does not specify any required speed, so it doesn't make sense to attribute speed to features of C. Consider that some C implementations produce more optimal machine code than others, and it might make more sense to attribute speed to aspects of specific implementations of C1. Don't confuse implementation and specification.
1: To make a meaningful comparison of the speed of specific implementations of C, you'd probably want to mention your OS (major and minor version), your compiler (major and minor version), your CPU (model), mainboard, memory (model and configuration) and the command line arguments you used.
While I am aware every answer to the question come from people far more knowledgeable than me in C (and I am out of my league actually), IMVHO and/or limited knowledge, pointers do improve efficiency.
To answer the OP's question (and ignoring the rest about program execution and fetching):
How can pointers improve program efficiency?
By avoiding duplication of data. Although this efficiency may only be notable when dealing with user-defined variables, "structures".
Here is a nice read I found on C pointers: Why C has Pointers
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Closed 11 years ago.
I was given this coding question in interview:
given a very very large number (say more than long or any in-built types) print out its factorial. you can not assume a max limit anywhere in the program.I had to make a working code on computer and during interview.
I am really curious, how long on average would it take for others?
this is subjective question but an average will set some ballpark figures and a benchmarks for such a coding question.
What I did?
I chose C and represented number by a linked list of characters (containing a single digit). though perhaps it can be made more efficient to store chunks in int/long and do int arithmetic than store it in chunk of characters.
I took 2 hours and spat out a code with things in place, major fns coded, but then interviewer said she wanted a completely working one and asked me to do it offline and mail it to her.
The good solution is to write a BigInt class that supports addition and mutilplication only. The number shouldn't be kept in base 10, rather in base 10000, i.e. each digit is a number 0-9999. Writing this is about 50-60 lines of code which should be relatively quick. I would also go with vector rather than list
Of course if you're not allowed to use an existing big int class.
Check the following links
calculate-the-factorial-of-an-arbitrarily-large-number-showing-all-the-digits
http://www.daniweb.com/software-development/cpp/code/216490
calculating-factorial-of-large-numbers-in-c
I'd start by suggesting a straight factorial in Common Lisp as Lisp already supports arbitrary precision arithmetic.
Assuming "no max limits anywhere" is a bit disingenuous since the computer has limited memory / disk space in any case but I understand the general gist.
Barring those two points of argument, you need to implement some sort of ADT for an arbitrary-sized number like Armen suggests.
To what accuracy? My first impulse would be to simply use Stirling's approximation.
There's no way I'm going to implement factorial for longs (bigger than ints) not to say above that.. It's totally pointless. No matter how fast my biginter library is.
32bit -> 4G, product of the numbers just from 1G till 4G.. well, lets just get a quick (under)estimation for the number of digits: 3G * 9 = 27G. rough estimation for the storage for that: 2^10=1024, so for 3 digits you need 1.25 bytes.. that's 11.25G. remember, this was a serious underestimation...
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Closed 11 years ago.
Hi I'm on my internship and my company told me that I've to implement password complexity using C language. The password must be Alpha numeric (eg h#ll0). Since I'm new to C , I found some difficulty. I google "password complexity in C " but no luck there. Can someone gave me some sample or explain me how to do it programmatically.
Thanks a lot in advance
Kevin
A better Google term would be "strong password":
http://en.wikipedia.org/wiki/Password_strength
But most of the articles you will find will not be for the C language, and they will probably suggest using a regular expression.
It would probably not be too hard to write your own low-level code to do the check as others have suggested. That would save you the trouble of generating a dependency on some C-language regular expression library to use. However, there is an advantage in using a regular expression because it means that non-C programmers would have a better chance at updating the rule at a later date, and it may make errors less likely to boot. It depends on your particular situation.
(Also, if other parts of your C code need regular expressions, then linking one in might be something you're going to need to do anyway and you'd get it "for free"...)
In any case, this StackOverflow question has a link to a regex.h tutorial, and more may be added to it in the future:
C - pellucid regex.h use tutorial
You don't provide enough information. By password complexity I assume you mean password strength.
I'm not in the business of writing code for someone, but if what you're looking to do is determine whether or not a password contains both a letter and a number, is at least n characters long, etc., C has functions you can do this with. isalnum(), isdigit(), and isalpha() come to mind for testing. These all return nonzero values to indicate true.
In terms of speed, C is fast on its own but remember with these that there is no need to parse the entire password -- all you need is for the function to return a nonzero value at some point. (All of these functions parse by character; C strings are char arrays.)
http://icecube.wisc.edu/~dglo/c_class/charfunc.html This is a good little reference for character parsing functions.
It depends on how the password is encoded, you may need an ASCII character chart or a unicode character chart. For each character in the input password, categorize it into groups number, uppercase letter, lowercase letter or special characters and so on.
here are the links to the tables:
http://www.asciitable.com/
http://www.tamasoft.co.jp/en/general-info/unicode.html
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Closed 10 years ago.
I am suppose to create a vector array in C to use in my project. I have not worked with such data structure before, and can't seem to find good information on it.
Can you provide a link to information or post the information which describes this data structure in regard to its usage, benefits, and the functions it has.
An implementation file would be also useful reference.
"... can't seem to find good information on it." Wat?
Google is pretty much king.
First understand what it is. Then implement based on what you research. You're going to need to understand not only what a vector is, but pointers and structs. Ask your instructor for help, or find a peer to work on this with.
It depends on what you mean by the terms. "Vector" has a very specific mathematical definition, but unfortunately without knowing what you goal is, "vector array" is sort of ambiguous because a vector is an array in a manner of speaking.
If you're doing mathematics in your software, you may actually want an array of vectors as opposed to an array aka vector. But, well, it depends on what you're looking to accomplish. (In my line of work, I need to deal with arrays of vector data, where the vectors are "locations" in 3D space.)
The shortest path would probably be to type:
Vector my_array[4];
...and see if that compiles. If it does not, then an array of Vector objects/structs is not available in your codebase. :)
Look into struct: C/C++ structures and classes.
Simple google search for vector array c
http://www.codecogs.com/d-ox/array/vector.php