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  • Pool Billiard AI

    - by Sebi
    Im implementing a pool billiard game in Java and it all works fine. It is a multiplayer game, but nevertheless, it should also be possible to play it alone. For this purpose I'm trying to implement a simple KI. At the moment, the KI choose just randomly a direction and a random intensity of the impulse (don't know the correct english word for that). Of course this AI is very poor and unlikely to ever challenge a player. So i thought about improving the KI, but there are several hard to solve problems. First I thought of just choosing the nearest ball and to try to put it directly into the nearest hole. This isn't that bad, but if there other balls in the line between, it isn't really working anymore. Additionally this dosn't solve te problem of calculating the intensity of the impulse. So are there any general advice? Or any ideas? Best practices?

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  • Formula needed: Sort array to array-"snaked"

    - by aw
    After the you guys helped me out so gracefully last time, here is another tricky array sorter for you. I have the following array: a = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] I use it for some visual stuff and render it like this: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Now I want to sort the array to have a "snake" later: // rearrange the array according to this schema 1 2 3 4 12 13 14 5 11 16 15 6 10 9 8 7 // the original array should look like this a = [1,2,3,4,12,13,14,5,11,16,15,6,10,9,8,7] Now I'm looking for a smart formula / smart loop to do that ticker = 0; rows = 4; // can be n cols = 4; // can be n originalArray = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]; newArray = []; while(ticker < originalArray.length) { //do the magic here ticker++; } Thanks again for the help.

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  • review of a codility test - pair_sum_even_count

    - by geoaxis
    I recently took an online test on codility as part of a recruitment process. I was given two simple problems to solve in 1 hour. For those who don't know codility, its an online coding test site where you can solve ACM style problems in many different languages. if you have 30 or so mins then check this http://codility.com/demo/run/ My weapon of choice is usually Java. So on of the problems I have is as follows (I will try to remember, should have taken a screenshot) Lets say you have array A[0]=1 A[1]=-1 ....A[n]=x Then what would be the smartest way to find out the number of times when A[i]+A[j] is even where i < j So if we have {1,2,3,4,5} we have 1+3 1+5 2+4 3+5 = 4 pairs which are even The code I wrote was some thing along the lines int sum=0; for(int i=0;i<A.length-1;i++){ for (int j=i+1;j<A.length;j++){ if( ((A[i]+A[j])%2) == 0 && i<j) { sum++; } } } There was one more restriction that if the number of pairs is greater than 1e9 then it should retrun -1, but lets forget it. Can you suggest a better solution for this. The number of elements won't exceed 1e9 in normal cases. I think I got 27 points deducted for the above code (ie it's not perfect). Codility gives out a detailed assessment of what went wrong, I don't have that right now.

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  • Where to find algorithms for standard math functions?

    - by dsimcha
    I'm looking to submit a patch to the D programming language standard library that will allow much of std.math to be evaluated at compile time using the compile-time function evaluation facilities of the language. Compile-time function evaluation has several limitations, the most important ones being: You can't use assembly language. You can't call C code or code for which the source is otherwise unavailable. Several std.math functions violate these and compile-time versions need to be written. Where can I get information on good algorithms for computing things such as logarithms, exponents, powers, and trig functions? I prefer just high level descriptions of algorithms to actual code, for two reasons: To avoid legal ambiguity and the need to make my code look "different enough" from the source to make sure I own the copyright. I want simple, portable algorithms. I don't care about micro-optimization as long as they're at least asymptotically efficient. Edit: D's compile time function evaluation model allows floating point results computed at compile time to differ from those computed at runtime anyhow, so I don't care if my compile-time algorithms don't give exactly the same result as the runtime version as long as they aren't less accurate to a practically significant extent.

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  • Personal project in Java

    - by Chuck
    My first project in java is going to be a program (eventually I have to create a GUI interface but for now CLI would do) to keep track of my books (something similar to what libraries have only a simpler). I need to be able to insert, update, remove, show all books, update, search(by name or author or date). For the design I was thinking one main class Library which will have all of the above as methods that connect to the db and retrieve the data. Is this approach ok? I realize it's simple but it's my first real project and I would appreciate a little feedback. Also, is it too soon to consider reading up on design patterns and database design ?

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  • Millions of 3D points: How to find the 10 of them closest to a given point?

    - by Kazoom
    A point in 3-d is defined by (x,y,z). Distance d between any two points (X,Y,Z) and (x,y,z) is d= Sqrt[(X-x)^2 + (Y-y)^2 + (Z-z)^2]. Now there are a million entries in a file, each entry is some point in space, in no specific order. Given any point (a,b,c) find the nearest 10 points to it. How would you store the million points and how would you retrieve those 10 points from that data structure.

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  • Javascript Number Random Shuffle

    - by stjowa
    Hi, I need a Javascript random number shuffler for my website. Seems simple, but I can not figure out how to do it. Can anyone help me out? I have the following array of numbers: 1 2 3 4 5 6 7 8 9 I would like to be able to have these numbers shuffled randomly. Like the following: 3 6 4 2 9 5 1 8 7 or 4 1 7 3 5 9 2 6 8 So, specifically, I would like a function that takes in an array of numbers (1 - n) and then returns that same array of numbers - shuffled randomly with different calls to the function. Maybe a noob function, but can't seem to figure it out. Thanks! NOTE: Thanks for the clarification on "Shuffle". Have found a lot more online about this with that term.

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  • "Undefined symbols" linker error with simple template class

    - by intregus
    Been away from C++ for a few years and am getting a linker error from the following code: Gene.h #ifndef GENE_H_INCLUDED #define GENE_H_INCLUDED template <typename T> class Gene { public: T getValue(); void setValue(T value); void setRange(T min, T max); private: T value; T minValue; T maxValue; }; #endif // GENE_H_INCLUDED Gene.cpp #include "Gene.h" template <typename T> T Gene<T>::getValue() { return this->value; } template <typename T> void Gene<T>::setValue(T value) { if(value >= this->minValue && value <= this->minValue) { this->value = value; } } template <typename T> void Gene<T>::setRange(T min, T max) { this->minValue = min; this->maxValue = max; } Using Code::Blocks and GCC if it matters to anyone. Also, clearly porting some GA stuff to C++ for fun and practice.

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  • Using local classes with STL algorithms

    - by David Rodríguez - dribeas
    I have always wondered why you cannot use locally defined classes as predicates to STL algorithms. In the question: Approaching STL algorithms, lambda, local classes and other approaches, BubbaT mentions says that 'Since the C++ standard forbids local types to be used as arguments' Example code: int main() { int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; std::vector<int> v( array, array+10 ); struct pair : public std::unary_function<int,bool> { bool operator()( int x ) { return !( x % 2 ); } }; std::remove_if( v.begin(), v.end(), pair() ); // error } Does anyone know where in the standard is the restriction? What is the rationale for disallowing local types?

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  • Most efficient sorting of calculation on DataTable column calculation

    - by byte
    Lets say you have a DataTable that has columns of "id", "cost", "qty": DataTable dt = new DataTable(); dt.Columns.Add("id", typeof(int)); dt.Columns.Add("cost", typeof(double)); dt.Columns.Add("qty", typeof(int)); And it's keyed on "id": dt.PrimaryKey = new DataColumn[1] { dt.Columns["id"] }; Now what we are interested in is the cost per quantity. So, in other words if you had a row of: id | cost | qty ---------------- 42 | 10.00 | 2 The cost per quantity is 5.00. My question then is, given the preceeding table, assume it's constructed with many thousands of rows, and you're interested in the top 3 cost per quantity rows. The information needed is the id, cost per quantity. You cannot use LINQ. In SQL it would be trivial; how BEST (most efficiently) would you accomplish it in C# without LINQ?

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  • Big-O of PHP functions?

    - by Kendall Hopkins
    After using PHP for a while now, I've noticed that not all PHP built in functions as fast as expected. Consider the below two possible implementations of a function that finds if a number is prime using a cached array of primes. //very slow for large $prime_array $prime_array = array( 2, 3, 5, 7, 11, 13, .... 104729, ... ); $result_array = array(); foreach( $array_of_number => $number ) { $result_array[$number] = in_array( $number, $large_prime_array ); } //still decent performance for large $prime_array $prime_array => array( 2 => NULL, 3 => NULL, 5 => NULL, 7 => NULL, 11 => NULL, 13 => NULL, .... 104729 => NULL, ... ); foreach( $array_of_number => $number ) { $result_array[$number] = array_key_exists( $number, $large_prime_array ); } This is because in_array is implemented with a linear search O(n) which will linearly slow down as $prime_array grows. Where the array_key_exists function is implemented with a hash lookup O(1) which will not slow down unless the hash table gets extremely populated (in which case it's only O(logn)). So far I've had to discover the big-O's via trial and error, and occasionally looking at the source code. Now for the question... I was wondering if there was a list of the theoretical (or practical) big O times for all* the PHP built in functions. *or at least the interesting ones For example find it very hard to predict what the big O of functions listed because the possible implementation depends on unknown core data structures of PHP: array_merge, array_merge_recursive, array_reverse, array_intersect, array_combine, str_replace (with array inputs), etc.

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  • Next month, same day in PHP

    - by Guillermo
    I got a last time (and urgent) requeriment of an "event" that needs to be scheduled the same day of every month. Say of you set the start date on the 1st May you should get the next events on the 1st of Jun, 1 Jul etc. The problem comes with a start date on the 31st (the next ones could be 30 or 28 depending on the month) Considering that there are months with different numbers of days (28,30,31) depending on the month itself and the year... what would ba an easy way to setup this? Consider the following (and flawed) nextmonth function: $events = array() function nextmonth($date) { return $date+(60*60*24*30); } $curr = $start; while($curr < $end) { $events[ = $curr; $curr = nextmonth($curr); } Edited to add: The problem for me is, simply enought, is to solve what the number of days of any given month is and thus get the next corresponding date..

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  • How to build, sort and print a tree of a sort?

    - by Tuplanolla
    This is more of an algorithmic dilemma than a language-specific problem, but since I'm currently using Ruby I'll tag this as such. I've already spent over 20 hours on this and I would've never believed it if someone told me writing a LaTeX parser was a walk in the park in comparison. I have a loop to read hierarchies (that are prefixed with \m) from different files art.tex: \m{Art} graphical.tex: \m{Art}{Graphical} me.tex: \m{About}{Me} music.tex: \m{Art}{Music} notes.tex: \m{Art}{Music}{Sheet Music} site.tex: \m{About}{Site} something.tex: \m{Something} whatever.tex: \m{Something}{That}{Does Not}{Matter} and I need to sort them alphabetically and print them out as a tree About Me (me.tex) Site (site.tex) Art (art.tex) Graphical (graphical.tex) Music (music.tex) Sheet Music (notes.tex) Something (something.tex) That Does Not Matter (whatever.tex) in (X)HTML <ul> <li>About</li> <ul> <li><a href="me.tex">Me</a></li> <li><a href="site.tex">Site</a></li> </ul> <li><a href="art.tex">Art</a></li> <ul> <li><a href="graphical.tex">Graphical</a></li> <li><a href="music.tex">Music</a></li> <ul> <li><a href="notes.tex">Sheet Music</a></li> </ul> </ul> <li><a href="something.tex">Something</a></li> <ul> <li>That</li> <ul> <li>Doesn't</li> <ul> <li><a href="whatever.tex">Matter</a></li> </ul> </ul> </ul> </ul> using Ruby without Rails, which means that at least Array.sort and Dir.glob are available. All of my attempts were formed like this (as this part should work just fine). def fss_brace_array(ss_input)#a concise version of another function; converts {1}{2}...{n} into an array [1, 2, ..., n] or returns an empty array ss_output = ss_input[1].scan(%r{\{(.*?)\}}) rescue ss_output = [] ensure return ss_output end #define tree s_handle = File.join(:content.to_s, "*") Dir.glob("#{s_handle}.tex").each do |s_handle| File.open(s_handle, "r") do |f_handle| while s_line = f_handle.gets if s_all = s_line.match(%r{\\m\{(\{.*?\})+\}}) s_all = s_all.to_a #do something with tree, fss_brace_array(s_all) and s_handle break end end end end #do something else with tree

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  • integer division properties

    - by aaa
    hi. does the following integer arithmetic property hold? (m/n)/l == m/(n*l) At first I thought I knew answer (does not hold), but now am not sure. Does it hold for all numbers or only for certain conditions, i.e. n > l?

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  • .NET Geometry Library

    - by dewald
    Does anyone know of a good (efficient, nice API, etc.) geometry open source library for .NET? Some of the operations needed: Data Structures Vectors (2D and 3D with floats and doubles) Lines (2D and 3D) Rectangles / Squares / Cubes / Boxes Spheres / Circles N-Sided Polygon Matrices (floats and doubles) Algorithms Intersection calculations Area / Volume calculations

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  • Fuzzy match two hash tables?

    - by alex
    Hi, I'm looking for ideas on how to best match two hash tables containing string key/value pairs. Here's the actual problem I'm facing: I have structured data coming in which is imported into the database. I need to UPDATE records which are already in the DB, however, it's possible that ANY value in the source can change, therefore I don't have a reliable ID. I'm thinking of fuzzy matching two rows, source and DB and make an "educated" guess if it should be updated and inserted. Any ideas would be greatly appreciated.

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  • millions of 3d points how to 10 closest to origin

    - by Kazoom
    A point in 3-d is defined by (x,y,z). Distance d between any two points (X,Y,Z) and (x,y,z) is d= Sqrt[(X-x)^2 + (Y-y)^2 + (Z-z)^2]. Now there are a million entries in a file, each entry is some point in space, in no specific order. Given any point (a,b,c) find the nearest 10 points to it. How would you store the million points and how would you retrieve those 10 points from that data structure.

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  • Find all substrings of a string - StringIndexOutOfBoundsException

    - by nazar_art
    I created class Word. Word has a constructor that takes a string argument and one method getSubstrings which returns a String containing all substring of word, sorted by length. For example, if the user provides the input "rum", the method returns a string that will print like this: r u m ru um rum I want to concatenate the substrings in a String, separating them with a newline ("\n"). Then return the string. Code: public class Word { String word; public Word(String word) { this.word = word; } /** * Gets all the substrings of this Word. * @return all substrings of this Word separated by newline */ public String getSubstrings() { String str = ""; int i, j; for (i = 0; i < word.length(); i++) { for (j = 0; j < word.length(); j++) { str = word.substring(i, i + j); str += "\n"; } } return str; } But it throws exception: java.lang.StringIndexOutOfBoundsException: String index out of range: -1 at java.lang.String.substring(String.java:1911) I stuck at this point. Maybe, you have other suggestions according this method signature public String getSubstrings(). How to solve this issue?

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  • Substring and its reverse in a string

    - by christa
    My professor was talking about this in a Dynamic programming class and asked us to think over it. She gave us some examples as well. Given a string, we were to find the longest continuous subsequence whose reverse is also a subsequence present in the given string. Example: INPUT: pqrstuvtsrv OUTPUT: i=3, k=2 rst -> tsr (rst found first at i=3 and for 2 more positions) INPUT: mpqrsrqp OUTPUT: i=2, k=6 pqrsrqp in reverse INPUT: mmpqssss OUTPUT: i=5, k=3 I thought of putting the string and its reverse into 2 different arrays and comparing character by character. But I'm sure this is not the best way to do it. Any suggestions as to what could be the most efficient ?

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