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• Position elements without overlap

  - by eWolf

  I have a number of rectangular elements that I want to position in a 2D space. I calculate an ideal position for each element. Now my problem is that many elements overlap as very often the ideal positions are concentrated in one region. I want to avoid overlap as much as possible (doesn't have to be perfect, though). How can I do this? I've heard physics simulations are suitable for this - is that correct? And can anyone provide an example/tutorial? By the way: I'm using XNA, if you know any .NET library that does exactly this job - tell me!

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• question about LSD radix sort

  - by davit-datuashvili

  hello i have following code public class LSD{ public static int R=1<<8; public static int bytesword=4; public static void radixLSD(int a[],int l,int r){ int aux[]=new int[a.length]; for (int d=bytesword-1;d>=0;d--){ int i, j; int count[]=new int[R+1]; for ( j=0;j<R;j++) count[j]=0; for (i=l;i<=r;i++) count[digit(a[i],d)+1]++; for (j=1;j<R;j++) count[j]+=count[j-1]; for (i=l;i<=r;i++) aux[count[digit(a[i],d)]++]=a[i]; for (i=l;i<=r;i++) a[i]=aux[i-1]; } } public static void main(String[]args){ int a[]=new int[]{3,6,5,7,4,8,9}; radixLSD(a,0,a.length-1); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } } public static int digit(int n,int d){ return (n>>d)&1; } } but it show me mistake java.lang.ArrayIndexOutOfBoundsException: -1 at LSD.radixLSD(LSD.java:19) at LSD.main(LSD.java:29) please help me

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• Aligning music notes using String matching algorithms or Dynamic Programming

  - by Dolphin

  Hi I need to compare 2 sets of musical pieces (i.e. a playing-taken in MIDI format-note details extracted and saved in a database table, against sheet music-taken into XML format). When evaluating playing against sheet music (i.e.note details-pitch, duration, rhythm), note alignment needs to be done - to identify missed/extra/incorrect/swapped notes that from the reference (sheet music) notes. I have like 1800-2500 notes in one piece approx (can even be more-with polyphonic, right now I'm doing for monophonic). So will I have to have all these into an array? Will it be memory overloading or stack overflow? There are string matching algorithms like KMP, Boyce-Moore. But note alignment can also be done through Dynamic Programming. How can I use Dynamic Programming to approach this? What are the available algorithms? Is it about approximate string matching? Which approach is much productive? String matching algos like Boyce-Moore, or dynamic programming? How can I assess which is more effective? Greatly appreciate any insight or suggestions Thanks in advance

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• Find a repeated numbers out of 3 boxes

  - by james1

  I have 3 boxes, each box contain 10 piece of numbered paper (1 - 10) but there is a number the same in all 3 boxes eg: box1 has number 4 and box2 has number 4 and box3 also has number 4. How to find that repeated number in java with an efficient/fastest way possible?

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• How does Amazon's Statistically Improbable Phrases work?

  - by ??iu

  How does something like Statistically Improbable Phrases work? According to amazon: Amazon.com's Statistically Improbable Phrases, or "SIPs", are the most distinctive phrases in the text of books in the Search Inside!™ program. To identify SIPs, our computers scan the text of all books in the Search Inside! program. If they find a phrase that occurs a large number of times in a particular book relative to all Search Inside! books, that phrase is a SIP in that book. SIPs are not necessarily improbable within a particular book, but they are improbable relative to all books in Search Inside!. For example, most SIPs for a book on taxes are tax related. But because we display SIPs in order of their improbability score, the first SIPs will be on tax topics that this book mentions more often than other tax books. For works of fiction, SIPs tend to be distinctive word combinations that often hint at important plot elements. For instance, for Joel's first book, the SIPs are: leaky abstractions, antialiased text, own dog food, bug count, daily builds, bug database, software schedules One interesting complication is that these are phrases of either 2 or 3 words. This makes things a little more interesting because these phrases can overlap with or contain each other.

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• Fast dot product for a very special case

  - by psihodelia

  Given a vector X of size L, where every scalar element of X is from a binary set {0,1}, it is to find a dot product z=dot(X,Y) if vector Y of size L consists of the integer-valued elements. I suggest, there must exist a very fast way to do it. Let's say we have L=4; X[L]={1, 0, 0, 1}; Y[L]={-4, 2, 1, 0} and we have to find z=X[0]*Y[0] + X[1]*Y[1] + X[2]*Y[2] + X[3]*Y[3] (which in this case will give us -4). It is obvious that X can be represented using binary digits, e.g. an integer type int32 for L=32. Then, all what we have to do is to find a dot product of this integer with an array of 32 integers. Do you have any idea or suggestions how to do it very fast?

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• Reverse engineering a bezier curve

  - by Martin

  Given a few sample points on a bézier curve, is it possible to work out the set of possible parameters of the curve? In my specific application there is a limited set of endpoints the curve may have, so I want to generate the set of possible curves, enumerate all of them and pick out all the ones which may end on a valid end point.

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• Chrome: automatically redirect me to highest ranking search result, like Firefox does

  - by Siim K

  How to emulate the Firefox (I'm using v3.6) address bar search redirection in Google Chrome? For example, if I type... imdb moon ...to the address bar and press Return in Firefox then it redirects me straight to http://www.imdb.com/title/tt1182345/ (and I've not visited the page before) When I try this is Chrome then I just get the google search page http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=imdb+moon So seems like Firefox redirects automatically to the highest ranking search result URL - is there a setting or add-on for Chrome to achieve the same behaviour?

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• Does anyone know how to do an "inverse" trilinear interpolation?

  - by Kaladze

  Trilinear interpolation approximates the value of a point (x, y, z) inside a cube using the values at the cube vertices. I´m trying to do an "inverse" trilinear interpolation. Knowing the values at the cube vertices and the value attached to a point how can I find (x, y, z)? Any help would be highly appreciated. Thank you!

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• Revisions: algorithm and data structure

  - by SODA

  Hi, I need ideas for structuring and processing data with revisions. For example, I have a database of objects (e.g. cars). Each object has a number of properties, which can be arbitrary, so there's no a set schema to describe these objects. These objects are probably saved as key-value pairs. Now I need to change property of an object. I don't want to completely rewrite it - I want to be able to go back and see history of changes to these properties, that's why I want to add new property and keep the old one (so I guess a timestamp would do the job of telling which property is the latest). At the same time I want to be able to get info about any object in a snap, with only latest versions of each of the properties. Any ideas what would be the best approach? At least please point me in the right direction. Thanks!

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• Finding the maximum weight subsequence of an array of positive integers?

  - by BeeBand

  I'm tring to find the maximum weight subsequence of an array of positive integers - the catch is that no adjacent members are allowed in the final subsequence. The exact same question was asked here, and a recursive solution was given by MarkusQ. He provides an explanation, but can anyone help me understand how he has expanded the function? How does this solution take into consideration non-adjacent members?

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• How can I generate an "unlimited" world?

  - by snowlord

  I would like to create a game with an endless (in reality an extremely large) world in which the player can move about. Whether or not I will ever get around to implement the game is one matter, but I find the idea interesting and would like some input on how to do it. The point is to have a world where all data is generated randomly on-demand, but in a deterministic way. Currently I focus on a large 2D map from which it should be possible to display any part without knowledge about the surrounding parts. I have implemented a prototype by writing a function that gives a random-looking, but deterministic, integer given the x and y of a pixel on the map (see my recent question about this function). Using this function I populate the map with "random" values, and then I smooth the map using a simple filter based on the surrounding pixels. This makes the map dependent on a few pixels outside its edge, but that's not a big problem. The final result is something that at least looks like a map (especially with a good altitude color map). Given this, one could maybe first generate a coarser map which is used to generate bigger differences in altitude to create mountain ranges and seas. Anyway, that was my idea, but I am sure that there exist ways to do this already and I also believe that given the specification, many of you can come up with better ideas. EDIT: Forgot the link to my question.

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• question about mergesort

  - by davit-datuashvili

  i have write code on mergesort here is code public class mergesort{ public static int a[]; public static void merges(int work[],int low,int high){ if (low==high) return ; else{ int mid=(low+high)/2; merges(work,low,mid); merges(work,mid+1,high); merge(work,low,mid+1,high); } } public static void main(String[]args){ int a[]=new int[]{64,21,33,70,12,85,44,99,36,108}; merges(a,0,a.length-1); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } } public static void merge(int work[],int low,int high,int upper){ int j=0; int l=low; int mid=high-1; int n=upper-l+1; while(low<=mid && high<=upper) if ( a[low]<a[high]) work[j++]=a[low++]; else work[j++]=a[high++]; while(low<=mid) work[j++]=a[low++]; while(high<=upper) work[j++]=a[high++]; for (j=0;j<n;j++) a[l+j]=work[j]; } } but it does nort work after compile this code here is mistake java.lang.NullPointerException at mergesort.merge(mergesort.java:45) at mergesort.merges(mergesort.java:12) at mergesort.merges(mergesort.java:10) at mergesort.merges(mergesort.java:10) at mergesort.merges(mergesort.java:10) at mergesort.main(mergesort.java:27)

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• Five unique, random numbers from a subset

  - by tau

  I know similar questions come up a lot and there's probably no definitive answer, but I want to generate five unique random numbers from a subset of numbers that is potentially infinite (maybe 0-20, or 0-1,000,000). The only catch is that I don't want to have to run while loops or fill an array. My current method is to simply generate five random numbers from a subset minus the last five numbers. If any of the numbers match each other, then they go to their respective place at the end of the subset. So if the fourth number matches any other number, it will bet set to the 4th from the last number. Does anyone have a method that is "random enough" and doesn't involve costly loops or arrays? Please keep in mind this a curiosity, not some mission-critical problem. I would appreciate it if everyone didn't post "why are you having this problem?" answers. I am just looking for ideas. Thanks a lot!

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• Removing elements from heap

  - by user193138

  I made a heap. I am curious if there's something subtley wrong with my remove function: int Heap::remove() { if (n == 0) exit(1); int temp = arr[0]; arr[0] = arr[--n]; heapDown(0); arr[n] = 0; return temp; } void Heap::heapDown(int i) { int l = left(i); int r = right(i); // comparing parent to left/right child // each has an inner if to handle if the first swap causes a second swap // ie 1 -> 3 -> 5 // 3 5 1 5 1 3 if (l < n && arr[i] < arr[l]) { swap(arr[i], arr[l]); heapDown(l); if (r < n && arr[i] < arr[r]) { swap(arr[i], arr[r]); heapDown(r); } } else if (r < n && arr[i] < arr[r]) { swap(arr[i], arr[r]); heapDown(r); if (l < n && arr[i] < arr[l]) { swap(arr[i], arr[l]); heapDown(l); } } } Here's my output i1i2i3i4i5i6i7 p Active heap: 7 4 6 1 3 2 5 r Removed 7 r Removed 6 p Active heap: 5 3 4 1 2 Here's my teacher's sample output: p Active heap : 7 4 6 1 3 2 5 r Removed 7 r Removed 6 p Active heap : 5 4 2 1 3 s Heapsorted : 1 2 3 4 5 While our outputs are completely different, I do seem to hold maxheap principle of having everything left oriented and for all nodes parent child(in every case I tried). I try to do algs like this from scratch, so maybe I'm just doing something really weird and wrong (I would only consider it "wrong" if it's O(lg n), as removes are intended to be for heaps). Is there anything in particular "wrong" about my remove? Thanks, http://ideone.com/PPh4eQ

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• How would you write a program to find the shortest pangram in a list of words?

  - by jonathanasdf

  Given a list of words which contains the letters a-z at least once, how would you write a program to find the shortest pangram counted by number of characters (not counting spaces) as a combination of the words? Since I am not sure whether short answers exist, this is not code golf, but rather just a discussion of how you would approach this. However, if you think you can manage to write a short program that would do this, then go ahead, and this might turn into code golf :)

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• Sync Algorithms

  - by Kristopher Johnson

  Are there any good references out there for sync algorithms? I'm interested in algorithms that synchronize the following kinds of data between multiple users: calendars documents lists and outlines I'm not just looking for synchronization of contents of directories a la rsync; I am interested in merging the data within individual files.

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• What is it about Fibonacci numbers?

  - by Ian Bishop

  Fibonacci numbers have become a popular introduction to recursion for Computer Science students and there's a strong argument that they persist within nature. For these reasons, many of us are familiar with them. They also exist within Computer Science elsewhere too; in surprisingly efficient data structures and algorithms based upon the sequence. There are two main examples that come to mind: Fibonacci heaps which have better amortized running time than binomial heaps. Fibonacci search which shares O(log N) running time with binary search on an ordered array. Is there some special property of these numbers that gives them an advantage over other numerical sequences? Is it a density quality? What other possible applications could they have? It seems strange to me as there are many natural number sequences that occur in other recursive problems, but I've never seen a Catalan heap.

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• How to find a factorial?

  - by hopefulLLl

  How can I write a program to find the factorial of any number?

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• Programming Contest Question: Counting Polyominos

  - by Martijn Courteaux

  Hi, An example question for a programming contest was to write a program that finds out how much polyominos are possible with a given number of stones. So for two stones (n = 2) there is only one polyominos: XX You might think this is a second solution: X X But it isn't. The polyominos are not unique if you can rotate them. So, for 4 stones (n = 4), there are 7 solutions: X X XX X X X X X X XX X XX XX XX X X X XX X X XX The application has to be able to find the solution for 1 <= n <=10 PS: Using the list of polyominos on Wikipedia isn't allowed ;) EDIT: Of course the question is: How to do this in Java, C/C++, C#

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• An efficient way to compute mathematical constant e

  - by Cinnamon

  Hello, The standard representation of constant e as the sum of the infinite series is very inefficient for computation, because of many division operations. So are there any alternative ways to compute the constant efficiently? Thanks!

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• Inverse relationship of two variables

  - by Jam

  this one is maybe pretty stupid.. Or I am just exhausted or something, but I just cant seem to solve it.. Problem : two variables X and Y, value of Y is dependent on value of X. X can have values ranging from some value to some value (lets say from 0 to 250) and y can have different values (lets say from 0.1 to 1.0 or something..) - but it is inverse relatonship (what I mean is: if value of X is e.g. 250, then value of Y would be 0.1 and when X decreases up to 0, value of Y raises up to 1.0.. So how should I do it? lets say I have function: -- double computeValue (double X) { /computation/ return Y; } Also, is there some easy way to somehow make the scaling of the function not so linear? - For example when X raises, Y decreases slower at first but then more rapidly in the end.. (rly dont know how to say it but I hope you guys got it) Thanks in advance for this stupid question :/

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• Javascript algorithm that calculates week number in Fiscal Year

  - by ForeignerBR

  Hi, I have been looking for a Javascript algorithms that gives me the week number of a given Date object within a custom fiscal year. The fiscal year of my company starts on 1 September and ends on 31 August. Say today happens to be September 1st and I pass in a newly instanced Date object to this function; I would expect it to return 1. Hopefully someone will be able to help me with it. thanks, fbr

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• How to find largest common sub-tree in the given two binary search trees?

  - by Bhushan

  Two BSTs (Binary Search Trees) are given. How to find largest common sub-tree in the given two binary trees? EDIT 1: Here is what I have thought: Let, r1 = current node of 1st tree r2 = current node of 2nd tree There are some of the cases I think we need to consider: Case 1 : r1.data < r2.data 2 subproblems to solve: first, check r1 and r2.left second, check r1.right and r2 Case 2 : r1.data > r2.data 2 subproblems to solve: - first, check r1.left and r2 - second, check r1 and r2.right Case 3 : r1.data == r2.data Again, 2 cases to consider here: (a) current node is part of largest common BST compute common subtree size rooted at r1 and r2 (b)current node is NOT part of largest common BST 2 subproblems to solve: first, solve r1.left and r2.left second, solve r1.right and r2.right I can think of the cases we need to check, but I am not able to code it, as of now. And it is NOT a homework problem. Does it look like?

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• How to sort a list so that managers are always ahead of their subordinates (How do I do a topologica

  - by James Black

  I am working on a project using Groovy, and I would like to take an array of employees, so that no manager follows their subordinates in the array. The reason being that I need to add people to a database and I would prefer not to do it in two passes. So, I basically have: <employees> <employee> <employeeid>12</employeeid> <manager>3</manager> </employee> <employee> <employeeid>1</employeeid> <manager></manager> </employee> <employee> <employeeid>3</employeeid> <manager>1</manager> </employee> </employees> So, it should be sorted as such: employeeid = 1 employeeid = 3 employeeid = 12 The first person should have a null for managers. I am thinking about a binary tree representation, but I expect it will be very unbalanced, and I am not certain the best way to do this using Groovy properly. Is there a way to do this that isn't going to involve using nested loops?

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