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• Which method should I use ?

  - by Ivan

  I want to do this exercise but I don't know exactly which method should I use for an exercise like this and what data will I use to test the algorithm. The driving distance between Perth and Adelaide is 1996 miles. On the average, the fuel consumption of a 2.0 litre 4 cylinder car is 8 litres per 100 kilometres. The fuel tank capacity of such a car is 60 litres. Design and implement a JAVA program that prompts for the fuel consumption and fuel tank capacity of the aforementioned car. The program then displays the minimum number of times the car’s fuel tank has to be filled up to drive from Perth to Adelaide. Note that 62 miles is equal to 100 kilometres. What data will you use to test that your algorithm works correctly?

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• What is the result of X(X,X)? [closed]

  - by Sorush Rabiee

  A friend who studies pure mathematics ask me to think about the following problem. Suppose that there is an algorithm named X that has 2 inputs: A and a_1...a_n, where 'A' stands for an arbitary algorithm and 'a_1..a_n' are inputs of A. X receives A and its inputs and returns true if A with a_1..a_n could be terminated, and false if A with a_1..a_n inputs fall into an infinite loop (never ends). Like this: A(n): while(n<5): write "I'm immortal!" and the result of X(A,6) is true and X(A,2) is false. So what is the result of X(X,X)? Also, do you know who was the first to introduce this problem?

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• Segmenting a double array of labels

  - by Ami

  The Problem: I have a large double array populated with various labels. Each element (cell) in the double array contains a set of labels and some elements in the double array may be empty. I need an algorithm to cluster elements in the double array into discrete segments. A segment is defined as a set of pixels that are adjacent within the double array and one label that all those pixels in the segment have in common. (Diagonal adjacency doesn't count and I'm not clustering empty cells). |-------|-------|------| | Jane | Joe | | | Jack | Jane | | |-------|-------|------| | Jane | Jane | | | | Joe | | |-------|-------|------| | | Jack | Jane | | | Joe | | |-------|-------|------| In the above arrangement of labels distributed over nine elements, the largest cluster is the “Jane” cluster occupying the four upper left cells. What I've Considered: I've considered iterating through every label of every cell in the double array and testing to see if the cell-label combination under inspection can be associated with a preexisting segment. If the element under inspection cannot be associated with a preexisting segment it becomes the first member of a new segment. If the label/cell combination can be associated with a preexisting segment it associates. Of course, to make this method reasonable I'd have to implement an elaborate hashing system. I'd have to keep track of all the cell-label combinations that stand adjacent to preexisting segments and are in the path of the incrementing indices that are iterating through the double array. This hash method would avoid having to iterate through every pixel in every preexisting segment to find an adjacency. Why I Don't Like it: As is, the above algorithm doesn't take into consideration the case where an element in the double array can be associated with two unique segments, one in the horizontal direction and one in the vertical direction. To handle these cases properly, I would need to implement a test for this specific case and then implement a method that will both associate the element under inspection with a segment and then concatenate the two adjacent identical segments. On the whole, this method and the intricate hashing system that it would require feels very inelegant. Additionally, I really only care about finding the large segments in the double array and I'm much more concerned with the speed of this algorithm than with the accuracy of the segmentation, so I'm looking for a better way. I assume there is some stochastic method for doing this that I haven't thought of. Any suggestions?

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• HPC (mainly on Java)

  - by Insectatorious

  I'm looking for some way of using the number-crunching ability of a GPU (with Java perhaps?) in addition to using the multiple cores that the target machine has. I will be working on implementing (at present) the A* Algorithm but in the future I hope to replace it with a Genetic Algorithm of sorts. I've looked at Project Fortress but as I'm building my GUI in JavaFX, I'd prefer not to stray too far from a JVM. Of course, should no feasible solution be available, I will migrate to the easiest solution to implement.

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• What container is easiest for combining JPEGS and MP3s as video?

  - by Ole Jak

  So I have N (for example, 1000) JPEG frames and 10*N ( for example, 100) seconds of MP3 sound. I need some container for joining them into one video file (at 10 frames/second) (popular containers like FLV or AVI or MOV are better). So what I need is an algorithm or code example of combining my data into some popular format. The code example should be in some language like C#, Java, ActionScript or PHP. The algorithm should be theoretically implementable with ActionScript or PHP. Can any one, please help me with that?

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• What is result of X(X,X)?

  - by Sorush Rabiee

  a friend who studies pure mathematics ask me to think about this problem: suppose that there is an algorithm named X that have 2 inputs: A and a_1...a_n, 'A' stands for an arbitary algorithm and 'a_1..a_n' are inputs of A. X recieves A and its inputs and returns true if A with a_1..a_n couold be terminated, and false if A with a_1..a_n inputs fall into infty loop (never ends). like this: A(n): while(n<5): write "I'm immortal!" and result of X(A,6) is true and X(A,2) is false. so what is the result of X(X,X)? ...and do you know who introduced this problem first time?

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• What is the fastest way to compare two list of items?

  - by edude05

  I have two folders with approximately 10,000 files each. I'd like to write a script or program that can tell me if these folders are in sync and then tell me what files are missing from each to make them in sync. Therefore, after generating a list of files, what is the fastest algorithm to sort them for unique files? What I'm thinking right now is comparing the first file on each list then if they are different remove one until they are the same, then remove both from the list (because they are not unique.) Is there a faster algorithm then this?

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• How do I check the validity of the Canadian Social Insurance Number in C#?

  - by user518307

  I've been given the assignment to write an algorithm in C# that checks the validity of a Canadian Social Insurance Number (SIN). Here are the steps to validate a SIN. Given an example Number: 123 456 782 Remove the check digit (the last digit): 123456782 Extract the even digits (2,4,6,8th digith): 12345678 Double them: 2 4 6 8 | | | | v v v v 4 8 12 16 Add the digits together: 4+8+1+2+1+6 = 22 Add the Odd placed digits: 1+3+5+7 = 16 Total : 38 Validity Algorithm If the total is a multiple of 10, the check digit should be zero. Otherwise, Subtract the Total from the next highest multiple of 10 (40 in this case) The check digit for this SIN must be equal to the difference of the number and the totals from earlier (in this case, 40-38 = 2; check digit is 2, so the number is valid) I'm lost on how to actually implement this in C#, how do I do this?

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• Tag/Keyword based recommendation

  - by Hellnar

  Hello I am wondering what algorithm would be clever to use for a tag driven e-commerce enviroment: Each item has several tags. IE: Item name: "Metallica - Black Album CD", Tags: "metallica", "black-album", "rock", "music" Each user has several tags and friends(other users) bound to them. IE: Username: "testguy", Interests: "python", "rock", "metal", "computer-science" Friends: "testguy2", "testguy3" I need to generate recommendations to such users by checking their interest tags and generating recommendations in a sophisticated way. Ideas: A Hybrid recommendation algorithm can be used as each user has friends.(mixture of collaborative + context based recommendations). Maybe using user tags, similar users (peers) can be found to generate recommendations. Maybe directly matching tags between users and items via tags. Any suggestion is welcome. Any python based library is also welcome as I will be doing this experimental engine on python language.

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• How would you sample a real-time stream of coordinates to create a Speed Graph?

  - by Andrew Johnson

  I have a GPS device, and I am receiving continuous points, which I store in an array. These points are time stamped. I would like to graph distance/time (speed) vs. distance in real-time; however, I can only plot 50 of the points because of hardware constraints. How would you select points from the array to graph? For example, one algorithm might be to select every Nth point from the array, where N results in 50 points total. Code: float indexModifier = 1; if (MIN(50,track.lastPointIndex) == 50) { indexModifier = track.lastPointIndex/50.0f; } index = ceil(index*indexModifier); Another algorithm might be to keep an array of 50 points, and throw out the point with the least speed change each time you get a new point.

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• Nesting Patterns Algorithms / Cutting Waste Problem

  - by WedTM

  First off, I'd like to say that I'm already looking into the "Cutting Stock Problem" algorithm, however I feel that I need a bit more clarification, and possibly some help with some of the math (Not my strong point). What I need to do is have an offset pattern that causes the circle to fit in the crevasse created by having the two circular dies sitting next to each other on the previous line, like so: O O O O O O O O O O O O O O O O O I'm hoping someone can point me towards the right algorithm for this! Thanks!

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• Implementing Dijkstra's Algorithm

  - by DeadMG

  I've been tasked (coursework @ university) to implement a form of path-finding. Now, in-spec, I could just implement a brute force, since there's a limit on the number of nodes to search (begin, two in the middle, end), but I want to re-use this code and came to implement Dijkstra's algorithm. I've seen the pseudo on Wikipedia and a friend wrote some for me as well, but it flat out doesn't make sense. The algorithm seems pretty simple and it's not a problem for me to understand it, but I just can't for the life of me visualize the code that would realize such a thing. Any suggestions/tips?

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• [Java] Implement a RSA algorithm

  - by Robin Monjo

  Hello everyone. I want to implement a RSA algorithm to encrypt an image (byte[]). To generate my two keys I used this piece of code : KeyPairGenerator keygen = KeyPairGenerator.getInstance("RSA"); keygen.initialize(512); keyPair = keygen.generateKeyPair(); Once public and private key are generated, I would like to show them to the user so he can distribute the public key and use the private key to decode. How can I get back those key ? Using keygen.getPrivateKey() and keygen.getPublicKey() give me all the information of the RSA algorithm, not only the keys I need. Thanks

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• Implementing password hashing/salting algorithm from crackstation.net

  - by Mason240

  I am trying to implement a password hashing/salting algorithm from crackstation.net, but I am unsure how implement it. Storing the password upon user registration seems to be as simple as passing the password into create_hash(). $password = create_hash($_POST['Password']; I'm not following how to validate upon user login. validate_password($password, $good_hash) returns either true or false, and takes $password as parameter, so it seems like a no brainer except for the second parameter $good_hash. Where does this param come from? It is my understanding that password is turned into a hash value every time its used, and that the hash value is what is stored and compared. So why would I have both the $password and $good_hash values? Quick overview of the functions: function create_hash($password){ calls pbkdf2() } function validate_password($password, $good_hash){ calls pbkdf2() calls slow_equals() } function slow_equals($a, $b){ } function pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output = false){ } Of course a different, better method for this would also be just as helpful. Thank you

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• Encrypt text using a number

  - by Adam Matan

  Project Euler I have recently begun to solve some of the Project Euler riddles. I found the discussion forum in the site a bit frustrating (most of the discussions are closed and poorly-threaded), So I have decided to publish my Python solutions on launchpad for discussion. The problem is that it seems quite unethical to publish these solutions, as it would let other people gain reputation without doing the programming work, which the site deeply discourages. My Encryption problem I want to encrypt my answers so that only those who have already solved the riddles can see my code. The logical key would be the answer to the riddle, which is always numeric. In order to prevent brute-force attacks on my answers, I want to find an encryption algorithm that takes a significantly long time (few seconds) to run. Do you know any such algorithm? I would fancy a Python package, which I can attach to the code, over an external program that might have portability issues. Thanks, Adam

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• Find valid assignments of integers in arrays (permutations with given order)

  - by evident

  Hi everybody! I am having a general problem finding a good algorithm for generating each possible assignment for some integers in different arrays. Lets say I have n arrays and m numbers (I can have more arrays than numbers, more numbers than arrays or as much arrays as numbers). As an example I have the numbers 1,2,3 and three arrays: { }, { }, { } Now I would like to find each of these solutions: {1,2,3}, { }, { } { }, {1,2,3}, { } { }, { }, {1,2,3} {1,2}, {3}, { } {1,2}, { }, {3} { }, {1,2}, {3} {1}, {2,3}, { } {1}, { }, {2,3} { }, {1}, {2,3} {1}, {2}, {3} So basically I would like to find each possible combination to assign the numbers to the different arrays with keeping the order. So as in the example the 1 always needs to come before the others and so on... I want to write an algorithm in C++/Qt to find all these valid combinations. Does anybody have an approach for me on how to handle this problem? How would I generate these permutations?

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• Discrete Curve evolution algorithm

  - by konidela

  hai , i am trying to implement discrete curve evolution algorithm in c++ do any one help me with psudo code or c code or some simple steps of your understanding

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• SIFT algorithm program

  - by twasul

  Iwant to use SIFT algorithm in matlab but ihavent tha program to generate it, can you give my this program?

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• Fermat factorization method limit

  - by Fakrudeen

  I am trying to implement Fermat's factorization [Algorithm C in Art of computer programming Vol. 2]. Unfortunately in my edition [ISBN 81-7758-335-2], this algorithm is printed incorrectly. what should be the condition on factor-inner loop below? I am running the loop till y <= n [passed in as limit]. (if (< limit y) 0 (factor-inner x (+ y 2) (- r y) limit)) Is there anyway to avoid this condition altogether, as it will double the speed of loop? (define (factor n) (let ( ( square-root (inexact->exact (floor (sqrt n))) ) ) (factor-inner (+ (* 2 square-root) 1) 1 (- (* square-root square-root) n) n) ) ) (define (factor-inner x y r limit) (if (= r 0) (/ (- x y) 2) (begin (display x)(display " ")(display y)(display " ")(display r)(newline) ;(sleep-current-thread 1) (if (< r 0) (factor-inner (+ x 2) y (+ r x) limit) (if (< limit y) 0 (factor-inner x (+ y 2) (- r y) limit)) ) ) ) )

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• Seaching for an element in a circular sorted array

  - by guirgis

  I wanted to share this with you, i had this problem in a google interview. we want to search for a given element in a circular sorted array in complexity not greater than O(Log n). ex: search for 13 in {5,9,13,1,3}. My idea was to convert the circular array into a regular sorted array then do a binary search on the resulting array, but my problem was the algorithm i came up was stupid that it takes O(n) in the worst case: for(i = 1; i < a.length; i++){ if (a[i] < a[i-1]){ minIndex = i; break; } } then the corresponding index of ith element will be determined from the following relation: (i + minInex - 1) % a.length it is clear that my conversion (from circular to regular) algorithm may take O(n), so we need a better one, any suggestions?

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• All minimum spanning trees implementation

  - by russtbarnacle

  I've been looking for an implementation (I'm using networkx library.) that will find all the minimum spanning trees (MST) of an undirected weighted graph. I can only find implementations for Kruskal's Algorithm and Prim's Algorithm both of which will only return a single MST. I've seen papers that address this problem (such as http://fano.ics.uci.edu/cites/Publication/Epp-TR-95-50.html) but my head tends to explode someway through trying to think how to translate it to code. In fact i've not been able to find an implementation in any language!

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• Is it a solvable problem to generate a regular expression that matches some input set?

  - by Roman

  I provide some input set which contains known separated number of text blocks. I want to make a program that automatically generate 1 or more regular expressions each of which matches every text block in the input set. I see some relatively easy ways to implement a brute-force search. But I'm not an expert in compilers theory. That's why I'm curious: 1) is this problem solvable? or there are some principle impossibility to make such algorithm? 2) is it possible to achieve polynomial complexity for this algorithm and avoid brute forcing?

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• Evenly distribute items on the screen

  - by abolotnov

  I am trying to solve this little puzzle (the algorithm): I have N image icons and I want to distribute them evenly on users screen. Say, I put them in a table. If there is one image, there will be one cell in a table. If two - one row with two columns, if three - one row and three columns, if four - two rows, two columns... and so on until row space is gone and since then the table should only grow in columns without adding extra rows. I'm trying to figure an algorithm for this and perhaps this is something that has a solution already somewhere? My attempt is so far something like this: obtain_max_rows() obtain_visible_columns() if (number_of_pictures > max_rows*max_columns) { columns = roundup(number_of_pictures/max_rows) for(max_rows){generate row;for columns{generate column}} } else { **here comes to trouble...** } This logic is bit silly though - it somehow needs to think cases where there are 12 pictures on first screen and 2 on the other trying to balance it say 8/6 or somehow like that.

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• A simple algorithm for polygon intersection

  - by Elazar Leibovich

  I'm looking for a very simple algorithm for computing the polygon intersection/clipping. That is, given polygons P, Q, I wish to find polygon T which is contained in P and in Q, and I wish T to be maximal among all possible polygons. I don't mind the run time (I have a few very small polygons), I can also afford getting an approximation of the polygons' intersection (that is, a polygon with less points, but which is still contained in the polygons' intersection). But it is really important for me that the algorithm will be simple (cheaper testing) and preferably short (less code). edit: please note, I wish to obtain a polygon which represent the intersection. I don't need only a boolean answer to the question of whether the two polygons intersect.

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• Given a number of rectangles that can be rotated, find an enclosing rectangle of minimum area

  - by efficiencyIsBliss

  So, I'm trying to implement an algorithm that takes in a number of rectangles as input and tries to pack them into a rectangle of minimum area. The rectangles can all be rotated by 90 degrees. I realize that this is similar to the bin packing problem, but I am unable to find a good algorithm that accounts for the rotation. I found a paper that discusses this at length here and while I understand the article itself, I was hoping to find something simpler. Any suggestions? -Edit- I think I misstated the problem earlier. We are given a number of rectangles, such that each can be rotated by 90 degrees. We need to find a rectangle that fits all the given rectangles such that no two rectangles overlap, while minimizing the area of the enclosing rectangle. The problem I face here is that we are asked to find the minimum, as opposed to being given an enclosing rectangle and checking if the given rectangles fit or something of that sort.

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