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  • Can anyone simplify this Algorithm for me?

    - by Titan
    Basically I just want to check if one time period overlaps with another. Null end date means till infinity. Can anyone shorten this for me as its quite hard to read at times. Cheers public class TimePeriod { public DateTime StartDate { get; set; } public DateTime? EndDate { get; set; } public bool Overlaps(TimePeriod other) { // Means it overlaps if (other.StartDate == this.StartDate || other.EndDate == this.StartDate || other.StartDate == this.EndDate || other.EndDate == this.EndDate) return true; if(this.StartDate > other.StartDate) { // Negative if (this.EndDate.HasValue) { if (this.EndDate.Value < other.StartDate) return true; if (other.EndDate.HasValue && this.EndDate.Value < other.EndDate.Value) return true; } // Negative if (other.EndDate.HasValue) { if (other.EndDate.Value > this.StartDate) return true; if (this.EndDate.HasValue && other.EndDate.Value > this.EndDate.Value) return true; } else return true; } else if(this.StartDate < other.StartDate) { // Negative if (this.EndDate.HasValue) { if (this.EndDate.Value > other.StartDate) return true; if (other.EndDate.HasValue && this.EndDate.Value > other.EndDate.Value) return true; } else return true; // Negative if (other.EndDate.HasValue) { if (other.EndDate.Value < this.StartDate) return true; if (this.EndDate.HasValue && other.EndDate.Value < this.EndDate.Value) return true; } } return false; } }

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  • Need to devise a number crunching algorithm

    - by Ravi Gupta
    I stumbled upon this question: 7 power 7 is 823543. Which higher power of 7 ends with 823543 ? How should I go about it ? The one I came up with is very slow, it keeps on multiplying by 7 and checks last 6 digits of the result for a match. I tried with Lou's code: int x=1; for (int i=3;i<=100000000;i=i+4){ x=(x*7)%1000000; System.out.println("i="+ i+" x= "+x); if (x==823543){ System.out.println("Ans "+i);} } And CPU sounds like a pressure cooker but couldn't get the answer :(

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  • Automatic tracking algorithm

    - by nico
    Hi everyone, I'm trying to write a simple tracking routine to track some points on a movie. Essentially I have a series of 100-frames-long movies, showing some bright spots on dark background. I have ~100-150 spots per frame, and they move over the course of the movie. I would like to track them, so I'm looking for some efficient (but possibly not overkilling to implement) routine to do that. A few more infos: the spots are a few (es. 5x5) pixels in size the movement are not big. A spot generally does not move more than 5-10 pixels from its original position. The movements are generally smooth. the "shape" of these spots is generally fixed, they don't grow or shrink BUT they become less bright as the movie progresses. the spots don't move in a particular direction. They can move right and then left and then right again the user will select a region around each spot and then this region will be tracked, so I do not need to automatically find the points. As the videos are b/w, I though I should rely on brigthness. For instance I thought I could move around the region and calculate the correlation of the region's area in the previous frame with that in the various positions in the next frame. I understand that this is a quite naïve solution, but do you think it may work? Does anyone know specific algorithms that do this? It doesn't need to be superfast, as long as it is accurate I'm happy. Thank you nico

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  • An algorithm Problem

    - by Vignesh
    For coverage, I've a set of run time variables of from my program execution. It happens that I get it from a series of executions(Automated testing). ie. its a vector<vector<var,value>> I've a limited set of variables with expected values and generate combination s, that is I have vector<vector<var,value>(smaller than the execution vector)>. Now I need to compare and tell which of the combination I generated were exactly executed in one of the tests. My algo is O(n^4). Is there any way to bring it down. Something like set intersection. I'm using java, and vectors because of thread safety.

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  • Algorithm for optimally choosing actions to perform a task

    - by Jules
    There are two data types: tasks and actions. An action costs a certain time to complete, and a set of tasks this actions consists of. A task has a set of actions, and our job is to choose one of them. So: class Task { Set<Action> choices; } class Action { float time; Set<Task> dependencies; } For example the primary task could be "Get a house". The possible actions for this task: "Buy a house" or "Build a house". The action "Build a house" costs 10 hours and has the dependencies "Get bricks" and "Get cement", etcetera. The total time is the sum of all the times of the actions required to perform. We want to choose actions such that the total time is minimal. Note that the dependencies can be diamond shaped. For example "Get bricks" could require "Get a car" (to transport the bricks) and "Get cement" would also require a car. Even if you do "Get bricks" and "Get cement" you only have to count the time it takes to get a car once. Note also that the dependencies can be circular. For example "Money" - "Job" - "Car" - "Money". This is no problem for us, we simply select all of "Money", "Job" and "Car". The total time is simply the sum of the time of these 3 things. Mathematical description: Let actions be the chosen actions. valid(task) = ?action ? task.choices. (action ? actions ? ?tasks ? action.dependencies. valid(task)) time = sum {action.time | action ? actions} minimize time subject to valid(primaryTask)

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  • Discovering a functional algorithm from a mutable one

    - by Garrett Rowe
    This isn't necessarily a Scala question, it's a design question that has to do with avoiding mutable state, functional thinking and that sort. It just happens that I'm using Scala. Given this set of requirements: Input comes from an essentially infinite stream of random numbers between 1 and 10 Final output is either SUCCEED or FAIL There can be multiple objects 'listening' to the stream at any particular time, and they can begin listening at different times so they all may have a different concept of the 'first' number; therefore listeners to the stream need to be decoupled from the stream itself. Pseudocode: if (first number == 1) SUCCEED else if (first number >= 9) FAIL else { first = first number rest = rest of stream for each (n in rest) { if (n == 1) FAIL else if (n == first) SUCCEED else continue } } Here is a possible mutable implementation: sealed trait Result case object Fail extends Result case object Succeed extends Result case object NoResult extends Result class StreamListener { private var target: Option[Int] = None def evaluate(n: Int): Result = target match { case None => if (n == 1) Succeed else if (n >= 9) Fail else { target = Some(n) NoResult } case Some(t) => if (n == t) Succeed else if (n == 1) Fail else NoResult } } This will work but smells to me. StreamListener.evaluate is not referentially transparent. And the use of the NoResult token just doesn't feel right. It does have the advantage though of being clear and easy to use/code. Besides there has to be a functional solution to this right? I've come up with 2 other possible options: Having evaluate return a (possibly new) StreamListener, but this means I would have to make Result a subtype of StreamListener which doesn't feel right. Letting evaluate take a Stream[Int] as a parameter and letting the StreamListener be in charge of consuming as much of the Stream as it needs to determine failure or success. The problem I see with this approach is that the class that registers the listeners should query each listener after each number is generated and take appropriate action immediately upon failure or success. With this approach, I don't see how that could happen since each listener is forcing evaluation of the Stream until it completes evaluation. There is no concept here of a single number generation. Is there any standard scala/fp idiom I'm overlooking here?

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  • Is using a FSM a good design for general text parsing?

    - by eSKay
    I am reading a file that is filled with hex numbers. I have to identify a particular pattern, say "aaad" (without quotes) from it. Every time I see the pattern, I generate some data to some other file. This would be a very common case in designing programs - parsing and looking for a particular pattern. I have designed it as a Finite State Machine and structured structured it in C using switch-case to change states. This was the first implementation that occured to me. DESIGN: Are there some better designs possible? IMPLEMENTATION: Do you see some problems with using a switch case as I mentioned?

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  • Algorithm for scoring user activity

    - by ManBugra
    I have an application where users can: Write reviews about products Add comments to products Up / Down vote reviews Up / Down vote comments Every Up/Down vote is recorded in a db table. What i want to do now is to create a ranking of the most active users in the last 4 weeks. Of course good reviews should be weighted more than good comments. But also e.g. 10 good comments should be weighted more than just one good review. Example: // reviews created in recent 4 weeks //format: [ upVoteCount, downVoteCount ] var reviews = [ [120,23], [32,12], [12,0], [23,45] ]; // comments created in recent 4 weeks // format: [ upVoteCount, downVoteCount ] var comments = [ [1,2], [322,1], [0,0], [0,45] ]; // create weight vector // format: [ reviewWeight, commentsWeight ] var weight = [0.60, 0.40]; // signature: activties..., activityWeight var userActivityScore = score(reviews, comments, weight); ... update user table ... List<Users> users = "from users u order by u.userActivityScore desc"; How would a fair scoring function look like? How could an implementation of the score() function look like? How to add a weight g to the function so that reviews are weighted heavier? How would such a function look like if, for example, votes for pictures would be added?

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  • Algorithm to produce Cartesian product of arrays in depth-first order

    - by Yuri Gadow
    I'm looking for an example of how, in Ruby, a C like language, or pseudo code, to create the Cartesian product of a variable number of arrays of integers, each of differing length, and step through the results in a particular order: So given, [1,2,3],[1,2,3],[1,2,3]: [1, 1, 1] [2, 1, 1] [1, 2, 1] [1, 1, 2] [2, 2, 1] [1, 2, 2] [2, 1, 2] [2, 2, 2] [3, 1, 1] [1, 3, 1] etc. Instead of the typical result I've seen (including the example I give below): [1, 1, 1] [2, 1, 1] [3, 1, 1] [1, 2, 1] [2, 2, 1] [3, 2, 1] [1, 3, 1] [2, 3, 1] etc. The problem with this example is that the third position isn't explored at all until all combinations of of the first two are tried. In the code that uses this, that means even though the right answer is generally (the much larger equivalent of) 1,1,2 it will examine a few million possibilities instead of just a few thousand before finding it. I'm dealing with result sets of one million to hundreds of millions, so generating them and then sorting isn't doable here and would defeat the reason for ordering them in the first example, which is to find the correct answer sooner and so break out of the cartesian product generation earlier. Just in case it helps clarify any of the above, here's how I do this now (this has correct results and right performance, but not the order I want, i.e., it creates results as in the second listing above): def cartesian(a_of_a) a_of_a_len = a_of_a.size result = Array.new(a_of_a_len) j, k, a2, a2_len = nil, nil, nil, nil i = 0 while 1 do j, k = i, 0 while k < a_of_a_len a2 = a_of_a[k] a2_len = a2.size result[k] = a2[j % a2_len] j /= a2_len k += 1 end return if j > 0 yield result i += 1 end end UPDATE: I didn't make it very clear that I'm after a solution where all the combinations of 1,2 are examined before 3 is added in, then all 3 and 1, then all 3, 2 and 1, then all 3,2. In other words, explore all earlier combinations "horizontally" before "vertically." The precise order in which those possibilities are explored, i.e., 1,1,2 or 2,1,1, doesn't matter, just that all 2 and 1 are explored before mixing in 3 and so on.

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  • Creating combinations that have no more one intersecting element

    - by khuss
    I am looking to create a special type of combination in which no two sets have more than one intersecting element. Let me explain with an example: Let us say we have 9 letter set that contains A, B, C, D, E, F, G, H, and I If you create the standard non-repeating combinations of three letters you will have 9C3 sets. These will contain sets like ABC, ABD, BCD, etc. I am looking to create sets that have at the most only 1 common letter. So in this example, we will get following sets: ABC, ADG, AEI, AFH, BEH, BFG, BDI, CFI, CDH, CEG, DEF, and GHI - note that if you take any two sets there are no more than 1 repeating letter. What would be a good way to generate such sets? It should be scalable solution so that I can do it for a set of 1000 letters, with sub set size of 4. Any help is highly appreciated. Thanks

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  • mysql/algorithm: Weighting an average to accentuate differences from the mean

    - by Sai Emrys
    This is for a new feature on http://cssfingerprint.com (see /about for general info). The feature looks up the sites you've visited in a database of site demographics, and tries to guess what your demographic stats are based on that. All my demgraphics are in 0..1 probability format, not ratios or absolute numbers or the like. Essentially, you have a large number of data points that each tend you towards their own demographics. However, just taking the average is poor, because it means that by adding in a lot of generic data, the number goes down. For example, suppose you've visited sites S0..S50. All except S0 are 48% female; S0 is 100% male. If I'm guessing your gender, I want to have a value close to 100%, not just the 49% that a straight average would give. Also, consider that most demographics (i.e. everything other than gender) does not have the average at 50%. For example, the average probability of having kids 0-17 is ~37%. The more a given site's demographics are different from this average (e.g. maybe it's a site for parents, or for child-free people), the more it should count in my guess of your status. What's the best way to calculate this? For extra credit: what's the best way to calculate this, that is also cheap & easy to do in mysql?

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  • Binary Search Tree for specific intent

    - by Luís Guilherme
    We all know there are plenty of self-balancing binary search trees (BST), being the most famous the Red-Black and the AVL. It might be useful to take a look at AA-trees and scapegoat trees too. I want to do deletions insertions and searches, like any other BST. However, it will be common to delete all values in a given range, or deleting whole subtrees. So: I want to insert, search, remove values in O(log n) (balanced tree). I would like to delete a subtree, keeping the whole tree balanced, in O(log n) (worst-case or amortized) It might be useful to delete several values in a row, before balancing the tree I will most often insert 2 values at once, however this is not a rule (just a tip in case there is a tree data structure that takes this into account) Is there a variant of AVL or RB that helps me on this? Scapegoat-trees look more like this, but would also need some changes, anyone who has got experience on them can share some thougts? More precisely, which balancing procedure and/or removal procedure would help me keep this actions time-efficient?

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  • algorithm for checking addresses for matches?

    - by user151841
    I'm working on a survey program where people will be given promotional considerations the first time they fill out a survey. In a lot of scenarios, the only way we can stop people from cheating the system and getting a promotion they don't deserve is to check street address strings against each other. I was looking at using levenshtein distance to give me a number to measure similarity, and consider those below a certain threshold a duplicate. However, if someone were looking to game the system, they could easily write "S 5th St" instead of "South Fifth Street", and levenshtein would consider those strings to be very different. So then I was thinking to convert all strings to a 'standard address form' i.e. 'South' becomes 's', 'Fifth' becomes '5th', etc. Then I was thinking this is hopeless, and too much effort to get it working robustly. Is it? I'm working with PHP/MySql, so I have the limitations inherent in that system.

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  • Using static vs. member find method on a STL set?

    - by B Johnson
    I am using a set because, i want to use the quick look up property of a sorted container such as a set. I am wondering if I have to use the find member method to get the benefit of a sorted container, or can I also use the static find method in the STL algorithms? My hunch is that using the static version will use a linear search instead of a binary search like I want.

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  • open source gossip-based membership protocol?

    - by Aaron
    I am looking for a library which I can plug into a distributed application which implements any gossip-based membership protocol. Such a library would allow me to send/receive membership lists, merge received membership lists, etc... Even better would be if the library implemented a protocol with performance O(logn) performance guarantees. Does anyone know of any open source library like this? It doesn't need to meet all of the aforementioned requirements; even something partially implemented would be helpful.

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  • Better algorithm for estimating download time

    - by Scott Smith
    We've all seen the download time running estimate that initially says something like "7 days", but keeps dropping wildly (e.g. "23 hours", "45 minutes", "1 min. 50 sec", etc) with each successive estimation as the chunks are downloaded. To avoid these initial (alarming) estimates, there are techniques one could try like suppressing display of the first n estimates, or waiting for the delta between estimates to drop below some threshold before you start displaying them, but these don't seem like a general, robust solution. There are corner cases involving too few samples, or samples that actually are wildly varying... I think I recall a general solution for this kind of thing in mathematics (statistics?) that reduced or eliminated these wild values. Does anyone know?

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  • Algorithm for bitwise fiddling

    - by EquinoX
    If I have a 32-bit binary number and I want to replace the lower 16-bit of the binary number with a 16-bit number that I have and keep the upper 16-bit of that number to produce a new binary number.. how can I do this using simple bitwise operator? For example the 32-bit binary number is: 1010 0000 1011 1111 0100 1000 1010 1001 and the lower 16-bit I have is: 0000 0000 0000 0001 so the result is: 1010 0000 1011 1111 0000 0000 0000 0001 how can I do this?

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  • Sorting data by relevance, from multiple tables

    - by Oden
    Hey, How is it possible to sort data from multiple tables by relevance? My table structure is following: I have 3 tables in my database, one table contains the name of solar systems, the second for e.g. of planets. There is one more table, witch is a connection between solar systems and planets. If I want to get data of a planet, witch is in the Milky Way, i post this data to the server, and it gives me a multi-dimensional array witch contains: The Milky Way, with every planet in it Every planet, witch name contains the string Milky Way (maybe thats a bat example because i don't think that theres but one planet with this name, but the main concept is on file) But, i want to set the most relevant restaurants to the top of the array. (for the relevance i would check the description of the restaurants or something like that) So, how would you do that kind of data sorting?

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  • algorithm advice for finding maximum items within a time period

    - by darren
    Hi everyone. I have a database schema that is similar to the following: | User | Event | Date |--------|---------------|------ | 111 | Walked dog | 2009-10-1 | 222 | Walked dog | 2009-10-2 | 333 | Fed Fish | 2009-10-5 | 222 | Did Laundry | 2009-10-6 | 111 | Fed Fish | 2009-10-7 | 111 | Walked dog | 2009-10-18 | 222 | Walked dog | 2009-10-19 | 111 | Fed Fish | 2009-10-21 I would like to produce a query that returns the maximum number of times a user performs some action within a time period. For example, given a time period of 5 days, what is the maximum number of times user 111 walked the dog? The most obvious solution would be to start at some zero point and move forward each day, summing up 5 day periods along the way, then taking the maximum total out of all the 5 day windows. the approach seems incredibly costly however. I would appreciate any suggestions you may have.

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  • Algorithm to split an array into N groups based on item index (should be something simple)

    - by serg
    I feel that it should be something very simple and obvious but just stuck on this for the last half an hour and can't move on. All I need is to split an array of elements into N groups based on element index. For example we have an array of 30 elements [e1,e2,...e30], that has to be divided into N=3 groups like this: group1: [e1, ..., e10] group2: [e11, ..., e20] group3: [e21, ..., e30] I came up with nasty mess like this for N=3 (pseudo language, I left multiplication on 0 and 1 just for clarification): for(i=0;i<array_size;i++) { if(i>=0*(array_size/3) && i<1*(array_size/3) { print "group1"; } else if(i>=1*(array_size/3) && i<2*(array_size/3) { print "group2"; } else if(i>=2*(array_size/3) && i<3*(array_size/3) print "group3"; } } But what would be the proper general solution? Thanks.

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  • Algorithm for finding similar users through a join table

    - by Gdeglin
    I have an application where users can select a variety of interests from around 300 possible interests. Each selected interest is stored in a join table containing the columns user_id and interest_id. Typical users select around 50 interests out of the 300. I would like to build a system where users can find the top 20 users that have the most interests in common with them. Right now I am able to accomplish this using the following query: SELECT i2.user_id, count(i2.interest_id) AS count FROM interests_users as i1, interests_users as i2 WHERE i1.interest_id = i2.interest_id AND i1.user_id = 35 GROUP BY i2.user_id ORDER BY count DESC LIMIT 20; However, this query takes approximately 500 milliseconds to execute with 10,000 users and 500,000 rows in the join table. All indexes and database configuration settings have been tuned to the best of my ability. I have also tried avoiding the use of joins altogether using the following query: select user_id,count(interest_id) count from interests_users where interest_id in (13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,508) group by user_id order by count desc limit 20; But this one is even slower (~800 milliseconds). How could I best lower the time that I can gather this kind of data to below 100 milliseconds? I have considered putting this data into a graph database like Neo4j, but I am not sure if that is the easiest solution or if it would even be faster than what I am currently doing.

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