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• find second smallest element in Fibonacci Heap

  - by Longeyes

  I need to describe an algorithm that finds the second smallest element in a Fibonacci-Heap using the Operations: Insert, ExtractMin, DecreaseKey and GetMin. The last one is an algorithm previously implemented to find and return the smallest element of the heap. I thought I'd start by extracting the minimum, which results in its children becoming roots. I could then use GetMin to find the second smallest element. But it seems to me that I'm overlooking other cases because I don't know when to use Insert and DecreaseKey, and the way the question is phrased seems to suggest I should need them.

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• Java Alphabetize Algorithm Insertion sort vs Bubble Sort

  - by Chris Okyen

  I am supposed to "Develop a program that alphabetizes three strings. The program should allow the user to enter the three strings, and then display the strings in alphabetical order." It's instructed that I need to use the String library compareTo()/charAt()/toLowerCase() to make all the characters lowercase so the Lexicon comparison is also a alphabetical comparison. Input Pseudo Code: String input[3]; Scanner keyboard = new Scanner(System.in); System.out.println("Enter three strings: "); for(byte i = 0; i < 3; i++) input[i] = keyboard.next() The sorting would be Insertion Sort: 321 2 3 1 2 31 231 1 23 1 2 3 1 23 1 23 123 Bubble Sort 321 231 213 123 Which would be more efficient in this case? The bubble sort seems to be more efficient though they seem to have equal stats for worst best and avg case, but I read the Insertion Sort is quicker for small amounts of data like my case.

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• Monkey Hunter algorithm - Interview question [closed]

  - by Estefany Velez

  Question asked in an Interview: You are a hunter in the forest. A monkey is in the trees, but you don't know where and you can't see it. You can shoot at the trees, you have unlimited ammunition. Immediately after you shoot at a tree, if the monkey was in the tree, he falls and you win. If the monkey was not in the tree, he jumps (randomly) to an adjacent tree (he has to). Find an algorithm to get the monkey in the fewest shots possible. SOLUTION: The correct answer according to me was in the comments, credit to @rtperson: You could eliminate this possibility by shooting each tree twice as you sweep left, giving you a worst case of O(2n). EDIT: ...that is, a worst case of O(2n-1). You don't need to shoot the last tree twice.

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• Fair 2-combinations

  - by Tometzky

  I need to fairly assign 2 experts from x experts (x is rather small - less than 50) for every n applications, so that: each expert has the same number of applications (+-1); each pair of experts (2-combination of x) has the same number of applications (+-1); It is simple to generate all 2-combinations: for (i=0; i<n; i++) { for (j=i+1; j<n; j++) { combinations.append(tuple(i,j)); } } But to assign experts fairly I need to assign a combination to an application i correct order, for example: experts: 0 1 2 3 4 fair combinations: counts 01234 01 11000 23 11110 04 21111 12 22211 34 22222 02 32322 13 33332 14 34333 03 44343 24 44444 I'm unable to come up with a good algorithm for this (the best I came up with is rather complicated and with O(x4) complexity). Could you help me?

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• Checking whether php script was resolved by optimal way

  - by user2135931

  Can anybody give some advise how to check the arbitrary php code on optimal solution. For example I create a simple algorithm and sent it on the special resource. After proccessing my algorithm this resource give me result whether my code is nice. If no it give me some advice and tell what is wrong (maybe I forgot check devision by zero etc). I looked for php code analyzer but could't find any variants. Maybe someone give me a resource where I can research this problem. Thanks in advance!

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• How to indicate reliability when reporting availability of competencies

  - by Jan Doggen

  We have employees with competencies: Pete Welder Carpenter Melissa Carpenter Assume they both work 40 hours/week, and have not yet been assigned work. We need to report the availability of these competencies, expressed in hours. As far as I can see now, we can report this in two ways: Method A. When someone has multiple competencies, count them both. Welder 40 hours Carpenter 80 hours Method B. When someone has multiple competencies, count an equal division of hours for each Welder 20 hours Carpenter 60 hours Method A has our preference: - A good planner will know to plan the least available competency first. If 30 hours of welding is planned, we will be left with 10 welder, 50 carpenter. - Method B has the disadvantage that the planner thinks he cannot plan the job when 30 hours of welding is required. However, if we report this we would like to give an estimate of the reliability of the numbers for each competency, i.e. how much are these over-reported? In my example A, would I say that carpenter is 100% over-reported, or 50%, or maybe another number? How would I calculate this for large numbers of competencies? I'm sure we are not the first ones dealing with this, is there a 'usual' way of doing this in planning? Additionally: - Would there be an even better method than A or B? - Optionally, we also have an preference order of competencies (like: use him/her in this order), Pete could be 1. welder 2. carpenter. Does this introduce new options?

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• MATLAB: Best fitness vs mean fitness, initial range

  - by Sa Ta

  Based on the example of Rastrigin's function. At the plot function, if I chose 'best fitness', on the same graph 'mean fitness' will also be plotted. I understand well about 'best fitness' whereby it plots the best function value in each generation versus iteration number. It will reach value zero after some times. I don't understand about 'mean fitness'in the graph plotted. What do those 'mean fitness' values mean? How does the 'mean fitness' graph help to understand Rastrigin's function? What are the meaning of the term initial population, initial score and initial range? I wish to have a better understanding of these terms. The default value for initial range is [0,1]. Does it mean that 0 is the lower bound (lb) and 1 is the upper bound (ub)? Do these values interfere with the lb and ub values I set in the constraints? I try to better understand about lb and ub. If my lb is 0 and ub is 5, does it mean that my final point values will be within 0 and 5? If I know the lb and ub for my problem is between 0 and 5, do I just set the initial range as [0,5] at all times and may I assume that this is the best option for initial range, and I need not try it with any other values?

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• is Microsoft LC random generator patented?

  - by user396672

  I need a very simple pseudo random generator (no any specific quality requirements) and I found Microsoft's variant of LCG algorithm used for rand() C runtime library function fit my needs (gcc's one seems too complex). I found the algorithm here: http://rosettacode.org/wiki/Linear_congruential_generator#C However, I worry the algorithm (including its "magic numbers" i.e coefficients) may by patented or restricted for use in some another way. Is it allowed to use this algorithm without any licence or patent restrictions or not? I can't use library rand() because I need my results to be exactly reproducible on different platforms

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• What is required for a scope in an injection framework?

  - by johncarl

  Working with libraries like Seam, Guice and Spring I have become accustomed to dealing with variables within a scope. These libraries give you a handful of scopes and allow you to define your own. This is a very handy pattern for dealing with variable lifecycles and dependency injection. I have been trying to identify where scoping is the proper solution, or where another solution is more appropriate (context variable, singleton, etc). I have found that if the scope lifecycle is not well defined it is very difficult and often failure prone to manage injections in this way. I have searched on this topic but have found little discussion on the pattern. Is there some good articles discussing where to use scoping and what are required/suggested prerequisites for scoping? I interested in both reference discussion or your view on what is required or suggested for a proper scope implementation. Keep in mind that I am referring to scoping as a general idea, this includes things like globally scoped singletons, request or session scoped web variable, conversation scopes, and others. Edit: Some simple background on custom scopes: Google Guice custom scope Some definitions relevant to above: “scoping” - A set of requirements that define what objects get injected at what time. A simple example of this is Thread scope, based on a ThreadLocal. This scope would inject a variable based on what thread instantiated the class. Here's an example of this: “context variable” - A repository passed from one object to another holding relevant variables. Much like scoping this is a more brute force way of accessing variables based on the calling code. Example: methodOne(Context context){ methodTwo(context); } methodTwo(Context context){ ... //same context as method one, if called from method one } “globally scoped singleton” - Following the singleton pattern, there is one object per application instance. This applies to scopes because there is a basic lifecycle to this object: there is only one of these objects instantiated. Here's an example of a JSR330 Singleton scoped object: @Singleton public void SingletonExample{ ... } usage: public class One { @Inject SingeltonExample example1; } public class Two { @Inject SingeltonExample example2; } After instantiation: one.example1 == two.example2 //true;

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• Finding links among many written and spoken thoughts

  - by Peter Fren

  So... I am using a digital voice recorder to record anything I see important, ranging from business to private, from rants to new business ideas. Every finalized idea is one wma-file. I wrote a program to sort the wma-files into folders. From time to time I listen to the wma-files, convert them to text(manually) and insert them into a mindmap with mindmanager, which I sort hierarchically by area and type in turn. This works very well, no idea is being lost, when I am out of ideas for a special topic, I listen to what I said and can get started again. What could a search system look like that finds links between thoughts(written in the mindmap and in the wma files) or in general gives me good search results even when the keyword I searched for is not present but a synonym of it or related topic(for instance flower should output entries containing orchid aswell, even if they contain orchid but not the very keyword flower). I prefer something ready-made but small adjustments to a given system are fine aswell. How would you approach this task?

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• Find points whose pairwise distances approximate a given distance matrix

  - by Stephan Kolassa

  Problem. I have a symmetric distance matrix with entries between zero and one, like this one: D = ( 0.0 0.4 0.0 0.5 ) ( 0.4 0.0 0.2 1.0 ) ( 0.0 0.2 0.0 0.7 ) ( 0.5 1.0 0.7 0.0 ) I would like to find points in the plane that have (approximately) the pairwise distances given in D. I understand that this will usually not be possible with strictly correct distances, so I would be happy with a "good" approximation. My matrices are smallish, no more than 10x10, so performance is not an issue. Question. Does anyone know of an algorithm to do this? Background. I have sets of probability densities between which I calculate Hellinger distances, which I would like to visualize as above. Each set contains no more than 10 densities (see above), but I have a couple of hundred sets. What I did so far. I did consider posting at math.SE, but looking at what gets tagged as "geometry" there, it seems like this kind of computational geometry question would be more on-topic here. If the community thinks this should be migrated, please go ahead. This looks like a straightforward problem in computational geometry, and I would assume that anyone involved in clustering might be interested in such a visualization, but I haven't been able to google anything. One simple approach would be to randomly plonk down points and perturb them until the distance matrix is close to D, e.g., using Simulated Annealing, or run a Genetic Algorithm. I have to admit that I haven't tried that yet, hoping for a smarter way. One specific operationalization of a "good" approximation in the sense above is Problem 4 in the Open Problems section here, with k=2. Now, while finding an algorithm that is guaranteed to find the minimum l1-distance between D and the resulting distance matrix may be an open question, it still seems possible that there at least is some approximation to this optimal solution. If I don't get an answer here, I'll mail the gentleman who posed that problem and ask whether he knows of any approximation algorithm (and post any answer I get to that here).

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• Application qos involving priority and bandwidth

  - by Steve Peng

  Our manager wants us to do applicaiton qos which is quite different from the well-known system qos. We have many services of three types, they have priorites, the manager wants to suspend low priority services requests when there are not enough bandwidth for high priority services. But if the high priority services requests decrease, the bandwidth for low priority services should increase and low priority service requests are allowed again. There should be an algorithm involving priority and bandwidth. I don't know how to design the algorithm, is there any example on the internet? Somebody can give suggestion? Thanks. UPDATE All these services are within a same process. We are setting the maximum bandwidth for the three types of services via ports of services via TC (TC is the linux qos tool whose name means traffic control).

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• Building general programming skills?

  - by toleero

  Hello :) I currently am quite new to programming, I've had exposure to a few languages (C#, PHP, JavaScript, VB, and some others) and I'm quite new to OOP. I was just wondering what is the best way to build up general programming/problem solving skills without being language specific? I was thinking maybe of something like Project Euler but more geared towards newbies? Thanks! Edit: I am looking at getting into Game Scripting/Programming, I'm already in Games but in a different discipline :)

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• How can I keep directories in sync

  - by Guillaume Boudreau

  I have a directory, dirA, that users can work in: they can create, modify, rename and delete files & sub-directores in dirA. I want to keep another directory, dirB, in sync with dirA. What I'd like, is a discussion on finding a working algorithm that would achieve the above, with the limitations listed below. Requirements: 1. Something asynchronous - I don't want to stop file operations in dirA while I work in dirB. 2. I can't assume that I can just blindly rsync dirA to dirB on regular interval - dirA could contain millions of files & directories, and terrabytes of data. Completely walking the dirA tree could take hours. Those two requirements makes this really difficult. Having it asynchronous means that when I start working on a specific file from dirA, it might have moved a lot since it appeared. And the second limitation means that I really need to watch dirA, and work on atomic file operations that I notice. Current (broken) implementation: 1. Log all file & directory operations in dirA. 2. Using a separate process, read that log, and 'repeat' all the logged operations in dirB. Why is it broken: echo 1 > dirA/file1 # Allow the 'log reader' process to create dirB/file1: log = "write dirA/file1"; action = cp dirA/file1 dirB/file1; result = OK echo 1 > dirA/file2 mv dirA/file1 dirA/file3 mv dirA/file2 dirA/file1 rm dirA/file3 # End result: file1 contains '1' # 'log reader' process starts working on the 4 above file operations: log = "write file2"; action = cp dirA/file2 dirB/file2; result = failed: there is no dirA/file2 log = "rename file1 file3"; action = mv dirB/file1 dirB/file3; result = OK log = "rename file2 file1"; action = mv dirB/file2 dirB/file1; result = failed: there is no dirB/file2 log = "delete file3"; action = rm dirB/file3; result = OK # End result in dirB: no more files! Another broken example: echo 1 > dirA/dir1/file1 mv dirA/dir1 dirA/dir2 # 'log reader' process starts working on the 2 above file operations: log = "write file1"; action = cp dirA/dir1/file1 dirB/dir1/file1; result = failed: there is no dirA/dir1/file1 log = "rename dir1 dir2"; action = mv dirB/dir1 dirB/dir2; result = failed: there is no dirA/dir1 # End result if dirB: nothing!

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• Filling array with numbers from given range so that sum of adjacent numbers is square number

  - by REACHUS

  Problem: Fill all the cells using distinct numbers from <1,25 set, so that sum of two adjacent cells is a square number. (source: http://grymat.im.pwr.wroc.pl/etap1/zad1etp1213.pdf; numbers 20 and 13 have been given) I've already solved this problem analytically and now I would like to approach it using an algorithm. I would like to know how should I approach these kind of problems in general (not a solution, just a point for me to start).

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• What is the usage of Spaly Trees in the real world?

  - by Meena

  I decided to learn about Balance search trees, so I picked 2-3-4 and splay trees. I'm wondering what are the examples of splay trees usage in the real world? In this Cornell: http://www.cs.cornell.edu/courses/cs3110/2009fa/recitations/rec-splay.html I read that splay trees are 'A good example is a network router'. But from rest of the explanation seams like network routers use hash tables and not splay trees since the lookup time is constant instead of O(log n). thanks!

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• Which is the most practical way to add functionality to this piece of code?

  - by Adam Arold

  I'm writing an open source library which handles hexagonal grids. It mainly revolves around the HexagonalGrid and the Hexagon class. There is a HexagonalGridBuilder class which builds the grid which contains Hexagon objects. What I'm trying to achieve is to enable the user to add arbitrary data to each Hexagon. The interface looks like this: public interface Hexagon extends Serializable { // ... other methods not important in this context <T> void setSatelliteData(T data); <T> T getSatelliteData(); } So far so good. I'm writing another class however named HexagonalGridCalculator which adds some fancy pieces of computation to the library like calculating the shortest path between two Hexagons or calculating the line of sight around a Hexagon. My problem is that for those I need the user to supply some data for the Hexagon objects like the cost of passing through a Hexagon, or a boolean flag indicating whether the object is transparent/passable or not. My question is how should I implement this? My first idea was to write an interface like this: public interface HexagonData { void setTransparent(boolean isTransparent); void setPassable(boolean isPassable); void setPassageCost(int cost); } and make the user implement it but then it came to my mind that if I add any other functionality later all code will break for those who are using the old interface. So my next idea is to add annotations like @PassageCost, @IsTransparent and @IsPassable which can be added to fields and when I'm doing the computation I can look for the annotations in the satelliteData supplied by the user. This looks flexible enough if I take into account the possibility of later changes but it uses reflection. I have no benchmark of the costs of using annotations so I'm a bit in the dark here. I think that in 90-95% of the cases the efficiency is not important since most users wont't use a grid where this is significant but I can imagine someone trying to create a grid with a size of 5.000.000.000 X 5.000.000.000. So which path should I start walking on? Or are there some better alternatives? Note: These ideas are not implemented yet so I did not pay too much attention to good names.

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• Elo system behaves oddly in program I've created

  - by adc

  Alright, so I'm looking to build a small program (C# and XAML) that, essentially, does this: Generate array of players. Each player has a current rating and a true rating. I set current rating to 1200 as a starting point right now; I've also tried setting it to true rating and the average of the two. True rating is what their skill level actually is. Their true rating is calculated based on percentages from the current League of Legends rating system; generating an array of 970 thousand generates results very similar to the data from here: (removed due to URL limit - but trust me, the results are very similar). This array is of length specified by the user. If need be, sort the array from smallest to largest. Play X number of games, again specified by the user. This is done by taking the array of players (which is sorted by Current Rating after being created) and running through it in groups of 10. The first five are on team one, the second five are on team two. It then takes the True Rating of these players and calculates an expected chance to win using the Elo system. It generates a random double and compares it to the expected chance to win; if the number is lower, team one wins - otherwise team two wins. I then update the rating of the players via, again, the Elo system - giving the winning team a score of 1 and the losing team a score of 0. I use a K value of 36 (but have tried 12, 24, and even higher ones) and an F value of 400. After going through the entire loop of players (which I have conveniently forced to be a multiple of ten), it sorts the array - again via current rating. This, if my understanding of the Elo system is correct, runs properly. However, it doesn't seem to work. I have a running test telling me how many players of the full array are within 100 current rating of their true rating. I would expect some portion of the population to be outside this range (as probability is not always going to go in their favor), but a full 40-45% of the population is outside of this range. I also have it outputting the maximum difference between true and current rating - and I have never seen this drop below 500! It hovers between 550-600, occasionally going over or under. I'm at a loss as to what to change - I've fiddled with the K and F values, where I start all the players, etc. but nothing changes the fact that eventually a good 40% of the population is outside the range. And it isn't that I have it playing too few games - it's now run through over 60 thousand games and the problem never disappears or really fluctuates. The full C# code, including everything except the XAML file and the Player class (pastebin is being very slow and I can only post two links, so I can't link to the XAML file): http://pastebin.com/rFcZRL84 The Player class: http://pastebin.com/4cJTdTRu I guess my question is did I do anything wrong? Is there a problem with the way I implemented the system, or is it just that Riot uses a significantly modified Elo system? I don't think it's the latter, as that still wouldn't explain the massive true and current rating differences to me, however.

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• Permission Management Algorithm

  - by Emerald214

  I have 3 levels of permission to see the product: Brand - Allow/Deny Category - Allow/Deny Product - Allow/Deny For example, product A has: Category: Allow Product: Deny = product A cannot be seen because product A isn't allowed in Product level. if(allowForCategory == true) { if(allowForProduct == false) return false; if(allowForProduct == true) return true; } else { ... } This is not a good choice because it will become more complex if we add brand level. if() { if() { if() {} } } So is there any general algorithm to deal with the permission problem just like 777 solution in Linux?

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• Async CTP Refresh for Visual Studio 2010 SP1 Released

  - by Reed

  The Visual Studio team today released an update to the Visual Studio Async CTP which allows it to be used with Visual Studio SP1.  This new CTP includes some very nice new additions over the previous CTP.  The main highlights of this release include: Compatibility with Visual Studio SP1 APIs for Windows Phone 7 Compatibility with non-English installations Compatibility with Visual Studio Express Edition More efficient Async methods due to a change in the API Numerous bug fixes New EULA which allows distribution in production environments Anybody using the Async CTP should consider upgrading to the new version immediately.  For details, visit the Visual Studio Asynchronous Programming page on MSDN.

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• Can this word search algorithm be made faster?

  - by Ashwin Singh

  Problem: Find a match of word S in text T Given: S and T are part of spoken and written English. Example: Match 'Math' in 'I love Mathematics' NOTE: Ignore CASES. My algorithm: STEP 1) Convert S, T to char[] STEP 2) for i=0, i < T.length , i++ STEP 3) for j=S.length-1, j>0 , j-- STEP 3 is the magic, instead of going about matching M,A,T,H, this matches M, H, T and finally A. This helps in eliminating a lot of possible partial matches. For example, if I go sequentially like M A as in Boyer Moore's method ... it can match Matter, Mass, Matchstick etc. using M _ _ H will bring down size of partial matches. STEP 4) if S[j]!=T[i] -> break; else if j==i -> PRINT MATCH

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• Algorithm to infer tag hierarchy

  - by Tom

  I'm looking for an algorithm to infer a hierarchy from a set of tagged items. E.g. if the following items have the tags: 1 a 2 a,b 3 a,c 4 a,c,e 5 a,b 6 a,c 7 d 8 d,f Then I can construct an undirected graph (or graphs) by tallying the node weights and edge weights: node weights edge weights a 6 a-b 2 b 2 a-c 3 c 3 c-e 1 d 2 a-e 1 <-- this edge is parallel to a-c and c-e and not wanted e 1 d-f 1 f 1 The first problem is how to drop any redundant edges to get to the simplified graph? Note that it's only appropriate to remove that redundant a-e edge in this case because something is tagged as a-c-e, if that wasn't the case and the tag was a-e, that edge would have to remain. I suspect that means the removal of edges can only happen during the construction of the graph, not after everything has been tallied up. What I'd then like to do is identify the direction of the edges to create a directed graph (or graphs) and pick out root nodes to hopefully create a tree (or trees): trees a d // \\ | b c f \ e It seems like it could be a string algorithm - longest common subsequences/prefixes - or a tree/graph algorithm, but I am a little stuck since I don't know the correct terminology to search for it.

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• What is the best way to keep track of the median?

  - by Steven Mou

  I read a question in one book: Numbers are randomly generated and stored into an (expanding) array, How would you keep track of the median? There are two data structures can solve the problem. One is the balanced binary tree, the other is two heaps which keep trace of the biggest half and the smallest half of the elements. I think these two solutions has the same running time as O(n lg n), but I am not sure of my judgement. In your opinions, What is the best way to keep track of the median?

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• Common mistakes made by new programmers without CS backgrounds [on hold]

  - by mblinn

  I've noticed that there seems to be a class of mistakes that new programmers without CS backgrounds tend to make, that programmers with CS backgrounds tend not to. I'm not talking about not understanding source control, or how to design large programs, or a whole host of other things that both freshly minted CS graduates and non-CS graduates tend to not understand, I'm talking about basic mistakes that having a CS background will prevent a programmer from making. One obvious and well trod example is that folks who don't have a basic understanding of formal languages will often try to parse arbitrary HTML or XML using regular expressions, and possibly summon Cthulu in the process. Another fairly common one that I've seen is using common data structures in suboptimal ways like using a vector and a search function as if it were a hash map. What sorts of other things along these lines would you look out for when on-boarding a batch of newly minted, non-CS programmers.

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• Algorithm to match items be value into sets base on total

  - by Ben

  Given n sets of items. Each item has a value. The items in a set have similar values but vary by a small amount. The goal is to create new sets containing three items selected from the original sets such that the total of the values is within a given range. Only one item a source set can be selected. For example: If we have the following starting sets: Set A - { 4.0, 3.8, 4.2 } Set B - { 7.0, 6.8, 7.2 } Set C - { 1.0, 0.9, 1.1 } Set D - { 6.5, 6.4, 6.6 } Set E - { 2.5, 2.4, 2.6 } Goal is to create sets containing three elements such that the total is between 11.9 and 12.1. For example { 3.8, 7.2, 1.0 } There can be unused elements. Can someone suggest an algorithm for this problem?

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