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• How to discriminate from two nodes with identical frequencies in a Huffman's tree?

  - by Omega

  Still on my quest to compress/decompress files with a Java implementation of Huffman's coding (http://en.wikipedia.org/wiki/Huffman_coding) for a school assignment. From the Wikipedia page, I quote: Create a leaf node for each symbol and add it to the priority queue. While there is more than one node in the queue: Remove the two nodes of highest priority (lowest probability) from the queue Create a new internal node with these two nodes as children and with probability equal to the sum of the two nodes' probabilities. Add the new node to the queue. The remaining node is the root node and the tree is complete. Now, emphasis: Remove the two nodes of highest priority (lowest probability) from the queue Create a new internal node with these two nodes as children and with probability equal to the sum of the two nodes' probabilities. So I have to take two nodes with the lowest frequency. What if there are multiple nodes with the same low frequency? How do I discriminate which one to use? The reason I ask this is because Wikipedia has this image: And I wanted to see if my Huffman's tree was the same. I created a file with the following content: aaaaeeee nnttmmiihhssfffouxprl And this was the result: Doesn't look so bad. But there clearly are some differences when multiple nodes have the same frequency. My questions are the following: What is Wikipedia's image doing to discriminate the nodes with the same frequency? Is my tree wrong? (Is Wikipedia's image method the one and only answer?) I guess there is one specific and strict way to do this, because for our school assignment, files that have been compressed by my program should be able to be decompressed by other classmate's programs - so there must be a "standard" or "unique" way to do it. But I'm a bit lost with that. My code is rather straightforward. It literally just follows Wikipedia's listed steps. The way my code extracts the two nodes with the lowest frequency from the queue is to iterate all nodes and if the current node has a lower frequency than any of the two "smallest" known nodes so far, then it replaces the highest one. Just like that.

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• Detect duplicate in a subset from a set of elements

  - by Abhinav Shrivastava

  I have a set of numbers say : 1 1 2 8 5 6 6 7 8 8 4 2... I want to detect the duplicate element in subsets(of given size say k) of the above numbers... For example : Consider the increasing subsets(for example consider k=3) Subset 1 :{1,1,2} Subset 2 :{1,2,8} Subset 3 :{2,8,5} Subset 4 :{8,5,6} Subset 5 :{5,6,6} Subset 6 :{6,6,7} .... .... So my algorithm should detect that subset 1,5,6 contains duplicates.. My approach : 1)Copy the 1st k elements to a temporary array(vector) 2) using #include file in C++ STL...using unique() I would determine if there's any change in size of vector.. Any other clue how to approach this problem..

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• Are there currently any modern, standardized, aptitude test for software engineering?

  - by Matthew Patrick Cashatt

  Background I am a working software engineer who is in the midst of seeking out a new contract for the next year or so. In my search, I am enduring several absurd technical interviews as indicated by this popular question I asked earlier today. Even if the questions I was being asked weren't almost always absurd, I would be tired nonetheless of answering them many times over for various contract opportunities. So this got me thinking that having a standardized exam that working software professionals could take would provide a common scorecard that could be referenced by interviewers in lieu of absurd technical interview questions (i.e. nerd hazing). Question Is there a standardized software engineering aptitude test (SEAT??) available for working professionals to take? If there isn't a such an exam out there, what questions or topics should be covered? An additional thought Please keep in mind, if suggesting a question or topic, to focus on questions or topics that would be relevant to contemporary development practices and realistic needs in the workforce as that would be the point of a standard aptitude test. In other words, no clown traversal questions.

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• Ways to dynamically render a real world 3d environment in Unity3D

  - by Jake M

  Using Unity3D and C# I am attempting to display a 3d version of a real world location. Inside my Unity3D app, the user will specify the GPS coordinates of a location, then my app will have to generate a 3d plane(anything doesn't have to be a plane) of that location. The plane will show a 500 metre by 500 metre 3d snapshot of that location. How would you suggest I achieve this in Unity3D? What methodology would you use to achieve this? NOTE: I understand that this is a very difficult endevour(to render real world locations dynamically in Unity3d) so I expect to perform many actions to achieve this. I just don't know of all the technologies out there and which would be best for my needs For example: Suggested methodology 1: Prompt user to specify GPS coords Use Google earth API and HTTP to programmatically obtain a .khm file describing that location(Not sure if google earth provides that capability does it?) Unzip the .khm so I have the .dae file Convert that file to a .3ds file using ??? third party converter(is there a converter that exists?) Import .3ds into Unity3D at runtime as a plane(is this possible)? Suggested methodology 2: Prompt user to specify GPS coords Use Google earth API and HTTP to programmatically obtain a .khm file describing that location(Not sure if google earth provides that capability does it?) Unzip the .khm so I have the .dae file Parse .dae file using my own C# parser I will write(do you think its possible to write a .dae parser that can parse the .dae into an array of Vector3 that describe the height map of that location?) Dynamically create a plane in Unity3D and populate it with my array/list of Vector3 points(is it possible to create a plane this way?) Maybe I am meant to create a mesh instead of a plane? Can you think of any other ways I could render a real world 3d environment in Unity3D?

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• Algorithm to reduce calls to mapping API

  - by aidan

  A random distribution of points lies on a map. This data lies behind an API, and I want to grab the complete set of points within a given bounding box. I can query the API with the bounding box and the API will return the set of points that fall within that box. The problem is that the API will limit the result set to 10 items, with no pagination and no indication if there are more points that have been omitted. So I made a recursive algorithm that takes a bounding box and requests the points that lie within it. If the result set is exactly 10 items, then I split the bounding box into four quadrants and recurse. It works fine but my question is this: if want to minimize the number of API calls, what is the optimal way to split the bounding box? Splitting it into quadrants was just an arbitrary decision. When there are a lot of points on the map, I have to drill down many levels before I start getting meaningful results. So I imagine it might be faster to split the box into, say, 9, 16, or more sections. But if I do that, then I eventually get to a point where a lot of requests are returning 0 results which isn't so efficient. Also, does the size of the limit on the results set affect the answer? (This is all assuming that I have no prior knowledge of nominal point density in the bounding box)

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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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• 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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• Microsoft Interview Preparation

  - by Manish

  I have 8 years of java background. Need help in identifying topics I need to prepare for Microsoft interview. I need to know how many rounds Microsoft will have and what all things these rounds consist of. I have identified the following topics. Please let me know if I need to prepare anything else as well. Arrays Linked Lists Recursion Stacks Queue Trees Graph -- What all I should prepare here Dynamic Programming -- again what all I need to prepare Sorting, Searching String Algos

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• What is this algorithm for converting strings into numbers called?

  - by CodexArcanum

  I've been doing some work in Parsec recently, and for my toy language I wanted multi-based fractional numbers to be expressible. After digging around in Parsec's source a bit, I found their implementation of a floating-point number parser, and copied it to make the needed modifications. So I understand what this code does, and vaguely why (I haven't worked out the math fully yet, but I think I get the gist). But where did it come from? This seems like a pretty clever way to turn strings into floats and ints, is there a name for this algorithm? Or is it just something basic that's a hole in my knowledge? Did the folks behind Parsec devise it? Here's the code, first for integers: number' :: Integer -> Parser Integer number' base = do { digits <- many1 ( oneOf ( sigilRange base )) ; let n = foldl (\x d -> base * x + toInteger (convertDigit base d)) 0 digits ; seq n (return n) } So the basic idea here is that digits contains the string representing the whole number part, ie "192". The foldl converts each digit individually into a number, then adds that to the running total multiplied by the base, which means that by the end each digit has been multiplied by the correct factor (in aggregate) to position it. The fractional part is even more interesting: fraction' :: Integer -> Parser Double fraction' base = do { digits <- many1 ( oneOf ( sigilRange base )) ; let base' = fromIntegral base ; let f = foldr (\d x -> (x + fromIntegral (convertDigit base d))/base') 0.0 digits ; seq f (return f) Same general idea, but now a foldr and using repeated division. I don't quite understand why you add first and then divide for the fraction, but multiply first then add for the whole. I know it works, just haven't sorted out why. Anyway, I feel dumb not working it out myself, it's very simple and clever looking at it. Is there a name for this algorithm? Maybe the imperative version using a loop would be more familiar?

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• Algorithm to measure how "diffused" 5,000 pennies are in an economy?

  - by makerofthings7

  Please allow me to use this example/metaphor to describe an algorithm I need. Objects There are 5 thousand pennies. There are 50 cups. There is a tracking history (Passport "stamp" etc) that is associated with each penny as it moves between cups. Definition I'll define a "highly diffused" penny as one that passes through many cups. A "poorly diffused" penny is one that either passes back and forth between 2 cups Question How can I objectively measure the diffusion of a penny as: The number of moves the penny has gone through The number of cups the penny has been in A unit of time (day, week, month) Why am I doing this? I want to detect if a cup is hoarding pennies. Resistance from bad actors Since hoarding is bad, the "bad cup" may simply solicit a partner and simply move pennies between each other. This will reduce the amount of time a coin isn't in transit, and would skew hoarding detection. A solution might be to detect if a cup (or set of cups) are common "partners" with each other, though I'm not sure how to think though this problem. Broad applicability Any assistance would be helpful, since I would think that this algorithm is common to Economics The study of migration patterns of animals, citizens of a country Other natural occurring phenomena ... and probably exists as a term or concept I'm unfamiliar with.

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• Algorithmic Forecasting and Pattern Recognition

  - by Ryan King

  Say a user could enter project data into my software. Each project has 2 variables "size" and "work" and they're related but the relationship is not known. Is there a way to programmatically determine the relationship between the variables based on previous data and forecast the amount of work provided if only given the size of the project in the future? For Example, say the user had manually entered the following projects. Project 1 - Size:1, Work: 4 Project 2 - Size:2, Work: 7 Project 3 - Size:3, Work: 10 Project 4 - Size:4, Work: x What should I look into to be able to programmatically determine, that Work = Size*3+1 and therefor be able to say that x=13?

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• Algorithm for perfect non-binary graph layout

  - by mariki

  I have a complex non-binary graph model. Each tree node can have multiple children&parents (a node can also have a connection to it's "brother"). A node is represented as square on screen with lines to the connected nodes. For that I want to use Draw2D and GEF libraries. The problem I am facing is the graph layout. I need a nice algorithm that can reposition the square nodes and the connections with minimum intersections and also make it symmetric as possible.

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• Finding duplicate files?

  - by ub3rst4r

  I am going to be developing a program that detects duplicate files and I was wondering what the best/fastest method would be to do this? I am more interested in what the best hash algorithm would be to do this? For example, I was thinking of having it get the hash of each files contents and then group the hashes that are the same. Also, should there be a limit set for what the maximum file size can be or is there a hash that is suitable for large files?

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• Algorithm for detecting windows in a room

  - by user2733436

  I am dealing with the following problem and i was looking to write a Pseudo-code for developing an algorithm that can be generic for such a problem. Here is what i have come up with thus far. STEP 1 In this step i try to get the robot where it maybe placed to the top left corner. Turn Left - If no window or Wall detected keep going forward 1 unit.. if window or wall detected -Turn right -- if no window or Wall detected keep going forward.. if window or wall detected then top left corner is reached. STEP 2 (We start counting windows after we get to this stage to avoid miscounting) I would like to declare a variable called turns as it will help me keep track if robot has gone around entire room. Turns = 4; Now we are facing north and placed on top left corner. while(turns0){ If window or wall detected (if window count++) Turn Right Turn--; While(detection!=wall || detection!=window){ move 1 unit forward Turn left (if window count++) Turn right } } I believe in doing so the robot will go around the entire room and count windows and it will stop once it has gone around the entire room as the turns get decremented. I don't feel this is the best solution and would appreciate suggestions on how i can improve my Pseudo-code. I am not looking for any code just a algorithm on solving such a problem and that is why i have not posted this in stack overflow. I apologize if my Pseudo-code is poorly written please make suggestions if i can improve that as i am new to this. Thanks.

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• Given a string of letters from alphabet insert frequency of each character in the string.in O(n) time and O(1) space [on hold]

  - by learner

  Below is my attempt void str_freq(char *str, int len) { char c; int cnt=0; c=str[0]; int i,j=0; for(i=0;i<len;i++) { if(c==str[i]) { cnt++; } else { c = str[i]; // printf(" %d ",cnt); str[j] = str[i-1]; str[j+1] = (char)(((int)'0')+cnt); j++; cnt=0; } } str[j+1]='\0'; printf("%s",str); } int main() { char str[] = "aaabbccccdeffgggg"; int length=strlen(str); str_freq(str,length); } I am getting wrong answer abcdef1 instead of a3b2c4d1e1f2g4. Please let me know where I am going wrong.

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• Defining formula through user interface in user form

  - by BriskLabs Pakistan

  I am a student and developing a simple assignment - windows form application in visual studio 2010. The application is suppose to construct formulas as per user requirement. The process: It has to pick data from columns of Microsoft Access database and the user should be able to pick the data by column name like we do in a drop down menu. and create reusable formulas in it ( configure it once and can change it again). followings are column titles from database that can be picked for example. e.g Col -1 : Marks in Maths Col -2 : Total Marks in Maths Col -3 : Marks in science Col -4 : Total marks in science Finally we should be able to construct any formula in the UI like (Col 1 + Col 3 ) / ( col 2 + col 4) = Formula 1 once this is formula is set saved and a name is assigned to it by user. he/she can use the formula and results shall appear in a window below. i.e He would be able to calculate his desired figures (formula) by only manipulating underlying data on the UI layer....choose the data for a period and apply the formula and get the answer Problem: It looks like I have to create an app where rules are set through UI....... this means no stored procedures are required in SQL.... please suggest the right approach.

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• Why does a proportional controller have a steady state error?

  - by Qantas 94 Heavy

  I've read about feedback loops, how much this steady state error is for a given gain and what to do to remove this steady state error (add integral and/or derivative gains to the controller), but I don't understand at all why this steady state error occurs in the first place. If I understand how a proportional control works correctly, the output is equal to the current output plus the error, multiplied by the proportional gain (Kp). However, wouldn't the error slowly diminish over time as it is added (reaching 0 at infinite time), not have a steady state error? From my confusion, it seems I'm completely misunderstanding how it works - a proper explanation of how this steady state error eventuates would be fantastic.

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• Indefinite loops where the first time is different

  - by George T

  This isn't a serious problem or anything someone has asked me to do, just a seemingly simple thing that I came up with as a mental exercise but has stumped me and which I feel that I should know the answer to already. There may be a duplicate but I didn't manage to find one. Suppose that someone asked you to write a piece of code that asks the user to enter a number and, every time the number they entered is not zero, says "Error" and asks again. When they enter zero it stops. In other words, the code keeps asking for a number and repeats until zero is entered. In each iteration except the first one it also prints "Error". The simplest way I can think of to do that would be something like the folloing pseudocode: int number = 0; do { if(number != 0) { print("Error"); } print("Enter number"); number = getInput(); }while(number != 0); While that does what it's supposed to, I personally don't like that there's repeating code (you test number != 0 twice) -something that should generally be avoided. One way to avoid this would be something like this: int number = 0; while(true) { print("Enter number"); number = getInput(); if(number == 0) { break; } else { print("Error"); } } But what I don't like in this one is "while(true)", another thing to avoid. The only other way I can think of includes one more thing to avoid: labels and gotos: int number = 0; goto question; error: print("Error"); question: print("Enter number"); number = getInput(); if(number != 0) { goto error; } Another solution would be to have an extra variable to test whether you should say "Error" or not but this is wasted memory. Is there a way to do this without doing something that's generally thought of as a bad practice (repeating code, a theoretically endless loop or the use of goto)? I understand that something like this would never be complex enough that the first way would be a problem (you'd generally call a function to validate input) but I'm curious to know if there's a way I haven't thought of.

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• Strategy/algorithm to divide fair teams based on history

  - by Vegar

  We are a group of people playing floorball together on a regular basis. Every session starts with the daunting task of dividing teams... So what would be better than an application to pick teams automatically? So, given a history of team-combinations and results, and a list of people showing up for this particular session, what would be a good strategy to find the optimal teams? By optimal, I mean teams as equal as possible. Any ideas? Edit: To make it clear, the date that I have to base the picking on, would be something like this: [{ team1: ["playerA", "playerB", "playerC"], team2: ["playerD", "playerE", "playerF"], goals_team1: 10, goals_team2: 8 }, { team1: ["playerD", "playerB", "playerC"], team2: ["playerA", "playerE", "playerG"], goals_team1: 2, goals_team2: 5 }, { team1: ["playerD", "playerB", "playerF"], team2: ["playerA", "playerE", "playerC"], goals_team1: 4, goals_team2: 2 }]

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• Why create a Huffman tree per character instead of a Node?

  - by Omega

  For a school assignment we're supposed to make a Java implementation of a compressor/decompresser using Huffman's algorithm. I've been reading a bit about it, specially this C++ tutorial: http://www.cprogramming.com/tutorial/computersciencetheory/huffman.html In my program, I've been thinking about having Nodes that have the following properties: Total Frequency Character (if a leaf) Right child (if any) Left child (if any) Parent (if any) So when building the Huffman tree, it is just a matter of linking a node to others, etc. However, I'm a bit confused with the following quote (emphasis mine): First, every letter starts off as part of its own tree and the trees are ordered by the frequency of the letters in the original string. Then the two least-frequently used letters are combined into a single tree, and the frequency of that tree is set to be the combined frequency of the two trees that it links together. My question: why should I create a tree per letter, instead of just a node per letter and then do the linking later? I have not begun coding, I'm just studying the algorithm first, so I guess I'm missing an important detail. What is it?

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• What is the runtime of this program

  - by grebwerd

  I was wondering what the run time of this small program would be? #include <stdio.h> int main(int argc, char* argv[]) { int i; int j; int inputSize; int sum = 0; if(argc == 1) inputSize = 16; else inputSize = atoi(argv[i]); for(i = 1; i <= inputSize; i++){ for(j = i; j < inputSize; j *=2 ){ printf("The value of sum is %d\n",++sum); } } } n S floor(log n - log (n-i)) = ? i =1 and that each summation would be the floor value between log(n) - log(n-i). Would the run time be n log n?

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• How many copies are needed to enlarge an array?

  - by user10326

  I am reading an analysis on dynamic arrays (from the Skiena's algorithm manual). I.e. when we have an array structure and each time we are out of space we allocate a new array of double the size of the original. It describes the waste that occurs when the array has to be resized. It says that (n/2)+1 through n will be moved at most once or not at all. This is clear. Then by describing that half the elements move once, a quarter of the elements twice, and so on, the total number of movements M is given by: This seems to me that it adds more copies than actually happen. E.g. if we have the following: array of 1 element +--+ |a | +--+ double the array (2 elements) +--++--+ |a ||b | +--++--+ double the array (4 elements) +--++--++--++--+ |a ||b ||c ||c | +--++--++--++--+ double the array (8 elements) +--++--++--++--++--++--++--++--+ |a ||b ||c ||c ||x ||x ||x ||x | +--++--++--++--++--++--++--++--+ double the array (16 elements) +--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--+ |a ||b ||c ||c ||x ||x ||x ||x || || || || || || || || | +--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--+ We have the x element copied 4 times, c element copied 4 times, b element copied 4 times and a element copied 5 times so total is 4+4+4+5 = 17 copies/movements. But according to formula we should have 1*(16/2)+2*(16/4)+3*(16/8)+4*(16/16)= 8+8+6+4=26 copies of elements for the enlargement of the array to 16 elements. Is this some mistake or the aim of the formula is to provide a rough upper limit approximation? Or am I missunderstanding something here?

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• Finding the order of a set's elements

  - by Maciej Stachowski

  A little rephrased, in the form of a game, real-life problem: Suppose there is a set of elements {1, 2, ..., n}. Player A has chosen a single permutation of this set. Player B wants to find out the order of the elements by asking questions of form "Is X earlier in the permutation than Y?", where X and Y are elements of the set. Assuming B wants to minimize the amount of questions, how many times would he have to ask, and what would be the algorithm?

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• Converting a bounded knapsack problem to 0/1 knapsack problem

  - by Ants

  I ran across a problem where goal was to use dynamic programming (instead of other approaches). There is a distance to be spanned, and a set of cables of different lengths. What is the minimum number of cables needed to span the distance exactly? To me this looked like a knapsack problem, but since there could be multiples of a particular length, it was a bounded knapsack problem, rather than a 0/1 knapsack problem. (Treat the value of each item to be its weight.) Taking the naive approach (and not caring about the expansion of the search space), the method I used to convert the bounded knapsack problem into a 0/1 knapsack problem, was simply break up the multiples into singles and apply the well-known dynamic programming algorithm. Unfortunately, this leads to sub-optimal results. For example, given cables: 1 x 10ft, 1 x 7ft, 1 x 6ft, 5 x 3ft, 6 x 2ft, 7 x 1ft If the target span is 13ft, the DP algorithm picks 7+6 to span the distance. A greedy algorithm would have picked 10+3, but it's a tie for minimum number of cables. The problem arises, when trying to span 15ft. The DP algorithm ended up picking 6+3+3+3 to get 4 cables, while the greedy algorithm correctly picks 10+3+2 for only 3 cables. Anyway, doing some light scanning of converting bounded to 0/1, it seems like the well-known approach to convert multiple items to { p, 2p, 4p ... }. My question is how does this conversion work if p+2p+4p does not add up to the number of multiple items. For example: I have 5 3ft cables. I can't very well add { 3, 2x3, 4x3 } because 3+2x3+4x3 5x3. Should I add { 3, 4x3 } instead? [I'm currently trying to grok the "Oregon Trail Knapsack Problem" paper, but it currently looks like the approach used there is not dynamic programming.]

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• Building general programming skills?

  - by toleero

  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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