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• reference list for non-IT driven algorithmic patterns

  - by Quicker

  I am looking for a reference list for non-IT driven algorithmic patterns (which still can be helped with IT implementations of IT). An Example List would be: name; short desc; reference Travelling Salesman; find the shortest possible route on a multiple target path; http://en.wikipedia.org/wiki/Travelling_salesman_problem Ressource Disposition (aka Regulation); Distribute a limited/exceeding input on a given number output receivers based on distribution rules; http://database-programmer.blogspot.de/2010/12/critical-analysis-of-algorithm-sproc.html If there is no such list, but you instantly think of something specific, please 'put it on the desk'. Maybe I can compile something out of the input I get here (actually I am very frustrated as I did not find any such list via research by myself). Details on Scoping: I found it very hard to formulate what I want in a way everything is out that I do not need (which may be the issue why I did not find anything at google). There is a database centric definition for what I am looking for in the section 'Processes' of the second example link. That somehow fits, but the database focus sort of drifts away from the pattern thinking, which I have in mind. So here are my own thoughts around what's in and what's out: I am NOT looking for a foundational algo ref list, which is implemented as basis for any programming language. Eg. the php reference describes substr and strlen. That implements algos, but is not what I am looking for. the problem the algo does address would even exist, if there were no computers (or other IT components) the main focus of the algo is NOT to help other algo's chances are high, that there are implementions of the solution or any workaround without any IT support out there in the world however the algo could be benefitialy implemented/fully supported by a software application = means: the problem of the algo has to be addressed anyway, but running an algo implementation with software automates the process (that is why I posted it on stackoverflow and not somewhere else) typically such algo implementations have more than one input field value and more than one output field value - which implies it could not be implemented as simple function (which is fixed to produce not more than one output value) in a normalized data model often times such algo implementation outputs span accross multiple rows (sometimes multiple tables), whereby the number of output rows depends on the input paraters and rows in the table(s) at start time - which implies that any algo implementation/procedure must interact with a database (read and/or write) I am mainly looking for patterns, not for specific implementations. Example: The Travelling Salesman assumes any coordinates, however it does not say: You need a table targets with fields x and y. - however sometimes descriptions are focussed on examples with specific implementations very much - no worries, as long as the pattern gets clear

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• Find possible variations of one item out of multiple baskets.

  - by tugberk

  I have three baskets of balls and each of them has 10 balls which have the following numbers: Basket 1: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Basket 2: 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 Basket 3: 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 What would be the possible variations If I were to pick one ball from each basket? I guess this is called as Probability in Mathematics but not sure. How would you write this code in C# (or any other programming language) to get the correct results? Edit: Based on @Kilian Foth's comment, here is the solution in C#: class Program { static void Main(string[] args) { IEnumerable<string> basket1 = new List<string> { "1", "2", "3", "4", "5", "6", "7", "8", "9", "10" }; IEnumerable<string> basket2 = new List<string> { "11", "12", "13", "14", "15", "16", "17", "18", "19", "20" }; IEnumerable<string> basket3 = new List<string> { "21", "22", "23", "24", "25", "26", "27", "28", "29", "30" }; foreach (var item1 in basket1) foreach (var item2 in basket2) foreach (var item3 in basket3) { Console.WriteLine("{0}, {1}, {2}", item1, item2, item3); } Console.ReadLine(); } }

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• What are startups expecting when they ask you to solve a programming challenge before interviewing? [closed]

  - by Swapnil Tailor

  I have applied to couple of startups and most of them are asking to solve programming challenge before they start on the interviewing candidate. I have submitted couple of the solutions and all the time getting rejected in the initial screening. Now what I think is, they will see my coding style, algorithm and OOD concepts that I have used to solve the problem. Can you guys input more on it as what other details are taken into consideration and how can I improve my coding for getting selected. By the way, I did all my coding in either Java/Perl. EDIT I feel the biggest reason for rejection is code didn't work for couple of use cases.

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• How should I compress a file with multiple bytes that are the same with Huffman coding?

  - by Omega

  On my great quest for compressing/decompressing files with a Java implementation of Huffman coding (http://en.wikipedia.org/wiki/Huffman_coding) for a school assignment, I am now at the point of building a list of prefix codes. Such codes are used when decompressing a file. Basically, the code is made of zeroes and ones, that are used to follow a path in a Huffman tree (left or right) for, ultimately, finding a byte. In this Wikipedia image, to reach the character m the prefix code would be 0111 The idea is that when you compress the file, you will basically convert all the bytes of the file into prefix codes instead (they tend to be smaller than 8 bits, so there's some gain). So every time the character m appears in a file (which in binary is actually 1101101), it will be replaced by 0111 (if we used the tree above). Therefore, 1101101110110111011011101101 becomes 0111011101110111 in the compressed file. I'm okay with that. But what if the following happens: In the file to be compressed there exists only one unique byte, say 1101101. There are 1000 of such byte. Technically, the prefix code of such byte would be... none, because there is no path to follow, right? I mean, there is only one unique byte anyway, so the tree has just one node. Therefore, if the prefix code is none, I would not be able to write the prefix code in the compressed file, because, well, there is nothing to write. Which brings this problem: how would I compress/decompress such file if it is impossible to write a prefix code when compressing? (using Huffman coding, due to the school assignment's rules) This tutorial seems to explain a bit better about prefix codes: http://www.cprogramming.com/tutorial/computersciencetheory/huffman.html but doesn't seem to address this issue either.

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• Algorithm to increase odds of matching when randomly selecting

  - by Bryan

  I am building a mobile game loosely based on dual n-back http://brainworkshop.sourceforge.net/tutorial.html Now with the game I have 9 squares (numbered 1 through 9) and 9 letters (A through K) In the current code, I randomly select a square (e.g. 3) and a letter (e.g. C), then repeat the random selection for the next turn. For 1-back, I test whether either, neither or both match the previous turn. The problem with my current code is I get very few matches - I can go through many turns without having either match. How can I increase the match frequency, or alternatively decrease the randomness so a match is more likely? I am not looking for specific code (but pseudo-code would be fine) - just more an approach to increase match frequency.

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• Logic or Algorithm to solve this problem [closed]

  - by jade

  I have two lists. List1 {a,b,c,d,e} and List2 {f,g,h,i,j} The relation between the two list is as follows a->g,a->h,h->c,h->d,d->i,d->j Now I have these two lists displayed. Based on the relation above on selecting element a from List1, List2 shows g,h. On selecting h from List2, in List1 c,d are shown in List1. On selecting d from List1 it shows i,j in List2. How to trace back to initial state by deselecting the elements in reverse order in which they have been selected?

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• Finding the median of the merged array of two sorted arrays in O(logN)?

  - by user176517

  Refering to the solution present at MIT handout I have tried to figure out the solution myself but have got stuck and I believe I need help to understand the following points. In the function header used in the solution MEDIAN -SEARCH (A[1 . . l], B[1 . . m], max(1,n/2 - m), min(l, n/2)) I do not understand the last two arguments why not simply 1, l why the max and min respectively. Thanking You.

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• In Search Data Structure And Algorithm Project Title Based on Topic

  - by Salehin Suhaimi

  As the title says, my lecturer gave me a project that i needed to finish in 3 weeks before final semester exams. So i thought i will start now. The requirement is to "build a simple program that has GUI based on all the chapter that we've learned." But i got stuck on WHAT program should i build. Any idea a program that is related to this chapter i've learned? Any input will help. list, array list, linked list, vectors, stacks, Queues, ADT, Hashing, Binary Search Tree, AVL Tree, That's about all i can remember. Any idea where can i start looking?

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• Possible applications of algorithm devised for differentiating between structured vs random text

  - by rooznom

  I have written a program that can rapidly (within 5 sec on a 2GB RAM desktop, 2.33 Ghz CPU) differentiate between structured text (e.g english text) and random alphanumeric strings. It can also provide a probability score for the prediction. Are there any practical applications/uses of such a program. Note that the program is based on entropy models and does not have any dictionary comparisons in its workflow. Thanks in advance for your responses

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• how to avoid or minimise use of check/conditional statement?

  - by Muneeb Nasir

  I have scenario, where i got stream and i need to check for some value. if i got my any new value i have to store it in any of data structure. well it seems very easy, i can place conditional statement if-else or can use contain method of set/map to check either received is new or not. but the problem is checking will effect my application performance, in stream i'll receive hundreds for value in second, if i start checking each and every value i received than for sure it effect performance. Any body can suggest me any mechanism or algorithm that solve my issue. either by bypassing checks or atleast minimize them?

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• Arranging the colors on the board in the most pleasing form

  - by Shashwat

  Given a rectangular board of height H and width W. N colors are given. ith color occupy Pi percentage of area on the board. Sum of Pis is 1. What can be algorithm to layout the colors on the board in the form of rectangles in the most pleasing form. By pleasing mean the aspect ratios (Width/Height) of rectangle of each color should be as close to 1 as possible. In an ideal case the board would be filled only with squares.

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• Common Substring of two strings

  - by Chander Shivdasani

  This particular interview-question stumped me: Given two Strings S1 and S2. Find the longest Substring which is a Prefix of S1 and suffix of S2. Through Google, I came across the following solution, but didnt quite understand what it was doing. public String findLongestSubstring(String s1, String s2) { List<Integer> occurs = new ArrayList<>(); for (int i = 0; i < s1.length(); i++) { if (s1.charAt(i) == s2.charAt(s2.length()-1)) { occurs.add(i); } } Collections.reverse(occurs); for(int index : occurs) { boolean equals = true; for(int i = index; i >= 0; i--) { if (s1.charAt(index-i) != s2.charAt(s2.length() - i - 1)) { equals = false; break; } } if(equals) { return s1.substring(0,index+1); } } return null; }

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• When calculating how many days between 2 dates, should you include both dates in the count, or neither, or 1?

  - by Andy

  I hope this question is alright to ask here. I am trying to make an algorithm that counts how many days between 2 dates. For example, 3/1/2012 and 3/2/2012. Whats the correct answer, or the most popular choice, and should be the one I use? So in this case, if I don't include both dates I am comparing, its 0. If I include one of them (both the start date), its 1. Lastly, if I include both, its 2. Thanks.

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• solve TOR edge node problem by using .onion proxy?

  - by rd.

  I would like to improve the TOR network, where the exit nodes are a vulnerability to concealing traffic. From my understanding, traffic to .onion sites are not decrypted by exit nodes, so therefore - in theory - a .onion site web proxy could be used to further anonymize traffic. Yes/no? perhaps you have insight into the coding and routing behind these concepts to elaborate on why this is a good/not good idea.

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• Approach to Authenticate Clients to TCP Server

  - by dab

  I'm writing a Server/Client application where clients will connect to the server. What I want to do, is make sure that the client connecting to the server is actually using my protocol and I can "trust" the data being sent from the client to the server. What I thought about doing is creating a sort of hash on the client's machine that follows a particular algorithm. What I did in a previous version was took their IP address, the client version, and a few other attributes of the client and sent it as a calculated hash to the server, who then took their IP, and the version of the protocol the client claimed to be using, and calculated that number to see if they matched. This works ok until you get clients that connect from within a router environment where their internal IP is different from their external IP. My fix for this was to pass the client's internal IP used to calculate this hash with the authentication protocol. My fear is this approach is not secure enough. Since I'm passing the data used to create the "auth hash". Here's an example of what I'm talking about: Client IP: 192.168.1.10, Version: 2.4.5.2 hash = 2*4*5*1 * (1+9+2) * (1+6+8) * (1) * (1+0) Client Connects to Server client sends: auth hash ip version Server calculates that info, and accepts or denies the hash. Before I go and come up with another algorithm to prove a client can provide data a server (or use this existing algorithm), I was wondering if there are any existing, proven, and secure systems out there for generating a hash that both sides can generate with general knowledge. The server won't know about the client until the very first connection is established. The protocol's intent is to manage a network of clients who will be contributing data to the server periodically. New clients will be added simply by connecting the client to the server and "registering" with the server. So a client connects to the server for the first time, and registers their info (mac address or some other kind of unique computer identifier), then when they connect again, the server will recognize that client as a previous person and associate them with their data in the database.

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• Grid Game Algorithm

  - by 7Aces

  Problem Link - http://www.iarcs.org.in/inoi/2009/zco2009/zco2009-1a.php You have to find the path with the maximum weight, from the top-left cell to the bottom-right cell. It could've been solved with a simple Dynamic Programming approach, if it were not for the special condition - you are allowed at most one move that can be either to the left or up. How do I now approach the problem with this special case? Also, I'm looking for a time-efficient approach. Thanks!

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• An algorithm for finding subset matching criteria?

  - by Macin

  I recently came up with a problem which I would like to share some thoughts about with someone on this forum. This relates to finding a subset. In reality it is more complicated, but I tried to present it here using some simpler concepts. To make things easier, I created this conceptual DB model: Let's assume this is a DB for storing recipes. Recipe can have many instructions steps and many ingredients. Ingredients are stored in a cupboard and we know how much of each ingredient we have. Now, when we create a recipe, we have to define how much of each ingredient we need. When we want to use a recipe, we would just check if required amount is less than available amount for each product and then decide if we can cook a dinner - if amount required for at least one ingredient is less than available amount - recipe cannot be cooked. Simple sql query to get the result. This is straightforward, but I'm wondering, how should I work when the problem is stated the other way round, i.e. how to find recipies which can be cooked only from ingredients that are available? I hope my explanation is clear, but if you need any more clarification, please ask.

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• What are the common techniques to handle user-generated HTML modified differently by different browsers?

  - by Jakie

  I am developing a website updater. The front end uses HTML, CSS and JavaScript, and the backend uses Python. The way it works is that <p/>, <b/> and some other HTML elements can be updated by the user. To enable this, I load the webpage and, with JQuery, convert all those elements to <textarea/> elements. Once they the content of the text area is changed, I apply the change to the original elements and send it to a Python script to store the new content. The problem is that I'm finding that different browsers change the original HTML. How do you get around this issue? What Python libraries do you use? What techniques or application designs do you use to avoid or overcome this issue? The problems I found are: IE removes the quotes around class and id attributes. For example, <img class='abc'/> becomes <img class=abc/>. Firefox removes the backslash from the line breaks: <br \> becomes <br>. Some websites have very specific display technicalities, so an insertion of a simple "\n"(which IE does) can affect the display of a website. Example: changing <img class='headingpic' /><div id="maincontent"> to <img class='headingpic'/>\n <div id="maincontent"> inserts a vertical gap in IE. The things I have unsuccessfully tried to overcome these issues: Using either JQuery or Python to remove all >\n< occurences, <br> etc. But this fails because I get different patterns in IE, sometimes a ·\n, sometimes a \n···. In a Python, parse the new HTML, extract the new text/content, insert it into the old HTML so the elements and format never change, just the content. This is very difficult and seems to be overkill.

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• Is using build-in sorting considered cheating in practice tests?

  - by user10326

  I am using one of the practice online judges where a practice problem is asked and one submits the answer and gets back if it is accepted or not based on test inputs. My question is the following: In one of the practice tests, I needed to sort an array as part of the solution algorithm. If it matters the problem was: find 2 numbers in an array that add up to a specific target. As part of my algorithm I sorted the array, but to do that I used Java's quicksort and not implement sorting as part of the same method. To do that I had to do: java.util.Arrays.sort(array); Since I had to use the fully qualified name I am wondering if this is a kind of "cheating". (I mean perhaps an online judge does not expect this) Is it? In a formal interview (since these tests are practice for interview as I understand) would this be acceptable?

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• Given two sets of DNA, what does it take to computationally "grow" that person from a fertilised egg and see what they become? [closed]

  - by Nicholas Hill

  My question is essentially entirely in the title, but let me add some points to prevent some "why on earth would you want to do that" sort of answers: This is more of a mind experiment than an attempt to implement real software. For fun. Don't worry about computational speed or the number of available memory bytes. Computers get faster and better all of the time. Imagine we have two data files: Mother.dna and Father.dna. What else would be required? (Bonus point for someone who tells me approx how many GB each file will be, and if the size of the files are exactly the same number of bytes for everyone alive on Earth!) There would ideally need to be a way to see what the egg becomes as it becomes a human adult. If you fancy, feel free to outline the design. I am initially thinking that there'd need to be some sort of volumetric voxel-based 3D environment for simulation purposes.

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• Algorithm for optimal combination of two variables

  - by AlanChavez

  I'm looking for an algorithm that would be able to determine the optimal combination of two variables, but I'm not sure where to start looking. For example, if I have 10,000 rows in a database and each row contains price, and square feet is there any algorithm out there that will be able to determine what combination of price and sq ft is optimal. I know this is vague, but I assume is along the lines of Fuzzy logic and fuzzy sets, but I'm not sure and I'd like to start digging in the right field to see if I can come up with something that solves my problem.

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• Labeling algorithm for points

  - by Qwertie

  I need an algorithm to place horizontal text labels for multiple series of points on the screen (basically I need to show timestamps and other information for a history of moving objects on a map; in general there are multiple data points per object). The text labels should appear close to their points--above, below, or on the right side--but should not overlap other points or text labels. Does anyone know an algorithm/heuristic for this?

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• Calculate pi to an accuracy of 5 decimal places?

  - by pgras

  In this message at point 18 I saw following programming question: Given that Pi can be estimated using the function 4 * (1 – 1/3 + 1/5 – 1/7 + …) with more terms giving greater accuracy, write a function that calculates Pi to an accuracy of 5 decimal places. So I know how to implement the given function and how to choose how "far" I should calculate, but how can I tell when I've reached the "accuracy of 5 decimal places" ?

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• Looking for a dynamic programming solution

  - by krammer

  Given a sequence of integers in range 1 to n. Each number can appear at most once. Let there be a symbol X in the sequence which means remove the minimum element from the list. There can be an arbitrarily number of X in the sequence. Example: 1,3,4,X,5,2,X The output is 1,2. We need to find the best way to perform this operation. The solution I have been thinking is: Scan the sequence from left to right and count number of X which takes O(n) time. Perform partial sorting and find the k smallest elements (k = number of X) which takes O(n+klogk) time using median of medians. Is there a better way to solve this problem using dynamic programming or any other way ?

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• Tiling Problem Solutions for Various Size "Dominoes"

  - by user67081

  I've got an interesting tiling problem, I have a large square image (size 128k so 131072 squares) with dimensons 256x512... I want to fill this image with certain grain types (a 1x1 tile, a 1x2 strip, a 2x1 strip, and 2x2 square) and have no overlap, no holes, and no extension past the image boundary. Given some probability for each of these grain types, a list of the number required to be placed is generated for each. Obviously an iterative/brute force method doesn't work well here if we just randomly place the pieces, instead a certain algorithm is required. 1) all 2x2 square grains are randomly placed until exhaustion. 2) 1x2 and 2x1 grains are randomly placed alternatively until exhaustion 3) the remaining 1x1 tiles are placed to fill in all holes. It turns out this algorithm works pretty well for some cases and has no problem filling the entire image, however as you might guess, increasing the probability (and thus number) of 1x2 and 2x1 grains eventually causes the placement to stall (since there are too many holes created by the strips and not all them can be placed). My approach to this solution has been as follows: 1) Create a mini-image of size 8x8 or 16x16. 2) Fill this image randomly and following the algorithm specified above so that the desired probability of the entire image is realized in the mini-image. 3) Create N of these mini-images and then randomly successively place them in the large image. Unfortunately there are some downfalls to this simplification. 1) given the small size of the mini-images, nailing an exact probability for the entire image is not possible. Example if I want p(2x1)=P(1x2)=0.4, the mini image may only give 0.41 as the closes probability. 2) The mini-images create a pseudo boundary where no overlaps occur which isn't really descriptive of the model this is being used for. 3) There is only a fixed number of mini-images so i'm not sure how random this really is. I'm really just looking to brainstorm about possible solutions to this. My main concern is really to nail down closer probabilities, now one might suggest I just increase the mini-image size. Well I have, and it turns out that in certain cases(p(1x2)=p(2x1)=0.5) the mini-image 16x16 isn't even iteratively solvable.. So it's pretty obvious how difficult it is to randomly solve this for anything greater than 8x8 sizes.. So I'd love to hear some ideas. Thanks

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