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• Finding a small image in a bigger one

  - by tur1ng

  Given an image with a large dimension ( 1.000 x 1.000). What is a good approach to find a small image (e.g. 50 x 50) in the big one? The smaller image can be rotated and differ in the size, but only with a 1:1 ratio. It's not related to any programming language - I'm just interested in pattern recognition. Thank you.

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• STL vector reserve() and copy()

  - by natersoz

  Greetings, I am trying to perform a copy from one vector (vec1) to another vector (vec2) using the following 2 abbreviated lines of code (full test app follows): vec2.reserve( vec1.size() ); copy(vec1.begin(), vec1.end(), vec2.begin()); While the call to vec2 sets the capacity of vector vec2, the copying of data to vec2 seems to not fill in the values from vec1 to vec2. Replacing the copy() function with calls to push_back() works as expected. What am I missing here? Thanks for your help. vectest.cpp test program followed by resulting output follows. Compiler: gcc 3.4.4 on cygwin. Nat /** * vectest.cpp */ #include <iostream> #include <vector> using namespace std; int main() { vector<int> vec1; vector<int> vec2; vec1.push_back(1); vec1.push_back(2); vec1.push_back(3); vec1.push_back(4); vec1.push_back(5); vec1.push_back(6); vec1.push_back(7); vec2.reserve( vec1.size() ); copy(vec1.begin(), vec1.end(), vec2.begin()); cout << "vec1.size() = " << vec1.size() << endl; cout << "vec1.capacity() = " << vec1.capacity() << endl; cout << "vec1: "; for( vector<int>::const_iterator iter = vec1.begin(); iter < vec1.end(); ++iter ) { cout << *iter << " "; } cout << endl; cout << "vec2.size() = " << vec2.size() << endl; cout << "vec2.capacity() = " << vec2.capacity() << endl; cout << "vec2: "; for( vector<int>::const_iterator iter = vec2.begin(); iter < vec2.end(); ++iter ) { cout << *iter << endl; } cout << endl; } output: vec1.size() = 7 vec1.capacity() = 8 vec1: 1 2 3 4 5 6 7 vec2.size() = 0 vec2.capacity() = 7 vec2:

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• How to check if a integer is sum of given integers?

  - by p3trix

  Lets say I have a integer result and an array of integers, lets say [a,b,c] (not a fixed length). I need to detect if result=a*i +b*j + c*k, with i,j,k=0. I prefer a solution in C/C# if it is possible. PS The problem is from a reservation system, a trip can be sold if its durations is a combination of given durations. Thanks!

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• Texture coordintes for a polygon and a square texture

  - by user146780

  basically I have a texture. I also have a lets say octagon (or any polygon). I find that octagon's bounding box. Let's say my texture is the size of the octagon's bounding box. How could I figure out the texture coordinates so that the texture maps to it. To clarify, lets say you had a square of tin foil and cut the octagon out you'd be left with a tin foil textured polygon.I'm just not sure how to figure it out for an arbitrary polygon. Thanks

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• Choice of programming language for learning data structures and algorithms

  - by bguiz

  Which programming language would you recommend to learn about data structures and algorithms in? Considering the follwing: Personal experience Language features (pointers, OO, etc) Suitability for learning DS & A concepts I ask because there are some books out there that are programming language-agnostic (written from a Mathematical perspective, and use pseudocode). If I learn from one of these I would like to work out the algorithms in a chosen language. Then, there are other books which introduce DS & A concepts with examples in a particular programming laguage - and I would follow these examples as well. Either way, I have to choose a language, and I would like to stick to one throughout. Which one best fits the bill.

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• Grouping php array items based on user and created time

  - by Jim

  This is an array of objects showing a user uploading photos: Array ( [12] => stdClass Object ( [type] => photo [created] => 2010-05-14 23:36:41 [user] => stdClass Object ( [id] => 760 [username] => mrsmith ) [photo] => stdClass Object ( [id] => 4181 ) ) [44] => stdClass Object ( [type] => photo [created] => 2010-05-14 23:37:15 [user] => stdClass Object ( [id] => 760 [username] => mrsmith ) [photo] => stdClass Object ( [id] => 4180 ) ) ) However instead of showing: mr smith uploaded one photo mr smith uploaded one photo I'd like to display: mr smith uploaded two photos by grouping similar items, grouping by user ID and them having added them within, let's say 15 minutes of each other. So I'd like to get the array in this sort of shape: Array ( [12] => stdClass Object ( [type] => photo [created] => 2010-05-14 23:36:41 [user] => stdClass Object ( [id] => 760 [username] => mrsmith ) [photos] => Array ( [0] => stdClass Object ( [id] => 4181 ) [1] => stdClass Object ( [id] => 4180 ) ) ) ) preserving the first item of the group and it's created time, and supplementing it with any other groupable photos and then unsetting any items that were grouped (so the final array doesn't have key 44 anymore as it was grouped in with 12). The array contains other actions than just photos, hence the original keys of 12 and 44. I just can't figure out a way to do this efficiently. I used to use MySQL and PHP to do this but am trying to just use pure PHP for caching reasons. Can anyone shed any insights? I thought about going through each item and seeing if I can group it with the previous one in the array but the previous one might not necessarily be relevant or even a photo. I've got total brain freeze :(

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• Test if single linked list is circular by traversing it only once

  - by user1589754

  I am a fresher and I was asked this question in a recent interview I gave. The question was --- By traversing each element of linked list just once find if the single linked list is circular at any point. To this I answered that we will store reference of each node while traversing the list in another linked list and for every node in the list being tested we will find if the reference exists in the list I am storing the references. The interviewer said that he needs a more optimized way to solve this problem. Can anyone please tell me what would be a more optimized method to solve this problem.

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• Given 4 objects, how to figure out whether exactly 2 have a certain property

  - by Cocorico

  Hi guys! I have another question on how to make most elegant solution to this problem, since I cannot afford to go to computer school right so my actual "pure programming" CS knowledge is not perfect or great. This is basically an algorhythm problem (someone please correct me if I am using that wrong, since I don't want to keep saying them and embarass myself) I have 4 objects. Each of them has an species property that can either be a dog, cat, pig or monkey. So a sample situation could be: object1.species=pig object2.species=cat object3.species=pig object4.species=dog Now, if I want to figure out if all 4 are the same species, I know I could just say: if ( (object1.species==object2.species) && (object2.species==object3.species) && (object3.species==object4.species) ) { // They are all the same animal (don't care WHICH animal they are) } But that isn't so elegant right? And if I suddenly want to know if EXACTLY 3 or 2 of them are the same species (don't care WHICH species it is though), suddenly I'm in spaghetti code. I am using Objective C although I don't know if that matters really, since the most elegant solution to this is I assume the same in all languages conceptually? Anyone got good idea? Thanks!!

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• Learning Algorithms and Data Structures Fundamentals

  - by valya

  Can you recommend me a book or (better!) a site with many hard problems and exercises about data structures? I'm already answering project Euler questions, but these questions are about interesting, but uncommon algorithms. I hardly used even a simple tree. Maybe there is a site with exercises like: hey, you need to calculate this: ... . Do it using a tree. Now do it using a zipper. Upload your C (Haskell, Lisp, even Pascal or Fortress go) solution. Oh, your solution is so slow! Self-education is very hard then you trying to learn very common, fundamental things. How can I help myself with them without attending to courses or whatever?

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• recursion tree and binary tree cost calculation

  - by Tony

  Hi all, I've got the following recursion: T(n) = T(n/3) + T(2n/3) + O(n) The height of the tree would be log3/2 of 2. Now the recursion tree for this recurrence is not a complete binary tree. It has missing nodes lower down. This makes sense to me, however I don't understand how the following small omega notation relates to the cost of all leaves in the tree. "... the total cost of all leaves would then be Theta (n^log3/2 of 2) which, since log3/2 of 2 is a constant strictly greater then 1, is small omega(n lg n)." Can someone please help me understand how the Theta(n^log3/2 of 2) becomes small omega(n lg n)?

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• PRIME1 problem in SPOj. i get a SIGSEGV error y?pls help me out

  - by R Karthikeyan

  #include<stdio.h> main() { long long int m,n,i,j; int t; scanf("%d",&t); while(t--) { scanf("%lld",&m); scanf("%lld",&n); long long int a[n+2]; for(i=0;i<=n;i++) { a[i]=1; } for(i=2;i<=sqrt(n);i++) { j=2; while((i*j)<=n) { a[i*j]=0; j++; } } for(i=m;i<=n;i++) { if(i==1) continue; if(a[i]!=0) printf("%lld\n",i); } } return 0; }

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• Maximum number of characters using keystrokes A, Ctrl+A, Ctrl+C and Ctrl+V

  - by munda

  This is an interview question from google. I am not able to solve it by myself. Can somebody shed some light? Write a program to print the sequence of keystrokes such that it generates the maximum number of character 'A's. You are allowed to use only 4 keys: A, Ctrl+A, Ctrl+C and Ctrl+V. Only N keystrokes are allowed. All Ctrl+ characters are considered as one keystroke, so Ctrl+A is one keystroke. For example, the sequence A, Ctrl+A, Ctrl+C, Ctrl+V generates two A's in 4 keystrokes. Ctrl+A is Select All Ctrl+C is Copy Ctrl+V is Paste I did some mathematics. For any N, using x numbers of A's , one Ctrl+A, one Ctrl+C and y Ctrl+V, we can generate max ((N-1)/2)2 number of A's. For some N M, it is better to use as many Ctrl+A's, Ctrl+C and Ctrl+V sequences as it doubles the number of A's. The sequence Ctrl+A, Ctrl+V, Ctrl+C will not overwrite the existing selection. It will append the copied selection to selected one.

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• Python script to calculate aded combinations from a dictionary

  - by dayde

  I am trying to write a script that will take a dictionary of items, each containing properties of values from 0 - 10, and add the various elements to select which combination of items achieve the desired totals. I also need the script to do this, using only items that have the same "slot" in common. For example: item_list = { 'item_1': {'slot': 'top', 'prop_a': 2, 'prop_b': 0, 'prop_c': 2, 'prop_d': 1 }, 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 }, 'item_3': {'slot': 'top', 'prop_a': 2, 'prop_b': 5, 'prop_c': 2, 'prop_d':-2 }, 'item_4': {'slot': 'mid', 'prop_a': 5, 'prop_b': 5, 'prop_c':-5, 'prop_d': 0 }, 'item_5': {'slot': 'mid', 'prop_a':10, 'prop_b': 0, 'prop_c':-5, 'prop_d': 0 }, 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 }, 'item_7': {'slot': 'bot', 'prop_a': 1, 'prop_b': 3, 'prop_c':-4, 'prop_d': 4 }, 'item_8': {'slot': 'bot', 'prop_a': 2, 'prop_b': 2, 'prop_c': 0, 'prop_d': 0 }, 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 }, } The script would then need to select which combinations from the "item_list" dict that using 1 item per "slot" that would achieve a desired result when added. For example, if the desired result was: 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0, the script would select 'item_2', 'item_6', and 'item_9', along with any other combination that worked. 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 } 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 } 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 } 'total': 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0 Any ideas how to accomplish this? It does not need to be in python, or even a thorough script, but just an explanation on how to do this in theory would be enough for me. I have tried working out looping through every combination, but that seems to very quickly get our of hand and unmanageable. The actual script will need to do this for about 1,000 items using 20 different "slots", each with 8 properties. Thanks for the help!

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• bellman forge, dijkstra's, prim's algorithm, kruskals, directed acrylic graph

  - by bfpri

  What are some real life examples where each one of these are used?

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• circuit/block-diagram drawing

  - by JCLL

  I'm looking for either algorithms or visualization tool for (nice) circuit/block-diagram drawing. I am also interested in a general formulation of the problem. By "circuit drawing", I mean the capability of exploring place & route for block-diagrams (rectangles) with I/O ports and their connections (wires). These block-diagrams can be hierarchical i.e some blocks may have some nested internal sub-structure etc. This topic is strongly related to classical graph-drawing, with the supplemental constraint of the need to take ports location into account, and possibly the shape of the blocks (rectangle of various sizes). Graphviz tools do not respond to the problem (at least my previous experiments have not been satisfactory). Force-directed algorithms retain my attention, but I have just found papers on classical directed graphs. Any hints ?

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• Number of different elements in an array.

  - by AB

  Is it possible to compute the number of different elements in an array in linear time and constant space? Let us say it's an array of long integers, and you can not allocate an array of length sizeof(long). P.S. Not homework, just curious. I've got a book that sort of implies that it is possible.

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• total number of magic square from 9 numbers

  - by Peeyush

  9 numbers need to be arranged in a magic number square. A magic number square is a square of numbers that is arranged such that every row and column has the same sum.(condition for diagonal has been relaxed) For example: 1 2 3 3 2 1 2 2 2 How do we calculate total number of distinct magic square from 9 numbers. Two magic number squares are distinct if they differ in value at one or more positions. For example, there is only one magic number square that can be made of 9 instances of the same number. e.g. for these 9 numbers { 4, 4, 4, 4, 4, 4, 4, 4, 4 }, answer should be 1. Also the complexity should be optimal. Do we need to iterate through all the permutations , discarding if a[0]+a[1]+a[2] %3!=0 such combinations ? moreover how do we remove duplicate magic square?

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• problem with evolutionary algorithms degrading into simulated annealing: mutation too small?

  - by Schnalle

  i have a problem understanding evolutionary algorithms. i tried using this technique several times, but i always ran into the same problem: degeneration into simulated annealing. lets say my initial population, with fitness in brackets, is: A (7), B (9), C (14), D (19) after mating and mutation i have following children: AB (8.3), AC (12.2), AD (14.1), BC(11), BD (14.7), CD (17) after elimination of the weakest, we get A, AB, B, AC next turn, AB will mate again with a result around 8, pushing AC out. next turn, AB again, pushing B out (assuming mutation changes fitness mostly in the 1 range). now, after only a few turns the pool is populated with the originally fittest candidates (A, B) and mutations of those two (AB). this happens regardless of the size of the initial pool, it just takes a bit longer. say, with an initial population of 50 it takes 50 turns, then all others are eliminated, turning the whole setup in a more complicated simulated annealing. in the beginning i also mated canditates with themselves, worsening the problem. so, what do i miss? are my mutation rates simply too small and will it go away if i increase them? here's the project i'm using it for: http://stefan.schallerl.com/simuan-grid-grad/ yeah, the code is buggy and the interface sucks, but i'm too lazy to fix it right now - and be careful, it may lock up your browser. better use chrome, even thought firefox is not slower than chrome for once (probably the tracing for the image comparison pays off, yay!). if anyone is interested, the code can be found here. here i just dropped the ev-alg idea and went for simulated annealing. ps: i'm not even sure about simulated annealing - it is like evolutionary algorithms, just with a population size of one, right?

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• Efficient data structure design

  - by Sway

  Hi there, I need to match a series of user inputed words against a large dictionary of words (to ensure the entered value exists). So if the user entered: "orange" it should match an entry "orange' in the dictionary. Now the catch is that the user can also enter a wildcard or series of wildcard characters like say "or__ge" which would also match "orange" The key requirements are: * this should be as fast as possible. * use the smallest amount of memory to achieve it. If the size of the word list was small I could use a string containing all the words and use regular expressions. however given that the word list could contain potentially hundreds of thousands of enteries I'm assuming this wouldn't work. So is some sort of 'tree' be the way to go for this...? Any thoughts or suggestions on this would be totally appreciated! Thanks in advance, Matt

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• Fastest primality test

  - by Grigory Javadyan

  Hi. Could you suggest a fast, deterministic method that is usable in practice, for testing if a large number is prime or not? Also, I would like to know how to use non-deterministic primality tests correctly. For example, if I'm using such a method, I can be sure that a number is not prime if the output is "no", but what about the other case, when the output is "probably"? Do I have to test for primality manually in this case? Thanks in advance.

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• mod,prime -> inverse possible

  - by Piet

  Hi all. I was wondering if one can do the following: We have: X is a product of N-primes, thus I assume unique. C is a constant. We can assure that C is a number that is part of the N-primes or not. Whichever will work best. Thus: X mod C = Z We have Z and C and we know that X was a product of N-primes, where N is restricted lets say first 100 primes. Is there anyway we can get back X?

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• Chain call in clojure?

  - by Konrad Garus

  I'm trying to implement sieve of Eratosthenes in Clojure. One approach I would like to test is this: Get range (2 3 4 5 6 ... N) For 2 <= i <= N Pass my range through filter that removes multiplies of i For i+1th iteration, use result of the previous filtering I know I could do it with loop/recur, but this is causing stack overflow errors (for some reason tail call optimization is not applied). How can I do it iteratively? I mean invoking N calls to the same routine, passing result of ith iteration to i+1th.

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• Recommend an algorithms exercise book?

  - by Parappa

  I have a little book called Problems on Algorithms by Ian Parberry which is chock full of exercises related to the study of algorithms. Can anybody recommend similar books? What I am not looking for are recommendations of good books related to algorithms or the theory of computation. Introduction to Algorithms is a good one, and of course there's the Knuth stuff. Ideally I want to know of any books that are light on instructional material and heavy on sample problems. In a nutshell, exercise books. Preferably dedicated to algorithms rather than general logic or other math problems. By the way, the Parberry book does not seem to be in print, but it is available as a PDF dowload.

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• Why do some questions get closed for no reason? [closed]

  - by IVlad

  Recently there was a question asking about generating all subsets of a set using a stack and a queue, which was closed (and now deleted it seems) as not a real question for no good reason, since it didn't fit into any of these conditions: It's difficult to tell what is being asked here. No, it was clear what was being asked. This question is ambiguous, vague, incomplete, or rhetorical and cannot be reasonably answered in its current form. Not ambiguous, not vague, not incomplete, definitely not rhetorical and could easily be answered if one knew the solution. Now, the exact same thing has happened with this question: http://stackoverflow.com/questions/2791982/a-shortest-path-problem-with-superheroes-and-intergalactic-journeys/2793746#2793746 I am interested in hearing a logical argument for why that question is either ambiguous, vague, incomplete, rhetorical or cannot reasonably be answered in its current form. It seems that (the same bunch of) people like to close questions that they think are homework questions, especially when they think people want to be served the solution on a platter, which is also not the case: Any suggestions or ideas of how this problem might be solved would be most welcomed. Most of the time the people asking these questions are very reasonable and appreciate even the most vague idea, yet their question is closed. Let's go further and assume that it IS a homework problem. So what? When I registered here I didn't see any rule that said not to post homework problems, nor do I see such a rule now. What is wrong with posting homework problems that makes people hunt them down with a passion to close them without even reading the entire question body? This site is full of questions asked by people who get paid to know the things they are asking, yet their questions are considered fine. How is solving someone's homework problem worse? In some places (like where I live), computer science is a mandatory high school subject, and not everyone is interested in it. How is helping at least those people worse than doing someone's JOB? Not answering homework questions is fine and it's everyone's choice, but I consider closing them to be an act of power abuse, selfishness, and an insult to the fellow community members who are also interested in a solution or want feedback on their proposed solution. So my questions are: - Why do questions like the above get closed for reasons that do not apply? Why do you close them? Why don't you? - Why doesn't a vote to reopen a question reopen it automatically? Needing 5 votes for a reopen takes too long, and it's not fair because one reopen vote basically cancels out a close vote, making it 4 close votes (or 5 to 1, which is the same as only 4 people wanting to close the question), which isn't enough to close the question. I think a question should only be closed when CloseVotes - ReopenVotes >= 5. I'm hoping this will stay up, but I realize it probably won't. In either case, I think this is worth saying and discussing, since it IS community-related.

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• UVA Online Judge 3n+1 : Right answer is Wrong answer

  - by Samuraisoulification

  Ive been toying with this problem for more than a week now, I have optimized it a lot, I seem to be getting the right answer, since it's the same as when I compare it to other's answers that got accepted, but I keep getting wrong answer. Im not sure what's going on! Anyone have any advice? I think it's a problem with the input or the output, cause Im not exactly sure how this judge thing works. So if anyone could pinpoint the problem, and also give me any advice on my code, Id be very appreciative!!! #include <iostream> #include <cstdlib> #include <stdio.h> #include <vector> using namespace std; class Node{ // node for each number that has teh cycles and number private: int number; int cycles; bool cycleset; // so it knows whether to re-set the cycle public: Node(int num){ number = num; cycles = 0; cycleset = false; } int getnumber(){ return number; } int getcycles(){ return cycles; } void setnumber(int num){ number = num; } void setcycles(int num){ cycles = num; cycleset = true; } bool cycled(){ return cycleset; } }; class Cycler{ private: vector<Node> cycleArray; int biggest; int cycleReal(unsigned int number){ // actually cycles through the number int cycles = 1; if (number != 1) { if (number < 1000000) { // makes sure it's in vector bounds if (!cycleArray[number].cycled()) { // sees if it's been cycled if (number % 2 == 0) { cycles += this->cycleReal((number / 2)); } else { cycles += this->cycleReal((3 * number) + 1); } } else { // if cycled get the number of cycles and don't re-calculate, ends recursion cycles = cycleArray[number].getcycles(); } } else { // continues recursing if it's too big for the vector if (number % 2 == 0) { cycles += this->cycleReal((number / 2)); } else { cycles += this->cycleReal((3 * number) + 1); } } } if(number < 1000000){ // sets cycles table for the number in the vector if (!cycleArray[number].cycled()) { cycleArray[number].setcycles(cycles); } } return cycles; } public: Cycler(){ biggest = 0; for(int i = 0; i < 1000000; i++){ // initialize the vector, set the numbers Node temp(i); cycleArray.push_back(temp); } } int cycle(int start, int end){ // cycles thorugh the inputted numbers. int size = 0; for(int i = start; i < end ; i++){ size = this->cycleReal(i); if(size > biggest){ biggest = size; } } int temp = biggest; biggest = 0; return temp; } int getBiggest(){ return biggest; } }; int main() { Cycler testCycler; int i, j; while(cin>>i>>j){ //read in untill \n int biggest = 0; if(i > j){ biggest = testCycler.cycle(j, i); }else{ biggest = testCycler.cycle(i, j); } cout << i << " " << j << " " << biggest << endl; } return 0; }

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