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• Python structure mistake

  - by jaddy123

  I'm writing a program in which I can Reverse the sequence and Replace all As with Ts, all Cs with Gs, all Gs with Cs, and all Ts with As. the program is to read a sequence of bases and output the reverse complement sequence. I am having trouble to do it so can anyone please help me with this by having a look on my code: word = raw_input("Enter sequence: ") a = word.replace('A', 'T') b = word.replace('C', 'G') c = word.replace('G', 'C') d = word.replace('T', 'A') if a == word and b == word and c == word and d == word: print "Reverse complement sequence: ", word And I want this sort of output: Enter sequence: CGGTGATGCAAGG Reverse complement sequence: CCTTGCATCACCG Regards

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• F# insert/remove item from list

  - by Timothy

  How should I go about removing a given element from a list? As an example, say I have list ['A'; 'B'; 'C'; 'D'; 'E'] and want to remove the element at index 2 to produce the list ['A'; 'B'; 'D'; 'E']? I've already written the following code which accomplishes the task, but it seems rather inefficient to traverse the start of the list when I already know the index. let remove lst i = let rec remove lst lst' = match lst with | [] -> lst' | h::t -> if List.length lst = i then lst' @ t else remove t (lst' @ [h]) remove lst [] let myList = ['A'; 'B'; 'C'; 'D'; 'E'] let newList = remove myList 2 Alternatively, how should I insert an element at a given position? My code is similar to the above approach and most likely inefficient as well. let insert lst i x = let rec insert lst lst' = match lst with | [] -> lst' | h::t -> if List.length lst = i then lst' @ [x] @ lst else insert t (lst' @ [h]) insert lst [] let myList = ['A'; 'B'; 'D'; 'E'] let newList = insert myList 2 'C'

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• How to make disconnected objects connected by adding a shortest path using MATLAB?

  - by user198729

  bwlabel can be used to get disconnected objects in an image: [L Ne] = bwlabel(image); I want to make the objects connected by adding a shortest path where necessary. How do I approach this?

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• R implementation of sorting by reversals

  - by user1357015

  I was wondering if there is an implementation in R where it sorts a permutation of n numbers into the original 1...n sequence and provides the number of reversals needed. Eg an implementation of the "sorting by reversals" or "sorting by translocation" as outlined in this ppt. Specifically, I have a permutation of a sequence of n elements, pi(n), and I want to figure out how close it is to the original sequence. The number of reversals seems a good metric. Thanks!

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• Optimizing / simplifying a path

  - by user146780

  Say I have a path with 150 nodes / verticies. How could I simplify if so that for example a straight line with 3 verticies, would remove the middle one since it does nothing to add to the path. Also how could I avoid destroying sharp corners? And how could I remove tiny variations and have smooth curves remaining. Thanks

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• Intersection() and Except() is too slow with large collections of custom objects

  - by Theo

  I am importing data from another database. My process is importing data from a remote DB into a List<DataModel> named remoteData and also importing data from the local DB into a List<DataModel> named localData. I am then using LINQ to create a list of records that are different so that I can update the local DB to match the data pulled from remote DB. Like this: var outdatedData = this.localData.Intersect(this.remoteData, new OutdatedDataComparer()).ToList(); I am then using LINQ to create a list of records that no longer exist in remoteData, but do exist in localData, so that I delete them from local database. Like this: var oldData = this.localData.Except(this.remoteData, new MatchingDataComparer()).ToList(); I am then using LINQ to do the opposite of the above to add the new data to the local database. Like this: var newData = this.remoteData.Except(this.localData, new MatchingDataComparer()).ToList(); Each collection imports about 70k records, and each of the 3 LINQ operation take between 5 - 10 minutes to complete. How can I make this faster? Here is the object the collections are using: internal class DataModel { public string Key1{ get; set; } public string Key2{ get; set; } public string Value1{ get; set; } public string Value2{ get; set; } public byte? Value3{ get; set; } } The comparer used to check for outdated records: class OutdatedDataComparer : IEqualityComparer<DataModel> { public bool Equals(DataModel x, DataModel y) { var e = string.Equals(x.Key1, y.Key1) && string.Equals(x.Key2, y.Key2) && ( !string.Equals(x.Value1, y.Value1) || !string.Equals(x.Value2, y.Value2) || x.Value3 != y.Value3 ); return e; } public int GetHashCode(DataModel obj) { return 0; } } The comparer used to find old and new records: internal class MatchingDataComparer : IEqualityComparer<DataModel> { public bool Equals(DataModel x, DataModel y) { return string.Equals(x.Key1, y.Key1) && string.Equals(x.Key2, y.Key2); } public int GetHashCode(DataModel obj) { return 0; } }

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• Fast matrix transposition in Python

  - by psihodelia

  Is there any fast method to make a transposition of a rectangular 2D matrix in Python (non-involving any library import).? Say, if I have an array X=[[1,2,3], [4,5,6]] I need an array Y which should be a transposed version of X, so Y=[[1,4],[2,5],[3,6]].

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• Find a common element within N arrays

  - by kunjaan

  If I have N arrays, what is the best(Time complexity. Space is not important) way to find the common elements. You could just find 1 element and stop. Edit: The elements are all Numbers. Edit: These are unsorted. Please do not sort and scan. This is not a homework problem. Somebody asked me this question a long time ago. He was using a hash to solve the problem. I was thinking if SO has solved similar problems.

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• question about quicksort

  - by davit-datuashvili

  i have write code of quicksort from programming pearls here is code public class Quick{ public static void quicksort(int x[], int l,int u) { if (l>=u) return ; int t=x[l]; int i=l; int j=u; do { i++; } while (i<=u && x[i]<t); do { j--; if (i>=j) break; } while ( x[j]>t); swap(x,i,j); swap(x, l,j); quicksort(x, l,j-1); quicksort(x, j+1,u); } public static void main(String[]args){ int x[]=new int[]{55,41,59,26,53,58,97,93}; quicksort(x,0,x.length-1); for (int i=0;i<x.length;i++){ System.out.println(x[i]); } } public static void swap(int x[], int i,int j){ int s=x[i]; x[i]=x[j]; x[j]=s; } } but it does not work here is output 59 41 55 26 53 97 58 93 any idea?

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• How to find the largest power of 2 less than the given number

  - by nazar_art

  I need to find the largest power of 2 less than the given number. And I stuck and can't find any solution. Code: public class MathPow { public int largestPowerOf2 (int n) { int res = 2; while (res < n) { res =(int)Math.pow(res, 2); } return res; } } This doesn't work correctly. Testing output: Arguments Actual Expected ------------------------- 9 16 8 100 256 64 1000 65536 512 64 256 32 How to solve this issue?

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• determine if line segment is inside polygon

  - by dato

  suppose we have simple polygon(without holes) with vertices (v0,v1,....vn) my aim is to determine if for given point p(x,y) any line segment connecting this point and any vertices of polygon is inside polygon or even for given two point p(x0,y0) `p(x1,y1)` line segment connecting these two point is inside polygon? i have searched many sites about this ,but i am still confused,generally i think we have to compare coordinates of vertices and by determing coordinates of which point is less or greater to another point's coordinates,we could determine location of any line segment,but i am not sure how correct is this,please help me

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• Finding users near other user

  - by Bunny Rabbit

  what algorithms should I explore to implement a feature which lets a user find other user located near him , the latitude and the longitudes of all the user are known in advance and are fixed [not dynamic]. Also i believe that there should be a better way to store such data then simply storing the lat , long of the user against his user id in a database.What are the efficient ways to handle this ?

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• Find all numbers that appear in each of a set of lists

  - by Ankur

  I have several ArrayLists of Integer objects, stored in a HashMap. I want to get a list (ArrayList) of all the numbers (Integer objects) that appear in each list. My thinking so far is: Iterate through each ArrayList and put all the values into a HashSet This will give us a "listing" of all the values in the lists, but only once Iterate through the HashSet 2.1 With each iteration perform ArrayList.contains() 2.2 If none of the ArrayLists return false for the operation add the number to a "master list" which contains all the final values. If you can come up with something faster or more efficient, funny thing is as I wrote this I came up with a reasonably good solution. But I'll still post it just in case it is useful for someone else. But of course if you have a better way please do let me know.

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• Fast ceiling of an integer division in C / C++

  - by andand

  Given integer values x and y, C and C++ returns as the quotient q = x/y the floor of the floating point valued equivalent. I'm interestd in a method of returning the ceiling instead? For example, ceil(10/5) = 2 and ceil(11/5) = 3. The obvious approach involves something like: q = x / y; if (q * y < x) ++q; This requires an extra comparison and multiplication; and other methods I've seen (used in fact) involve casting as a float or double. Is there a more direct method that avoids the additional multiplication (or a second division) and branch, and that also avoids casting as a floating point number?

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• How can I detect common substrings in a list of strings

  - by danio

  Given a set of strings, for example: EFgreen EFgrey EntireS1 EntireS2 J27RedP1 J27GreenP1 J27RedP2 J27GreenP2 JournalP1Black JournalP1Blue JournalP1Green JournalP1Red JournalP2Black JournalP2Blue JournalP2Green I want to be able to detect that these are three sets of files: EntireS[1,2] J27[Red,Green]P[1,2] JournalP[1,2][Red,Green,Blue] Are there any known ways of approaching this problem - any published papers I can read on this? The approach I am considering is for each string look at all other strings and find the common characters and where differing characters are, trying to find sets of strings that have the most in common, but I fear that this is not very efficient and may give false positives. Note that this is not the same as 'How do I detect groups of common strings in filenames' because that assumes that a string will always have a series of digits following it. [Edited 15/09/09 to add more sample strings]

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• Special simple random number generator

  - by psihodelia

  How to create a function, which on every call generates a random integer number? This number must be most random as possible (according to uniform distribution). It is only allowed to use one static variable and at most 3 elementary steps, where each step consists of only one basic arithmetic operation of arity 1 or 2. Example: int myrandom(void){ static int x; x = some_step1; x = some_step2; x = some_step3; return x; } Basic arithmetic operations are +,-,%,and, not, xor, or, left shift, right shift, multiplication and division. Of course, no rand(), random() or similar staff is allowed.

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• How would I use for_each to delete every value in an STL map?

  - by stusmith

  Suppose I have a STL map where the values are pointers, and I want to delete them all. How would I represent the following code, but making use of std::for_each? I'm happy for solutions to use Boost. for( stdext::hash_map<int, Foo *>::iterator ir = myMap.begin(); ir != myMap.end(); ++ir ) { delete ir->second; // delete all the (Foo *) values. } (I've found Boost's checked_delete, but I'm not sure how to apply that to the pair<int, Foo *> that the iterator represents). (Also, for the purposes of this question, ignore the fact that storing raw pointers that need deleting in an STL container isn't very sensible).

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• Simple Big O with lg(n) proof

  - by halohunter

  I'm attempting to guess and prove the Big O for: f(n) = n^3 - 7n^2 + nlg(n) + 10 I guess that big O is n^3 as it is the term with the largest order of growth However, I'm having trouble proving it. My unsuccesful attempt follows: f(n) <= cg(n) f(n) <= n^3 - 7n^2 + nlg(n) + 10 <= cn^3 f(n) <= n^3 + (n^3)*lg(n) + 10n^3 <= cn^3 f(n) <= N^3(11 + lg(n)) <= cn^3 so 11 + lg(n) = c But this can't be right because c must be constant. What am I doing wrong?

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• Separating text and graphics in an image

  - by avd

  I dont know whether should I post this question here or not? But if someone knows it, please answer? What are the algorithms for determining which region in an image is text and which one is graphic? Means how to separate such regions? (figure or diagram)

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• If the n-body problem is chaotic, why isn't it used as a RNG?

  - by David Titarenco

  I'm probably missing something pretty basic here, but if the n-body problem yields chaotic results (except in specific highly-symmetric conditions), couldn't it be used as a "true" random number generator (with initial pseudo-random seeds for masses and velocities) given its non-deterministic nature?

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• algorithms that destruct and copy_construct

  - by FredOverflow

  I am currently building my own toy vector for fun, and I was wondering if there is something like the following in the current or next standard or in Boost? template<class T> void destruct(T* begin, T* end) { while (begin != end) { begin -> ~T(); ++begin; } } template<class T> T* copy_construct(T* begin, T* end, T* dst) { while (begin != end) { new(dst) T(*begin); ++begin; ++dst; } return dst; }

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• How can we find second maximum from array efficiently?

  - by Xinus

  Is it possible to find the second maximum number from an array of integers by traversing the array only once? As an example, I have a array of five integers from which I want to find second maximum number. Here is an attempt I gave in the interview: #define MIN -1 int main() { int max=MIN,second_max=MIN; int arr[6]={0,1,2,3,4,5}; for(int i=0;i<5;i++){ cout<<"::"<<arr[i]; } for(int i=0;i<5;i++){ if(arr[i]>max){ second_max=max; max=arr[i]; } } cout<<endl<<"Second Max:"<<second_max; int i; cin>>i; return 0; } The interviewer, however, came up with the test case int arr[6]={5,4,3,2,1,0};, which prevents it from going to the if condition the second time. I said to the interviewer that the only way would be to parse the array two times (two for loops). Does anybody have a better solution?

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• finding middle element of an array

  - by senthil

  Hi all, I came cross a question in my interview. Question: Array of integers will be given as the input and you should find out the middle element when sorted , but without sorting. For Example. Input: 1,3,5,4,2 Output: 3 When you sort the given input array, it will be 1,2,3,4,5 where middle element is 3. You should find this in one pass without sorting. Any solutions for this?

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• Solving a recurrence T(n) = 2T(n/2) + n^4

  - by user563454

  I am studying using the MIT Courseware and the CLRS book Introduction to Algorithms. Solving recurrence T(n) = 2T(n/2) + n4 (page 107) If I make a recurrence tree I get: level 0 n^4 level 1 2(n/2)^4 level 2 4(n/4)^4 level 3 8(n/8)^4 The tree has lg(n) levels. Therefore the recurrence is T(n) = Theta(lg(n)n^4)) But, If I use the Master method I get. Apply case 3: T(n) = Theta(n^4) If I apply the substitution method both seem to hold. Which one is ri?

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• User submitted content filtering

  - by Jim

  Hey all, Does anyone have any ideas on what could be used as a way to filter untrustworthy user submitted content? Take Yelp for instance, they would need to prevent competitors writing business reviews on their competitors. They would need to prevent business owners favourably reviewing their own business, or forcing friends/family to do so. They would need to prevent poor quality reviews from affecting a businesses rating and so on. I can't think what they might use to do this: Prevent multiple users from the same IP reviewing certain things Prevent business owners reviewing their own business (maybe even other businesses in the same categories as their own?) Somehow determine what a review is about and what the actual intentions behind it are Other than the first and second points, I can't think of any clever/easy way to filter potentially harmful reviews from being made available, other than a human doing it. Obviously for a site the size of Yelp this wouldn't be feasible, so what parameters could they take into consideration? Even with human intervention, how would anyone know it was the owners best buddy writing a fake review without knowing the people? I'm using this as an example in a larger study on the subject of filtering user content automatically. Does anyone have any ideas how these systems may work and what they take into consideration? Thanks!

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