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  • Catching the return of main function before it deallocates resources

    - by EpsilonVector
    I'm trying to implement user threads in Linux kernel 2.4, and I ran into something problematic and unexpected. Background: a thread basically executes a single function and dies, except that when I call thread_create for the first time it must turn main() into a thread as well (by default it is not a thread until the first call, which is also when all the related data structures are allocated). Since a thread executes a function and dies, we don't need to "return" anywhere with it, but we do need to save the return value to be reclaimed later with thread_join, so the hack I came up with was: when I allocate the thread stack I place a return address that points to a thread_return_handler function, which deallocates the thread, makes it a zombie, and saves its return value for later. This works for "just run a function and die" threads, but is very problematic with the main thread. Since it actually is the main function, if it returns before the other threads finish the normal return mechanism kicks in, and deallocates all the shared resources, thus screwing up all the running threads. I need to keep it from doing that. Any ideas on how it can be done?

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  • Recursion problem in algorithm

    - by Marthin
    I'm not sure if this is the right place to post this, but the problem actually belongs to a programming assignment. Solve the recursion: T(0) = 2; T(n) = T(n-1) + 2; Solution: T(n) = 2(n+1) Could someone please show me how they got to that solution?

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  • Returnimng collection of interfaces

    - by apoorv020
    I have created the following interface public interface ISolutionSpace { public boolean isFeasible(); public boolean isSolution(); public Set<ISolutionSpace> generateChildren(); } However, in the implementation of ISolutionSpace in a class called EightQueenSolutionSpace, I am going to return a set of EightQueenSolutionSpace instances, like the following stub: @Override public Set<ISolutionSpace> generateChildren() { return new HashSet<EightQueenSolutionSpace>(); } However this stub wont compile. What changes do I need to make? EDIT: I tried 'HashSet' as well and had tried using the extends keyword. However since 'ISolutionSpace' is an interface and EightQueenSolutionSpace is an implementation(and not a subclass) of 'ISolutionSpace', it is still not working.

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  • help implementing All Nearest Smaller Values algorithm

    - by davit-datuashvili
    http://en.wikipedia.org/wiki/All_nearest_smaller_values this is site of the problem and here is my code but i have some trouble to implement it import java.util.*; public class stack{ public static void main(String[]args){ int x[]=new int[]{ 0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15 }; Stack<Integer> st=new Stack<Integer>(); for (int a:x){ while (!st.empty() && st.pop()>=a){ System.out.println( st.pop()); if (st.empty()){ break; } else{ st.push(a); } } } } } and here is pseudo code from site S = new empty stack data structure for x in the input sequence: while S is nonempty and the top element of S is greater than or equal to x: pop S if S is empty: x has no preceding smaller value else: the nearest smaller value to x is the top element of S push x onto S

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  • Modular Inverse and BigInteger division

    - by dano82
    I've been working on the problem of calculating the modular inverse of an large integer i.e. a^-1 mod n. and have been using BigInteger's built in function modInverse to check my work. I've coded the algorithm as shown in The Handbook of Applied Cryptography by Menezes, et al. Unfortunately for me, I do not get the correct outcome for all integers. My thinking is that the line q = a.divide(b) is my problem as the divide function is not well documented (IMO)(my code suffers similarly). Does BigInteger.divide(val) round or truncate? My assumption is truncation since the docs say that it mimics int's behavior. Any other insights are appreciated. This is the code that I have been working with: private static BigInteger modInverse(BigInteger a, BigInteger b) throws ArithmeticException { //make sure a >= b if (a.compareTo(b) < 0) { BigInteger temp = a; a = b; b = temp; } //trivial case: b = 0 => a^-1 = 1 if (b.equals(BigInteger.ZERO)) { return BigInteger.ONE; } //all other cases BigInteger x2 = BigInteger.ONE; BigInteger x1 = BigInteger.ZERO; BigInteger y2 = BigInteger.ZERO; BigInteger y1 = BigInteger.ONE; BigInteger x, y, q, r; while (b.compareTo(BigInteger.ZERO) == 1) { q = a.divide(b); r = a.subtract(q.multiply(b)); x = x2.subtract(q.multiply(x1)); y = y2.subtract(q.multiply(y1)); a = b; b = r; x2 = x1; x1 = x; y2 = y1; y1 = y; } if (!a.equals(BigInteger.ONE)) throw new ArithmeticException("a and n are not coprime"); return x2; }

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  • MPI Odd/Even Compare-Split Deadlock

    - by erebel55
    I'm trying to write an MPI version of a program that runs an odd/even compare-split operation on n randomly generated elements. Process 0 should generated the elements and send nlocal of them to the other processes, (keeping the first nlocal for itself). From here, process 0 should print out it's results after running the CompareSplit algorithm. Then, receive the results from the other processes run of the algorithm. Finally, print out the results that it has just received. I have a large chunk of this already done, but I'm getting a deadlock that I can't seem to fix. I would greatly appreciate any hints that people could give me. Here is my code http://pastie.org/3742474 Right now I'm pretty sure that the deadlock is coming from the Send/Recv at lines 134 and 151. I've tried changing the Send to use "tag" instead of myrank for the tag parameter..but when I did that I just keep getting a "MPI_ERR_TAG: invalid tag" for some reason. Obviously I would also run the algorithm within the processors 0 but I took that part out for now, until I figure out what is going wrong. Any help is appreciated.

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  • what is the best algorithm to use for this problem

    - by slim
    Equilibrium index of a sequence is an index such that the sum of elements at lower indexes is equal to the sum of elements at higher indexes. For example, in a sequence A: A[0]=-7 A[1]=1 A[2]=5 A[3]=2 A[4]=-4 A[5]=3 A[6]=0 3 is an equilibrium index, because: A[0]+A[1]+A[2]=A[4]+A[5]+A[6] 6 is also an equilibrium index, because: A[0]+A[1]+A[2]+A[3]+A[4]+A[5]=0 (sum of zero elements is zero) 7 is not an equilibrium index, because it is not a valid index of sequence A. If you still have doubts, this is a precise definition: the integer k is an equilibrium index of a sequence if and only if and . Assume the sum of zero elements is equal zero. Write a function int equi(int[] A); that given a sequence, returns its equilibrium index (any) or -1 if no equilibrium indexes exist. Assume that the sequence may be very long.

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  • How can I implement a splay tree that performs the zig operation last, not first?

    - by Jakob
    For my Algorithms & Data Structures class, I've been tasked with implementing a splay tree in Haskell. My algorithm for the splay operation is as follows: If the node to be splayed is the root, the unaltered tree is returned. If the node to be splayed is one level from the root, a zig operation is performed and the resulting tree is returned. If the node to be splayed is two or more levels from the root, a zig-zig or zig-zag operation is performed on the result of splaying the subtree starting at that node, and the resulting tree is returned. This is valid according to my teacher. However, the Wikipedia description of a splay tree says the zig step "will be done only as the last step in a splay operation" whereas in my algorithm it is the first step in a splay operation. I want to implement a splay tree that performs the zig operation last instead of first, but I'm not sure how it would best be done. It seems to me that such an algorithm would become more complex, seeing as how one needs to find the node to be splayed before it can be determined whether a zig operation should be performed or not. How can I implement this in Haskell (or some other functional language)?

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  • R Tree 50,000 foot overview?

    - by roufamatic
    I'm working on a school project that involves taking a lat/long point and finding the top five closest points in a known list of places. The list is to be stored in memory, with the caveat that we must choose an "appropriate data structure" -- that is, we cannot simply store all the places in an array and compare distances one-by-one in a linear fashion. The teacher suggested grouping the place data by US State to prevent calculating the distance for places that are obviously too far away. I think I can do better. From my research online it seems like an R-Tree or one of its variants might be a neat solution. Unfortunately, that sentence is as far as I've gotten with understanding the actual technique, as the literature is simply too dense for my non-academic head. Can somebody give me a really high overview of what the process is for populating an R-Tree with lat/long data, and then traversing the tree to find those 5 nearest neighbors of a given point? Additionally the project is in C, and I don't have to reinvent the wheel on this, so if you've used an existing open source C implementation of an R Tree I'd be interested in your experiences.

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  • Trouble with arraylist and stack

    - by helloman
    I am having trouble starting out this program, I am suppose to write a program that will create an ArrayList, asking the user for 10 numbers. Then this will be put into the Array. Then after the list is made navigate it and if a number is even remove it from the ArrayList and copy it to a stack of integers. import java.io.* ; import java.util.*; public class Test { public static void main(String[] args){ Scanner input = new Scanner (System.in); ArrayList<Integer> integers = new ArrayList<Integer>(); System.out.print ("Enter Number: \n"); for (int i = 0; i < 10; i++){ integers.add(input.nextInt()); } for (int i = 0; i < 10 ; i++){ if (i %2==0) } } }

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  • Flow charts and algorithms

    - by Dave
    Hello there, I am from a networking background and completely new to algorithm and flow charts, so could you please assist me with the following? Draw flow charts for the following algorithmss: State whether a number entered at the keyboard is even or odd. Calculate the mean of a five numbers entered by the user from the keyboard Count the number of characters and the number of words that are in a text file Many thanks in advance!

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  • Linked list Recursion ...

    - by epsilon_G
    hey , I'd like to make a recursive function using C++ I make this class class linklist { private: struct node { int data; node *link; }*p; void linklist::print_num(node* p) { if (p != NULL) { cout << p->data << " "; print_num (p->link); } } in the main program what should I write ...

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  • How can I compute the average cost for this solution of the element uniqueness problem?

    - by Alceu Costa
    In the book Introduction to the Design & Analysis of Algorithms, the following solution is proposed to the element uniqueness problem: ALGORITHM UniqueElements(A[0 .. n-1]) // Determines whether all the elements in a given array are distinct // Input: An array A[0 .. n-1] // Output: Returns "true" if all the elements in A are distinct // and false otherwise. for i := 0 to n - 2 do for j := i + 1 to n - 1 do if A[i] = A[j] return false return true How can I compute the average cost (i.e. number of comparisons for a given n) for this algorithm? What is a reasonable assumption about the input?

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  • I keep getting a no match for call to error!!??

    - by Timothy Poseley
    #include <iostream> #include <string> using namespace std; // Turns a digit between 1 and 9 into its english name // Turn a number into its english name string int_name(int n) { string digit_name; { if (n == 1) return "one"; else if (n == 2) return "two"; else if (n == 3) return "three"; else if (n == 4) return "four"; else if (n == 5) return "five"; else if (n == 6) return "six"; else if (n == 7) return "seven"; else if (n == 8) return "eight"; else if (n == 9) return "nine"; return ""; } string teen_name; { if (n == 10) return "ten"; else if (n == 11) return "eleven"; else if (n == 12) return "twelve"; else if (n == 13) return "thirteen"; else if (n == 14) return "fourteen"; else if (n == 14) return "fourteen"; else if (n == 15) return "fifteen"; else if (n == 16) return "sixteen"; else if (n == 17) return "seventeen"; else if (n == 18) return "eighteen"; else if (n == 19) return "nineteen"; return ""; } string tens_name; { if (n == 2) return "twenty"; else if (n == 3) return "thirty"; else if (n == 4) return "forty"; else if (n == 5) return "fifty"; else if (n == 6) return "sixty"; else if (n == 7) return "seventy"; else if (n == 8) return "eighty"; else if (n == 9) return "ninety"; return ""; } int c = n; // the part that still needs to be converted string r; // the return value if (c >= 1000) { r = int_name(c / 1000) + " thousand"; c = c % 1000; } if (c >= 100) { r = r + " " + digit_name(c / 100) + " hundred"; c = c % 100; } if (c >= 20) { r = r + " " + tens_name(c /10); c = c % 10; } if (c >= 10) { r = r + " " + teen_name(c); c = 0; } if (c > 0) r = r + " " + digit_name(c); return r; } int main() { int n; cout << endl << endl; cout << "Please enter a positive integer: "; cin >> n; cout << endl; cout << int_name(n); cout << endl << endl; return 0; } I Keep getting this Error code: intname2.cpp: In function âstd::string int_name(int)â: intname2.cpp:74: error: no match for call to â(std::string) (int)â intname2.cpp:80: error: no match for call to â(std::string) (int)â intname2.cpp:86: error: no match for call to â(std::string) (int&)â intname2.cpp:91: error: no match for call to â(std::string) (int&)â

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  • SQL where clasue to work with Group by clasue after performing a count()

    - by Matt
    Tried my usual references at w3schools and google. No luck I'm trying to produce the following results. QTY is a derived column | Position | QTY -------------------- 1 Clerk 2 2 Mgr 2 Here's what I'm not having luck with: SELECT Position, Count(position) AS 'QTY' FROM tblemployee Where ('QTY' != 1) GROUP BY Position I know that my Position is set up as varchar(255) Count produces a integer data and my where clasue is accurate so that leads me to believe that that Count() is jamming me up. Please throw up an example so I can reference later. Thanks for the help!

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  • staying within boundaries of image?

    - by codefail
    So I am to loop through copyFrom.pixelData and copy it into pixelData. I realize that I need to check the conditions of i and j, and have them not copy past the boundaries of pixelData[x][y], I need another 2 loops for that? I tried this, but was getting segmentation fault.. Is this the right approach? void Image::insert(int xoff, int yoff, const Image& copyFrom, Color notCopy) { for (int x = xoff; x < xoff+copyFrom.width; x++) { for (int y = yoff; y < yoff+copyFrom.height; y++) { for (int i = 0; i<width; i++){ for (int j = 0; j<height; j++){ if (copyFrom.pixelData[i][j].colorDistance(notCopy)>20 ) pixelData[x][y]=copyFrom.pixelData[i][j]; } } } } }

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  • im writing this code so the user would enter his/her name and followed by his/her marks to get the a

    - by WM
    What if the user wanted to enter his/her grades in the following way: Will 23, 34, 45, 45 how would i get rid of the commas public class StudentAverage { public static void main(String[] args) { int markSum = 0; double average = 0; Scanner input1 = new Scanner(System.in); System.out.print("Enter student record : "); String name = input1.next(); Scanner input2 = new Scanner(input1.nextLine()); int countTotal = 0; while (input2.hasNextInt()) { countTotal++; markSum += input2.nextInt(); } average = markSum / countTotal; // to calculate the total average System.out.print( name + " " + average ); } }

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  • Write a function int mystrlen(char *s) that returns the number of characters in a string wuthout str

    - by henry
    heres what i did, i just have ne error that i cant figure out. int mystrlen(char string[]) { char string1[LENGHT], string2[LENGHT]; int len1, len2; char newstring[LENGHT*2]; printf("enter first string:\n"); len1 = mystrlen(string1); printf("enter second string:\n"); len2 = mystrlen(string2); if(len1 == EOF || len2 == EOF) exit(1); strcpy(newstring, string1); strcat(newstring, string2); printf("%s\n", newstring); return 0;

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