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  • Generate Permutations of a List

    - by Eric Mercer
    I'm writing a function that takes a list and returns a list of permutations of the argument. I know how to do it by using a function that removes an element and then recursively use that function to generate all permutations. I now have a problem where I want to use the following function: (define (insert-everywhere item lst) (define (helper item L1 L2) (if (null? L2) (cons (append L1 (cons item '())) '()) (cons (append L1 (cons item L2)) (helper item (append L1 (cons (car L2) '())) (cdr L2))))) (helper item '() lst)) This function will insert the item into every possible location of the list, like the following: (insert-everywhere 1 '(a b)) will get: '((1 a b) (a 1 b) (a b 1)) How would I use this function to get all permutations of a list? I now have: (define (permutations lst) (if (null? lst) '() (insert-helper (car lst) (permutations (cdr lst))))) (define (insert-helper item lst) (cond ((null? lst) '()) (else (append (insert-everywhere item (car lst)) (insert-helper item (cdr lst)))))) but doing (permutations '(1 2 3)) just returns the empty list '().

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  • Implementing a server side push for a small number of clients

    - by Helper Method
    For an web application I am working on I have the following requirements: Clients need to be able to log in via a web brower. After logging in, they will be able to change configurations (normal request/response) will be able to receive alarms sent by the server (a server side push) Now, the question is how to implement the alarms. I first thought of using some long polling approach (Comet), but as the amount of clients will definitely belimited to 5-10, I'm now thinking to go with a simpler approach. What are the options I have? Would it be okay to just let the clients poll the server? Important aspects are: Alarms should be delivered in (nearly) real-time. Alarms must not get lost (a lost alarm could cause harm to real people).

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  • Programming in Python; writing a Caesar Cipher using a zip() method

    - by user1068153
    I'm working on a python program for homework and the problem asks me to develop a program that encrypts a message using a caesar cipher. I need to be able to have the user input a number to shift the encryption by, such as 4: e.g. 'A' to 'E'. The user also needs to input the string to be translated. The book says to use a zip() to do the problem. I am confused on how I would do this though. I have this but it doesn't do anything >>>def ceasarCipher(string, shift): strings = ['abc', 'def'] shifts = [2,3] for string, shift in zip(strings, shifts): print ceasarCipher(string,shift) >>>string = 'hello world' >>>shift = 1

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  • error in assigning a const character to a usigned char array in C++

    - by mekasperasky
    #include <iostream> #include <fstream> #include <cstring> using namespace std; typedef unsigned long int WORD; /* Should be 32-bit = 4 bytes */ #define w 32 /* word size in bits */ #define r 12 /* number of rounds */ #define b 16 /* number of bytes in key */ #define c 4 /* number words in key */ /* c = max(1,ceil(8*b/w)) */ #define t 26 /* size of table S = 2*(r+1) words */ WORD S [t],L[c]; /* expanded key table */ WORD P = 0xb7e15163, Q = 0x9e3779b9; /* magic constants */ /* Rotation operators. x must be unsigned, to get logical right shift*/ #define ROTL(x,y) (((x)<<(y&(w-1))) | ((x)>>(w-(y&(w-1))))) #define ROTR(x,y) (((x)>>(y&(w-1))) | ((x)<<(w-(y&(w-1))))) void RC5_DECRYPT(WORD *ct, WORD *pt) /* 2 WORD input ct/output pt */ { WORD i, B=ct[1], A=ct[0]; for (i=r; i>0; i--) { B = ROTR(B-S [2*i+1],A)^A; A = ROTR(A-S [2*i],B)^B; } pt [1] = B-S [1] ;pt [0] = A-S [0]; } void RC5_SETUP(unsigned char *K) /* secret input key K 0...b-1] */ { WORD i, j, k, u=w/8, A, B, L [c]; /* Initialize L, then S, then mix key into S */ for (i=b-1,L[c-1]=0; i!=-1; i--) L[i/u] = (L[i/u]<<8)+K[ i]; for (S [0]=P,i=1; i<t; i++) S [i] = S [i-1]+Q; for (A=B=i=j=k=0; k<3*t; k++,i=(i+1)%t,j=(j+1)%c) /* 3*t > 3*c */ { A = S[i] = ROTL(S [i]+(A+B),3); B = L[j] = ROTL(L[j]+(A+B),(A+B)); } } void printword(WORD A) { WORD k; for (k=0 ;k<w; k+=8) printf("%02.2lX",(A>>k)&0xFF); } int main() { WORD i, j, k, pt [2], pt2 [2], ct [2] = {0,0}; unsigned char key[b]; ofstream out("cpt.txt"); ifstream in("key.txt"); if(!in) { cout << "Cannot open file.\n"; return 1; } if(!out) { cout << "Cannot open file.\n"; return 1; } key="111111000001111"; RC5_SETUP(key); ct[0]=2185970173; ct[1]=3384368406; for (i=1;i<2;i++) { RC5_DECRYPT(ct,pt2); printf("\n plaintext "); printword(pt [0]); printword(pt[1]); } return 0; } when i run this code i get two warnings and also an error saying that i cant assign a char value to my character array . Why is that ?

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  • can i know how to fix this error? is delete method

    - by user334101
    import javax.swing.*; import java.io.File; public class Third { public static void main(String[] args) throws Exception { String humanName; humanName = JOptionPane.showInputDialog(null, "Enter the file name"); File file = new File(+ humanName".txt"); System.out.println(file.delete()); JOptionPane.showMessageDialog(null, "File deleted" + humanName); } }

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  • how can JIRA soap API not have this method?

    - by oo
    I want to be able to get a list of issues given a: Project Name and Release Version this seems like a basic JIRA soap API 101 request It seems, looking at the documentation: http://docs.atlassian.com/software/jira/docs/api/rpc-jira-plugin/latest/index.html?com/atlassian/jira/rpc/soap/JiraSoapService.html you can get issues by: Filter SearchTerms SearchTerms and Project but not the above. Is this a complete oversight or i am missing something i would expect to see something like this: RemoteIssue[] issues = _soapService.getIssues(string project_, string version_) any help? UPDATE: I see that JIRA 4.0 is out but i can't find any documentation if the API has changed to support this request above. Can anyone find this link to answer that questions.

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  • C programming and TDD

    - by Helper Method
    Is Test Driven Development limited to OO? Or is it possible/useful to use it in conjunction with a procedural language? I have to start a greater project in C the next few weeks and I'm thinking of ways how to the developing.

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  • Delphi 2010 - Why can't I declare an abstract method with a generic type parameter?

    - by James
    I am trying to do the following in Delphi 2010: TDataConverter = class abstract public function Convert<T>(const AData: T): string; virtual; abstract; end; However, I keep getting the following compiler error: E2533 Virtual, dynamic and message methods cannot have type parameters I don't quite understand the reason why I can't do this. I can do this in C# e.g. public abstract class DataConverter { public abstract string Convert<T>(T data); } Anyone know the reasoning behind this?

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  • Is there a way to make this C# method shorter and more readable with the help of Linq?

    - by Hamish Grubijan
    The following works, but I figured - since it is all based on IEnumerable, Linq can come handy here is well. By the way, is there an equivalent to Directory.GetFiles() which would return an IEnumerable instead of the array? If it exists, then would it make the code run any faster? The last part of the question is inspired by Python language which favors lightweight generators over concrete lists. private IEnumerable<string> getFiles(string strDirectory, bool bCompressedOnly) { foreach (var strFile in Directory.GetFiles(strDirectory)) { // Don't add any existing Zip files since we don't want to delete previously compressed files. if (!bCompressedOnly || Path.GetExtension(strFile).ToLower().Equals(".zip")) { yield return strFile; } } foreach (var strDir in Directory.GetDirectories(strDirectory)) { foreach (var strFile in getFiles(strDir, bCompressedOnly)) { yield return strFile; } } }

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  • Why does Ordered[A] use a compare method instead of reusing compareTo?

    - by soc
    trait Ordered[A] extends java.lang.Comparable[A] { def compare(that: A): Int def < (that: A): Boolean = (this compare that) < 0 def > (that: A): Boolean = (this compare that) > 0 def <= (that: A): Boolean = (this compare that) <= 0 def >= (that: A): Boolean = (this compare that) >= 0 def compareTo(that: A): Int = compare(that) } Isn't it a bit useless to have both compare and compareTo? What is the huge benefit I'm missing here? If they had just used compareTo I could just had replaced Comparable with Ordered in my code and be done.

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  • Question about the String.replaceAll() and String.replaceFirst() method.

    - by Java Doe
    I need to do a simple string replace operation on a segment of string. I ran into the following issue and hope to get some advice. In the original string I got, I can replace the string such as to something else. BUT, in the same original string, if I want to replace a much long string such as the following, it won’t work. Nothing gets replaced after the call. <div class="more"><a href="http://SERVER_name/profiles/atom/mv/theboard/entries/related.do?email=xyz.com&ps=20&since=1273518953218&sinceEntryId=abc-def-123-456">More...</a></div> I tried these two methods: originalString.replaceFirst(moreTag, newContent); originalString.replaceAll(moreTag, newContent); Thanks in advance.

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  • C problem, left of '->' must point to class/struct/union/generic type ??

    - by Patrick
    Hello! Trying to understand why this doesn't work. I keep getting the following errors: left of '-nextNode' must point to class/struct/union/generic type (Also all the lines with a - in the function new_math_struct) Header file #ifndef MSTRUCT_H #define MSTRUCT_H #define PLUS 0 #define MINUS 1 #define DIVIDE 2 #define MULTIPLY 3 #define NUMBER 4 typedef struct math_struct { int type_of_value; int value; int sum; int is_used; struct math_struct* nextNode; } ; typedef struct math_struct* math_struct_ptr; #endif C file int get_input(math_struct_ptr* startNode) { /* character, input by the user */ char input_ch; char* input_ptr; math_struct_ptr* ptr; math_struct_ptr* previousNode; input_ptr = &input_ch; previousNode = startNode; /* as long as input is not ok */ while (1) { input_ch = get_input_character(); if (input_ch == ',') // Carrage return return 1; else if (input_ch == '.') // Illegal character return 0; if (input_ch == '+') ptr = new_math_struct(PLUS, 0); else if (input_ch == '-') ptr = new_math_struct(MINUS, 0); else if (input_ch == '/') ptr = new_math_struct(DIVIDE, 0); else if (input_ch == '*') ptr = new_math_struct(MULTIPLY, 0); else ptr = new_math_struct(NUMBER, atoi(input_ptr)); if (startNode == NULL) { startNode = previousNode = ptr; } else { previousNode->nextNode = ptr; previousNode = ptr; } } return 0; } math_struct_ptr* new_math_struct(int symbol, int value) { math_struct_ptr* ptr; ptr = (math_struct_ptr*)malloc(sizeof(math_struct_ptr)); ptr->type_of_value = symbol; ptr->value = value; ptr->sum = 0; ptr->is_used = 0; return ptr; } char get_input_character() { /* character, input by the user */ char input_ch; /* get the character */ scanf("%c", &input_ch); if (input_ch == '+' || input_ch == '-' || input_ch == '*' || input_ch == '/' || input_ch == ')') return input_ch; // A special character else if (input_ch == '\n') return ','; // A carrage return else if (input_ch < '0' || input_ch > '9') return '.'; // Not a number else return input_ch; // Number } The header for the C file just contains a reference to the struct header and the definitions of the functions. Language C.

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  • Perl/SQLite - How do I select / update a row with the prepare method?

    - by somebody
    I have the following code my $db = DBI->connect( "dbi:SQLite:data.db", "", "", { RaiseError => 1, AutoCommit => 1, PrintError => 0 } ); my $row = $db->selectall_arrayref( "SELECT * FROM something WHERE name=\'$hash->{name}\'"); print Dumper $row; How do I do the same with my $sql = $db->prepare("......"); $sql->execute($hash->{name}); so that it's escaped correctly and I have the selected data in $row?

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