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• Traverse a XML using Recursive function

  - by Kaja

  How can I traverse (read all the nodes in order) a XML document using recursive functions in c#? What I want is to read all the nodes in xml (which has attributes) and print them in the same structure as xml (but without Node Localname) Thanks

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• Millionth number in the serie 2 3 4 6 9 13 19 28 42 63 ... ?

  - by HH

  It takes about minute to achieve 3000 in my comp but I need to know the millionth number in the serie. The definition is recursive so I cannot see any shortcuts except to calculate everything before the millionth number. How can you fast calculate millionth number in the serie? Serie Def n_{i+1} = \floor{ 3/2 * n_{i} } and n_{0}=2. Interestingly, only one site list the serie according to Goolge: this one. Too slow Bash code #!/bin/bash function serie { n=$( echo "3/2*$n" | bc -l | tr '\n' ' ' | sed -e 's@\\@@g' -e 's@ @@g' ); # bc gives \ at very large numbers, sed-tr for it n=$( echo $n/1 | bc ) #DUMMY FLOOR func } n=2 nth=1 while [ true ]; #$nth -lt 500 ]; do serie $n # n gets new value in the function throught global value echo $nth $n nth=$( echo $nth + 1 | bc ) #n++ done

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• How can I implement a tail-recursive list append?

  - by martingw

  A simple append function like this (in F#): let rec app s t = match s with | [] -> t | (x::ss) -> x :: (app ss t) will crash when s becomes big, since the function is not tail recursive. I noticed that F#'s standard append function does not crash with big lists, so it must be implemented differently. So I wondered: How does a tail recursive definition of append look like? I came up with something like this: let rec comb s t = match s with | [] -> t | (x::ss) -> comb ss (x::t) let app2 s t = comb (List.rev s) t which works, but looks rather odd. Is there a more elegant definition?

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• Segmentation fault C++ in recursive function

  - by user69514

  Why do I get a segmentation fault in my recursive function. It happens every time i call it when a value greater than 4 as a parameter #include <iostream> #include <limits> using namespace std; int printSeries(int n){ if(n==1){ return 1; } else if( n==2){ return 2; } else if( n==3){ return 3; } else if( n==4){ return printSeries(1) + printSeries(2) + printSeries(3); } else{ return printSeries(n-3) + printSeries((n-2) + printSeries(n-1)); } } int main(){ //double infinity = numeric_limits<double>::max(); for(int i=1; i<=10; i++){ cout << printSeries(i) << endl; } return 0; }

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• Elegant way to aggregate multi-dimensional array by index key

  - by Stephen J. Fuhry

  How can I recursively find the total value of all children of an array that looks something like this? [0] => Array ( [value] => ? // 8590.25 + 200.5 + 22.4 [children] => Array ( [0] => Array ( [value] => ? // 8590.25 + 200.5 [children] => Array ( [0] => Array ( [value] => 8590.25 // leaf node ) [1] => Array ( [value] => 200.05 // leaf node ) ) ) [1] => Array ( [value] => 22.4 // leaf node ) ) )

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• C++ Function Calling Itself

  - by Ben

  Suppose I wish to have a function that fills an array either in pattern x,y,x,y,x,ywhere x and y are variables defined by some algorithm and x,y,z,x,y,z where x, y and z are variables defined by the same algorithm. This should continue for all number of variables. Is this a viable way to implement it. int recurse_n(int n) { while(n > 0) { --n; recurse_n(n); n = 0; // Use algorithm here } }

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• Would this predicate work ? this came on my quiz to find the position of element X in a data structure called list

  - by M.K

  example: position(1,list(1,list(2,nil)),Z). Z = 1. position(3,list(1,list(2,list(3,nil)),Z). Z = 3. where Z is the position of element X in a data structure of a list in the above format Here was my solution: position(X,list(nil),0). %empty list position(X,list(X,T),1). %list with X as head or first element position(X,list(H,T),Z):- position(X,list(T,nil),Z1), %X is in tail of list (H,T) Z is Z1 + 1.

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• C++ Recursive function that reverses the order of an array's indexes between two bounds

  - by CPT Kirk

  I am trying to write a recursive function that has three arguments; an array and two array indexes. The function should reverse the order of the values between the two indexes. I would like to understand what is happening instead of just being told an answer. Here is my code so far: #include <iostream> using namespace std; char switchAroo(char a[], int b1, int b2); int main() { char a[6] {'A', 'B', 'C', 'D', 'E', '\0'}; cout << a; switchAroo(a, 2, 5); return 0; } char switchAroo(char a [], int b1, int b2) { char temp; if (b1 == b2) cout << "The array after switchAroo is " << a << endl; else { temp = a[b1]; a[b1] = a[b2]; a[b2] = temp; b1++; b2--; return switchAroo(a, b1, b2); } } I am getting the following warning code: warning C4715: 'switchAroo' : not all control paths return a value Any help would be greatly appreciated.

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• best way to write a-> ..->[a] recursive functions in haskell

  - by Roman A. Taycher

  So I keep having this small problem where I have something like func :: a -> b -> [a] -- or basically any a-> ...-> [a] where ... is any types -> func x y = func' [x] y -- as long as they are used to generate a list of [a] from x func' :: [a] -> b -> [a] func = undefined --situation dependant generates a list from each element and returns it as one long list should I keep it like this? should I use func' hidden by a where? should I only use the [a] - b - [a] version and leave the responsibility of passing [variable] to the callee? I might well need to compose these functions and might want to mess around with the order so I'm leaning towards option 3. What do you think?

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• Global variable in a recursive function how to keep it at zero?

  - by Grammin

  So if I have a recursive function with a global variable var_: int var_; void foo() { if(var_ == 3) return; else var_++; foo(); } and then I have a function that calls foo() so: void bar() { foo(); return; } what is the best way to set var_ =0 everytime foo is called thats not from within itself. I know I could just do: void bar() { var_ =0; foo(); return; } but I'm using the recursive function a lot and I don't want to call foo and forget to set var_=0 at a later date. Does anyone have any suggestions on how to solve this? Thanks, Josh

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• Elegant way to aggregate multi-demensional array by index key

  - by Stephen J. Fuhry

  How can I recursively find the total value of all children of an array that looks something like this? [0] => Array ( [value] => ? // 8590.25 + 200.5 + 22.4 [children] => Array ( [0] => Array ( [value] => ? // 8590.25 + 200.5 [children] => Array ( [0] => Array ( [value] => 8590.25 // leaf node ) [1] => Array ( [value] => 200.05 // leaf node ) ) ) [1] => Array ( [value] => 22.4 // leaf node ) ) )

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• Returning a list in this recursive coi function in python.

  - by Nate

  Hello. I'm having trouble getting my list to return in my code. Instead of returning the list, it keeps returning None, but if I replace the return with print in the elif statement, it prints the list just fine. How can I repair this? def makeChange2(amount, coinDenomination, listofcoins = None): #makes a list of coins from an amount given by using a greedy algorithm coinDenomination.sort() #reverse the list to make the largest position 0 at all times coinDenomination.reverse() #assigns list if listofcoins is None: listofcoins = [] if amount >= coinDenomination[0]: listofcoins = listofcoins + [coinDenomination[0]] makeChange2((amount - coinDenomination[0]), coinDenomination, listofcoins) elif amount == 0: return listofcoins else: makeChange2(amount, coinDenomination[1:], listofcoins)

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• Return NSString from a recursive function

  - by Dave

  Hi, I have a recursive function that is designed to take parse a tree and store all the values of the tree nodes in an NSString. Is the algorithm below correct? NSString* finalString = [self parseTree:rootNode string:@""]; -(NSString*)parseTree:(Node*)currentNode string:(NSMutableString*)myString { [myString appendText:currentNode.value]; for(int i=0;i<[currentNode.children length];i++){ return [self parseTree:[currentNode.children] objectAtIndex:i] string:myString]; } }

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• Write a recursive function in C that converts a number into a string

  - by user3501779

  I'm studying software engineering, and came across this exercise: it asks to write a recursive function in C language that receives a positive integer and an empty string, and "translates" the number into a string. Meaning that after calling the function, the string we sent would contain the number but as a string of its digits. I wrote this function, but when I tried printing the string, it did print the number I sent, but in reverse. This is the function: void strnum(int n, char *str) { if(n) { strnum(n/10, str+1); *str = n%10 + '0'; } } For example, I sent the number 123 on function call, and the output was 321 instead of 123. I also tried exchanging the two lines within the if statement, and it still does the same. I can't figure out what I did wrong. Can someone help please? NOTE: Use of while and for loop statements is not allowed for the exercise.

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• How to change recursively change folder permissions on WAMP server

  - by user1543227

  How do I change folder permissions recursively in Windows 7? Specifically, for my WAMP server, I want to change the permissions of my "www" folder so that its contents can be viewed over the Internet, and I want all of its subfolders to have the same permissions. Currently, for each folder, I'm getting the following message in my browser: "You don't have permission to access / on this server." I believe there's a simple command I could enter in a terminal for recursively changing folder permissions for global access; I just don't know what it is.

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• Can somebody please explain this recursive function for me?

  - by capncoolio

  #include <stdio.h> #include <stdlib.h> void reprint(char *a[]) { if(*a) { printf("%d ",a); reprint(a+1); printf("%s ",*a); } } int main() { char *coll[] = {"C", "Objective", "like", "don't", "I", NULL}; reprint(coll); printf("\n"); return EXIT_SUCCESS; } As the more experienced will know, this prints the array in reverse. I don't quite understand how! I need help understanding what reprint(char *a[]) does. I understand pointer arithmetic to a degree, but from inserting printf's here and there, I've determined that the function increments up to the array end, and then back down to the start, only printing on the way down. However, I do not understand how it does this; all I've managed to understand by looking at the actual code is that if *a isn't NULL, then call reprint again, at the next index. Thanks guys!

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• Why can't i define recursive variable in code block?

  - by senia

  Why can't i define a variable recursively in a code block? scala> { | val fibs: Stream[Int] = 1 #:: fibs.scanLeft(1){_ + _} | } <console>:9: error: forward reference extends over definition of value fibs val fibs: Stream[Int] = 1 #:: fibs.scanLeft(1){_ + _} ^ scala> val fibs: Stream[Int] = 1 #:: fibs.scanLeft(1){_ + _} fibs: Stream[Int] = Stream(1, ?) lazy keyword solves this problem, but i can't understand why it works without a code block but throws a compilation error in a code block.

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• Java How to find a value in a linked list iteratively and recursively

  - by Roxy

  Hi I have a method that has a reference to a linked list and a int value. So, this method would count and return how often the value happens in the linked list. So, I decided to make a class, public class ListNode{ public ListNode (int v, ListNode n) {value = v; next = n;) public int value; public ListNode next; } Then, the method would start with a public static int findValue(ListNode x, int valueToCount){ // so would I do it like this?? I don't know how to find the value, // like do I check it? for (int i =0; i< x.length ;i++){ valueToCount += valueToCount; } So, I CHANGED this part, If I did this recursively, then I would have public static int findValue(ListNode x, int valueToCount) { if (x.next != null && x.value == valueToCount { return 1 + findValue(x, valueToCount);} else return new findvalue(x, valueToCount); SO, is the recursive part correct now?

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• What SQL query should I perform to get the result set expected?

  - by texai

  What SQL query should I perform to get the result set expected, giving the first element of the chain (2) as input data, or any of them ? table name: changes +----+---------------+---------------+ | id | new_record_id | old_record_id | +----+---------------+---------------+ | 1| 4| 2| | -- non relevant data -- | | 6| 7| 4| | -- non relevant data -- | | 11| 13| 7| | 12| 14| 13| | -- non relevant data -- | | 31| 20| 14| +----+---------------+---------------+ Result set expected: +--+ | 2| | 4| | 7| |13| |14| |20| +--+ I know I should consider change my data model, but: What if I couldn't? Thank you in advance!

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• Using ANTLR with Left-Recursive Rules

  - by CNevin561

  Basically Ive written a Parse for a language with just basic arithmetic operators ( +, -, * / ) etc, but for the minus and plus cases, the Abstract Syntax Tree which is generated has parsed them as right associative when they need to be left associative. Having a googled for a solution, i found a tutorial that suggests rewriting the rule from: Expression ::= Expression <operator> Term | Term as Expression ::= Term <operator> Expression*. However in my head this seems to generate the tree the wrong way round. Any pointers on a way to resolve this issue?

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• Java : Count even values in a Binary Search Tree recursively

  - by user307682

  Hi, I need to find out how many even values are contained in a binary tree. this is my code. private int countEven(BSTNode root){ if ((root == null)|| (root.value%2==1)) return 0; return 1+ countEven(root.left) + countEven(root.right); } this i just coded as i do not have a way to test this out. I'm not able to test it out at the moment but need an answer so badly. any help is deeply appreciated.

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• Java iterative vs recursive

  - by user1389813

  Can anyone explain why the following recursive method is faster than the iterative one (Both are doing it string concatenation) ? Isn't the iterative approach suppose to beat up the recursive one ? plus each recursive call adds a new layer on top of the stack which can be very space inefficient. private static void string_concat(StringBuilder sb, int count){ if(count >= 9999) return; string_concat(sb.append(count), count+1); } public static void main(String [] arg){ long s = System.currentTimeMillis(); StringBuilder sb = new StringBuilder(); for(int i = 0; i < 9999; i++){ sb.append(i); } System.out.println(System.currentTimeMillis()-s); s = System.currentTimeMillis(); string_concat(new StringBuilder(),0); System.out.println(System.currentTimeMillis()-s); } I ran the program multiple time, and the recursive one always ends up 3-4 times faster than the iterative one. What could be the main reason there that is causing the iterative one slower ?

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• Scala: recursive search avoiding cycles

  - by user1826663

  How can I write a recursive search that I avoid cycles. My class is this: class Component(var name: String, var number: Int, var subComponent: Set[Component]) Now I need a way to check whether a component is contained within its subcomponent or between subcomponent of its subcomponent and so on.Avoiding possible cycles caused by other Component. My method of recursive search must have the following signature, where subC is the Set [component] of comp. def content (comp: Component, subC: Set[Component]) : Boolean = { } Thanks for the help.

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• Segmentation fault in a function to reverse a singly linked list recursivley.

  - by Amanda

  I am implementing a function to recursively reverse a linked-list, but getting seg-fault. typedef struct _node { int data; struct _node *next; } Node, *NodeP; NodeP recursiveReverseList(NodeP first){ if(first == NULL) return NULL; if(first->next == NULL) return first; NodeP rest = recursiveReverseList(first->next); rest->next = first; first->next = NULL; return first; } Can you please help? P.S. The iterative version is working fine though. Its not homework. Just practicing C. Thank you all :)

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• Returning binomal as a tuple

  - by Mike

  I want to save the results of my function binomal_aux to a tuple but I don't have an idea how to, here is my code I have right now. def binomal (n): i=0 for i in range(n): binomal_aux(n,i) #want this to be in a tuple so, binomal (2) = (1,2,1) return def binomal_aux (n,k): if (k==0): return 1 elif (n==k): return 1 else: return (binomal_aux(n-1,k) + binomal_aux(n-1,k-1))

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