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0
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2answers
105 views

How to mentally keep track of recursion

I have great trouble doing recursion, especially trying to visualize it. A great example is the aging wine problem described in the top answer of this link: https://www.quora.com/Are-there-any-good-...
1
vote
1answer
55 views

Recursive interface implementation causes empty method

TLDR: I have a situation where interface implementations accept other implementations of that very interface. Only a subselection of these interface implementations should carry a certain method - but ...
2
votes
5answers
273 views

Recursion in Merge Sort algorithm. How is it obvious to use this type of recursion?

I dont want to put too much code so I'll just put the code that involves recursion. This algorithm is fairly well known so I think everybody knows the basic code. void mergeSort(int array[], int l, ...
0
votes
1answer
44 views

Reflexive calls of objects in the same hierarchy

I am not sure how to phrase this. I believe this should have been asked somewhere, but I am unable to find it because I don't know the keywords. Basically, I have some types like this: interface Foo ...
-2
votes
1answer
119 views

How does this recursive function exit? [closed]

In the merge_sort part, there are multiple calls to the same function within the recursive. How are the other two executed when the definition holds that till a condition is false, the recursion does ...
0
votes
2answers
61 views

Implementing map with tail recursion

I am trying to solve this exercise. It is about reimplementing the map function in haskell for learning purpose. I found a solution which doesn't browse all the elements of the list (simple linked ...
1
vote
0answers
53 views

String Pattern Matching from Lookup Table - Non-Exponential Solution?

Given the problem... Given a String comprising of non-alhpabetical symbols, and a Lookup Table where a subset of those symbols may equate to a single alphabetical character, output all ...
1
vote
1answer
109 views

Understanding recursive solution of some algorithm

Most of the time we need to understand someone else' code for example I am studying Graph Algorithms from Sedgewick's online resources, the particular code example is taken from cycle detection ...
0
votes
0answers
24 views

Reverse lookup of data based on user input

I have an array in the format: $array = array( 0 => array( 'name' => 'Item 1', 'level' => 1, 'points' => 10 ), 1 => array( 'name' => '...
0
votes
1answer
80 views

Achieving permutation using recursion [closed]

Though I like recursions and understand it, I fail to master it! I am stuck with a problem which I know that recursion can solve, but I do not know how. I have an array of strings like: "hundred", "...
-2
votes
1answer
154 views

For loop and recursion for a new shell in C [closed]

I code a new shell in C, that could be done in several ways: Flex/bison, finite state machine, abstract syntax tree or just a tokenizer in C. Now I've written a for-loop that changes the condition of ...
3
votes
1answer
81 views

Term for the current iteration of a recursive function call

Is there a standard or widely accepted term for referring to a variable within the current call of a recursive function where the last value of the same variable is passed as an argument? I am trying ...
1
vote
1answer
153 views

Complexity of recursive calls

my brain is a little stuck as I am trying to compile an example for my blog. I am presenting an algorithm that draws a number from an array, adds it to a sum and calls itself recursively. func solve(...
5
votes
1answer
168 views

Algorithm to generate all sets of m points in n x n x n cubic lattice which are unique under symmetry

I am implementing an algorithm which is going to be quite computationally complex, and want to try to make sure I'm not doing unnecessary work. There is an n x n x n cubic lattice, e.g. if n=2 this ...
8
votes
1answer
191 views

Finding all possible ways of inserting a pattern into a string

I've been thinking about this problem for a while, and I can only find a recursive solution but I'm feeling that there is a dynamic programming way to do it, I just can't figure it out. Is this a ...
2
votes
1answer
135 views

Enumerating the primitive recursive functions

How can I enumerate (by expression tree size, for example) all of the primitive recursive functions that map natural numbers to natural numbers in a traditional programming language like C? For ...
-1
votes
1answer
107 views

Problem on recursion

void function(int x){ if(x<=0) return; function(x--); } This is a recursion function which is called with the value of x = 20. The Recursive call will take place in this way ...
7
votes
3answers
363 views

What would be a good approach to generate a tree of folders?

Say I have an array of strings, like this: var folders = new[] { "Foo", "Bar", "Foo\Bar" "Foo\Bar\Baz" }; And that I have an object that represents a folder - something like this: ...
3
votes
3answers
131 views

What can qualify for potential tail call recursion (TCO) optimization or tail recursion elimination (TRE)

Short question is: what can qualify for potential tail call recursion optimization (TCO) or tail recursion elimination (TRE) if the compiler or interpreter supports it. The summary of this question ...
0
votes
1answer
186 views

False recursion vs. true recursion [closed]

I have been warned by my professor to avoid "false recursion", where a function behaves recursively, but does no useful recursive work. I believe I understand recursion, but would like to double ...
113
votes
11answers
12k views

Is there anything that can be done with recursion that can't be done with loops?

There are times where using recursion is better than using a loop, and times where using a loop is better than using recursion. Choosing the "right" one can save resources and/or result in fewer lines ...
0
votes
3answers
182 views

Is recursion a bad idea for large input sizes due to the limited call stack size? [duplicate]

Call stack size in JavaScript: Three results: - Node.js: 11034 - Firefox: 50994 - Chrome: 10402 It seems like it would be a bad idea to use recursion for things like BST insertion, because there's ...
3
votes
2answers
206 views

What was the first language to support convenient user-land recursion?

What was the first programming language to support convenient user-land recursion? I know that early languages did not support it, but can find no specifics on when it was introduced.
1
vote
0answers
49 views

Recursive(?) algorithm design help

I have a requirement to allow my end users to input formula much like a spreadsheet. I have an array like this: $table = array( 1=>array( "id"=>1, "Name"=>"...
4
votes
1answer
423 views

Why does `length - 2` recursively give you the center of a linked list?

I am reading through an Algorithms book and am working through a recursive solution to the following question: Implement a function to check if a linked list is a palindrome This is an easy ...
0
votes
2answers
176 views

A Python program that illustrates the tree-like structure of recursion [closed]

I want to write a program in Python that illustrates the tree-like feature of recursion, using the example of "fibo(n)" function. I wonder how to modify the following program: def fibo(n): if n==...
3
votes
4answers
614 views

Why can't I call a constructor in itself?

I am currently porting the class NumberRange from Java to C#. I am writing this constructor and I wonder whether I can call a constructor in itself. Something like this: public NumberRange(Double ...
1
vote
4answers
2k views

How does recursive backtracking work ?

I am trying to figure out recursive backtracking, i have good understanding of recursion and till some extent the concept of backtracking too but i am having difficulty understand the chronological ...
1
vote
1answer
219 views

Why do I need to use recursion on the classic employee manager database relationship?

Take the data from the Oracle scott database. I have modified it to have multiple levels of management from the original, select * from scott.emp order by mgr desc; empno ename job ...
2
votes
1answer
128 views

How to calculate number of indirect dependencies of a class?

Most of the static code analysis tools which analyse class dependencies generate dependency pairs of classes where each pair represents a direct dependency between two classes. Given those dependency ...
0
votes
0answers
34 views

What's the bound of the following recurrence?

Given the following recurrence: T(n) = T(n-1) + n^2 How can I prove it to be O(n^3) with the substitution method? The O(n^3) guess derives from the fact that at every step of the recursion we pay n^...
2
votes
2answers
213 views

Why left recursion not looping?

I'm trying to read the parser of PHP, that says: top_statement_list: top_statement_list top_statement | /* empty */ ; It is a left-recursion, but why it don't looping infinitely? My ...
0
votes
1answer
106 views

Recursion, iteration, and …? [closed]

Here are three common code structures that apply a function multiple times: foo(x) { if basecase(x) return k else return foo(g(x)) } uses recursion. for i in 0..10 { n *= bar(i) } uses ...
1
vote
1answer
391 views

What are the time and space complexities of this recursive method that reverses a singly linked list?

What are the Time and Space complexities of this Java method that reverses a singly linked list (of length n)? I'm more interested in knowing the reasoning behind the space complexity. Let me know if ...
4
votes
1answer
4k views

General Way to convert a loop (while/for) to recursion or from a recursion to a loop?

This problem is mainly focusing on the algorithm, maybe something abstract and more acedemic;) The example is offering a thought, I wanna a generic way, so example is only used as to make us more ...
0
votes
2answers
123 views

Given a tree calculating Max Sum from top to bottom suing DFS? optimization?

given a tree i want to calculate max sum of each path from top to bottom. I used DFS for the operation. Here is the function which takes root as input and gives max sum of the path from top to bottom :...
1
vote
3answers
402 views

Check distance between all elements in a list of numbers in O(n*lg(n))

I have an exercise for my algorithms and data structures class, where I basically have to implement a divide and conquer algorithm or function called check_distance to determine whether all numbers in ...
3
votes
4answers
2k views

Robot in a grid

This was recently asked to someone I know. A robot has to move in a grid which is in the form of a matrix. It can go to A(i,j)--> A(i+j,j) (Down) A(i,j)--> A(i,i+j) (Right) ...
0
votes
2answers
137 views

Trouble understanding simple recursion in c [duplicate]

My function: int num(int x) { if(x>0) num(x-1); else return 0; printf("%d",x); } This function takes a input x and prints the numbers from 1 upto x.I can't seem to ...
1
vote
1answer
121 views

Why does this recursion method work? I have explored it for a day or two, and I cannot figure out why

Problem Statement: I have a tree with node values ( i , j ) where i , j < 1. The children of each node take on the values (i - 1, j), (i - 1, j - 1), and (i, j - 1) respectively. Now, i and j have ...
3
votes
2answers
163 views

Is there a (systematic) way to convert a recursive program to a version using user stack?

I have an image (an array of 1000 x 1000 pixels) of 1s and 0s. I was asked to do edge detection, so I wrote this program in C to traverse the figure. My idea was to convert every pixel surrounded by ...
0
votes
2answers
420 views

Is recursion a declarative approach to solve the problems?

I have noticed many problems in algorithms textbook are solved by recursion (divide and conquer, backtracking,...) As I tried to enhance my skills in writing them, I have noticed, I just need to ...
43
votes
4answers
13k views

Why doesn't Java have optimization for tail-recursion at all?

From what I have read: The reason is because it is not easy to determine which method will actually be called as we have inheritance. However, why doesn't Java at least have tail-recursion ...
0
votes
2answers
140 views

Time complexity analysis for recurrence relation

I was asked to figure out the time complexity analysis for the following recurrence relation T(n) = 4*T(n-1) + c. Basically, I did a replacement.. T(n-1) = 4 * T(n-2) + c and so on.. T(n) = 4^k T(1) ...
6
votes
4answers
357 views

How to convert the following node evaluation procedure to a non recursive solution?

I have the following recursive method. It evaluates a node (that represent a logical expression), using deep first search traversal : EvaluateNode(Node node) { bool result; switch(node.Type) ...
0
votes
1answer
100 views

Handling the process of large-scale lists [closed]

What are the efficient ways to process huge lists (+10 millions), and things to consider while manipulating huge lists. First question, when should I use recursion, and when I shouldn't. In both ...
1
vote
1answer
434 views

Is it possible to apply Master Theorem for finding the square and cube root

I was asked to calculate the running time of an algorithm which finds the square root and cube root of a given number. Is it possible to apply Master theorem with regards to this? First, I need to ...
2
votes
1answer
2k views

how to enumerate/generate all possible binary trees from N leaves and N-1 nodes?

I am trying to implement the 24 Game in ansi C. This game goes as follows: For a list of four given numbers, try to find a solution involving these four numbers, that, using addition(+), subtraction(-...
3
votes
1answer
378 views

Do compilers un-inline recurrent expressions?

Does a compiler look for recurrent expressions to convert it into 'function' to reduce binary size and improve performance? Of course, the obvious answer might be "some do it, some don't", so I ask ...
3
votes
3answers
10k views

Find all possible subarrays of an Array

I am lost I just can't seem to get my head around backtracking/recursion approaches. I understand how simple recursion problems like factorials work I can even trace those by hand. But when it comes ...