# Tagged Questions

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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-...
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 ...
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, ...
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### 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 ...
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 ...
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 ...
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 ...
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 ...
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### 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' => '...
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### 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", "...
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 ...
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 ...
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(...
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 ...
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 ...
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 ...
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 ...
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: ...
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 ...
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 ...
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 ...
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### 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 ...
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### 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.
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### 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"=>"...
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### 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 ...
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==...
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 ...
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 ...
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### 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 ...
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 ...
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### 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^...
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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 :...
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 ...
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) ...
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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 ...
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) ...
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) ...
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### 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 ...
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 ...
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(-...