Questions tagged [recursion]
Recursion in computer science is a method of problem solving where the solution to a problem depends on solutions to smaller instances of the same problem.
771 questions
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When given 7 letters, find all possible words with length 3 to 7
I am writing a program in JavaScript to find all possible words given 7 letters. The words have to be 3 or more characters, and for right now I am limiting it to 7 characters long. The code below ...
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1answer
20 views
Scheme function to duplicate every element of a list a specified number of times
This code takes a list and a integer and duplicates every element in the list the specified number of times.
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5
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2answers
117 views
Finding all possible letter combinations from an inputted phone number
Prompt:
Given a string containing digits from 2-9 inclusive, return all
possible letter combinations that the number could represent.
A mapping of digit to letters (just like on the ...
2
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1answer
82 views
Find the kth-to-last element of a singly linked list
I wrote this code for finding the \$k\$th-to-last element in a singly linked list.
...
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0answers
134 views
Filling values for nested dictionaries
I have a text file where any name followed with sequence word is considered a dictionary. The task is to go through the keys and values of a particular dictionary, which is already identified, and see ...
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2answers
21 views
Extract and divide algorithm implementation in Elixir
I just started learning Elixir and stumbled upon this challenge over on Programming Puzzles & Code Golf. It is a well-suited task for beginners, so I chose to give it a go (to be clear, give it a ...
1
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1answer
43 views
Rearrange an array in place such that the first and last halves are interleaved
Given an array of n elements in the following format { a1, a2, a3, a4,
….., an/2, b1, b2, b3, b4, …., bn/2 }. The task is shuffle the array
to {a1, b1, a2, b2, a3, b3, ……, an/2, bn/2 } without ...
3
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0answers
81 views
All the paths from the root to the leaves
Given a binary tree, return all root-to-leaf paths.
Example:
-- 1
/ \
2 3
\
5
Output should be: ["1->2->5", "1->3"]
My approach: I walk the branches ...
2
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2answers
61 views
NxN Sudoku Solver
I have written a Sudoku solver which can solve arbitrary NxN grids via backtracking.
Since I'm relativly new to C any feedback is welcome.
Code:
...
4
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3answers
690 views
Recursion: Count from x until n and backwards
I wrote this recursive function to print a number sequence from x to n and n to x back.
Here is one of the ideas I had to improve it, but it didn't work out (use another ternary operator at the end ...
1
vote
1answer
45 views
Recursive function to find the number of ways a number can be generated out of a set of numbers
I had a job interview test and the question I got was about making a function which would return the number of ways a number could be generated by adding numbers from a certain set, where any number ...
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1answer
81 views
Count number of islands 2d grid
This is a recursive approach using DFS to counting the number of islands. However, I would like to improve performance, while keeping the code clean concise and readable. Better yet can this be solved ...
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36 views
Is this a good way of retrying operations using recursion?
This is in context of a springboot application. I considered using Spring @Retryable too but found that it didn't work with function with return types. Is this approach considered good?
...
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0answers
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Searching through a TreeView by expanding found results and collapsing others [closed]
I have a WPF TreeView which is populated with many child controls. All of them with children themselves are ...
4
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1answer
109 views
Recursive implementation of power set in Python
I was doing a recursion problem called power set, and would like to get code review. Here's the problem.
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3
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1answer
75 views
Recursively generating the look-and-say sequence
I have a pattern where every number is counted by the number of repetitions. A new resulting number is formed by adding that repetition to the front of that value. The resulting pattern would look ...
3
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3answers
178 views
Find k-distinct partitions which contain at least two perfect squares
Problem Statement:
A k-distinct-partition of a number \$n\$ is a set of \$k\$ distinct positive integers that add up to \$n\$. For example, the 3-distinct partitions of 10 are
\$1+2+7\$
\$...
2
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0answers
31 views
Creating a series of relationship hierarchies from a list of nodes and connections
I have put together some code that creates a tree structure from a large list of nodes (entities) and connections and am looking to speed it up.
HierarchyWorker: Converts the list data into the tree
...
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0answers
58 views
Sudoku solver using NumPy
I come from the R language and I gradually switch to Python (Numpy and Pandas). I coded this python code for fun to solve a Sudoku grid. Could you tell me if my code is pythonic enough? For example, ...
5
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0answers
173 views
Codewars: N-dimensional Von Neumann Neighborhood in a matrix
Task:
For creating this challenge on Codewars I need a very performant function that calculates Von Neumann Neighborhood in a N-dimensional array. This function will be called about 2000 times
The ...
2
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2answers
69 views
Finding the closest pair of points divide-and-conquer speed improvement
This is a follow up to a previously asked Finding the closest pair of points divide-and-conquer question . The original code changed significantly based on answers from @AJNeufeld therefore I created ...
0
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1answer
62 views
Counting contiguous subarrays with a negative sum
I'm doing a coding challenge that asks to count the number of contiguous subarrays that have a negative sum:
A subarray of an n-element array is an array composed from a contiguous block of the ...
4
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2answers
302 views
Finding the closest pair of points divide-and-conquer
Here is my code for the famous "finding the closest pair of points" problem from CLRS book section 33.4 using a divide-and-conquer approach (this code returns the minimum distance between pair of ...
6
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2answers
115 views
Find the second largest number in an array with at most n + log2 n - 2 comparisons
This exercise is from Roughgarden's (excellent) course on algorithms on Coursera:
You are given as input an unsorted array of n distinct numbers, where
n is a power of 2. Give an algorithm that ...
1
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1answer
49 views
Possible letter combinations of a dial pad in linear time using a recursive approach
Time complexity: I walk the initial unzipped array of keys representing the number O(N) backwards. I then do an inner walk of the proceeding array of letters *O(L^2), mapping it to every value in the ...
3
votes
2answers
71 views
Memoized solution to Count number of ways to climb n steps
Problem statement : A Child is climbing up n steps with either 1 , 2, 3 hops ..how many ways can the child climb up the stairs?
source: cracking the coding interview book.
I have two solutions the ...
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1answer
185 views
All subsets of a String in java using recursion
I wrote this code for printing all sets of a String. It also prints the empty subset. Is this the right approach
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2answers
80 views
Find all N-Queens solution
This code is a multi-threading recursive backtracking DFS algorithm to find all solutions to the N-Queens problem. The board size is indicated by BOARD_SIZE. ...
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0answers
25 views
Recursive Generator Exceeds Call Stack
I have this recursive generator that fetches 100 messages from an API and gets the next 100 until there are no more messages to get:
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4answers
97 views
Hackerrank Day 9: Recursion
Write a factorial function that takes a positive integer, N as a parameter and prints the result of N! (N factorial).
Note: If you fail to use recursion or fail to name your recursive function ...
2
votes
1answer
60 views
Determine all ways a string can be split into valid words, given a dictionary of all words
This function word_break(s, dictionary) receives a string s and a set of all valid words ...
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2answers
85 views
Find all root to leaf paths in binary tree
Description:
Given a binary tree, return all root-to-leaf paths.
Leetcode
...
3
votes
1answer
80 views
Find minimum depth in a binary tree
Description:
Given a binary tree, find its minimum depth.
The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
Note: A leaf is a node ...
7
votes
1answer
95 views
Fast and flexible Sudoku Solver in C++
After seeing a lot of Sudoku solvers on Code Review I decided to implement my own.
My implementation aims to be very fast and flexible, supporting some Sudoku variations (irregular boxes, extra ...
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2answers
105 views
Generate all combinations of length N through M
I've started learning programming and as matter of practice I've decided to make a program that will output all possible string combinations and put them in a file.
I've manged to do that and it works ...
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0answers
98 views
+50
Modeling tabular structure in MSSQL to store data like Excel sheet applying Column inheritance
I've created this database structure to store tabular information (it's a simplification of my real structure but enough to show the point). In it I have Sheets and ...
1
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2answers
111 views
Cycle in Directed graph to vector
I created a class of a directed graph and a method for finding if graph has an Euler cycle and updating a vector accordingly.Is there any optimization or a nicer way to do this.
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5
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3answers
523 views
Bisection to find roots in C++
I have written a short C/C++ code finding root by bisection. (This is a simple iterative numerical method allowing to find the root of an equation i.e. x such that f(x) = 0). Bisection Method
The ...
2
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3answers
117 views
Finding all possible paths between two points in a grid using recursion
I'm trying to find all possible paths made of 0 from bottom left to top right, only by moving either up or to the right. The input file contains a grid of characters, where ...
2
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0answers
148 views
Robot on a Grid: Find a path between two corners with forbidden cells on the road
Problem statement
The problem is defined in the book as following:
8.2 Robot in a Grid Imagine a robot sitting on the upper left corner of grid with r rows and <...
6
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3answers
165 views
Recursive Quadtree implementation in C++
I've been working on a recursive quadtree in C++. How can I improve my code? My primary goals are improving the performance/speed, as well as practice.
QuadTree.h
...
3
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2answers
103 views
Check whether array is sorted recursively
I'm trying to implement isSorted method checking whether given array is sorted recursively. I've written two types, one is similar to merge sort logic, the another ...
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2answers
136 views
Binary search for integers
I've written binary search with only my own efforts 💪💪 without glancing at anywhere. I stuck on finding base case. At final, I think that if last checking is less than first index or first checking ...
1
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1answer
116 views
Recursive merge-sort inversion count algorithm very slow
I am trying to implement a recursive count of inversions in a list of integers by using merge sort and counting the number of split inversions on each recursion. My code works but runs painfully ...
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1answer
45 views
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0answers
86 views
Multiplying big numbers using Karatsuba's method
The Karatsuba algorithm, first published in 1962, aims to speed up the multiplication of big numbers by reducing the number of 'single-digit-multiplications' involved.
Because of its complexity (...
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2answers
133 views
Number of Paths (BackTracking) in Java
Illustration
You're testing a new driverless car that is located at the Southwest
(bottom-left) corner of an n×n grid. The car is supposed to get to the
opposite, Northeast (top-right), corner ...
3
votes
2answers
248 views
N Queens in Python
I used Python very occasionally, today I solved n queens in Python just for fun. I am sure there are better way of doing certain things in Python and can't wait for improvement suggestions!
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3
votes
1answer
52 views
python magic square finder for arbitrary numbers
I wrote this code to get all possible magic squares that can be made with a list you put in. The only contraints are that the count of numbers is a square and that each number is unique. It even works ...
