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Questions tagged [combinatorics]

Combinatorics is a branch of mathematics concerning the study of finite or countable discrete structures.

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Interleave two lists, preserving the order of elements in their original list

I need to write an OCaml program that return all possible zip of two lists together while preserving the order of the element in each list. For example, if we zip the lists [1;2] and [3;4], we get [[1;...
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Iterative version of a permutations algorithm

For learning purposes: I've written an iterative version of a [recursive] algorithm for generating the set of permutations for a given set of unique integers. Can I make any improvements to increase ...
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326 views

Compute all the permutations for a given vector of integers

The task is to compute all the permutations for a given vector of integers (but of course the specific integer type is not relevant for the solution) The strategy is based on recursion + iterations ...
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Leetcode Next Permutation in Python

My solution to Leetcode Next Permutation in Python. Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers. If such arrangement is ...
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2answers
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Iteratively generating permutations with repetitions

I tried to solve the simple problem of generating all permutations of length n with m distinct elements where repetition is allowed. Doing this recursively took me like 10 minutes: ...
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1answer
182 views

Best way to performance permutations

This has been my white whale for a while, the idea is convert all the symbols to the goal symbol using all the pieces. I did an algorithm like 5 years ago (now is lost) and reach lvl 48 but got stuck ...
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2answers
86 views

Number of possible numbers in roman number string

I just started learning programming a few months ago, and I'm intrigued by Haskell. To learn a bit I tried to adapt some code I have in Java so I can see what are equivalent solutions in Haskell. The ...
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itertools.produce reduced and filtered

I need to generate list of all allowable test combination values of of actor, action and ...
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2answers
86 views

PermCheck Codility

The following code gets 100% on the PermCheck task on Codility. It should be O(N). The question is: A non-empty array A consisting of N integers is given. A permutation is a sequence ...
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Checking if an integer permutation is cyclic in Java

A an integer permutation array[] is said to be cyclic if and only if we can choose an arbitrary element at position i, move it ...
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2answers
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Grid search parameter combinations in Python

For a computation engineering model, I want to do a grid search for all feasible parameter combinations. Each parameter has a certain possibility range, e.g. (0 … 100) and the parameter combination ...
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1answer
52 views

Worker placement in Orleans board game/combinations

I am trying to program the board game Orleans. I am planning on making a computer player that plays randomly at first. The part of the game that I'm struggling to code elegantly at the moment has to ...
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3answers
168 views

Generate all possible permutations of a string in C++

This is my version of the possible permutations of a string challenge. Please give me feedback or criticism. There are two vectors here: positions and ...
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1answer
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Find the combination of matches which are closest to each other

Problem - Given three sorted arrays find combinations which are closest to each other. example - ...
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Counting paths between 3 cities in C++

The task is to make a program that prints out how many possible paths a driver can use to visit three cities so that he visits each city exactly n times. The program must be executed within 1 minute ...
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2answers
248 views

Print out all possible letter combinations a given phone number can represent

I am working on a problem in which given a 7 digit telephone number, we need to print out all possible combinations of letters that each number could represent. I came up with below code and I was ...
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1answer
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General nested for

I needed a general-purpose function that accepts some sequence_container<sequence_container<T>> and iterates all permutations of the inner container. To ...
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1answer
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Python finding next word permutation with function generator

Learning how to use function generators in Python I practiced with the following code that finds the next permutation of a word and then uses this new word as input for the next one until there are no ...
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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 ...
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732 views

Generating the powerset in C

I am solving another problem in leetcode. Given a set, generate all the subsets of the set. Input: [1,2,3] Output: ...
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2answers
468 views

Generating all permutations of 1 digit, 2 equal letters and 2 different letters efficiently

I created a function that generates all the combinations of 1 digit, 2 equal letters and 2 different letters. I reduced the numbers and letters to make it more easy to calculate: ...
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2answers
229 views

Sequence-based enumeration of permutations with Heap's algorithm

Heap's algorithm is an algorithm to generate all permutations of a given array. It ... generates each permutation from the previous one by interchanging a single pair of elements; the other n−2 ...
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3answers
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Disjoint cycles of a permutation

Given an element of the permutation group, expressed in Cauchy notation, it is often useful to have it expressed in disjoint cycles (for example to apply the permutation to the keys of a dictionary). ...
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2answers
68 views

Forming all multiples of 3 using the given digits

I'm working on this kata from Codewars. The task is: Given a certain number, how many multiples of three could you obtain with its digits? Supose that you have the number 362. The numbers that ...
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2answers
121 views

Lattice path from Project Euler with Python solution

I was trying to solve this problem called lattice path from Project Euler: Count the number of unique paths to travel from the top left to the bottom right of a lattice of squares. How many such ...
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1answer
764 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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1answer
443 views

n choose k combination in JavaScript

I was asked to solve a problem for \$\binom{n}{k}\$. I did the following implementation and am wondering if there's any feedback. Input: n = Integer ...
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3answers
664 views

Master Locksmith

Description Master Locksmith has just finished the work of his life: a combination lock so big and complex that no one will ever open it without knowing the right combination. He's done testing ...
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2answers
787 views

Generate Letter Combinations of a Phone Number

The task: Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. and my solution: ...
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1answer
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Fitter Nearest-Neighbor function with three nested loops

Background Problem Consider a set of students that we want to place into Ng groups each of which contains Ns students. Let's ...
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4answers
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Project Euler #15: counting paths through a 20 × 20 grid

I've recently solved Project Euler's 15th problem stating: Starting in the top left corner of a 2×2 grid, and only being able to move to the right and down, there are exactly 6 routes to the bottom ...
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1answer
773 views

Generalized Cartesian Product

Much to my chagrin, neither STL nor Boost has a cartesian product. Namely, given as arguments one or more iterables, create an iterator producing std::tuples of ...
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1answer
56 views

Total of maximum values in all subarrays

This is the crux of a problem found on one of those code challenge sites. I'm fairly new to programming and this was a difficult challenge. I've attempted to solve this with stacks and calculating ...
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2answers
546 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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3answers
739 views

Calculator of combinations without repetition

I am interested to find an absolute value (not an approximation) of "combination without repetition" for given \$n\$ and \$k\$, or \$\binom{n}{k}\$. The brute force solution would look like this <...
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47 views

Count number of cycles in permutation

Write a function that a receives file name and an integer N as arguments, that represent a binary file which contains N integers,...
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1answer
209 views

Bovine Shuffle using a queue (USACO Dec 2017 Silver)

I am working on the "Bovine Shuffle" problem from the December 2017 USA Computing Olympiad, and have got it to work for every test case beside two. When I run these two cases on my own computer, they ...
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1answer
313 views

Splitting URLs into hierarchy-level directories

The goal is to split a URL like http://q.com/a/b/c to: ['http://q.com/a', 'http://q.com/a/b', 'http://q.com/a/b/c'] My code: ...
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1answer
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Mutative Heap's algorithm (permutations generator) in Clojure

For a side project I'm working on, I need to be able to generate permutations. Instead of relying on an existing library like math.combinatorics, I decided to write ...
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1answer
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Custom container for iterating over combinations of elements from multiple sets

Motivated by some SO quesitons [1, 2] I made an attempt at implementing a custom container with a bi-directional custom iterator for iterating over all combinations of elements from multiple sets. I ...
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3answers
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Get all combinations of selecting k elements from an n-sized array

Was asked this today in an interview. Didn't see it before, and spent quite a lot of time getting it to work (tricky with all the recursion). The goal was to find all possible combinations of ...
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2answers
882 views

Maximum sub-array of non-negative numbers

This is the "Maximum sub-array" problem from CodeChef: Find out the maximum sub-array of non negative numbers from an array. The sub-array should be continuous. That is, a sub-array ...
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1answer
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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 ...
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Python solution to Code Jam's 'Rounding Error'

The "Rounding Error" problem of Round 1B of Google Code Jam 2018 is as follows: Problem To finally settle the age-old question of which programming language is the best, you are asking a total ...
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1answer
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Algorithmic complexity of this algorithm to find all ordered permutations of length X

I have written a recursive function to generate the list of all ordered permutations of length X for a list of chars. For instance: ['a', 'b', 'c', 'd'] with X=2 will give [['a', 'a'], ['a', 'b'], ['...
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1answer
114 views

Combinatoric problem in Haskell

I am new to functional programming. Just now I solved my first "real world" task using Haskell and now I'm wondering whether I got it "right" and what can be improved. The problem arises from tensor ...
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3answers
2k views

Determine if one string is a permutation of the another

Can anyone give me some feedback if I'm using std::unordered_multimap optimally? I don't know the ins-and-outs of the ...
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1answer
279 views

A little next combination program in C++

An implementation of next combination function at Discrete Mathematics and Its Applications, Rosen p.438. How it works: Input: The size n of a integer set {1, 2, ..., n}, which is where you choose ...
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1answer
720 views

Permutations with a sum constraint

I have made the following function that gives the combinations permuted of n elements with a constrain/rule. This consist on creating a dataframe with all combination of numbers from 0 to n that sums ...
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2answers
338 views

Python calculate arrangements of sequence

I have just started thinking about probabilities. A Problem that come up was how to calculate all the potential arrangements for a given sequence. By arrangement I mean unique permutation. I ...