# Questions tagged [combinatorics]

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

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0answers
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### Is my approach not correct? [closed]

Numbers of length N and value less than K I have been trying this mathematical question, from past few hours The approach I followed is simple, we can put less valued digits, at each position of given ...
1answer
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### Building a tree containing all permutations of arithmetic expressions given some numbers

Given any series of numbers, for example 1,2,3,4,5 and given the arithmetic operands + - * / including parenthesis, what would be the most optimal way to build a tree that contains all permutations ...
1answer
92 views

### Find all combinations of numbers of a set that add up to a given target - avoid for loops

I am thinking about the following problem: Consider a 3-numbers lock, i.e. a lock which has three little number wheels that opens whenever the sum of these three numbers equals 75. I know, this doesn'...
2answers
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### Rust implementation of next-permutation

I am translating this next permutation algorithm in C++: ...
2answers
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### Generate all possible unique combinations of positive numbers these have sum equal to N

This is my function to generate all possible unique combinations of positive numbers these have sum equal to N. For example: If the input is 4 The output should ...
0answers
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### Fast bruth force numpy array combination

I want to extract combinations of numpy arrays in that way: ...
2answers
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### Find All Permutations of String in Scala

I created the following function, permutations, to produce all permutations of a List[A]. Example: ...
2answers
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### Next different permutation in C

This is a program which you can get the next "different", i.e. elements in A[] can be identical, permutation at each call. I've written a C++ program for ...
1answer
131 views

### Generating permutations fast

I run into a performance bottleneck in a program. I have to generate all permutations for a given sequence with size up to n=11. My code: ...
1answer
63 views

### Count the different positions reached in a cycle of permutations

I have come across a problem on cyclic permutations. It is about swapping numbers around. It starts out with input N < 100,000 which makes the first N natural numbers as orders: 1 2 3 ... N-1 N ...
1answer
41 views

### Generating random permutation with forced change of order (Secret Santa)

I wrote this function to generate random permutation of input vector, while making sure every element has switched place (for a Secret Santa like purpose). ...
3answers
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### Ruby: possible Poker holds for a hand of length n

Hello everyone and thanks in advance for taking the time to read my post!! In the process of learning Ruby, I'm writing a video poker machine that analyzes hands represented by arrays of Cards, like ...
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### Creating some Loaded Dice to make our board game fairer

Some friends and I were playing a board game and decided that the random dice rolls just weren't fair! So we came up with a scheme for making the rolls slightly more evenly distributed, and I ...
1answer
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### Summing Sequence with Combinatorics

I am looking for help for two things. proof of correctness (the tests have passed, but I do not now how to prove it correct) Improvements on the Algorithm Efficiency. The algorithm goes through 2 ...
1answer
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### How to find the next sequence of integers?

I was thinking of the following problem: List all sequences $a_1, a_2, a_3, a_4, a_5, a_6, a_7$ of positive integers where $1 \le a_1 < a_2 < \ldots < a_7 \le 39$. For any sequence ...
2answers
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### Best Algorithm for solving USACO: Photoshoot - Python

I was trying to solve this problem with Python 3.8. I couldn't find a way other than to brute-force calculate all the possible permutations then check which permutation was valid. The program works ...
1answer
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### Combinatorics, C++ and optimization

Note: I have a working solution, my question is about optimization and other approaches. Problem Description Hello, I'm re-writing an old program I made that solves nonograms. As part of solving it, I ...
1answer
237 views

### Simple generic cartesian product in C++

The idea is to take a sequence of sequences (of the same type) and use tuples of [iterator, current index, sequence size] to keep track of the current state, such ...
2answers
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### Combinatorics challenge solved it Python

The easiest way to explain this problem is to show these two test cases: ...
1answer
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### Permutations in C

I searched on the internet for an algorithm for permutations in C and I found the following function: ...
2answers
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### Method to generate a List<string> containing permutation of an input string

I'm working to understand Big O notation. As such I'm going through examples and the algorithm below generates the permutations for a given input string which contains only distinct characters. IE no ...
1answer
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### Filter out unwanted substrings while generating all possible relevant substrings

Write a Program that determines where to add periods to a decimal string so that the resulting string is a valid IP address. There may be more than one valid IP address corresponding to a string, ...
1answer
143 views

### Generating all variations of M*N matrix containing boolean values

I've implemented an algorithm that generates all variations of a matrix of size $M*N$. My approach is that I see a matrix as a list where the position of elements can be calculated from the position ...
1answer
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### Time and Space Complexity of Leetcode Problem #31. Next Permutation

The question is as follows: Given a collection of distinct integers, return all possible permutations. Example: ...
1answer
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### Printing all permutations of digits of a number

So, a long time ago, I've made a program that prints all the permutations of digits of a number in AEC. Now I have refactored it a bit, and I would be interested in what you think about it. ...
2answers
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### Performance is too low, online compiler wants a faster way to find all possible combinations of k numbers out of 1…n

I have to find a method (using backtracking) to list all possible combinations, in lexicographical order,of k numbers out of the interval [1,n].. duplicates are not allowed. i.e: input: 5 3output:1 2 ...
1answer
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### An r-length permuter in c++

In relation to the question I asked here, I myself came up with an answer. I would like constructive criticism and tips to improve it to make it efficient like the other answers that have been posted. ...
1answer
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### Finding Possible Strings from Series of Numbers

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 is done just like they are arranged on a ...
1answer
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### Finding permutations efficiently

I have the following: A set of K time-series in a numpy array with dimensions T x K. A set of ...
3answers
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### Refactor the code which performs “cross-product”, “reduce”, “product of list” and “sum of list”

I have come up with a sequence of steps to find the maximum product of y positive numbers which add up to x. But the program is ...
4answers
226 views

### Check whether a permutation with one fixed point can be rotated into one with two fixed points

A friend gave me the following riddle: Given n people with n distinct names, you place n names tags on a round table with n seats. If the n people now sit at those seats randomly such that exactly ...
3answers
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### BFF Word Finder

Inspired by this question on Puzzling.StackExchange, I've decided to write a small python script that determines if a word is a BFF Word. Below are the parameters, solved by Puzzling user Stiv, also ...
1answer
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### Count number of ways that sequences contain at least one of the given subsequences

Peter loves dices and some special numbers. Therefore he thrown dice n times and concatenate the numbers. Compute the probability that if he throws 6 to 27 seven times dice and concatenate the numbers,...
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63 views

### Find only one subset sum with a specified value in python for large sets

how can I optimize my code for a large set (10000 elements)? ...
2answers
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### Permutations with replacement in Python

Many a times, I've had the need to use a permutations with replacement function. So, I've written a function to do just that: ...
1answer
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### Performance of mask (1,2,4,8,16) convertor in python

My mask translator is performing poorly in scenario where I have 30 masks and 10,000 ownerships. This is a bit field and similar to bit masks such as enum.IntFlag. ...
1answer
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### Outputting flavor text depending on inputted strings

I have this program that takes two strings from the user, stores them in mixArray, then "mixes" them with mixItUp() and outputs ...
1answer
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### Minimum amount of spaces inserted in a given string, such that it gets composed only of elements from a given list

The Challenge Given a big string and a list of smaller strings, find the minimum amount of spaces that must be inserted between characters of the string in such way that it becomes composed only of ...
1answer
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### Calculating every possible answer given a set of formulas

Problem Given a set of formulas (AKA "Rules"), get a list containing every possible answer that does not break any formula. Formula variables can have a maximum equal to the number of characters. ...
2answers
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### MaxProductOfThree in C#

This is my solution for the MaxProductOfThree from codility, it scores 100%, but I'm not a fan of the if if if structure it has going on. Task description ...
2answers
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### Letter Combinations of a phone number using a Dictionary

Problem statement (online source) Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone ...
1answer
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### Recursive code to generate a parametric sweep of input values

I generate a set of data based off every combination of inputs. The source range that's inputs requires headers to identify the parameters. In its present state I'm not content as it's not as ...
2answers
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### Earliest time frog can jump to the other side of a river in C#

I'm new to C#, I programmed a little in Java in the past. I had the two previous exercises reviewed here (permCheck, cyclicRotation, with a 100% score, just like this one), and I'm applying what the ...
2answers
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### Codility's Permutation Check in C#

I've made a few things in Java, and now I'm learning C#. The code passes the tests with 100% final score. I want to know what things can be improved in my code. Task description A non-empty ...
2answers
252 views

### Go function to generate permutations of a given integer array

I'm writing a function to generate a permutation of given []int: ...
2answers
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### Counting block combinations I: Project Euler 114

Problem statement (For more detailed description (including pictures), please, visit the link): A row measuring seven units in length has red blocks with a minimum length of three units placed on ...
1answer
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### Counting Bouncy Numbers: Project Euler #113

Problem statement: Working from left-to-right if no digit is exceeded by the digit to its left it is called an increasing number; for example, 134468. Similarly if no digit is exceeded by ...
3answers
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### Mapping words to letters which contains

Given sentence for example: ala ma kota, kot koduje w Javie kota I should to every letter occurring in the sentence I should map every string that this letter ...