Questions tagged [combinatorics]
Combinatorics is a branch of mathematics concerning the study of finite or countable discrete structures.
448
questions
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1answer
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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).
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2answers
14 views
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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0answers
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2answers
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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 ...
2
votes
1answer
40 views
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 ...
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vote
1answer
101 views
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 ...
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2answers
168 views
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 ...
7
votes
1answer
373 views
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 ...
6
votes
1answer
114 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 ...
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2answers
71 views
Combinatorics challenge solved it Python
The easiest way to explain this problem is to show these two test cases:
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5
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1answer
138 views
Permutations in C
I searched on the internet for an algorithm for permutations in C and I found the following function:
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8
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2answers
122 views
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 ...
4
votes
1answer
54 views
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, ...
2
votes
1answer
137 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 ...
2
votes
1answer
33 views
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:
...
2
votes
1answer
40 views
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.
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2
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2answers
106 views
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 ...
2
votes
1answer
31 views
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.
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2
votes
1answer
61 views
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 ...
3
votes
1answer
75 views
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 ...
7
votes
3answers
218 views
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 ...
5
votes
4answers
156 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 ...
3
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3answers
88 views
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 ...
2
votes
1answer
48 views
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,...
2
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0answers
39 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)?
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2answers
2k views
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:
...
5
votes
1answer
172 views
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.
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4
votes
1answer
64 views
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 ...
5
votes
1answer
63 views
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 ...
5
votes
1answer
101 views
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. ...
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2answers
134 views
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
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7
votes
2answers
241 views
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 ...
11
votes
1answer
116 views
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 ...
10
votes
2answers
1k views
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 ...
6
votes
2answers
494 views
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 ...
4
votes
2answers
162 views
Go function to generate permutations of a given integer array
I'm writing a function to generate a permutation of given []int:
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2
votes
2answers
186 views
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 ...
4
votes
1answer
217 views
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 ...
2
votes
3answers
98 views
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 ...
3
votes
3answers
141 views
Counting numbers that are divisible by 3 and can be produced from the digits of a given number
I'm trying to solve this problem from codewars.
Problem
Given a certain number, how many multiples of three could you obtain with its digits? Suppose that you have the number ...
6
votes
4answers
2k views
LINQ for generating all possible permutations
Permutate() is supposed to generate all possible permutations of the source sequence:
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3
votes
2answers
79 views
Fixed Content Necklace Generator
I wrote a class that generates combinatorial necklaces with fixed content as per Sawada: A fast algorithm to generate necklaces with fixed content. The class is instantiated with an input list that ...
11
votes
3answers
473 views
Print sums of all subsets
Print sums of all subsets of a given set
Problem summary : Print all subset sums of a given set of integers
My approach is to store previous results and use them to calculate new (similar idea as ...
3
votes
2answers
174 views
Challenge: phone keypad to letters - return all possible strings
The challenge:
Given a mapping of digits to letters (as in a phone number), and a digit string, return all possible letters the number could represent. You can assume each valid number in the ...
2
votes
2answers
217 views
Project Euler # 24 Lexicographic permutations in Python
A permutation is an ordered arrangement of objects. For example, 3124 is one possible permutation of
the digits 1, 2, 3 and 4. If all of the permutations are listed numerically or alphabetically, we ...
4
votes
2answers
394 views
Letter case permutation
The question can be found here https://leetcode.com/problems/letter-case-permutation
Given a string S, we can transform every letter individually to be
lowercase or uppercase to create another ...
2
votes
2answers
626 views
Staircase challenge - Python
Your task is to print all unique ways to climb a staircase of length n where, from each step, you can take steps of size x where ...
6
votes
1answer
131 views
A straightforward method for computing the Binomial probability mass function
I've been writing up code to test an alternate way of calculating the Binomial probability mass function. The Binomial random variable is the number of heads out of N coin tosses with coins that have ...
4
votes
2answers
88 views
Array of all permutations in C
Is this a good compromise between readability and verbosity? Are there any bugs, additional error checking, or extraneous code as well?
...
11
votes
6answers
4k views
HackerRank: Electronics Shop
Challenge from Hacker Rank -
Monica wants to buy a keyboard and a USB drive from her favorite electronics store. The store has several models of each. Monica wants to spend as much as possible for ...
