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

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Heap's algorithm - integer permutation

Integer permutation using Heap's algorithm: ...
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1answer
60 views

Permutations of a list in Haskell

I have this piece of code which given a list returns another list which combines every element with every other element (without repetitions) using a given function as a combiner. I came up with three ...
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2answers
197 views

You need to diversify your strings

Challenge: Write a program which prints all the permutations of a string in alphabetical order. Specifications: Your program should accept a file as its first argument. The file contains ...
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1answer
34 views

Sentence maker with thesaurus

I'm teaching myself Ruby by rewriting PHP solutions, such as this one. The program should match words in a sentence with a dictionary of synonyms and then make combinations with them. ...
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1answer
65 views

Print permutations in an iterative way

I've written the following code to print all the permutations of a list. For example: \$[1, 2, 3]\$ has these permutations: \$[1,2,3]\$, \$[1,3,2]\$, \$[2,1,3]\$, \$[2,3,1]\$, \$[3,1,2]\$, and ...
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2answers
76 views

Summing all numbers that can be formed from a list of integers

Following a challenge on HackerRank, I want to find the sum of all numbers that have no more than x 4's, y 5's, and ...
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4answers
862 views

Staircase problem solved using recursion

Problem Question taken from here. I want to go up a flight of stairs that has n steps. I can either take 1 or 2 steps each time. How many different ways can I go up this flight of stairs? Write a ...
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2answers
62 views

Applicative permutation to generate knight moves

I want to understand Haskell better by trying to stretch possibilities of Functor, Applicative, and Monad as much as possible and study how they behave. So in Learn You a Haskell there's an exercise ...
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2answers
53 views

Linear cryptanalysis of a substitution permutation network

I was translating a script I had that would automate linear cryptanalysis of SP networks from Python to C++. For those who aren't familiar with cryptography, linear cryptanalysis involves finding ...
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1answer
92 views

Stable reversed Tartaglia's triangles

Inspired by Minimising the triangle I am writing a fully tested program to solve the following problem: A triangle needs a good foundation. Every row in the triangle is derived from the sum of ...
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2answers
77 views

Count the number of combinations with gap-restriction for every pair of values

A lottery draw consists of choosing 6 different values from 1 to 50. I want to calculate the number of combinations with gaps of at least 3 between every pair of values. I have used the following ...
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2answers
88 views

Minimum number of coins to make change

I am new to programming and I am taking CS50 2014 online through iTunes University. This is the change-making problem in Problem Set 1: Write a program that first asks the user how much change is ...
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1answer
60 views

Printing all factorizations of a number

For example, if we have 120, the answer should contain (2,2,2,3,5),(2,60),(4,30),... Here is my not-so-good attempt ...
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1answer
141 views

Counting unordered factorizations with distinct parts

Trying to solve this combinatorics problem, I wrote some functions to count the number of unordered distinct factorizations of an integer n into ...
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1answer
43 views

Project Euler #70: Time Efficiency Improvement

The problem was to find which \$n\$ for which \$\varphi(n)\$ is a permutation of \$n\$ and \$n/\varphi(n)\$ is minimum,now as we all know that means (simple conclusions from mathematics): ...
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1answer
71 views

Counting friends of friends of friends

Can you comment, review or suggest things for this? Maybe it should be broken into two methods? friends is a list of strings of ...
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1answer
47 views

Project Euler #62 + Java 8 streams

(inspired by: Finding the smallest cube for which exactly five permutations of its digits are cube) The digits of the cube, 41063625 (3453), can be permuted to produce two other cubes: ...
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2answers
269 views

Minimising the triangle

A triangle needs a good foundation. Every row in the triangle is derived from the sum of the two values below it. However, there can be no repeated values, if a value shows up more than once the ...
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5answers
584 views

Finding the smallest cube for which exactly five permutations of its digits are cube

(Project Euler #62) The digits of the cube, 41063625 (3453), can be permuted to produce two other cubes: 56623104 (3843) and 66430125 (4053). In fact, 41063625 is the smallest cube which ...
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2answers
164 views

All upper and lowercase permutations of a string

A couple of questions: Is the algorithm wasting CPU time or memory unnecessarily? If there is something in the code that is not idiomatic Python, how to improve on that? ...
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2answers
149 views

Permutations in C#

I have a program that will get all possible permutations of a certain equation: A + 13 * B / C + D + 12 * E - F - 11 + G * H / I - 10 == 66 Where A, B....I is a value 1-9, and where each digit ...
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3answers
229 views

Letter combinations of phone dial pad number

In preparation for interviews, I have written a solution to this question: Given a sequence of numbers (34128) and an input map such as a dial pad on a phone (2->[a,b,c], 3->[d,e,f], ...
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1answer
71 views

Safe cracker string with all combinations

Imagine a safe with a 4-digit code, and accepting a continuous stream of code entries, such that when the 4 digits are seen in the right sequence, the safe opens. Generate a short string that ...
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2answers
60 views

Solver for Jumble puzzle

Here is my first attempt to solve Jumble puzzle: ...
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1answer
131 views

Password Attacker (Google apac test problem)

Original Problem Short Summary: Given a \$M\$ possible characters all of which must be used at least once, find the number of possible combinations of length (exactly) \$N\$. The ...
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5answers
157 views

Permutation of n lists

I have code which gives permutations for 10 lists. The code works fine for small number of lists with small number of values. Result : It should return all possible permutations. I have to store the ...
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1answer
566 views

Solving the 'Vietnamese school maths problem'

Having read Can you do the maths puzzle for Vietnamese eight-year-olds that has stumped parents and teachers?, which presented the problem of filling in numbers 1 to 9 to satisfy $$ a + 13 ...
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2answers
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Unique combinations of sets with N min selections of overall set

I'm in the process of attempting to write a parser compiler. In this, sets play a major role. I'm in the 'lexical ambiguity' isolation phase, and to that, I need to yield a set of every possible ...
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1answer
82 views

Generating alphanumeric combinations

I was happy with my shell script that needed to generate alphanumeric combinations of length N (in this case, 3) for i in {a..z}{a..z}{a..z}; do ... Now I became ...
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1answer
37 views

Generating combinations of n elements in groups of k

I've written this program that writes all the combinations (without repetition) of n elements in groups of k. I think the code is good, but I like to know if you have some better (or faster) ...
3
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1answer
70 views

Necklace counting problem-with consecutive prime constraint

This is codeEval challenge to count the number of chains possible to make with beads holding numbers. Constraint is sum of the consecutive beads of chain should be a prime number. The standard ...
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2answers
80 views

Permutation and combination calculator

I wanted to make something for the Community Challenge, so I made a simple permutation and combination calculator. I'd like input on: The overall design - any suboptimal choices that could be ...
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2answers
69 views

Printing all the permutations of a string in alphabetical order-ver1.1

I adapted most of the suggestions from answers for my previous question Printing all the permutations of a string in alphabetical order to rewrote my solution again. Please let me know any more ...
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2answers
124 views

Genetic algorithm for solving a puzzle (v. 2)

Thanks to your wonderful comments regarding the first version of my code, I have been able to improve it. This new version is more readable (I guess). The problem is that it seems to me that there is ...
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3answers
1k views

Genetic algorithm for solving a puzzle

Edit. Version 2. I am working on a genetic algorithm in order to solve a little "puzzle." Given a text file with N rows with 4 int each, the idea is to ...
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4answers
144 views

Printing all the permutations of a string in alphabetical order

It is a code eval challenge question https://www.codeeval.com/open_challenges/14/. My answer was accepted, and I modified my code again to improve it. Please let me know is it possible to improve it ...
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1answer
57 views

Calculate number of possible combinations to make $100 with all US denominations

I know that this could be made much more efficient, I am just not sure as to how. This program ignores the 100 dollar denomination to cut computation time in half and just starts ...
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2answers
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Generating letter combinations

It's about two months since I posted this question on CodeReview. I've been working hard to improve the code posted there and came up with the following. ...
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2answers
153 views

Consecutive Primes challenge at CodeEval.com and memory allocation issue

I finally solved this challenge with using recursion and figured out why the automatic scorer wasn't passing my previous solutions. I was using NSMutableArray to ...
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1answer
130 views

Consecutive Primes challenge at CodeEval.com

I am working through a new challenge on CodeEval.com and I think I am getting a correct result but I can't get through their grader. I am not exactly sure where error is. I didn't post this on stack ...
3
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1answer
44 views

Fast canonical indexing of elements in array

Given two arrays of elements: aaabbccdefaa zzzccddafgzz I want to check whether these two arrays are equivalent up to a relabeling. My strategy is to map them into a canonical form and ...
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2answers
137 views

Is_permutation() on sequence containers in O(n) complexity - follow-up

This question is a continuation of my previous question: Check is_permutation on a pair of same sized arrays. I improved the implementation to generalize for all sequence containers. Please let me ...
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1answer
68 views

Modified Coupon Collector's Problem in Java

What is Coupon Collector's Problem? In probability theory, the coupon collector's problem describes the "collect all coupons and win" contests. It asks the following question: Suppose that there ...
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2answers
87 views

Expected value (and distribution) of sum of six balls labeled 1-49, no replacement

This code finds expectation and standard deviation of sum(x) of 6 digited base-49 numbers with all digits distinct. The expectation is: \$\mu={\rm ...
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2answers
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Project Euler 78: Counting Partitions

Project Euler problem 78: Let \$p(n)\$ represent the number of different ways in which \$n\$ coins can be separated into piles. For example, five coins can be separated into piles in exactly seven ...
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2answers
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Check is_permutation on a pair of same sized arrays

After considering the suggestions of my previous question Check whether given a pair of arrays are permutation of each other, I changed the code. Resolved the bug reported earlier In place of ...
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1answer
108 views

Calculating 24 from 4 numbers (math Poker game)

This is a game of math in Poker. Two people each have a pile of cards. They then each place 2 cards on the table at the same time. Every card is treated as a number. The players need to find a way to ...
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1answer
96 views

Generate all permutations

I have written this Java snippet to generate all permutations of a given array of integers. Can somebody review it and give some pointers as to how to make it more generic? I.e. instead of dealing ...
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2answers
126 views

Simple Factorial Interview Task

I did this code for an interview. Can you tell me how it looks? I didn't get the job, so I'm wondering what I could do better in my code. ...
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2answers
244 views

Finding a word within a pre-defined set using a search string with wildcards

The other day I was intrigued by this question (originally from here): Write a program that answers YES/NO search queries containing * placeholders. Example: if the data you have is (hazem, ...