Combinatorics is a branch of mathematics concerning the study of finite or countable discrete structures.
6
votes
2answers
57 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 ...
1
vote
1answer
51 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
...
1
vote
0answers
25 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 ...
2
votes
1answer
42 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):
...
1
vote
1answer
63 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 ...
4
votes
1answer
42 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:
...
3
votes
0answers
56 views
Minimising the triangle
Below is some code that will solve the problem:
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 ...
5
votes
5answers
554 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 ...
3
votes
2answers
145 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?
...
3
votes
2answers
124 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 ...
3
votes
3answers
128 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], ...
4
votes
1answer
49 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 ...
4
votes
2answers
54 views
4
votes
1answer
94 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 ...
4
votes
5answers
149 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 ...
5
votes
1answer
533 views
Solving the 'Vietnamese school maths problem' [closed]
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 ...
0
votes
2answers
70 views
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 ...
2
votes
1answer
74 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 ...
2
votes
1answer
33 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
votes
1answer
52 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 ...
3
votes
2answers
62 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 ...
3
votes
2answers
65 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 ...
2
votes
2answers
119 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 ...
8
votes
3answers
966 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 ...
2
votes
4answers
136 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 ...
4
votes
1answer
49 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 ...
3
votes
3answers
70 views
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.
...
5
votes
2answers
120 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 ...
1
vote
1answer
118 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
votes
1answer
41 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 ...
3
votes
2answers
126 views
Is_permutation() on sequence containers in O(n) complexity
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 ...
4
votes
1answer
58 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 ...
4
votes
2answers
78 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 ...
3
votes
2answers
63 views
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 ...
3
votes
2answers
89 views
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 ...
7
votes
1answer
96 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 ...
0
votes
1answer
75 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 ...
3
votes
2answers
104 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.
...
12
votes
2answers
225 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, ...
3
votes
1answer
86 views
Letter Combinations of a Phone Number
I was asked to code a solution in Python in 15 mins. Print all possible word combinations for a given phone number. Numbers 0 and 1 will not be part of the phone number, the numbers can be repeated, ...
1
vote
1answer
114 views
Optimizing Diwali Lights problem in C
I was trying to solve the Diwali Lights challenge on HackerRank.
Problem Statement
On the eve of Diwali, Hari is decorating his house with a serial light
bulb set. The serial light bulb set ...
2
votes
2answers
248 views
3
votes
0answers
63 views
Generating all permutations of a template pack
AllPermutedPacks<Pack<Types...>>::type is to be the pack of packs consisting of all permutations of Types.... For ...
0
votes
1answer
52 views
Permutations of a string
I wrote the following code to permute the characters of a string assuming there is no repeated character.
I also want to make sure the space complexity of this algorithm is \$O(n*n!)\$: There are ...
1
vote
0answers
46 views
Approximately putting integers into buckets such that the sum of bucket differences is minimized
I have the need for load balancing in my MSD-radix sort routine and doing it optimally is not an option. So I tried to play with two simple routines for putting integers into a prespecified amount of ...
1
vote
2answers
94 views
0
votes
2answers
101 views
Two permutation iterators for classes in Python with and without a generator
I am just testing out a couple of small classes for learning purposes. Here is my current working code:
...
4
votes
4answers
165 views
Finding Lottery odds - Topcoder #268
I have implemented the question #268 from Topcoder. The question is that there are 4 conditions for a lottery ticket:
CHOICES - numbers available (10 ≤ CHOICES ≤ 100)
BLANKS - number of numbers that ...
4
votes
1answer
60 views
String manipulations (reverse a string by characters, permutation)
I'm trying to solve simple Java problems in various ways. Could anyone comment about the code, like how it could be better, and what could be a problem?
...
2
votes
1answer
67 views
Accessing list elements when counting the number of rectilinear paths
I am trying to solve the RIVALS problem on SPOJ: Starting from (0, 0), how many paths are there to reach point (X, Y), only taking one-unit steps moving to the right or up? Constraints: 0 ≤ X ≤ 106, ...
