Combinatorics is a branch of mathematics concerning the study of finite or countable discrete structures.
4
votes
3answers
234 views
Compute (x+yCx)%mod
I want to compute, as quickly as possible,
$$ \dfrac{(x+y)!}{x!y!} \mod m $$
with \$x,y \le 10^6\$ and a prime \$m=10^9+7\$ (called mod in my code).
My current ...
12
votes
2answers
652 views
TopCoder problem “Lottery” - SRM 144 (Division I Level Two)
The problem statement
Summary:
The rules of a lottery are defined by two integers (choices and blanks) and two boolean variables (sorted and unique). choices represents the highest valid number ...
12
votes
3answers
433 views
Random permutation of int[] and ArrayList<Integer>
I wrote a simple program using int[] and ArrayList<Integer> which aims to get a random permutation output between 1 to 10, ...
6
votes
1answer
148 views
Generate Cartesian product of List in Java
My code, which generates Cartesian product of all lists given as arguments:
...
8
votes
2answers
96 views
Optimizing String combinations in Java
I need to obtain all combinations of a String of length k from the given elements.
For example, for
...
5
votes
4answers
225 views
Character permutations - Revisited
Several hours ago I posted this question about Generating character permutations in Python.
User rolfl said that my main problem was not using the right tool for the job, as Python is interpreted it ...
3
votes
2answers
189 views
Generating character permutations
I want to generate a 'dictionary' containing all 8 character permutations of upper-case letters such that the output file looks like:
...
3
votes
2answers
81 views
A (basic) Knights and Knaves Solver
In case you're not familiar with Knights and Knaves, it's a classic type of logic problem.
Here's an example:
"A very special island is inhabited only by knights and knaves. Knights always tell ...
2
votes
1answer
179 views
Nsum problem: find all n elements in an array whose sum equals a given value
I am implementing the algorithm for the following problem with Python. I am pretty new to Python, so I want to listen to any advice that improve my coding style in a "pythonic" way, even about naming ...
14
votes
4answers
707 views
Count number of ways to paint a fence with N posts using K colors
A friend sent me this question, and I'd love somebody to review this and give his opinion.
Write an algorithm that counts the number of ways you can paint a
fence with N posts using K colors ...
0
votes
1answer
211 views
Generating all possible permutations of the string
This generates all possible permutations of the string. I am also unable to understand the time complexity of this problem. Can someone please explain the complexity to me?
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3
votes
1answer
46 views
Python small brute-forcer
I have 20+ key set. Keyset is like:
Key[0] = { "PossibleKey0", "PossibleKey0Another", "AnotherPossibleKey0" }
Key[1] = { ....
There is an encryption which needs ...
17
votes
2answers
178 views
Advanced and Detailed Minesweeper Probabilities
In an earlier question, I showed my code for calculating the mine probability for each and every field in a Minesweeper board. But it doesn't stop there. In that very same Minesweeper Analyze project, ...
8
votes
2answers
140 views
A Specific Combination
This code is going to be included in my Minesweeper Probabilities project. (so far it only exists on the develop-branch)
The purpose is to return a specific combination, let's say for example that ...
2
votes
3answers
110 views
Finding combinations of 3 numbers
What this code tries to do is find possible combinations of three numbers. For example, let's say I have the following numbers:
1, 2, 3, 4, 5, 6, 7
Some ...
5
votes
2answers
91 views
'Countdown' Numbers round - combine numbers arithmetically to reach a target
Countdown is a British gameshow where contestants compete in word and number challenges. During the numbers round, six numbers are chosen semi-randomly and the task is to combine them using addition, ...
1
vote
1answer
320 views
Print all permutations of a given string in Java
I want to print all permutations of a given string in Java. To do this I create one auxiliary array boolean used[] to check if I have used some character or not.
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5
votes
1answer
1k views
Print all possible combinations of size r, from an array of size n
This is my working solution for the following problem: given an array of integers of size n, print all possible combinations of size r.
Before I proceed to the solution, I have the following ...
1
vote
1answer
61 views
Combinations with replacement
I am still new to Scala and wrote a small snippet to find all the combinations with replacement of a sequence (e.g. cwr(ab, 3) should give aaa, aab, abb, bbb).
The slow way would be to generate all ...
4
votes
1answer
884 views
Recursive function that generates the permutations of a string
I am looking for a review of my recursive function that generates the permutations of a string. Are there better ways to do this?
...
6
votes
2answers
97 views
How can I optimize this combination method?
I have this method that is working perfectly fine, but it's very slow, and sometimes I have to wait 15 minutes to get a good result, which is ok. I'm wondering if I can make it faster.
Basically I'm ...
4
votes
3answers
127 views
Another permutator
This is a solution to this problem. The problem statement:
write a program to display all possible permutations of a given input
string--if the string contains duplicate characters, you may have
...
6
votes
1answer
77 views
Generating Cartesian product of strings in R
Sometimes I need to create character vectors like this one:
...
5
votes
2answers
149 views
Binomial coefficient
I wrote a C++ function to calculate the binomial coefficient, trying to avoid overflows as much as possible.
...
5
votes
2answers
87 views
Possible combinations following a rule
The problem is the following:
We have a number of months to buy a number of supplies. The sooner we finish buying them, the better, but we don't know how much we can buy per month and would like to ...
4
votes
1answer
188 views
Seeking improved Objective-C permutation algorithm
This algorithm seeks to find all of the possible permutations of a word:
...
12
votes
3answers
1k views
Generate all possible combinations of letters in a word
This is a JavaScript function that returns ALL the possible combinations of whatever word the user enters. I am looking to clean this code up a bit...any and all suggestions are welcome!
...
4
votes
1answer
215 views
Permutations program in Python
This code asks for letters and a number of letters per word and generates all possible permutations. Then compares those permutations with an English dictionary and creates a list with all the words ...
3
votes
1answer
95 views
Finding the 'Minimum' AND of all the possible subsets of a set
The subset size should be greater than or equal to 2.
How can I speed up this code?
...
8
votes
1answer
116 views
Verifying boardgame mathematics with MATLAB
I recently bought this math-based boardgame for my little cousins, and am now trying to verify its design with some MATLAB code. The relevant parts of the game are:
A board with numbers from 1 to ...
24
votes
3answers
584 views
Analyzing Minesweeper Probabilities
Calculating probabilities in Minesweeper might sound like an easy task, but I've seen so many probability calculators that's either incorrect, horribly slow, or with ugly code (or all of them) so I ...
6
votes
5answers
649 views
Improving efficiency of Project Euler 185 (16-place Mastermind)
This a solution for Project Euler Problem 185. It works fine for the example but slow for the problem statement. How can I improve its speed and efficiency?
...
3
votes
2answers
849 views
Calculate all possible combinations of an array of arrays or strings
I'm using code adapted from this Stack Overflow question to calculate all possible combinations from an array, which may contains strings.
For example:
...
14
votes
7answers
3k views
Is my solution to return kth row of the Pascal's triangle suitable for a job interview?
Question:
Given an index \$k\$, return the \$k\$th row of the Pascal's triangle.
For example, given \$k = 3\$, return \$[1,3,3,1]\$. Bonus points for using \$O(k)\$ space.
Can it be ...
7
votes
3answers
1k views
Get distinct combinations of numbers
The below code returns all distinct combinations based on the logic that 1,2,3 = 3,2,1 = 2,3,1, so it only returns 1 instance of that set of numbers.
...
1
vote
1answer
56 views
Find triangles from line
I have some lines that form triangles. I'd like to challenge the fastest way to find all triangles.
In particular the code should take an ArrayList of Line2D object and return an ArrayList of ...
7
votes
2answers
96 views
Simplified Bin Packing using JavaScript
This code determines the maximum number of boxes (one size) that can fit into the back of a truck, checking all possible orientations to ensure maximum Bin Packing excitement. This is (hopefully) the ...
6
votes
1answer
156 views
Given a shape, return all triangles that can be formed
Given a shape, get all triangles that can be possible by connecting the points.
Example: given 3 points, only 1 triangle is possible, but given a pentagon, 10 are possible.
Also the ...
4
votes
4answers
134 views
Better way to achieve looped output result
I have 4 variables - say A, B, C and D
Each variable can have 4 values - say 1, 2, 3 and 4
I need to generate all possible combinations of values
Example of Expected Output:
...
3
votes
3answers
83 views
Curious fractions in functional Ruby
Problem 33 in Project Euler asks:
The fraction 49/98 is a curious fraction, as an inexperienced
mathematician in attempting to simplify it may incorrectly believe
that 49/98 = 4/8, which is ...
7
votes
1answer
129 views
Speeding up subset sum implementation
Important fact: the number of the input is greater than 1. How do I use this fact to speed up this solution?
...
7
votes
3answers
262 views
Optimizing unique partitions of integers
I am working on a project involving the unique partitioning of integers. I.e. I am looking to have all of the partitions of n = x1 + x2 + x3 + ... + xk, where xi = xj implies i = j.
For example, if I ...
7
votes
1answer
72 views
Compute stats on two class vectors
Below is a full working code example of code which is used to compute stats on two class vectors (partitions).
There are two functions:
pairwise_indication and
...
10
votes
2answers
695 views
Printing permutations of a given string
I want some feedback on the program I developed in C for printing the permutations of a given string.
...
0
votes
1answer
138 views
Finding the number of permutations of an integer array with equaling difference (not in order)
The array size is <= 16. The difference is defined as:
diff[i] = array[i+1] - array[i];
I need to find the number of permutations of the original array, which ...
4
votes
0answers
346 views
Nonogram puzzle solution space
I've written some code to brute-force enumerate the solution space of nonogram puzzles up to a certain size. It does a good job up to the first ~4 billion puzzles, but I run out of disk space to store ...
7
votes
2answers
147 views
Generate permutations with symbols
Goal: Create a combination of emails based from inputted first name, last name, middle name, and a domain. Add in common separators. Then I'll check which one is correct with the rapportive API. This ...
4
votes
3answers
614 views
Prints out all ways to multiply smaller integers that equal the original number
Write a program in Java that takes a positive integer and prints out all ways to multiply smaller integers that equal the original number, without repeating sets of factors. In other words, if ...
5
votes
1answer
128 views
Project Euler #15 in haskell
I've solved Project Euler #15 in Haskell, but I feel like there might be a better way to express my solution that I'm not seeing. I start out defining my types:
...
3
votes
2answers
1k views
Permutation of a string eliminating duplicates
This code lists the permutations of the string, and eliminates duplicates if any.
I'm looking for code review, best practices, optimizations etc.
Also verifying complexity: O(n! * n) as time ...
