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

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4
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4answers
117 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
32 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
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1answer
64 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, ...
9
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1answer
79 views

Minesweeper analyze goes to N-Queensland

As @rolfl recently solved the N-Queens problem, I figured that it was time also for me to solve it. My approach is significantly different from @rolfl's. I quickly realized that the N-Queens problem ...
4
votes
3answers
315 views

Truth Table Calculator

In of my software engineering classes, I had to write a truth table calculator in the language of my choice. This is what I came up with, and I would like to know what I should do better next time: ...
1
vote
1answer
29 views

Print all subsets and permutations of a string

The following code is designed to accept a string from the user that is at most 5 characters long. It will then find each possible substring of the string and print all possible permutations of each ...
8
votes
3answers
222 views

Pairwise combinations of an array in Javascript

I wrote a Javascript function that seems to successfully generate the unique pairwise combinations of a list: ...
4
votes
1answer
101 views

Tracking Eye Movements

The following class (that was my first class ever in python) was used in an eye tracking context. Imagine a context where you always will have a single gaze-point and some closed contours. How can I ...
5
votes
3answers
151 views

Finding the given word from jumbled letters

I have tried to write JavaScript code to check whether I can form a word from the given string (jumbled): ...
3
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2answers
88 views

Print all permutations with some constraints

I've the following problem: Print all valid phone numbers of length n subject to following constraints: 1.If a number contains a 4, it should start with 4 2.No two consecutive ...
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1answer
43 views

Generating all permutations of a list [closed]

I'm looking for feedback on the following functions to generate permutations of a list. I'm new to programming and did this as an exercise after taking an on line algorithms course. I think it is ...
3
votes
1answer
72 views

Decompose a value as a sum of square numbers

My daughter had a question on her maths homework which was to write a value as a sum of 4 or fewer square numbers. For example, x = 73 could be 36 + 36 + 1. I came up with a really brute force ...
3
votes
3answers
67 views

Listing the representations of integer M as a sum of three squares M = x^2 + y^2 + z^2

I am trying a number as the sum of 3 squares. For my particular project I will require a complete list since the next step is to compute nearest neighbors (here). In any case we'd like to find \$ M ...
5
votes
3answers
247 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
712 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
612 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
288 views

Generate Cartesian product of List in Java

My code, which generates Cartesian product of all lists given as arguments: ...
8
votes
2answers
110 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
240 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
238 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
540 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
818 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
768 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? ...
3
votes
1answer
50 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 ...
20
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3answers
247 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
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2answers
153 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
163 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
113 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, ...
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1answer
572 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. ...
5
votes
1answer
2k 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
64 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
2k 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
101 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
131 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
108 views

Generating Cartesian product of strings in R

Sometimes I need to create character vectors like this one: ...
5
votes
2answers
202 views

Binomial coefficient

I wrote a C++ function to calculate the binomial coefficient, trying to avoid overflows as much as possible. ...
5
votes
2answers
92 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
248 views

Seeking improved Objective-C permutation algorithm

This algorithm seeks to find all of the possible permutations of a word: ...
12
votes
3answers
2k 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
332 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
101 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
120 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 ...
23
votes
3answers
654 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
703 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
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2answers
1k 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: ...
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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. ...
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vote
1answer
60 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
103 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 ...