A permutation is a particular ordering of some list of objects. Problems tagged with permutation usually involve finding or generating permutations.
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What are the five most powerful characters in your language?
Choose any five characters your language supports. There are 5! = 5×4×3×2×1 = 120 ways these can be arranged into a 5-character string that contains each character once; 120 ...
13
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2answers
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Match the permutations!
Your challenge is to create a regex that matches every string permutation of itself, and nothing else. The match must also be case-sensitive.
So, for example, if your regex is:
ABC
It should match (...
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Alphabetically permute a string
Task
Your goal, should you choose to accept it, is to write a program, that, given an input string (or array of characters), outputs every possible permutation of the letters in that string. I'm ...
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8answers
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Generate antsy permutations
Introduction
I defined the class of antsy permutations in an earlier challenge.
As a reminder, a permutation p of the numbers from 0 to r-1 is antsy, if for every entry p[i] except the first, there ...
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Antsy permutations
Introduction
Suppose you have a ruler with numbers from 0 to r-1.
You place an ant between any two of the numbers, and it starts to crawl erratically on the ruler.
The ruler is so narrow that the ant ...
10
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2answers
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Wolves and Chickens Puzzle Golf
Wolves and Chickens
There's a river and there are wolves and chickens on one side of the river. They have a raft and they all need to get to the other side. However, the raft cannot travel on its own....
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15answers
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Compute the Eulerian number
The Eulerian number A(n, m) is the number of permutations of [1, 2, ..., n] in which exactly m elements are greater than the previous element. These are also called rises. For example, if n = 3, there ...
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Inverse permutation index
Introduction
The lexicographical permutations of a list with n elements can be numbered from 0 to n! - 1. For example, the 3! = 6 permutations of (1,2,3) would be (1,2,3), (1,3,2), (2,1,3), (2,3,1), (...
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List all ordered partitions of n
The challenge is to list all ordered partitions (composition (combinatorics)) of a given positive integer n. These are the lists of numbers from 1 to n whose sum is n. For example, given input n = 4, ...
17
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8answers
876 views
Prime factors buddies
Given an integer N > 1, output all other numbers which prime decompositions have the same digits as the prime decomposition of N.
For example, if N = 117, then the output must be [279, 939, 993, ...
9
votes
15answers
765 views
Shuffle a mapping
We define a map as a set of key-value pairs. For this challenge, you need to take each of the values and assign them to a randomly chosen key.
You must randomly shuffle the values, and output the ...
2
votes
9answers
298 views
Noah's (upgraded) ark
As preparation for the nth Exodus, Noah decides to write a program that will decide If he will let animals on his ark. However, Noah wants to go back to grass roots. Thus he decides that the program ...
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20answers
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Greater than less than greater than something fishy
Given a length N string of less-than and greater-than signs (<, >), insert the integers 0 through N at the start and end and in between each pair of signs such that all the inequalities are ...
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votes
22answers
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Sheffle tho vawols ureund!
Given an input string, output that string with all vowels a, e, i, o and u swapped at random between each other.
For example, in the string this is a test, there are 4 vowels: [i, i, a, e]. A valid ...
10
votes
5answers
212 views
Steps of Permutation
Write a function which takes a set of integers and prints every permutation of the set, and the swap performed in between each step
Input
a set of integers, for example (0, 1, 2)
Output
the list ...
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8answers
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The Permutation Pigeon-hole Principle
In the game of sudoku, many players like to "pencil in" possible numbers that can go in each square:
The above row can be represented as an array:
[[1,2,9], [6], [5], [7], [1,2,9], [1,2,9], [3], [1,...
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votes
1answer
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Extendable Train Swapping Problem
Extended Train Swapping Problem
Part 1: Normal Train Swapping Problem
In the 1996 CCC (Canadian Computing Competition), the first Stage 2 problem was a Train Swapping Problem. You can visit the link ...
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1answer
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Check if input is permutation of source [duplicate]
Inspired by Input ∩ Source Code.
Task
Your task is to determine whether the input is a permutation of the source code.
Input
A string. Input is flexible; it should be able to handle the character ...
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14answers
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Permutapalindromic numbers
Given an integer N as input, output the Nth permutapalindromic number.
A permutapalindromic number is a strictly positive integer such that there is at least one permutation of its digits that ...
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votes
3answers
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Permute a string using Bit-Reversal
Previously, we computed the Bit-Reversal Permutation where we found how the order of indices would be permuted. In that case, we received an input n which was the order of the permutation of the ...
21
votes
12answers
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Number of cycles of a permutation
Consider a permutation of the integers 1, ..., n, such as this one for n = 6:
[5,2,4,3,6,1]
If you view the permutation as a mapping from [1,2,3,4,5,6] to [5,2,4,3,6,1], the permutation can be ...
9
votes
6answers
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Print the “even” permutations of symmetric group Sn in cyclic notation
THE TASK
DEFINITIONS
Consider the points {1,2,3,4,5} and all their permutations. We can find the total number of possible permutations of these 5 points by a simple trick: Imaging filling 5 slots ...
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votes
2answers
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Marching Through A City
There is a parade marching through a city! There are 3 main groups of marchers: the (B)and, Poster (C)arriers, and (F)lag Holders. Also, every (P)oliceman in the whole city is on duty.
Flag holders (...
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votes
21answers
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Golf bit weaving
Note: the first half of this challenge comes from Martin Ender's previous challenge, Visualize Bit Weaving.
The esoteric programming language evil has an interesting operation on byte values which it ...
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votes
15answers
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Bit-Reversal Permutations
Your goal is to create a function or a program to reverse the bits in a range of integers given an integer n. In other words, you want to find the bit-reversal permutation of a range of 2n items, zero-...
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18answers
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Faro shuffle an array
A Faro shuffle is a technique frequently used by magicians to "shuffle" a deck. To perform a Faro shuffle you first cut the deck into 2 equal halves then you interleave the two halves. For example
[1 ...
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votes
16answers
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Case Permutation
Who needs to compare things case insensitively when you're able to generate every permutation of uppercase and lowercase? No one! That's the answer. No one does. Your task is to achieve this feat; ...
11
votes
7answers
438 views
Find a function with cycles of every length
A function is said to have a cycle of length n if there exists an x in its domain such that fn(x) = x and fm(x) ≠ x for 0 < m < n, where the superscript n denotes n-fold application of f. Note ...
12
votes
2answers
191 views
Rotation-safe Latin squares
A Latin square is a square that has no repeated symbols in either the X or Y columns. For example:
ABCD
DABC
CDAB
BCDA
is one such square. Notice how every column and row contains a ...
12
votes
10answers
624 views
Permutations with Indistinguishable Items
Given a list of integers, output the number of permutations of the integers, with indistinguishable permutations counted once. If there are n integers, and each group of indistinguishable numbers has ...
12
votes
6answers
711 views
Magic number of a given length
Your program must take an input (n for the purpose of description) and output all permutations of a number that is n digits long with no repeating digits, where each of the digits preceding and ...
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votes
11answers
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All possible ways to interleave two strings
I recently saw this question on stackoverflow. It's a great question, but there's one fatal problem with the question. They are asking for the best way to do it. E.g, easiest to read, most idiomatic, ...
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24answers
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Random array without repetition
I was answering one challenge here and this task was part of the challenge. I've got a 73 bytes solution in javascript. But I think it is too much for a simple thing.
Challenge
Given as input two ...
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votes
3answers
331 views
Permutation Square Root
In math, a permutation σ of order n is a bijective function from the integers 1...n to itself. This list:
2 1 4 3
represents the permutation σ such that σ(1) = 2, σ(2) = 1, σ(3) = 4, and σ(4) = 3.
...
17
votes
11answers
538 views
Maximise the squared difference
Consider a permutation of the integer values from 1 to N. E.g. this example for N = 4:
[1, 3, 4, 2]
We'll consider this list to be cyclic, such that 1 and 2 are treated as adjacent. One quantity we ...
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votes
19answers
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Rearranging the sequence
Introduction
Let's observe the following sequence (non-negative integers):
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, ...
For example, let's take the first three numbers. These are 0, 1, 2. ...
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votes
8answers
666 views
Spiral Permutation Sequence
We can roll up the natural numbers in a rectangular spiral:
17--16--15--14--13
| |
18 5---4---3 12
| | | |
19 6 1---2 11
| | |
20 7---8---9--10
...
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votes
2answers
221 views
The absent-minded linguist
Background
Your friend, a linguist, has recorded and analyzed some simple conversation snippets in various languages.
Being quite absent-minded, they have forgotten which language each snippet was in....
13
votes
6answers
478 views
Letters, Get Moving! Pt. 2
The first Letters, Get Moving! was very popular, but had limited participation. This one will be easier to solve, but hopefully involve some tricks in golfing.
You are given a string of only ...
14
votes
2answers
235 views
Can the Array be Unshuffled?
Background
Very skilled card handlers are capable of a technique whereby they cut a deck perfectly in half, then perfectly interleave the cards. If they start with a sorted deck and perform this ...
17
votes
2answers
533 views
Random Golf of the Day #6: Roll a d20
About the Series
First off, you may treat this like any other code golf challenge, and answer it without worrying about the series at all. However, there is a leaderboard across all challenges. You ...
16
votes
6answers
370 views
Find maximal matching in divisibility relation
You are given a set of positive integers. You must arrange them into pairs such that:
Each pair contains 2 numbers, one of which is a multiple of another. For example, 8 is a multiple of 4, and 9 is ...
9
votes
4answers
270 views
Rearrangement Inequality
Background
The Rearrangement Inequality is an inequality that is based on rearranging numbers. If I have two lists of numbers of the same length, x0, x1, x2...xn-1 and y0, y1, y2...yn-1 of the same ...
12
votes
8answers
479 views
Typesetting multidimensional labels
In a steam-punk multidimensional world, our boss wants to affix printed index labels to each drawer in our conglomerate's multidimensional file cabinet.
The boss wants to typeset the entire label ...
17
votes
14answers
720 views
Fun With Permutations
Who doesn't absolutely love permutations, right? I know, they are amazing––so much fun!
Well, why not take this fun and make it funner?
Here's the challenge:
Given an input in the exact form: nPr, ...
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votes
19answers
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Imitate an ordering
Given two lists of numbers, a source and a pattern, reorder the source to match the relative ordering of the pattern. Any two entries of the reordered source should compare the same way as the entries ...
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votes
2answers
777 views
The Combinatorics of Transistor
The video game Transistor features a very interesting ability system. You collect 16 "Functions" which you can use in 16 different slots. What's interesting is that there are 3 types of slots and ...
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3answers
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Possible Tetris sequences
Write code to figure out whether a run of Tetris pieces could be generated by the official Tetris algorithm. Fewest bytes wins.
Official Tetris games generate the sequence of falling pieces in a ...
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6answers
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Can you reach this number by doubling and rearranging?
Inspired by this question on Math.SE.
Starting with 1 you can repeatedly perform one of the following two operations:
Double the number.
or
Rearrange its digits in any way you want, except that ...
9
votes
5answers
526 views
Cycle lengths for Perfect shuffles of decks of any size
Challenge
In the shortest amount of code:
Compute the length of the permutation cycle of a perfect shuffle on a deck of cards of any size n (where n ≥ 2 and n is even).
Output a table of all cycle ...
