Questions tagged [permutations]
A permutation is a particular ordering of some list of objects. Problems tagged with permutation usually involve finding or generating permutations, including anagrams of text.
216 questions
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Sticks expectation
This was originally a question from interviewstreet.com over a decade ago
You are given an array (or whatever - your choice of input) of positive integers \$y_1,\ldots,y_n\$ that represents \$n\$ line ...
- 219
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4
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Identify Last-Layer Perm of a Rubik's Cube
A popular method for solving Rubik's cube consists of:
solving its first two layers, by convention starting with the white side
orienting the last layer's pieces so they face the same direction with ...
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23
votes
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Write two very different programs with the same characters
Your task is to write two programs/functions, in the same language.
Program 1: Verify that two inputs are anagrams of each other.
Program 2: Verify that two inputs differ from each other at every ...
- 8,074
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Triangular Transposition Cipher
A text that can be arranged triangularly in some fashion can be read back in some other fashion effectively enciphering it.
Narrowing down a set of plausible triangular numberings allows to ...
- 2,463
12
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9
answers
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All possible swaps for the permutation
Given a permutation of {1,2,...,n} named A, do each swap of form swap A[i], A[j] exactly once, where ...
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12
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8
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Unap_peel_ing permutations
Given the height, \$h\$, and width, \$w\$, describing a rectangle of the first \$hw\$ natural numbers in row-major order produce the numbers in the order they are encountered by repeatedly removing a ...
- 115k
13
votes
13
answers
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Meandering over ℤ
The easiest way to understand this task is to look at this
graph,
which you can change interactively.
It defines a sequence n -> a(n) like this:
a(0) = 0; thereafter a(n) is the least integer (in ...
- 1,742
8
votes
6
answers
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Ranking of binary trees
Let N = [0,1,2,...n-1] be the initial segment of the natural
numbers of length n, then all permutations of N can be sorted
lexicographically, starting with the identity. The index into this
sorted ...
- 1,742
6
votes
3
answers
651
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Implement any rotation-invariant function on colored dodecahedrons
Each of a regular dodecahedron's 12 faces can be painted either red or blue. Your task is to implement a function \$f\$ that takes a painted dodecahedron (as 12 booleans, in whatever order and format ...
- 871
7
votes
12
answers
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Counting constrained permutations
Challenge:
Write a program or function that, given positive integers n, t, b, c, counts permutations of 1..n where:
Exactly t numbers are in their original position
Exactly b numbers are higher than ...
- 79
3
votes
4
answers
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Create 251610 matrices as quickly as possible
There are 251610 6 by 6 binary matrices that are inequivalent. We say two matrices are equivalent if there is some permutation of their rows and/or columns that makes them equal.
For example:
...
- 3,167
5
votes
9
answers
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Reorder a string of length \$2^n\$ by permuting the \$n\$ binary digits of every index
Given a binary string \$s\$ of length \$2^n\$ and a permutation \$\sigma\$ of \$\{1,\dots,n\}\$, generate the binary string \$u\$ of length \$2^n\$ which is a reordering of \$s\$ such that \$u[i^\...
- 871
13
votes
8
answers
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Lexicographically earliest permutation of the initial segment of nonnegative integers subject to divisibility constraints
The challenge is simple: Reorder the first integers {0, 1, 2, ..., n} into an ordered list so that the following three conditions are met:
If k is the last element in the list, then all of its prime ...
- 251
4
votes
18
answers
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Check if two lists are permutations of each other [duplicate]
Challenge
Given two lists of equal length, find if one of them is a permutation of the other. Output truthy or falsy values, or 1 or 0.
Test case Examples
...
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votes
8
answers
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Find the child anagrams of a word
Select any word from https://websites.umich.edu/~jlawler/wordlist with length greater than 1. For each letter on that word, remove it and check if any rearrangement of the remaining letters is present ...
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