Questions tagged [array]

A competition to solve a particular problem through the usage and manipulation of arrays.

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43 votes
46 answers
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An Array of Challenges #1: Alternating Arrays

Alternating Arrays An alternating array is a list of any length in which two (not necessarily different) values are alternating. That is to say, all even-indexed items are equal, and all odd-indexed ...
16 votes
9 answers
2k views

Search the deepest depths of an array

Given a ragged array, find the length of the largest subarray that contains the depth of that subarray. The base array layer has a depth of 0. Here is an example: ...
10 votes
5 answers
1k views

Contract a tensor

Introduction Tensor contraction is an operation that can be performed on a tensor. It is a generalization of the idea of the trace of a matrix. For example, if we have a rank-2 tensor (a matrix) and ...
21 votes
31 answers
2k views

Cosine similarity of two vectors

The cosine similarity of two vectors \$A\$ and \$B\$ is defined using their dot product and magnitude as: \$\frac{A\cdot B}{\|A\|\|B\|}\$ Or in other terms \$\frac{\sum_{i=1}^nA_iB_i}{\sqrt{\sum_{i=1}^...
24 votes
40 answers
2k views

Diagonalize a vector

Diagonalize a vector into a matrix. Input A vector, list, array, etc. of integers \$\mathbf{v}\$ of length \$n\$. Output A \$n \times n\$ matrix, 2D array, etc. \$A\$ such that for each element \$a_i \...
36 votes
28 answers
8k views

Could you please stop shuffling the deck and play already?

Challenge: Input: A list of distinct positive integers within the range \$[1, \text{list-size}]\$. Output: An integer: the amount of times the list is riffle-shuffled. For a list, this means the list ...
23 votes
23 answers
3k views

Longest Zero Sum Sub-array

Given an array of integers. Find out its longest sub-array (contiguous subsequence) whose sum is 0. The sub-array for output may be an empty array. Input Input an array of integers. Output Output the ...
26 votes
23 answers
1k views

Remove falsy rows and columns

Your challenge is to, given a matrix of nonnegative integers, remove all rows and columns that contain a 0. For example, with this matrix: ...
18 votes
25 answers
2k views

What and where is the max?

This small challenge derives from my annoyance at discovering that numpy doesn't have a built in function for it. Input An n by m matrix of integers. Output The maximum value in the matrix and the 2d ...
30 votes
82 answers
6k views

Swap every two elements in a list

Challenge Let's have a list L of n elements. The task is to swap every two elements in this list. Constrains the list ...
24 votes
26 answers
3k views

Diamondize a Matrix

Given a matrix, output a representation of the matrix where the top left element is on top, the anti-diagonal is the central row and the bottom right element is at the bottom. For example, consider ...
18 votes
25 answers
1k views

Trim elements from the ends of a list

The aim is to trim elements in from the ends of a list, depending on if they are in a second list of "falsey" results. For example, if the first list is ...
24 votes
17 answers
2k views

Reconstruct Matrix from its diagonals

Given the diagonals of a matrix, reconstruct the original matrix. The diagonals parallel to the major diagonal (the main diagonals) will be given. Diagonals: ...
19 votes
25 answers
1k views

Remove first encountered elements from a second list

Inspired by this question on Stackoverflow. The task Let's have two lists/arrays of integers: L1 and L2 of equal length. You ...
50 votes
90 answers
6k views

The shortest way to find one unique value when all other values are the same

In this question at Code Review they tried to find the fastest way to return the unique element in an array where all the elements are the same except one. But what is the shortest code that ...
29 votes
28 answers
2k views

Recursive Z-matrix

Originally from a CMC I proposed for the last BMG event Challenge Given a non-negative integer \$n\$, create a 2D array of size \$2^n × 2^n\$ which is generated in the following manner: Divide the ...
10 votes
3 answers
621 views

Follow the border

Inspired by Is this Flow Free puzzle trivial? by @Bubbler. Lengthy chunks of this challenge are borrowed from there. This may be one step of a solution for the linked challenge, depending on chosen ...
26 votes
31 answers
3k views

Different Way Forward

Given a list of integers produce a Forward Difference at a specified order/depth. For the list of integers: (10, 18, -12, 4, 8, -3, -5, 67, 9, 14) The Forward ...
51 votes
41 answers
3k views

Moving modest minimum

Inspired by a question over at Stack Overflow. The title here is entirely my fault. The challenge Given a list of positive integers containing at least two entries, replace each number by the ...
25 votes
16 answers
2k views

Multi-dimensional reversal

Given an N-dimensional orthogonal (non-ragged) array of non-negative integers, and an indication of which dimensions to reverse, return the array but reversed along those dimensions. The indication ...
28 votes
63 answers
3k views

Are All the Items the Same?

Given a list of non-negative integers, return whether or not that list is all the same number. Rules Input and output can be taken/given in any reasonable and convenient format Truthy/Falsey values ...
33 votes
36 answers
2k views

Targeted duplicate removal

The task In this challenge, you are given a number and a list. Your task is to remove from the list all occurrences of the given number except the first (leftmost) one, and output the resulting list. ...
22 votes
48 answers
3k views

Split into three!

Given a string, you've to split it into groups of three characters (by padding _ at the end). Related, but still it's different. Sample I/O: ...
11 votes
30 answers
1k views

Multiplicative undelta

Let us define the "multiplicative deltas" of values \$[\; a_0, \cdots a_N, \;]\$ as: $$ [\; a_1 / a_0, \cdots, a_{i+1} / a_i, \cdots, a_N / a_{N-1} \;] $$ The reverse operation - namely "...
5 votes
1 answer
533 views

Conways's Game of Life: Most newborn generating starting pattern

General rules The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, alive or dead. Every cell interacts with ...
7 votes
4 answers
368 views

Busy Letters & Evil CEOs

Imagine you are given an array/string containing \$5\$ letters of the English alphabet, with each letter having any value from A to Z (inclusive). Every day, each letter will perform a job, which can ...
18 votes
6 answers
1k views

Retaining Water

Your task is to check the volume of water in a pool. Your have to create a program that takes in a input that is represented by an 10 by 10 grid of integers, with ...
28 votes
64 answers
3k views

Create an array with repeated numbers

Challenge Your task in this question is to write a program or a named function which takes a positive integer n (greater than 0) as input via STDIN, ARGV or ...
48 votes
35 answers
3k views

Sever-sort an array

Challenge Given a non-empty array of integers, e.g.: [5, 2, 7, 6, 4, 1, 3] First sever it into arrays where no item is larger than the previous (i.e. non-...
21 votes
43 answers
2k views

Binary Reduce a List By Addition With a Right Bias

Given a list of 2 or more strictly positive integers, sum the first and last half of the list, with the middle element being counted only in the right half if the list has an odd number of elements ...
33 votes
66 answers
4k views

Triangle a number!

We are used to the term "squaring" n to mean calculating n2. We are also used to the term "cubing" n to mean n3. That being said, why couldn't we also triangle a number? How to triangle a number? ...
24 votes
15 answers
3k views

"Perfect" an array

Given an n non-negative integers, how many numbers must be changed so that each number x appears x times? You cannot add or remove elements, only replace them with other numbers. For example: ...
27 votes
17 answers
2k views

Falsify brief truths

Find the longest run of true in a list of booleans. Return the same list, with all other trues falsified. Input, output A list; any usual format (e.g., a delimited list as a string). Details True and ...
23 votes
19 answers
2k views

Deep Search a List

For this challenge, a list is considered valid if and only if it consists entirely of integers and valid lists (recursive definitions \o/). For this challenge, given a valid list and an integer, ...
47 votes
28 answers
5k views

Remove every N-th N

The task In this challenge, your input is a non-empty list of positive integers, given in the native format of your language. Your output is that same list, in the same format, with some elements ...
23 votes
25 answers
1k views

How many laps around the permutation?

Your input is an array of numbers: a permutation of \$\{1, 2 \dots n\}\$ for some integer \$n \geq 2\$. How many times must you repeat this list before you can "pick out" the numbers \$[1, 2 ...
19 votes
30 answers
2k views

Zip uneven lists

In this challenge you will take two lists as input and you will zip them. The zip can be defined with this recursive expression: \$ \mathrm{zip}(a,b) = \begin{cases} \left[\,\,\right] & a = \left[...
10 votes
6 answers
907 views

Unnecessary Fluff

Following the great advice (what do you mean it's not advice?!) on Adding unnecessary fluff we can devise the following task: Take a list of positive integers and a positive integer \$m\$ as input. ...
17 votes
13 answers
2k views

Extend a matrix in all directions

Given a multidimensional, rectangular array and a list of dimensions, such as: [ [1, 2], [3, 4] ] [3, 4] Your challenge is to extend the matrix to the ...
12 votes
23 answers
1k views

Move to Right and left

Task Your task is to take an array of numbers as input, and produce a new one where each number has been shifted both right and left, leaving 0s if no number fills ...
27 votes
52 answers
3k views

Shortest Code to Find the Smallest Missing Positive Integer

Description Given an unsorted array of integers, find the smallest positive integer that does not appear in the array. Your task is to write the shortest code possible to solve this problem. Input A ...
34 votes
25 answers
3k views

The Three 'R's: Reverse, Reorder, Repeat

While doodling around with numbers, I found an interesting permutation you can generate from a list of numbers. If you repeat this same permutation enough times, you will always end up back at the ...
16 votes
21 answers
2k views

Just another traffic jam!

One lane is closed, the vehicles have to thread their way in according to the zip-lock system: One car from one lane, the next car from the other lane, always taking turns. Input: Two vehicle queues, ...
6 votes
4 answers
239 views

Is it stuck in a counting loop? [duplicate]

Given a list of non-negative integers the function \$f\$ replaces every integer with the number of identical integers preceding it (not necessarily contiguously). So ...
31 votes
33 answers
3k views

Print a Block-Diagonal Matrix

Here is a simple, bite-sized (byte-sized?) code golf: given a non-empty list of positive integers less than 10, print a block-diagonal matrix, where the list specifies the size of the blocks, in order....
10 votes
7 answers
1k views

Night hike partitioning

We want to go on a night hike with the youth group, but of course not everyone has their torch, even though we told them we planned to split up. What options are there for group formation if n teens ...
10 votes
9 answers
530 views

Sort musical pitches

Given an unordered list of musical pitches, write the shortest program/function (scored in bytes) to sort the list from lowest pitch to highest. Pitches will be given in scientific pitch notation, ...
16 votes
8 answers
953 views

One-dimensional map colouring

It is a well-known fact that you can colour a two-dimensional map with four colours in such a way that two countries with a common border always have different colours. There have already been enough ...
16 votes
16 answers
4k views

Which skill to train?

Story (skip, if you prefer the naked task): You need five skills for an imaginary sport: Speed, strength, endurance, accuracy and tactics. If you achieve a score in each of these disciplines, you can ...
34 votes
70 answers
4k views

Sum the array times n, except the last

I've been posting relatively hard challenges recently, so here goes an easy one. Task Given an array \$A\$ and a number \$n\$, calculate the sum of all numbers of \$A\$ multiplied by \$n\$, except the ...

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