Questions tagged [matrix]
A matrix is a list of numbers arranged in a rectangle with rows and columns. In programming, it is also known as a 2D array. Use this tag if your challenge is about manipulating matrices.
187
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Implement the 2D Hadamard Transform
The Hadamard transform works similarly to the Fourier transform: it takes a vector and maps it to its frequency components, which are the Walsh functions. Instead of sine waves in the Fourier ...
31
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21answers
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I transpose the source code, you transpose the input!
Rip-off of a rip-off of a rip-off of a rip-off. Go upvote those!
Your task, if you wish to accept it, is to write a program/function that outputs/returns its input/argument¹. The tricky part is that ...
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votes
20answers
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Reorder a matrix, twice
You are given a square \$n \times n\$ matrix \$A\$, and a list (or vector) \$u\$ of length \$n\$ containing the numbers \$1\$ through \$n\$ (or \$0\$ through \$n-1\$). Your task is to reorder the ...
9
votes
0answers
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Decompose Commutators
A theorem in this paper1 states that every integral n-by-n matrix M over the integers with trace M = 0 is a commutator, that means there are two integral matrices A,B of the same size ...
9
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7answers
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An array battle with odd secret powers
Here is a relatively simple two dimensional array challenge.
Imagine a battlefield of 625 foot soldiers. You command the odd troops, but unfortunately the strength of the even troops overwhelms you. ...
21
votes
6answers
978 views
Subtract the Folded Matrix
Challenge:
Given an NxN matrix where \$N\geq2\$ and one of eight distinct 'folding options', output a 2D array/list with the subtracted values.
The eight folding options are: left-to-right; right-to-...
22
votes
22answers
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Overlapping String-Blocks
Challenge:
Given a list of multi-line strings, overlap them (in the top-left) and output the result.
Example:
Input: ["aaaa\naaaa\naaaa\naaaa","bb\nbb\nbb","c"]
...
20
votes
11answers
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Make all the squares explode
You are given a square matrix of width \$\ge2\$, containing square numbers \$\ge1\$.
Your task is to make all square numbers 'explode' until all of them have disappeared. You must print or return the ...
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23answers
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12answers
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Slither Like a Snake
The Idea
We've done matrix spirals before, and full rotations, and even diagonal
rotations,
but not, as far as I can find, snake rotations!
What is a snake rotation?
Imagine the rows of a matrix ...
25
votes
11answers
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Is this Pascal's Matrix?
In Pascal's triangle each number is the sum of the two numbers directly above it, treating empty spots as zero:
By rotating the triangle, we can cut out square matrices of varying sizes and rotations ...
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votes
6answers
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Black Hole challenge from codewars
I came across this challenge from codewars. I wish to know how to solve this problem. The problem description is given below.
Its elements are in range[1..n^2]. The matrix is filled by rings, from ...
8
votes
2answers
336 views
Can this container hold this much liquid?
Can this container hold this much liquid?
Challenge Synopsis
As you most likely know, liquids have an indefinite shape and a definite volume. As such, they always take the shape of their container. ...
25
votes
8answers
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Exploding Numbers
sandbox (deleted)
Lets define a matrix of 9s as:
$$ N = \begin{bmatrix} 9&9&9\\9&9&9\\9&9&9 \end{bmatrix} $$
Lets define an exploding number as a number at position \$(x,y)\$...
10
votes
4answers
411 views
Cell phone Charge
Challenge Taken with permission from my University Code Challenge Contest
The dependence we have on mobile phones makes us charge them every night up to the maximum level of the battery, so we do not ...
16
votes
7answers
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Borderless table
In this challenge you are going to place letters from the alphabet in a Cartesian plane and output the result as a text.
Your input will consist in a list of list with 3 parameters:
X coordinate
Y ...
17
votes
14answers
1k views
Spot all (anti)diagonals with duplicated values
Challenge:
Given a matrix input, determine the amount of diagonals and anti-diagonals with duplicated numbers.
So if we have a matrix like this:
...
13
votes
6answers
756 views
Binary self-rotation
Given a binary 3D array, for each layer, cyclically rotate up each of its columns as many steps as indicated by the binary encoding of the columns of the layer above it, and then cyclically rotate ...
12
votes
3answers
400 views
Matrix rotation sort
Lets define a non-empty, unsorted and finite matrix with unique numbers as follow:
$$N = \begin{Bmatrix} 4&5&7\\1&3&6 \end{Bmatrix}$$
Lets define 4 matrix moves as:
↑* (up): Moves a ...
58
votes
20answers
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Dig a border trench
Background: Too many illegal immigrants from Blandia are crossing the border to Astan. The emperor of Astan has tasked you with digging a trench to keep them out, and Blandia must pay for the expenses....
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15answers
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Matrix Jigsaw Puzzles
Input:
An integer n
Two equal-sized square matrices (with their width/height being a multiple of n)
Output:
One of two ...
10
votes
15answers
333 views
Matrix Jigsaw Puzzle Pieces
(Randomly inspired by https://codegolf.meta.stackexchange.com/a/17272/42963)
Given a rectangular matrix of digits (i.e., 0 - 9), output the "pieces" of the matrix ...
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votes
18answers
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Most contributing rows
Given a non-empty matrix of non-negative integers, answer which unique rows contribute most to the sum total of elements in the matrix.
Answer by any reasonable indication, for example a mask of the ...
12
votes
13answers
489 views
Count the contiguous submatrices
Migrated from chat
Given two non-empty non-negative integer matrices A and B, answer the number of times A occurs as a contiguous, possibly overlapping, submatrix in B.
Examples/Rules
0. There may ...
6
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5answers
193 views
Find equally-weighted complete graphs
Graph theory is used to study the relations between objects. A graph is composed of vertices and edges in a diagram such as this:
...
85
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25answers
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The Hungry Mouse
Sixteen piles of cheese are put on a 4x4 square. They're labeled from \$1\$ to \$16\$. The smallest pile is \$1\$ and the biggest one is \$16\$.
The Hungry Mouse is so hungry that it always goes ...
13
votes
16answers
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Trim that distracting background off!
Isn't it annoying when you're taking a picture, but the background detracts from the actual substance of the image? I'd say it is. I need to know how much I should crop so that I get rid of this ...
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votes
15answers
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Output the anti-clockwise inward spiral of a 2D array
From this stackoverflow question
Given a 2D array of size \$ M \times N \$, output the values in a anti-clockwise fashion. The output must start from the outside to the inside and the initial point ...
asked Oct 11 '18 at 17:46
Luis felipe De jesus Munoz
6,6412 gold badges18 silver badges75 bronze badges
19
votes
12answers
2k views
Is the Matrix Positive-Definite?
Introduction
Today we're gonna take care of the bane of first-year linear algebra students: matrix definiteness! Apparently this doesn't yet have a challenge so here we go:
Input
A \$n\times n\$ ...
6
votes
3answers
484 views
Ordinary Least Squares Regression
I am quite surprised that a variant of linear regression has been proposed for a challenge, whereas an estimation via ordinary least squares regression has not, despite the fact the this is arguably ...
10
votes
7answers
654 views
Whose neighbours are hostile?
Introduction
For the purposes of this challenge, we will define the neighbours of an element \$E\$ in a square matrix \$A\$ (such that \$E=A_{i,j}\$) as all the entries of \$A\$ that are immediately ...
21
votes
14answers
2k views
Chop off the matrix to get the desired sum
Definition
Given a matrix \$M\$ of non-negative integers and a non-negative integer \$k\$, we define \$F_k\$ as the "chop-off" function that removes all rows and all columns in \$M\$ that contain \$k\...
18
votes
14answers
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Square-Random-Symmetrical
Challenge
Write a program or a function that returns or prints a square-random-symmetrical matrix.
Input
N: The size of the matrix i.e 6 x 6
Output
The matrix. ...
20
votes
11answers
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A knight's graph on an N-by-N board
In chess, a knight can only move to the positions marked with X relative to its current position, marked with ♞:
A Knight's Graph is a graph that represents all legal moves of the knight chess piece ...
11
votes
5answers
328 views
Minimal Centrosymmetrization
Topically related.
Objective: Given a matrix of positive integers \$M\$, output the smallest centrosymmetric matrix which contains \$M\$ (this matrix may contain non-positive integers as well).
A ...
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16answers
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16answers
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Roman Army Shields
Sandbox post (deleted)
The old roman army formations are very famous around the world. In these formations roman legionaries grouped in a geometric shape (usually a rectangle) protecting the flanks ...
asked Aug 2 '18 at 19:55
Luis felipe De jesus Munoz
6,6412 gold badges18 silver badges75 bronze badges
27
votes
16answers
3k views
Beware of the matrix tornado!
The matrix tornado is just like any other tornado: it consists of things rotating around a center. In this case, elements of the matrix instead of air.
Here is an example of a matrix tornado:
First ...
18
votes
20answers
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Collapsing Matrices
Related: Let's design a digit mosaic, Print/Output the L-phabet. Sandbox post here
Given 2 inputs C = columns and rows, S = starting point output a matrix as ...
asked Jul 19 '18 at 13:37
Luis felipe De jesus Munoz
6,6412 gold badges18 silver badges75 bronze badges
22
votes
16answers
3k views
Find the inverse of a 3 by 3 matrix
Challenge
Given nine numbers, a, b, c, d, e, f, g, h, i, as input which correspond to the square matrix:
$$\mathbf{M} = \begin{pmatrix}a& b& c\\ d& e&...
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15answers
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Find the Cell's Neighbours
...or Toroidal Moore Neighbourhoods
Given positive integers h, w and a non-negative integer ...
37
votes
28answers
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Is the matrix centrosymmetric… and so is the code?
Defintion
A centrosymmetric matrix is a square matrix that is symmetric about its center. More rigorously, a matrix \$A\$ of size \$n \times n\$ is centrosymmetric if, for any \$i,\: j \in ([1, n] \...
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votes
16answers
581 views
2D Array Middle Point
Given dimensions of a 2D array, except 1xn, that results in an odd number of elements, find the midpoint index.
Example: Input is 3x5, representing the 2D array
[0,0] [0,1] [0,2] [0,3] [0,4]
[...
5
votes
3answers
446 views
Saddle points in a matrix
A matrix can be thought of as the altitudes of a surface in 3D space.
Consider the 8 neighbours (orthogonal and diagonal) of a cell as a cyclic sequence in clockwise (or anticlockwise) order. Some ...
12
votes
11answers
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Find the Number With the Highest Sum of Neighbors
The Challenge
Given a grid of numbers (10 <= N <= 99)
Return number with the highest sum of the four numbers adjacent to it; that is the numbers above, below, right, and left of the number, but ...
16
votes
8answers
655 views
Classify a region by its slope
Definitions
The kth ring of a square matrix of size N, where 1 ≤ k ≤ ceiling(N/2) is the list formed by the elements of the kth and (N-k+1)th rows and columns, but without the first and last k-1 ...
2
votes
1answer
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Array-of-array string conversion to and from matrix [closed]
Matrix challenges are popular. There's an issue of how to provide test cases. A common method is the row-wise array-of-arrays representation, such as:
...
18
votes
2answers
333 views
Is this a Weyr matrix?
There's a type of n×n matrix W called the basic Weyr canonical form. Such a matrix is described by its blocks and has the following properties, using the following reference diagram:
the main ...
0
votes
13answers
342 views
Beginners 10x10 multiplication matrix [duplicate]
I was looking for a very easy task to look how short of a code can be produced on a beginners exercise.
The goal is to produce a simple table that looks like this common java/c# code is about 4 lines....
11
votes
12answers
832 views
Sum of replicated matrices
Given a list of numbers [ a1 a2 ... an ], compute the sum of all the matrices Aᵢ where Aᵢ is defined as follows (m is the maximum of all aᵢ):
...
