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.
217
questions
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Validating a Battleship board
Do you know the game Battleship? Well, I want to play with my little brother, but before we can begin we need to set up our ships on the board. This is your input.
Now, we need to check that the ships ...
26
votes
10answers
2k views
Help Stack Exchange transpose tables
Stack Exchange doesn't know how to transpose tables. Let's help.
Given a markdown table, transpose it.
Input assumptions:
There will be at least two rows (including header) and two columns
Either all ...
27
votes
20answers
3k views
Calculate the inverse of a matrix
Somehow, we don't yet have a challenge for finding the inverse of an arbitrarily-sized square matrix, despite having ones for 3x3 and 4x4, as well as a more complex version.
Your task is, given a ...
asked Oct 20 '20 at 20:35
caird coinheringaahing
22.1k5 gold badges51 silver badges157 bronze badges
9
votes
1answer
219 views
Thin Paper Folding
Thin Paper Folding
This is a "lighter" version of the challenge Paper Folding for the win. This challenge is being posted as a different challenge with many modifications in order to try ...
25
votes
24answers
2k views
Antisymmetry of a Matrix
A matrix is antisymmetric, or skew-symmetric, if its transpose equals its negative.
The transpose of a matrix can be obtained by reflecting its elements across the main diagonal. Examples of ...
17
votes
1answer
336 views
Paper Folding for the win
Paper Folding for the win
"How many times can you fold a paper?" - This well known question led to many arguments, competition, myths and theories.
Well, the answer to that question depends ...
13
votes
13answers
1k views
Help me accelerate linear recurrence relation!
Background
A linear recurrence relation is a description of a sequence, defined as one or more initial terms and a linear formula on last \$k\$ terms to calculate the next term. (For the sake of ...
12
votes
0answers
247 views
Checkerboard the Matrix
Task
Given a matrix, your program/function should output a row-equivalent matrix in checkerboard form ( \$A_{ij}=0\$ if and only if \$i+j\$ is odd).
Two matrices are defined to be row-equivalent if ...
18
votes
10answers
2k views
Complete the Magic Square
Background
A magic square is an nĆn matrix consisting of one of each of the integers from \$1\$ to \$n^2\$ where every row, column, and diagonal sum to the same ...
8
votes
0answers
141 views
Cover positions with snakes of same 'colour'
Imagine a grid where the origin square \$(0,0)\$ is at the top left of the screen, and positive \$x\$ is rightwards whereas positive \$y\$ is downwards. Coloured squares are at various positions on ...
14
votes
5answers
955 views
What is the Subspace Dimension?
Challenge
Given the Cartesian coordinates of two or more distinct points in Euclidean n-space (\$\mathbb{R}^n\$), output the minimum dimension of a flat (affine) subspace that contains those points, ...
26
votes
21answers
2k views
Logo Pack LAPACK
This is the logo for LAPACK, a widely used software library for numerical linear algebra.
Your task is to print the logo (color and matrix brackets not required) as this exact string. Trailing ...
15
votes
3answers
266 views
Identify the smallest possible tile in the matrix
Challenge
Given a matrix of digits (0-9), find the smallest (in terms of area) rectangular matrix of digits where one or more copies of itself, possibly rotated, can tile the original matrix. ...
2
votes
2answers
176 views
Create a text image by manual automation
Challenge
Premise
It's 2006, and Alice is trying to send Bob their her completed notes on their newly ended expeditions into the labyrinthine school library, which the two of them found suffers from a ...
21
votes
6answers
2k views
The matrix has U
Given a matrix of size at least 3Ć3 formed by positive integers, determine if it contains at least one "U" pattern, defined as
...
12
votes
7answers
677 views
Toroidally magnify-blur a matrix
Task
Given a matrix of numbers \$M\$ with \$r\$ rows and \$c\$ columns, and the magnification factor \$n\$, build the matrix with \$rn\$ rows and \$cn\$ columns where the original elements are spaced ...
10
votes
1answer
305 views
Positioning a fake mirror for best effect
Challenge
Premise
Consider a mosaic of \$m\times n\$ tiles, in \$k\$ unique colours designated by integers. Example (\$3\times6\$, four colours):
...
17
votes
3answers
677 views
Make a rectangle from a collection of (sliced) squares
Inspired by Make a Rectangle from a Triangle.
Task
There is a famous formula on the sum of first \$n\$ squares:
$$
1^2 + 2^2 + \dots + n^2 = \frac{n(n+1)(2n+1)}{6}
$$
It is known that this number ...
22
votes
17answers
3k views
Make a Rectangle from a Triangle
You can depict a triangular number, T(N), by writing one 1 on a line, then two 2's on the line below, then three 3's on the line below that, and so on until N N's. You end up with a triangle of T(N) ...
19
votes
16answers
1k views
(RGS 4/5) Inverting matrices modulo m
Task
Given an integer matrix M and a modulus m, find an inverse of M modulo ...
17
votes
10answers
449 views
Decomposition of a matrix in \$ SL_2(\mathbb{Z}) \$
Background
The special linear group \$ SL_2(\mathbb{Z}) \$ is a multiplicative group of \$ 2 \times 2 \$ matrices whose elements are integers and determinant is 1.
It is known that every member of \$...
19
votes
2answers
682 views
Find the number of n-by-n (-1, 0, 1) matrices with zero permanent as quickly as possible
The permanent of an \$n\$-by-\$n\$ matrix \$A = (a_{i,j})\$ is defined as:
$$\operatorname{perm}(A)=\sum_{\sigma\in S_n}\prod_{i=1}^n a_{i,\sigma(i)}$$
For a fixed \$n\$, consider the \$n\$-by-\$n\$ ...
19
votes
21answers
2k views
Clockwise matrix rotation
The title pretty much describes it all. Given as input a \$n \times m\$ matrix and an integer \$i\$ create a complete function/program that returns the matrix \$i\$ times clockwise rotated by \$90^\...
10
votes
17answers
7k views
Euclidean Distance Between Two Matrices
Your task is to write the shortest algorithm in a language of your choosing that accomplishes the following:
Given two matrices it must return the euclidean distance matrix. The euclidean distance ...
25
votes
14answers
3k views
ASCII texturing
Write a function or a full program that applies an ASCII texture to a 2d shape.
Inputs: shape, texture, dimensions(optionally).
Both Shape and Texture can be given by any convenient method (2d ...
47
votes
14answers
5k views
In Flanders Fields
Today is November 11th, which for many regions is Remembrance Day.
If you don't know anything about the history or context of Remembrance Day, you can read about it in the wiki page, but it's not ...
31
votes
4answers
1k views
Expand a recursive pattern
Given a description of the base state of a recursive ASCII pattern, output an expanded state somewhere along the recursion steps.
More specifically: Let the following be an example:
...
28
votes
17answers
4k views
Implement the Max-Pooling operation from Convolutional Neural Networks
In convolutional neural networks, one of the main types of layers usually implemented is called the Pooling Layer. Sometimes, the input image is big (and therefore time consuming especially if you ...
32
votes
6answers
2k views
Slash the matrix
You are given a matrix of forward and back slashes, for instance:
//\\
\//\
//\/
A slash cuts along the diagonal of its cell corner-to-corner, splitting it in ...
2
votes
0answers
85 views
Generate square sub-matrices of 1's [duplicate]
Back again, stealing another question from stackoverflow.
You are given a list of integers >= 0. Generate in order square 1-matrices where the side length is given by the list entry of the current ...
26
votes
9answers
3k views
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 ...
36
votes
24answers
6k views
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/argumentĀ¹. The tricky part is that ...
21
votes
20answers
2k views
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 ...
16
votes
1answer
347 views
Decompose Commutators
A theorem in this paper1 states that every integral n-by-n matrix M over the integers with traceĀ MĀ =Ā 0 is a commutator, that means there are two integral matrices A,B of the same size as M such that MĀ ...
11
votes
7answers
1k views
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. ...
22
votes
6answers
1k 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-...
23
votes
22answers
2k views
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
2k views
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 ...
29
votes
23answers
4k views
24
votes
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
2k views
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 ...
7
votes
6answers
579 views
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 the ...
8
votes
2answers
365 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
2k views
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)\$...
asked Feb 20 '19 at 17:34
Luis felipe De jesus Munoz
9,7312 gold badges20 silver badges76 bronze badges
10
votes
4answers
442 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 ...
asked Feb 15 '19 at 15:04
Luis felipe De jesus Munoz
9,7312 gold badges20 silver badges76 bronze badges
16
votes
7answers
2k views
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 ...
asked Feb 5 '19 at 14:53
Luis felipe De jesus Munoz
9,7312 gold badges20 silver badges76 bronze badges
18
votes
15answers
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
791 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
450 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:
ā* (up): Moves a ...
asked Jan 17 '19 at 17:17
Luis felipe De jesus Munoz
9,7312 gold badges20 silver badges76 bronze badges
60
votes
20answers
6k views
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....
