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Questions tagged [matrix]

This tag is for challenges involving matrices. A matrix, also known as a 2D array, is a list of numbers arranged in a rectangle with rows and columns.

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103 votes
24 answers
18k views

Where's the 0xBEEF?

This challenge was inspired by this Wendy's commercial from 1984. Illustration by T S Rogers Your task is to find a hexadecimal 0xBEEF on a binary bun. The 'beef' consists of the following pattern: ...
Arnauld's user avatar
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99 votes
27 answers
7k views

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 ...
Arnauld's user avatar
  • 194k
76 votes
13 answers
4k views

Friar simulator

The brethren from the order of St Golfus the Concise have a tradition of reciting a short prayer whenever they see someone make the sign of the cross. Due to the high level of sin measured among ...
ngn's user avatar
  • 15.3k
61 votes
20 answers
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....
Adám's user avatar
  • 30.6k
53 votes
12 answers
7k views

Seats in a Finnish cinema

You're given the map of a cinema theatre as a boolean matrix: 0 represents a free seat, 1 - occupied. Each Finn who walks in chooses the seat farthest away (Euclidean distance) from the nearest ...
ngn's user avatar
  • 15.3k
49 votes
107 answers
6k views

Construct the Identity Matrix

The challenge is very simple. Given an integer input n, output the n x n identity matrix. The identity matrix is one that has <...
Seadrus's user avatar
  • 1,395
48 votes
16 answers
6k views

Zigzagify a Matrix

As part of its compression algorithm, the JPEG standard unrolls a matrix into a vector along antidiagonals of alternating direction: Your task is to take a matrix (not necessarily square) and return ...
Martin Ender's user avatar
48 votes
14 answers
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 ...
hyper-neutrino's user avatar
  • 42.5k
45 votes
21 answers
2k views

Summon the sevens

You are given a \$3\times3\$ square matrix where each cell is any digit between \$0\$ and \$9\$ except \$7\$. Your task is to figure out the minimum number of digits that must be replaced with \$7\$'s ...
Arnauld's user avatar
  • 194k
41 votes
51 answers
7k views

Cops: Make a regex - Make a snake

This is the cop's thread. The robber's thread is here. Write a code that takes an input n and creates a n-by-n "snake matrix". A snake matrix is a matrix that ...
Stewie Griffin's user avatar
41 votes
33 answers
4k views

Remove surrounding zeroes of a 2d array

This is a 2-dimensional version of this question. Given a non-empty 2-dimensional array/matrix containing only non-negative integers: $$ \begin{bmatrix} {\color{Red}0} & {\color{Red}0} & {\...
alephalpha's user avatar
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40 votes
13 answers
5k views

Recreate Minecraft's lighting

Minecraft has a fairly unique lighting system. Each block's light value is either one less than the brightest one surrounding it, or it is a light source itself. Your task is to write a method that ...
Chspsa's user avatar
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38 votes
41 answers
4k views

Is my Matrix Arrowhead?

Definition An arrowhead matrix is a matrix that has all entries equal to 0, except the ones on the main diagonal, top row and leftmost column. In other words, the matrix should look like this: * * * *...
Mr. Xcoder's user avatar
  • 42.4k
38 votes
25 answers
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/argument¹. The tricky part is that ...
Adám's user avatar
  • 30.6k
37 votes
39 answers
4k views

Determinant of an Integer Matrix

Given a square integer matrix as input, output the determinant of the matrix. Rules You may assume that all elements in the matrix, the determinant of the matrix, and the total number of elements in ...
user avatar
37 votes
28 answers
4k views

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] \...
Mr. Xcoder's user avatar
  • 42.4k
36 votes
28 answers
4k views

Sum of first row and column, then second row and column ... and so on

Take a non-empty matrix / numeric array containing positive integers as input. Return, in this order, the sums of the first row and column, then the second row and column and continue until there aren'...
Stewie Griffin's user avatar
35 votes
5 answers
2k views

Rotating a 2D Matrix

Let's say I have the following (2D) matrix: [[1, 2, 3, 4 ], [5, 6, 7, 8 ], [9, 10, 11, 12], [13, 14, 15, 16]] Rotate the matrix counterclockwise ...
StepUp's user avatar
  • 461
34 votes
32 answers
5k views

Make it explode!

Take a matrix of positive integers as input, and make it explode! The way you explode a matrix is by simply adding zeros around every element, including the outside borders. Input/output formats are ...
Stewie Griffin's user avatar
33 votes
15 answers
4k views

Fryer simulator

Your task is to model the effects of batter on pieces of food. Please add three layers of crust. ...
ngn's user avatar
  • 15.3k
32 votes
59 answers
3k views

Create a checkerboard matrix

Take a positive integer n as input, and output a n-by-n checkerboard matrix consisting of 1 and 0. The top left digit should always be 1. Test cases: ...
Stewie Griffin's user avatar
32 votes
34 answers
3k views

Rebuild a rectangular array from a corner

I once had a beautiful rectangular array. It was very symmetrical, but unfortunately it has fallen apart and now I only have the top left corner. Your task will be to rebuild the original array. Your ...
Pavel's user avatar
  • 9,377
32 votes
20 answers
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 ...
ibrahim mahrir's user avatar
32 votes
6 answers
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 ...
ngn's user avatar
  • 15.3k
31 votes
55 answers
2k views

Generate this number table

Given an integer \$1 < n < 10 \$ generate a table like below. For \$n = 5\$, 1 2 3 4 5 2 2 3 4 5 3 3 3 4 5 4 4 4 4 5 5 5 5 5 5 For \$n = 8\$, ...
BadCoder's user avatar
  • 461
31 votes
4 answers
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: ...
hyper-neutrino's user avatar
  • 42.5k
30 votes
9 answers
6k views

Calculate the permanent as quickly as possible

The challenge is to write the fastest code possible for computing the permanent of a matrix. The permanent of an n-by-n matrix ...
user avatar
29 votes
23 answers
4k 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 ...
caird coinheringaahin g's user avatar
29 votes
31 answers
3k 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 ...
golf69's user avatar
  • 2,059
29 votes
35 answers
2k views

Rotation summation

Take a square matrix containing positive integers as input, and calculate the "rotated sum" of the matrix. Rotated sum: Take the sum of the original matrix and the same matrix rotated 90, 180 and ...
Stewie Griffin's user avatar
29 votes
23 answers
6k views

Binary Numbers Magic Trick

The challenge is simply; output the following six 2D integer arrays: ...
Kevin Cruijssen's user avatar
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 ...
Bubbler's user avatar
  • 77.5k
29 votes
17 answers
5k 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 ...
ihavenoidea's user avatar
  • 1,219
29 votes
26 answers
2k views

Vandermonde Determinant

Given a vector of \$n\$ values \$(x_1,x_2,x_3,\ldots,x_n)\$ return the determinant of the corresponding Vandermonde matrix \$V(x_1, x_2, \ldots, x_n) = \begin{bmatrix}1 & x_1 & x_1^2 & x_1^...
flawr's user avatar
  • 43.9k
29 votes
10 answers
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 ...
Adám's user avatar
  • 30.6k
29 votes
9 answers
2k views

Fire propagation simulator

Suppose we have a matrix like this: 11111 12221 12321 12221 11111 This matrix represents a terrain, and each cell represents a portion of terrain. The number in ...
Charlie's user avatar
  • 12.9k
29 votes
7 answers
2k views

We ended up where we started!…

Challenge: Input: You take two inputs: - A string only containing printable ASCII (excluding spaces, tabs or new-lines) - A printable ASCII character Output: The first line will contain the string-...
Kevin Cruijssen's user avatar
28 votes
36 answers
2k views

Index of the row with most non-zero elements

This is a simple one: Take a matrix of integers as input, and output the index of the row with the most non-zero elements. You may assume that there will only be one row with the most non-zero ...
Stewie Griffin's user avatar
27 votes
47 answers
3k views

Output a Latin Square

An \$n\times n\$ Latin Square is a grid containing exactly \$n\$ distinct values where the values in each row and column are distinct. For example, $$\begin{matrix} A & B & C \\ C & A &...
caird coinheringaahin g's user avatar
27 votes
58 answers
3k views

Orthodiagonal steps

It's a common problem to navigate in a 2D matrix. We've seen it many times and will see again. So let's help future us and develop the shortest solutions to generate all eight possible steps in a 2D ...
Dead Possum's user avatar
  • 3,434
27 votes
20 answers
3k views

Is it a stochastic matrix?

A stochastic matrix is a matrix of probabilities used in the context of Markov chains. A right stochastic matrix is a matrix where each row sums to 1. A left ...
Fatalize's user avatar
  • 38.9k
27 votes
22 answers
6k views

Is it a good 2048 board?

This is my first question here, so any suggestions in the comments would be appreciated! Thanks ;) Introduction One very common strategy for the 2048 game is never ever swiping down. This positions ...
dv02's user avatar
  • 393
27 votes
27 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 ...
Fatalize's user avatar
  • 38.9k
27 votes
19 answers
3k views

Create Bernard from Desmos

Background In the online graphing calculator Desmos, there is a certain shape that appears in the lower left portion of the graph in many high detail graphs, which the Desmos community has dubbed &...
Aiden Chow's user avatar
  • 13.7k
27 votes
21 answers
4k views

Generate a Walsh Matrix

A Walsh matrix is a special kind of square matrix with applications in quantum computing (and probably elsewhere, but I only care about quantum computing). Properties of Walsh matrices The ...
Khuldraeseth na'Barya's user avatar
27 votes
9 answers
5k 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 ...
HiddenBabel's user avatar
27 votes
10 answers
4k views

Symbolic matrix multiplication

There are lots of different ways to explain matrix multiplication. I'll stick with a single figure since I believe most people here are familiar with it (and the figure is very descriptive). If you ...
Stewie Griffin's user avatar
27 votes
8 answers
590 views

Interlaced Rotations

Challenge Given a square matrix of characters (single-byte printable ASCII characters), rotate each "ring" of the matrix in opposite directions. Let's take an example: ...
hyper-neutrino's user avatar
  • 42.5k
27 votes
3 answers
1k views

Golf A Free Lunch

Find a maximally profitable sequence of exchanges given an exchange rate table. As an example consider the currencies Ariary (your home currency), Baht, Cedi, and Denar where the rate from one to ...
Jonathan Allan's user avatar
26 votes
21 answers
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 ...
qwr's user avatar
  • 12.1k

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