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.
274
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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: ...
- 4,871
15
votes
11
answers
1k
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Flood fill by distance
Say I have a grid with some obstacles:
----
| X |
| |
|XX |
| |
----
I can fill this with numbers, as distance from the top left corner. But, because ...
- 31.9k
23
votes
16
answers
2k
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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 &...
- 8,416
5
votes
1
answer
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fastest matrix multiplication on x86
This challenge requires integration with C, so you can stop reading if you're not interested.
Matrix multiplication is a simple operation, but the performance depends a lot on how efficiently the code ...
- 2,273
10
votes
15
answers
339
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center a matrix [closed]
The words "center a" probably give flashbacks to any decent HTML developer. Luckily, we are not working with divs, we are working with matrices.
Given a matrix where w=h, and given a "...
- 691
14
votes
10
answers
1k
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Storing a band matrix
Related challenge
A band matrix is a matrix whose non-zero entries fall within a diagonal band, consisting of the main diagonal and zero or more diagonals on either side of it. (The main diagonal of a ...
- 34.3k
12
votes
10
answers
975
views
Convert J brackets back to 2-D list
Let's say we have a 2-D list, like the following one:
\$
\begin{bmatrix}
\color{red}{1} & \color{red}{2} & \color{red}{3} & \color{red}{4} \\
\color{blue}{5} & \color{blue}{6} & \...
- 10.9k
13
votes
12
answers
2k
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Simulate the ripple effect
Imagine throwing a rock into a pond. You get to see perfect circles of ripples spreading out over the pond, bouncing off of each other. Of course, nothing can be as serene as that in coding, but, we ...
- 691
40
votes
13
answers
4k
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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 ...
- 691
20
votes
12
answers
920
views
Convert between graph representations
What?
Let's say I have this graph:
1
\
\
2 3
\ /
\ /
4
I can represent it in 2 ways:
A list of connected vertices. ...
- 1,654
12
votes
3
answers
277
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Line Islands in a Word Search
My third word search related challenge in a row. :)
Challenge:
Brief explanation of what a word search is:
In a word search you'll be given a grid of letters and a list of words. The idea is to cross ...
- 108k
2
votes
5
answers
147
views
Generate this string table [duplicate]
For the given string s, generate generate a table like below.
...
- 1,805
5
votes
1
answer
427
views
NxM List Combination Closest to Target
Given a list of N lists, each containing M positive integers, and a separate list of M positive integers (target values), return a list of N scalars (integers with a value of 0 or more) that ...
- 727
3
votes
3
answers
318
views
Appease the Picky Eater
Your friend Jack is a picky eater. He only likes certain foods, and he only likes to eat a certain amount of them each day. Despite this, Jack has very strict calorie and macronutrient goals that he ...
- 727
2
votes
2
answers
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Resize the image
Given an \$n\times m\$ matrix \$A\$ and two integers \$w,h\$, output a matrix of \$w\times h\$ called \$B\$, such that $$B_{i,j} = \int_{i-1}^i\mathbb dx\int_{j-1}^j A_{\left\lceil \frac xw\cdot n\...
- 13k
21
votes
12
answers
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Bandwidth of a matrix
A band matrix is a matrix whose non-zero entries fall within a diagonal band, consisting of the main diagonal and zero or more diagonals on either side of it. (The main diagonal of a matrix consists ...
- 34.3k
7
votes
2
answers
219
views
Count the ways to transform (2)
Your input is a matrix (2d array) of positive integers. For example:
\begin{matrix}
1 & 1 & 4 & 7\\
1 & 3 & 5 & 6\\
2 & 1 & 4 & 5 \\
\end{matrix}
A semi-continuous ...
- 6,775
12
votes
7
answers
718
views
Knights Jam | Chess
The knight is a chess piece that, when placed on the o-marked square, can move to any of the x-marked squares (as long as they ...
- 3,049
12
votes
5
answers
891
views
Simulating Bombs
More advanced version of this
The aim of this puzzle is to simulate the impact of the shock wave of bombs on a square grid. The grid initially contains cells labelled ...
- 3,049
22
votes
6
answers
764
views
Check if a matrix is Zarankiewicz-maximal
My final-year project at the National University of Singapore is on Zarankiewicz's problem:
What is the maximum number of 1s in an \$m×n\$ binary matrix (\$m\$ rows and \$n\$ columns) with no \$a×b\$ ...
- 833
20
votes
13
answers
1k
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Output the 12 Bar Blues
Note to those without experience in music: Through making an attempt to solve this problem, you may find that music and computer programming are similar in the ways that they implement rules and ...
- 727
14
votes
14
answers
772
views
SuperSquares NxN
Given an integer N from 1-9, you must print an NxN grid of NxN boxes that print alternating 1s and Ns, with each box having an alternating starting integer.
Examples
...
- 727
7
votes
12
answers
702
views
Ragged Matrix Indexing
A ragged matrix, is a matrix that has a different number of elements in each row. Your challenge is to write a program in any favorable language to find the indices of all occurrences of target in the ...
- 3,049
23
votes
18
answers
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Print a NxN integer involute
Given an integer \$N\$, you must print a \$N\times N\$ integer involute with the numbers increasing in a clockwise rotation. You can start with either 0 or 1 at the top left, increasing as you move ...
- 421
8
votes
8
answers
448
views
Count the ways to transform
A rigid transformation of a square array is a mapping from square arrays of a certain size to square arrays of the same size, which rearranges the elements of the array such that the distance to each ...
- 90.3k
10
votes
7
answers
300
views
Cell Evolution Matrix
Your lab needed to simulate how a particular cell evolves over time in a 2D grid space. A sample 2D grid space below shows a single cell at the centre of the grid.
...
- 3,049
13
votes
13
answers
2k
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Mat Printing Matrix
A manufacturing company wants to print a design on mats of varying dimensions, and they hired you to program a robot to make these mats. The design consists of alternating rings of any 2 symbols on a ...
- 3,049
15
votes
4
answers
681
views
Simulate weathering of a rock
Inspired by my geography class, Sandboxed
Simulate weathering / erosion.
Input
Input will be given as a string of any 2 characters (or see below) you like in the shape of the rock (here i use spaces ...
- 1,654
18
votes
6
answers
750
views
Is it an elementary matrix?
Consider a linear system of equations, in \$n\$ unknowns, expressed as
$$A \textbf x = \textbf b$$
where \$A \in M_{n,n}(\mathbb Z)\$ is an \$n \times n\$ matrix of integers, \$\textbf x\$ is a column ...
- 48.1k
19
votes
13
answers
2k
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Compute matrix blockiness
Consider a non-empty binary matrix M and a natural number n. For the purposes of this challenge, M is said to have blockiness n if it can be built using adjacent square blocks of size n, where each ...
- 100k
16
votes
10
answers
800
views
Remove submatrices
Given two integer matrices a and b, your challenge is to replace any occurences of b in <...
- 31.9k
6
votes
1
answer
538
views
Fast Matrix Multiplicator Evaluator
A triplet of real tensors \$(A,B,C)\$ of size \$\gamma \times \gamma \times \sigma\$ represents a matrix multiplication algorithm with \$\sigma\$ elementary multiplications iff the following function ...
- 69
22
votes
9
answers
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Bird's Algorithm for Computing Determinants
There is a division-free algorithm for computing determinants published by R.S.Bird in 2011 that uses only matrix multiplications. Given a \$n×n\$ matrix \$X\$, the matrix \$Y=μ(X)\$ is another \$n×n\$...
- 369
20
votes
19
answers
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Checkered grid with X mark
Challenge
Given two integer values \$a \ge 2\$ and \$0 \le b < a\$, generate a \$(2a-1) \times (2a-1)\$ matrix consisting of the integers 0, 1, and 2 as follows:
Create a checkerboard of 0s and 1s ...
- 66.1k
24
votes
18
answers
2k
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Double trace of a square matrix
Inspired by a question (now closed) at Stack Overflow.
Given a square matrix, let its double trace be defined as the sum of the entries from its main diagonal and its anti-diagonal. These are marked ...
- 100k
13
votes
8
answers
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Find the number of paths in a n×n grid
Information
Given a non-negative odd integer (let's call it \$n\$), find the number of all possible paths which covers all squares and get from the start to end on a grid.
The grid is of size \$n\$×\$...
- 1,654
17
votes
15
answers
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Drop down the numbers
This was inspired by Apply gravity to this matrix
Your challenge is to input a matrix with non-negative one-digit integers and drop down the 1's down 1 column, the 2's down 2 columns, the 3's down 3 ...
- 3,129
22
votes
25
answers
3k
views
Apply gravity to this matrix
This was inspired by this question.
Given an \$m\times n\$ matrix of \$0\$'s and \$1\$'s, apply "gravity" to it. This means to drop down all the \$1\$'s as if they were affected by gravity.
...
- 799
18
votes
4
answers
587
views
Calculate the integer square root of a matrix
Let \$A\$ be a square matrix that is at least \$2 \times 2\$ where each element is an integer. \$A^2 = A \times A\$ will then have the same dimensions as \$A\$, and will have integer elements. For ...
- 48.1k
21
votes
10
answers
2k
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Is this a Jordan matrix?
Background
A Jordan matrix is a block-diagonal matrix where each block on the diagonal has the structure of
$$
\begin{bmatrix}
\lambda & 1 & 0 & \cdots & 0 \\
0 &...
- 66.1k
29
votes
26
answers
2k
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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 ...
- 66.1k
17
votes
10
answers
608
views
To raise \$ e \$ to the power of a matrix
Inspired by this 3Blue1Brown video
Given a square matrix \$ M \$, compute its matrix exponential \$ \exp(M) \$, which is defined, using an extension of the Maclaurin series for \$ e^x \$, as
$$ \exp(M)...
- 22.6k
18
votes
11
answers
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Count my Pluses
Your task is, to count how many pluses I have.
What Pluses?
The no plus: 0 Points
-
The naïve Plus: 1 Point
+
The double ...
- 4,871
16
votes
7
answers
1k
views
Drop some boxes
Say I have a pile of boxes:
AAA
BBB
I can create it in two steps:
BBB
↓
(empty)
---
AAA
↓
BBB
But with this:
...
- 31.9k
15
votes
17
answers
804
views
Square chunk my matrix
Your challenge is to write a function/program that takes a matrix of integers m and a number n as input and:
Splits m into n by n chunks
Replaces each chunk with the most common value in that chunk (...
- 31.9k
26
votes
9
answers
2k
views
Is it a valid Parker Square
5 Years ago, this happened, and then it became sort of a meme.
Challenge
The Challenge today is, to check if a "magic square" is a valid parker square.
What is a Real Magic square?
All the ...
- 4,871
27
votes
46
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\$,
...
- 421
9
votes
15
answers
769
views
Construct a Modulo Multiplication Table
Consider a n x n multiplication table and replace each item with its remainder of division by n. For example, here is a ...
- 1,025
26
votes
21
answers
3k
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I'm Lazy*: Top-left align my text
* and don't have a word processor with top-left align support :D
Take several lines of input, with at least four unique characters of your choice including newline and space. The input can also be ...
- 1,450
22
votes
2
answers
977
views
Minecraft piston pushing
In Minecraft, pistons are blocks that can move other blocks. However, they can only move at most twelve blocks, and won't work at all if any obsidian is in the way. Also, slime blocks are sticky and ...
- 31.9k